Turning during locomotion involves considerable changes of the body’s center of mass and reduced stability, as well as lower limb kinematics and kinetics. However, many previous studies have been carried out to evaluate the effectiveness and applications of orthotic insoles as well as different types of orthotic materials in various clinical symptoms, which are focused primarily on straight line walking. Hence, the influence of custom-made insoles with the use of advanced three-dimensional spacer fabrics on biomechanics parameters in terms of plantar pressure distribution and lower limb electromyography during turning movement was studied.Twelve subjects performed 180-degree turning at a speed 3.07-3.74 km/h for five successful trials under 3 insoles conditions: wearing traditional ethylene vinyl acetate insoles and two different spacer-fabricated insoles, with the plantar pressure and lower limb muscle activity collected simultaneously. Turning movement was broken down into 3 phases for analysis: Turning initiation, turn around and turn termination.p < 0.05). Compared to the traditional insoles, insoles made of a spacer fabric reduced the peak pressure (>12 %) and pressure–time integral (>13 %) in toes, metatarsal head 1 and metatarsal heads 2–3 at turning initiation; (>15 %) and (>17 %) in medial midfoot and medial heel at turn around. Insoles with spacer fabrics on the top and middle layer reduced both pressure parameters (>18 %) in toes and MTH 1 at turn termination. In terms of muscle activities, insoles with two-layer spacer fabrics could lower maximum muscle activities of vastus lateralis  at turn around.There was a statistically significance difference in plantar pressure between the traditional insoles and the insoles made of a spacer fabric as the top layer (Insoles with different fabrications could offer various pressure offloading patterns across the plantar and muscle activity changes while turning. Insoles with a spacer fabric on the top tend to reduce plantar pressure loading at different regions during turn initiation and turn around phases, while two-layer spacer-fabricated insoles may contribute to reduced vastus lateralis muscle activation during turn around. More importantly, this study provides a new dimension in the potential use of the textile-fabricated insoles which may widen the range of insole materials selection in the design and development of insoles so as to enhance the effectiveness of orthotic treatment. Turning is a common occurrence, accounting for approximately 35-45 % of all steps in activities of daily living –3. It isFoot orthotic treatment is one of the primary means to handle various foot problems such as reducing the occurrence or recurrence of ulceration which is due to the excessive shearing together with abnormal levels of repeated pressure that occur within the foot leading to severe damage to soft tissue , 10. EveCustom-made orthotic insoles, which are designed to relieve and reduce plantar pressure over a wider surface area, have been widely used and highly promoted in the treatment of foot deformities and/or neuropathic conditions of the foot –24. TheyTo improve the quality of foot rehabilitation treatment, a thorough understanding of foot plantar loading behaviors and lower limb muscles activation patterns when foot orthoses are worn during the process of turning is imperative. The purpose of this article was to explore whether the novel textile materials could have a better performance in plantar pressure and muscle activity reduction during turning in healthy participants. Hence, the specific aim of the study was to examine the changes of plantar pressure distribution and lower limb muscle activity in response to custom-made textile insoles and traditional insoles during different phases of turning. It was hypothesized that 1) the overall distribution of plantar pressure and muscle activities associated with turning could be reduced, 2) the magnitude of pressure and muscle activities reductions vary at different turning phases by the use of textile insoles made of spacer fabrics.In this within-subject repeated measures study, the participants wore three types of insoles made with different materials combinations. The plantar pressure distribution and muscle activity were measured during the wear trials.2 (SD: 2.6). Their foot sizes ranged from European 40 to 43  and 37 to 40 . All participants signed a written consent in accordance with the ethics policy on human subjects as stipulated by the university before participation. The experimental protocol was approval by the Human Subjects Ethics Sub-committee of the Research Committee.Twelve healthy subjects, 6 men and 6 women, who did not have any history of orthopedic or neurological conditions and were free of foot pain during the time of study participated in the study. Their average age was 23.0 (SD: 4.3); and body mass index (BMI) was 20.3 kg/mWhile the subjects were in an upright sitting position , the foot contour with the subtalar neutral position was captured by a contact digitizer of the Amfit® technology system . The CAD/CAM mill connected to the digitizer receives the foot images and fabricates the 3D bottom layers of the insoles by a certified orthotist/prosthetist. Each participant was fitted with 3 pairs of custom-made multilayer insoles that were made with the same combinations of materials as shown in Table The data for each subject were collected on the same day. The subjects went through a 4-h acclimatising period of each insole wear  for 3 to 4 days before the data acquisition. Previous studies have found that subjects, especially those with healthy foot conditions, probably feel uncomfortable for the contoured shape of the insoles and the overall comfort is likely influenced by arch comfort . In thisPressure was measured at 160 Hz using the Pedar®-X in-shoe pressure measurement system  on the dominant foot. Each Pedar® insole sensor, which was 2 mm in thickness and consisted of sampling with 99 sensors, was fitted in accordance with foot size and placed inside each shoe between the foot and the insole. The participants wore the standard sports shoes, socks and insoles provided during data collection. The plantar pressure map was divided into nine subareas: hallux, toes, metatarsal head (MTH) 1, MTHs 2–3, MTHs 4–5, medial and lateral midfoot (MF) and medial and lateral heel by using the Novel Multimask software  as shown in Fig. th order Butterworth low-pass filter with a band-pass filtered at 10–500 Hz and stored for office analysis . The sEMG data were analyzed by converting the data into root mean square values, which were calculated for a 400-ms window. The resultant maximum and mean amplitudes were averaged under each condition and normalized to the MVC of each subject which was expressed as a percentage. The average of five successful trials was then used for data analysis.During the gait trials with each insole condition, surface electromyography (sEMG) data for the vastus lateralis, tibialis anterior and lateral gastrocnemius muscles were simultaneously collected with the plantar pressure distribution by using a 10-channel Datalog sEMG system at a sampling frequency of 2048 Hz . Bipolar Ag/AgCl surface electrode pairs were placed parallel to the alcohol cleaned and shaven surface of the skin overlying the corresponding muscle bellies. The electrodes were 10 mm in diameter and had 22 mm inter-electrode separation distance. Electrode placement followed the recommendations of Surface ElectroMyoGraphy for the Non-Invasive Assessment of Muscles (SENIAM) . All sEMAll of the data are reported as mean (SD). The IBM SPSS software (version 16) was used for data analysis. Two-factor repeated measures analysis of variance (ANOVA) was performed to explore each measurement of the plantar pressure distribution, and muscle activity across the three insole conditions. There were two within-subject independent variables for each measurement: type of insole and subarea; and type of insole and muscle. In addition, one-factor repeated-measures ANOVA was used to further examine the difference between each dependent variable in each measurement among the three insole conditions. Bonferroni post hoc test was used for multiple pairwise comparisons when there was a demonstrated significant difference in both types of ANOVA.Table 2,22 = 18.5, p < 0.001; F8,88 = 20.6, p < 0.001 respectively), and during turn termination . There is no interaction effect during turn initiation. The two-way interaction (insole-subareas) is only significant for the PP (p < 0.02) during turn termination. The post hoc tests indicate that when compared with insole I, there were statistically significant differences in PP during the turn initiation (120.5 vs. 105.1), turn around (97.0 vs. 87.2), and turn termination (120.1 vs. 112.4) in insole II. Insole II resulted in lower peak pressures compared to insole I during various turning phases. Reduction in PP was also found in insole III during turn initiation  and turn termination . No significant differences were shown with reference to turn around.The insoles and subareas have statistically significant effects on PP during turn initiation (Fp < 0.05). Statistically significant pressure differences were also found in medial MF and medial heel at turn around. The Bonferroni pair-wise comparison showed significant pressure differences at toes (mean difference (SD): 34.4 (5.5), % change: 24.0 %, p < 0.001), MTH 1 (22.7 (8.4), 16.3 %, p = 0.01) and medial MF (9.6 (1), 16.0 %, p = 0.012) during turn initiation, and medial MF (11.6 (3.0), 15.8 %, p = 0.041) and medial heel (23.7 (6.8), 19.1 %, p = 0.005) during turn around between insole I and insole II. Similar trend of pressure reduction was also observed in Insole III at hallux (27.5 (0.7), 18.4 %, p = 0.011), toes (26.4 (1.8), 18.0 %, p = 0.007) and MTH 1 (23.0 (0.3), 18.7 %, p = 0.03) during turn termination when compared to Insole I. No significant differences were shown with reference to heel areas during turn initiation and termination, while no significant difference was found in forefoot areas during turn around. When comparing PP in different phases as shown in Fig. The results in Table 2,22 = 8.0, p = 0.002; F8,88 = 7.8, p < 0.001 respectively), turn around  and turn termination . Nevertheless, none of the two-way interaction (insole-subareas) is significant. The post hoc tests indicate that insole II reduced PTI at turn initiation  and turn around  compared with insole I.Analysis of the PTI yielded similar results, whereby the insoles and subareas have statistically significant effects on the PTI during turn initiation (Fp < 0.05) amongst different insole conditions. Significant differences were also found in hallux, medial MF and medial heel at turn around. In the pairwise comparison, significant PTI differences at toes (9.4 (2.0), 23.7 %, p = 0.001), MTH 1 (7.8 (1.0), 19.5 %, p = 0.007) during turn initiation, and hallux (8.8 (0.4), 19.2 %, p = 0.02), medial MF (5.3 (0.9), 17.2 %, p = 0.025) and medial heel (11.0 (5.3), 24.5 %, p = 0.007) during turn around between insole I and insole II. Similar trend of PTI reduction was also observed in insole III at toes (9.4 (2.0), 18.5 %, p = 0.024) and MTH 1 (7.9 (2.4), 23.9 %, p = 0.013)) during turn termination when compared to insole I. No significant differences were shown with reference to midfoot and heel areas during turn initiation and termination.With reference to Table Table 2,22 = 4.9, p = 0.017) is only significant for the maximum muscle activity during turn termination. The two-way interaction (insole-muscle) or pair-wise comparison of insoles is not significant (p > 0.05). The results in Table p < 0.05) is detected only in the vastus lateralis muscle across insoles during turn around, where insole III reduced the maximum muscle activity (3.8 (0.1), 16.9 %, p = 0.044) compared to insole I in the pairwise comparison. No significant differences were found in any muscle group amongst insole conditions during turn initiation and termination. Besides, when comparing maximum muscle activity in different phases as shown in Fig. The main effect of the muscle type , turn around  and turn termination  but the two-way interaction (insole-muscle) is not significant (p > 0.05). The post hoc tests indicate that reduction in the mean muscle activity in insole I during turn initiation , turn around , and turn termination  when compared to insole II. Results shown in Table The main effect of the insole type is significant for the mean muscle activity during turn initiation , textile-fabricated insoles could reduce pressure loading in various plantar subareas during different phases of the turning. In this study, when the insole consists of one layer of textile material (i.e. insole II), the PP and PTI are significantly reduced mostly in forefoot regions such as Toes, MTH 1 and MTHs 2–3 at turning initiation and a significant reduction in the medial side of midfoot and heel are found at turn around. In regard to the insole composing of two-layer textile materials (i.e. insole III), the pressure loading is significantly reduced in toes and MTH 1 during turn termination. This may be attributed to the soft sandwiched structure of spacer fabrics that spacer fabrics are used as the top layer of insoles II and III with direct contact with the foot for better resilience and recovery performance , 34, thuIn this study, the redistribution of the body center of mass may also induce the turn-related sensory feedback which leads to activate more muscles around the knee of the inner limb during the stance phase to enable body support and maintain whole body stability while turning –50. For With respect to the noticeable decrease in the maximum and mean muscle activity of almost all of the muscle groups after the use of textile insoles during different phases of turning, the reason may be related to the material