Search query: Scanning tunneling spectroscopy amorphous

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abstract: Using scanning tunneling microscopy (STM) and spectroscopy (STS) at the liquid/solid interface, morphology evolution process and energetic level alignment of very thin solid films (thickness: <700 pm) of the low molecular weight molecule DRCN5T and DRCN5T:[70]PCBM blend are analyzed after applying thermal annealing at different temperatures. These films exhibit a worm like pattern without thermal annealing (amorphous shape) however, after applying thermal annealing at 120 degC, the small molecule film domains crystallize verified by X ray diffraction: structural geometry becomes a well defined organized array. By using STS, the energy band diagrams of the semiconductor bulk heterojunction (blended film) at the donor acceptor interface are determined; morphology and energy characteristics can be correlated with the organic solar cells (OSC) performance. When combining thermal treatment and solvent vapor annealing processes as described in previous literature by using other techniques, OSC devices based on DRCN5T show a very acceptable power conversion efficiency of 9.0%
author_names: Irving Caballero-Quintana

Daniel Romero-Borja

Jose-Luis Maldonado

Juan Nicasio-Collazo

Olivia Amargos-Reyes

Antonio Jimenez-Gonzalez
title: Interfacial Energetic Level Mapping and Nano Ordering of Small Molecule/Fullerene Organic Solar Cells by Scanning Tunneling Microscopy and Spectroscopy
venue: Nanomaterials
year: 2020

abstract: The structural and electronic properties of ultrathin insulator Al2O3 films on CoAl(100) have been studied using a combination of scanning tunneling spectroscopy and microscopy. The analysis of the differential conductance yields a band gap of 2.6 2.9eV for amorphous Al2O3. In the case of a well ordered alumina film, the band gap is increased to 4.5eV. On each of the oxide phases, the barrier height is to a large extent independent of local variations such as the surface corrugations or oxide steps.
author_names: Volker Rose

Rene Franchy
title: The band gap of ultrathin amorphous and well ordered Al2O3 films on CoAl(100) measured by scanning tunneling spectroscopy
year: 2009

abstract: We have investigated the temporal behavior of Sb2Te3 after irradiation with picosecond (ps) pump laser pulses using scanning tunneling microscope (STM) light emission synchronized with ps probe laser pulses delayed by times t after individual pump pulses. We determined the gap energy D E at the F point in the band diagram of Sb2Te3 from the STM light emission spectra as a function of the delay time t. We found that D E increased monotonically with t from the original value of 1.62 eV for a delay time of 0 to 15.3 ps and it decreased toward that original value (1.62 eV) for t in the time span between 15.3 and 28 ps; we saw no change in D E for t 28 ps. By comparing this t dependence of D E with the dielectric functions of the crystalline and amorphous phases of Sb2Te3, we have concluded that the phase transition from the crystalline phase toward the amorphous phase is induced by the pump pulses. The phonon energy of the A2u mode is clearly seen in the STM light emission spectra when D E is 1.62 eV, but not when D E is increased above 1.62 eV by pump pulse irradiation. This feature appears to be consistent with the Raman signals, which are much stronger for the crystalline phase than for the amorphous phase.We have investigated the temporal behavior of Sb2Te3 after irradiation with picosecond (ps) pump laser pulses using scanning tunneling microscope (STM) light emission synchronized with ps probe laser pulses delayed by times t after individual pump pulses. We determined the gap energy D E at the F point in the band diagram of Sb2Te3 from the STM light emission spectra as a function of the delay time t. We found that D E increased monotonically with t from the original value of 1.62 eV for a delay time of 0 to 15.3 ps and it decreased toward that original value (1.62 eV) for t in the time span between 15.3 and 28 ps; we saw no change in D E for t 28 ps. By comparing this t dependence of D E with the dielectric functions of the crystalline and amorphous phases of Sb2Te3, we have concluded that the phase transition from the crystalline phase toward the amorphous phase is induced by the pump pulses. The phonon energy of the A2u mode is clearly seen in the STM light emission spectra when D.
author_names: Yoichi Uehara

Masashi Kuwahara

Satoshi Katano

Takenori Tanno

Joe Sakai
title: Pump probe scanning tunneling microscope light emission spectroscopy of Sb2Te3
year: 2018

abstract: Atomic scale knowledge and control of oxidation of GaSb(100) which is a potential interface for energy efficient transistors, are still incomplete, largely due to an amorphous structure of GaSb(100) oxides. We elucidate these issues with scanning tunneling microscopy and spectroscopy. The unveiled oxidation induced building blocks cause defect states above Fermi level around the conduction band edge. By interconnecting the results to previous photoemission findings, we suggest that the oxidation starts with substituting second layer Sb sites by oxygen. Adding small amount of indium on GaSb(100) resulting in a (4 x 2) In reconstruction, before oxidation produces a previously unreported, crystalline oxidized layer of (1 x 3) O free of gap states.
author_names: Jaakko Makela

Marjukka Tuominen

Muhammad Yasir

Mikhail V Kuzmin

Johnny Dahl

Marko Patrick John Punkkinen

Pekka Laukkanen

Kalevi Kokko

Robert M Wallace
title: Oxidation of GaSb(100) and its Control Studied by Scanning Tunneling Microscopy and Spectroscopy
year: 2015

abstract: We have investigated the electronic properties of ultrathin Pb films by low temperature scanning tunneling microscopy and spectroscopy. Our results show that 30 nm thick Pb(111) films grown on atomically flat highly oriented pyrolytic graphite (HOPG) and on amorphous SiO2 are both in the strong coupling limit with transition temperature and energy gap close to the bulk value. Conductance maps and spectroscopy in the vortex state reveal a bound state at the center of the vortices, which suggest that the films are in the clean limit. Measurements of 3 nm Pb films grown on HOPG show a clear crossover to the weak coupling regime and dirty limit.
author_names: S A Moore

