Junction characteristics of chemically-derived graphene/p-Si heterojunction solar cell

Experimental and theoretical investigations on the heterojunction of silicon (Si) with chemically derived graphene have been presented. The stability study of graphene oxide and reduced graphene oxide (rGO) in aqueous medium were performed by visual observation and surface charge measurement. The detailed characterization by FT-IR, UV–Vis, and Raman spectroscopy exhibited the formation of rGO with a high optical band gap of 3.6 eV. The atomic force microscopy analysis for rGO sample revealed the formation of flakes with thickness ≈ 10 nm. The rGO was spin-coated on the p-Si substrate for fabrication of a heterojunction device, with the structure of rGO/p-Si. In the fabricated device, incident light was transmitted through the thin rGO film to reach the junction interface, generating photoexciton, and thereby a photo-conversion efficiency of 0.02% was achieved. The theoretical simulation of rGO/p-Si heterojunction device using solar cell capacitance simulation 1D software showed the efficiency of 1.32%. Such large deviations in efficiency between experiment and theory have been discussed in details.     

Real-time DNA detection using Pt nanoparticle-decorated reduced graphene oxide field-effect transistors

A large-area, continuous, few-layer reduced graphene oxide (rGO) thin film has been fabricated on a Si/SiO(2) wafer using the Langmuir-Blodgett (LB) method followed by thermal reduction. After photochemical reduction of Pt nanoparticles (PtNPs) on rGO, the obtained PtNPs/rGO composite is employed as the conductive channel in a solution-gated field effect transistor (FET), which is then used for real-time detection of hybridization of single-stranded DNA (ssDNA) with high sensitivity (2.4 nM). Such a simple, but effective method for fabrication of rGO-based transistors shows great potential for mass-production of graphene-based electronic biosensors.     

Improved charging/discharging behavior of electropolymerized nanostructured composite films of polyaniline and electrochemically reduced graphene oxide

In this work, a simple electrochemical reduction procedure has been applied to nanostructured composite films of polyaniline (PANI) and graphene oxide (GO) having a globular surface morphology with the grain size of 50 nm. The reduction converts GO to reduced GO (rGO) which improves the electroactivity of the PANI composite films with 30%. Cyclic voltammetry confirmed the reduction of GO to rGO whereas electrochemical impedance spectroscopy showed that the rGO network increases the redox capacitance of the composite films with 15% to 77 mF cm⁻². In a three-electrode cell, the anodic charge of the PANI film containing GO increased with 18.7% during the potential cycling stability test for 10,000 cycles between −0.2 and 0.5 V, indicating that the film had a good stability against degradation. This composite film type still maintained a high capacitance of 15 mF cm⁻² in a symmetric two-electrode cell after 10,000 potential cycles between 0 and 0.4 V. The electrochemically prepared PANI composite films reported here are aimed to be used in capacitor applications where it is crucial to deposit thin PANI layers on well-defined small surfaces where other polymerization or deposition techniques cannot be used and in solid-state chemical sensors as ion-to-electron transducer interfaces.     

石墨烯/玻璃块体复合材料的制备及性能

本文报道了还原氧化石墨烯/钠钙硅(rGO/SLS)玻璃块体复合材料的热压制备和力学性能。首先以3-氨基丙基三乙氧基硅烷为表面活性剂修饰玻璃粉微粒;然后在水溶液中带负电的氧化石墨烯(GO)纳米片通过静电自组装与被氨基修饰过带正电的玻璃颗粒相结合生成复合颗粒。通过高温真空热压烧结,GO被还原成rGO,从而原位生成rGO/SLS玻璃块状复合材料。结果表明,rGO均匀分布在玻璃基质中,并明显增强了复合材料的机械性能。rGO/SLS玻璃块体复合材料中rGO的含量为0.5%(质量分数)时,复合材料的弯曲强度比纯的SLS玻璃提高了约一倍。     

Spherical graphene and Si nanoparticle composite particles for high-performance lithium batteries

