Search Results (13)

This study proposes an alternative process for obtaining ZnO/ZnS:rGO heterostructures for use in DSSCs and as promising materials for potential applications in other photonic process, such as photocatalysis and photodetection. The compound was obtained through a microwave-assisted hydrothermal method, where the electromagnetic waves and temperature were crucial points for forming ZnO, ZnO/ZnS and reducing graphene oxide (GO). The XRD, Raman, FT-IR, and FESEM results presented the structural, morphological, and chemical structures, which suggest the conversion of ZnO to ZnS for samples with higher concentrations of reduced graphene oxide (rGO). Additionally, the optical properties were analyzed through photoluminescence and UV-Vis measurements. The electrical behavior of the photoelectrodes was investigated through J-V measurements in light and dark conditions. In addition, electrochemical impedance spectroscopy (EIS) was performed and Bode phase plots were created, analyzing the recombination processes and electron lifetime. The J-V results showed that for smaller amounts of rGO, the dye-sensitized solar cells (DSSC) efficiency improved compared to the ZnO/ZnS single structure. However, it was observed that with more significant amounts of rGO, the photocurrent value decreased due to the presence of charge-trapping centers. On the other hand, the best results were obtained for the ZnO/ZnS:1% rGO sample, which showed an increase of 14.2% in the DSSC efficiency compared to the pure ZnO/ZnS photoelectrode. Full article

Cuprous oxide (Cu₂O) has great potential in photodynamic therapy for implant-associated infections due to its good biocompatibility and photoelectric properties. Nevertheless, the rapid recombination of electrons and holes weakens its photodynamic antibacterial effect. In this work, a new nanosystem (Cu₂O@rGO) with excellent photodynamic performance was designed via the in situ growth of Cu₂O on reduced graphene oxide (rGO). Specifically, rGO with lower Fermi levels served as an electron trap to capture photoexcited electrons from Cu₂O, thereby promoting electron-hole separation. More importantly, the surface of rGO could quickly transfer electrons from Cu₂O owing to its excellent conductivity, thus efficiently suppressing the recombination of electron-hole pairs. Subsequently, the Cu₂O@rGO nanoparticle was introduced into poly-L-lactic acid (PLLA) powder to prepare PLLA/Cu₂O@rGO porous scaffolds through selective laser sintering. Photochemical analysis showed that the photocurrent of Cu₂O@rGO increased by about two times after the incorporation of GO nanosheets, thus enhancing the efficiency of photogenerated charge carriers and promoting electron-hole separation. Moreover, the ROS production of the PLLA/Cu₂O@rGO scaffold was significantly increased by about two times as compared with that of the PLLA/Cu₂O scaffold. The antibacterial results showed that PLLA/Cu₂O@rGO possessed antibacterial rates of 83.7% and 81.3% against Escherichia coli and Staphylococcus aureus, respectively. In summary, this work provides an effective strategy for combating implant-related infections. Full article

Metal-organic frameworks (MOFs) have attracted considerable interests for sensing, electrochemical, and catalytic applications. Most significantly, MOFs with highly accessible sites on their surface have promising potential for applications in high-performance computing architecture. In this paper, Mg-MOF-74 (a MOF built of Mg(II) ions linked by 2,5-dioxido-1,4-benzenedicarboxylate (DOBDC) ligands) and graphene oxide composites (Mg-MOF-74@GO) were first used as an active layer to fabricate ternary memory devices. A comprehensive investigation of the multi-bit data storage performance for Mg-MOF-74@GO composites was discussed and summarized. Moreover, the structure change of Mg-MOF-74@GO after introducing GO was thoroughly studied. The as-fabricated resistive random access memory (RRAM) devices exhibit a ternary memristic behavior with low SET voltage, an R_HRS/R_IRS/R_LRS ratio of 10³:10²:1, superior retention (>10⁴ s), and reliability performance (>10² cycles). Herein, Mg-MOF-74@GO composite films in constructing memory devices were presented with GO-mediated ternary memristic properties, where the distinct resistance states were controlled to achieve multi-bit data storage. The hydrogen bonding system and defects of GO adsorbed in Mg-MOF-74 are the reason for the ternary memristic behavior. The charge trapping assisted hopping is proposed as the operation mechanism, which is further confirmed by XRD and Raman spectra. The GO-mediated Mg-MOF-74 memory device exhibits potential applications in ultrahigh-density information storage systems and in-memory computing paradigms. Full article

