Prevention of microbially induced corrosion (MIC) is of great significance in many environmental applications. Here, we report the use of an ultra-thin, graphene skin (Gr) as a superior anti-MIC coating over two commercial polymeric coatings, Parylene-C (PA) and Polyurethane (PU). We find that Nickel (Ni) dissolution in a corrosion cell with Gr-coated Ni is an order of magnitude lower than that of PA and PU coated electrodes. Electrochemical analysis reveals that the Gr coating offers ~10 and ~100 fold improvement in MIC resistance over PU and PA coatings respectively. This finding is remarkable considering that the Gr coating (1–2 nm) is ~25 and ~4000 times thinner than the PA (40–50 nm), and PU coatings (20–80 μm), respectively. Conventional polymer coatings are either non-conformal when deposited or degrade under the action of microbial processes, while the electro-chemically inert graphene coating is both resistant to microbial attack and is extremely conformal and defect-free. Finally, we provide a brief discussion regarding the effectiveness of as-grown vs. transferred graphene films for anti-MIC applications. While the as-grown graphene films are devoid of major defects, wet transfer of graphene is shown to introduce large scale defects that make it less suitable for the current application. Literature indicates that the annual costs for corrosion14535Metal coatings and alloys have been commercially379111213142O3 nanoparticles) caused a significant improvement in the corrosion resistance of monolayer grapheneGraphene (Gr), a two-dimensional sheet of sp1819202122242527The objective of this study was to investigate the effectiveness of nano-scale graphene coatings to prevent MIC of the immersed, metallic structure under galvanic conditions. More specifically, the MIC resistance of Ni was compared in presence of three different coatings: i) parylene-C coating on Ni (PA/Ni), ii) polyurethane coating on Ni (PU/Ni) and iii) graphene coating on Ni (Gr/Ni). A Ni foam−1) in Chemical vapor deposition (CVD- see methods section) was used to obtain a uniform coating of PA–C on the Ni surface . The thi3031The corrosion cells  were opeThe Nyquist plots  shows thct) and interfacial capacitance (Cm). The seepage of anolyte through the PU coating is responsible for the charge transfer reactions associated with the corrosion process. In order to model diffusion limitations of corrosion by-products through the porous electrode, a Warburg element (WO) is added in series to the corrosion impedance. Within the pore length, the electrolyte resistance is Rint, and the insulating part of the coating can be considered to be a capacitor Cdl which is in parallel with the impedance in the pore (el) is added in series with the previous impedance.the pore . The eleel), the anolyte/PA interfacial impedance and PA/Ni interfacial impedance (int). Similarly, the interfacial capacitance at the anolyte/PU interface is modeled as Cdl. The charge transfer reactions associated with Ni corrosion at the anolyte/PA interface were incorporated as a parallel combination of charge transfer resistance (Rct) and interfacial capacitance (Cint)34The thickness of the parylene coating in the PA/Ni system is ~3 orders of magnitude smaller than that of PU in PU/Ni. We therefore used an alternate equivalent circuit model based of the anolyte resistance (Rmpedance . At the ct of Gr/Ni (~35.8 kΩ.cm2) was ~10-fold higher than that of PU/Ni (~1.57 kΩ.cm2), and ~100-fold higher than that of PA/Ni (~0.38 kΩ.cm2)  increased linearly. In Gr/Ni, the corrosion rates remained in the 1.5–3 mg/L/day range in all the three cycles. The cell with Gr/Ni demonstrated an improvement in the corrosion resistance . The higher values of Ni concentrations in PU/Ni and PA/Ni cells during subsequent weeks denote an eventual failure of the polymer coatings. The lower corrosion rates in the Gr/Ni are likely due to a combination of the following: i) minimal defects in the Gr coating compared to PA and PU coatings, ii) limited diffusion of corrosion by-products from the Ni to the bulk liquid due to restricted access through the few-layered Gr coating, and iii) adhesion of polysaccharides and insoluble biomass to the hydrophobic graphene surface which plugs the few defect sites that may exist on the Gr film surface.Scanning electron microscopy (SEM) was used to observe the extent of corrosion-induced debilitation of the PA/Ni and PU/Ni surfaces. We found micron-length tears on the PU/Ni surfaces  while th373839in-situ on a copper foil by CVD, was transferred layer-by-layer onto SiO2 using wet chemistry based transfer methods2 (~80 μm × 80 μm).On having established that CVD-grown (few-layer) graphene offers superior resistance to MIC, we sought to characterize the defectiveness of the as-grown graphene coating when compared to graphene films that are transferred , as compared to the Gr films transferred onto SiO2 and half the value for monolayer Gr as-grown on Cu foil. This is visually represented in the Raman map for the few-layer graphene grown on Ni foam  sulfide-oxidizing bacteria convert HS− to sulfate that is quickly oxidized to sulfuric acid and abruptly decrease the local pH (<1.0) to enhance the Ni corrosion.Corrosion characteristics are determined by the corroding and the corroded species. In order to better understand the interactions between the microbial community and the coated nickel surfaces, a phylogenetic microbial community analysis was carried out and its results are presented in this section . The ana4243In our experiments, we observed a change of the anolyte color from yellow to black within 48 hours of initial operation  which ca502+ concentration  corrosion current and ii) Nintration  in the Gin-situ with minimimal defect density. Further, the few defects that may be present on the surface can be plugged by biofilms through the production of non-conductive polymeric debris. On exposure to similar harsh microbial environments, parylene C failed by extensive microbial degradation and polyurethane due to its non-conformal adhesion to the metallic surface. In order to study the feasibility of Gr coatings as MIC resisting elements on non-CVD surfaces, we study the effect of wet-transfer on the quality of graphene. The study revealed that transferred graphene films are significantly more defective than their as-grown counterparts, thereby warranting future research targeting defect-free transfer of graphene for surfaces that are not amenable to CVD growth.Graphene coatings have not been explored in detail for corrosion prevention in biotic environments. The current study shows that graphene coatings outperforms its polymer counterparts (parylene C and polyurethane) by offering 1 and 2 orders of magnitude better impedance against microbial corrosion. The shortcomings associated with defect based corrosion of graphene coatings in abiotic environments has been countered in this study by the use of 3–4 layer graphene films that are grown −). The cell configuration enables the Ni anode to be immersed in a 0.2 L electrolyte that supports the growth of a diverse set of mixed microbial communities. The Ni anode is coupled to a graphite cathode to promote the bimetallic corrosion. Further, a ferricyanide system  with a faster redox kinetics was used as an electron acceptor in the cathode , counter electrode (graphite cathode), and a reference electrode . The observed reflected light was used to determine ratios of the amplitude (ψ) and phase changes of the p and s components of polarized light (Δ)57Clean Ni foam and Si wafer samples (~2 × 2 cm) were placed in a Union Carbide chemical deposition chamber and pumped down to low vacuum conditions of 50 mTorr. A 0.5 g of PA C dimer  was sublimed at 150–170 °C and pyrolized at 650 °C. The pyrolized vapors were deposited on the Ni sample at room temperature. A NA Krylon clean polyurethane spray operation was used to establish the polyurethane coating on the Ni foam.2 and Ar atmosphere at 1000 °C to remove the layer of metal oxide. Methane was then introduced to the CVD chamber for 5 mins at ambient pressure. Next, the chamber was rapidly cooled to precipitate the dissolved carbon as a multilayer graphene on the Ni surfaceThe chemical vapor deposition (CVD) process was used to grow graphene on the Ni foam. The Ni foam was annealed in H2-transferred graphene (80 μm × 80 μm) and CVD-grown graphene (30 μm × 30 μm copper and nickel foam) samples. After data collection, Lorentzian curve fitting was used to fit the D, G and 2D peaks in order to create maps of the spectral features.A Raman microscope  with a confocal pinhole was used to obtain a Raman mapping of SiOPost experiments, the electrodes were immediately fixed using 2.5% glutaraldehyde buffered with 0.1 M phosphate buffer (pH 7.4). The fixed samples were refrigerated for 24 hours, dehydrated in ethanol series  for 5 minutes at each gradation. The sample was left in 100% ethanol in refrigerator overnight, and dried using an automated critical point dryer . Post dehydration, a thin layer of Platinum (few nm) was sputtered on the electrode. The samples were then examined in SUPRA® Focused Ion Beam (FIB) under EHT voltage ~1 kV and magnification of 10 kx. The Gr/Ni foam and the transferred Gr samples were viewed without any surface preparation at 3 kV EHT and at low magnifications upto 100x.The Ni foam samples (biotic and abiotic) were analyzed using Al K-alpha X-ray gun at 40W on a Phi Versaprobe® XPS system. After a basic background scan, a detailed scan was conducted with 20 eV pass energy. To confirm the presence of sulfur on a large surface area, a 100 μm × 100 μm sample was chosen with large acquisition time (~75 minutes).Voltage data was acquired periodically using DAQ/54 modules  across a resistance substitutor . Electrochemical impedance spectroscopy was used to analyze the corrosion specimens  with GAMRY ®Reference 3000™. A small AC RMS current (~1 mA) was applied as a perturbation signal in order to measure the impedance response of the anode in a frequency range of 0.1 Hz–10 kHz. The cyclic voltammograms were recorded in the voltage range of −0.8 V–1.0 V and at a scan rate of 25 mV/s.2+) in the three corrosion cells were quantified using 1-(2 Pyridylazo)-2-Napthol (PAN) indicator methodThe concentration of free Ni ions  following manufacturer’s guidelines. The 16S rDNA V4 region amplicons (single index) were produced by PCR and sequenced on the MiSeq platform (Illumina) using the 2 × 250 bp protocol yielding pair-end reads that overlap by ~247 bps. Following sequencing, raw BCL files were retrieved from the MiSeq platform and called into fastqs by Casava v1.8.3 (Illumina). The read pairs were demultiplexed based on unique molecular barcodes, filtered for PhiX using Bowtie2 v2.2.1, and reconstituted into two fastq files for each read using standard BASH. A barcodes file was generated from a raw fastq base called previously preserving the original barcode qualities associated per read cluster. Reads were merged using USEARCH v7.0.1001  and a barcodes file was generated for the merged set in the same manner they were generated for the raw reads. Processing of sequencing reads included quality-filtering using USEARCH v7.0.1001 (maximum expected error method). Sequences were demultiplexed using QIIME v1.8.0 and then clustered using the UPARSE pipeline. Operational taxonomic unit (OTU) classification was achieved by mapping the UPARSE OTU table to the SILVA database. Abundances were recovered by mapping the demultiplexed reads to the UPARSE OTUs. A custom script constructed an OTU table from the output files generated in the previous two steps. The OTU table was used to calculate alpha-diversity, beta-diversity, provide taxonomic summaries, and in a variety of other analyses built into QIIME that allowed for the characterization of individual and group of samples. Bacterial diversity in each sample was assessed by determining richness based on the calculation of Alpha diversity and Beta diversity in addition to computing diversity indices such as Chao, Simpson, and Shannon.How to cite this article: Krishnamurthy, A. et al. Superiority of Graphene over Polymer Coatings for Prevention of Microbially Induced Corrosion. Sci. Rep.5, 13858; doi: 10.1038/srep13858 (2015).


