PYCR1 was upregulated in HCC compared to adjacent nontumor tissues (P < 0.05). These data were verified using quantitative real-time polymerase chain reaction, western blotting, and immunohistochemistry analysis. Additionally, patients with low PYCR1 expression showed a higher overall survival rate than patients with high PYCR1 expression. Furthermore, PYCR1 overexpression was associated with the female sex, higher levels of alpha-fetoprotein, advanced clinical stages (III and IV), and a younger age (< 45 years old). Silencing of PYCR1 inhibited cell proliferation, invasive migration, epithelial-mesenchymal transition, and metastatic properties in HCC in vitro and in vivo. Using RNA sequencing and bioinformatics tools for data-dependent network analysis, we found binary relationships among PYCR1 and its interacting proteins in defined pathway modules. These findings indicated that PYCR1 played a multifunctional role in coordinating a variety of biological pathways involved in cell communication, cell proliferation and growth, cell migration, a mitogen-activated protein kinase cascade, ion binding, etc. The structural characteristics of key pathway components and PYCR1-interacting proteins were evaluated by molecular docking, and hotspot analysis showed that better affinities between PYCR1 and its interacting molecules were associated with the presence of arginine in the binding site. Finally, a candidate regulatory microRNA, miR-2355-5p, for PYCR1 mRNA was discovered in HCC. Overall, our study suggests that PYCR1 plays a vital role in HCC pathogenesis and may potentially serve as a molecular target for HCC treatment.Overexpression of pyrroline-5-carboxylate reductase 1 (PYCR1) has been associated with the development of certain cancers; however, no studies have specifically examined the role of PYCR1 in hepatocellular carcinoma (HCC). Based on The Cancer Genome Atlas expression array and meta-analysis conducted using the Gene Expression Omnibus database, we determined that  Furthermore, RNA sequencing (RNA-seq), bioinformatics analyses, and molecular docking were used to elucidate protein interactions that are associated with the function of PYCR1. The results will probably provide us a potential drug target for therapy or a biomarker for diagnosis and prognosis. These results will help us better understand the role of PYCR1 in the pathogenesis and development of HCC.In the present study, we aimed to analyze the relationship between PYCR1 silencing and HCC 2 at 37 °C.The HCC cell lines used in this study included Huh7 cells and LM3 cells. Because the PYCR1 expression of these two cells were higher than the other cells . The HCCThe following antibodies were used in immunoblotting and immunofluorescence studies: anti-β-actin , anti-PYCR1 , anti-E-cadherin , anti-β-catenin , anti-N-cadherin , and anti-vimentin .Reagents and materials used for the analysis of cell proliferation, migration, and invasion and for RNA-seq included Cell Counting Kit‑8 , Transwell plates , RNA Nano 6000 assay kit , and NEB Next® Ultra™ RNA library prep kit for Illumina® .A total of 106 tumor samples and adjacent nontumor liver tissues were obtained from patients who had been pathologically diagnosed with HCC and undergone a partial hepatectomy at The Affiliated Hospital of the Guilin Medical University. None of the patients received adjuvant chemotherapy or radiotherapy prior to surgery, and all cases were independently confirmed by two senior pathologists. The clinicopathological information for all cases was retrieved from the hospital's clinical database. This study was approved by the ethics committee of the Guilin Medical University, and informed consent was obtained from the patients.http://www.ncbi.nlm.nih.gov/geo/). Multiple probes were used for the detection of the PYCR1 gene, and the mean expression value was calculated for each probe PYCR1 mRNA in HCC tissues were extracted from the datasets using the R software, and then a meta-analysis was performed. Standardized mean differences and 95% confidence intervals were calculated for pooled values and indicated expression differences. Cochran's Q and I2 tests were used to evaluate heterogeneity. Based on the level of heterogeneity, two models were applied to the overall meta-analysis. A random-effect model was chosen when there was significant heterogeneity among all samples , and a fixed-effect model was used when there was no significant heterogeneity, as indicated by statistical analysis Seven microarray datasets  were downloaded from the Gene Expression Omnibus database (https://xena-browser.net/). Gene expression was quantified experimentally using the Illumina HiSeq 2000 RNA-seq platform. Three TCGA datasets including gene expression RNA-seq  dataset, phenotype (n=438) dataset, and miRNA expression RNA-seq  dataset were used in the study, which belongs to TCGA Liver Cancer cohort. A total of 413 samples, including 363 HCC tissues and 50 adjacent non-HCC tissues were selected for this study. Detailed patient information and PYCR1 expression levels are summarized in Table Clinical and RNA-seq data for TCGA cohorts were downloaded from the Xena Public Data Hubs (https://www.mirnet.ca), miRDB (http://www.mirdb.org), miRTarBase (http://mirtarbase.mbc.nctu.edu.tw/php/index.php), and TargetScan (http://www.targetscan.org/vert_72/) were used to predict the upstream regulatory miRNAs of PYCR1. Only miRNAs appearing in two or more sets of the results were chosen as candidate miRNAs.Four frequently used online tools, including miRNet  according to the manufacturer's instructions. Quantitative real-time polymerase chain reaction (qRT-PCR) was performed using a SYBR Green master mix  with a StepOne sequence detection system (Applied Biosystems). The qRT-PCR cycling conditions were as follows: initial denaturation at 95 °C for 10 min, followed by 40 cycles of denaturation at 95 °C for 15 s, annealing at 58-60 °C for 60 s, and extension at 72 °C for 10 s. The mRNA expression level was quantified using the 2Proteins were extracted using RIPA lysis buffer  containing a protease inhibitor cocktail . Protein quantification was performed using a bicinchoninic acid protein assay kit . Proteins were separated on 10% sodium dodecyl sulfate-polyacrylamide gels and transferred onto polyvinylidene difluoride membranes. The membranes were blocked with 5% skim milk and then incubated with primary antibodies, including β-actin , PYCR1 , E-cadherin , β-catenin , N-cadherin , and vimentin , at 4 ℃ overnight. After being washed with Tris-buffered saline with Tween 20 for four times, the membranes were incubated with a horseradish peroxidase-conjugated secondary antibody at room temperature for 1 h. Immunoreactive bands were visualized using the BeyoECL Plus kit (Beyotime).Formalin-fixed and paraffin-embedded 4 μm-thick tissue sections were deparaffinized, rehydrated, and heated with citric acid buffer for antigen retrieval for 15 min. The samples were then placed in 0.3% hydrogen peroxide for 30 min to block endogenous peroxidase activity and treated with blocking serum for 20 min. The slides were incubated with an anti-PYCR1 primary antibody  at a 1:900 dilution at 4 ℃ overnight, followed by incubation with a biotinylated secondary antibody for 25 min. The negative control slides were incubated with PBS only. The slides were rinsed in phosphate-buffered saline , then counterstained with hematoxylin, dehydrated, and mounted in a neutral resin. The staining intensities and the proportions of positive cells in all tissues were analyzed and scored by two experienced pathologists. The results were analyzed using immunoreactivity scores based on the staining intensity and the proportion of stained cells. The staining intensity was scored as follows: 0 = unstained; 1 = weakly stained; 2 = moderately stained; and 3 = strongly stained. The proportion of stained cells was scored as follows: 0 = negative; 1 = 1-10%; 2 = 11-50%; 3 = 51-80%; and 4 > 80%. The intensity score was multiplied by the proportion of staining score to obtain an immunoreactivity score. A total score greater than 3 was considered positive expression; that of 1 to 3 was considered low expression; and 0 was considered negative expression.PYCR1 was achieved using the following three interfering RNAs (RNAis): RNAi 1, 5'-gaGGGTCTTCACCCACTCCTA-3'; RNAi 2, 5'-tgAGAAGAAGCTGTCAGCGTT-3'; and RNAi 3, 5'-caCAGTTTCTGCTCTCAGGAA-3'. The RNAis were obtained from Shanghai GeneChemCo and were inserted between the AgeI and EcoRI sites of the GV248 vector. The short hairpin RNAs (shRNA) of GV-NC-shRNA and GV-PYCR1-shRNA were constructed as control lentivirus and shPYCR1 lentivirus for further experiment. To establish stable HCC cell lines with silenced PYCR1, 1.5 μg/mL puromycin was added to the culture media 48 h after the initiation of virus infection, and the expression of the green fluorescent protein (GFP) was observed. Cells were then trypsinized and cultured in a 100 cm2 dish to allow for expansion. The silencing of PYCR1 was confirmed by qRT-PCR and immunoblotting assays. Empty vectors were used as controls.Downregulation of . Briefly, Huh7 cells (1.5 × 103) from the shNC and shPYCR1 groups were seeded into a 96-well plate. After 24, 48, 72, 96, and 120 h of treatment, 10 μL of the CCK-8 solution was added to each well, and incubation continued for 2 h. The absorbance was measured at 450 nm using a microplate reader . Each experiment was performed in triplicate.Cell proliferation was assessed using the CCK-8 solution according to the manufacturer's instructions6 cells/well) and incubated for 24 h to reach 80% confluence. A sterile 10 μL pipette tip was then used to gently and slowly scratch the cell monolayer. Images of the wound were captured in 10 random fields using a light microscope  at a 100× magnification. The gap width in the PYCR1-silenced cell groups was compared to that in the control using the Photoshop software at different time points. Each experiment was repeated three times.Huh7 and LM3 cells were seeded in a serum-free DMEM into 6-well plates . Cells (1 × 104) of Huh7 and LM3 were suspended in 200 µL of a serum-free DMEM, seeded into the upper Transwell chamber, and cultured at 37 °C for 24 h, while 600 µL of DMEM containing 10% FBS was simultaneously added to the lower chamber. The invaded cells were fixed with methanol, stained with a 2.5% crystal violet stain solution (Solarbio), and then observed and photographed using an optical microscope. Five visual fields were randomly selected for quantification in each group.The 5/mL, the cells were incubated with fluorescent antibodies at room temperature for 25 min, then pelleted, and resuspended. The samples were analyzed using a flow cytometer (BD Biosciences) and the FlowJo software.Allophycocyanin-conjugated annexin V and 7-aminoactinomycin D  were used to analyze the cell apoptosis rate. Huh7-shNC and Huh7-shPYCR1 cells were washed twice with PBS and treated with 0.25% pancreatin (without EDTA) to facilitate digestion. After adjusting the cell density to 1 × 107 cells in 100 µL of DMEM) were injected subcutaneously into the upper left flank region of the mice. Tumor diameters were measured using digital calipers every 4 days. After 4 weeks of observation, the mice were sacrificed under anesthesia, and xenograft tissues were collected. All animal procedures were performed in accordance with the protocol approved by the Guilin Medical University Experimental Animal Center.Male BALB/c nude mice (6-7 weeks old) were obtained from the Shanghai Institute of Materia Medica . Cells stably transfected with the