Herein, the impact of thermal annealing on the interaction between monolayer MoS 2 and Au using Raman spectroscopy is investigated. It is found that MoS 2 has two main modes of interactions with the underlying Au being either weakly coupled or strongly coupled. The regions strongly coupled to Au are hybridized to Au, minimally strained, and electron doped. The weakly coupled regions are found to be slightly hole doped with tensile strain of 1.0%. The overall areal coverage of the strongly coupled regions is not increased by thermal annealing, and the variability in the degree of hybridization increases at annealing temperatures above 100 °C. The data also show that monolayer MoS 2 starts to decouple from Au around 100 °C, becoming fully decoupled above 200–250 °C, suggesting that monolayer MoS 2 produced by Au‐assisted mechanical exfoliation may be more easily transferred off Au at elevated temperatures.

The family of transition-metal dipnictides has been of theoretical and experimental interest because this family hosts topological states and extremely large magnetoresistance (MR). Recently, T a A s 2 , a member of this family, has been predicted to support a topological crystalline insulating state. Here, by using high-resolution angle-resolved photoemission spectroscopy (ARPES), we reveal both closed and open pockets in the metallic Fermi surface (FS) and linearly dispersive bands on the ( 2 ‾ 01 ) surface, along with the presence of extreme MR observed from magneto-transport measurements. A comparison of the ARPES results with first-principles computations shows that the linearly dispersive bands on the measured surface of T a A s 2 are trivial bulk bands. The absence of symmetry-protected surface state on the ( 2 ‾ 01 ) surface indicates its topologically dark nature. The presence of open FS features suggests that the open-orbit fermiology could contribute to the extremely large MR of T a A s 2 .

Nickel ditelluride is an unusual member of the transition metal dichalcogenide family which has garnered interest due to potential valley spin-polarized surface states near the Fermi level and the presence of Dirac nodes in its electronic band structure. In this work, exfoliation of bulk nickel ditelluride is performed under ultra-high vacuum in order to generate a clean surface for scanning tunneling microscopy and spectroscopy at 4.8 K. Multiple features in the observed electronic density of states are observed in the vicinity of the Fermi level and compared to calculated band structures to elucidate their origins. Our results are consistent with the presence of the spin-polarized surface states, yet indicate trivial states, which are close to the Fermi level, can interfere with their potential utility in spintronic applications.

Photodetectors operating in the ultraviolet (UV) play a pivotal role in applications such as ozone monitoring and biosensing. One key factor to successfully implementing such photodetectors is that they must be solar-blind to avoid detecting ambient visible and infrared light. Unfortunately, UV photodetectors based on silicon and other typical semiconductors are not natively solar-blind, since their band gap energies are in the visible range. Hexagonal boron nitride (h-BN) is an example of a wide band gap semiconductor which shows promise for use as the absorbing medium in a UV photodetector device, since its band gap is wide enough to make it inherently insensitive to light in the visible range and above. Here we report on the fabrication and characterization of a graphene-h-BN-heterostructure photodetector which utilizes a vertical geometry, in principle allowing for highly scalable production. We find that our device shows a finite photoresponse to illumination by a 254nm light source, but not to a 365nm source, thus suggesting that our device is solar-blind.

Recent studies have shown that MoS2 can undergo a structural phase transition from the 2H to 1T' phase on Au substrates at moderate temperatures. Here, we use ultraviolet and x-ray photoelectron spectroscopy, Raman and photoluminescence spectroscopy, and scanning tunneling microscopy/spectroscopy to probe the impact of annealing exfoliated, monolayer MoS2 on Au. Our results across multiple length scales indicate that 2H-MoS2 becomes hybridized with Au upon thermal annealing without inducing the 1T' structural phase and the bandgap can be modulated to zero width depending on the degree of hybridization. These results can be used to control the resistance of metal-MoS2 contacts at the atomic scale without introduction of defects or structural phase

Scanning tunneling microscopy and spectroscopy (STM/STS) are used to electronically switch atomically-thin memristors, referred to as “atomristors”, based on a graphene/molybdenum disulfide (MoS_2)/Au heterostructure. A gold-assisted exfoliation method was used to produce near-millimeter (mm) scale MoS_2 on Au thin-film substrates, followed by transfer of a separately exfoliated graphene top layer. Our results reveal that it is possible to switch the conductivity of a graphene/MoS_2/Au memristor stack using an STM tip. These results provide a path to further studies of atomically-thin memristors fabricated from heterostructures of two-dimensional materials such as graphene and transition metal dichalcogenides (TMDs).

We have investigated BisGMA-TEGDMA dental composites with varying mass fractions of hydroxyapatite and silica filler. Commercially available dental composites with 60% silica filler were synthesized in the presence of nanometer-sized hydroxyapatite crystals. We have compared the mechanical properties of BisGMA-TEGDMA samples filled with silica only and those filled with silica and hydroxyapatite particles. We report on hardness as a function of crystalline content as determined by nanoindentation and microindentation.