 Subjects -> INSTRUMENTS (Total: 63 journals)
|
|
|
- Real-time monitoring of photocatalytic methanol decomposition over
Cu2O-loaded TiO2 nanotube arrays in high vacuum- Authors: Hikaru Masegi, Hayato Goto, Shivaji B. Sadale, Kei Noda
Abstract: Journal of Vacuum Science & Technology B, Volume PCSI2020, Issue 1, October 2020.
We report a real-time investigation on the photocatalytic decomposition of methanol over Cu2O-loaded TiO2 nanotube arrays (TNAs) in high vacuum. Cu2O-loaded TNAs were fabricated using all-electrochemical processes. TNAs were prepared by anodizing Ti foils, and Cu2O nanoparticles (CNPs) were pulse-electrodeposited onto anodized TNA surfaces. The photocatalytic decomposition of methanol was monitored using a quadrupole mass analyzer in high vacuum, where the partial pressures of intermediate and final reaction products were measured. Switching phenomena in the partial pressures of hydrogen (H2), formaldehyde (CH2O), water (H2O), and carbon monoxide (CO) were observed simultaneously according to the ON/OFF sequence of ultraviolet irradiations over TNA/CNP composites, thereby revealing that Cu2O can facilitate proton reduction like noble-metal-based cocatalysts such as platinum, even in a high vacuum environment. The intermediate reaction products suggest that the photocatalytic oxidation of gaseous methanol over TNA/CNP proceeds under the coexistence of direct and indirect hole transfer mechanisms.
Citation: Journal of Vacuum Science & Technology B
PubDate: 2020-09-03T04:23:14Z
DOI: 10.1116/6.0000194@jvb.2020.PCSI2020.issue-1
- Detection of some amino acids with modulation-doped and
surface-nanoengineered GaAs Schottky P-I-N diodes- Authors: Tamador Alkhidir, Maguy Abi Jaoude, Deborah L. Gater, Christopher Alpha, A. F. Isakovic
Abstract: Journal of Vacuum Science & Technology B, Volume PCSI2020, Issue 1, October 2020.
Most current techniques for analyzing amino acids require substantial instrumentation and significant sample preprocessing. In this study, we designed, fabricated, and tested a scalable diode-based microdevice that allows for direct sensing of amino acids. The device is based on modulation-doped GaAs heterostructure with a Schottky contact on one side. The relatively high mobility and relatively small dielectric constant of GaAs are naturally helpful in this problem. We also paid attention to a proper etching procedure allowing for substantial modification of the surface properties, thereby further boosting the sensing performance. Transport data (I-V, differential conductance) are presented for three qualitatively different classes of amino acids (i.e., nonpolar with aliphatic R-group, polar uncharged R-group, and charged R-group) with glycine, cysteine, and histidine as specific examples, respectively. The conductance for the GaAs-amino acid interface measured using a scanning tunneling microscope (STM) was previously reported to have distinct spectral features. In this paper, we show that measuring the differential conductance of a GaAs diode, whose surface is in direct contact with an aqueous solution of amino acid, is a simple methodology to access useful information, previously available only through sophisticated and equipment-demanding STM and molecular electronics approaches. Density functional theory calculations were used to examine which adsorption processes were likely responsible for the observed surface conductance modification. Last, in future and ongoing work, we illustrate how it might be possible to employ standard multivariate data analysis techniques to reliably identify distinct (95[math]) single amino acid specific features in near-ambient differential conductance data.
Citation: Journal of Vacuum Science & Technology B
PubDate: 2020-08-17T01:14:08Z
DOI: 10.1116/6.0000186@jvb.2020.PCSI2020.issue-1
- Extending the metal-induced gap state model of Schottky barriers
- Authors: John Robertson, Yuzheng Guo, Zhaofu Zhang, Hongfei Li
Abstract: Journal of Vacuum Science & Technology B, Volume PCSI2020, Issue 1, October 2020.
Fermi level pinning at Schottky barriers strongly limits the minimization of contact resistances in devices and thereby limits the scaling of modern Si electronic devices, so it is useful to understand the full range of behaviors of Schottky barriers. The authors find that some semiconductor interfaces with compound metals like silicides have apparently weaker Fermi level pinning. This occurs as these metals have an underlying covalent skeleton, whose interfaces with semiconductors lead to miscoordinated defect sites that create additional localized interface states that go beyond the standard metal-induced gap states (MIGSs) model of Schottky barriers. This causes a stronger dependence of Schottky barrier height on the metal and on interface orientation. These states are argued to be an additional component needed to extend the MIGS model.