Jan Fedor

Maria Iavarone
title: Low temperature scanning tunneling microscopy and spectroscopy measurements of ultrathin Pb films
year: 2015

abstract: Amorphous nitrogenated carbon films with nitrogen atomic concentration between 12% and 29% were deposited using a filtered cathodic vacuum arc and a Kaufman type ion source. The surface topography of the samples has been investigated by scanning tunneling microscopy in ultrahigh vacuum, showing that the roughness of the film surface decreases with nitrogen concentration. Scanning tunneling spectroscopy is employed to understand the role of nitrogen in the change of the surface microstructure and electronic structure near the Fermi level. The tunneling current (I) bias voltage (V) curve is flat at low bias regions indicating a finite gap for the sample with low (12% nitrogen concentration. An increase of tunneling current and its nonlinearity along with the decrease of energy gap occurs in the samples with increase of N concentration. The observed surface density of states (dI/dV)(I/V) has been fitted as a square root function of bias voltage. An improvement of the quality of these fits in the films wi.
author_names: Somnath Bhattacharyya

Karsten Walzer

Michael Hietschold

Frank Richter
title: Nitrogen doping of tetrahedral amorphous carbon films: Scanning tunneling spectroscopy
year: 2001

abstract: Using a combination of in situ ultra high vacuum variable temperature scanning tunneling microscopy, ex situ Raman spectroscopy, and scanning electron microscopy, we investigated the growth of graphene using benzene on Pd(111) at temperatures up to 1100 K. Benzene adsorbs readily on Pd(111) at room temperature and forms an ordered superstructure upon annealing at 473 K. Exposure to benzene at 673 K enhances Pd step motion and yields primarily amorphous carbon upon cooling to room temperature. Monolayer graphene domains, 10 30 nm in size, appear during annealing this sample at 873 K. Dosing benzene at 1100 K results in graphene domains with varying degrees of crystallinity, while post deposition annealing at 1100 K for 1200 s yields monolayer graphene domains larger than 150 x 150 nm2. Our results, which indicate that graphene growth on Pd(111) using benzene requires deposition/annealing temperatures higher than 673 K, are in striking contrast with the reported growth of graphene using benzene at temperatures as low as 373 K on relatively inert Cu surfaces.
author_names: Pedro J Arias

Jan Tesar

Abby Kavner

Tomas Sikola

Suneel Kodambaka
title: In Situ Variable Temperature Scanning Tunneling Microscopy Studies of Graphene Growth Using Benzene on Pd(111)
venue: ACS nano
year: 2019

abstract: The surface electronic density of states of tetrahedral amorphous carbon has been measured by scanning tunneling microscopy and calculated by density functional theory. An analysis of these results and their comparison is presented here for a series of structures with different microscopic mass densities. The experimental structures were obtained by pulsed laser deposition with varying conditions resulting in diamond like carbon thin films. The calculated carbon structures were generated by simulating a melting cooling cycle with molecular dynamics using the density functional energetics within the local density approximation. The experimental and calculated densities of states show good agreement. Graphitic like surface reconstruction is both observed at the sp3 rich tetrahedral amorphous carbon (ta C) sample and found in the calculated ta C slab structure.
author_names: K Jarmo Koivusaari

Tapio T Rantala

J Levoska

Seppo Leppavuori
title: Surface electronic density of states of tetrahedral amorphous carbon investigated by scanning tunneling spectroscopy and ab initio calculations
year: 2000

abstract: Scanning Tunneling Microscopy (STM) was used to investigate the initial stages of growth of hydrogenated amorphous carbon a C:H) films. The films were deposited on highly oriented pyrolytic graphite (HOPG) and silicon substrates both on the powered (negatively self biased) and on the grounded electrodes from a methane r.f. plasma (13.56 MHz) at 68 to 70 mTorr and room temperature. On graphite substrates, films formed at the powered electrode were observed to nucleate in clusters approximately 50A in diameter. Cluster density increased with deposition time, while cluster size remained relatively constant. The atomic structure of individual clusters was amorphous. The C H bonding in these clusters was observed by high resolution electron energy loss spectroscopy. Films formed on graphite substrates placed at the grounded electrode produced very noisy images due to an unstable tunneling gap, indicative of the material's poor electrical conductivity. On silicon substrates placed at the powered electrode, film deposition was uniform and no cluster formation was observed. The films formed were measured to be flat to within 3A rms.
author_names: Mitsuo Kawasaki
title: Lawrence Berkeley National Laboratory Recent Work Title Observation of the Initial Stages of Growth of Hydrogenated Amorphous Carbon Films by Scanning Tunneling Microscopy
year: 2013

abstract: The most important methods for studying the surface of amorphous diamond like carbon are scanning tunneling microscopy and scanning tunneling spectroscopy. In this review, publications concerned with studying the topography and electronic properties of the surface of amorphous diamond like carbon films using a tunneling microscope are considered; related publications devoted to the microprobe study of field emission from amorphous carbon and to the tunneling microscopy of metal carbon nanocomposites are also reviewed.
author_names: V I Ivanov-omskii

A B Lodygin

Sergey Yastrebov
title: The scanning tunneling microscopy and scanning tunneling spectroscopy of amorphous carbon
year: 2000