features that make up the insoles. For instance, the viscoelastic and shock-absorbing properties of Poron® together with the transversal compressible spacer fabric with a high pile height in insole II could possibly reduce the frequency of the overuse of the foot . This maMost previous studies have been conducted on investigating the effects of different orthotic insoles on plantar pressure distribution and muscular activities during straight line walking. The major novelty of our work is focusing on turning which had been further differentiated into turn initiation, turn around and turn termination. Related studies have reported that plantar peak pressure is redistributed across the plantar with the insertion of contoured shape insoles when compared to no insole condition. In Redmond’s study, custom made insoles with EVA insertion at heel posts could reduce peak pressure 12.7 % and 17.2 % at heel area when compared to prefabricated insole and control shoe conditions respectively . Hinza iIt is noted that there are some limitations in this study. The sample size is relatively small and therefore might have limited the generalizability of the results. The current turning task was merely a single subset of turning gait, which may not be representative of all types of turns that occur during daily ambulation and of all human turnings. More rigorous and various types of turning in daily tasks would be necessary for further studies. Also, it is recognized that only the immediate effect of the insole was tested. Further research is required to evaluate the long term effects of the materials on pressure loading and to investigate the durability of the materials when exposed to prolonged wear and tear. As footwear comfort is emerging as an important research field, further work is necessary to identify the determining factors. It is recognized that the use of young healthy adults may be responsible for the lack of differentiation between the effects of the material on plantar and muscle response because they may have been able to modify their gait or plantar loading to prevent any foot areas from excessive stress. Nonetheless, the study provides preliminary evidence that supports the use of spacer fabrics in designing orthotic insoles, thereby providing a basis for future studies to highlight the high flexibility of spacer with its significant thermal features in further developments.Turning is one of the major motions and makes up a large portion of steps taken during activities and therefore should be taken account of during lower limb kinematic and kinetic investigations of different insole designs. The present study has provided a novel approach on the use of spacer fabricated insoles, which not only reduces/redistributes plantar pressure, but also lowers muscle activity of the lower limbs during various phases of turning. The wide availability, versatility and cost effectiveness of knitted spacer fabrics and/or advanced textile materials also allow practitioners to widen their selection of insole materials in the design and development of orthotic insoles. It is suggested that a spacer fabric is used as the top layer while a soft and cushioning material is used as the middle layer for orthotic insoles, and that different pile heights and thicknesses be used for patients with different needs and support requirements.EVA, ethylene vinyl acetate; MF, midfoot; MTH, Metatarsal head; MVC, maximum voluntary contractions; PP, peak pressure; PTI, pressure time integral, sEMG, surface electromyography


However, diameter dependence of thermal conductivity of SWCNTs received less attentions. So far, diverse trends of the diameter dependence have been discussed by different methods and all the previous results were based on empirical interatomic potentials. In this paper, we emphasize to clarify accurate κ values of SWCNTs with different diameters and in-plane κ of graphene. All the studies were under the framework of anharmonic lattice dynamics and Boltzmann transport equation (BTE) based on first principle calculations. We try to infer the right trend of diameter dependent thermal conductivity of SWCNTs. We infer that graphene is the limitation as SWCNT with an infinite diameter. We analyzed the thermal conductivity contributions from each phonon mode in SWCNTs to explain the trend. Meanwhile, we also identify the extremely low thermal conductivity of ultra-thin SWCNTs.The effects of temperature, tube length, defects, and surface functionalization on the thermal conductivity ( In their research, the κ of SWCNTs is smaller than graphene and exists a minimum value at a certain diameterκ for SWCNTs and compared with graphene, which can be regarded as the SWCNT with diameter approaching infinity in structural configuration.In the previous study of density functional theory (DFT), the vibrational properties of SWCNTs are studied including the radial breathing modes (RBM), tangential totally symmetric modes, zone folding approximation for phonons of nanotubes, phonon dispersion relations with the helical Brillouin zone, and the electron-phonon coupling effects15κ of SWCNTs with different diameters. We try to investigate the high κ values of the SWCNTs accurately and clarify the relationship between κ and diameter. The calculation results agree very well with the experimental data that have been reported. From the first principle calculation results, we can infer that κ of SWCNTs increases with diameter decreasing, and κ of graphene shows to be the lowest boundary value of these SWCNTs. We also study the thermal transport in ultra-thin SWCNTs with diameters 2.07 Å and 2.71 Å. We demonstrate that the ultra-thin SWCNTs possess relatively lower thermal conductivities than graphene, which agrees with the recent MD simulations resultIn this work, we applied the method which considers the anharmonic three-phonon scattering based on ab initio calculation and combines with BTE to study the κ obviouslyκ for these SWCNTs and graphene at room temperature are displayed in κ of graphene from our calculation is 3409.08 W/mK. This result excellently agrees with recent research by first principlesSeven armchair SWCNTs and one chiral ultra-thin SWCNT  were calculated. In previous report, the chirality of SWCNTs does not effect κ of SWCNTs increases with the diameter descending from 10.85 Å to 4.07 Å. In this diameter range, the diffusive phonon thermal conductivity κ of SWCNTs are larger than in-plane κ of graphene. From κ along the tube direction will approach to the graphene in-plane value.From the data in κ contribution in percentage from each phonon mode of SWCNTs and graphene. κ along the tube-direction for SWCNT, SWCNT and SWCNT respectively. Color bar indicates the contribution magnitude of each phonon mode. Red data point on phonon spectrum represents the large contribution phonon mode to κ. From the phonon spectrum of SWCNTs we see that there are four acoustic phonon branches and two degenerated transverse acoustic branchesκ along tube-direction mainly originates from four acoustic phonon branches and one optical branch near the Γ point. Comparing with the phonon spectrums of SWCNT and SWCNT, we can see that with the diameter increasing there are more optical phonon branches participating to the lattice thermal transport. These optical phonon modes concentrate on the area away from Γ point in k-space at relatively low frequency. That means there are more optical phonons participating into the optical-acoustic scattering process. This mechanism causes the total calculated κ in tube-direction descending with the diameter value increasing. This trend is the same with previous MD simulation study by Thomas et al.κ in SWCNT becomes weaker in the SWCNT and SWCNT. In these three phonon dispersions shown here, the phonons with frequency higher than 30 THz contribute little to the κ. This results is the same with the results of spectral energy density method based on MD simulationTo analyze the mechanism behind the phonon transport behavior, in κ of graphene. In the 3D phonon dispersion, we use the color to map the different contributions to the κ along κ. From the contributions in 3D phonon dispersion, we can see clearly the out-of-plane flexural (ZA) modes contribute the most to the total κ along κ at room temperature21κ contribution along κ contributions of phonon modes distribute in two in-plane lattice directions that are equivalent in terms of geometric symmetry. And from the average κ contributions of ZA modes map on 2D BZ, the in-plane isotropic property is revealed clearly. In our method we calculate the in-plane phonons diffusive transport behaviors of graphene, and there do not exist the zigzag and armchair boundaries in our model. That is the origin of isotropic κ of graphene.κ of ultra-thin SWCNT and SWCNT are much lower than graphene. From cross-sectional view of their atomic structures  and SWCNT, the data points with very small κ contribution (<0.1%) concentrates in the range of 1 ~ 10 THz, due to the strong scattering among these phonons. This is consistent with our previous analysis in κ of graphene. It indicates clearly that the contributions from ZA modes are much higher than that from other modes, and in another way reflect the same information in Summarizing the information from κ contributions information verse frequency , SWCNT and SWCNT, while for graphene, 90% of in-plane κ originates from phonons below 12.95 THz. However, for SWCNT because the much more optical phonon modes each one carries a little contribution to κ, the 90% contribution threshold is increased to 17.15 THz.In cumulative requency , we can κ of graphene for comparison with the same method. Our results suggest that lattice thermal conductivity of SWCNTs increases with diameter descending and graphene behaves as lower limit of SWCNTs with infinite diameter. We also indicate that the ultra thin SWCNTs have relatively small κ. From the analysis of each phonon mode contribution to overall κ (phonon polarization), we clarify that the SWCNT with larger diameter has more optical phonons participating in the scattering process, leading to the reduced κ with diameter increasing, and finally approaching the graphene limit. For graphene, by analyzing phonon mode specific group velocity and phonon lifetime, we observe the dominant role of ZA modes, originating from the overwhelming enhancement in their phonon lifetime compensating the low phonon group velocity. However, due to the limitation of the computing resource and the huge computational demand, the κ of SWCNTs with larger diameters do not exhibit here. More calculations are still needed to reveal the real trend about the κ behavior of SWCNTs with much larger diameters. Nevertheless, we expect that our work provides deeper insight into the phonon transport mechanism in small diameter carbon nanotubes and offers a clear and reliable trend for device applications involving thin carbon nanotubes in the future.In conclusion, we studied the lattice thermal conductivities of seven armchair SWCNTs from  to  and one chiral ultra-thin SWCNT through the lattice anharmonic dynamic coupled with BTE method based on the first principle calculations. We also provide the in-plane Thermal conductivity is introduced through Fourier′s lawJ is the net heat flux, κ is the thermal conductivity tensorJ can also be expressed as:where V is the system volume, p and q denote the phonon branch and wave vector respectively, vg is the phonon group velocity and δf is the net diffusive change of phonon distribution. In steady state, the rate of phonon distribution total change is zero. This condition renders the BTE form:where where the diffusive term can be treated as linear with the gradient of temperature:Combining Eqs τ is the phonon lifetime, Cph is the specific heat capacity of system:where Cph and vg from the harmonic phonon dispersion calculated by the second order IFCs, and get the scattering rate 1/τ from the third order IFCswhere s2) electrons, with the 2s2 and 2p2 electrons of carbon considered as valence electrons. The kinetic energy cutoff of wave functions was set as 500 eV, and Monkhorst-pack k-mesh 4*4*24 including Γ point was used to sample the Brillouin Zone (BZ). A vacuum layer 10 Å was used to hinder the self-interactions between cylinders arising from the employed periodic boundary condition. All geometries were fully optimized with the Hellmann—Feynman force tolerance is Both second and third IFCs were obtained from the first-principle calculations. Before the IFCs calculations we optimized the structures of each case in unit cell. All first-principles calculations were performed based on the density functional theory (DFT) as implemented in the Vienna Ab-initio Simulation Package (VASP)4245κ, anharmonic third order IFCs are also necessary. The same supercell and k-mesh were used to get the anharmonic third order IFCs, and interactions between atoms were taken into account up to forth nearest neighbors. The total number of third order IFC evaluations depends on the number of carbon atoms in the supercell. With the third order IFCs, we solved the phonon BTE with iterative method with ShengBTE code developed by Li et alκ. The grid convergence in k-space of all cases were examinedκ reported here was the converged value . In details for ShengBTE calculations of SWCNTs and graphene, the interactive length we took is 3.4 Å which is the van der Waals force radius of carbon atoms. For the SWCNTs with diameter longer than 3.4 Å, we used the cross-sectional areaS = πdh, where d is the diameter of SWCNT and h = 3.4 Å. In ultra-thin SWCNTs which their diameters shorter than 3.4 Å, the cross-sectional area we used was For the calculation of How to cite this article: Yue, S.-Y. et al. Diameter Dependence of Lattice Thermal Conductivity of Single-Walled Carbon Nanotubes: Study from Ab Initio. Sci. Rep. 5, 15440; doi: 10.1038/srep15440 (2015).