The electrical characteristic of cancer cells is neglected among tumor biomarkers. The development of nanoprobes with opposing charges for monitoring the unique electrophysiological characteristics of cancer cells. Micro-nano size adsorption binding necessitates consideration of the nanoprobe’s specific surface area. On the basis of the electrophysiological characteristics of circulating tumor cells (CTCs), clinical application and performance assessment are determined. To demonstrate that cancer cells have a unique pattern of electrophysiological patterns compared to normal cells, fluorescent nanoprobes with opposing charges were developed and fabricated. Graphene oxide (GO) was used to transform three-dimensional (3D) nanoprobes into two-dimensional (2D) nanoprobes. Compare 2D and 3D electrophysiological magnetic nanoprobes (MNP) in clinical samples and evaluate the adaptability and development of CTCs detection based on cell electrophysiology. Positively charged nanoprobes rapidly bind to negatively charged cancer cells based on electrostatic interactions. Compared to MNPs(+) without GO, the GO/MNPs(+) nanoprobe is more efficient and uses less material to trap cancer cells. CTCs can be distinguished from normal cells that are fully unaffected by nanoprobes by microscopic cytomorphological inspection, enabling the tracking of the number and pathological abnormalities of CTCs in the same patient at various chemotherapy phases to determine the efficacy of treatment. The platform for recognizing CTCs on the basis of electrophysiological characteristics compensates for the absence of epithelial biomarker capture and size difference capture in clinical performance. Under the influence of electrostatic attraction, the binding surface area continues to influence the targeting of cancer cells by nanoprobes. The specific recognition and detection of nanoprobes based on cell electrophysiological patterns has enormous potential in the clinical diagnosis and therapeutic monitoring of cancer. Full article

Among the different graphene derivatives, graphene oxide is the most intensively studied material as it exhibits reliable and repeatable resistive switching. The operative mechanisms that are responsible for resistive switching are being intensively investigated, and three models explaining the change in the resistive states have been developed. These models are grounded in the metallic-like filamentary conduction, contact resistance modification and the oxidation of/reduction in the graphene oxide bulk. In this work, using Al/GO/n-Si structures, we demonstrate that all three of these operative mechanisms can simultaneously participate in the resistive switching of graphene oxide. Multiple point-like conduction channels in the graphene oxide films were detected by the electron beam-induced current (EBIC) technique. At the same time, large areas with increased conductivity were also revealed by EBIC. An analysis of these areas by Raman spectroscopy indicates the change in the graphene oxide bulk’s resistive properties. The EBIC data along with the measurements of the capacitance–voltage characteristics provided strong evidence of the involvement of an aluminum/graphene oxide interface in the switching processes. In addition, by using Al/GO/n-Si structures, we were able to identify unique local properties of the formed conductive channels, namely the change of the charge state of a conductive channel due to the creation of negatively charged traps and/or an increase in the GO work function. Full article

Tristable memristic switching provides the capability for multi-bit data storage. In this study, all-inorganic multi-bit memory devices were successfully manufactured by the attachment of graphene quantum dots (GQDs) onto graphene oxide (GO) through a solution-processable method. By means of doping GQDs as charge-trapping centers, the device indium-tin oxide (ITO)/GO:0.5 wt%GQDs/Ni revealed controllable memristic switching behaviors that were tunable from binary to ternary, and remarkably enhanced in contrast with ITO/GO/Ni. It was found that the device has an excellent performance in memristic switching parameters, with a SET1, SET2 and RESET voltage of −0.9 V, −1.7 V and 5.15 V, as well as a high ON2/ON1/OFF current ratio (10³:10²:1), and a long retention time (10⁴ s) together with 100 successive cycles. The conduction mechanism of the binary and ternary GO-based memory cells was discussed in terms of experimental data employing a charge trapping-detrapping mechanism. The reinforcement effect of GQDs on the memristic switching of GO through cycle-to-cycle operation has been extensively investigated, offering great potential application for multi-bit data storage in ultrahigh-density, nonvolatile memory. Full article

