scholarly journals Thickness-Dependent Band Gap Modification in BaBiO3

Nanomaterials ◽  
2021 ◽  
Vol 11 (4) ◽  
pp. 882
Author(s):  
Rosa Luca Bouwmeester ◽  
Alexander Brinkman ◽  
Kai Sotthewes
Keyword(s):  
Band Gap ◽  
Phonon Mode ◽  
Scanning Tunneling ◽  
Metallic State ◽  
Tunneling Microscopy ◽  
Breathing Mode ◽  
Oxygen Breathing ◽  
Wide Gap ◽  
Raman Response

The material BaBiO3 is known for its insulating character. However, for thin films, in the ultra-thin limit, metallicity is expected because the oxygen octahedra breathing mode will be suppressed as reported recently. Here, we confirm the influence of the oxygen breathing mode on the size of the band gap. The electronic properties of a BaBiO3 thickness series are studied using in-situ scanning tunneling microscopy. We observe a wide-gap (EG> 1.2 V) to small-gap (EG≈ 0.07 eV) semiconductor transition as a function of a decreasing BaBiO3 film thickness. However, even for an ultra-thin BaBiO3 film, no metallic state is present. The dependence of the band gap size is found to be coinciding with the intensity of the Raman response of the breathing phonon mode as a function of thickness.

Ge-Quantum Dots on SI(001) Tailored by Carbon Predeposition

1998 ◽  
Vol 533 ◽  
Author(s):  
O. Leifeld ◽  
D. Grützmacher ◽  
B. Müller ◽  
K. Kern
Keyword(s):  
Surface Roughness ◽  
Critical Thickness ◽  
Carbon Deposition ◽  
Compressive Strain ◽  
Second Step ◽  
Scanning Tunneling ◽  
Tunneling Microscopy ◽  
Island Nucleation ◽  
Facet Formation

AbstractThe morphology of Si(001) after carbon deposition of 0.05 to 0.11 monolayers (ML) was investigated in situ by ultrahigh vacuum scanning tunneling microscopy (UHV-STM). The carbon induces a c(4×4)-reconstruction of the surface. In addition, carbon increases the surface roughness compared to clean Si(001) (2×1). In a second step, the influence of the carbon induced restructuring on Ge-island nucleation was investigated. The 3D-growth sets in at considerably lower Ge coverage compared to the clean Si(001) (2×1) surface. This leads to a high density of small though irregularly shaped dots, consisting of stepped terraces, already at 2.5 ML Ge. Increasing the Ge-coverage beyond the critical thickness for facet formation, the dots show { 105 }- facets well known from Ge-clusters on bare Si(001) (2×1). However, they are flat on top with a (001)-facet showing the typical buckled Ge rows and missing dimers. This indicates that the compressive strain is not fully relaxed in these hut clusters.

Stm Studies at Electrochemically Controlled Interfaces

1994 ◽  
Vol 332 ◽  
Author(s):  
S.M. Lindsay ◽  
J. Pan ◽  
T.W. Jing
Keyword(s):  
Electron Tunneling ◽  
Point Contact ◽  
Localized States ◽  
Scanning Tunneling ◽  
Zero Field ◽  
Tunneling Microscopy ◽  
Dna Oligomers ◽  
Synthetic Dna ◽  
Quantum Point

ABSTRACTWe use electrochemical methods to control the adsorption of molecules onto an electrode for imaging in-situ by scanning tunneling microscopy. Measurements of the barrier for electron tunneling show that the mechanism of electron transfer differs from vacuum tunneling. Barriers depend upon the direction of electron tunneling, indicating the presence of permanently aligned dipoles in the tunnel gap. We attribute a sharp dip in the barrier near zero field to induced polarization. We propose a ‘tunneling’ process consisting of two parts: One is delocalization of quantum-coherent states in parts of the molecular adlayer that hybridize strongly (interaction ≥ kT) with Bloch states in the metal. This gives rise to a quantum-point-contact conductance, Gc ≤ 2e2/h at a height zo. The other part comes from the exponential decay of the tails of localized states, G = Gc exp{−2K(z − z0)}. Because measured decay lengths, (2K‘)−1, are small (≈ 1 Å), STM contrast is dominated by the contour along which G[z0 (x,y)] = Gc. Measured changes in z0 are used to calculate images which are in reasonable agreement with observations. We illustrate this with images of synthetic DNA oligomers.

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