shPYCR1 or shNC , and RNA integrity and concentration were measured using the RNA Nano 6000 assay kit for the Bioanalyzer 2100 system (Agilent Technologies). A total of 2 μg of RNA from each sample was used as an input material for the RNA sample preparation. Sequencing libraries were generated using the NEB Next® Ultra™ RNA library prep kit for Illumina® according to the manufacturer's instructions. After library analysis, RNA-seq was completed using the Illumina HiSeq X Ten sequencing platform, and paired-end sequence reads were obtained.https://www.bioinformatics.babraham.ac.uk/). Clean RNA-seq reads were aligned to the GRCh38 human genome using HISAT v2.1.0 with default settings Quality control of the raw sequencing data was performed using the FastQC tool v0.11.9  networks were established using the STRING database.https://www.rcsb.org/). The preparation of the PDB files, including the removal of extraneous water molecules, addition of hydrogen molecules, and adjustment of pH-sensitive protonation, was performed using the SYBYL-X 2.0 software. Protein-protein docking was performed using the docking program HEX 8.0.0. The KFC2 (Knowledge-based FADE and Contacts) server was used to calculate protein-protein binding interface hotspots, which are defined as small fractions of residues accounting for a large fraction of the binding affinity -1) was calculated to assess the docking profile in our study. Further details were recorded in The structures of PYCR1 and its interacting proteins were downloaded from the RCSB Protein Data Bank (PDB) database . Data are presented as the mean ± standard deviation. One-way analysis of variance was used to compare differences between multiple groups, and Student's Data were extracted from seven published and publicly available HCC datasets. Only datasets containing both HCC and their adjacent nontumor samples were used for further analysis. A meta-analysis approach was applied to these datasets as outlined in Figure PYCR1 mRNA was analyzed in 413 samples, including 363 HCC tissues and 50 adjacent nontumor tissues, from the TCGA dataset. Increased PYCR1 expression was found in the HCC tissues compared with the adjacent nontumor tissues  levels, higher clinical staging (stages III and IV), and a younger age (< 45 years old) . However, recurrence-free survival indicated that there was no difference in the prognosis between high and low PYCR1-expressing patients . Furthermore, we quantified the expression levels of proteins associated with epithelial-mesenchymal transition (EMT) and determined whether their expression was affected by downregulation of PYCR1. Our results suggested that the expression of E-cadherin and β-catenin was significantly increased in cells with downregulated PYCR1 expression, whereas that of N-cadherin and vimentin was decreased . Based on these parameters, 569 genes were found. After removing noncoding genes, 425 DEGs were identified, of which 298 were upregulated and 127 were downregulated following PYCR1 silencing  cascade, ion binding, immune stimulus, cell component, transport, and catalytic activity. PPI analysis further demonstrated that many of the proteins were associated with each other  for PYCR1 and its eight target proteins were determined to be as follows: apoptogenic protein 1 , glutamate ionotropic receptor kainite type subunit 2 , RhoGD12 , dual specificity phosphatase 9 , chorionic gonadotropin subunit alpha , retinol-binding protein 4 , nuclear receptor subfamily 1 group H member 4 , and serpin family E member 1 . The complexes generated during docking are shown in Figure total values reflect the possibility of binding, with a lower value correlating with easier and stronger binding to other proteins The structures of eight interacting proteins, which were associated with key pathway modules, such as MAPK pathways, cell migration, cell communication, and cell proliferation/growth, and identified downstream of PYCR1, were found in the PDB database. The information obtained from the PDB files and HEX docking results is shown in Table PYCR1 mRNA. Based on the TCGA RNA-seq data, only miR-2355-5p was differentially expressed between HCC tissues and adjacent nontumor tissues and was downregulated in HCC samples compared to adjacent nontumor samples , and a younger age (< 45 years old). Furthermore, PYCR1 upregulation was found to be associated with a poor OS. These results suggest that PYCR1 expression may be an effective predictive factor for OS in patients with HCC. Similar correlations between PYCR1 expression and clinical features  were also observed in our patients with HCC; however, there was no association between PYCR1 expression and AFP level or sex. This discrepancy may be due to a largely Caucasian population in the TCGA database, whereas our HCC tissues were exclusively obtained from Chinese patients. Thus, ethnic diversity may impact the effect of PYCR1 on HCC development. Additional HCC samples from patients of different ethnicities should be included in further studies.In the present study, PYCR1 induces apoptosis and cell cycle arrest PYCR1 in Huh7 and LM3 HCC cells and to determine the effect of PYCR1 on various cellular functions. The results revealed that silencing PYCR1 induced a marked inhibition of cell proliferation, migration, and invasion. Further, the results of the HCC xenograft mouse study indicated that silencing PYCR1 significantly inhibited the tumor growth.A previous study has shown that silencing of PYCR1 caused increased expression of E-cadherin and β-catenin and decreased expression of N-cadherin and vimentin. These results suggest that PYCR1 promotes HCC migration and invasiveness by inducing EMT.EMT has been shown to play an important role in tumorigenesis by inhibiting epithelial function and upregulating the expression of mesenchymal-related genes to enhance invasiveness and metastasis PYCR1 silencing. Two specific genes, namely, secreted phosphoprotein 1 (SPP1) and C-X-C motif chemokine 12 (CXCL12) were identified to be strongly associated with PYCR1. Previous studies have reported that PYCR1 can activate SPP1 to regulate cell adhesion To better understand the downstream molecular events involved in the effects of PYCR1 on HCC invasiveness and metastasis, we performed RNA-seq to obtain DEG profiles following PYCR1. Furthermore, HRG inhibits the tumor growth by facilitating clearance of dying tumor cells The results of our functional analysis showed that the identified DEGs were primarily enriched in 14 functional categories, including cell communication, MAPK cascade, and cell migration. Cell communication is crucial for morphogenesis, cell differentiation, homeostasis, growth, and cell-cell interaction PYCR1 silencing. IRS1 is a cytoplasmic substrate of the insulin receptor and insulin-like growth factor 1 receptor and plays prominent roles in human malignancies. Phosphorylation of IRS1 leads to the recruitment of downstream effectors and to the activation of the MAPK cascade, which promotes the activation of the PI3K cascade PYCR1 silencing. Silencing of PYCR1 could interfere cell proliferation through the alteration of IRS1/JNK signaling pathway which subsequently inhibited MAPK pathways.A previous study has also suggested that p38 MAPK pathways may be activated by PYCR1 and by increased expression of its downstream targets that regulate cell proliferation and metastasis PYCR1 has been associated with the inhibition of proliferation and invasiveness of breast cancer cell lines via activation of the AKT/ERK signaling pathway Other studies have reported that APOA1 may inhibit the formation of tumor vessels and induce an antitumor immune microenvironment, thereby preventing tumor progression PYCR1-silenced cells. In particular, glycosylation, cell differentiation, homeostasis, cell adhesion, neuron/nervous system, cell component, and immune stimulus categories were identified. Taken together these results suggest that downregulation of PYCR1 induces the activation of these functional pathways, which may subsequently influence the development of HCC.Many other functional categories were found to be associated with the DEGs identified in total value  compared with those of two other complexes (APOA1-PYCR1 and GRIK2-PYCR1). Further, complexes of PYCR1 with proteins that are most strongly related to cell migration and cell communication exhibited the lowest Etotal values, namely, SERPINE1-PYCR1  and NR1H4-PYCR1 . Previous research has suggested that lower Etotal values are associated with easier and stronger binding between a ligand and a receptor The results of our molecular docking analysis suggest that PYCR1 binds to its interacting proteins via binding hotspots. In the MAPK cascade, the DUSP9-PYCR1 complex exhibited the lowest EAnalysis of hotspots revealed that several amino acid residues in DUSP9 and SERPINE1 exclusively contributed to PYCR1 binding, whereas no hotspots were identified in other protein-protein complexes involved in the MAPK cascade, cell migration, and cell-cell communication. Moreover, several hotspots in the CGA-PYCR1 complex were found to be involved in cell proliferation and growth. These results suggest that the CGA-PYCR1 complex is multifunctional. Interestingly, all of the identified PYCR1 hotspots included Arg, which may imply that Arg is vital for the binding between PYCR1 and its interacting proteins. It has been reported that the depletion of Arg may suppress the proliferation of HCC cells because reduced Arg levels would interfere with intracellular glutamine metabolism and inhibit the synthesis of proteins and thymidine in silico prediction revealed that miR-2355-5p might be an upstream regulator for PYCR1 mRNA. Importantly, when PYCR1 levels were upregulated, miR-2355-5p was downregulated in HCC tissues. These results indicated that miR-2355-5p could serve as a negative regulator of PYCR1 expression, and low miR-2355-5p expression could promote the accumulation of PYCR1 in HCC tissues. Furthermore, miR-2355-5p has been reported to be a master regulator of target genes in other diseases, including chondrosarcoma and intervertebral disc degeneration Various studies have demonstrated that noncoding RNAs participate in HCC development PYCR1 expression was silenced, the proliferation, migration, invasion, metastasis, and EMT, as well as the tumorigenic capacity, were significantly inhibited in HCC cells. The mechanisms responsible for these effects involved many proteins, which were associated with many functional categories and signaling pathways. Analysis of protein-protein interactions indicated that specific hotspots might facilitate the formation of HCC-specific PYCR1 complexes and promote the development of HCC. We therefore propose that PYCR1 may be an effective novel target for the development of diagnostic or therapeutic options for HCC.In summary, our results suggest a role of PYCR1 in inducing the development of HCC. PYCR1 was found to be upregulated in HCC tissues compared to paired adjacent nontumor tissues. Using a TCGA dataset, we found that patients with low PYCR1 expression exhibited a higher OS rate than in patients with high PYCR1 expression. Meanwhile, higher PYCR1 expression was observed in females than in males and correlated with elevated AFP levels, higher clinical staging (stages III and IV), and a younger age (< 45 years old). In Chinese patients, two features, namely, higher clinical staging (stages III and IV) and a younger age (<45 years old), were related to higher PYCR1 expression. When Supplementary figures and tables.Click here for additional data file.