Silicon/carbon composite electrodes are in the spotlight as an anode with a high capacity and a long cycle life. For this purpose, it is important to make a uniformly dispersed composite material. We fabricated spherical composite particles of reduced graphene oxide (rGO) and silicon nanoparticle (Si NP) using a spray drying method. The composite microparticle fabricated by drying the suspended droplets forms a well-agglomerated rGO/Si NP composite and forms a pore structure by crumpled rGO. The rGO/Si NP microparticles were applied as the anode of the lithium-ion battery. We achieved a reversible capacity of 1,246 mAh/g at 1A/g after 200 charge/discharge cycles and a capacity retention of 83%. Considering that the Si NP microparticle without rGO showed a capacity of 365 mAh/g and a retention of 12%, the rGO matrix improves the electrical conductivity and effectively alleviates stress during charge and discharge cycles.     

Thiourea assisted one-pot easy synthesis of CdS/rGO composite by the wet chemical method: Structural,optical, and photocatalytic properties

We report on the synthesis of CdS/reduced graphene oxide (rGO) composite by a wet chemical method. Thiourea was used both as a sulfur source and as a reducing agent to convert graphene oxide to rGO. The structural and morphological confirmation for the reduction of graphene oxide and the formation of the CdS/rGO composite was demonstrated by X-ray diffractometry, Raman spectroscopy, Fourier transform infrared spectroscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy analyses. Photoluminescence spectra of the composite exhibited a more efficient luminescence quenching in comparison with pure CdS nanoparticles. The composite demonstrated 99% photodegradation of methyl orange under UV irradiation, which is much superior than the photodegradation of methyl orange under similar conditions exhibited by CdS nanoparticles (72%).     

Solvothermal synthesis of various C3N4 films on FTO substrates and their photocatalytic and sensing applications

This paper reports solvothermal syntheses of pristine and KOH–NaCl-modified melon and melon–rGO composite films without post annealing and their applications in photocatalysis and Cu²⁺ sensing. Melon seed-layer coating enhanced film adhesion to fluorine-doped tin oxide substrates. X-ray diffraction, transmission electron microscopy, Fourier transform infrared spectroscopy, and Raman spectroscopy were used to verify melon film structures. Assorted complex agents were studied to tailor film morphologies. (001)-Oriented nanorods were observed in KOH–NaCl-modified melon films. Constituent elements were determined based on their binding energies using X-ray photoelectron spectroscopy. Ultraviolet–visible and ultraviolet photoelectron spectroscopy were employed to confirm band gaps and valence band positions, respectively, of melon films. Associated energy-band diagrams were then constructed. The melon–rGO composite films exhibited superior photodegradation of methylene blue (degradation rate constant [k] ≅ 6.4 × 10⁻³/min) and rhodamine B (k ≅ 2.5 × 10⁻³/min) under visible-light irradiation. The performance was confirmed by nanorod structures, low photoluminescence emission, and high electrochemical surface areas. Furthermore, a reliable photoelectrochemical current density (~0.5 mA/cm²) at a 0.6-V bias was obtained for KOH–NaCl-modified melon and melon–rGO composite films. The KOH–NaCl-modified melon films demonstrated excellent selectivity between Cu²⁺ and Cr⁶⁺, indicating promising applications in Cu²⁺ sensing.     

Enhancing toughness and strength of SiC ceramics with reduced graphene oxide by HP sintering

In this paper, the silicon carbide-reduced graphene oxide (SiC/rGO) composites with different content of rGO are investigated. The hot pressing (HP) at 2100?°C for 60?min under a uniaxial pressure of 40?M?Pa resulted in a near fully-dense SiC/rGO composite. In addition, the influence of graphene reinforcement on the sintering process, microstructure, and mechanical properties (fracture toughness, bending strength, and Vickers hardness) of SiC/rGO composites is discussed. The fracture toughness of SiC/rGO composites (7.9MPam^1/2) was strongly enhanced by incorporating rGO into the SiC matrix, which was 97% higher than the solid-state sintering SiC ceramics (SSiC) by HP. Meanwhile, the bending strength of the composites reached 625?M?Pa, which was 17.3% higher than the reference materials (SSiC). The microstructure of the composites revealed that SiC grains were isolated by rGO platelets, which lead to the toughening of the composite through rGO pull out/debonding and crack bridging mechanisms.     