Clinical trials of immune checkpoints modulators, including both programmed cell death-1 (PD-1) and programmed cell death-ligand 1 (PD-L1) inhibitors, have recently shown promising activity and tolerable toxicity in pre-treated NSCLC patients. However the predictive role of PD-L1 expression is still controversial. This pooled analysis aims to clarify the association of clinical objective responses to anti PD-1/PD-L1 monoclonal antibodies (MoAbs) and tumor PD-L1 expression in pre-treated NSCLC patients.Data from published studies, that evaluated efficacy and safety of PD-1/PD-L1 inhibitors in pre-treated NSCLC patients, stratified by tumor PD-L1 expression status , were collected by searching in PubMed, Cochrane Library, American Society of Clinical Oncology, European Society of Medical Oncology and World Conference of Lung Cancer, meeting proceedings. Pooled Odds ratio (OR) and 95% confidence intervals (95% CIs) were calculated for the Overall Response Rate (ORR) , according to PD-L1 expression status.A total of seven studies, with 914 patients, were eligible. Pooled analysis showed that patients with PD-L1 positive tumors (PD-L1 tumor cell staining ≥1%), had a significantly higher ORR, compared to patients with PD-L1 negative tumors .PD-L1 tumor over-expression seems to be associated with higher clinical activity of anti PD-1/PD-L1 MoAbs, in pre-treated NSCLC patients, suggesting a potential role of PD-L1 expression, IHC cut-off point 1%, as predictive biomarker for the selection of patients to treat with immune-checkpoint inhibitors. Cancer immunotherapy is emerging as a very promising therapeutic strategy for several solid tumors, including non-small cell lung cancer (NSCLC). Differently from other treatment approaches directed against the tumor, such as chemotherapy or targeted therapy -6, targeOur search, according to the aforementioned criteria, performed in October 2015, identified 211 publications. Among these, after a careful selection procedure, only seven studies (914 patients) met our inclusion criteria and were included in the pooled-analysis  had a significantly higher ORR compared to patients with PD-L1 negative tumors  . The results of this work have shown that tumor PD-L1 positivity (PD-L1 tumor cell staining ≥1%) is associated with significantly higher ORR, suggesting a potential role of tumor PD-L1 over-expression as predictive biomarker for clinical setting. After the recent approval of Nivolumab by FDA for the second-line treatment of squamous NSCLC, searching for predictive biomarkers has become an urgent issue for clinical research. A validated biomarker would allow to select those patients who could benefit more from immune-therapies, sparing the others from ineffective high-cost treatments, as well as futile immune-related toxicities. In this scenario, tumor PD-L1 expression represents the predictive biomarker most evaluated in clinical studies. Although the majority of such studies suggested a significant association between tumor PD-L1 expression and anti-PD-1/PD-L1 MoAbs activity , 24, 27,Despite several limitations our pooled-analysis shows that tumor PD-L1 expression, IHC cut-off >1%, is associated with significantly higher ORRs to anti PD-1/PD-L1 MoAbs, in pre-treated NSCLC patients. These data suggest that PD-L1 at the lowest expression level, though still limited by varied testing approaches and definitions of positivity, has a potential role as predictive biomarker for clinical setting. Probably, as suggested by recent studies, a combination of tumor PD-L1 expression with other “immune-biomarkers” will enhance our ability to identify not only the best candidate to receive immune-therapies, but also the mechanisms of immune-evasion at a single patient level, and ultimately personalize the immune-treatments and combination strategies.We performed our pooled-analysis according to a predefined written protocol. We searched for all published studies, that report the ORR of patients with NSCLC treated with anti PD1/PD-L1 MoAbs, who received prior chemotherapy regimens, stratified by tumor PD-L1 expression status (IHC cut-off point 1%). Publications were identified by an electronic search in Medline, using PubMed online service, updated in October 2015. The search for publications was made by other databases including the Cochrane Library and EMBASE. However the search on PubMed allowed the widest collection of publications about this topic. The following search terms were used: “PD-1”, “PD-L1”, “lung cancer”, “NSCLC”, “non-small cell lung cancer”, “predictive biomarker”, “anti-PD1”, “anti-PD-L1”, “monoclonal antibodies”, “cancer immunotherapy”. The search was limited to human studies in the English language. The results were supplemented with manual searches of American Society of Clinical Oncology (ASCO), European Society of Medical Oncology (ESMO), and World Conference of Lung Cancer (WCLC), meeting proceedings, references of selected articles and published reviews. A systematic review on this topic in the Cochrane database of systematic reviews was not found.According to this search clinical trials were taken into account if they had to fulfil all the following inclusion criteria: 1) only patients with metastatic NSCLC were included; 2) only patients who received prior therapies were included 3) studies that report the ORR of NSCLC patients treated with an anti-PD1/PD-L1 MoAb as single agent; 4) studies that report the ORR, stratified according to the PD-L1 expression status (IHC cut-off point 1%).Two authors independently selected studies according to the aforementioned inclusion criteria. If these two authors could not reach a consensus, another author was consulted and a final decision was made by consensus. Information was carefully extracted by overall selected studies. The following data were collected and organized from eligible studies: first author name, journal and year of publication, study design, study treatment, baseline characteristics of patients , and ORR stratified according to tumor PD-L1 expression status. The proportion of patients for each outcome was calculated basing on the percentages reported in included trials, when it was not reported as absolute number. Data extraction was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines .Patients were stratified according to PD-L1 expression status into 2 groups: PD-L1 positive (PD-L1 tumor cell staining ≥1%) and PD-L1 negative. The outcome measure was ORR, defined as the percentage of patients who have a complete or partial tumor response according to World Health Organization (WHO) criteria or Response Evaluation Criteria in Solid Tumors (RECIST), calculated in PD-L1 positive over PD-L1 negative NSCLC patients. The number of events (i.e. objective responses) was extracted from each study or calculated from the percentage provided, and the proportion of patients was calculated for each group. The association between these endpoints and PD-L1 expression status was expressed as an odds ratio (OR) of PD-L1 positive over PD-L1 negative patients. Thus, an OR greater than 1 indicates that PD-L1 overexpression (PD-L1 tumor cell staining ≥1%) is associated with higher ORR in pre-treated NSCLC patients. A pooled-analysis of ORs was performed to calculate a pooled OR for such outcome, using a fixed-effect or random-effect, based on statistical significance of Q-test, according to Mantel-Haenszel method. The heterogeneity between trials was tested using the Cochran Q-test, with a predefined significance threshold of 0.1. Publication bias for ORR analysis were assessed using Begg's funnel plots and Egger's test. The level of significance was set at 5% . All statistical analyses were performed with Review Manager 5.3.5  and Comprehensive Meta-Analysis software .