We explore the substrate-dependent charge carrier dynamics of large area graphene films using contact-free non-invasive terahertz spectroscopy. The graphene samples are deposited on seven distinct substrates relevant to semiconductor technologies and flexible/photodetection devices. Using a Drude model for Dirac fermions in graphene and a fitting method based on statistical signal analysis, we extract transport properties such as the charge carrier density and carrier mobility. We find that graphene films supported by substrates with minimal charged impurities exhibit an enhanced carrier mobility, while substrates with a high surface roughness generally lead to a lower transport performance. The smallest amount of doping is observed for graphene placed on the polymer Zeonor, which also has the highest carrier mobility. This work provides valuable guidance in choosing an optimal substrate for graphene to enable applications where high mobility is required. For example, graphene has already been implemented into a broadband image sensor array for enhanced photodetection4 as well as memristors based on layered two-dimensional materials5. Graphene was also demonstrated to be a sensitive chemical and biological sensor8. With the development of large-scale production techniques such as epitaxial growth or chemical vapor deposition (CVD), large area graphene shows increasing promise for implementation into macroscale modern devices9.Graphene, an atomic layer of carbon atoms arranged in a honeycomb lattice, is not only a rich playground for uncovering new physical phenomena, but also a potential component in future electronic and optoelectronic technologies10. Intrinsic limiting factors include scattering from lattice defects, grain boundaries14, or phonons16. Due to the formation of grain boundaries and defects during the CVD growth, such scattering mechanisms could be more pronounced in large-area graphene compared to micron-scale mechanically exfoliated samples18. Among extrinsic limiting factors, scattering due to charged impurities is known to play a significant role19. Charged impurities can be present in the underlying substrate20, trapped between the film and substrate21, or on the surface of graphene in fabrication residues22.Among its many properties, the high mobility of the massless Dirac fermions in graphene plays a key role in the implementation of high-speed electronic devices. Therefore, it is imperative to develop better understanding and control over the factors that affect scattering mechanisms in graphene films. Factors that limit large-area graphene’s mobility can be either intrinsic or extrinsic2, Si3N4, quartz or silicon is reported to have carrier mobilities varying between 500 and 10,000 cm2V−1 s−125. Efforts to engineer substrates that minimize the presence of trapped charges and mechanical deformations led to three orders of magnitude improvement, with the highest mobilities (larger than 106 cm2/(Vs)) reported in freely suspended devices27 or on top of atomically flat boron nitride (BN) crystals28. It is therefore critical that the graphene-substrate interaction be well understood for successful integration of large-area graphene films with high mobility. Substrates that ensure high mobility for graphene films could be exploited for improving device performance in future graphene integrated electronics.Graphene supported by common substrates such as SiO230. Electrical transport was also used to investigate large-scale graphene deposited on several dielectrics commonly used in the semiconductor industry. The highest mobility was achieved when graphene was placed on Si3N4, which outperformed SiO2, HfO2, Al2O3, and tetraethyl orthosilicate. This work indicated that carrier density fluctuation caused by the substrates is one of the main contributing factors for mobility degradation31. Other studies relied on time-resolved THz spectroscopy to explore the substrate effect on graphene placed on sapphire, silicon, germanium, polyethylene naphthalate (PEN), polyethylene terephthalate (PET), and quartz33. This technique provided information about the graphene DC conductivity, but the experimental spectral bandwidth, limited to frequencies up to 3 THz, could not resolve features attributed to carrier scattering. As a result, no information was obtained on carrier density or mobility. Finally, there has been more work that measured36 and even spatially resolved37 the transport properties of wafer scale graphene using THz spectroscopy. These studies, however, are restricted to only one specific substrate, or do not investigate the substrate dependent dynamics at play.To date, graphene-substrate interactions have been studied in devices by measuring the unpumped/non-excited carrier dynamics with both optical techniques and electrical transport techniques. For example, far-infrared spectroscopy (3–16 THz) was used to characterize graphene on different polar dielectric and organic polymer films. Graphene on hexamethyldisilazane (HMDS) notably exhibits a mobility four times higher than on SiO38. Moreover, the THz technique is sensitive to the Drude mobility instead of the field effect mobility. For electrical measurements, the measured field effect mobility and conductivity is affected by surface defects such as grain boundaries, wrinkles and bubbles. Time-domain THz spectroscopy is sensitive to the microscopic conductivity averaged over the distance travelled by an electron during one oscillating cycle of the optical field25. Since this length typically corresponds to few tens of nanometers in graphene11, while defects occur on the micrometer, or even millimeter scale, the Drude mobility and conductivity obtained with THz spectroscopy is minimally sensitive to large scale surface imperfections. Previous works compared the THz technique with other characterization methods relying on van der Pauw structures25, back gate measurements32, a micro four-point probe39, or micro Raman spectroscopy39. These studies confirmed the potential of THz spectroscopy to remotely map the electrical properties of large graphene sheets and optimize the integration of graphene into electronics or opto-electronics devices37.Here, we perform time-domain terahertz transmission spectroscopy over a bandwidth contained within 0.5 to 5.5 THz to measure graphene’s transport properties when supported by substrates with different charged impurity densities, dielectric constants, and surface roughness. Our THz spectral window, extending beyond the limit of most commercial systems, is sufficiently broad to capture the spectral-dependent change in conductivity associated to the Drude roll-off frequency and therefore allows for measurement of both carrier density and Drude mobility. In comparison to other characterization methods based on electrical measurements, THz spectroscopy is a non-invasive technique that does not alter the graphene structure or rely on the deposition of electrical contacts, which composition and configuration often affect the measured transport parameters1. We compare the mobility of graphene deposited on different materials: two gate dielectrics (SiO2 and Si3N4) which are traditional materials for computational-based applications, silicon with three doping concentrations, and a hydrophobic, flexible, transparent polymer (Zeonor). We find that substrates with minimal amount of charged impurities and substrates that are flat generally exhibit the highest carrier mobilities. Notably, graphene on high-purity silicon and insulating Zeonor outperform the popular gate dielectrics. Our results guide the field of graphene integrated technologies, by providing valuable insights into the transport potential of graphene supported by substrates commonly used in devices.The selection of substrates in this work is guided by the promise for graphene to be implemented into “beyond Moore” technologies2 in Fig. 2D/IG = 1.94) shown in Fig. In this work all samples are identically prepared, using graphene synthesized by CVD on Cu foil and transferred onto a substrate as schematically represented in Fig. 11, such that:41. The frequency-dependent Drude model, which has been broadly used to describe carrier intra-band scattering behavior in graphene36, yields:σDC is the DC conductivity, ω is the radial frequency, and τ is the scattering time. As a result, we are able to extract values for both σDC and τ from the THz data. In general, the analysis of time-domain THz measurements is restricted to data points within a carefully selected spectral window centered around the maximum THz signal, where experimental noise is considered negligible. Here, we use instead a scan-to-scan statistics to include a larger bandwidth while error bars objectively determine the precision of each spectral data point. More specifically, experimental data are fitted to the Drude model , Si with three doping concentrations corresponding to a resistivity of 10 kΩ cm (intrinsic doping), 15 Ω cm (p-doped), and 5 Ω cm (p-doped), and finally the flexible polymer Zeonor, a cyclo-olefin copolymer. We note that all bare substrates display high transparency to our broadband THz probe. Assuming a diffusive Drude-type transport regime45, we can then calculate graphene’s carrier concentration (NS) and the mobility (μ) from the extracted σDC and τ using the following relations:vF≈ 106 m/s. As a result, THz measurements enable an effective and non-invasive method for probing the influence of the substrate on the transport properties of graphene films.We use the experimental procedure described above to obtain the parameters σDC, τ, NS and NS in graphene is strongly dependent on the substrate. This variation, by more than an order of magnitude, can be attributed to the densities of free and trapped charges in the substrate, which have previously been identified as two dominant parameters affecting NS43. For the insulating substrates, trapped charges are particularly relevant, as those present at the surface may directly transfer charges to graphene and those beneath the surface may still capacitively induce charges in graphene. For the conductive substrates, NS is largely due to direct charge transfer. In our experiment, the largest values of NS are obtained for graphene placed on doped Si and approach 1013 cm−2, corresponding to graphene’s Fermi level being 350 meV away from the Dirac point. This value is comparable to epitaxial graphene grown on SiC46. Insulating substrates, including typical gate dielectrics (SiO2 and Si3N4), high-resistivity Si (ρ = 104 Ω cm) and the polymer Zeonor (ρ = 1016 Ω cm), lead to a lower NS. The lowest doping level we measured corresponds to graphene on Zeonor (NS = 8 × 1011 cm−2), indicating that this substrate has a minimal amount of free and trapped charges contributing to the doping of the 2D material on its surface.In Fig. NS. We obtain higher mobilities for less doped samples, consistent with the notion that substrate charged impurities create an electrostatic potential that limits the mobility20. Interestingly, graphene on high-resistivity Si shows a higher mobility than the one on gate dielectric substrates although these samples have a similar carrier concentration NS. This result can be attributed to a more uniform electrostatic potential profile at the surface of the high-resistivity Si substrate, which results in a longer scattering time τ and, according to Eq.  and the highest mobility, even though this substrate has the lowest dielectric constant among the samples measured. This indicates that the screening of charged impurities in the substrate is not necessarily the main contributor to the high mobility, but other factors come into play, such as the density of trapped and free charges in the substrate, as discussed previously. In general, Fig. The dielectric constant κ of the substrate or environment can play an important role in the transport properties of graphene; larger values of κ imply the ability of an environment to readily screen charged potentials created by trapped scattering centers, and therefore enhance the scattering time and, consequently, the carrier mobilityRq) of the seven substrates used in this experiment  and vice-versa. For example, we measure τ = 91 fs for Si-10 kΩ cm (Rq = 220 pm) while τ = 36 fs for wet SiO2 (Rq = 380 pm). However, we note two exceptions in our experiment: (1) graphene on doped Si features a short scattering time although the substrate is relatively smooth. This suggests that Coulomb scattering could be a dominant mechanism in this case. (2) At the other extreme, graphene on Zeonor has a relatively long scattering time while the substrate roughness is higher, Rq = 650 pm. To assess the adhesion of graphene to Zeonor, we measured the roughness of the graphene sheet on Zeonor, which shows a smoother morphology (Rq = 520 pm), suggesting relatively poor adhesion of the graphene to the substrate. As a result, graphene may experience a reduced influence from the substrate roughness. Note that the mobility in Fig. 51 and HMDS30 demonstrated reduced ambient doping and hysteresis compared to those on SiO2.Although much less systematically studied, substrate roughness can also affect the carrier mobility in graphene since a smooth interface contributes to reduced strain of the film or eliminates wrinkles and edges that could induce scattering. Using atomic force microscopy, we measure the roughness , for graphene supported by distinct substrates. When comparing the results on different substrates, we find the highest mobility for graphene placed on pure silicon and the polymer Zeonor, which outperformed commonly used gate dielectrics. This highlights that the densities of trapped and free charged impurities in the substrate are likely key limiting factors of the graphene film’s mobility. We also find the mobility of devices to be generally improved for substrates that are smoother, except for graphene on Zeonor. In this case, we interpret the high mobility to be due to both the poor adhesion between Zeonor and graphene, minimizing the substrate effect, and to the low density of trapped charged impurities at the interface. A flexible polymer, therefore, can be considered as a promising alternative to some gate dielectrics. These results provide valuable guidance for the effective integration of graphene into technological platforms where high mobility is necessary.In summary, we have demonstrated the implementation of terahertz transmission spectroscopy for probing the equilibrium transport properties of CVD graphene supported by seven substrates, distinct in their density of charged impurities, dielectric constant and surface roughness. We find that the resulting conductivity spectra for graphene films agree well to a Drude model for intraband behavior, consistent with other reports. We have demonstrated a method for weighted Drude fitting based on statistical averaging and extracted transport properties , which is transferred onto a substrate using a standard PMMA-based wet etching technique54. These pulses are focused onto a nonlinear GaP crystal where THz transients are generated by difference frequency mixing. The time-domain detection relies on electro-optic sampling inside a second GaP crystal55. The measurements are performed in a transmission geometry. Apodization of the time-domain signal allows us to exclude Fabry-Pérot echoes. Therefore, only the pulse directly transmitted through the sample is considered in extracting the graphene transport parameters. The samples, at room temperature and under normal ambient conditions, are placed at the focus of an off-axis parabolic mirror, with a numerical aperture NA = 0.5, focusing the THz beam to a 400 µm diameter (1/e2) at 1 THz. The optical probe size is significantly larger than any local defects, such as wrinkles, bubbles and other imperfections revealed by AFM images of the samples. Large scale anisotropy reported in previous work37, is accounted for by performing measurements at different locations on the sample at a ~ 5 mm separation. Note that we purge the system with dry air (< 0.5% RH) to minimize THz absorption in water vapor.The time-resolved THz system is based on a near-infrared source delivering 180 fs pulses at 1035 nm, which can be compressed to ~ 50 fs pulses using spectral broadening in a gas-filled hollow-core photonic crystal fiber and dispersion compensation opticsSupplementary Information