Citation: Journal of Vacuum Science & Technology B
PubDate: 2020-07-21T01:20:56Z
DOI: 10.1116/6.0000164@jvb.2020.PCSI2020.issue-1
- Strain-dependent luminescence and piezoelectricity in monolayer transition
metal dichalcogenides- Authors: Alex C. De Palma, Gabriel Cossio, Kayleigh Jones, Jiamin Quan, Xiaoqin Li, Edward T. Yu
Abstract: Journal of Vacuum Science & Technology B, Volume PCSI2020, Issue 1, October 2020.
The modification of optical and electronic properties of transition metal dichalcogenides via mechanical deformation has been widely studied. Their ability to withstand large deformations before rupture has enabled large tunability of the bandgap, and further, the spatially varying strain has been shown to control the spatial distribution of the bandgap and lead to effects such as carrier funneling. Monolayer transition metal dichalcogenides exhibit a significant piezoelectric effect that could couple to a spatially inhomogeneous strain distribution to influence electronic and optical behavior. We investigate both experimentally and theoretically an example case of photoluminescence in structures with a strain distribution similar to that employed in single-photon emitters but generated here via nanoindentation. Using a mechanical model for strain induced by nanoindentation, we show that piezoelectricity can result in charge densities reaching 1012 e/cm2 and can generate electrostatic potential variations on the order of ±0.1 V across the suspended monolayer. We analyze the implications of these results for luminescence and exciton transport in monolayer transition metal dichalcogenides with spatially varying strain.
Citation: Journal of Vacuum Science & Technology B
PubDate: 2020-07-06T01:30:45Z
DOI: 10.1116/6.0000251@jvb.2020.PCSI2020.issue-1
- Adsorption behavior of cobalt phthalocyanine submonolayer coverages on
B-Si(111)-[math] R 30°- Authors: Milan Kubicki, Susi Lindner, Martin Franz, Holger Eisele, Mario Dähne
Abstract: Journal of Vacuum Science & Technology B, Volume PCSI2020, Issue 1, October 2020.
The molecular arrangement and electronic properties of submonolayer coverages of cobalt phthalocyanine (CoPc) molecules on the deactivated B-Si(111)-[math] surface are analyzed using scanning tunneling microscopy and spectroscopy. On the ideal surface, the dangling bonds, which typically prevent an ordered growth of molecules on semiconductors, are removed. However, the presence of single defects enables the opportunity to study the influence of their dangling bonds on the adsorption behavior in detail. Here, we focus on coverage densities below and above the Si-Si([math]) defect density. Our data demonstrate that for all submonolayer coverages, the CoPc molecules adsorb in a flat-lying geometry, with either a circular or a four-leaf cloverlike appearance. Initially, each CoPc molecule adsorbs on top of a Si-Si([math]) defect, while later, also passivated Si adatoms become occupied. For the adsorption on Si-Si([math]) defects, hybridization between its [math] orbital and the [math] orbital of the Co atom of the molecule occurs, leading to additional hybridization states observed in the tunneling spectra.
Citation: Journal of Vacuum Science & Technology B
PubDate: 2020-06-16T03:59:29Z
DOI: 10.1116/6.0000242@jvb.2020.PCSI2020.issue-1
- Insulating regions in a TiO2 thin film defined by laser irradiation
- Authors: Syeed E. Ahmed, Jesse Huso, Jacob R. Ritter, John Igo, Yi Gu, Matthew D. McCluskey
Abstract: Journal of Vacuum Science & Technology B, Volume PCSI2020, Issue 1, October 2020.
Titanium dioxide (TiO2) has a range of applications including catalysis, hydrogen production, and water purification. In this work, anatase TiO2 was annealed in vacuum at 800 °C, resulting in a conductive thin film. Exposure to subgap laser light (532 nm wavelength) caused a seven order-of-magnitude increase in resistance. Laser-irradiated regions showed an increase in optical transmission, consistent with a reduction in oxygen vacancy concentration. Scanning electron microscopy and Raman spectroscopy indicate that laser irradiation did not change the morphology, composition, or phase of the material.
Citation: Journal of Vacuum Science & Technology B
PubDate: 2020-03-31T12:38:25Z
DOI: 10.1116/1.5142402@jvb.2020.PCSI2020.issue-1
|
Hybrid journal (It can contain Open Access articles)
