Arthur Linz

Bio: Arthur Linz is an academic researcher. The author has an hindex of 1, co-authored 1 publications receiving 60 citations.

Thin films of fullerene-like MoS2 nanoparticles with ultra-low friction and wear

Abstract: The tribological properties of solid lubricants such as graphite and the metal dichalcogenides MX2 (where M is molybdenum or tungsten and X is sulphur or selenium) are of technological interest for reducing wear in circumstances where liquid lubricants are impractical, such as in space technology, ultra-high vacuum or automotive transport. These materials are characterized by weak interatomic interactions (van der Waals forces) between their layered structures, allowing easy, low-strength shearing. Although these materials exhibit excellent friction and wear resistance and extended lifetime in vacuum, their tribological properties remain poor in the presence of humidity or oxygen, thereby limiting their technological applications in the Earth's atmosphere. But using MX2 in the form of isolated inorganic fullerene-like hollow nanoparticles similar to carbon fullerenes and nanotubes can improve its performance. Here we show that thin films of hollow MoS2 nanoparticles, deposited by a localized high-pressure arc discharge method, exhibit ultra-low friction (an order of magnitude lower than for sputtered MoS2 thin films) and wear in nitrogen and 45% humidity. We attribute this 'dry' behaviour in humid environments to the presence of curved S-Mo-S planes that prevent oxidation and preserve the layered structure.

Impact of Intrinsic Atomic Defects on the Electronic Structure of MoS2 Monolayers

Abstract: Monolayer MoS2 is a direct band gap semiconductor which has been recently investigated for low-power field effect transistors. The initial studies have shown promising performance, including a high on/off current ratio and carrier mobility with a high-κ gate dielectric. However, the performance of these devices strongly depends on the crystalline quality and defect morphology of the monolayers. In order to obtain a detailed understanding of the MoS2 electronic device properties, we examine possible defect structures and their impact on the MoS2 monolayer electronic properties, using density functional theory in combination with scanning tunneling microscopy to identify the nature of the most likely defects. Quantitative understanding based on a detailed knowledge of the atomic and electronic structures will facilitate the search of suitable defect passivation techniques. Our results show that S adatoms are the most energetically favorable type of defect and that S vacancies are energetically more favorable than Mo vacancies. This approach may be extended to other transition-metal dichalcogenides (TMDs), thus providing useful insights to optimize TMD-based electronic devices.

Optical Properties and Color‐Center Formation in Thin Films of Molybdenum Trioxide

Abstract: The optical absorption spectrum of thin films of MoO3 has been measured over the temperature range from 77° to 290°K. The fundamental absorption edge occurs at 3300 A with an absorption coefficient of 105 cm−1. A stoichiometric film of MoO3 shows three absorption peaks at 3350, 2880, and 2700 A, respectively, and these are suggested to be due either to exciton formation or to transitions involving a split valence band.Values for the refractive index have been measured in the wavelength range 0.42–1.2μ. The low‐frequency dielectric constant (18.0±1) has been measured and the comparison with the high‐frequency dielectric constant (5.70) indicates that the bonding is predominantly ionic.The electrical conductivity has been measured on a polycrystalline sample in the temperature range 298° to 900°K and the activation energies of conduction found to be 1.83 eV (intrinsic) and 0.56 eV (impurity).On irradiating a thin film (0.2μ) of MoO3 with light of wavelength shorter than 3300 A, three color‐center bands having maxima around 5000, 6250, and 7700 A are formed. The same type of color centers are also formed on heating the film in oxygen in inert atmosphere. The color centers thus formed cannot be bleached optically. However, they can be bleached thermally in oxygen at 300°C. The growth and decay of color centers has been studied in detail.The formation of color centers is associated with increased dark conductivity of the MoO3. Very weak photoconductivity and photovoltaic effects with threshold energy corresponding to the fundamental absorption edge at 3300 A have been observed.An ESR signal characteristic of Mo5+ state has been observed in a film of MoO3. There is a small increase of ESR signal on color‐center formation which disappears completely on heating in air at 300°C.An energy‐level diagram has been proposed to account for the optical and electrical properties as well as the color‐center formation in MoO3.