Lithium-ion capacitors (LICs) are attracting increasing attention because of their potential to bridge the electrochemical performance gap between batteries and supercapacitors. However, the commercial application of current LICs is still impeded by their inferior energy density, which is mainly due to the low capacity of the cathode. Therefore, tremendous efforts have been made in developing novel cathode materials with high capacity and excellent rate capability. Graphene-based nanomaterials have been recognized as one of the most promising cathodes for LICs due to their unique properties, and exciting progress has been achieved. Herein, in this review, the recent advances of graphene-based cathode materials for LICs are systematically summarized. Especially, the synthesis method, structure characterization and electrochemical performance of various graphene-based cathodes are comprehensively discussed and compared. Furthermore, their merits and limitations are also emphasized. Finally, a summary and outlook are presented to highlight some challenges of graphene-based cathode materials in the future applications of LICs. With the increasing global energy consumption, the growing concerns of the depletion of fossil fuels, the corresponding climate change and environmental pollution have arisen ,2,3. Thu+ diffusion rate in the bulk electrode and low electrical conductivity of the cathode lead to inferior power density, while the continuous and usually uncontrollable decomposition of electrolytes and the serious deterioration of material structure result in a poor cycle life for LIBs . . 2CO3 anmAh g−1) . Specififor LICs ,103. Forout 5 nm f. Conseqout 5 nm g–h.2) nanoparticles were uniformly deposited onto the graphene oxide sheets via an aqueous-solution-based regular deposition process. Then, the SnO2/GO suspension was spray-dried to obtain a spherical composite, which was heated to induce the selective decomposition of the graphene adjacent to the SnO2 nanoparticles. It is noteworthy that the temperature should be carefully adjusted to be lower than the carbon combustion temperature in the catalytic carbon gasification process. Finally, the spherical SnO2/rGO was refluxed in HI to etch the catalysts and to reduce GO. The as-prepared HG has a spherical morphology and porous structure with rich in-plane holes of about 5 nm corresponding to the metal oxide size  with abundant in-plane pores using this method . The synide size b. The N2esopores c. This resopores c, which esopores d. As exp kh kg−1 e. The ouIn summary, benefitting from the 3D continuous porous structure and inherently high conductivity of graphene, pure graphene-based porous materials could deliver high capacity and superb rate capability and thus achieve high energy and power densities and cycling stability when used as a cathode in LICs, as summarized in Benefitting from the layered structure, graphenes are good 2D building blocks for constructing 3D porous composites . Elabora2 g−1 and excellent bulk conductivity (up to 303 S m−1) because of the introduction of graphene. Taking the sucrose-based 3DGraphene, for example, it achieves an ultrahigh SSA of 3355 m2 g−1 with a well-controlled pore size of primarily 2–6 nm for the samples of optimized ratio  with GO sheets and biomass or polymers  using standard industry steps of in situ hydrothermal polymerization/carbonization and KOH activation a 24]. T. T24]. Ted ratio e,f, makiapacitor g 74]. L. L2 g−1 2 g−1 and the largest pore volume of 1.67 cm3 g−1 were obtained  and a capacitance retention of 84.8% after 5000 cycles. Sun et al. fabricated a single carbon nanotube (SWCNT) and graphene composite (SG) by inserting the SWCNT into the space between the graphene nanosheets [In the previous reports, conductive extra spacers  were usually introduced to prevent the restack of graphene-based materials by forming 3D composites, which leads to high SSA and/or electrical conductivity, and thus excellent specific capacitance and rate capability could be obtained ,121. Simnosheets . As show2 anode, the full LIC cell exhibited an ultralong cycling life with 96% capacity retention after 10,000 cycles at 5 A g−1  can also be applied as spacers to inhibit the restacking of graphene sheets considering their unique merits of high conductivity, excellent flexibility and high capacity derived from fast redox reaction. Ock et al. proposed a high-capacity and high-rate PANI@rGO and used it as a capacitor-type electrode . PANI@rG 5 A g−1 d. Moreov kW kg−1 e. The en3 treatment, the final product was obtained. N-GMCS possesses a hierarchical porous structure, 3D conductive network as well as high packing density (0.6 g cm−3), making it a promising capacitor-type electrode for high-energy devices. As expected, LICs with N-GMCS as the cathode delivered maximum energy and power densities of 80 Wh kg−1 and 352 kW kg−1, respectively (corresponding to 66.7 Wh L−1 and 292 kW L−1) , which always leads to inferior volumetric energy density . Therefo kW L−1) b.2 g−1 and its electrode density is still as high as 0.71 g cm−3, which is around 173% of that of AC. Hence, although AC/G-57 shows relatively lower gravimetric specific capacity compared with pristine AC, it has the largest volumetric specific capacity of 45 mAh cm−3, which is 137% of AC and 147% of HPGM, respectively  composite as the capacitor-type cathode for high gravimetric/volumetric energy density LICs . The typectively g. Furtheectively h. Conseqectively i,j. A siBased on the above discussion, graphene-based 3D composites show obvious advantages compared with reduced GO and pristine porous graphene, as summarized in LICs possess the merits of a high energy density, high power density, large operation voltage, wide working temperature range and long cycling stability, and thus are considered to be one of the ideal energy storage devices to overcome the disadvantages of batteries and supercapacitors. Although LICs have the potential to bridge the gap between batteries and supercapacitors, their electrochemical performance still fails to reach the requirements of commercial applications. Especially, the unsatisfactory energy density of state-of-the-art LICs is one of the main obstacles preventing their applications, which is mainly due to the low capacity of the capacitor-type electrode and the kinetics and capacity imbalances between the cathode and anode. For instance, traditional capacitor-type materials such as AC suffer from inferior specific capacity and poor rate performance because of a relatively low SSA and electrical conductivity. Hence, developing high-capacity capacitor-type materials is significantly important to obtain high-energy LICs. Thanks to their unique 2D structure, high electrical conductivity, large SSA, tunable surface chemistry and excellent chemical and electrochemical stability, graphene-based cathode materials have demonstrated remarkable achievements in LICs. In this review, a systematic summary of graphene-based capacitor-type materials has been presented. It could be easy to conclude from the above results that graphenes, either as active materials or as building blocks to form composites with other materials, have shown great potential in capacitor-type cathode candidates for LICs.(1)High-capacity capacitor-type materials are urgently needed. To match the high capacity of battery-type anodes, developing cathode materials with improved capacity is the top priority. The cathode stores energy through a physical adsorption/desorption process at the electrolyte/electrode interface, which leads to a fast charge/discharge rate. On the other hand, the non-Faradaic energy storage mechanism also results in low capacity because it is critically influenced by the SSA. A high SSA could provide more active sites for ion adsorption and, to a certain extent, the capacity is raised with the increase in the SSA. However, it should be pointed out that not all the surface can be accessible by the electrolyte ions . Therefo(2)The preparation of graphene-based cathode materials at low cost is one of the critical factors for large-scale applications. Although pure graphene-based porous materials can serve as outstanding capacitor-type electrodes due to their high electrical conductivity and large SSA, the high cost impedes their further commercial utilization. Forming composites with other materials is a facile but feasible method to solve this problem, such as biomass or polymer/graphene hydrogel-derived graphene-based 3D porous materials initially proposed by Chen’s group . In such(3)Developing battery-type materials with a high rate and long-term stability is another big challenge but imperative issue. High-capacity anodes ensure the high energy of the full cell. However, the high energy density of state-of-the-art LICs could only be realized at the cost of low power output because of the sluggish redox reaction and/or inferior electrical conductivity of battery-type anodes. Hence, designing nanostructured materials with tunable porosity and compositing with highly conductive materials are always applied to achieve high-rate anodes. These strategies could help to reduce the capacity and kinetics imbalances between the cathode and anode, leading to improved energy and power densities . With th(4)The volumetric performance of graphene-based materials should receive more attention for commercial applications. Graphene-based cathode materials have shown enhanced gravimetric capacity compared with commercial AC. However, their large SSA and highly porous structure result in a low taping density and consequently low volumetric energy density, which is a big obstacle for practical utilization. In addition, more binders and solvents are needed in the electrode fabrication process because of the highly porous nanostructured carbon materials, increasing the manufacturing cost and decreasing the energy density. Thus, the porosity and taping density should be well balanced. To achieve high volumetric energy density at a low cost, future research can focus on forming graphene-based 3D composites by using capillary drying or rapid drying processes ,132.(5)Advanced electrolytes with a wide working voltage and high safety are also needed. Currently, typical LICs commonly adopt organic electrolytes to achieve a high operation voltage. However, they suffer from safety issues associated with volatility, flammability and toxicity. Hence, other novel electrolytes have been explored. For example, ionic liquids are regarded as a promising alternative to the organic electrolyte owing to their large working voltage, high conductivity and excellent thermal stability without risk of catching fire ,138. Rec(6)The decomposition of electrolytes should not be ignored. Generally, electrolyte decomposition on the cathode and anode takes place during the charge/discharge process, especially at a high working voltage, resulting in gas emission, impedance increase and low energy conversion efficiency. At the anode side, this phenomenon can be largely restrained by forming a stable solid–electrolyte interface (SEI) during the first several cycles. However, an effective strategy to suppress the electrolyte decomposition at the cathode side is still absent . Fortuna(7)Besides the above discussion, other critical issues should also be solved before industrial-level production and widespread applications. First of all, feasible pre-lithiation technology should be developed because the anode, especially nanostructured materials with a large SSA and rich porosity, would consume a large amount of lithium ions when forming a stable SEI ,149. Wel(8)Additionally, considering the limited and uneven distribution of lithium resources, other metal-ion capacitors are drawing increasing attention and have recently become the research hotspot. In particular, monovalent ion systems  are the most promising alternatives to LICs because they have a similar cell configuration and energy storage mechanism as well as abundant resources ,157. HowNevertheless, the performance of the current graphene-based capacitor-type electrodes is still far from the practical requirements. Moreover, other remaining challenges related to battery-type anodes, the production of graphene-based materials, volumetric performance, electrolytes, performance imbalance between the anode and cathode and pre-lithiation technologies should be given more attention, too. Thus, the following several aspects should be considered to overcome the present challenges and to realize the commercialization of LICs:In conclusion, LICs have witnessed tremendous progress during the last decade, especially in electrode materials. Their development steps are speeding up and large-scale application will be realized in the near future. Without a doubt, graphene-based nanomaterials could play a vital role in achieving high performance due to their outstanding electrochemical properties.