Graphene-quantum dot nanocomposites attract significant attention for novel optoelectronic devices, such as ultrafast photodetectors and third-generation solar cells. Combining the remarkable optical properties of quantum dots (QDs) with the exceptional electrical properties of graphene derivatives opens a vast perspective for further growth in solar cell efficiency. Here, we applied (3-mercaptopropyl) trimethoxysilane functionalized reduced graphene oxide (f-rGO) to improve the QDs-based solar cell active layer. The different strategies of f-rGO embedding are explored. When f-rGO interlayers are inserted between PbS QD layers, the solar cells demonstrate a higher current density and a better fill factor. A combined study of the morphological and electrical parameters of the solar cells shows that the improved efficiency is associated with better layer homogeneity, lower trap-state densities, higher charge carrier concentrations, and the blocking of the minor charge carriers. Full article

A tristable memory device with a trilayer structure utilizes poly(methyl methacrylate) (PMMA) sandwiched between double-stacked novel nanocomposite films that consist of 2-(4-tert-butylphenyl)-5-(4-biphenylyl)-1,3,4-oxadiazole (PBD) doped with graphene oxide (GO). We successfully fabricated devices consisting of single and double GO@PBD nanocomposite films embedded in polymer layers. These devices had binary and ternary nonvolatile resistive switching behaviors, respectively. Binary memristic behaviors were observed for the device with a single GO@PBD nanocomposite film, while ternary behaviors were observed for the device with the double GO@PBD nanocomposite films. The heterostructure GO@PBD/PMMA/GO@PBD demonstrated ternary charge transport on the basis of I–V fitting curves and energy-band diagrams. Tristable memory properties could be enhanced by this novel trilayer structure. These results show that the novel graphene-based memory devices with trilayer structure can be applied to memristic devices. Charge trap materials with this innovative architecture for memristic devices offer a novel design scheme for multi-bit data storage. Full article

Solution-processable nonvolatile memory devices, consisted of graphene oxide (GO) embedded into an insulating polymer polymethyl methacrylate (PMMA), were manufactured. By varying the GO content in PMMA nanocomposite films, the memristic conductance behavior of the Ni/PMMA:GO/Indium tin oxide (ITO) sandwiched structure can be tuned in a controllable manner. An investigation was made on the memristic performance mechanism regarding GO charge-trap memory; these blends were further characterized by transmission electron microscope (TEM), scanning electron microscope (SEM), Fourier transform infrared spectra (FTIR), Raman spectra, thermogravimetric analysis, X-ray diffraction (XRD), ultraviolet-visible spectroscopy, and fluorescence spectra in particular. Dependent on the GO content, the resistive switching was originated from the charges trapped in GO, for which bipolar tunable memristic behaviors were observed. PMMA:GO composites possess an ideal capability for large area device applications with the benefits of superior electronic properties and easy chemical modification. Full article