Tailoring the properties of cerium doped zinc oxide/reduced graphene oxide composite: Characterization,photoluminescence study,antibacterial activity

Ce doped ZnO/rGO composite materials were prepared by a one-pot hydrothermal process without any surfactant. The size, crystallography and morphology of the composite were investigated in detail by X- ray diffraction (XRD) studies, Raman spectroscopy, scanning electron microscopic (SEM), transmission electron microscopic (TEM) studies, UV–Vis spectroscopic analysis and X-ray photoelectron spectroscopic (XPS) analysis. The XRD pattern substantiates the formation of Ce doped ZnO/rGO composite revealing the wurtzite structure of ZnO. The SEM micrograph illustrates flower-like morphology for ZnO/rGO composite which coalesced further after cerium incorporation. Additionally, TEM image illustrated that ZnO hexagons were disoriented from its flower structure in Ce/ZnO/rGO composite. The XPS spectra further reaffirm the formation of cerium doped ZnO/rGO composite. The photoluminescence (PL) spectra confirms that emission occurs in the UV and visible region and several active sub-levels were observed in visible region on deconvolution, due to the incorporation of cerium. Antibacterial activity towards B. subtills and V. harveyi affirmed that the incorporation of Ce in ZnO/rGO composite leads to an improved antibacterial activity.     

氮化硅薄膜生长随时间演化过程及其特性研究

氮化硅SiN_x薄膜凭借介电常数高和稳定性好的特点而被广泛应用于光电器件中,但薄膜的厚度对器件的性能有重要影响。针对此问题采用等离子体化学气相沉积技术,以高纯NH₃、N₂和SiH₄为反应气体,优化其他沉积参数,通过改变沉积时间来生长SiN_x薄膜。用X射线衍射谱(XRD),紫外-可见光光谱(UV-VIS)、傅里叶变换红外光谱(FTIR)和扫描电镜(SEM)对薄膜结构进行表征,详细研究了沉积时间与薄膜厚度的关系以及沉积时间对薄膜性能的影响。试验结果表明:所制备的样品为非晶SiN_x薄膜结构,薄膜厚度随沉积时间均匀增加;薄膜折射率随沉积时间的增加而增大,光学带隙基本不随时间变化。SEM测试结果表明,随着沉积时间增加,薄膜致密性与均匀性越来越好,氧含量也越来越少,说明薄膜致密性提高可以有效阻挡O原子进入薄膜,阻止后氧化现象的发生。     

A facile one step electrostatically driven electrocodeposition of polyviologen–reduced graphene oxide nanocomposite films for enhanced electrochromic performance

Polyviologen (PV)–reduced graphene oxide (rGO) nanocomposite films were fabricated by simple, one-step reductive electropolymerization of cyanopyridinium based precursor monomer (CNP) in an aqueous dispersion of graphene oxide (GO). Since the polymer formation and reduction of graphene oxide occurs within the same potential window, electrocodeposition method was preferred for obtaining nanostructured PV–rGO films. Cyclic voltammetry experiments of PV–rGO displayed two well resolved, reversible one-electron redox processes typical of viologen. Being a redox polymer, incorporation of rGO further enhances the electroactivity of the PV in the composite films. Vibrational spectral analysis with surface characterization revealed structural changes after composite formation along with subsequent reduction of GO within the polymer matrix. The PV–rGO nanostructured film exhibits a high-contrast electrochromism with low driving voltage induced striking color changes from transparent (0 V) to purple (−0.6 V), high coloration efficiency, fast response times and better cycling stability compared to a pristine PV film. This improved performance can be attributed to the high stability of the electrochrome in the composite assembly induced by electrostatically driven non-covalent interactions between redox PV²⁺ and negatively charged rGO, improved electrical conductivity and enlarged surface area accessed through reinforced nanostructured graphene sheets for tethering PV molecules.     