The multiple-sandwich structure of UV-light sensors with graphene having high conductivity, flexibility, and impermeability is suggested to be beneficial for the facile fabrication of UV photodetectors with extremely efficient performances.Ultraviolet (UV) light photodetectors constructed from solely inorganic semiconductors still remain unsatisfactory because of their low electrical performances. To overcome this limitation, the hybridization is one of the key approaches that have been recently adopted to enhance the photocurrent. High-performance UV photodetectors showing stable on-off switching and excellent spectral selectivity have been fabricated based on the hybrid structure of solution-grown ZnS nanobelts and CVD-grown graphene. Sandwiched structures and multilayer stacking strategies have been applied to expand effective junction between graphene and photoactive ZnS nanobelts. A multiply sandwich-structured photodetector of graphene/ZnS has shown a photocurrent of 0.115 mA under illumination of 1.2 mWcm Photodetectors are a type of electronic devices for sensing light, and they have been found to have broad applications including flame monitoring, missile-plume detection, and space communication1233456789115131516171920212224262728313234356 times than the reported values of graphene-free UV photodetectors based on ZnS nanobeltsIn this work, we present that high-performance UV photodetectors showing stable on-off switching and spectral selectivity have been fabricated via a facile process based on the hybrid structure of solution-grown ZnS nanobelts and CVD-grown graphene. Sandwich structures and multi-layer stacking strategies have been applied to the photodetectors for the increment of the effective-junction region between graphene and ZnS. Three kinds of UV photodetectors, ZnS spin-coated on the surface of double-layer graphene (D-G/ZnS), ZnS sandwiched between two graphene layers (S-G/ZnS), and multiply sandwiched graphene and ZnS (MS-G/ZnS), have been demonstrated in ambient conditions at a low bias voltage. The photo-response behavior of a photodetector has been found to depend considerably on the stacking sequence of graphene and ZnS, as well as on the number of layers. An optimized photodetector based on S-G/ZnS shows a high photocurrent of 37 μA, which is higher 102 wafer  and the 2D-band (at 2692 cm−1)−1)The TEM image of −2 on and off periodically in ambient conditions. The net photocurrent can be obtained by subtracting the dark current from the light current. For a S-G/ZnS photodetector (Rλ), defined as the photocurrent generated per unit power of the incident light on the active area of the device, and the external quantum efficiency (EQE), defined as the number of electrons detected per incident photon, are crucial parameters for photodetectorsλ and EQE can be expressed as Iλ/(PλS) and hcRλ/(eλ), respectively, where Iλ is the difference between the photocurrent and the dark current, Pλ is the light power, S is the active area of the device, h is the Planck’s constant, c is the velocity of light, λ is the excitation wavelength, and e is the electronic charge. Our as-fabricated device has a channel length of 80 μm and a channel width of 20 μm. Therefore, the active area of the device is 1.6 × 10−5 cm2. According to our experimental results, Rλ and EQE for a S-G/ZnS photodetector have been calculated as 1.9 × 103 AW−1 and 8.0 × 105%, respectively, under an applied bias voltage of 1 V with 300 nm illumination of 1.2 mWcm−2. The response time is another important parameter of a photodetector. The rise and decay times  of a S-G/ZnS photodetector have been measured as 2.8 and 7.5 s, respectively. The multiple stacking of graphene and ZnS (MS-G/ZnS) has facilitated the photocurrent enhancement up to 115 μA  and H2 (3 SCCM) as the reaction source. After coating a poly(methylmethacrylate) (PMMA) polymer layer on the as-grown graphene of one side of the Cu foil, the graphene on the other side of the Cu foil was removed by oxygen plasma. After the Cu foil was etched with an ammonium persulfate (APS) solution and rinsed with distilled water several times, the graphene was transferred on a target substrate. The sample was soaked in acetone to remove the PMMA layer.Graphene was synthesized on a copper foil  via a chemical vapor deposition (CVD) method at 1,000 °C using a mixed gas of CH2+ was prepared by adding 1.0 mmol of ZnCl2(s) into 7.5 mL of water and 7.5 mL of C2H4(NH2)2(l) slowly with mild stirring; the stock solution was stirred further for 20 min to make a clear solution. A stock solution of S2− was prepared by adding 1.0 mmol of S(s) into 15 mL of N2H4·H2O(l) with vigorous stirring for 20 min. The stock solutions of Zn2+ and S2− were mixed together and stirred vigorously for 5 min. The mixture solution was then loaded into a Teflon-lined stainless-steel autoclave of 50 mL capacity, placed in a preheated oven at 180 °C for 9 h, and cooled to room temperature. A white precipitate produced in the reaction mixture was washed three times with water and two times with ethanol, vacuum-dried, and kept in a vial for further characterization.Single-crystalline wurtzite ZnS nanobelts were prepared via a hydrothermal process according to the reported method2 (300 nm) wafer by thermal evaporation, and graphene was transferred on the top of the electrodes. After spin coating of ZnS nanobelts dispersed ethanol on graphene for 20 s at 500 rpm, additional graphene was transferred on the top of the as-prepared sample.Titanium (3 nm) and gold (30 nm) electrodes were deposited on a Si/SiORaman spectra and their mapping profiles were obtained by a Raman spectrometer , and AFM images were measured at a noncontact mode using an atomic force microscope . TEM images and their SAED and FFT patterns were obtained with an electron microscope  operating at 300 kV, and FE-SEM images were measured with another electron microscope . While optical microscopy images were obtained with a microscope , HRXRD patterns were obtained with a diffractometer  using Cu Kα radiation (0.15418 nm). Extinction spectra were obtained with a UV-vis spectrophotometer . The current-voltage behaviors of photodetectors were measured using a probe nanovoltmeter  with a Xe lamp  as the light source.How to cite this article: Kim, Y. et al. High-performance ultraviolet photodetectors based on solution-grown ZnS nanobelts sandwiched between graphene layers. Sci. Rep.5, 12345; doi: 10.1038/srep12345 (2015).