In the proposed structure, a refractive index grating is formed at the subwavelength scale due to the periodical distributions of amorphous and crystalline states, and the structure is intrinsically flat. The numerical simulation shows that nearly 100% absorption can be achieved at the wavelength of 1550 nm, and the Q factor is more than hundreds due to the loss-less value of Sb2S3 in the near-infrared region. The absorption spectra can be engineered by changing the crystallization fraction of the Sb2S3 as well as by varying the duty cycle of the grating, which can be employed not only to switch the resonant wavelength but also to achieve resonances with higher Q factors. This provides a promising method for realizing integrated graphene optoelectronic devices with the desired functionalities.Graphene absorbers have attracted lots of interest in recent years. They provide huge potential for applications such as photodetectors, modulators, and thermal emitters. In this letter, we design a high-quality (Q) factor resonant graphene absorber based on the phase change material Sb Graphene absorbers have attracted lots of interest in recent years ,2,3. ThePhase change materials (PCM), such as ong time ,31,32, song time , dynamicong time ,35,36, bong time , and ligong time ,39,40,41ong time ,43. Elecong time . HoweverIn this study, we propose a high Q rewriteable resonant graphene absorber with the phase change material antimony trisulphide . Since our structure is assumed to be “infinitely extending” in the y direction, we use a two-dimensional model for simulations (x–z plane). We used Floquet periodic boundary conditions in the x-direction, and port boundary conditions at the top and bottom of the model along the z-direction. In the simulation, urements , and thety model :(1)σω=σid is the thickness of graphene. For the graphene monolayer, we have Here, graphene . Figure f = 0.5 to f = 0.1, the resonance wavelength shifts from 1547.9 nm to 1542.4 nm and the maximum resonant absorption decreases from 99.83% to 40.88%. At the same time, the spectral linewidths (FWHM) decrease from 2.4 nm to 1.4 nm, corresponding to an increase of the Q factor from 644 to 1101 (Q = The excitation of the guided mode resonance can be controlled by changing the geometric parameters of the structure (such as period and duty cycle), as mentioned above. We now fix the period of the grating, and tune the absorption spectra by changing the duty cycle. As shown in the e theory , that is (γ + α) , the FWHf is reducing, and it can be avoided so long as the effective absorption rate of graphene f = 0.1 and f = 0.2 as the example, as shown in the f = 0.1 and f = 0.2 are 0.23 nm and 0.88 nm, corresponding to high Q of 6726 and 1760, respectively, which is the consequence of the decrease of the mode leakage rate This type of mismatch results from the decrease of the mode leakage rate f = 0.5 and vary the crystallization fraction of A previous work has demonstrated that there is an intermediate state of of Sb2S3 . The effmix rule :(3)εeffλTo investigate the influence of the boundary between amorphous and crystalline PCM, we also set a linear graded-index with the width of 100 nm at each boundary between amorphous and crystalline  see the c.f = 0.1 and a spacing layer between the phase change material-based grating and graphene to reduce both the coupling rate and the absorption rate. This type of high Q resonant of two-dimension materials of the integrated phase change metadevice can also be applied to other atomical materials, such as In all, we have proposed a type of subwavelength resonant graphene absorber based on the phase change material witching ,55, couliderable . This priderable .


The degree of doping increased with DUV exposure time. However, n-type doping by DUV in vacuum reached saturation after 60 min of DUV irradiation. The p-type doping by DUV in air was observed to be quite stable over a long period in a laboratory environment and at higher temperatures, with little change in charge carrier mobility. The p-doping in pure O2 showed ~15% de-doping over 4 months. The n-type doping in pure N2 exhibited a high doping effect but was highly unstable over time in a laboratory environment, with very marked de-doping towards a pristine condition. A lateral pn-junction of graphene was successfully implemented by controlling the radiation environment of the DUV. First, graphene was doped to n-type by DUV in vacuum. Then the n-type graphene was converted to p-type by exposure again to DUV in air. The n-type region of the pn-junction was protected from DUV by a thick double-coated PMMA layer. The photocurrent response as a function of Vg was investigated to study possible applications in optoelectronics.The electronic properties of single-layer, CVD-grown graphene were modulated by deep ultraviolet (DUV) light irradiation in different radiation environments. The graphene field-effect transistors (GFETs), exposed to DUV in air and pure O There are several methods to attain single-layer graphene, such as mechanical exfoliation of graphite, epitaxial growth of graphene, and chemical vapor deposition (CVD) on a metal (Cu or Ni) foil substrate ), as shown in energy band diagram in  surface . The mobg are shown in CNP in sample-2 was observed around 5 V which readily shifted towards negative gate voltages (−14 V after 60 min-DUV) with increased treatment time, indicating n-type doping. Sample-2 exhibited a saturation point for n-type doping behavior after 60 min of DUV exposure. − or H2O−) by hole recombination (h+ + O2− = O2) and releases electrons. With small changes in carrier mobility and no major changes in the graphene structure, these liberated electrons induce an n-type doping activity in graphene [F is increased above ED, as shown in the energy band diagram in g for sample-3 (DUV irradiation in pure O2), illustrating the p-type doping in graphene for 60 min of exposure time. The photo-assisted oxidation by DUV irradiation in a pure O2 environment induces p-type doping to the graphene. The transfer characteristics of sample-4 (DUV irradiation in pure N2) are shown in 2 environment. The shift in VCNP for sample-4 (VCNP = ~−17.8 V) was higher compared with sample-2 (VCNP = ~−13.7 V) for 60 min of DUV exposure time. The N2 gas in the presence of DUV irradiation dissociates into atoms which are absorbed on the surface of the graphene. These N2 atoms react with the oxygen atoms present on the surface of the graphene and produce O2 molecules that are removed [2 atoms under DUV attach to the graphene surface and become the major source of electrons, inducing higher n-type doping. The transfer characteristics for sample-5 were investigated for 60 min DUV in pure N2, followed by 60 min irradiation in vacuum, as shown in CNP = −24.6 V). Under further DUV exposure in vacuum, the N2 atoms attached to the graphene surface induce a further doping effect. Both N2 atoms and larger exposure times are responsible for a higher n-type doping effect. CNP (CNP after DUV Doping—CNP before DUV Doping) and VCNP for DUV doping in different irradiation environments. The ∆VCNP shows a higher shift in the CNP position for the air condition in p-type doping, and for pure N2 followed by the vacuum condition in n-type doping, for 60 min of DUV exposure time.The electric transport characteristics for sample-2 (DUV irradiation in vacuum) with resistivity as a function Vgraphene . This do removed ,31,32,393P) atoms dissociated from oxygen in air under DUV were attached to the most stable bridge sites of graphene, exhibiting stable p-type doping behavior [CNP = 13.7 V to 11.3 V. It was predicted that the oxygen from air in the ambient laboratory conditions would attach to the graphene surface over time, inducing a de-doping effect. The oxidation of the graphene layer over the period is the main reason behind the de-doping effect observed in graphene. 2 molecules which were unable to find stable bridge sites would detach from the graphene surface. The doping stability of sample-4 was investigated over 4 months, exhibiting a high de-doping effect of around 54%, as shown in 2 atoms attached to the graphene surface, inducing n-type doping, were detached over time because of weak dangling bonds. The oxygen from the ambient air also reacted with the graphene, inducing a large de-doping effect in n-type behavior because of the oxidation. 2 atoms attached to the graphene surface with weak dangling bonds detached and the O2 atoms from the ambient air reacted, resulting in very high de-doping towards a pristine state. Thus, from our studies, we observed that p-type doping stability in sample-1 was very high compared to sample-3, which exhibited a small de-doping effect in sample-3 over time. The n-type doping stability in sample-2 with little de-doping was considerably better compared to sample-4 and sample-5 which showed a large de-doping effect over time.The stability of the doping level of graphene is an important factor for its application in electronic devices. behavior . Figure CNP, similar to pristine graphene. No change in electronic properties and the doping effect in graphene by DUV irradiation were observed for the device coated with a thick PMMA layer. As previously reported, the transmission of light through the PMMA layer decreases when the thickness of the film is increased [CNP positions for pristine graphene, single layer PMMA (1274 nm), and double-layer PMMA (2548 nm) coated graphene, respectively. It can be readily observed that sample-7, with a thicker layer of PMMA (2548 nm), showed a negligible shift in the CNP position for different DUV exposure times. Furthermore, the effect of DUV light irradiation on graphene, covered with PMMA, was investigated by assessing the transfer characteristics of the device for different DUV treatment times, as shown in ncreased ,43. The d as a function of Vg in sample-10 for the pn-junction, p, and n regions of the device. An optical image of the device with defined n, p, and pn-regions is shown in the inset of CNP of around −8 V. The red transfer curve exhibited the counter