Electrochemical Synthesis of Reduced Graphene Oxide–Wrapped Polyaniline Nanorods for Improved Photocatalytic and Antibacterial Activities

This study depicts the electrochemical synthesis of nanocomposites based on polyaniline nanorods (NRs) wrap with reduced graphene oxide (PANI–rGO) on ITO substrates for photocurrent generation, photodegradation, and antibacterial applications. The synthesis of PANI–rGO nanocomposites was elaborated by the incorporation of rGO into PANI thin films during electropolymerization in the presence of sulfuric acid. The synthesis of rGO was done by modification on the well-known Hammer’s method. The thin film nanocomposites were characterized by X-ray photoelectron spectroscopy (XPS), Scanning electron microscopy (FESEM), UV–Visible and electrochemical photocurrent spectroscopy. FESEM revealed the formation of PANI NRs with diameters of between 50 and 150 nm. The XPS was employed to confirm the compositions of the PANI–rGO nanocomposites. From photoelectrochemical results, the generated photocurrent was improved in the presence of rGO in PANI NRs. Whereas experimental findings show that the introduction of rGO into PANI improved the photoresponse from 7 to 13 µA cm^?2. Integration of 3D rGO into PANI results in better photocatalytic performance for the degradation of Congo red (CR). The enhanced photocatalytic activity with the presence of rGO revealed the good potential of PANI-GO nanocomposites for dye degradation. The effective removal of CR of up to 90% has been observed in an acidic medium and is acceptable compared to the surface area of the substrate. At optimum conditions, also the nature of the antibacterial activities has been investigated by ITO/PANI and ITO/PANI–rGO thin films, and the results have shown exhibited antibacterial activity against the growth of E. coli gram-negative bacteria.

Graphical Abstract

     

聚苯胺修饰纳米ZnO薄膜及其光致阴极保护性能

从金属材料腐蚀特性及腐蚀保护要求出发,首先利用阳极氧化法制得ZnO薄膜,再通过恒电位法将ZnO薄膜用聚苯胺修饰得到ZnO/PANI复合薄膜。采用扫描电镜分析（SEM）、X射线衍射分析（XRD）、光电流、开路电位（OCP）及电化学阻抗等方法对制得的ZnO薄膜和ZnO/PANI复合薄膜进行物性分析和光电性能评价。研究表明：成功制得ZnO/PANI复合薄膜,且表现出优良的腐蚀保护性能。OCP实验表明,ZnO/PANI复合薄膜腐蚀保护性能与纳米ZnO薄膜相比提升了2～3倍。其中,光照后ZnO薄膜的光电流增加7μA,OCP下降5mV,复合薄膜的光电流增加22μA,OCP下降13mV。最后,失重实验对两种薄膜的光致阴极保护性能的分析数据显示,ZnO薄膜和ZnO/PANI复合薄膜都能对316L不锈钢和Q235碳钢起到光致阴极保护效果,但复合薄膜对316L不锈钢的保护效果尤为明显,其受腐蚀速率与在ZnO薄膜保护状态下相比降低了1倍以上。     

CuxNi1-xO nanostructures and their nanocomposites with reduced graphene oxide: Synthesis,characterization, and photocatalytic applications

NiO nanostructure was synthesized using a simple co-precipitation method and was embedded on reduced graphene oxide surface via ultrasonication. Structural investigations were made through X-ray diffraction (XRD) and functional groups were confirmed by Fourier transform infrared spectroscopy (FTIR). XRD analysis revealed the grain size reduction with doping. Fourier transform infrared spectroscopy confirmed the presence of metal-oxygen bond in pristine and doped NiO nanostructure as well as the presence of carbon containing groups. Scanning electron microscopy (SEM) indicated that the particle size decreased when NiO nanostructure was doped with copper. BET surface area was found to increase almost up to 43 m²/g for Cu doped NiO nanostructure/rGO composite. Current-voltage measurements were performed using two probe method. UV–Visible spectroscopic profiles showed the blue and red shift for Cu doped NiO nanostructure and Cu doped NiO Nanostructure/rGO composite respectively. Rate constant for Cu doped NiO nanostructure/rGO composite found to increase 4.4 times than pristine NiO nanostructure.     

