Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userFermi level pinning at the Ge(001) surface - A case for non-standard explanation
105
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
To explore the origin of the Fermi level pinning in germanium we investigate the Ge(001) and Ge(001):H surfaces. The absence of relevant surface states in the case of Ge(001):H should unpin the surface Fermi level. This is not observed. For samples with donors as majority dopants the surface Fermi level appears close to the top of the valence band regardless of the surface structure. Surprisingly, for the passivated surface it is located below the top of the valence band allowing scanning tunneling microscopy imaging within the band gap. We argue that the well known electronic mechanism behind band bending does not apply and a more complicated scenario involving ionic degrees of freedom is therefore necessary. Experimental techniques involve four point probe electric current measurements, scanning tunneling microscopy and spectroscopy.
rate research
Read More
Normal incidence 1 keV Ar$^+$ ion bombardment leads to amorphization and ultrasmoothing of Ge at room temperature, but at elevated temperatures the Ge surface remains crystalline and is unstable to the formation of self-organized nanoscale patterns of ordered pyramid-shaped pits. The physical phenomenon distinguishing the high temperature patterning from room temperature ultrasmoothing is believed to be a surface instability due to the Ehrlich-Schwoebel barrier for diffusing vacancies and adatoms, which is not present on the amorphous material. This real-time GISAXS study compares smoothing of a pre-patterned Ge sample at room temperature with patterning of an initially flat Ge sample at an elevated temperature. In both experiments, when the nanoscale structures are relatively small in height, the average kinetics can be explained by a linear theory. The linear theory coefficients, indicating surface stability or instability, were extracted for both experiments. A comparison between the two measurements allows estimation of the contribution of the Ehrlich-Schwoebel barrier to the self-organized formation of ordered nanoscale patterns on crystalline Ge surfaces.
We report on the energy level alignment evolution of valence and conduction bands of armchair-oriented graphene nanoribbons (aGNR) as their band gap shrinks with increasing width. We use 4,4-dibromo-para-terphenyl as molecular precursor on Au(111) to form extended poly-para-phenylene nanowires, which can be fused sideways to form atomically precise aGNRs of varying widths. We measure the frontier bands by means of scanning tunneling spectroscopy, corroborating that the nanoribbons band gap is inversely proportional to their width. Interestingly, valence bands are found to show Fermi level pinning as the band gap decreases below a threshold value around 1.7 eV. Such behavior is of critical importance to understand the properties of potential contacts in graphene nanoribbon-based devices. Our measurements further reveal a particularly interesting system for studying Fermi level pinning by modifying an adsorbates band gap while maintaining an almost unchanged interface chemistry defined by substrate and adsorbate.
By combining scanning probe microscopy with Raman and x-ray photoelectron spectroscopies, we investigate the evolution of CVD-grown graphene/Ge(001) as a function of the deposition temperature in close proximity to the Ge melting point, highlighting an abrupt change of the graphenes quality, morphology, electronic properties and growth mode at 930 degrees. We attribute this discontinuity to the incomplete surface melting of the Ge substrate and show how incomplete melting explains a variety of diverse and long-debated peculiar features of the graphene/Ge(001), including the characteristic nanostructuring of the Ge substrate induced by graphene overgrowth. We find that the quasi-liquid Ge layer formed close to 930 degrees is fundamental to obtain high-quality graphene, while a temperature decrease of 10 degrees already results in a wrinkled and defective graphene film.
We investigate the valence band structure of Pb on Ge(001) by Angle-Resolved Photoelectron Spectroscopy. Three Ge bands, G1, G2, and G3, were observed on Ge(001) 2x1 clean surface. In addition to these three bands, a forth band (R band) is found in the 2 ML of Pb coverage. The R band continues to appear even when the surface superstructure changed. The position of the R band does not depend on Pb coverage. These results indicate that the R band derives from Ge subsurface states known as surface resonance states. Furthermore, the effective mass of G3 is significantly reduced when this forth band exists. We found that this reduction of the G3 effective mass was explained by the interaction of the G3 and the surface resonance band. Consequently, the surface resonance band penetrates the Ge subsurface region affecting the Ge bulk states. We observed the hybridization between Ge states and the surface resonance states induced by Pb adsorption.
The role of Fermi arc surface-quasiparticle states in topological metals (where some Fermi surface sheets have non-zero Chern number) is examined. They act as Fermi-level plumbing conduits that transfer quasiparticles among groups of apparently-disconnected Fermi sheets with non-zero Chern numbers to maintain equality of their chemical potentials, which is required by gauge invariance. Fermi arcs have a chiral tangential attachment to the surface projections of sheets of the bulk Fermi Surface: the total Chern number of each projection equals the net chirality of arc-attachments to it. Information from the Fermi arcs is needed to unambiguously determine the quantized part of the anomalous Hall effect that is not determined at the bulk Fermi surface.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