A humidity microsensor integrated with a readout circuit on-a-chip fabricated using the commercial 0.18 μm CMOS  process was presented. The integrated sensor chip consists of a humidity sensor and a readout circuit. The humidity sensor is composed of a sensitive film and interdigitated electrodes. The sensitive film is titanium dioxide prepared by the sol-gel method. The titanium dioxide is coated on the interdigitated electrodes. The humidity sensor requires a post-process to remove the sacrificial layer and to coat the titanium dioxide. The resistance of the sensor changes as the sensitive film absorbs or desorbs vapor. The readout circuit is employed to convert the resistance variation of the sensor into the output voltage. The experimental results show that the integrated humidity sensor has a sensitivity of 4.5 mV/RH% (relative humidity) at room temperature. The conductivity of the humidity-sensing film changed upon adsorption/desorption of water vapor. Lazarus and Fedder [et al. [et al. [Humidity sensors are important devices for application in industrial and electronic equipment. Various traditional sensors have been miniaturized as microsensors using micromachining technology. Micromachined sensors have the benefits of high performance, low cost, small size, and easy mass-production . Many huet al.  used mic [et al.  develope [et al.  presente [et al.  manufact [et al.  proposed [et al.  employedd Fedder  fabricat [et al. , was fab [et al.  utilized [et al.  were not [et al. . In thisThe commercial CMOS process has been used to develop various microsensors and microactuators –14. Micr2.OP represents the operational amplifier, Vin is the input voltage of the circuit; Vout is the output voltage of the circuit; Rs is the resistance of the humidity sensor; R1–R7 are the resistances of the circuit.As shown in R1 = 5 kΩ, R2 = 5 kΩ, R3 = 30 kΩ, R4 = 30 kΩ, R5 = 20 kΩ, R6 = 30 kΩ, R7 = 10 kΩ and Rs = 100 kΩ are set, and the input voltage Vin is 2.5 V. The bias voltage of the amplifier is 3.3 V. The resistance of the humidity sensor varies from 400 to 100 kΩ. The simulated results revealed that the output voltage of the readout circuit decreased from 2.39 to 2.14 V as the resistance of the sensor changed from 400 to 100 kΩ. To characterize the relation between the output voltage and temperature for the readout circuit, the readout circuit is simulated at different temperatures. Vin is 2.5 V. The resistance of the humidity sensor is 120 kΩ, and the resistances are R1 = 5 kΩ, R2 = 5 kΩ, R3 = 30 kΩ, R4 = 30 kΩ, R5 = 20 kΩ, R6 = 30 kΩ and R7 = 10 kΩ. The temperature changes from 20 to 80 °C. The results showed that the output voltage of the readout circuit increased from 2.1485 to 2.1491 V as the temperature changes from 20 to 80 °C, in which the output voltage varies about 0.6 mV.The software HSPICE  is utilized to simulate the characteristics of the readout circuit. 3.3H7)4) precursor of 3 mL  was dissolved in isopropanol   with stirring for 30 min until the solution was mixed uniformly. Deionized water (40 mL) was added into the mixed solution with stirring for 1 h. Then, HNO3 solution of 5 mL  was added into the mixed solution and stirred for 20 min, followed by aging for 30 min. The slurry of titanium dioxide was filtered, and then rinsed with deionized water. Finally, the titanium dioxide was coated on the substrate with calcinations at 400 °C for 1 h.The sensitive film of the humidity sensor was titanium dioxide prepared by the sol-gel method ,26. The Scanning electron microscopy  was used to measure the surface morphology of the titanium dioxide film. 4.The commercial 0.18 μm CMOS process of Taiwan Semiconductor Manufacturing Company  was employed to manufacture the integrated humidity sensor chip. 5.The performances of the humidity microsensor were tested by a power supply, a test chamber , a LCR meter and an oscilloscope. The test chamber could supply a humidity range of 25–90 RH% and a temperature range of 0–100 °C. Temperature and humidity in the test chamber could be tuned separately and maintained at constant levels. The power supply was used to provide the bias voltage and the input voltage to the readout circuit.The humidity sensor without readout circuit was tested in order to characterize the resistance variation of the sensor. The humidity sensor without readout circuit was set in the test chamber, and its resistance variation under different humidity was measured by the LCR meter. The humidity sensor with readout circuit was set in the test chamber. The test chamber provided different humidity levels to the humidity sensor. When the humidity in the test chamber rose or dropped, the resistance of the humidity sensor produced a change. The readout circuit converted the resistance variation of the sensor into the output voltage, and the oscilloscope recorded the output voltage. To characterize the influence of temperature, the humidity sensor was measured under different temperatures. The output voltage of the humidity sensor was detected at different temperatures. 6.A humidity sensor equipped with a readout circuit was successfully manufactured using the commercial 0.18 μm CMOS process and a post-process. The post-process was compatible with the commercial CMOS process. The humidity sensor consisted of a sensitive film and interdigitated electrodes. The sensitive film of the humidity sensor was titanium dioxide that was prepared by the sol-gel method. The titanium dioxide was deposited on the interdigitated electrodes. The humidity sensor generated a change in resistance as the sensitive film absorbed or desorbed water vapor. The resistance variation of the sensor was converted by the readout circuit into the output voltage. The sensor integrated with readout circuit on-a-chip would reduce noise and interference. The experiments showed that the output voltage of the humidity sensor decreased from 2.27 to 2.05 V as the humidity changed from 30 to 90 RH% at 25 °C. The humidity sensor had a sensitivity of 4.5 mV/RH% at room temperature.


We fabricate a nonlinear optical device based on a fiber pigtail cross-section coated with a single-layer graphene grown by chemical vapor deposition (CVD) method. Using the fabricated graphene-assisted nonlinear optical device and employing Nyquist 16-ary quadrature amplitude modulation (16-QAM) signal, we experimentally demonstrate phase conjugated wavelength conversion by degenerate four-wave mixing (FWM) and transparent wavelength conversion by non-degenerate FWM in graphene. We study the conversion efficiency as functions of the pump power and pump wavelength and evaluate the bit-error rate (BER) performance. We also compare the time-varying symbol sequence for graphene-assisted phase conjugated and transparent wavelength conversions of Nyquist 16-QAM signal. Recently, a variety of graphene-based photonic devices have been reported, including wide bandwidth polarizers7912131415(3) nonlinearities20Graphene234It is well known that the increase of spectral efficiency has become an effective way when scaling up the data rate2327In this paper, considering the combination of advanced optical modulation format signal  and the optical nonlinearity of a single-layer graphene coated fiber device, we show an experimental observation of degenerate/non-degenerate FWM based wavelength conversion of a 5 Gbaud Nyquist 16-QAM signal. We study the wavelength tuning properties and the conversion efficiency as functions of the pump wavelength and pump power. Moreover, we characterize the performance of Nyquist 16-QAM wavelength conversion by measuring the BER as a function of the received optical signal-to-noise ratio (OSNR). Time-varying symbol sequence for phase conjugated wavelength conversion by degenerate FWM and transparent wavelength conversion by non-degenerate FWM are also measured for comparison.The line-width of ECL1 laser is 100 KHz. At the transmitter, the information data is firstly mapped into 16-QAM format and then packed into data frames. In each frame, 38400 data symbols are transmitted after the preamble. We insert 1 pilot in every 63 data symbols for phase recovery. The preamble includes two 63-symbol M-sequences as synchronization sequences and four 127-symbol M-sequences as training sequences. After 2 samples per symbol up-sampling, the signals are digitally shaped with a root-raised-cosine (RRC) filter. The roll-off factor of the RRC is 0.01. After digital to analog convertors (DAC), electrical low-pass filters with the bandwidth of 4.4 GHz are used as anti-aliasing filters to remove out-of-band radiation. At the receiver, a matched RRC filter is adopted. After synchronization, the signals are re-sampled to 2 samples per symbol and the training sequences are picked up for time-domain channel estimation and equalization. After equalization, the phase is corrected with pilots and further estimated with the blind phase search (BPS) algorithm. Finally, the bit error ratio (BER) is measured by error counting. The RF spectrums of Nyquist pulse waveform before RRC filter and after RRC filter is shown in We first demonstrate the wavelength conversion of Nyquist 16-QAM signal based on degenerate FWM process in the single-layer graphene coated fiber device. In the experiment, the signal wavelength is fixed at 1552.52 nm. pump = 1550.12 nm, λsignal = 1552.52 nm). The conversion efficiency increases with the pump power. The conversion efficiency η of FWM can be approximately expressed as η = (γ∙Pp∙L)γ is the effective nonlinear coefficient, Pp is the pump power, and L is the length. In fact, the conversion efficiency curve in pump and a data signal at wavelength λsignal are combined together and sent into a graphene-assisted nonlinear device with high third order nonlinearity (χ(3)). Due to the energy conservation in the degenerate FWM process, the wavelength of the newly converted idler wave can be written by 1/λconv = 2/λpump−1/λsignal. Hence, one can achieve tunable wavelength simply by adjusting the pump wavelength or the signal wavelength, i.e. variable λpump or λsignal results in changeable λconv. So the converted idler wavelength can be tuned simply by changing the pump wavelength, i.e. tunable wavelength conversion even for a fixed input signal wavelength. We define the conversion efficiency as the power ratio of converted idler to signal. pump1 = 1549.32, λpump2 = 1552.52 nm, λsignal = 1551.32 nm).We then demonstrate the wavelength conversion of Nyquist 16-QAM signal based on non-degenerate FWM process in the single-layer graphene coated fiber device. idler ∝ E2pumpE*signal, where Eidler, Epump and Esignal represent the complex electric fields of newly converted idler, input pump and input signal, respectively. “∗” denotes the complex conjugate of the electric field. Hence, the newly converted idler does not take the same data information carried by the original signal but its “phase conjugated” copy.For the wavelength conversion based on degenerate FWM process as shown in idler ∝ Epump1EsignalE*pump2, where Epump1 and Epump2 represent the complex electric fields of two input pumps. Therefore, the newly converted idler copies exactly the same data information carried by the original signal, i.e. fully transparent wavelength conversion.For the wavelength conversion based on non-degenerate FWM process as shown in The converted idler is “phase conjugated” copy of the original data signal in the process of graphene-based degenerate FWM−3 (7% forward error correction (FEC) threshold) for Nyquist 16-QAM wavelength conversion with the converted idler at 1547.71 nm. The received OSNR penalties of ~1.4 dB at a BER of 1 × 10−3 are observed for converted idlers at 1546.12 and 1544.52 nm. The increased OSNR penalty is mainly due to the reduced conversion efficiency for converted idlers at 1546.12 and 1544.52 nm. −3. The right insets of To characterize the performance of Nyquist 16-QAM wavelength conversion, we further measure the BER curve as a function of the received OSNR for back to back (B-to-B) signal and newly converted idler. (3) nonlinearities. Therefore, the nonlinear optical device based on a fiber pigtail cross-section coated with a single-layer graphene grown by CVD might show favorable performance in practical applications.Luo and co-authors(3) nonlinearities−20 m2/W, ~10−18 m2/W and ~10−11 m2/W, respectively313217Due to possessing linear band structure that allows interband optical transitions at ultrabroadband range (across the infrared and visible range), graphene has been suggested as a material that might have large χ(3) of graphene could also give rise to nonlinear Kerr-effects such as FWM, TPA, stimulated Raman scattering (SRS), stimulated Brillouin scattering (SBS), SPM, and XPM. So, on may wonder whether the graphene based phase conjugated and transparent wavelength conversions still can occur, especially for advanced optical modulation formats signal, e.g., Nyquist 16-QAM. One may also wonder what is the influence of the XPM, SPM on the signal quality  in the process of graphene-assisted FWM based wavelength conversion of Nyquist 16-QAM signal. Previous experiments on enhanced FWM in graphene-assisted nonlinear optical devices have been demonstrated with impressive performance, such as the works by C. W. Wong and Y. J. Rao18202137(3) nonlinearities, and compatibility with existing optical fiber transmission systems might enable novel architectures for optical signal processing applications.The phenomena of degenerate and non-degenerate FWM have been demonstrated in semiconductor optical amplifiers−3 with the converted idler generated at 1547.71, 1546.12 and 1544.52 nm, respectively. For transparent wavelength Nyquist 16-QAM conversion based on non-degenerate FWM, the observed OSNR penalty is around 1.6 dB at a BER of 1 × 10−3 with the converted idler generated at 1548.11 nm. It is expected that graphene-assisted nonlinear optical devices might find more interesting optical signal processing applications.Firstly, FWM in graphene which is mechanically transferred on the end face of optical fiber has been experimentally observed. The degenerate/non-degenerate FWM based wavelength conversion of advanced modulation format signal (e.g. Nyquist 16-QAM) is further demonstrated in the experiment. Secondly, we compare in detail the measured conversion efficiency with and without graphene. The power of converted idler without graphene is observed to be ~5.8 dB lower than the one with graphene. We also clarify that the enhanced conversion efficiency mainly comes from the high nonlinearity of graphene. Additionally, the converted idler wavelength can be flexibly tuned by changing the pump wavelength and the conversion efficiency varies slightly. Lastly, for phase conjugated Nyquist 16-QAM wavelength conversion based on degenerate FWM, the observed OSNR penalties are around 1, 1.4 and 1.4 dB at a BER of 1 × 103 solution. Then, the floating PMMA/graphene sheet is mechanically transferred onto the fiber pigtail cross-section and dried in a cabinet. After drying at room temperature for about 24 hours, the carbon atoms could be self-assembled onto the fiber end-facet thanks to the strong viscosity of graphene. The PMMA layer is finally removed by boiling acetone. By connecting this graphene-on-fiber component with another clean and dry FC/PC fiber connector, the nonlinear optical device is thereby constructed for degenerate/non-degenerate FWM based wavelength conversion applications. Here, the fiber is standard single mode fiber and serves as the brace. The grown graphene sheet is transferred on silicon-on-insulter (SOI) for SEM characterization as show in −1, respectively. The measured I2D /IG ratio of 1.65 confirms the formation of monolayer graphene2/Si substrate is almost defect-freeTo fabricate the nonlinear optical device based on a single-layer graphene, as shown in How to cite this article: Hu, X. et al. Phase Conjugated and Transparent Wavelength Conversions of Nyquist 16-QAM Signals Employing a Single-Layer Graphene Coated Fiber Device. Sci. Rep.6, 22379; doi: 10.1038/srep22379 (2016).