Saccharomyces cerevisiae, appear to be beneficial during growth under stress conditions. In order to reveal the pattern of intron retention within intron-poor yeast species and better understand the mechanisms of intron evolution, we generated a comprehensive set of 250 orthologous introns in the 20 species that comprise the Saccharomycetaceae, by analyzing RNA deep-sequencing data and alignments of intron-containing genes. Analysis of these intron sets shows that intron loss is at least two orders of magnitude more frequent than intron gain. Fine mapping of intron positions shows that intron sliding is rare, and that introns are almost always removed without changing the primary sequence of the encoded protein. The latter finding is consistent with the prevailing view that homologous recombination between reverse-transcribed mature mRNAs and the corresponding genomic locus is the primary mechanism of intron loss. However, we also find evidence that loss of a small number of introns is mediated by micro-homology, and that the number of intron losses is diminished in yeast species that have lost the microhomology end joining and nonhomologous end joining machinery.Introns in protein-coding genes are very rare in hemiascomycetous yeast genomes. It has been suggested that these species have experienced extensive intron loss during their evolution from the postulated intron-rich fungal ancestor. However, no intron-devoid yeast species have been identified and some of the introns remaining within the genomes of intron-poor species, such as  The origin and evolution of introns in eukaryotic genomes are intensively debated topics . Two lonDaphnia pulex , followed by extensive loss of one copy of most paralogous genes (S. cerevisiae have been well annotated due to the extensive efforts of the yeast scientific community (Saccharomyces Genome Database [SGD]). However, introns in most other yeast species are poorly annotated, and intron analyses therefore rely either on automatic annotation or small manually curated sets of intron orthologs. This impedes the estimation of intron number and subsequent evolutionary studies. Nonetheless, even with limited intron information, interesting evolutionary observations have been made for the Saccharomycotina subphylum. For example, hemiascomycetous yeasts contain only the U2 spliceosome; all the components specific to U12 spliceosome have been lost in the Ascomycota  , togetheSaccharomyces cerevisiae strain BY4741, Saccharomyces kudriavzevii, and Naumovia castellii were cultured in standard YPD media in 30 °C and Saccharomyces uvarum NCYC 2669 at 28 °C with shaking at 200 rpm, to an absorbance of 0.5 at 600 nm. RNA of S. cerevisiae was extracted using Trizol , precipitated in lithium chloride , washed twice with 70% ethanol and the pellet resuspended in dH2O. RNA of the other three species was extracted using Qiagen RNA extraction kit according to manufacturer’s instructions. Ten micrograms of total RNA from each S. cerevisiae, S. kudriavzevii, S. uvarum, and N. castellii was processed with the RiboMinus Transcriptome Isolation Kit for Yeast and Bacteria (Invitrogen) to deplete the rRNA. cDNA libraries for each species were constructed and sequenced using the SOLiD 4.0 System from Life Technologies according to the standard manufacturer’s protocol. Saccharomyces cerevisiae cDNA was deposited on one-quadrant of a slide with one other barcoded library (not presented here). The other three libraries were barcoded and deposited on one-quadrant of a slide. Sequencing yielded a total of 77,286,181 reads for S. cerevisiae, 23,993,647 reads for S. uvarum, 6,287,432 reads for S. kudriavzevii, and 7,909,274 reads for N. castellii, all of 50 bps. Raw reads were filtered to obtain only reads with an average quality >20 using the approach described by S. cerevisiae genes according to SGD, release 64) (ease 64) . The RNAS. cerevisiae were extracted from SGD . The orthologs of the intron-containing genes in the S. cerevisiae clade were retrieved from the YGOB Pillar file   , which ph mLAGAN , and theh mLAGAN  to ensurh mLAGAN . BrieflyS. cerevisiae (SGD). We then used the resulting alignments as seeds for iterative HMMER searches as described above. We analysed the sequence surrounding the potential snoRNA matches to establish if they are encoded within introns of paralogous genes. Lastly, we used syntenic information provided by YGOB to establish if the snoRNA hits lie in regions paralogous to those included in the seed alignment.To detect orthologs of intronic snoRNAs, we extracted the portion of each intron alignment that corresponded to a snoRNA annotation in Syntenic relationships between intron-containing genes were extracted from YGOB. Paralogous genes arising from WGD were grouped to represent one ancestral gene, and multiple introns in the same gene were treated separately. The phylogenetic tree used to map intron gains and losses was taken from YGOB  and BP (TACTAAC) sequences that are indicative of Saccharomycetaceae introns. We found 216, 163, 200, and 155 predicted introns in S. cerevisiae, S. kudriavzevii, S. uvarum, and N. castellii, respectively. Of these, three introns in S. cerevisiae, four in S. uvarum and ten in N. castellii are novel—not present in the latest annotation in SGD—although some have been previously experimentally validated . Comparing the numbers of reads mapped to each intron among the various species revealed an even stronger correlation between species (B). These results provide preliminary evidence that intron splicing and expression is generally highly conserved among the Saccharomyces sensu stricto species, but more specific investigation of levels of intron splicing is warranted.Next, we counted the reads spanning each identified junction in nscripts A. Compar species B. These S. cerevisiae (SGD) and introns predicted from the RNAseq data obtained for S. cerevisiae, S. uvarum, and N. castellii. We extracted the orthologous genes from YGOB and investigated the presence of introns for those species in which the host genes were present. Manual refinement of these alignments highlighted five additional unannotated introns in genes HOP2, CGI121, YPR170W-B, YPR153W, and YPL109C, of which only the HOP2 intron is present in S. cerevisiae  we investigated the differences in the distance between the BP and the 3′-splice site (referred to as the S2 distance) among 20 species. As reported previously, we found increased S2 distances in C. glabrata, K. lactis and to lesser extent in Saccharomyces sensu stricto, Kazachstania sp. and Naumovozyma sp. All those species have lost the U2AF1 splicing factor postulated to be correlated with short S2 distances . We examined the U2AF1 gene and protein structure in detail, and found that T. blattae and T. phaffii are the only species without the intron splitting the initial cysteine codon of the first zinc finger domain. The T. blattae and T. phaffii U2AF1 proteins also contain 105 and 60 amino acid insertions, respectively, but maintain all crucial domains (B). The V. polyspora U2AF1 gene contains the intron in the typical position and does not have extensive insertions. It was previously suggested that the loss of the U2AF1 protein might be responsible for increased S2 distance . The majority of missing introns  left the gene replaced with its cDNA version . There were 33 instances in 14 genes when intron removal was accompanied by a deletion or insertion of 3–40 codons. We found one clear case of intron sliding in the RPS22B gene in Eremothecium cymbalariae, E. gossypii, and K. lactis, where the 5′-UTR intron has been moved into the open reading frame (ORF) and is present after the initial A (fig. 5B). Finally, 310 additional introns, mainly in 5′-UTRs, appear to have been lost, but the mechanism of loss is unclear.Across the 20 species and 235 ancestral genes, there were total of 5,553 “intron sites,” defined as sites that could contain an intron based on the presence of an intron at that position in at least one other species. In total, 1,168 of these intron sites are without an intron (0.21 introns missing per site per species) and 4,385 contained an intron . We found only 13 cases where an intron encoding a snoRNA was lost from the host gene. Only in the case of snR191 in the NOG2 gene of Naumovozyma dairenensis did intron loss lead to snoRNA removal from the genome. Kazachstania africana has lost the same intron, but an additional copy of snR191 is present in a region non-paralogous to NOG2. In the five cases where the intron encoding the snoRNA was lost, the snoRNA was retained within the intron of the paralogous gene, and for another six cases a copy of snoRNA was present in the paralogous region but without the associated protein-coding gene (fig. 7B). This last mode of gene loss with retention of the intronic snoRNAs was previously described as “snoRNA deintronization” and has been shown to be common in the evolution of snoRNA genes in the Saccharomycetaceae . This result, together with the strong conservation of spliced transcript number and intron expression . In summary, distinctive patterns for RPG intron conservation in different species lead us to conclude that the unusual characteristics of RPG introns are not shared by the whole Saccharomycetaceae, and are probably restricted to the Saccharomyces sensu stricto species.In the  as well A. This rpression , suggestnogaster , thus it introns B. In sumY. lipolytica  and the Vanderwaltozyma clade (represented by V. polyspora)  . In contrevisiae . We therSaccharomyces sensu stricto, individual species have lost between 15% and 46% of their introns, except for the Lachancea clade, where 7% of the introns tested appeared to have been lost on average. The most extreme case of intron retention is L. kluyveri for which we observe a total of nine introns missing, seven of which are probably intron gains in other species. Interestingly, L. kluyveri has undergone an unprecedented loss of the proteins mediating NHEJ and MMEJ pathways of DNA repair .


Community detection is the process of assigning nodes and links in significant communities  and its development has led to a better understanding of complex networks. When applied to sizable networks, we argue that most detection algorithms correctly identify prominent communities, but fail to do so across multiple scales. As a result, a significant fraction of the network is left uncharted. We show that this problem stems from larger or denser communities overshadowing smaller or sparser ones, and that this effect accounts for most of the undetected communities and unassigned links. We propose a generic cascading approach to community detection that circumvents the problem. Using real and artificial network datasets with three widely used community detection algorithms, we show how a simple cascading procedure allows for the detection of the missing communities. This work highlights a new detection limit of community structure, and we hope that our approach can inspire better community detection algorithms. Over the course of the last decade, network science has attracted an ever growing interest since it provides important insights on a large class of interacting complex systems. One of the features that has drawn much attention is the structure of interactions highlighted by the network representation. Indeed, it has become increasingly clear that global structural patterns emerge in most real networks . One sucWhile the exact definition of communities is still not agreed upon , the genBy developing techniques to extract this organization, one assumes that communities are encoded in the way nodes are interconnected, and that their structure may be recovered from limited and/or incomplete topological information. Various algorithms and models have been proposed to tackle the problem, each featuring a different definition of the community structure while sharing the same general objective. Although these tools have been used with success in several different contexts , 5, 6, ashadowing phenomenon in 3 widely used algorithms. Then, we propose and develop a general cascading approach to community detection that addresses this specific problem. Next, we validate our first implementation of the cascading method by applying our algorithms to real complex networks, and then to synthetic benchmark networks. The former set of calculations acts as a proof of concept and shows that, despite its apparent simplicity, the algorithm detects several shadowed communities. The latter set helps us determine under which conditions the algorithm is expected to perform adequately. Finally, based on our results, we gather in the Conclusion ways in which our method can be improved.The paper is organized as follows. First, we argue that current algorithms tend to overlook small communities found in the neighborhood of larger, denser ones, under very general conditions. In the following sections, we investigate the exact mechanisms that cause this so-called non-overlapping partitions of the network. This resolution limit has been rigorously shown to affect modularity  for the high mixing case. A precise and general criterion cannot be formulated, because its specifics depends on the hidden parameters of the network and algorithm of choice, as illustrated by this example.In a normal situation, where built-in communities are not known, the results shown in structural communities in real networks based on the above qualitative criterion, because their detected community structure is similar to that of LF networks (See μ〉 = 0.13) with average memberships number (〈Ω〉 = 2.06), and network densities (〈ρ〉 = 0.002) that all roughly correspond to the parameters used in the left panel of cv suggests that shadowing of structural communities definitely occurs in the Email (cv = 5.51), and Internet networks (cv = 2.42). No definitive conclusion can be drawn for the other networks, since their calculated variability of cv > 0.7 lie slightly below the optimal threshold for low mixing cases, except for the Power network (cv = 0.48). These results must be considered with care since LF networks do not capture all the structural complexity of real networks  (left to right). All networks consists of N = 5 000 nodes of average degree 〈k〉 = 20, that belongs to Ω = 2 communities (if they overlap), with a mixing parameter μ = 0.1. Each subplot shows the number of communities of x nodes in the neighborhood of communities of y nodes, for all x, y ≤ 100. Communities that share at least one node are defined as neighbors. In all cases, large communities are found in the vicinity of smaller communities of all sizes . This pattern is however more pronounced in the highly heterogeneous region (right-hand side of the figure), where shadowing occurs (See μ = 0.6 (not shown).This array samples 25 points of the parameter space, i.e. fractions of overlapping nodes set to f = /5, 1 (bo(PDF)Click here for additional data file.S3 Figx nodes in the neighborhood of communities of y nodes, for all x, y ≤ 100. Communities that share at least one node are defined as neighbors. To identify the possibility of shadowed communities, one must look for large communities in the vicinity of small ones, i.e. for off diagonal elements in the rows / columns corresponding to community sizes that are present in the network. For CPA, one need not look far away from the diagonal, since small communities can shadow even smaller communities , GCE (center) and LCA (right). Each subplot shows the number of communities of (PDF)Click here for additional data file.


