Fabrication of encapsulated graphene-based heterostructure using molybdenum as edge-contacts

Graphene is an intriguing platform to study exotic quantum transport phenomena due to its intrinsically high mobility and remarkable electronic properties. To achieve high-performance device, graphene is usually encapsulated between thin sheets of hexagonal boron nitride (hBN) to protect graphene layer from extrinsic impurities. Cr/Au is typically employed to make contacts with the edges of the heterostructure. In this research, Mo is used as an alternative electrode for graphene without adhesion layer to simplify the fabrication process. hBN-graphene-hBN heterostructures were fabricated by a pick-up technique and etched in O2/CHF3 gases to expose graphene edges. Mo contacts were deposited onto the substrates by sputtering. We achieved ohmic contacts between graphene and Mo. The contact resistance reaches the maximum of around 1,300 Ω·μm at charge neutrality point and decreases to 975 Ω·μm at the density of 4×1012 cm−2. We observed that the contact resistance increases over time likely due to the oxidation of Mo but remained ohmic after 2 months. The intrinsic transport characteristics of graphene can still be obtained by using four-probe measurement. Here, we realized a high-quality twisted bilayer graphene device with a room-temperature mobility of 27,000 cm2/V·s indicating that Mo can be used as edge-contacts to probe the transport properties of graphene.

ENHANCING ADHESION STRENGTH AND WEAR PERFORMANCE OF ALCRN COATING ON COOL-WORK TOOL STEEL THROUGH INTRODUCING CRNX ADHESION LAYER

Hard thin coating directly deposited on soft steel substrate often suffers low adhesion strength and load-bearing capacity. In this work, CrN[Formula: see text]-type adhesion layers (ALs) were introduced between hard AlCrN coating and soft cool-work tool steel substrate to enhance the adhesion strength and wear performance. The microstructure of CrN[Formula: see text] ALs prepared with different nitrogen pressure and its influence on adhesion strength and tribological properties were investigated. The results show that with the nitrogen pressure increase from 0.5 Pa to 3.0 Pa, the phase transformation sequences occurring in ALs are: Cr + Cr2N [Formula: see text] Cr2N + CrN [Formula: see text] CrN. The adhesion strength increases with the increase of nitrogen pressure due to the formation of CrN which provides better load support resistance than the fragile Cr2N and soft Cr. In addition, the adhesion strength of the samples with ALs is always higher than that of the one without ALs. The improvement of adhesion strength for samples with CrN[Formula: see text]-type ALs is beneficial for improving wear resistance, especially at high wearing loads.

Combinatorial Materials Design Approach to Investigate Adhesion Layer Chemistry for Optimal Interfacial Adhesion Strength

A combinatorial material adhesion study was used to optimize the composition of an adhesion promoting layer for a nanocrystalline diamond (NCD) coating on silicon. Three different adhesion promoting metals, namely W, Cr, and Ta, were selected to fabricate arrays of co-sputtered binary alloy films, with patches of seven different, distinct alloy compositions for each combination, and single element reference films on a single Si wafer (three wafers in total; W–Cr, Cr–Ta, Ta–W). Scratch testing was used to determine the critical failure load and practical work of adhesion for the NCD coatings as a function of adhesion layer chemistry. All tested samples eventually exhibit delamination of the NCD coating, with buckles radiating perpendicularly away from the scratch track. Application of any of the presented adhesion layers yields an increase of the critical failure load for delamination as compared to NCD on Si. While the influence of adhesion layers on the maximum buckle length is less pronounced, shorter buckles are obtained with pure W and Cr–Ta alloy layers. As a general rule, the addition of an adhesion layer showed a 75% improvement in the measured adhesion energies of the NCD films compared to the NCD coating without an adhesion layer, with specific alloys and compositions showing up to 125% increase in calculated practical work of adhesion.

Surface Plasmon Resonance (SPR) based biosensor using MXene as a BRE layer and Magnesium Oxide (MgO) as an Adhesion layer

In this paper a plasmonic sensor consist of bimetallic layer of Ag and Au, a nono-thin layer of two dimension material MXene and a thin layer of Magnesium oxide (MgO) is proposed to operate in visible region. By using Kretschmann configuration based structure and transfer matrix method, the change in the refractive index of liquid Biosample have been observed at a fixed incident wavelength. By using the distinctive properties of Ti3C2Tx MXene and MgO we have investigated the performance of Surface Plasmon Resoance (SPR) biosensor. Significant performance parameters like Sensitivity, Figure of Merit (FoM) and Detection Accuracy (DA) calculated for different cases to prove the capability of proposed sensing structure. We also compared the sensitivity and sharpness of SPR curve obtained when using conventional adhesion layers like titanium (Ti), chromium (Cr), tantalum (Ta). A detailed investigation is carried out to observe the role of polymer as an adhesion layer and its thickness impact on FoM and resonance angle sharpness. The concept of Long range SPR (LR-SPR) and Short range SPR (SR-SPR) also discussed.

Measurement of Effects of Different Substrates on the Mechanical Properties of Submicron Titanium Nickel Shape Memory Alloy Thin Film Using the Bulge Test

This study investigated the effects of different substrates on the mechanical properties of Ti-60at%Ni shape memory alloys (SMA). Two types of samples were prepared for this experiment: (1) a Ti-60at%Ni deposited on SiNx, and (2) a Ti-60at%Ni deposited on SiNx/Cr; both had a 600 nm thick film of Ti-60at%Ni. Deposition was done using the physical vapor deposition (PVD) process, and the microstructural changes and crystallization phase changes were observed through scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results showed that the TiNi thin film with a Cr adhesion layer had better mechanical properties. The bulge test showed that TiNi thin film with a Cr adhesion had a higher Young’s modulus and lower residual stress. From the thermal cycling experiment, it was found that the Cr adhesion layer buffered the mismatch between TiNi and SiNx. Additionally, the thermal cycling test was also used to measure the thermal expansion coefficient of the films, and the fatigue test showed that the Cr layer significantly improved the fatigue resistance of the TiNi film.