RESUMEN
In this study, operando photoelectron spectroscopy was used to characterize the performance of graphene field-effect transistors under working conditions. By sweeping the back-gate voltages, the carrier concentration of the graphene channel on the 150 nm Si3N4/Si substrate was tuned. From the C1s core level spectra acquired under the application of different gate voltages, the binding energy shifts caused by electric-field effects were obtained and analyzed. Together with the C1s peak shape information and the photoluminescence spectrum of the Si3N4/Si substrate, the presence of local potential across the x-ray beam spot associated with defects and gate leakage current in amorphous Si3N4was identified. The presence of defects in Si3N4/Si substrate could not only screen the partial electric field generated by the back gate but also serve as long-range scattering centers to the carriers, thus affecting charge transport in the graphene channel. Our findings will help further investigate the dielectric/graphene interface properties and accelerate the utilization of graphene in real device applications.
RESUMEN
Indium selenide (InSe) features intriguing thickness-dependent optoelectronic properties, and a simple, and precise way to identify the thickness is essential for the rapid development of InSe research. Here, a red, green, and blue (RGB) color contrast method with regression analysis for quantitative correlation of three optical contrasts from RGB channels with the InSe thickness (1-35 nm), is demonstrated. The lower accuracy of the thickness identification obtained from the individual channels was discussed. Moreover, the effective refractive indices in the three RGB regions can be extracted from the Fresnel equation and numerical analysis by finding the best fit to the experimental optical contrast. After further consideration of the wavelength-dependent refractive indices, the slope of the regression line between the estimated thickness and that obtained from the atomic force microscope was improved from 1.59 ± 0.05 to 0.97 ± 0.02. The complex refractive index spectra of InSe (1-10 layers) generated fromab initionumerical calculation results were also adopted to identify the InSe thickness. Compared to dispersion, the evolution of the band structure had less effect on thickness identification. This work could be extended to other layered materials, facilitate the thickness-dependent study of layered materials, and expedite the realization of their practical applications.
RESUMEN
As the continuous miniaturization of floating-gate transistors approaches a physical limit, new innovations in device architectures, working principles, and device materials are in high demand. This study demonstrated a nonvolatile memory structure with multilevel data storage that features a van der Waals gate architecture made up of a partially oxidized surface layer/indium selenide (InSe) van der Waals interface. The key functionality of this proof-of-concept device is provided through the generation of charge-trapping sites via an indirect oxygen plasma treatment on the InSe surface layer. In contrast to floating-gate nonvolatile memory, these sites have the ability to retain charge without the help of a gate dielectric. Together with the layered structure, the surface layer with charge-trapping sites facilitates continual electrostatic doping in the underlying InSe layers. The van der Waals gating effect is further supported by trapped charge-induced core-level energy shifts and relative work function variations obtained from operando scanning X-ray photoelectron spectroscopy and Kelvin probe microscopy, respectively. On modulating the amount of electric field-induced trapped electrons by the electrostatic gate potential, eight distinct storage states remained over 3000 s. Moreover, the device exhibits a high current switching ratio of 106 within 11 cycles. The demonstrated characteristics suggest that the engineering of an InSe interface has potential applications for nonvolatile memory.