However, there is a trade-off between the electrical resistance and the optical transmittance, and the fixed absorption rate in graphene limits is use when fabricating devices. Therefore, a more efficient method which continuously controls the optical and electrical properties of graphene is needed. Here, we introduce a method which controls the optical transmittance and the electrical resistance of graphene through various thicknesses of the top Cu layers with a Cu/Ni metal catalyst structure used to fabricate a planar mesh pattern of single and multi-layer graphene. We exhibit a continuous transmittance change from 85% (MLG) to 97.6% (SLG) at an incident light wavelength of 550 nm on graphene samples simultaneously grown in a CVD quartz tube. We also investigate the relationships between the sheet resistances.Graphene has been received a considerable amount of attention as a transparent conducting electrode (TCE) which may be able to replace indium tin oxide (ITO) to overcome the significant weakness of the poor flexibility of ITO. Given that graphene is the thinnest 2-dimensional (2D) material known, it shows extremely high flexibility, and its lateral periodic honeycomb structure of sp Cu and Ni are well-known metal catalysts for the growth of large-area single- and multilayer CVD graphene, respectively114151415In this report, Cu and Ni are the only elements used as catalysts for synthesizing large-area graphene, and control of the optical and electrical properties of simultaneously grown multilayer and single-layer graphenes can be obtained under the same growth conditions for SLG growth with Cu foil. We demonstrate these controlled properties with two methods: graphene growth with Cu thickness control on a Cu/Ni metal catalyst structure, and the size-width control of a SLG-MLG mesh pattern using the optimized SLG growth condition derived from the first method.2 substrate. Our graphene samples were grown simultaneously on substrates structured with the Cu/Ni metal catalyst with various upper Cu thicknesses ranging from 0.3 μm to 0.7 μm in increments of 0.1 μm. The thickness of the Ni layer in Cu/Ni structure was fixed at 0.3 μm for all substrates. The same growth condition for single-layer graphene growth with the Cu foil was applied to our CVD growth condition  is proportional to the degree of light absorption and the thick.% of Ni. Moreover, because the areas of Cu and Ni are equal, the volume % of Ni is proportional to dG,avg. Thus, we assume that our method to control the Cu thickness of the Cu/Ni structure results in controlling the volume % of Ni, which then controls the amount of carbon supplied to the growing graphene and add-layers. Furthermore, the sheet resistance is inversely proportional to the film thickness as described by the following equation, ρ is the resistivity and d is the thickness. The other fittings ; and T is the transmittance of light. Using G value is 1.26 × 106 S/m. This value is comparable to the previously reported result of 1.1 × 106 S/m from CVD-grown SLGwhere 2 substrate (Ni/SiO2/Si). 2 substrate shows that the SLG-MLG patterns were continuously connected. During the thermal annealing process, Cu and Ni may diffuse vertically and laterally affect each other at the interface between the SLG and the MLG. However, the SLG area maintains an optimal condition without add-layers, despite the sensitive control over the Cu thickness, as shown in 2D/IG) exceeds 2.In order to determine the applicability of our Cu-thickness-controlled graphene, we deposited a 0.7-μm-thick Cu pattern using a shadow mask on a 0.3-μm-thick Ni-deposited SiOD/IG ratio of approximately 0.1 and I2D/IG ratio close to 2 with small distributions.Furthermore, we succeeded in the fabrication of SLG array patterns . Althoug2) is etched away, followed by the formation of electrode patterns. If we use a MLG sheet with minimally patterned SLG at the graphene channel position, handling during the transfer process could be much easier than it is with large-area SLG-only graphene. Moreover, MLG can be utilized as an electrodeThis SLG-MLG patterning growth enables the selective positioning of SLG elements for wafer-scale graphene device fabrication. One of the main topics in the research on graphene is large-area graphene growth and transfer processes124142/Si substrate using a shadow mask. After CVD growth, we transferred the SLG-MLG mesh-patterned sheet onto flexible polyethersulfone (PES) film and a glass substrate with a supporting layer of PMMA. As shown in Although the fabrication of graphene-layer-controlled patterns for graphene-based devices is fascinating, forming various thickness-controlled Cu patterns on graphene sheets with various properties remains complicated. In order to achieve more efficient control of the optical and electrical properties of graphene such that these processes become applicable to TCE, we developed a mesh-patterned graphene sheet using only two optimal growth conditions of ‘Cu 0.7 μm/Ni 0.3 μm’ for SLG and ‘Ni 0.3 μm’ for MLG. 3) and 63 wt% nitric acid (HNO3) for 5 minutes to reduce the sheet resistance. Chloroform has been used to reduce PMMA residue, but it is known to contribute to the doping effect of graphene233 was reported as one of the most effective chemical agents for the p-doping of graphene6 S/m, and the chloroform and HNO3 treatment resulted in values of 1.77 × 106 S/m and 2.67 × 106 S/m, respectively. Therefore, we were able to control the electrical properties of mesh-patterned graphene by means of chemical doping without changing the optical properties.We analyzed the Tr value as a function of the SLG area ratio, finding a Rs value of 840 Ω/□ at a Tr (at 550 nm) value of 97.6% for the Cu 0.7 μm sample (SLG). The Ni-only (Cu 0 μm) sample exhibited an Rs value of 489 Ω/□ at a Tr value of 88% . Interestingly, the Tr results of the mesh-pattered films show linear variations between the MLG-only and the SLG-only films . We also2, glass substrates, and transparent polymer substrates , respectively. The Cu/Ni/SiO2/Si substrate was heated up to 1,000 °C inside of a quartz tube under H2 atmosphere, and then the graphene was grown on the Cu/Ni/SiO2/Si substrate flowing gas mixtures of H2 : CH4 = 10 : 15 (sccm) for 20 min. After growing the graphene, PMMA (950 PMMA A6), which served as an adhesive supporting layer, was spin-coated on a graphene at 3000 RPM for 30 s. The PMMA/graphene/metal catalyst was separated from Si substrate during floating on buffered HF (BOE). It takes several minutes for separation. Then, the PMMA/graphene/metal catalyst was floated on 0.1 M ammonium persulfate solution (APS) to etch the metal catalyst. After rinsed the PMMA/graphene in DI-water over a few hours, the PMMA/graphene was transferred to the target substrate and baked at 75 °C for few minutes for increasing the adhesion between graphene and target substrate. The PMMA was removed with acetone and IPA.The graphene was synthesized on Cu/Ni metal catalyst layers by the thermal chemical vapor deposition (T-CVD). For Cu (0.3 ~ 0.7 μm) and Ni (0.3 μm) metal catalysts, DC sputter and E-beam evaporator were used to deposit on a thermally oxidized SiOThe optical transmittance was obtained using S-4100 PDA UV-Vis spectrophotometer from SCINCO. The sheet resistance was measured based on the van der Pauw method by using HL5500IU Hall system from ACCENT. In order to carry out the optical property measurement, the graphene sample was transferred onto transparent substrate. Indium ingot  was used as a contact pad for measuring sheet resistance by attaching on 4 edges of rectangular shape transferred graphene.How to cite this article: Choi, J. S. et al. Facile fabrication of properties-controllable graphene sheet. Sci. Rep.6, 24525; doi: 10.1038/srep24525 (2016).


Simply integrating an inexpensive bioinspired polymer coating onto the Mn-graphene nanocomposite increased ORR performance significantly, with a peak potential shift of over +730 mV. This indicates that the material can reduce oxygen at a higher rate but with lower energy usage, revealing its excellent potential as an ORR electrocatalyst in fuel cells.Platinum electrodes are commonly used electrocatalysts for oxygen reduction reactions (ORR) in fuel cells. However, this material is not economical due to its high cost and scarcity. We prepared an Mn(III) catalyst supported on graphene and further coated with polydopamine, resulting in superior ORR activity compared to the uncoated PDA structures. During ORR, a peak potential at 0.433 V was recorded, which is a significant shift compared to the uncoated material’s −0.303 V (both versus SHE). All the materials reduced oxygen in a wide pH range via a four-electron pathway. Rotating disk electrode and rotating ring disk electrode studies of the polydopamine-coated material revealed ORR occurring via 4.14 and 4.00 electrons, respectively. A rate constant of 6.33 × 10 The electrochemical reduction of oxygen to water is an essential cathodic half reaction in proton exchange membrane fuel cells. Platinum-based catalysts are the most efficient materials for oxygen reduction reactions (ORR) and are currently used in commercial fuel cells1368p-styrenesulfonate) modified reduced graphene oxide18Graphene and MWCNTs possess unique physical, morphological, electrical, and chemical properties, including a large surface area and electrical conductivity, which make them excellent candidates as active components in energy-related applications111213One widely-used method to develop superior ORR catalysts is the integration of heteroatom dopants such as nitrogen into the nanomaterial framework222324An example of a “green” nitrogen precursor material is polydopamine (PDA), which is non-toxic and biocompatible. PDA is an eco-friendly, bio-inspired mussel adhesive molecule that is generated by self-polymerization of dopamine, which forms a thin film on various substrates without any surface pretreatment28306 mol−1s−1, which is, to our knowledge, the highest rate constant recorded among similar bioinspired synthetic catalysts employed for ORR.Here, we present a nanocomposite that combines the usefulness and efficacy of metal complexes, carbon nanomaterials, and PDA to perform superior ORR. We have designed a Mn(III) catalyst of an amidomacrocyclic ligand supported on graphene structures and thoroughly characterized by a combination of analytical techniques. This nanocomposite was further coated with PDA at room temperature to enhance its reactivity and stability in ORR studies . Electro1  analyses were run to determine the chemical states of some of the elements in the Mn-graphene nanocomposite and PDA-Mn-graphene nanocomposite  was set ectively . A narroectively . The firphene352 38, with phene352 37.2O32 in the Mn-graphene nanocomposite2, the Mn center is reduced from +3 to +2 oxidation state.Mn2p and Mn3s narrow scans of the Mn-graphene nanocomposite were collected (Scanning electron microscopy (SEM) image of the Mn-graphene nanocomposite  indicate40Atomic force microscopy (AFM) imaging of the Mn-graphene  and PDA-−1 (Mn-graphene) and 1345 and 1570 cm−1 , which has been observed in graphene materials. The G band is indicative of the graphene carbons, and the D band indicates the defect present within the graphene structure. The slight shift in the two bands in PDA-Mn-graphene was due to the presence of PDA, an effect that has been reported earlierD/IG) changed slightly from 1.53 to 1.11 in the Mn-graphene and PDA-coated materials, respectively. In the lower range of the spectra, the presence of 2 is observed. −1. The Mn-N bond in 2 is observed at 410 cm−1 in the Mn-graphene nanocomposite and slightly shifted to 416 cm−1 in the PDA-coated materialRaman spectroscopy of the Mn-graphene and the PDA-Mn-graphene material were compared, and the spectra are given in 2)- and nitrogen (N2)-saturated pH 2.0 electrolyte solution. As is shown in 2 and a low current density under anaerobic conditions. However, when the study was performed in an O2-saturated solution, the current density displayed a significant increase toward ORR. Additionally, the peak potential shifted positively about +60 mV.The electrochemical activity of the nanocomposite to catalytically reduce oxygen was evaluated using cyclic voltammetry (CV). Initial evaluation of the Mn-graphene nanocomposite compared the efficacy of the material under an oxygen , with an approximate current density value of 1.37 mA/cm2.Electrochemical studies of Next, the effect of the type of nanomaterial was tested by comparing graphene- and MWCNT-supported electrocatalysts. As 2 and graphene was compared to determine the optimal pairing of the two. As seen in 2 was grafted onto graphene, the current density decreased slightly. However, the peak potential shifted negatively with a slightly higher overpotential than the 1:2 ratio sample. At this point, the graphene material was being saturated with 2. The decreased oxygen reduction and higher overpotential resulted from the smaller amount of graphene reducing the ability to transfer electrons between the nanomaterial and 2.The ratio of 2-saturated solution with a much lower current density. In comparison to the Mn-graphene nanocomposite, the peak potential has a significant +730 mV shift. When compared to the PDA-coated graphene nanocomposite , the current density of the PDA-Mn-graphene material was almost twice as large and, therefore, demonstrates the need for the Mn catalyst for higher ORR activity.We then studied the effect of PDA on the Mn-graphene nanocomposite to observe any positive influences on peak potential and/or current density. 