The aim of this opinion article is to understand to what extent idiopathic pulmonary fibrosis (IPF) can be considered, in its clinical and pathogenic features, similar to cancer. Indeed, IPF has common risk factors with cancer, a low survival, and, most importantly, epigenetic and genetic alterations, abnormal expression of microRNAs, cellular and molecular aberrances, and the activation of similar signalling pathways.The pathogenic link between the two diseases may have a number of practical consequences. It may improve our understanding of IPF drawing on cancer biology knowledge. In addition, the recognition of similar pathogenic pathways may also encourage the use of cancer drugs for the treatment of IPF. Nintedanib, an inhibitor of tyrosine kinase receptors initially developed for cancer, has been recently approved for the treatment of IPF thanks to the observation that these receptors are also abnormally activated in IPF.The vision of IPF as a cancer-like disease may improve our understanding of the pathogenesis of this disease also opening new scenarios for repositioning cancer drugs for IPF. In addition, it may increase the level of awareness towards this dreadful disease at the public, political, and healthcare level. According to the current pathogenic hypothesis, idiopathic pulmonary fibrosis (IPF) is the result of chronic damage of the alveolar epithelium leading to a series of events responsible for abnormal tissue repair and the profound changes of the alveolar structure that characterize this disease . This alHowever, the study of the association between IPF and lung cancer with the relative clinical and therapeutic implications is far beyond the objectives of this opinion article. The aim of this article is instead to go through the scientific reasons that may support the intriguing vision of IPF as a disease with a cancer-like nature and to understand if this point of view may have positive consequences on the overall management of IPF.Aging, cigarette smoke, diet, and chemical and physical factors, through the methylation of suppressor genes or the hypomethylation of oncogenes, may affect the activity of some genes without changing their DNA sequences. It is recognized that these “epigenetic” changes are involved in the initiation and progression of cancer. For instance, the reduced expression of the Thy-1 glycoprotein, due to the hypermethylation of the promoter region of the gene coding for this glycoprotein, is associated with a more invasive behaviour of cancer. Similarly, the loss of expression of the same glycoprotein in IPF is related to the differentiation of fibroblasts into myofibroblasts within “fibroblast foci” , 9. MoreTissue homeostasis is maintained by cell-to-cell communication through junctional channels named connexins that facilitate the interaction and coordination of cell functions. Cancer cells are instead characterized by an impairment of intercellular communication suggesting that, in order to proliferate, these cells need to isolate themselves from the influence of surrounding normal cells. Lower levels of connexin 43 (Cx43) have been described in many cancers, including lung and gastric cancer. Similarly, IPF myofibroblasts, have a reduced ability to express connexin 43, suggesting that the loss of proliferative control in IPF cells could be caused by an altered fibroblast-to-fibroblast communication caused by a reduced expression of connexin 43 –27. The ex vivo fibroblast cell lines. Furthermore, both p110γ pharmacological inhibition and gene silencing were able to significantly inhibit proliferation rate as well as a-SMA expression in IPF fibroblasts. This suggests that PI3K p110γ isoform may have an important role in the pathogenesis of IPF and can be a specific pharmacological target. More recently, researchers have focused on another signal transduction pathway frequently altered in many cancers: the JAK-STAT pathway [in vitro and in vivo in a rat model of bleomycin-induced fibrosis [A large variety of signal transduction pathways are involved in the pathogenesis of cancer and IPF. The Wnt/β-catenin signalling pathway regulates the expression of molecules involved in cancer progression and tissue infiltration such as matrilysin, laminin, and cyclin-D1. This pathway is also strongly activated in IPF lung tissue as evidenced by extensive nuclear accumulation of β-catenin at different involved sites such as bronchiolar lesions, damaged alveolar structures, and fibroblast foci , 39. The pathway . This pa pathway , a lower pathway , 46. Thefibrosis , 48. Thefibrosis . NintedaAccording to the long list of pathogenic analogies between cancer and IPF, we might easily conclude that these two diseases are indeed similar. However, there are at least three arguments, apparently against this concept, that still need to be clarified: (1) myofibroblasts within fibroblast foci are polyclonal whereas cancer cells are thought to be monoclonal; (2) IPF is limited to the lungs, cancer metastasizes; and (3) IPF is by definition bilateral, cancer is always unilateral. These arguments, in our opinion, are largely based on general beliefs and do not weaken in any way the concept of the cancer-like character of IPF. Effectively, a number of studies have unequivocally shown that only some cancers are monoclonal whereas many others are instead marked by the same cytogenetic heterogeneity observed in IPF cells. Similarly to IPF, myofibroblastic cancers, such as desmoid tumours, are locally aggressive but unable to metastasize and ultimately 2–6 % of cancers have a bilateral and synchronous involvement –58.Having removed any conceptual obstacle to the view of IPF as a disease with a close link to cancer biology, this commentary will briefly underline the main reasons explaining why this vision may be relevant not just conceptually but also clinically. The awareness of cancer as a severe and potentially deadly disease is widespread in public opinion, leading to fund-raising campaigns and gatherings of private and governmental funds, resulting in the continuous progression of basic and clinical research. The development of dedicated diagnostic tools, the realization of large screening programs, the launch of a variety of new anti-cancer drugs, as well as the creation of personalized treatments have been achieved due to the fight against cancer during the last few decades. On the contrary, the awareness of IPF as a fatal disease, with a prognosis worse than the majority of cancers, is still limited to few experts and to those patients and families who are directly involved with the disease. The concept of IPF as a cancer-like disorder of the lung may help in meeting the urgent need for a better understanding of the disease and may increase the attention given to IPF at a public, political, and healthcare level. In addition, the existence of pathogenic links between IPF and cancer may improve our understanding of the pathogenesis of IPF, taking advantage of the large knowledge that already exists of cancer biology or even “borrowing” drugs, as in the case of nintedanib, which have been developed or used for cancer. Finally, the recognition of new common pathogenic mechanisms between IPF and cancer may also encourage new IPF clinical trials with other common oncologic drugs, alone or in combination with other drugs, or even through personalized treatments as largely experimented in cancer.


