High mobility graphene on EVA/PET

Transparent conductive film on a plastic substrate is a critical component in low cost, flexible and lightweight optoelectronics. CVD graphene transferred from copper- to ethylene vinyl acetate (EVA)/polyethylene terephthalate (PET) foil by hot press lamination has been reported as a robust and affordable alternative to manufacture highly flexible and conductive films. Here, we demonstrate that annealing the samples at 60\ua0∘C under a flow of nitrogen, after wet etching of copper foil by nitric acid, significantly enhances the Hall mobility of such graphene films. Raman, Scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) were used to evaluate the morphology and chemical composition of the graphene

Substrate Effect in Electron Beam Lithography

Electron Beam Lithography (EBL) process strongly depends on the type of the applied lithographic system, composed of electron sensitive polymers and the substrate. Moreover, applied acceleration voltage changes the volume of Backscattered Electrons (BSE) participation in total energy absorption in resist layers. Proper estimation of energy distribution in used materials, due to electron scattering, is the key in final resist profile calculation and critical parameter in the designing process of the lithography exposure. In the presented paper, the Monte Carlo (MC) simulations of electron beam influence on lithographic system, consisting of positive tone resists (PMMA/MA and CSAR-62) spin coated on different substrates, will be presented. For high accuracy, obtained point spread functions were modelled by double-Gaussian function for Si, GaAs, AlGaN/GaN and InP substrates, respectively. Extracted scattering parameters of forward and backward electrons will be shown and their differences will be discussed. Results of simulated and conducted process of 100 nm metallic path fabrication on mentioned materials will be presented and compared. The practical usage of EBL technique will be shown in the aspect off low resolution application in low energy range of primary electron beam

Qualitative Assessment of the UV Exposition Process Near the Diffraction Limits

In the presented work the technological parameters that influence the shape of the resist structures are reported. The experimental results are compared with the simulations results, based on the solution of Maxwell’s equations using the RF module of COMSOL Multiphysics software. The electric field intensity distribution in the resist layer was analyzed for the mask slits that are larger and comparable to the applied wavelength. The differences in wave energy absorption in the resist layer are presented and discussed. For both cases, the impact of the chromium film thickness of the mask on the pattern profile of the resist is studied and the comparison is performed between the simulation and experimental results

Current-induced enhancement of photo-response in graphene THz radiation detectors

Thermoelectric readout in a graphene terahertz (THz) radiation detector requires a p-n junction across the graphene channel. Even without an intentional p-n junction, two latent junctions can exist in the vicinity of the electrodes/antennas through the proximity to the metal. In a symmetrical structure, these junctions are connected back-to-back and therefore counterbalance each other with regard to rectification of the ac signal. Because of the Peltier effect, a small dc current results in additional heating in one and cooling in another p-n junction, thereby breaking the symmetry. The p-n junctions then no longer cancel, resulting in a greatly enhanced rectified signal. This allows simplifying the design and controlling the sensitivity of THz radiation detectors

Temperature Dependent Zero-Field Splittings in Graphene

Graphene is a quantum spin Hall insulator with a 45 $\mu$eV wide non-trivial topological gap induced by the intrinsic spin-orbit coupling. Even though this zero-field spin splitting is weak, it makes graphene an attractive candidate for applications in quantum technologies, given the resulting long spin relaxation time. On the other side, the staggered sub-lattice potential, resulting from the coupling of graphene with its boron nitride substrate, compensates intrinsic spin-orbit coupling and decreases the non-trivial topological gap, which may lead to the phase transition into trivial band insulator state. In this work, we present extensive experimental studies of the zero-field splittings in monolayer and bilayer graphene in a temperature range 2K-12K by means of sub-Terahertz photoconductivity-based electron spin resonance technique. Surprisingly, we observe a decrease of the spin splittings with increasing temperature. We discuss the origin of this phenomenon by considering possible physical mechanisms likely to induce a temperature dependence of the spin-orbit coupling. These include the difference in the expansion coefficients between the graphene and the boron nitride substrate or the metal contacts, the electron-phonon interactions, and the presence of a magnetic order at low temperature. Our experimental observation expands knowledge about the non-trivial topological gap in graphene.Comment: Main text with figures (20 pages) and Supplementary Information (14 pages) Accepted in Phys. Rev.

Exposition time analysis of AlGaN/GaN HEMT fabrication by electron beam lithography

Electron beam lithography, due to the high design flexibility and high pattering resolution can be used as an exclusive lithography method in device fabrication in R&D reality. To achieve the reasonable time of process exposition, some essential steps and actions must be done. In the article, the main technical and technological dependences, based on AlGaN/GaN HEMT transistor fabrication, will be presented and discussed. As a result of conducted studies, the total time of the most important lithography process expositions will be shown and explained

Proximity effect in gate fabrication using photolithography technique

n the paper the technological factors influencing test structure gate length were described. The influence of test structure gate placement (Schottky metallization between ohmic contacts, on mesa and on GaN surface) was analyzed and discussed. Moreover, various distances between ohmic contacts paths were tested. Except for experimental investigations, simulations using finite elements method in COMSOL were performed for the same structure. The modelling results revealed crucial impact of a gap beyond the mask on the electric field distribution in photoresist layer. The smallest value of relative error of test finger lengths was observed for finger parts placed between ohmic paths on mesas. It was explained by thicker lift-off double layer between ohmic paths and the smallest Y-gap compared to test fingers placed on mesa and outside of it. Simulation did not bring an explanation of larger values of relative error for smaller distance between ohmic paths

Correction: Khan et al. High Mobility Graphene on EVA/PET. Nanomaterials 2022, 12, 331

The authors wish to make following corrections in this paper [...