2 carbon network in graphene, which creates defects in the adjacent sites. This, in turn, changes in the charge density, resistance in charge transfer, and hydrophilicity of the material to assist in ORR2 carbon framework in graphene and the lone pairs of electrons on the nitrogen in PDA to give better electrochemical transfer towards ORR with a lower overpotential.A possible explanation for the dramatic shift observed in the ORR potential lies within the interaction between PDA and graphene. The nitrogen atoms in PDA interacts with the spRatio studies were also performed with the PDA-Mn-graphene nanocomposite to observe any changes in the current density and/or peak potential . From th2 (as noted in The Mn-graphene nanocomposite was further tested in a wide range of pH conditions. lim), Levich (JLev) and kinetic currents (Jk). Theoretical slopes where the number of electrons, n, equals 2 and 4 were also plotted for comparison. From the slope, the Levich equation was used to calculate the number of electrons in the electrochemical reaction.RDE was conducted in both pH 2.0 and 10.0 at an increasing number of rotations. In pH 2.0, RDE  showed tk = 103 nFkCΓ, where k is the rate constant and Γ is the concentration of the catalyst deposited on the electrode surface. In acidic media, the rate constant was 1.3 × 106 mol−1s−1, which is larger than that of a similar Co electrocatalyst5 mol−1s−1)5 mol−1s−1)5 mol−1s−1. The decrease resulted from the higher overpotential encountered at higher pH, which decreased the rate of ORR. The PDA-Mn-graphene nanocomposite gave a rate constant of 6.33 × 106 mol−1s−1, which is over twenty-four times higher than the non-PDA-coated nanocomposite at pH 10.0 and higher than that of a Co-porphyrin-MWCNT electrocatalyst (1.3 × 106 mol−1s−1)2-porphyrin (3.0 × 105 mol−1s−1)5 mol−1s−1)c oxidaseThe rate constant was determined for each experimental condition by the kinetic current using the equation JWe also conducted RRDE, which possesses a platinum ring surrounded by a graphite disk. The nanocomposite was deposited onto the disk, carefully avoiding the platinum ring. As the electrode rotates at a constant speed, the initial oxygen reduction occurs at the disk. Any formation of peroxide intermediate is diffused outward towards the platinum ring, where it is further reduced to water and any accumulation of peroxide will be observed by a ring current.The RRDE in pH 2.0 is plotted for the Mn-graphene  and the −) in higher pH. The Mn(III) interacts with oxygen and water in the presence of two electrons to yield a hydroperoxo intermediate. Next, the hydroperoxide species is rapidly reduced via a two-electron process to hydroxide and regenerates the Mn(III) catalyst.The proposed general mechanism of the Mn-graphene nanocomposite in acidic and alkaline media is given below. From the XPS results, the Mn2p and Mn3s narrow scans showed the presence of a Mn(III) species in the Mn-graphene nanocomposite. It has been previously shown that PDA’s catechol groups can covalently graft with metal salts and even reduce the metal ions to their corresponding metallic form495048In order to show the effect of acidic media on the Mn catalyst’s stability, we conducted stability studies. The Mn-graphene modified electrode was left in pH 2.0 phosphate buffer solution for several days. Periodically, CV was performed to observe changes in the peak potential position and/or current density. 2. Using time dependence studies, UV/Vis was conducted for 2 and after the addition of the pH 10.0 buffer solution , a peak at 580 nm is associated with the dark yellow solution of 2. This peak has been found in other Mn(III) complexesStudies with the alkaline medium were also conducted using ultraviolet-visible spectroscopy (UV/Vis) to observe any changes in the absorbance of solution . Scans wIn this study, an Mn(III)-amidomacrocyclic complex was synthesized and used for the first time in ORR activity. The catalyst was supported on graphene and tested in a wide range of pH. CV of the nanocomposite showed increased current density in comparison to the Mn catalyst and graphene alone. This revealed that the synergy between the catalyst and graphene produces a nanocomposite capable of reducing oxygen more efficiently than the two individual components. When the nanocomposite was further coated with PDA, the multicomponent material revealed a significant increase in ORR peak potential from −0.303 V to 0.433 V (both versus SHE).6 mol−1s−1—for quick reduction of oxygen. During the formation of the PDA coating, the Mn(III) complex was reduced to a Mn(II) complex. This oxidation state change, along with the possible interaction of PDA with graphene, furnished a nanocomposite with enhanced ORR activity. Furthermore, the RRDE ring current did not increase, which suggests that no hydroperoxide intermediate is involved in the ORR mechanism. To our knowledge, this is the first use of a PDA-Mn-graphene nanocomposite for ORR applications.Varying the pH revealed increased current density in alkaline media accompanied with slightly higher overpotential. The PDA-coated nanocomposite also showed catalytic activity in a wide pH range, which is advantageous in fuel cell applications. Reaction kinetics from the hydrodynamic studies revealed a four-electron pathway with one of the highest rate constants—6.33 × 10−1 Raman shift.Chemicals used in this study were purchased from Sigma-Aldrich, USA, Acros Organics, USA, or VWR International and were used without further purification unless otherwise noted. Graphene was obtained from Angstron Materials  and used without any additional modification. MWCNTs were purchased from Bayer MaterialScience (Baytubes C150P RD SAM) and used as received. Nitrogen gas (ultrahigh purity) and oxygen gas (ultrahigh purity) were obtained from NLR Welding Supply Inc. Buffer solutions of different pH  were prepared using published procedure1 was synthesized as previously described  was added and dissolved with dry THF (20 mL) under N2. The temperature was lowered to 0 °C by placing the flask in an ice bath. Once the solution was cooled, n-butyllithium  was added, followed by anhydrous manganese(II) chloride . The reaction was slowly heated to room temperature and allowed to stir overnight. The reaction yielded a yellowish-brown precipitate. The solution was exposed to air to allow the metal to oxidize from Mn(II) to Mn(III). The solvent was removed via rotary evaporator to yield a solid yellowish brown product and dried under vacuum. Yield: 75% (247.5 mg). λmax = 408 nm, ε = 1.21 × 102 M−1cm−1. This catalyst was used in aqueous solutions for all the UV/Vis studies. The remaining studies used 2 with PPh4+ as the counter ion, which was synthesized following literature procedure2 was dissolved in distilled water, from which the PPh4+ salt of the catalyst was precipitated using PPh4Cl. The precipitate was filtered and dried under vacuum. Anal. Calcd for [C43H34MnN4O4P]·H2O: C, 66.66; H, 4.68; N, 7.23. Found: C, 66.92; H, 4.50; N, 7.37%.The amidomacrocyclic ligand escribed 5758. Syn dry THF  mL under2 was dissolved in 5 mL of methanol. From this solution, 2 mL of the Mn catalyst was transferred to a new vial. 4 mg of the carbon nanomaterial (MWCNTs or graphene) was added to the solution and methanol was further added to give a 1 mg/mL suspension. The mixture was sonicated for 30 min. 40 μL of Nafion® was added and the suspension was sonicated for an additional 30 min. Other ratios used in this study were prepared similarly by changing the amount of 2 and carbon nanomaterial.5 mg of 2 and 10 mg of graphene were added and suspended in 50 mL NaOH solution (pH 8). This was sonicated for 15–30 min. 125 mg (0.659 mmol) dopamine was added to the suspension and vigorously stirred for 3 h. 40 μL of Nafion® was added and the suspension was sonicated for an additional 30 min. Additional ratios of the PDA-coated nanocomposite were prepared similarly by changing the amount of 2 and graphene used.The PDA-coated nanocomposites were prepared by following literature procedure with some alterationsCV was performed with a potential range of 0.6 V to −1.0 V (versus Ag/AgCl) at a scan rate of 100 mV/s, unless otherwise noted. CV studies were performed in a three-electrode system using a glassy carbon working electrode, Ag/AgCl reference electrode, and platinum counter electrode. The glassy carbon working electrode was then modified with the previously prepared Mn-graphene or PDA-Mn-graphene nanocomposite. A 10 μL aliquot of the nanocomposite was drop casted onto the electrode and dried at room temperature. Within the electrochemical cell, a phosphate buffer solution was added and purged with either oxygen or nitrogen gas for at least 1 h prior to electrochemical testing. The peak potential values are given with respect to SHE.−9 mbar. Samples were then mounted to the sample holder using double-sided tape. All spectra were collected with the charge neutralization flood gun turned on. The typical pressure during the analysis with the flood gun on was 2 × 10−7 mbar. The collected data were processed using the Thermo Scientific Advantage XPS software package. Spectral charge correction was performed using the main C1s peak due to hydrocarbon (C-C/C-H bonds) set to 284.8 eV. Mixed Gaussian-Lorentzian peak shapes as well as a Shirley/Smart type background subtraction were used for the peak analysis and fitting.XPS studies were carried out by using a Thermo Scientific Model K-Alpha XPS instrument using monochromatic Al Kα radiation (1486.7 eV) with the X-ray spot size 200 μm for each sample. The base pressure in the analysis chamber was typically 1 × 10TEM observations of nanocomposite samples were performed by JEOL JEM 2100F equipped with a field emission gun at 80 kV acceleration voltage and an EDS (EDAX Corporation) used for elemental analysis. Each sample was dispersed into ethanol and a few drops were deposited and allowed to dry on a TEM holey carbon covered copper grid.Nanocomposite was suspended in methanol, and the resulting solutions were pipetted onto freshly cleaved mica . Tapping mode AFM images were acquired using an Asylum Research MFP-3D AFM. Silicon probes  were used with force constants of 7–8 N/m, nominal resonant frequencies of 150 kHz, and average tip radios less than 6 nm.How to cite this article: Parnell, C. M. et al. Polydopamine-Coated Manganese Complex/Graphene Nanocomposite for Enhanced Electrocatalytic Activity Towards Oxygen Reduction. Sci. Rep.6, 31415; doi: 10.1038/srep31415 (2016).