In this system, the enhanced capacitance of the hybrid structure can be understood by the formation of a space charge layer at the graphene/Al2O3 interface. The electrical properties of the interface can be further explained by the electrical double layer (EDL) model dominated by the diffuse layer.Graphene heterostructures are of considerable interest as a new class of electronic devices with exceptional performance in a broad range of applications has been realized. Here, we propose a graphene-embedded Al However, the leakage current due to the quantum tunneling effect has become a significant problem, which limits further scale down of the SiO2 layer. Alternatively, the use of high-k dielectric materials such as hafnium oxide (HfO2), zirconium oxide (ZrO2), and aluminum oxide (Al2O3) that may provide high capacitance without scaling down to nano-sizes has received a great deal of interest24567911121315171819The fabrication of field effect transistors (FETs) with low operating voltage and input power has been researched for decades. According to the drain current equation of FETs, reduction of operating voltage and input power can be achieved with enhancement of the mobility of channel materials or the capacitance of the gate dielectricxide Al2O that mayet al.Meanwhile, graphene, which is well known for its unique properties due to carbon-based two-dimensional structures, has a relatively low density of states compared to other metals because of its linear energy-momentum relationship near the Dirac point2223242O3 capacitors deposited by atomic layer deposition (ALD) with a relatively high dielectric constant and negligible dielectric loss. For the characterization of the interface between graphene and Al2O3, we measured the frequency and gate voltage dependence of capacitance by varying the thickness of the Al2O3 layer and the number of graphene layers for further analysis of the space charge layer. With the obtained results, we also suggest a reason for enhanced capacitance, which is the formation of an electrical double layer (EDL) due to the space charge at the interface.Here, we propose thermal chemical vapor deposition (TCVD)-grown graphene-embedded Al2O3 films were deposited on cleaned ITO-coated glass using the ALD process and the graphene was synthesized utilizing the same method as previous works (see Methods)2O3 film by a poly(methyl methacrylate) (PMMA) assisted wet transfer method. The graphene was patterned by Al pre-patterning and subsequent O2 plasma etching. The lateral dimension of patterned graphene was 0.8 × 1.0 mm. On the transferred graphene, Al2O3 was deposited again through the ALD process. Finally, the top electrode (Cr/Au of 5 nm/70 nm) was deposited by thermal evaporation with a shadow mask for capacitance measurements. The chemical and structural characterization of Al2O3 and the interface properties between graphene and Al2O3 were investigated using X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and transmission electron microscopy (TEM). As shown in the cross-sectional TEM image . The RMS roughness was about 0.305 nm, which was compared with Al2O3 on ITO  and the space charge polarization (right semicircle) at the interface. The relaxation time, τ0, equals the reciprocal of the frequency at the local maxima of the semicircles; hence, the calculated relaxation time of space charge polarization is about 5.78 μs, which means that the response time is appropriate for practical applications. The correlation between ac-conductivities and frequency for both capacitors is plotted in −10 S/m at 100 Hz, we can safely assume that actual leakage is even lower and conclude that leakage is negligible.2O3, charge carrier concentration is rather diffuse, the capacitance from the diffuse layer is expected to be limiting. 2O3 capacitor and a graphene-embedded capacitor. A frequency of 1 kHz was adopted for this measurement because we expect to see the EDL behavior only at a frequency lower than 10 kHz. We observed gate voltage-independent behavior in capacitance for the Al2O3 capacitor without graphene, which is similar to the graphene-embedded capacitor at frequencies of 100 kHz and higher , l is the geometrical thickness, a is the applied potential. The total capacitance of the graphene-embedded capacitor consists of two diffuse layer capacitances in series because two interfaces are formed: one between the upper Al2O3 layer and graphene, and another between graphene and the lower Al2O3 layer. Thus, total capacitance in the low frequency region is given by:where εCD1 and CD2 are the diffuse layer capacitances of the upper and the lower layer, respectively. The total capacitance was slightly asymmetric with the direction of dc bias, causing a slight shift in the C–V curve. There are two possible reasons for this; one is that the formation of a direction-dependent potential due to the work function difference between the upper (Au) and lower (ITO) electrodes. Another is that the difference in dielectric constants of upper and lower Al2O3 layers is presumably due to the difference in surface conditions when depositing the layers. To extract the value of 2O3 layer. The result was fitted by combining 2O3 layers by fitting are approximately 19 and 27 nm, and dielectric constants are 4 and 8, respectively. The dielectric constant of upper Al2O3 layer is lower than that of the lower layer292O3 layer decreases below the calculated where 2O3 to explore the effects of the number of graphene layers to the diffuse layer formed at the interface, where a PMMA layer-by-layer transfer technique2O3 interface. It was reported in previous literature that the hole concentration in graphene is proportional to the number of graphene layersD calculated from Single, bi-, and tri-layer graphene sheets were inserted in Al2O3 to charge carrier transfer at the graphene/Al2O3 interface. The charge carrier transport will induce a highly intense accumulation of negative charges on graphene (inner Helmholtz layer); then, the positive charges form a diffuse layer at the interface between the graphene and Al2O3 due to the Coulombic attraction, forming the EDLs as stated above. Since Al2O3 is an insulator with low carrier concentration, the diffuse layer is typically broad and becomes the limiting factor in induced capacitance. When the graphene layer is increased from a single to a tri-layer, the diffuse layer becomes narrow, indicating that charge carrier concentration within the diffuse layer has increased. Such an increase in charge carrier concentration occurs because electrostatic interaction has become stronger at the graphene/Al2O3 interface due to increasing carrier density within graphene caused by band structure overlap.We attribute the formation of EDL in graphene-embedded Al2O3 capacitor with a relatively high dielectric constant of 15.5 and low leakage current, especially with insertion of tri-layer graphene. For characterization of the interface between graphene and Al2O3, we measured the frequency and gate voltage dependence of capacitance by varying the thickness of the Al2O3 layer and varying the number of graphene layers for further analysis of the space charge layers formed on both sides of the graphene. Results obtained from various thicknesses of Al2O3 indicate that such enhancement of capacitance occurs due to the formation of a pair of EDLs at the graphene/Al2O3 interface. Capacitance dependence on applied gate voltage measurements suggest that the diffuse layer of EDL is the limiting and controlling factor of the capacitance enhancement, which is reasonable since Al2O3 can be considered as a very diffuse system with low carrier concentration. We also calculated the width of the diffuse layer for single, bi-, and tri-layer graphene-embedded capacitors, and they were 27.0, 24.5, and 23.3 nm, respectively. This result was explained by the change of carrier density in graphene. Even though the proposed dielectric material is not suitable for high-frequency applications such as radio frequency devices due to the limitation of response time, the enhancement of capacitance for a gate dielectric material with such a simple fabrication method can be considered a valuable asset in rapid-free device applications such as sensors and integrated circuit for display. Other properties of graphene, such as its superior mechanical strength, can make this method applicable in devices for various purposes, making graphene-insulator heterostructures even more appealing.In summary, we proposed a graphene-embedded Al2 (2 Torr) atmosphere at 1050 °C for 30 min, after which 1:50 mixture of CH4 and H2 was introduced for 20 min. The samples were cooled down to room temperature to complete the synthesis.Graphene was synthesized on 25 μm-thick copper (Cu) foils (Sigma Aldrich) using conventional TCVD. Cu foils were located in the quartz tube and pre-annealed under H2O3, trimethylaluminum (TMA) was employed as the precursor with H2O reactant as the oxidant. Each cycle consists of the TMA exposure of 0.3 s, Ar purging of 10 s, water vapor exposure of 1 s, and another Ar purging of 10 s in sequence at the substrate temperature of 100 °C. Total of 300 cycles was performed.For the deposition of Al2O3 capacitors with/without graphene sheet was conducted over the frequency range of 100 Hz–1 MHz with ac amplitude of 50 mV.All room temperature dielectric measurements were performed using an Agilent 4284A impedance analyzer. The measurement of dielectric performance of the AlHow to cite this article: Ki Min, B. et al. Electrical Double Layer Capacitance in a Graphene-embedded Al2O3 Gate Dielectric. Sci. Rep.5, 16001; doi: 10.1038/srep16001 (2015).


Characterization of the electrodes was performed by scanning electron microscopy (FESEM and SEM). The electrochemical properties of the modified graphene electrodes were inspected by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), and amperometry.A rapid prototyping of an inexpensive, disposable graphene and copper nanocomposite sensor strip using polymeric flexible substrate for highly sensitive and selective nonenzymatic glucose detection has been developed and tested for direct oxidization of glucose. The CuNPs were electrochemically deposited on to the graphene sheets to improve electron transfer rates and to enhance electrocatalytic activity toward glucose. The graphene based electrode with CuNPs demonstrated a high degree of sensitivity (1101.3±56 μA/mM.cm Current glucose sensor technology relies mostly on enzymatic sensing strips that require repeated painful pricking methods to measure glucose concentration. The typical range of sensitivity for a blood glucose sensor is from 1.0 mM to 60 mM  + 2mM K4[Fe(CN)6] in the frequency range of 0.1 Hz to 100 kHz was used to obtain information on electron transfer rates between the electrolyte and the electrode surface. EIS normally includes a semicircular part and a linear part. The semicircular part at higher frequencies corresponds to the electron transfer limited process, and the diameter is equivalent to the electron transfer resistance . The processing method for the prototyping requires only several minutes of processing time at room temperatures, enables direct fabrication on flexible polymer substrates without an additional transfer step, and delivers strong surface adhesion between the few graphene layers and the flexible polymer substrates. Following the fabrication of the SCT/PRG base, the electrode was rinsed to remove loose graphene flakes and dried with low pressure argon gas to prepare for electrochemical deposition of copper nanoparticles.For this investigation, simple processing integrates inexpensive materials  to form the Graphene three electrode base. First, a PVC mask was prepared by removing a three-electrode channel into the PVC sheet using a laser engraving machine. Second, one side of the PVC sheet was taped using regular scotch tape, forming a flexible substrate with an adhesive three-electrode channel. Third, the graphene powder (≈0.25 mg for making a series of 4 strips) was placed on the three-electrode adhesive channel and physically rubbed against the surface of the adhesive Scotch Tape (SCT) in a gentle manner to form the uniform Physically Rubbed Graphene (PRG) electrodes. In the next two steps, electrodes were copper taped and then passivated by using a thin Kapton tape. Silver glue was used to enhance better connectivity in the copper-graphene intersection. An Ag/AgCl reference electrode was formed by gluing the tip of the electrode on the left side of the strip using a silver-silver chloride paste. The strip was stored in an ambient temperature for one day, for the paste to completely dry. An illustration of layers and the final strip is shown in the CuNPs were electrochemically deposited on the surface of the working electrode. Since the sensitivity and the linear range of the sensor is highly dependent on the size and population density of CuNPs, the deposition of Copper nanoparticles on the working electrode is optimized systematically to achieve the smallest possible nanoparticles with a great population density. A large copper population will maximize the output signal of the biosensor due to an increased chemical reaction between the D-Glucose molecule and the CuNPs. The applied voltage during deposition improves the graphene surface and controls the electrodeposition parameters that contribute to optimal NP population with uniform distribution . The forct for the modified electrode with CuNps (SCT/PRG/CuNPs) was smaller than the bare graphene electrode (SCT/PRG); demonstrating that the SCT/PRG/CuNPs electrode has a higher charge transfer rate than the bare graphene electrode. The copper nanoparticles are acting as electron mediators in the electron transfer process . Subsequently, CuO is electrochemically oxidized to Cu(III) species such as CuOOH or Cu(OH)4− [CuO + OH− →CuOOH or CuO + H2O + 2OH− → Cu(OH)4− + e−]. Finally, glucose is oxidized by the Cu(III) species and forms hydrolyzate gluconic acid [Cu(III) + glucose → gluconolactone + Cu(II)] [Gluconolactone → gluconic acid (hydrolysis)]  , 14. Forolysis)] –26; seveThe effect of 250 μM Ascorbic Acid (AA), 250 μM Uric Acid (UA), 100 μM dopamine (DA), and 100 μM acetaminophen (ACT), as electrochemically active interferents found with glucose in human serum, was investigated on the sensor. This was carried out by systematically examining the amperometric response of the sensor upon successive addition of these interferents with their respective concentrations, as compared to 0.3 mM glucose in the order shown in 2 and a standard deviation of 37.7 was calculated from the 9 sensor samples  that was used as the stability measure of the sensor shows only a 17.2% of signal loss in the sensor strip  bio-sensing strip by the GOx as the functionalizing agent. The use of the GOx instead the CuNPs is expected to allow a wider detection and linear range while delivering high level of sensitivity in the sensorFurthermore, it should be considered that the compatibility of the sensor’s fabrication method with the screen printing technology would create opportunities for further development of the sensor in the following ways. First, the construction of a microfluidic channel on the strip would allow for a safe tear sample collection directly from the eye. Second, an accurate passivation and padding on the sensor strip would be expected to eliminate the human error during the fabrication step and increase the reproducibility rate of the sensor to percentages even higher than what is reported in this study. Third, mass production for commercialization of the biosensor.The behavior of most nonenzymatic glucose sensors is a direct function of the electrode material on which the glucose is oxidized. Recent efforts have exploited different materials and fabrication processes for these electrodes. Nanocomposite structure of graphene-metals or metal oxides offer large surface area for the oxidation of glucose. In this research, an inexpensive, disposable graphene and copper nanocomposite through a rapid prototyping process for highly selective nonenzymatic glucose detection was developed and tested for direct oxidization of glucose. The CuNPs effectively improve electron transfer rates and enhance electrocatalytic activity toward glucose. The graphene based electrode with CuNPs displayed good sensitivity, stability, linear range, detection limit, and selectivity against interfering molecules.S1 File(XLSX)Click here for additional data file.