Superior ammonia sensing properties of PET-supported polyaniline/reduced graphene oxide/zinc ferrite ternary nanocomposite thin film at room temperature

This article introduces a ternary nanocomposite-based flexible thin film ammonia sensor developed on transparent polyethylene terephthalate (PET) substrate in the well-known in situ chemical oxidative polymerization technique. The nanocomposite consists of three different materials: polyaniline (PANI), reduced graphene oxide (rGO), and zinc ferrite (ZF). Keeping the PANI amount constant, seven PANI/rGO/ZF (PRZ) samples are produced by performing stoichiometric variation between rGO and ZF. Later on, various structural, morphological, and spectroscopic analysis of all the composite materials is accomplished with field emission scanning electron microscopy (FESEM), high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), and ultraviolet–visible spectroscopy (UV–Vis). The sensing performance of the as-produced sensors toward ammonia (NH₃) is examined in the concentration range from 250 ppb to 100 ppm. The study reveals the excellent sensing ability of the PRZ3 sensor (rGO = 30%, ZF = 20%) achieving minimum and maximum responsivity values of ~51% and ~1052%, respectively, at the lowest (250 ppb) and highest (100 ppm) concentration of ammonia. The sensor also exhibits admirable repeatability, good dynamic responsivity, rapid response (t_res ~2.9–5 s), moderately faster recovery (t_rec ~37.9–69.7 s), superb linearity against ppm variation (R² ~ 0.989), low detection limit (~123 ppb), and exceptional selectivity toward ammonia. The substrate temperature variation divulges that room temperature (30°C) is the ideal temperature for getting outstanding responsivity of the sensor. The study is further accompanied by humidity variation in the incoming air and bending flexibility test of the substrate. A compulsory and legitimate model regarding the sensing mechanism is presented at the end.     

Mechanical properties and biomedical applications of a nanotube hydroxyapatite-reduced graphene oxide composite

As a result of the growing interest in the biological and mechanical performance of hydroxyapatite (HA)–graphene nano-sheets (GNs) composite systems, reduced graphene oxide (rGO) reinforced hydroxyapatite nano-tube (nHA) composites were synthesized in situ using a simple hydrothermal method in a mixed solvent system of ethylene glycol (EG), N,N-dimethylformamide (DMF) and water, without using any of the typical reducing agents. The consolidation process was performed by hot isostatic pressing (HIP) at 1150 °C and 160 MPa. The composites were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy, enabling confirmation of the synthesis and reduction of the nHA and rGO, respectively. The structure of the synthesized powder and cell attachment on the sintered sample was confirmed by field emission scanning electron microscopy (FESEM). The effects of the rGO on the mechanical properties and the in vitro biocompatibility of the nHA based ceramic composites were investigated. The elastic modulus and fracture toughness of the sintered samples increased with the increase of the rGO content when compared to the pure nHA by 86% and 40%, respectively. Cell culture and viability test results showed that the addition of the rGO promotes osteoblast adhesion and proliferation, thereby increasing the biocompatibility of the nHA–rGO composite.     

新型还原氧化石墨烯/氮化碳复合纳滤膜制备及其性能

高性能石墨烯基复合膜的制备是目前国际研究热点,但是石墨烯基纳滤膜在脱盐中水通量较低,限制其在脱盐中的应用。采用聚多巴胺(PDA)改性聚砜(PSF)膜为基膜,将还原氧化石墨烯(rGO)和超薄氮化碳(uCN)纳米片通过真空抽滤法在基膜表面自组装制备新型还原氧化石墨烯/氮化碳复合纳滤膜。通过场发射扫描电子显微镜、透射电子显微镜、X 射线衍射仪、傅里叶变换红外光谱仪和X射线光电子能谱仪等研究uCN添加对膜结构和形貌的影响,并考察不同uCN添加比例、rGO用量及压力复合纳滤膜性能变化规律。结果显示当在100 mg·L^-1的rGO中添加uCN为20 mg·L^-1时所制备的rGO/uCN复合纳滤膜不仅保持良好盐离子截留率(对Na₂SO₄截留率85.86%,对NaCl截留率30.17%),且水渗透系数是rGO膜的2.15倍(88.50 L·m^-2·h^-1·MPa^-1)。     