Substitutional chemical doping is one way of introducing an electronic bandgap in otherwise semimetallic graphene. A small change in dopant arrangement can convert graphene from a semiconducting to a semimetallic state. Based on ab initio Density Functional Theory calculations, we discuss the electron structure of BN-doped graphene with Bravais and non-Bravais lattice-type defect patterns, identifying semiconducting/semimetallic configurations. Semimetallic behavior of graphene with non-Bravais lattice-type defect patterns can be explained by a phase cancellation in the scattering amplitude. Our investigation reveals for the first time that the symmetry of defect islands and the periodicity of defect modulation limit the phase cancellation which controls the semimetal-semiconductor transition in doped graphene. For instance, it has been shown that electronic bandgap of graphene antidot lattices depends on the shape and size of the holesh-BN) islands in zigzag-edged hexagonal supercells. The periodicity of supercells can in general be defined by two lattice vectors, et al., a supercell is denoted by four integers n, such that supercell geometry is described by the combination n × n. Both Bravais lattice-type patterns, where supercell lattice points are replaced by single defect sites and non-Bravais lattice-type patterns, where supercell lattice points are replaced by more than one defect site, are considered in this work.We considered two types of B/N-based defects: atomically separated B and N (isolated scatterers) and hexagonal BN  was used for the exchange and correlation functional with a 45 Ry energy cutoff for plane wave expansion. A 6 × 6 × 1 Monkhorst-Pack grid was used to sample the Brillouin zone. All geometries were optimized to forces less than 0.025 eV/Å.All calculations were done using ab initio Density Functional Theory (DFT) as it is implemented in the h-BN islands in n × n zigzag-edged hexagonal periodic supercells.In this section, we discuss how the electronic properties of graphene depend on periodicity of dopant modulation by considering Bravais lattice-type defect patterns. We considered two defect types: isolated B scatterers and n × n zigzag-edged hexagonal periodic supercells  as depicted in n × 3n where n is an integer, the bandgap closes , and the bandgap decreases when the dopant concentration is reduced otherwise25n × 3n or into K (or K′) point if the defect periodicity is n × 3n, two Dirac points merge into the Γ point destroying intervalley scattering. Thus no bandgap opening is observed. Therefore, semimetal-semiconductor transition is possible as the periodicity of defect modulation changes2425We considered isolated B scatterers in h-BN islands in zigzag-edged hexagonal supercell of graphene as shown in h-BN islands. Electronic bandgap is observed at the Γ point or K point depending on the supercell periodicity. The bandgap decreases with the decreasing defect concentration. However, this pattern is slightly deviated for 3n × 3n defect periodicity as shown in B and N co-doping can break the A-B sublattice symmetry of host lattice of graphene; thus are attractive in graphene defects engineeringWithin these two observations, it is clear that both translational and sublattice symmetry breaking are important in tuning the bandgap of graphene. To explore more about the effect of symmetry on bandgap tuning, we considered defects with non-Bravais lattice-type patternsk is the wave vector and τj is the position of the jth defect site. A phase cancellation can occur for particular defect patterns, which destroys the scattering between two sublattices at the Dirac point. For a given chemical composition, a small change in the defect pattern can change graphene from semimetallic to semiconducting behavior. In order to understannd the effect of sublattice symmetry breaking and the effect of symmetry of defect sites on the semimetal-semiconductor transition, we investigated electronic structures of several non-Bravais lattice-type defect patterns in graphene.In non-Bravais lattice-type defect patterns, more than one defect site replace the lattice points described by two vectors We considered four cases, where there are two isolated B and/or N scatterers in 8 × 8 zigzag-edged hexagonal supercell, as shown in g = 0.10 eV –g = 0.15 eV –When there is only a single B scatterer in the 8 × 8 zigzag-edged hexagonal supercell of graphene (Bravais lattice-type defect pattern), 0.06 eV electronic bandgap is observed . Bandgaph-BN islands. h-BN island in the 8 × 8 zigzag-edged hexagonal supercell. B and N atoms of the h-BN island take the positions of sublattice A and sublattice B respectively. In addition to the h-BN island, g ~ 0.12 eV is observed for graphene 8 × 8 zigzag-edged supercell with a single h-BN island , it is not possible for the structure factor to be zero, irrespective of the atomic arrangement. Therefore, no semimetal-semiconductor transition is observed for inverted and non-inverted systems in the 9 × 9 systems. This suggests that a semimetal-semiconductor transition in graphene with non-Bravais lattice-type defect patterns is limited by the supercell periodicity of the system.The same investigation was carried out for systems with two h-BN islands both of which have C3 symmetry shows an electronic bandgap 0.66 eV. B and N atoms take positions of same sublattice in these two h-BN islands. Semimetallic behaviour is observed for the configuration shown in h-BN island is restored by the second h-BN island. In contrast, the configuration in h-BN islands where similar defect atoms take the same sublattice positions shows a 0.68 eV bandgap, whereas the bandgap does not close when similar defect atoms take positions of opposite sublattices .


Staphylococcus aureus), by varying the ratios between AuNPs and graphene-PDDA. AuNPs/graphene-PDDA in the ratio of AuNPs/graphene-PDDA = 4:1 exhibited the strongest SERS signal in SERS detection of adenine and S. aureus. Thus, it is promising in the application of rapid and label-free bio-detection of bacteria or tumor cells.In this research, graphene nanosheets were functionalized with cationic poly  (PDDA) and citrate-capped gold nanoparticles (AuNPs) for surface-enhanced Raman scattering (SERS) bio-detection application. AuNPs were synthesized by the traditional citrate thermal reduction method and then adsorbed onto graphene-PDDA nanohybrid sheets with electrostatic interaction. The nanohybrids were subject to characterization including X-ray diffraction (XRD), transmission electron microscopy (TEM), zeta potential, and X-ray photoelectron spectroscopy (XPS). The results showed that the diameter of AuNPs is about 15–20 nm immobilized on the graphene-PDDA sheets, and the zeta potential of various AuNPs/graphene-PDDA ratio is 7.7–38.4 mV. Furthermore, the resulting nanohybrids of AuNPs/graphene-PDDA were used for SERS detection of small molecules (adenine) and microorganisms ( Escherichia coli (E. coli) and various molecules. This is possible because of the enhancement of the Raman signal. Gold and silver nanoparticles are widely used for SERS enhancement [9, thereby easily detecting the presence of various bacteria or molecules. Once metal (gold and silver) become nanoparticles with a unique size and morphology, their optical, electrical, and magnetic properties also change. Recent research on SERS technology emphasize on controlling the size and morphology of the nanoparticles. When the gap of the metal nanoparticles is within 10 nm, it will produce “hot spot” effect, which will further enhance the intensity of the SERS signal. Therefore, it is important to develop the SERS bio-detection by controlling the gap and the particle size of the metals nanoparticles.Raman scattering was discovered by CV Raman in 1928, and further, the use of surface-enhanced Raman scattering (SERS) technology was developed by Fleischman and others in 1974. SERS is used widely in various applications such as label-free sensing of bacteria ancement  via thei2/Vs with a resistance value (10–6 Ω·cm) even lower than silver or copper [Graphene  is an alr copper , which ir copper –12.Poly (PDDA) is a homopolymer and synthesized by George Butler in 1957 –14. PDDAStaphylococcus aureus for SERS rapid detection. Various ratios of AuNPs/graphene-PDDA were evaluated in order to create an optimum surface-enhanced Raman scattering (SERS) signal for SERS bio-detection [(S. aureus).In this experiment, Au/graphene-PDDA nanocomposite was fabricated by adsorbed gold nanoparticles (AuNPs) onto the graphene-PDDA nanosheets as shown in Fig. etection –20 of sm2SO4, 96.5 %, Baker; fuming nitric acid, HNO3, ≧99.5 %, Sigma-Aldrich; potassium permanganate, KMnO4, Baker; PDDA, 35 % , Aldrich; hydrogen peroxide, H2O2(aq), 35 %, Acros; hydrochloric acid, HCl(aq), 37 %, Scharlau; sodium citrate dehydrate, Na3Ct·2H2O, ≧99.5, Sigma-Aldrich; hydrogen tetrachloroaurate(III) trihydrate, HAuCl4·3H2O, 99 %, Sigma-Aldrich; nitric acid, HNO3(aq), 69 %, Panreac; silicon Oil, Choneye Pure Chemical; Luria-Bertani (LB broth), Difco™ , Oxoid; and adenine, C5H5N5, ≧99 %, Sigma.The materials used in this study were as follows: graphite powder, <20 μm, synthetic, Aldrich; sulfuric acid, H3Ct·2H2O) as a reducing agent to reduce Au3+ of HAuCl4·3H2O. The experimental procedure is as follows. (1) Ninety-six milliliters of 0.307 mM tetrachloroauric acid solution was prepared. (2) The solution was heated, and after boiling for 10 min, 4 mL of 1 % sodium citrate solution was added and the color changed from yellow to dark red.Citrate thermal reduction method was used to prepare gold nanoparticles. It is an oxidation-reduction reaction, which uses sodium citrate (NaGraphene oxide (GO) was prepared by using the modified Hummers method. Potassium permanganate was added to the graphite, and the surface of the graphite will have many oxidized functional groups. The experimental procedure is as follows. (1) Thirty-six milliliters of concentrated sulfuric acid was added to 1.0 g of graphite powder and stirred for 1 h. (2) The solution was stirred continuously in ice bath, 12 mL of fuming nitric acid was added dropwise, and then, 5 g of potassium permanganate was slowly added. (3) The solution was stirred for 120 h under room temperature. (4) One hundred twenty milliliters of deionized water was added slowly and stirred for 2 h under room temperature. (5) Six milliliters of hydrogen peroxide solution was added and stirred for 2 h and left at room temperature for 24 h. (6) The top layer of the clear solution was removed, and 200 mL of deionized water, 1 mL of hydrogen peroxide solution, and 1 mL of hydrochloric acid were added. The solution was mixed for 2 h and centrifuged. (7) Step 6 was repeated three times. (8) The top layer was washed with deionized water until the solid pH is close to 7. (9) After the solid was collected, it was placed in a vacuum oven and dried at 40 °C for 48 h. The final product was graphene oxide powder.The experimental procedure is as follows. (1) Sixty milligrams of graphene oxide powder was mixed with 20 mL of deionized water. (2) The solution was sonicated for 10 min. (3) Eight hundred microliters of PDDA was added and stirred for 10 min. (4) The solution was heated to 90 °C under reflux for 12 h. (5) The solution was centrifuged, and the upper layer solution was removed. The step was repeated for several times. (6) Deionized water was added to the final product.4 solutions were prepared as shown in Table 4 to graphene-PDDA were as follows: 1:2, 2:1, 4:1, 8:1, 16:1, referred as Au1/G2, Au2/G1, Au4/G1, Au8/G1, and Au16/G1.Different proportions of graphene-PDDA and HAuClS. aureus (ATCC 6538P). The experimental procedure is as follows. (1) Fifty microliters of the varied AuNPs/graphene-PDDA and 50 μL of S. aureus solutions (1 × 105 CFU/mL grown for 18 h at 37 °C) or adenine (concentration of adenine