The recent observation of extremely large magnetoresistance (MR) in the transition-metal dichalcogenide MoTe2 has attracted considerable interest due to its potential technological applications as well as its relationship with novel electronic states predicted for a candidate type-II Weyl semimetal. In order to understand the origin of the MR, the electronic structure of MoTe2−x (x = 0.08) is systematically tuned by application of pressure and probed via its Hall and longitudinal conductivities. With increasing pressure, a monoclinic-to-orthorhombic (1 T′ to Td) structural phase transition temperature (T*) gradually decreases from 210 K at 1 bar to 58 K at 1.1 GPa, and there is no anomaly associated with the phase transition at 1.4 GPa, indicating that a T = 0 K quantum phase transition occurs at a critical pressure (Pc) between 1.1 and 1.4 GPa. The large MR observed at 1 bar is suppressed with increasing pressure and is almost saturated at 100% for P > Pc. The dependence on magnetic field of the Hall and longitudinal conductivities of MoTe2−x shows that a pair of electron and hole bands are important in the low-pressure Td phase, while another pair of electron and hole bands are additionally required in the high-pressure 1 T′ phase. The MR peaks at a characteristic hole-to-electron concentration ratio (nc) and is sharply suppressed when the ratio deviates from nc within the Td phase. These results establish the comprehensive temperature-pressure phase diagram of MoTe2−x and underscore that its MR originates from balanced electron-hole carrier concentrations.

The effectiveness of conductive carbon films for cell adhesion and growth was demonstrated.

Porous conductive carbon films are useful for application in fuel cells and biomedical sensors. Controllability of the porosity in conductive carbon films was investigated by using unbalanced magnetron sputtering (UBMS). Here, we show through porosity analysis and plasma diagnostics that carbon films can be tuned to have porosity ranging from amorphous to porous by varying the working pressures from 3 to 140 mTorr in UBMS. The porosity control is attributed to the carbon adatom energy change by control of the working pressures. This approach enabled us to obtain porous carbon films of 44–68% with a high conductivity of 20–0.001 S/cm, implying the feasibility of porous conductive carbon films for advanced applications.

Carbon-based materials have attracted much attention in biological applications like interfacing electrodes with neurons and cell growth platforms due to their natural biocompatibility and tailorable material properties. Here we have fabricated sputtered carbon thin film electrodes for bioelectrical measurements. Reactive ion etching (RIE) recipes were optimized with Taguchi method to etch the close field unbalanced magnetron sputtered carbon thin film (nanocarbon, nC) consisting of nanoscale crystalline sp 2-domains in amorphous sp 3-bonded backbone. Plasma etching processes used gas mixtures of Ar/O 2 /SF 6 /CHF 3 for RIE and O 2 /SF 6 for ICP-RIE. The highest achieved etch rate for nanocarbon was 389 nm/min and best chromium etch mask selectivity was 135:1. Biocompatibility of the material was tested with rat neuronal cultures. Next, we fabricated multielectrode arrays (MEA) with carbon recording electrodes and metal wiring. Organotypic brain slices grown on the MEAs were viable and showed characteristic spontaneous electrical network activity. The results demonstrate that interactions with nanocarbon substrate support neuronal survival and maturation of functional neuronal networks. Thus the material can have wide applications in biomedical research.