In this work, the piezoresistive effects of defective graphene used on a flexible pressure sensor are demonstrated. The graphene used was deposited at substrate temperatures of 750, 850 and 1000 °C using the hot-filament thermal chemical vapor deposition method in which the resultant graphene had different defect densities. Incorporation of the graphene as the sensing materials in sensor device showed that a linear variation in the resistance change with the applied gas pressure was obtained in the range of 0 to 50 kPa. The deposition temperature of the graphene deposited on copper foil using this technique was shown to be capable of tuning the sensitivity of the flexible graphene-based pressure sensor. We found that the sensor performance is strongly dominated by the defect density in the graphene, where graphene with the highest defect density deposited at 750 °C exhibited an almost four-fold sensitivity as compared to that deposited at 1000 °C. This effect is believed to have been contributed by the scattering of charge carriers in the graphene networks through various forms such as from the defects in the graphene lattice itself, tunneling between graphene islands, and tunneling between defect-like structures. Since the discovery of graphene by Novoselov and Geim in 2004, immense efforts have been focused on potential applications of graphene in optoelectronics, flexible electronics, transparent conducting electrodes, and sensors2/Vs), very large surface area of 2630 m2/g and high elastic stiffness of 340 N/m with a stretchability of up to 20%2Graphene, a two-dimensional 2D) carbon material consisting of hexagonally packed carbon atoms bonded by spD carbon x) suspended membrane pressure sensor with graphene meander patterns, working in a broad pressure regime of 0–70 kPa, was fabricated by Zhu et al.Graphene has been popularly exhibited as a sensing material for sensor devices due to its excellent mechanical and electrical properties. A miniature fiber tip pressure sensor that uses graphene as a diaphragm was demonstrated in order to enhance the sensitivity. However, only the pressures in a small range 0 to 13 kPa) could be measured due to leakage, which resulted in the non-ideal adhesion of the graphene layer to the silica capillary endface kPa coulPereira et al.10Recently, piezoresistive sensing mechanism, which translates a mechanical displacement into an electrical signal, has been widely used because of its advantages, which include feasible preparation, low cost, and easy signal collection7In this context, we chose to explore the role of graphene defects on the pressure sensing performance and incorporate these results to produce highly sensitive flexible pressure sensors. The graphene was synthesized using a hot-filament thermal chemical vapor deposition (HFTCVD) technique by varying the deposition temperature  to induce defects in the graphene films in a controlled manner. This technique was utilized because of the higher temperature ramping rate, which has great potential for the large-scale, energy efficient, and rapid manufacture of graphene, and also for producing excellent step coverage and uniform films12−5 mbar. Prior to the fabrication process, the W hot-filament was set at ~1750 °C by using an external optical pyrometer and substrate temperature at 1000 °C. A cleaning treatment was performed on the Cu foil in H2 at a flow rate of 50 sccm at 3.3 × 10−1 mbar for 20 min to remove the native oxide and increase the Cu grain boundaries. Then, the filament temperature was adjusted to the required temperature of ~1550, ~1650 or ~1750 °C to set the substrate temperature at 750, 850 or 1000 °C, respectively, for the three sets of films studied in this work. The growth of the graphene films was carried out in a CH4/H2 (50 sccm for CH4 and 10 sccm for H2) gas mixture for 30 min at a pressure of 3.7 × 10−1 mbar. Finally, the samples were slowly cooled to ~200 °C (cooling rate: ~2 °C) by reducing the external power supply and were convectively cooled to room temperature in N2 gas at 100 sccm.Graphene was fabricated on Cu foils  in a custom-made HFTCVD system2CO3). The undeveloped photoresist was etched away. Then, the unwanted, exposed portions of the Cu were removed in a 1.0 mol ferric chloride etching solution. After the exposed Cu was completely etched away, the remaining photoresist was dissolved slowly in a 3 wt% NaOH stripping solution for 120 seconds to create an IDE array with 500-μm tracks and 200-μm gap widths and two terminal electrodes. The Cu patterns were then finalized with Au electroplating with 0.3 ± 0.02 μm to provide a substantial stable nature towards oxidation.The fabrication method of interdigitated electrode (IDE) array on polyimide film substrate is presented in −1 in the range of 1000–3000 cm−1 and were calibrated using the 520.5 cm−1 line of a silicon wafer.The surface morphology of fabricated graphene-based flexible pressure sensor was characterized by optical microscopy (Olympus MX80), field emission scanning electron microscopy (JEOL JSM-7500F) at a 2-kV accelerating voltage, and atomic force microscopy in semi-contact mode . In addition, a Raman spectroscopy system (Renishaw InVia micro Raman) was utilized to obtain the Raman spectra of the films to determine the thickness and crystalline quality of the graphene layers. The Raman spectra were excited by a 514-nm laser (~2 μm spot size) at a resolution of 2 cm2 with patterned IDE/polyimide film substrate. To demonstrate the pressure sensing performance, the fabricated sensor was initially attached to the substrate with a square cavity area of 5 × 5 mm2 using epoxy. It was then sealed and clamped completely on a test jig by epoxy bonding and carbon tape to prevent gas leakage . The length of pipeline from the valve to the fabricated pressure sensor and the commercial pressure sensor was fixed at 20 cm. In this case, the applied pressure on the fabricated pressure sensor was assumed to be equal to the measurement of the reference pressure sensor. Both the diaphragm and graphene experienced deformation under the applied pressure , and the resistance changes were simultaneously measured using a source-meter  at ambient conditions.In order to develop a flexible pressure sensor, the as-transferred graphene sheet was incorporated onto an effective sensing area of 5 × 5 mmkage see . A diffe2O, which acts as nucleation site for graphene4−1, respectively . From the results, it can be seen that the evolution of the D peak shows the strong temperature dependence of the substrate temperature , suggesting a major change in the defect concentration in the graphene. The intensity of the ID/IG ratio has often been used to identify the defect density inside graphene, given that a higher ratio indicates more defects and vice versa. This is probably due to the evolutionary kinetics of the graphene formation on the copper substrate as a result of the effects of the adsorption, dissociation, dehydrogenation and copper sublimation2D/IG ratio value, where an I2D/IG larger than 1.5 indicates monolayer graphene growth on copper substrate, and good correlations have been reported in the literature14Further, these three morphologies of graphene films were selected to develop flexible pressure sensors. The morphological characteristics of the resultant transferred graphene on the sensor platform are shown in 2/Si (100) substrate with patterned Pt electrodes  were studied using the Van der Pauw method. The graphene channel’s width and length were fixed equally at 1000 μm. The contact resistance of the Pt electrodes was found to be ~3.0 Ω. The transferred graphene for a growth temperature of 750 °C exhibited a higher sheet resistance of about 1222 ± 18.3 Ω/sq. (ohms per square), but this decreased to 166 ± 6.4 Ω/sq. as the growth temperature increased to 1000 °C, as listed in 17Gao et al.The transport properties of the transferred graphene on the SiOI-V curve was performed, where the current increased linearly as the bias voltage increased from 0 to 2 V, as shown in S = (ΔR/R0)/ΔP) and the unit is kPa−1, in which ΔR is the change in resistance (Ω), R0 is the initial resistance (kΩ), and ΔP is the pressure difference (kPa). The sensitivities for graphene grown at 750, 850 and 1000 °C based on the slope of the fitted lines can be calculated as 0.0045, 0.0025 and 0.0012 kPa−1, respectively. These experimental results demonstrate that this piezoresistive effect in the graphene networks could be improved by lowering the graphene growth temperature.Prior to testing the performance of the sensor devices to applied pressure see , their i−1)−1)−1)−1, which is comparable to the sensitivity of a discrete pressure sensor. The results of repeated cycling are shown in In the present work, it has been successfully demonstrated that a higher sensitivity of sensor device can be achieved by utilizing highly-dense graphene defects as compared to previous works demonstrated for flexible pressure sensor such as the rGO-polyurethane sponge (0.001 kPaa to b) or their overlap area (from c to d); resistance by tunneling or electron hopping effect between neighboring graphene islands (from b to c); resistance by tunneling effect through defects-like line disruptions (from e to f); and resistance by point defects-like vacancies or substitutional impurities (from g to h). In view of that, measurable changes in the resistance can be predicted by exploiting the aforementioned mechanisms which could result from even small modifications to the lattice distortion in the graphene itself, contact area or tunneling distance between neighboring graphene islands with structural defects.For pristine graphene grown at a higher growth temperature, the piezoresistive effect under deformation is limited to the structure deformation-dependence of the graphene lattice distortion, which only leads to a modified electronic band structure, so the overall variation of resistance is smalleri), tunneling between the defect-like line disruptions structure (Rd), defects in the graphene lattice itself (Rg) and the contact between the graphene and IDE array (Rc). Hence, any changes to these parameter as a function of applied pressure would induce strained in graphene lattice structure and scattering of charge carriers from the increased in tunneling distance, thus resulting in a significant resistance change  to be at 0.30, 0.20 and ~0.05 μm at 750, 850 and 1000 °C, respectively. From the graph, the concentration of the defects within the graphene layer is inversely proportional to the growth temperature. It has been established that based on the tunneling mechanism, a larger tunneling distance under applied strain or pressure would enhance the change in the resistance of the graphene material. In this work, it has been demonstrated that the same characteristic is also valid for the fabricated graphene-based pressure sensor, but with further scattering effects on localized defects supporting line disruptions and dislocations. At a growth temperature of 750 °C, the deformation of the high defect density had a more prominent influence on the resistance changes than that of