Scanning tunneling spectroscopy reveals a silicon dangling bond charge state transition (original) (raw)
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Tunnel coupled dangling bond structures on hydrogen terminated silicon surfaces
The Journal of Chemical Physics, 2011
We study both experimentally and theoretically the electronic behavior of dangling bonds (DBs) at a hydrogen terminated Si(100)-2×1 surface. Dangling bonds behave as quantum dots and, depending on their separation, can be tunnel coupled with each other or completely isolated. On n-type highly doped silicon, the latter have a net charge of −1e, while coupled DBs exhibit altered but predictable filling behavior derived from an interplay between interdot tunneling and Coulomb repulsion. We found good correlation between many scanning tunneling micrographs of dangling bond structures and our theoretical results of a corresponding extended Hubbard model. We also demonstrated chemical methods to prevent tunnel coupling and isolate charge on a single dangling bond.
Surface Science, 1998
Atomic scale desorption and deposition of hydrogen (H) atoms on Si(001)-(2×1)-H and Si(001)-(3×1)-H surfaces have been studied using clean and H covered tips from a scanning tunneling microscope. We report desorption of H atoms from these surfaces at positive and negative sample bias voltages with a resolution of one to two atomic rows and atomic scale phase transitions from 3×1 structures to 2×1 structures and vice versa. At positive sample bias, phase transitions from the 3×1 to 2×1 structures are accompanied with a large number of dangling bonds on the newly crated 2×1 structures, because the desorption of H from the 2×1 structure occurs at a lower tunnel current than the formation of the phase transition. At negative sample bias <−5 V, the situation is reversed with the desorption from the 2×1 structure occurring at a larger tunnel current than the formation of the phase transition, and ''clean'' local 2×1 structures with few dangling bonds can be achieved. Using H covered tips and increasing the substrate temperatures of Si(001)-(2×1)-H surfaces to #400 K, opposite local phase transitions from 2×1 structure to 3×1 structures are also reported, but such phase transitions were only observed at negative sample bias.
Altering the Charge State of Surface Silicon Dangling Bonds using Nanoscale Schottky Contacts
2010
The study of surface defects, and in particular, dangling bonds (DBs) on semiconductor surfaces and at interfaces has been an area of interest for years. Interest has been driven from the unique characteristics of the DB, due to fact that the DB state lies within the bandbap of the semiconductor and can assume various charged states. Recently, we have demonstrated that negatively charged dangling bonds can act as a gate electrode to control the flow of current through single molecules. We have also shown that DB clusters enter into a tunnel coupled relationship at close distances providing a means to implement room temperature QCA schemes. In order advance these experiments, it is important to develop strategies that can control the charge state of DBs. This presentation will show that nanoscale Schottky contacts of Titanium disilicide on hydrogen terminated silicon surfaces can change the charge state of DBs. DBs created within the depletion region have a reduced charge compared to...
Applied Physics Letters, 1998
It has been demonstrated in this letter that spectral shifts arising from the tip-induced band bending on the lightly doped silicon can be eliminated by forming an accumulation layer in p-type silicon or an inversion layer in n-type silicon by using a Pt-Ir tip. Illumination is also required for n-type silicon in order to eliminate shifts associated with deep depletion caused by tunneling leakage currents. Using the approaches described herein, energy gaps of approximately 1.1 eV are determined for both p-type and n-type silicon. Furthermore, identical bias polarity is observed in current-voltage curves for both n-type and p-type silicon, and can be explained by the direction of the band bending induced by Pt-Ir on lightly doped samples. These results suggest that scanning tunneling spectroscopy can be used to reveal various features associated with surface states and bulk properties in lightly doped samples by using high work function metals such as Pt-Ir in place of lower work function metals such as W.
Chemical methods for the hydrogen termination of silicon dangling bonds
Chemical Physics Letters, 2007
Highly ordered hydrogen-terminated silicon surfaces are ideal testing grounds for molecular electronics. However, upon formation of these surfaces it is inevitable that some surface sites are not capped by hydrogen. These remaining dangling bonds can interfere with the chemical and electronic properties of nanostructures formed on the silicon surface. In this work, using scanning tunneling microscopy, high resolution electron energy loss spectroscopy and ab initio computational methods, we explore two chemical approaches to refining the hydrogen termination process. We investigate the utility of diimide (N 2 H 2) and N,N-diethylhydroxylamine (DEHA) as hydrogen atom sources that have the ability to cap dangling bonds.
Physical Review B, 2009
We present a comparative study of the electronic properties of the clean Si͑100͒ and the hydrogenated Si͑100͒:H surfaces performed with a low-temperature ͑5 K͒ scanning tunneling microscope. Various surface structures such as single silicon dangling bonds and bare silicon dimers created by local desorption of hydrogen atoms from the Si͑100͒:H surface are also investigated. The experimental scanning tunneling spectroscopy ͑STS͒ curves acquired locally on each of these structures are compared with STS measurements performed on the Si͑100͒ and Si͑100͒:H surfaces. First principle density-functional theory calculations of the projected local density of states, taking into account the influence of the dopant atoms ͑As͒, enable to assign the observed STS spectra.
Applied Physics Letters, 1994
Scanning tunneling microscopy has been applied to observe hydrogen-terminated Si(111) surfaces at room temperature. A clear image was easily observed for a Si surface prepared by rinsing in pure water with very low dissolved oxygen after removal of native oxide by 1% HF solution dipping. A smooth surface in an atomic scale was exhibited in a 50×50 nm area. Completely triangular-shaped holes were observed on the surface. The holes were surrounded by steps which were very likely directed toward 〈112̄〉. The treatment of the surface was remarkably stable even after a 3 h air exposure. Furthermore, nm size pits were found at the bottom part of the triangular-shaped holes. The results imply that the nm size pits appeared to be due to microdefects and that the pits might be the origin of surface etching at the Si surface.
Atom-resolved surface chemistry studied by scanning tunneling microscopy and spectroscopy
Physical review, 1989
We have used scanning tunneling microscopy and spectroscopy to study the reaction of Si(111)-(7X 7) with NH3. We have found that by use of topographs obtained at different energies, as well as atom-resolved spectra, reacted and unreacted surface sites can be imaged selectively. Thus we have been able to probe the spatial distribution of the surface reaction on an atom-by-atom basis. We find that there are significant differences in reactivity between the various dangling-bond sites on the Si(111)-(7X 7) surface. Specifically, rest-atom sites are more reactive than adatom sites and, moreover, center-adatom sites are more reactive than corner-adatom sites. We ascribe the reduced reactivity at adatom sites to the delocalized nature of their dangling-bond state. We suggest that a bonding interaction between adatoms and the Si atoms directly below them is responsible for this behaviora suggestion supported by electronic-structure calculations. Thus, while reaction at a rest-atom site can be considered a dangling-bond saturation process, reaction at an adatom site involves the formation of a hypervalent (fivefold-coordinated) adatom. We tentatively ascribe the reactivity differences between center and corner adatoms to differences in the strain they induce upon reaction on the dimer bonds. Atom-resolved spectroscopy allows us to probe interactions and charge transfer between surface sites, and for the first time, we can directly observe how chemisorption affects the substrate electronic structure at neighboring unreacted sites.
1992
Scanning tunneling microscopy measurements of local surface photovoltage of the Si(00 I) surface reveal the existence of local charging produced by the tunneling current. Since the tunneling current is confined to a region of near atomic dimensions, charge transport between surface and bulk electronic states is probed with high spatial resolution. The surface charge is enhanced while tunneling at the bonded, type-B atomic step and at specific point defects demonstrating atomic-scale variations in the charge dynamics .