Graphene oxide (GO) has been actively utilized in nonvolatile resistive switching random access memory (ReRAM) devices due to solution-processability, accessibility for highly scalable device fabrication for transistor-based memory, and cross-bar memory arrays. Uncontrollable oxygen functional groups of GO, however, restrict its application. To obtain stable memory performance, 2-tert-butylphenyl-5-biphenyl-1,3,4-oxadiazole (PBD) a that can serve as 1,3,4-oxadiazole acceptor was carefully introduced onto the GO framework. Better stability was achieved by increasing the weight ratio of the chemical component from 2:1 to 10:1 in all GO-based solutions. Particularly, rewritable nonvolatile memory characteristics were dependent on the ratio between PBD and GO. PBD:GO devices with a proportion of 10:1 w/w exhibited better memory performance, possessed a higher ON/OFF ratio (>10²) at a lower switching voltage of −0.67 V, and had a long retention ability. The interaction between PBD and GO can be demonstrated by transmission electron microscope, scanning electron microscope, thermogravimetric analysis, fourier transform infrared spectra, Raman spectra, X-ray diffraction, and fluorescence spectra. The superior ReRAM properties of the multilayers of GO blended with the PBD nanocomposite are attributed to electron traps caused by the strong electron acceptors. Full article

2,6-Diaminoanthracene (AnDA)-functionalized graphene oxide (GO) (AnDA-GO) was prepared and used to synthesize a graphene oxide-based polyimide (PI-GO) by the in-situ polymerization method. A PI-GO nanocomposite thin film was prepared and characterized by infrared (IR) spectroscopy, thermogravimetric analysis (TGA) and UV-visible spectroscopy. The PI-GO film was used as a memory layer in the fabrication of a resistive random access memory (RRAM) device with aluminum (Al) top and indium tin oxide (ITO) bottom electrodes. The device showed write-once-read-many-times (WORM) characteristics with a high ON/OFF current ratio (I_on/I_off = 3.41 × 10⁸). This excellent current ratio was attributed to the high charge trapping ability of GO. In addition, the device had good endurance until the 100th cycle. These results suggest that PI-GO is an attractive candidate for applications in next generation nonvolatile memory. Full article

The surface of ZnWO₄ nanorods was decorated with Cu₂O nanoparticles (Cu₂O/ZnWO₄) prepared through a precipitation method. The Cu₂O nanoparticles were tightly deposited on the ZnWO₄ surface and had average diameters of 20 nm. The nanoparticles not only promoted the absorption and utilization of visible light but also facilitated the separation of photogenerated charge carriers. This brought an improvement of the photocatalytic activity. The 5 wt % Cu₂O/ZnWO₄ photocatalyst displayed the highest degrade efficiency for methylene blue (MB) degradation under visible light, which was 7.8 and 2 times higher than pure ZnWO₄ and Cu₂O, respectively. Meanwhile, the Cu₂O/ZnWO₄ composite photocatalyst was able to go through phenol degradation under visible light. The results of photoluminescence (PL), photocurrent, and electrochemical impedance spectra (EIS) measurements were consistent and prove the rapid separation of charge, which originated from the match level structure and the close contact with the interface. The radical and hole trapping experiments were carried out to detect the main active substances in the photodegradation process. The holes and ·O₂⁻ radicals were predicted to dominate the photocatalytic process. Based on the characterization analysis and experiment results, a possible photocatalytic mechanism for enhancing photocatalytic activity was proposed. Full article

Capacitive-type transduction is now widely used in MEMS microphones. However, its sensitivity decreases with reducing size, due to decreasing air gap capacitance. In the present study, we proposed and developed the Electret Gate of Field Effect Transistor (ElGoFET) transduction based on an electret and FET (field-effect-transistor) as a novel mechanism of MEMS microphone transduction. The ElGoFET transduction has the advantage that the sensitivity is dependent on the ratio of capacitance components in the transduction structure. Hence, ElGoFET transduction has high sensitivity even with a smaller air gap capacitance, due to a miniaturization of the transducer. A FET with a floating-gate electrode embedded on a membrane was designed and fabricated and an electret was fabricated by ion implantation with Ga⁺ ions. During the assembly process between the FET and the electret, the operating point of the FET was characterized using the static response of the FET induced by the electric field due to the trapped positive charge at the electret. Additionally, we evaluated the microphone performance of the ElGoFET by measuring the acoustic response in air using a semi-anechoic room. The results confirmed that the proposed transduction mechanism has potential for microphone applications. Full article