perfect graphene due to the quantum confinement effects in the presence of point defects and line disruption defects. The strong dependence of the resistance changes in the high defect density of the graphene networks on the structural deformation could be attributed to the creation of charge carrier scattering. Under the application of pressure, the tunneling distortion among overlapped and adjacent graphene islands and defect-like structures became more significant, which in turn increased the density of the tunneling per graphene area. This led to a higher probability of electron scattering in the percolating networks, which further reduced the density of the conducting paths, thereby effectively increasing the rate of the resistance change. On the other hand, different percolation schemes through specific type of defects  may have a significant impact to the piezoresistive effect of graphene-based flexible pressure sensors which can be further study, but these cases exceed the scope of this work.The concentration of the defects within the graphene layer which relates to the nanoparticle density, overlapping region and I−1 has been attained for the sensor using graphene grown at the lowest substrate temperature of 750 °C. However, the sensitivity could be further enhanced by patterning smaller IDE channel or lowering the thickness of the diaphragm. This investigation provided a better understanding of the use of graphene in highly sensitive piezoresistive-based flexible pressure sensors.In this work, a fabricated flexible pressure sensor incorporating graphene synthesized at various substrate temperatures of 750, 850 and 1000 °C through the hot-filament thermal chemical vapor deposition (HFTCVD) technique has been successfully demonstrated. The experimental results show that the graphene grown at a lower temperature has a higher structural-defect density as compared to those grown at a higher substrate temperature. A linear piezoresistive effect has been observed for the applied pressure within the range of 0 to 50 kPa. The sensitivity of the fabricated pressure sensor could easily be modified by varying the state of the substrate temperature. In this work, the highest sensitivity of 0.0045 kPaHow to cite this article: Mohammad Haniff, M. A. S. et al. Piezoresistive effects in controllable defective HFTCVD graphene-based flexible pressure sensor. Sci. Rep.5, 14751; doi: 10.1038/srep14751 (2015).


Structural inhomogeneities, such as the wrinkles and ripples within a graphene film after transferring the free-standing graphene layer to a functional substrate, degrade the physical and electrical properties of the corresponding electronic devices. Here, we introduced titanium as a superior adhesion layer for fabricating wrinkle-free graphene films that is highly applicable to flexible and transparent electronic devices. The Ti layer does not influence the electronic performance of the functional substrates. Experimental and theoretical investigations confirm that the strong chemical interactions between Ti and any oxygen atoms unintentionally introduced on/within the graphene are responsible for forming the clean, defect-free graphene layer. Our results accelerate the practical application of graphene-related electronic devices with enhanced functionality. The large-area monolayer graphenes were prepared by a simple attachment of the Ti layer with the multi-layer wrinkle-free graphene films. For the first time, the graphene films were addressed for applications of superior bottom electrode for flexible capacitors instead of the novel metals. Since its initial preparation by mechanical exfoliation, the chemical vapor deposition (CVD) of graphene onto Ni23478911121315161718202/Si, glass, and polymers2223Platinum (Pt) is commonly used as the bottom electrode in thin-film devices due to its high work function (5.12–5.93 eV) and excellent chemical stability at high temperatures. A titanium (Ti) layer is generally used to improve the adhesion between Pt and oxygen-containing or oxygen-philic substrates, such as Si (with native oxide), SiOHere, we hypothesize that Ti interacts with the oxygen in the substrates to form strong Ti-O chemical bonds and utilize this concept to transfer wrinkle-free graphene films to various functional substrates by introducing a Ti adhesion layer. We demonstrate that defect-free graphene films on Ti adhesion layers can be used as transparent, reliable bottom electrodes without degrading the performance, even with mechanical bending, unlike conventional Pt electrodes.x phases such as TiO, TiO2, Ti2O3, and Ti3O5 as well as metallic Ti were found at the Ti-SiO2 (main phase of glass) interface, suggesting that a large portion of the Ti interacted chemically with oxygen (oxidized), which might be from the glass substrate  after an exposure at an air atmosphere. Various TiOubstrate  and 1b. ubstrate  were connterface  and 1b. nterface . These rnterface .Chemically synthesized graphene films are inevitably exposed to oxygen-rich conditions during post processing via physical or chemical treatments. Therefore, the final graphene products incorporate oxygen species2021In these contexts, we used the Ti layer as a binding layer between the graphene film and a transferred substrate. Naturally existing oxygen species at the graphene film surface provide the oxygen for the formation of strong Ti-O chemical bonds, which benefits the adhesion between graphene and the substrate.2 using graphene films transferred to the 10 nm-thick Ti layers, respectively. Compared with the image observed at a small area  images for a graphene layer transferred to a glass substrate without a Ti adhesion layer showed severe wrinkling , which i–4.0 nm, , which i–4.0 nm, . Our finWe used density functional theory (DFT) calculations and studied the Ti-graphene interface morphology to determine the role the Ti–O chemical bonds and under-coordinated Ti sites play in forming a wrinkle-free graphene layer on the Ti adhesion layer . The DFTx) interface were confirmed via composition sensitive annual dark field (ADF) imaging and electron energy loss spectroscopy (EELS) mapping. The transferred graphene films consisted of approximately 5-6 layers in the ADF image  of the Ti-C(O) is higher than that of the C-C bonding  between the layers of the graphene. Accordingly, Ti adhesion layer coated on the glass substrate may strongly bind with the first layer of the graphene by a mechanical attachment. If this concept is possibly realized, actual monolayer graphene can be obtained from the multi-layer graphenes transferred to the substrates as well as an additional demonstration for a strong adhesion between Ti layers with the graphene. The preparation of large-area monolayer graphene from the wrinkle-free multi-layer graphene films transferred to the Ti (10 nm)/glass substrate was performed using the method shown in an inset of 2Mg2/3Nb4/3O7 (BMNO) dielectric materials with pyrochlore structures were chosen to provide a high dielectric permittivity in amorphous films grown at room temperature, which is critical for flexible devices−8 A/cm2 at 10 V and a dielectric permittivity of approximately 40–60 at 100 kHz2829Wrinkle-free graphene films on a Ti adhesion layer were addressed for the bottom electrode applications in transparent and flexible thin film capacitors. For thin film capacitors, Bi5 Hz because of the high resistivity (~10−4 Ω-cm) of graphene. Using oxide electrodes, such as indium and Al-doped ZnO (AIZO)30.5Sr0.5CoO3 (LSCO)5 Hz due to their higher resistivity (~10−4 Ω-cm) relative to the metals 2) using an applied voltage of ±5 V (−8 A/cm2 at ±5 V), which approached those of conventional capacitors with a Pt/Ti bottom electrode. The capacitors containing the Ti adhesion layers exhibited stable electrical properties (approximately 3 × 10−7 A/cm2) even at a voltage range of ±20 V /Si substrates using dc sputtering under argon atmosphere at room temperature with a 2 inch Ti metal target (purity: 99.99%). DC power for the thin film deposition was maintained at 20 W. Thin film morphologies were characterized using atomic force microscopy  and field-emission scanning electron microscope ). The interface of the Ti substrates has been investigated using X-ray photoelectron spectroscopy . To rationalized the effect of oxygen involved in the substrate, the adhesion test of the Ti layer deposited onto the oxide layer (SiO2/Si) and non-oxide layer (CrN/Si) was performed by the scratch test using a scratch tester , and the amount of the residual Ti in the scratched regions was measured using energy dispersive spectroscopy (EDS).In order to investigate the role of the adhesion layer of the Ti films, 50 nm-thick Ti thin films were deposited onto the glass and SiO3) solution was used as an oxidizing etchant to remove the nickel layersGraphene films were grown at 900°C onto the Ni (250 nm)/Si substrate via rapid-thermal pulse chemical vapor deposition  and an aqueous iron chloride (1 M FeClThe new Ti/glass substrates (top sample) were mechanically putted on the multi-layer graphene films/Ti/glass (bottom sample) in a vacuum atmosphere to prevent the oxidation of the Ti layer deposited on the glass substrate. Here, the Ti layer in a new Ti/glass substrate was attached to the graphene films transferred to the Ti/glass substrate. The schematic structure for the preparation of the new graphene films from the wrinkle-free graphene films was inserted at 2 sample was fixed and the other side was pushed for 30 s at each point. Variations in rms roughness of the samples after bending at each point were measured by AFM. The 150 nm-thick Ni top electrodes (100 × 100 μm2 size) were deposited for the electrical measurement after the bending of the BMNO/graphene/Ti/PET.200 nm-thick BMNO high dielectric constant thin films were deposited at room temperature under an oxygen atmosphere via pulsed laser deposition (PLD) using a BMNO target (purity of 99.99%) with a diameter of one in. onto the graphene/Ti/glass  and PET (200 μm) substrates. The dielectric properties of the BMNO thin films were evaluated as a function of frequency using an impedance gain phase analyzer (HP4194A). The leakage current characteristics of the BMNO capacitors were investigated via HP4145B semiconductor parameter analysis. Bending tests of the graphene/Ti (10 nm)/PET and the 200 nm-thick BMNO films/graphene/Ti /PET were performed by the method shown in the inset of −4 eV and 0.01 eV/Å, respectively. We used the Gaussian smearing method with a finite temperature width of 0.1 eV in order to improve convergence of states near the Fermi level. A single layer graphene with 72 carbon atoms and a 5 × 5 Ti (0001) slab with three Ti layers was used to describe a graphene film and a Ti adhesion layer, respectively. The bottom Ti layer was fixed during structural optimization whereas the others were released. Initially, a graphene film was oxidized with 25 oxygen atoms to produce a graphene oxide layer and the graphene-oxide film was subsequently attached to the Ti slab. Seven more oxygen atoms were appropriately added to the Graphene-Ti interface to fill out the Ti vacancies formed upon the graphene-Ti interaction.We performed GGA-level spin-polarized DFT calculations with the VASP codeRealization of Large-Area Wrinkle-Free Monolayer Graphene Films Transferred to Functional Substrates