doped p-type behavior of the graphene with a VCNP position at around 30 V f. On investigation of the transfer characteristics of the pn-region, it exhibited two distinct CNPs at negative and positive Vg, each corresponding to the n-type and p-type doping effect in graphene, shown by the black transfer curve in d-Vd characteristics of the n, p, and pn-regions at different Vg with Id sweep from −2 V to 2 V, are shown in d on positive gate voltages for n-type and a decrease in Id on positive gate voltages for p-type regions, respectively. d-Vd characteristics of the n, p, and pn-regions at different Vg with Id sweep from −2 V to 2 V, are shown in d on positive gate voltages for n-type and a decrease in Id on positive gate voltages for p-type regions, respectively. The DUV induced n and p-type doping are reversible under controlled conditions ,22,25,30p) (the difference of Id under light and Id without light illumination) as a function of Vg was investigated for graphene pn-junction devices using an ultraviolet light (λ = 365 nm and 350 µWcm−2 intensity) source (Mightex P/N WLS-22-A light source) as shown in d of 1 V, is shown in p for the pn-junction was readily enhanced as compared to the p and n region of the graphene because of an increase in the photocarrier’s generated built-in potential created by the formation of the pn-junction [g. The Ip curve depicts a positive photocurrent at negative Vg which undergoes a sign reversal and becomes negative for positive Vg, which is consistent with previously reported studies [p can be modulated by Vg [++p, p+n, and n+n+, respectively [n-type and CNPp-type) formed by the hole and electron conduction regions confirm the formation of the pn-junction in the graphene single channel [2 led to an increase in conductivity, and the electric field effect in the graphene was enhanced due to applied gate voltages resulting in increased mobility, as also observed in other semiconducting 2D materials [g and can modulate the polarity and magnitude of Ip with applied gate voltages [p was observed around a Vg of −20 V outside the pn-junction region of the device which usually has the maximum potential difference of the p and n regions. This can be explained by the fact that light was illuminated on the whole device which includes not only the p+n region but also the metal and interface junction in p++p and n+n+ regions of the graphene [The photocurrent . The shift in G and 2D peaks of Raman spectra towards higher wavenumbers and the shift of CNP towards positive Vg values in transfer characteristics confirmed the p-type doping for graphene devices with an increase in DUV exposure time in air and pure O2 environments. The p-type doped graphene exhibited high stability over time with a minor de-doping (14%) effect in the pure O2 environment. The shift in G and 2D peaks towards smaller wavenumbers in Raman spectra and the CNP shift towards negative gate voltages in transfer characteristics confirmed the n-type doping in graphene exposed to DUV irradiation in vacuum and pure N2 environments. The n-type doping with a small de-doping (16%) effect for the device exposed in vacuum was considerably better compared to highly unstable n-type doping with a large de-doping (54% and 90%) effect over time for devices exposed to DUV in pure N2 and pure N2 followed by a vacuum environment. The thick PMMA (2548 nm) layers reduced the DUV irradiation effect on graphene by increased light absorbance and reduced light transmittance. A lateral pn-junction in a single graphene channel was fabricated in a controlled DUV irradiation environment and specified doping in selected regions with and without PMMA coating. The back gate-dependent transfer and Id-Vd characteristics for n, p, and pn regions of the device validate the process to be a suitable technique to alter the electronic properties of graphene, without varying the physical and chemical properties of graphene. The results of photo-response current measurement as a function of back-gate voltage showed increased photo-response of the device because of increased field-effect mobility in the graphene channel. This study has presented a possible photo-assisted technique under defined conditions for the modification of the electronic properties of graphene for potential future application in electronic and optoelectronic devices.In this study, we thoroughly investigated the DUV-irradiation-induced doping effect in CVD-grown graphene, under controlled irradiation environments (air, vacuum, pure O


This work introduces a novel humidity sensor based on a nanocomposite material comprising graphene decorated with three-dimensional flower-like structures of zinc oxide (Gr/3D–ZnO) fabricated via a hydrothermal method with various weight percentages of graphene. The surface structure and morphology of the Gr/3D–ZnO nanocomposite were analyzed using XRD, EDS, SEM, TEM, and Raman spectroscopy. The influence of humidity on the electrical properties of the nanocomposite was also investigated. Experiment results revealed that the nanocomposite with 70 wt% of graphene provided high sensitivity (S = 446) with rapid response times (120 s) and recovery times (160 s). These results demonstrate the excellent potential of the proposed Gr/3D–ZnO nanocomposite in monitoring atmospheric humidity. A discussion on the mechanism underlying the effects of humidity on the Gr/3D–ZnO nanocomposite is also provided. Atmospheric levels of water vapor  can profoundly affect electronic devices, meteorological phenomena, agriculture, manufacturing, and food storage . Efforts2 nanopowders [3 nanosheets [2O3 nanopowders [2 nanorods [2 nanofibers [2 bonded carbon atoms, has a large surface to volume ratio and excellent conductivity [Numerous types of humidity sensors have been developed using resistive ,5 and caopowders  and nanoopowders , ZnO nanopowders , WO3 nannosheets , Fe2O3 nopowders , graphenopowders , organicopowders , ZrO2 nananorods , and NiOnofibers . Among tnofibers . ZnO cannofibers , nanorodnofibers , nanoshenofibers , nanoparnofibers , nanofibnofibers , hollow nofibers , and nannofibers . Despitenofibers . Nonethenofibers . Graphenuctivity ,35,36, wuctivity ,39,40,41uctivity ,43. The uctivity ,45.Our objective in this study was to fabricate a sensor based on a nanocomposite material comprising graphene decorated with three-dimensional flower-like structures of zinc oxide (Gr/3D–ZnO). The surface structure and morphology of the Gr/3D–ZnO nanocomposite were characterized using XRD, EDS, SEM, TEM, and Raman spectroscopy. We also investigated the influence of humidity on the electrical properties of the nanocomposite. The completed humidity sensor exhibited ultra-high sensitivity with fast recovery and response times over a broad range of relative humidity (RH) levels.3)2·6H2O, 98%), anhydrous alcohol , L-histidine , urea ((NH2)2CO, 99.5%), and polyvinyl alcohol  were purchased from Sigma-Aldrich Co., Inc.Commercial graphene film of high purity (>99%) was purchased from UniRegion Bio-Techn  and Sigma–Aldrich Co., Inc. . Zinc nitrate hexahydrate . The crystal structure of Gr/3D–ZnO was characterized using an XRD-6000 Shimadzu X-ray diffractometer with Cu Kα radiation of 1.5405 Å at 40 kV and 30 mA between 10° and 80° (2θ) at intervals of 2°/min. Infrared spectra were measured using an Agilent Cary spectrophotometer. The characteristic Raman spectrum of the Gr/3D–ZnO nanocomposite was measured at RT under excitation from a laser source at a wavelength of 532 nm .2), whereupon the chips were heated to 80 °C and held at that temperature for 0.5 h before undergoing calcination at 400 °C for 2 h.A solution of 10% PVA was added to promote the binding of the composite. A pair of comb-like gold electrodes were applied to an alumina substrate via dip-coating  and Rh is the resistance under a specific level of humidity [The experiment setup used to assess the performance of the humidity sensor is described in our previous work . Brieflyhumidity . The humHumidity hysteresis error (H) was calculated using the following equation:e output . The rese output . RH was −1 and 1568 cm−1) were presumably due to in-plane bond stretching of sp2 hybridized carbon atoms and the corresponding combinational modes and overtones [−1 are the vibrational modes of ZnO [As shown in vertones ,51. The s of ZnO . The Gr/We assessed the sensitivity of Gr/3D–ZnO nanocomposite materials  to humidity based on impedance measurements obtained using AC voltage (1V) at a frequency of 1 kHz. As shown in Humidity hysteresis is an important factor in evaluating the reliability of humidity sensors . As showResponse and recovery times largely determine the practical applicability of humidity sensors. As shown in 12%/R90% = 446). The response to other gas species was as follows: CO (1.55), NH3 (1.41), NO2 (1.36), and NO (1.18). Overall, the Gr/3D–ZnO nanocomposite exhibited excellent selectivity for humidity.Selectivity is another crucial parameter in assessing the performance of humidity sensors. 2O or H3O+ was on the discontinuous water layer was difficult [2O or H3O+. Grotthuss and Casalbore-Miceli et al. outlined an ion transfer mechanism involving the transfer of H2O or H3O+ on serial water layers: H2O + H3O+ → H3O+ + H2O [At low relative humidity (RH), the probability of contact between water molecules and Gr/3D–ZnO nanocomposite particles was low, so only the outer particles came into contact with the water molecules, as shown in ifficult . TherefoO+ + H2O ,60. ThisIn this work we have succeeded in fabricating Gr/3D–ZnO nanocomposites via a hydrothermal process to create a novel low-cost humidity sensor based on Gr/3D–ZnO nanocomposite material. Experiment results revealed that the nanocomposite with 70 wt% graphene provided a high sensitivity (S = 446) with rapid response times (120 s) and recovery times (160 s). The highest humidity hysteresis error was only 2.32% over a wide range of RH values. These results demonstrate the excellent potential of the proposed Gr/3D–ZnO nanocomposite for the development of low-cost sensors to monitor atmospheric humidity.


