Result of the Month (ROM)
The Result of the Month (ROM) section is an institution with a long history. Our goal is to present remarkable and interesting measurements and/or papers done by our customers with Scienta Omicron systems and instruments to the scientific community.
High Speed Dynamic and Operando Experiments: Thermal Reduction of Titanium Oxides
The thermal reduction of Titanium oxides was observed in-situ by time-resolved XPS using a new type of multi peak monitoring allowing to observe several XPS lines in a timely manner (figure 1&2). The color-coded maps show multiple XPS spectra over time where the x-axis represents the energy axis and y-axis the time. Intensity is shown from dark red (low count rate) to blue (high count rate). The oxygen reduction occurred within ~ 1 minute by applying a rapid temperature ramp and was found to be a step-wise process with an initial transition from 4+ to suboxide and the metallic state of Titanium at intermediate temperatures between 600 K and 725 K before further reduction of the 3+ oxidation state at temperatures > 725 K.
Controlled Growth of Transition Metal Dichalcogenide Monolayers using Knudsen-Type Effusion Cells for the Precursors
In this work, Antony George & Andrey Turchanin et al present a simple method for controlling the precursor flow rates using the Knudsen-type effusion cells. They characterised the grown MoS2 and WS2 monolayers by optical, atomic force and transmission electron microscopies as well as by X-ray photoelectron, Raman and photoluminescence spectroscopies, and by electrical transport measurements showing their high optical and electronic quality based on the single crystalline nature. XPS was performed in a ultra-high vacuum Multiprobe System from Scienta Omicron using a monochromatized x-ray source and an electron analyser Argus CU with a spectral energy resolution of 0.6 eV.
Selective Triplet Exciton Formation in a Single Molecule
In this work, Kimura K. et al report a single-molecule investigation of electroluminescence using a scanning tunneling microscope and demonstrate a simple method of selective formation of T1 excitons that utilizes a charged molecule. All experiments were conducted using a Scienta Omicron LT STM operating at 4.7 K under ultrahigh vacuum.
Electronic Band Dispersion Determination in Azimuthally Disordered Transition-Metal Dichalcogenide Monolayers
In this work, N Koch et al. demonstrate that the ARPES spectra of azimuthally disordered transition metal dichalcogenide monolayers with 2H phase are dominated by their band dispersion along the two high symmetry directions Γ-K and Γ-M. They exemplify this by analysing the ARPES spectra of four prototypical TMDCs within a mathematical framework, which allows to consistently explain the reported observations. The spectra for an azimuthally disordered WSe2 monolayer/highly oriented pyrolytic graphite (HOPG) sample were measured using Scienta Omicron ARPES Lab equipped with a DA30-L analyser and a VUV5k He source.
A Time- and Angle-Resolved Photoemission Spectroscopy with Probe Photon Energy up to 6.7 eV
In this Review, Prof. Wentao Zhang et al. introduce the development of an advanced trARPES system with probe photon energy up to 6.7 eV. The system is based on a Yb-based laser, KBe2BO3F2 (KBBF) and BBO nonlinear optical crystals, and a hemispherical electron analyser DA30-L 8000 from Scienta Omicron.
Evaluation of Sn-Doped Indium Oxide Film and Interface Properties on a-Si Formed by Reactive Plasma Deposition
Aiming to improve the performance of heterojunction Si solar cells, we evaluated the Sn-doped indium oxide (ITO) / a-Si structure using conventional and hard X-ray photoelectron spectroscopy (XPS, HAXPES), and the cause of the solar cell performance Identified deterioration. HAXPES allows non-destructive evaluation of the SiOx layer at the ITO / a-Si interface. The formation of SiOx at the ITO / a-Si interface increases the contact resistance, which can be reduced by post-deposition annealing (PDA). In addition, PDA facilitated Fermi level evaluation, ITO component precipitation in the a-Si layer, and increased interface roughness. Before the PDA, diffusion of a-Si Sn atoms was observed. In addition, PDA confirmed that Si atoms diffused into ITO. These reactions at the ITO / a-Si interface may be part of the deterioration factor of Si solar cells.
Multiple Topological States in Iron-Based Superconductors
In this work, Peng Zhang & Shik Shin et al. identified topological insulator and Dirac semimetal states near the Fermi energy in different iron-based superconducting compounds. More specifically, they 1) observe that TI bands reminiscent of Fe(Te,Se) exist in Li(Fe,Co)As; 2) predict and observe topological Dirac semimetal (TDS) bands in Li(Fe,Co)As and Fe(Te,Se); and 3) discuss phase diagram of these superconducting topological state4s as a function of doping. The ARPES measurements were performed with R4000 electron analyzer and spin-resolved ARPES measurements were carried out with DA30-L analyser – both from Scienta Omicron.