Silicene is an exciting two-dimensional material that shares many of graphene’s electronic properties, but differs in its structural buckling. This buckling allows opening a bandgap in silicene through the application of a perpendicular electric field. Here we show that this buckling also enables highly effective modulation of silicene’s conductance by means of an in-plane electric field applied through silicene side gates, which can be realized concurrently within the same silicene monolayer. We illustrate this by using silicene to implement Self-Switching Diodes (SSDs), which are two-dimensional field effect nanorectifiers realized within a single silicene monolayer. Our quantum simulation results show that the atomically-thin silicene SSDs, with sub-10 nm dimensions, achieve a current rectification ratio that exceeds 200, without the need for doping, representing a 30 fold enhancement over graphene SSDs. We attribute this enhancement to a bandgap opening due to the in-plane electric field, as a consequence of silicene’s buckling. Our results suggest that silicene is a promising material for the realization of planar field effect devices. Graphene has long been envisaged as a promising candidate for post-CMOS electronics. However, graphene lacks an electronic bandgap, making it difficult to turn a graphene device off effectively by means of an electric field. Accordingly, many efforts have been redirected towards finding other two-dimensional materials that have an electronic bandgap but still exhibit many of graphene’s desirable electronic properties, such as its high electron mobility. Amongst numerous candidates, silicene, a new material composed of a monolayer of silicon atoms, has attracted the interest of theorists123567891215161822Here we implement SSDs using silicene and study their transport properties using Non-Equilibrium Green’s Function (NEGF) formalismOur results suggest a similarity between the electronic properties and behaviour of silicene SSDs and graphene SSDs, but show superior performance of silicene SSDs, up to a 30 fold enhancement in rectification ratio, suggesting that an in-plane electric field has much stronger control on the conductivity of silicene nanoribbons in comparison to graphene nanoribbons. We attribute this enhanced performance in silicene SSDs to a bandgap opening that results due to silicene’s buckled structure, as will be discussed later on in the discussion section. Our findings suggest that silicene could potentially be a very promising material for the realization of planar field effect devices.In the next section we present the simulation results for the transport properties of silicene SSDs followed by their discussion in the final discussion section. The calculation method is described separately in the methods sections at the end of the paper.A self-switching diode is formed by etching two L-shaped trenches through a two-dimensional material. These two L-shaped trenches define a nanoribbon in between them, which acts as the nano-channel of the device, through which conduction occurs. This nano-channel is surrounded by two side gating nanoribbons, which are used to apply a self-induced electric field onto the channel in order to control its conductance. The two side gates are illustrated through With no bias voltage applied to the device, as shown in Since the channel in a silicene SSD is a nanoribbon, it can have either armchair or zigzag edges depending on the orientation of the etched L-shaped trenches. The channel of the device illustrated in In this sub-section we investigate the transport properties of silicene SSDs with armchair nanoribbon channels. One important observation in The presented findings on silicene SSDs with armchair channels are consistent with our previous findings for graphene SSDs with armchair channelsIn this next subsection we investigate a special class of silicene SSDs; the all-silicene self-switching MISFED, Metal-Insulator-Semiconductor Field Effect Diode.p and 3p + 1 atoms, where p is an integer, have sizable bandgaps making them semiconductingp + 2 atoms have vanishingly small bandgaps, making them behave as if they were metallicIn graphene, armchair nanoribbons have a unique property, in which the bandgap of the nanoribbon varies with its width27sg), marked on p + 2 atoms. This class of graphene SSDs achieves superior rectification when compared to the other two classes of graphene SSDs with semiconducting side-gatesBy utilizing the property of being able to tune armchair graphene nanoribbons from metallic to semiconducting by width variation, we had previously proposed the all-graphene self-switching MISFED The operation principle of this class of SSDs is illustrated through the schematic diagrams in sg), are 5 (3p + 2), 6 (3p) and 7 (3p + 1) atoms respectively. The device in p + 2 type, which are expected to have metallic behaviour, and therefore, the device is expected to behave in a similar fashion to a graphene self-switching MISFEDBuilding upon the similarity between graphene and silicene nanoribbons1The calculated current-voltage (I–V) characteristics of the three devices are plotted in In order to quantify the performance of the three devices of 2, bulk materials such as compound semiconductor heterostructures30In contrast, the achieved rectification ratio for a silicene self-switching MISFED , withoutin situ using Al2O3. The Al2O3/silicene/Ag film stack is then transferred to a device substrate and patterned into the device structure using electron beam lithography (EBL) and etching, with the native Ag(111) film patterned into electrodes for contacting the device.While silicene synthesis and its subsequent stability in air has proven to be a challenge, the recently demonstrated synthesis-transfer-fabrication method named ‘silicene encapsulated delamination with native electrodes’ (SEDNE) processWhile EBL would not be able to define nanoribbons with atomic precision, narrow nanoribbons with sub-20 nm widths and rough edges can be achieved, and these would behave as semiconducting nanoribbons required to construct the channel of the SSD device. To produce metallic side gates, for the silicene MISFEDs, nanoribbons with a width greater than 50 nm can be implemented for the side gates, which would ensure that they are semi-metallic, achieving stronger control over the channel’s conductivity.Finally it is worth mentioning that with such a process, the fabricated device may not be stable in air for a long period of time, however, the planar 2D architecture of SSD allows further capping, lamination or deposition of other material layers onto silicene, which may be able to help stabilize the silicene lattice. The challenge of silicene’s stability remains to be an open area that needs further investigation, however promising progress is being made towards achieving this endeavour.Silicene shares many of graphene’s electronic properties, but differs in the fact that it exhibits a buckled structure. When a perpendicular electric field is applied to silicene, as shown in When an in-plane electric field is applied to an armchair silicene nanoribbon by two side gates with equal voltage, as in a SSD, the electric field lines between the side gates and the channel would have the distribution shown in In summary, we have investigated the effect of an in-plane electric field on silicene and showed that it results in strong control over its conductivity. The control that is achieved by the in-plane electric field on silicene is much stronger than what can be achieved on graphene due to the buckled structure of silicene, which allows bandgap tunability. We have demonstrated how this effect can be utilized in order to realize high performance planar silicene self-switching diodes. Quantum simulation results show that silicene SSDs can achieve current rectification ratios that exceed 200, without the need for doping or special passivation. This is a 30 fold improvement over what can be achieved with similar graphene devices. Our findings suggest that silicene might offer an attractive platform for the realization of next generation planar field effect devices.In order to capture silicene’s buckling property, its atomic structure was optimized using the Density Functional Theory (DFT) as implemented in Atomistix Toolkit (ATK) package137Transport calculations were conducted on each device using the Extended Huckel methodL), central scattering region (C), and semi-infinite right electrode (R). The mesh points in real space calculation were defined as uniformly spaced k points of 1 × 10 × 50, with 50 sample points along the transport direction, and 10 points along the width (induced electric field direction). In the used tight-binding model the tight-binding Hamiltonian is parameterized using a two-centre approximation, where the matrix elements are described in terms of overlaps between Slater orbitals at each site. The weighting scheme used for the orbital energies of the offsite Hamiltonian was according to WolfsburgL) and (R) with Fermi levels μL and μR through (C) according to the Landauer formulaThe device structure was partitioned as three regions: semi-infinite left electrode  is the transmission probability of incident electrons with energy E from (L) to (R), f0(E − μL(R)) is the Fermi-Dirac distribution function of electrons in (L) and (R) respectively, and V = (μR − μL)/e is the potential difference between (L) and (R).where T, is correlated with L) and (R) to (C) respectively, according to the following equation:Transmission probability, L(R) are the electrodes’ self-energies describing coupling with (C).where ∑I(V) with the summed energy dependent transmission probability, T, we need to express local current components at the atomic level along the chemical bonds to describe the variation of coherent electron transport through the system. Local current components may be investigated by extracting local transmission components. The total transmission coefficient can be split into local bond contributions, Tij, which are represented in ATK by lines along the bond lengths, called transmission pathways. The relationship between the total transmission coefficient and the local bond contributions is:As the Landauer approach only connects the external electrode current A and B represent pairs of atoms separated by an imaginary surface perpendicular along the bond length. The total transmission coefficient is the sum of the local bond contributions between all pairs of atoms A and BTij corresponds to back scattered electrons along the bond, whilst a positive value corresponds to transmitted electrons. The same calculation method was used and is described in greater details in previous work2223where How to cite this article: Al-Dirini, F. et al. Highly Effective Conductance Modulation in Planar Silicene Field Effect Devices Due to Buckling. Sci. Rep.5, 14815; doi: 10.1038/srep14815 (2015).