Graphene and its derivatives, such as graphene oxide (GO) or reduced graphene oxide (rGO), due to their properties, have been enjoying great interest for over two decades, particularly in the context of additive manufacturing (AM) applications in recent years. High-impact polystyrene (HIPS) is a polymer used in 3D printing technology due to its high dimensional stability, low cost, and ease of processing. However, the ongoing development of AM creates the need to produce modern feedstock materials with better properties and functionality. This can be achieved by introducing reduced graphene oxide into the polymer matrix. In this study, printable composite filaments were prepared and characterized in terms of morphology and thermal and mechanical properties. Among the obtained HIPS/rGO composites, the filament containing 0.5 wt% of reduced graphene oxide had the best mechanical properties. Its tensile strength increased from 19.84 to 22.45 MPa, for pure HIPS and HIPS-0.5, respectively. Furthermore, when using the HIPS-0.5 filament in the printing process, no clogging of the nozzle was observed, which may indicate good dispersion of the rGO in the polymer matrix. Additive manufacturing (AM), commonly known as 3D printing, has only seen a significant increase in interest for around three decades ,2. The IThe huge increase in interest in additive manufacturing is the result of the many advantages that this technique has over conventional manufacturing techniques such as subtractive processes, formative processes, and joining processes . The maiDue to its numerous advantages, 3D printing has found application in many areas of our lives. The majority of them certainly include biomedicine , aerospace and the automotive industry, electronics, buildings, and sports ,11,12,13Fused filament fabrication is one of the most widely used and rapidly developing AM technologies . Its proA polymer gaining more and more attention in additive manufacturing is high-impact polystyrene (HIPS). It is widely used in prototyping as it is characterized by high dimensional stability, low cost, and ease of processing and coloring ,29. ThisTo the best of our knowledge, this is the first article to describe and research printable high-impact polystyrene/reduced graphene oxide composite filaments for fused filament fabrication. The obtained filaments were characterized in terms of morphology and thermal and mechanical properties. The printed parts were made of a material characterized by the best parameters, using a commercial FFF 3D printer . The paper also presents the preliminary test results of the obtained printed parts.4, 98% H2SO4, 30% H2O2 . The obtained graphene oxide was purified with hydrochloric acid . Reduced graphene oxide was prepared via thermal reduction. The interlayer distance and the average number of layers for rGO were 0.37 nm and 6, respectively. The elemental composition of rGO was 18.4 at.% O and 81.6 at.% C. The method of preparation and detailed characteristics of rGO can be found in the High-impact polystyrene (HIPS) (POLYSTYRENE IMPACT 3450)  pellets were supplied by Total Refining & Chemicals . The following reagents were used to obtain graphene oxide: graphite powder with the grain size < 20 µm , and KMnOThe two-stage process was used to produce the HIPS/rGO filaments. The first step consists in preparing a masterbatch with the addition of 10 wt% rGO. The masterbatch was obtained using a Zamak Mercator EHP-2x16S co-rotating twin-screw extruder . The equipment parameters are 15.8 mm (screw diameter) and the length/diameter ratio of 40. The temperature range from hopper to head ranged from 140 °C to 240 °C. Next, the masterbatch was chopped into pellets and re-extruded to prepare a filament with a uniform diameter of 1.75 mm, which fit the commercialized 3D printer. The composite filaments were obtained with 0.1, 0.5, 1, and 2 wt% content of reduced graphene oxide. The tensile test specimens were fabricated using an Urbicum DX 3D printer . The FFF printing parameters are listed in A Phenom ProX scanning electron microscope (SEM)  was used to observe the morphology of the filaments. Cross-sections samples were prepared by the fracturing of the filaments after cooling in liquid nitrogen. All samples were coated with ~10 nm layer of gold using Leica EM ACE200 sputter coater . The energy-dispersive spectrometer (EDS) was applied to analyze the elemental composition of the reduced graphene ox-ide. The measurements were taken at a voltage of 15 kV.−1, the spectral range from 4000 to 400 cm−1 with 256 scans and deuterated triglycine sulphate (DTGS) detector. OMNIC software  was applied to collect data and post-processing.Fourier Transform Infrared Spectroscopy (FTIR) measurements were conducted using a Nicolet 6700 FT-IR spectrometer . The apparatus was equipped with an MTEC model 300 photoacoustic accessory . The spectra were registered at the resolution of 8 cmA differential scanning calorimetry (DSC) was performed using Universal V4.5A TA Instruments . The samples were heated from 0 to 210 °C at a heating rate of 20 °C/min. Measurements were carried out under a nitrogen atmosphere with a purge flow of 40 mL/min. DSC curves were recorded during the first and second (after melting) heating cycles. The glass transition temperatures were determined based on the curves, and the enthalpy relaxation peaks were evaluated.The thermal properties of the samples were determined by a Thermogravimetric Analyzer Q500 . All measurements were con-ducted at a temperature range of 30–550 °C and a heating rate of 20 °C/min in a nitrogen atmosphere (60 mL/min). The Universal V4.5A software supplied by TA Instruments was used to analysis of DSC and TGA curves.The melt flow rate (MFR) measurements were performed according to PN-EN ISO 1133-1: 2011 (Procedure A) using a Modular Melt Flow, Model 7023.000 . The MFR measurements were carried out at 200 °C with an applied load of 5 kg.The tensile properties of HIPS filaments were tested using an Instron 5544 (with a maximum load force of 5 kN) at a constant temperature of 25 °C and humidity of 50% RH. A gauge length of 50 mm and crosshead speed of 20 mm/min were used to determine the tensile strength, Young’s modulus, and elongation at break. The results are the average of at least 20 samples.−1 are shown in −1, 3059 cm−1, and 3025 cm−1 as a result of radiation absorption by C–H stretching oscillators in the phenyl ring. This indicates a strong interaction between the phenyl substituent ring in HIPS and the rGO rings and probably affects their spatial arrangement to the aliphatic chain. Moreover, changes in the frequency of resonance vibrations of C–H stretching oscillators in the aliphatic chain are observed at 2948–2841 cm−1, which may indicate changes in the conformation of the chain within the aromatic substituent under the influence of rGO addition.FTIR test results for pure HIPS filament samples and samples of different rGO content in the range of 3150–2780 cm−1, which is the result of radiation absorption by the C–H stretching oscillators in the tertiary group. For composites, an increase in the intensity of radiation absorption was also observed at 1182–1069 cm−1, originating from deformation vibrations of the C–H oscillator. This may indicate strong spatial interactions between the additive and the matrix, which affect the geometrical arrangement of these oscillators. The single band for the HIPS filament without the addition of rGO visible at 1169 cm−1, resulting from the deformation vibrations of the C–H oscillator in the ring, is divided into two bands of different resonant frequencies at 1182 cm−1 and 1153 cm−1.In the comparison of FTIR spectra for the fingerprint region , a clearIn the case of FFF 3D printing processes, it is crucial to know the extrusion temperatures, as well as the flowability of the printed materials, as this can lead to greater accuracy and precision of the printing process . The melDSC calorimetric tests of HIPS filaments with the addition of reduced graphene oxide were performed in the range of 0.1 to 2 wt%. In order to emphasize the tendency of the observed changes, a masterbatch containing 10 wt% of rGO was also tested. Measurements were carried out on the samples as received, as well as after melting. In both cases, only the glass transition of the HIPS matrix is visible in the DSC curves. The transition is reflected as a characteristic line jump of the calorimetric signal corresponding to a surge in specific heat values in the glass transition temperature range. The glass transition area analysis for HIPS filament samples is shown in g value. However, it should be noted that it is only 0.8 °C lower than the Tg for filaments containing 0.5–2 wt% of rGO. The glass transition temperature only for the masterbatch is slightly shifted towards higher temperatures (up to 103.3 °C). The increase in the glass transition temperature shows a decrease in molecular mobility due to filler–matrix interactions [g values determined based on the DSC curves registered in the second heating cycle, i.e., after melting the filaments  shows the lowest Tractions ,51, whicilaments , they arg value, shifts monotonically towards higher temperatures from 105.6 °C for pure HIPS to 107.9 °C for a masterbatch containing 10 wt% of rGO. At the same time, the specific enthalpy of apparent melting decreases in the same order from 0.18 to 0.09 J/g. This clearly proves the influence of the reduced graphene oxide on the HIPS structure. The additive being in the form of rigid graphene micro-sheets hinders the spontaneous arrangement of the structure. This arrangement is destroyed each time the samples are heated to a temperature above Tg, as a result of which an endothermic peak of apparent melting is formed on the curves.The impact of the rGO becomes apparent only when the additional thermal effect accompanying the change in glass transition is considered. It is the endothermic peak of enthalpy relaxation, i.e., so-called apparent melting . This efThe discussion of the impact of rGO on the thermal properties of HIPS samples was continued based on the results of thermogravimetric studies. In the first stage of the analysis, the initial shape of the TG curves was studied, and the thermal stability of the samples during heating under a nitrogen atmosphere was determined in two ways . The firThe considerations concerning the influence of the reduced graphene oxide on the thermal properties of HIPS based on thermogravimetric studies were also continued at higher temperatures corresponding to the thermal dissociation of the matrix. The analysis of the DTG curves  demonstrBased on the thermogravimetric studies, it was demonstrated that the thermal stability of the composite samples was reduced at temperatures above 250 °C. The reduced graphene oxide used in the studies is almost completely stable in the considered temperature range . A similHIPS is a polymer with a continuous phase of polystyrene (PS) matrix and dispersed phase of rubber particles with PS occlusions . High-img of pure HIPS and HIPS/rGO composites differed only slightly. The glass transition temperature also did not change after remelting, i.e., under conditions comparable to the printing process. For this reason, it is possible to use the same printing parameters for pure HIPS and HIPS/rGO composites. The obtained printed parts were examined in terms of their mechanical properties. Preliminary results for tensile strength, elongation, and Young’s modulus can be found in the The next stage of research on HIPS filaments reinforced with reduced graphene oxide was checking their suitability for 3D printing. A printed prototype was prepared using a filament that contained 0.5 wt% of rGO  3D printing applications was described. HIPS/rGO composite filaments were prepared in a two-step process by melted extrusion using a twin-screw extruder. The filaments were characterized in terms of morphology and thermal and mechanical properties.Based on the analysis of the SEM images, it was demonstrated that the use of the additive in a concentration above 0.5 wt% causes the formation of rGO agglomerates. Their presence affects the properties of the obtained filaments, contributing, among others, to a decline in tensile strength. The glass transition temperature of the pure polymer and composite filaments differs slightly, which means that it is possible to use the same printing parameters for pure HIPS and HIPS composites. The thermogravimetric studies show that above 250 °C, the obtained composites are characterized by lower thermal stability as compared to pure high-impact polystyrene. However, below this temperature, i.e., within the printing parameters, filaments containing reduced graphene oxide exhibit thermal stability close to that of the pure polymer. Among the obtained HIPS/rGO composites, the filament containing 0.5 wt% of reduced graphene oxide was characterized by the best mechanical properties. For these reasons, the printability of this composite was verified. The HIPS-0.5 filament was successfully printed. The production of a filament containing reduced graphene oxide presents an opportunity for expanding the application of this additive due to the wide interest in additive manufacturing in many areas of our lives.


