Bias voltage-dependent scanning tunneling microscopy images of a GaAs(110) surface with small Ag clusters (original) (raw)
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Physical Review B, 2002
Atomically resolved, voltage-dependent scanning tunneling microscopy ͑STM͒ images of GaAs͑110͒ are compared to the results of a one-dimensional model used to calculate the amount of tip-induced band bending for a tunneling junction between a metal and a semiconductor. The voltage-dependent changes in the morphology of the atomic lattice are caused by the four surface states of the GaAs͑110͒ surface contributing in varying relative amounts to the total tunneling current. Tip-induced band bending determines which of these states contributes to the total tunneling current at a given bias voltage, and thus has a profound influence on the voltage-dependent STM-images. It is shown that certain voltage regions exist, for which none of the surface states present at the GaAs͑110͒ surface can contribute to the tunneling current. For these voltages, tunneling occurs between the tip and bulk states of the sample through a surface depletion layer several nm wide. Nevertheless, we observe atomic, surface like corrugation for these circumstances.
Applied Surface Science, 1998
Using scanning tunneling microscopy, Coulomb blockade of tunneling electrons was realized on a simple metal/semiconductor system, by taking a sample of individual Ag clusters formed on the clean GaAs(110) surface. The second barrier of a two tunneling junction is at a space interval at the Ag/GaAs(110) interface, which is naturally formed due to a lattice match of the cluster and the GaAs(110) substrate. Images of differential conductance taken of the clusters by current image tunneling spectroscopy (CITS) demonstrate that the electron tunneling is closely related to detailed atomic structures of the clusters.
2012
Since more than twenty years it is known that deposition of Ag onto Si(111)-(7×7) leads under certain conditions to the formation of so-called "ring-like" clusters, that are particularly stable among small clusters. In order to resolve their still unknown atomic structure, we performed voltage dependent scanning tunneling microscopy (STM) measurements providing interesting information about the electronic properties of clusters which are linked with their atomic structure. Based on a structural model of Au cluster on Si(111)-(7×7) and our STM images, we propose an atomic arrangement for the two most stable Ag "ring-like" clusters.
Fixing the Energy Scale in Scanning Tunneling Microscopy on Semiconductor Surfaces
Physical Review Letters, 2013
In scanning tunneling experiments on semiconductor surfaces, the energy scale within the tunneling junction is usually unknown due to tip-induced band bending. Here, we experimentally recover the zero point of the energy scale by combining scanning tunneling microscopy with Kelvin probe force spectroscopy. With this technique, we revisit shallow acceptors buried in GaAs. Enhanced acceptorrelated conductance is observed in negative, zero, and positive band-bending regimes. An Anderson-Hubbard model is used to rationalize our findings, capturing the crossover between the acceptor state being part of an impurity band for zero band bending and the acceptor state being split off and localized for strong negative or positive band bending, respectively.
Influence of surface states on tunneling spectra of n-type GaAs (110) surfaces
2009
We show that surface states within the conduction band of n-type GaAs͑110͒ surfaces play an important role in reducing the tunneling current out of an accumulation layer that forms due to an applied potential from a nearby probe tip. Numerical computation of the tunneling current combined with an electrostatic potential computation of the tip-induced band bending ͑TIBB͒ reveals that occupation of the surface states limits the TIBB, thus leading to the limitation of the accumulation. As a result, the tunneling current out of the accumulation layer is strongly suppressed, which is in quantitative agreement with the experiment.
2002
Ga-rich GaAs (001) surfaces are successfully observed during high-temperature annealing by scanning tunneling microscopy (STM). With a substrate temperature of 550 C, reflection high-energy diffraction patterns and reflectance anisotropy spectra confirm a (4x2) Ga-stabilized surface. STM images clearly show alteration of the surface reconstructions while scanning. It is postulated that detaching and attaching of Ga adatoms may be the cause
Scanning tunneling microscopy of semiconductor surfaces
Surface Science Reports, 1996
This review describes advances in understanding the structural, electronic, and chemical properties of clean low-index semiconductor surfaces during the first decade following the advent of the scanning tunneling microscope (STM). The principles of STM are discussed together with the instrumentation required to perform STM measurements on semiconductor surfaces in ultrahigh vacuum. A comprehensive review of the structures of the clean, low-index surfaces of elemental and compound semiconductors is presented. These structures are discussed using the general physical principles that determine them.
Bulletin of the American Physical Society, 2009
and CREST-JST-We studied local optical properties of AlGaAs/GaAs multilayer structures by scanning tunneling microscope cathodoluminescence (STM-CL) spectroscopy, where low-energy (∼100 eV) electrons field-emitted from STM tips were used as bright excitation sources. The STM-CL measurements were performed at the (110) cross-sectional surface of the AlGaAs/GaAs multilayer structure. We found that the field-emitted electron beam (FEEB) diameter mainly determined the spatial resolution of this system in STM-CL spectroscopy by evaluating some contributors: the thermalization length and the diffusion length of generated hot electrons. We also clarified that the shift of the STM-CL measurement position from the STM tip position was caused by the FEEB angled from the surface normal.
Physical Review B, 2007
The electronic properties of shallow acceptors in p-doped GaAs{110} are investigated with scanning tunneling microscopy at low temperature. Shallow acceptors are known to exhibit distinct triangular contrasts in Scanning tunneling microscopy images for certain bias voltages. Spatially resolved I(V)-spectroscopy is performed to identify their energetic origin and behavior. A crucial parameter -the STM tip's work function -is determined experimentally. The voltage dependent potential configuration and band bending situation is derived. Ways to validate the calculations with the experiment are discussed. Differential conductivity maps reveal that the triangular contrasts are only observed with a depletion layer present under the STM tip. The tunnel process leading to the anisotropic contrasts calls for electrons to tunnel through vacuum gap and a finite region in the semiconductor.
Physical Review B, 2008
Cross-sectional scanning tunneling microscopy ͑STM͒ measurements on molecular beam epitaxy grown Mn doped GaAs͑110͒ at 5 and 77 K are presented. The enhanced mechanical stability of the STM at low temperature allows a detailed study of the electronic contrast of Mn atoms in the GaAs͑110͒ surface. According to reproducible and distinguishable contrast patterns of single Mn atoms, we present statistical evidence for a layer by layer identification of Mn atoms embedded in the first few monatomic layers of the crystal. A comparison with a bulklike theoretical approach reveals a semiquantitative agreement with the measurements. Remaining differences between theory and experiment indicate the influence of the surface as an important factor to understand the contrast of impurities close to the surface. Furthermore, we report the injection of transition-metal atoms into the surface. Finally, reproducible complexes consisting of a surface Mn and an adsorbate atom are found and manipulated.