Preparation of Ag/reduced graphene oxide reinforced copper matrix composites through spark plasma sintering: An investigation of microstructure and mechanical properties

The reduced graphene oxide (rGO) decorated with Ag nanoparticles was synthesized by the chemical reduction of graphene oxide in an aqueous solution containing AgNO₃, in the presence of hydrazine hydrate as a reducing agent. The reduction of graphene oxide was confirmed by FT-IR and raman spectroscopy analyses. The x-ray diffraction pattern and UV–visible investigations demonstrated the formation of Ag particles on the surface of rGO sheets. After successful decoration, the Ag/rGO nano-composite was used as the reinforcement in the copper matrix composite. Cu–Ag/rGO composites with different percentages of Ag/rGO (0.4, 0.8, 1.6 and 3.2 vol%.) were prepared by mechanical milling and spark plasma sintering (SPS). The effects of the Ag/rGO content on the consolidation process, micro-hardness, bending strength and also, fracture surface of the prepared samples were then investigated. The three-point bending strength of the sintered samples was increased from 285 to 472 MPa by the addition 0.8 vol%. of Ag/rGO, as compared to the pure Cu. Moreover, increasing the reinforcement content to the 3.2 vol%. Ag/rGO led to decreasing the bending strength to 433 MPa. The highest micro-hardness (81 Hv) was obtained for the composite sample containing the 1.6 vol%. Ag/rGO. By increasing Ag/r-GO as the reinforcement (3.2 vol%.), the Vickers hardness was decreased to 69 Hv. Also, investigation of the fracture surface morphology showed transformation of fracture mechanism from plastic changes to brittle ones by raising the Ag/rGO content volume from 0.8 to 1.6 vol %.     

Characterization of superhydrophobic a-C:F thin film deposited on porous silicon via laser ablation of a PTFE target

Fluorinated amorphous carbon (a-C:F) thin films are deposited on both flat silicon and porous silicon (PS) surfaces via laser ablation of a polished polytetrafluoroethylene (PTFE). Porous silicon (PS) is prepared by anodic etching of p-type silicon wafers in HF based solution. The film deposited on the flat silicon surface exhibits a highly hydrophobic state with water contact angle (WCA) of ~ 146°. In comparison, the surface of film deposited on PS layer shows a roll-off superhydrophobic state, where the water droplet is seen to roll off without wetting its surface with contact angle hysteresis of ~ 4.5°. Micro-Raman results show that the graphite domain of the film deposited on PS has higher disorder level and lower average gain size. The effect of substrate porosity on chemical composition of deposited films has been investigated by using both Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS). It is found that the porous substrate improves the incorporation of the fluorine into the film. Atomic force microscopy (AFM) results revealed that the film deposited on PS has higher surface roughness and lower grain size as compared to the film deposited on flat silicon surface.     

Boron-doped hydrogenated amorphous carbon films grown by surface-wave mode microwave plasma chemical vapor deposition

We report the effects of boron (B) doping on optical and structural properties of the hydrogenated amorphous carbon thin films grown by surface-wave mode microwave plasma (SW-MWP) chemical vapor deposition (CVD) on n-type silicon and quartz substrates at room temperature. Argon and acetylene were used as a carrier and carbon source gases respectively. Analytical methods such as X-ray photoelectron spectroscopy (XPS), Nanopics 2100/NPX200 surface profiler, JASCO V-570 UV/VIS/NIR spectroscopy, Fourier transform infrared spectroscopy (FT-IR) and Raman spectroscopy were employed to investigate the properties of the films. Low atomic concentration of B (0.08 at.%) was found in the doped film. The optical band gap of the undoped film was 2.6 eV and it decreased to 1.9 eV for the B-doped film. Structural property shows the crystalline structure of the film and it has changed after incorporating B as a dopant. The structural modifications of the films leading to being more graphite in nature were confirmed by the Raman and FT-IR characterization.