is 10−4 M) were placed in 1.5 mL micro-centrifuge tubes and mixed well. (2) Five microliters of each sample was dropped on the aluminum sheet. Raman spectra in the range of 400 to 1800 cm−1 were evaluated for the samples. The intensity of the Raman signal at 733 cm−1  was investigated also for the samples.A Raman microscope  with He-Ne laser (632.8 nm) was used to detect the presence of The interaction between AuNPs and graphene-PDDA were analyzed by X-ray photoelectron spectroscope , and surface electric properties of AuNPs/graphene-PDDA samples were analyzed by zeta potential analyzer  as described below.Various ratios of AuNPs to graphene-PDDA nanohybrids were prepared, including Au1/G2 (AuNPs to graphene-PDDA ratio = 1:2), Au2/G1, Au4/G1, Au8/G1, and Au16/G1. The morphology and distribution of the Au/graphene-PDDA nanohybrids were analyzed by transmission electron microscopy (TEM), as shown in Fig. X-ray diffraction of Au/graphene-PDDA Fig.  shows th2 functional group in the PDDA, which enables it to attach to the negative charge of AuNPs. The higher addition of AuNPs would decrease the average zeta potential of the nanocomposites. In Fig. Zeta potential also confirmed successful fabrication of Au/graphene-PDDA, as shown in Fig. 7/2 (from 84.8 to 84.5 eV) and 4f5/2 (from 88.6 to 88.1 eV), respectively. The binding energy of pristine AuNPs in XPS peaks would decrease after some molecules were grated due to the increase of electrons [XPS analysis Fig.  shows thlectrons . It provS. aureus, SA) was used as a model for SERS detection, and integrated intensity of the Raman signal at 733 cm−1  was examined, as shown in Fig. S. aureus by Au/graphene-PDDA nanohybrids detection. The different ratios of Au/graphene-PDDA nanohybrids were used to detect SA for optimum SERS signal. The results showed that AuNPs/graphene-PDDA in the ratio of AuNPs/graphene-PDDA = 4:1 exhibited the strongest SERS signal in the detection of S. aureus.Bacterium (S. aureus or adenine. An increase in the ratio of 4:1 would cause the aggregation of AuNPs to induce the laser scattering or decrease the surface plasmon effects (hot junctions effects) due to the contact of AuNPs with each other. Therefore, SERS signal intensity would decrease.In addition, the small molecules  also were tested by SERS detection. Figure S. aureus and adenine. Graphite was chemically exfoliated, and PDDA was π-π stacked onto the surface of graphene nanosheets, and later, gold nanoparticles were synthesized and attached onto the surface of graphene-PDDA by surface charge interaction. The resulting Au/graphene-PDDA nanocomposites greatly enhanced the Raman signal of S. aureus and adenine. Various ratios of AuNPs to graphene-PDDA were tested to make optimum SERS enhancement effects. AuNPs/graphene-PDDA in the ratio of AuNPs/graphene-PDDA = 4:1 exhibited the strongest SERS signal in the bio-detection of small biomolecules (adenine) and microorganisms (S. aureus). AuNPs/graphene-PDDA was shown to have enhanced Raman signal capability and unique ability to adsorb onto the microorganisms. Thus, it can be further applied in the rapid and label-free bio-sensing of biomolecules and microorganisms.This paper demonstrates in detail the synthesis of Au/graphene-PDDA nanocomposites and its application in SERS detection of


We extensively investigated the conductivity of single-layer graphene decorated with iridium deposited in ultra-high vacuum at low temperature (7 K) as a function of Ir concentration, carrier density, temperature, and annealing conditions. Our results are consistent with the formation of Ir clusters of ~100 atoms at low temperature, with each cluster donating a single electronic charge to graphene. Annealing graphene increases the cluster size, reducing the doping and increasing the mobility. We do not observe any sign of an energy gap induced by spin-orbit coupling, possibly due to the clustering of Ir.Graphene decorated with 5 We measure the conductivity as a function of Ir concentration, carrier density, temperature, and annealing conditions. The results are consistent with the formation of clusters of Ir on graphene, even for deposition at low temperature, with each cluster containing ~100 Ir atoms and donating ~1 electron to graphene and acting as a charged impurity scattering center. Annealing Ir-decorated graphene to room temperature greatly reduces the doping and increases the mobility, consistent with greatly increased cluster size. No signature of any significant bandgap in graphene decorated with Ir adatoms was observed and is attributed to the formation of Ir clusters.In this work, we investigate the σ(Vg) was measured. σ(Vg) for the pristine device and the device with four different Ir doping concentrations. With increasing Ir deposition, several features become apparent: 1) the gate voltage of minimum conductivity Vg,min shifts to more negative values, 2) the mobility μ decreases, 3) the minimum conductivity σmin decreases. All of these features are similar to the effect of charged impurities on graphene, observed previously by deposition of potassiumIr was deposited via electron-beam evaporation in UHV. To vary the coverage, the device was exposed to a controlled flux with sequential exposures at a fixed sample temperature of 7 K. Following each deposition, the conductivity as a function of gate voltage σ(Vg) at high |Vg| toWe fit Vg − Vg,min > 0) and hole conduction  in order to determine the electron and hole mobilities μe and μh, the threshold shift ΔVg,min, and the residual conductivity σres, where n is the carrier density, e is the electronic charge and cg is the gate capacitance per area. μe and hole mobility 1/μh versus Ir coverage, both of which are linear, demonstrating the mobility depends inversely on the density of impurities 1/μ ∝ nimp (Matthiessen’s rule)separately for electron conduction  for electrons (holes), about two orders of magnitude larger than found for K adatoms, indicating Ir is about 2 order of magnitude less effective at scattering electrons in graphene. g,min and σmin as a function of 1/μe, respectively. The results of both ΔVg,min and σmin agree well with that of potassium adatoms and can be well described by the previous theoretical predictions generated for impurity charge Ze with Z = 1, and impurity–graphene distance d = 0.3 nm–1.0 nm3Vg,min = Znimp, the scattering cross-section of an impurity scales as Z2 however the density of impurities nimp scales as 1/Z, hence the mobility scales as Z. Thus the results strongly suggest scattering by charged impurities with Z ≈ 1. Together with the observation of C about two orders of magnitude larger for Ir adatoms than for K adatoms, we infer that scattering is due to clusterse. This is entirely consistent with the observation of ΔVg,min about two orders of magnitude lower at a given Ir concentration than for a similar concentration of K adataoms. Note also that the charge transferred by Ir in clusters is much smaller than the value for isolated Ir adatoms calculated by density functional theory (Z = 0.22)T = 7 K. However the calculated barrier for an Ir adatom to diffuse through the bridge site on graphene is very small, ~50 meVwhere ry Z = 0.T = 7 K. Vg,min as a function of Ir coverage; σ(Vg) was measured during the continuous deposition of Ir. At the beginning of deposition, Ir tends to form uniform clusters randomly distributed on the graphene surface, and Vg,min drops fast and is roughly linear with increasing Ir coverage. At higher coverages Vg, min drops at a slower rate, consistent with the formation of larger clusters, and finally reaches a saturated value at the Ir coverage of 1.2 ML. This presumably marks the transition from clusters to a continuous film. With increased coverage beyond this point, Vg,min gradually recovers. The results are similar to those obtained for Ptn-type doping, with a reduction or even reversal of doping as a continuous film is formed. Monolayer graphene on single crystal Ir is known to be slightly p-doped. We conclude that the larger the cluster size, the smaller the charge transfer efficiency. Although Vg, min begins to recover for coverages above 1.2 ML, the resistivity at the Dirac point (ρxx) continues to rise with increasing Ir coverage, as shown in the inset of We also explored very high Ir coverages (>1 ML). Vg, min of graphene with 0.085 ML Ir deposited at T = 7 K [σ(Vg) data shown in Vg,min first shifts slightly towards negative gate voltage and then for T > 90 K shifts more rapidly to positive, eventually reaching its initial value before Ir deposition. The Vg, min shift reflects the rearrangement of Ir clusters, while the diffusion, growth and nucleation of atoms on the surface is a complex process, we speculate that below 90 K, Ir clusters do not grow appreciably, while some movement of individual adatoms leads to the negative gate voltage shift of Vg,min. Above 90 K, Ir clusters grow by Ostwald ripening, reducing the charge transfer efficiency and positively shifting Vg,min. Unsurprisingly, formation of large clusters at higher temperature (350 K) is found to be irreversible when re-cooling to low temperature, i.e. the ripening process is irreversible, as shown in g) for pristine graphene and Ir-decorated graphene annealed to form large clusters. Vg,min remains almost the same, indicating there is no change in charge transfer between large Ir clusters and graphene, consistent with charged-impurity-dominated scattering, σmin is nearly unchanged, and μ barely decreases, from 7000 to 6000 cm2/Vs. In contrast to small clusters, large clusters have low impact on the conductivity of graphene. The results are similar to those seen with Au clusters4We also explored temperature as a means to tune the cluster size after depositionxx of graphene decorated with Ir to search for an energy gap induced by spin-orbit couplingxx increases with decreasing temperature, and is well described by ρxx(T) ~ ln(T). Since the Ir cluster ripening process is irreversible when increasing and decreasing temperature (as shown in xx(T) curves of warming and cooling do not overlap. Comparing to the cooling curve, the Ir clusters rearrangement also provides additional contribution to the T dependence when warming. We also plot ρxx in logarithmic scale as a function of inverse temperature (inset of xx(T) is poorly described by the simple thermal activation model Eg < 1 meV, which is nonphysical, in that it is smaller than the measurement temperature kBT and much smaller than the disorder energy scale of order 50 meV. The roughly logarithmic ρxx(T) may originate from increased weak localization in graphene, has been observed in other noble metal-decorated grapheneWe further studied the temperature dependence of ρinset of  and findd transitional metal Ir. Ir tends to form clusters on graphene, acting as charged impurity scattering centers with a single electronic charge per cluster. No topological gap induced by spin-orbit coupling is observed, either due to the lack of such a gap in graphene with clustered Ir, or the lack of a global gap in transport due to inhomogeneity in graphene with adatom clusters. These findings provide guidance for future experiments aimed at achieving strong spin-orbit coupling in metal-decorated graphene.In summary, we have investigated the electronic transport properties of graphene decorated with 52/Si substrate and are identified by color contrast in optical microscope imaging and confirmed by Raman spectroscopy. The electrical contacts are defined with standard electron beam lithography and thermally evaporated Cr/Au (5 nm/100 nm). After annealing in H2/Ar gas at 350 °C to remove resist residueGraphene flakes are obtained by mechanical exfoliation of graphite on a 300-nm-SiOHow to cite this article: Wang, Y. et al. Electronic transport properties of Ir-decorated graphene. Sci. Rep.5, 15764; doi: 10.1038/srep15764 (2015).