We challenged four big brown bats to maneuver through abrupt turns in narrow corridors surrounded by dense acoustic clutter. We quantified bats' performance, sonar beam focus, and sensory acquisition rate. Performance was excellent in straight corridors, with sonar beam aim deviating less than 5° from the corridor midline. Bats anticipated an upcoming abrupt turn to the right or left by slowing flight speed and shifting beam aim to “look” proactively into one side of the corridor to identify the new flightpath. All bats mastered the right turn, but two bats consistently failed the left turn. Bats increased their sensory acquisition rate when confronting abrupt turns in both successful and failed flights. Limitations on biosonar performance reflected failures to switch beam aim and to modify a learned spatial map, rather than failures to update acquisition rate.  •Echolocating bats use sonar to identify flightpaths through dense, cluttered scenes•Bats learn new flightpaths by switching beam aim before encountering obstacles•Bats see their environment in depth Biological Sciences; Zoology; Animals; Ethology Eptesicus fuscus, modifies the direction and timing of its biosonar calls when flying through a cluttered environment requiring maneuvers through tight turns. As in natural clutter, multiple objects in this environment are located nearer than the upcoming opening in the scene, so the bat has to peer through a screen of echoes to discern the place where a turn will be necessary to maintain the flightpath.Echolocating bats intercept flying prey and navigate through their environments using information provided by reflected echoes. To identify obstacles and open flightpaths, they actively modulate the number, temporal patterning, and spatial direction of their biosonar calls . Many baBig brown bats have a versatile biosonar system. They capture prey in open spaces as well as on the ground and in or near vegetation; they fly above the forest canopy, between gaps in foliage, and within caves and other roosting spots . Their sBesides changing beam aim, big brown bats also modify their sensory acquisition rate when flying in cluttered environments compared to flying in the open . In the One issue with the hypothesis that changes in pulse timing reflect the bat's own interpretation of an acoustic scene as “easy” or “difficult” is that in many flight and obstacle avoidance experiments, big brown bats exhibit excellent performance, with few or no errors . They naFour big brown bats were challenged to fly through a 40-cm-wide corridor surrounded by an array of 217 hanging plastic chains that produced intense, extended echoes  did not differ significantly from that in the Straight condition (pairwise comparisons: p = 0.096). All four bats, regardless of whether they had previous laboratory experience in flying amid clutter, experienced a large drop in performance on the first day of the Right Turn condition, with success rate ranging from 0% to 69% (M = 45.1%). Success rate reached M = 84.8% within the first 3–4 days of this condition . ExperieSuccess rate in the Left Turn condition differed considerably among bats. Bat 1 and Bat 2 improved their performance over flight days, with success rate increasing from M = 26.5% on the first day of flights to M = 100% on the last day of flights. On the other hand, neither Bat 3 nor Bat 4 completed the task successfully, with success rates of 0% on both the first and the last day of flights.= 0.90, respectively]. Conversely, Bat 3's performance differed significantly across conditions . This bat performed equally well in the Straight and Right Turn conditions (pairwise comparisons: p = 0.85), but significantly worse in the Left Turn compared with Right Turn condition (pairwise comparisons: p < 0.001). Bat 4's performance also differed significantly across conditions . This bat performed similarly in the Straight and Right Turn conditions (pairwise comparisons: p = 0.36), but significantly worse in the Left Turn compared with the Right Turn condition (pairwise comparisons: p < 0.001).We statistically analyzed performance on a bat-by-bat basis. Bat 1 and Bat 2 both showed similar performance across conditions . Consistent with the data from successful flights, the majority of SSGs in failed flights  = 2,825, p < 0.001; Bat 4: Right versus Left, χ2 = 1,247, p < 0.001], with the difference due to production of more SSGs of 3–8 pulses.We calculated the proportions of SSGs in successful and failed flights in all three flight conditions. The non-linear way in which bats modify the timing of their calls is also visualized by plots of the distribution of pre-IPI values of every call against the corresponding post-IPI values . These pThis experiment required big brown bats to navigate down narrow corridors and through sharp 90° turns embedded in intense acoustic clutter produced by a dense array of surrounding chains. We hypothesized that bats would find this task challenging, and our results support this hypothesis. Bats were able to fly down Straight corridors with a mean success rate of 94% (four bats). This high success rate is consistent with those found in other experiments that also challenged bats to navigate narrow straight or curved corridors surrounded by various densities of clutter  to achieve final success. In the Right Turn condition, performance improved for all bats, reaching 100% correct in one animal, as they gained more experience with the flightpath over experimental days. After initial failures, two bats were able to achieve a success rate of 100% in the Left Turn condition; however, two other bats were unable to master that condition over the duration of the experiment, even with practice. These large individual differences indicate that the Left Turn was not intrinsically more difficult due to its closer proximity to the flight room wall. Moreover, bats' previous experience with flying down narrow corridors does not explain this individual variability; the same bat that achieved a high level of performance in earlier corridor experiments  had a suA previous experiment quantifying beam aim required big brown bats to fly through an open room or through openings in mist nets to catch a tethered insect prey . In the We hypothesized that bats flying toward abrupt 90° turns would aim their sonar beam in the direction of these turns before reaching them. Our results support this hypothesis. Bats that were able to navigate in the Turn conditions shifted their beam in the appropriate direction between 30 and 65 cm (224–359 ms) before reaching the turns. These anticipatory times are at the upper edge of the time range quantified by Consistent with the formation of a spatial map , bats adA strategy of focusing the center of the sonar beam on the nearest obstacle preventing a turn is an adaptive strategy that allows bats to localize and navigate tight spaces, such as gaps in foliage, more accurately. The center of the beam provides the highest signal-to-noise ratio (SNR) for echoes from any potential obstacle compared with the periphery . FocusinChanging beam aim based on an acquired spatial memory of the flightpath is beneficial to bats that must navigate tight spaces, allowing them to collect as much information as possible about upcoming obstacles in the direction of flight. However, an early proactive movement of the beam may make the bat less able to adapt to abrupt changes in the environment, even after multiple encounters with a new flightpath. Bats may incur a perceptual cost by shifting their acoustic gaze too early; a portion of their approach to the turn is spent echolocating off-axis from the area into which they will fly before entering the turn. Any echoes received from this immediately upcoming area would be perceived as clutter and perceptually blurred , making Insectivorous echolocating bats increase their sensory acquisition rate as background clutter becomes physically closer or denser, and as they approach a landing surface or wall . The chaWe predicted that more calls would be emitted as SSGs in the more difficult Turn conditions, and the data support this prediction. These data are also consistent with previous work showing more call clustering in tasks presumed to be more perceptually difficult . SSG proThe visualization of pre/post-IPI distributions for individual bats indicates that individual bats use unique patterns of call timing in order to solve the same perceptual task, and that these unique patterns within individuals are consistent across changes in the surrounding environment. Indeed, the pre-IPI to post-IPI distributions in failed flights were similar to those in successful flights by the same individual. Variability in task performance among bats is not attributable to changes in the temporal patterns of sensory acquisition, but rather due to individual differences in the spatial sampling strategies employed.Together, these findings paint a picture of how bats modify their biosonar behaviors to perceive upcoming obstacles (chains), adjust their calling patterns to avoid these obstacles, and adapt their beam aim to drastic changes in the spatial environment. Bats localizing and navigating a gap within dense acoustic clutter focus their calls on the nearest obstacle defining the edges of the gap in order to best localize the relatively small gap. In effect, they make sonar “looks” into the surrounding clutter to identify upcoming openings amid multiple nearer objects and echoes arriving earlier than the absence of echoes signifying the opening. In this way, they can identify an open flightpath. These proactive beam aim changes are tightly integrated with a spatial memory of the bat's environment, which is built up with experience. This is best exemplified by the persistence of some bats in aiming their calls in the direction required by a previous condition, even after substantial experience in a new spatial layout. This spatial memory, required for successful navigation, may also inhibit the ability of bats to adapt to sudden changes in the environment. Bats that were able to unlearn a pattern of beam aim were more successful in navigating a novel, orthogonal flightpath compared with other bats that became “stuck” in a learned pattern of beam aim. These differences between individual bats could lead to significant differences in their ability to navigate and survive in volatile, physically changing environments. We conclude that failures in navigating complex flightpaths are due to the bat being unable to alter its beam aim, not to an inability to change its sensory acquisition rate. Final success reflects the bat's ability to form a new spatial map of its environment .One issue raised by this experiment concerns the poor performance of two of the four bats in the Left Turn condition. It is possible that the Left Turn was more challenging because it was closer to the flight room wall. The simultaneous use of the flight room for other experiments prevented locating the experimental corridor in a more symmetrical manner. The better performance of these two bats in a Reversed Right Turn condition suggests that proximity to the wall did not affect their performance; rather, they did poorly in the Left Turn because they became “stuck” in aiming their beam toward the right. However, this new condition could only be run for one day, because of the bats' refusal to continue flying. These two bats were in good health during the experiment, and remained so for one year after its end. Finally, although the LMM model controlled statistically for the fixed order of conditions, future experiments should randomize conditions. It is also more difficult to quantify changes in temporal patterning that may have occurred in response to spatial changes, as time spent in the experiment is a confounding factor for all bats.Andrea_Simmons@brown.edu).Further information and requests should be directed to and will be fulfilled by the corresponding author, Andrea Simmons (Please contact the corresponding author.https://doi.org/10.26300/0mpw-9f40.Original data have been deposited in the Brown Digital Repository: All methods can be found in the accompanying