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. 

Flat Bands in Twisted Bilayer Transition Metal Dichalcogenides

Result of the Month, September 2020

In this Nature Physics (2020), Zhang, Z, Wang, Y, Watanabe, K et al show the existence of a flat band in the electronic structure of 3° and 57.5° twisted bilayer WSe2 via Scanning Tunnelling Microscopy (STM) and Scanning Tunnelling Spectroscopy (STS). The featured figure shows the STM topography of the sample, both a graphene/hBN moiré pattern. The STM/STS measurements were performed in the ultrahigh-vacuum LT-STM from Scienta Omicron operating at 4.6 K.

Tomonaga–Luttinger Liquid in the Edge Channels of a Quantum Spin Hall Insulator

Result of the Month, July 2020

In this study, Stühler, R., Reis, F., Müller, T. et al. explore the impact of electronic correlations on highly localized edge states of the unique quantum spin Hall material bismuthene on SiC(0001). Exploiting the advantage of having an accessible monolayer substrate system, they use STM/STS to visualize the close-to-perfect one-dimensional confinement of the edge channels and scrutinize their suppressed density of states at the Fermi level. Based on the observed spectral behavior and its universal scaling with energy and temperature, they demonstrate the correspondence with a (helical) Tomonaga–Luttinger liquid. The STM/STS measurements have been performed with a low-temperature STM from Scienta Omicron under UHV conditions.

Effects of Nitridation on SiC/SiO2 Structures Studied by Hard X-ray Photoelectron Spectroscopy

Result of the Month, June 2020

This research paper investigates device-relevant stacks of SiC and SiO2 using energy-dependent X-ray photoelectron spectroscopy and combines results from both laboratory and synchrotron HAXPES systems to form a complete picture of the depth distribution and chemical states of nitrogen.

This paper contributes to investigating the main challenge that the semiconductor industry is tackling now, the quality of the interface between SiC and its native dielectric SiO2, which currently limits further improvement of device performance.

New Progress in the Basic Research for Topological Quantum Computing: Zero-Energy Bound States in the High-Temperature Superconductors at Two-Dimensional Limit

Result of the Month, May 2020 

In this work, Prof. Jian Wang Group at Peking University detected novel Majorana zero-energy bound state (ZEBS) resembling the characteristics of Majorana zero modes (MZMs) in interstitial Fe adatoms deposited on the high-temperature superconducting thin films at two-dimensional limit.

This research was enabled by a Lab10 MBE and multiprobe LT STM from Scienta Omicron. 

Light Induced Non-Volatile Switching of Superconductivity in Single Layer FeSe on SrTiO3 Substrate

Result of the Month, April 2020

In this study, Ming Yang et al. show that, in FeSe/SrTiO3 heterostructures, the superconducting transition temperature in FeSe monolayer can be effectively raised by the interband photoexcitations in the SrTiO3 substrate. This research was enabled by a Materials Innovation Platform (MIP) from Scienta Omicron combining two MBE chambers, VT STM, LT STM, and a ARPES Lab including a DA30L-8000 and VUV5k.

High Speed Dynamic and Operando Experiments: Thermal Reduction of Titanium Oxides

Result of the Month, March 2020

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

Result of the Month, February 2020

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

Result of the Month, January 2020

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

Result of the Month, December 2019

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

Result of the Month, November 2019

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

Result of the Month, October 2019

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

Result of the Month, September 2019

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.