摘要:

The physical principles of low energy electron microscopy (LEEM) are discussed. The application of this nonscanning imaging method to the study of surface phenomena on the 10 nm scale is illustrated by examples of the growth and desorption of metal films on metal and semiconductor substrates as well as by phase transitions in these films.

ISSN:0734-211X    

DOI:10.1116/1.585581

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

Using electroluminescence associated with scanning tunneling microscope in AlxGa1−xAs heterostructures, we show that: (a) luminescence due to recombination can be induced within single quantum wells of dimensions down to a few nm and can also be used to image them, (b) the energy of bulk bands can be determined, and (c) transport parameters can be measured, e.g., the thermalization length and the diffusion length of minority electrons. This technique opens up new possibilities for the study and characterization of semiconductors and devices—including the possibility of studying surface states and single trapping centers associated with lattice defects, impurities, chemisorbed species, etc.

ISSN:0734-211X    

DOI:10.1116/1.585582

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

The consequences of tip–substrate interactions are investigated using large‐scale molecular dynamics simulations for a large (001) gold tip and a Ni(001) surface. The simulations reveal processes of adhesive contact formation upon approach of the tip to the substrate, tip elongation, and formation of an extended ordered neck upon retraction of the tip from contact, (111) reconstruction of the interfacial gold layers and the atomistic mechanisms of tip flattening and increase in contact area upon compression past the adhesive contact point. The hysteresis in the force versus tip to sample distance relationship, found upon approach and subsequent separation of the tip from the sample, is related to processes induced by adhesion and intermetallic bonding. The atomic‐scale mechanisms underlying the jump‐to‐contact phenomenon at small tip to surface separation (∼4.2 Å) and of the inelastic processes and structural transformations involved in tip elongation, neck formation, and tip compression are discussed, and the results are compared to our earlier studies of a nickel tip interacting with a gold surface.

ISSN:0734-211X    

DOI:10.1116/1.585583

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

The early stages of Si(111)‐7×7 oxidation using scanning tunneling microscopy and scanning tunneling and photoemission spectroscopies have been studied. It has been found that there are at least two different oxygen‐containing sites being formed. Their different surface site distributions and behavior as a function of O2‐ exposure show them to be two distinct early products. By correlating the spectroscopic results and the results of theoretical calculations one is able to identify one of these products as involving an O atom tying up an adatom dangling bond with a second O atom inserted in one of the adatom back bonds, while the other involves a single O atom inserted in an adatom back bond. The preference of these products for the faulted half of the 7×7 unit cell and for corner‐adatom sites is explained in terms of a site‐dependent sticking coefficient involving a process analogous to the gas‐phase ‘‘harpooning’’ processes. It is shown that the majority of the resulting molecular precursors involve O2interacting with a single dangling‐bond site. Finally, mechanisms are proposed for the early steps of the oxidation process.

ISSN:0734-211X    

DOI:10.1116/1.585584

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

We present an overview of scanning force microscopy with applications to electrostatic, magnetostatic, and atomic forces operating in the contact and noncontact mode, and highlight the main achievements in this field.

ISSN:0734-211X    

DOI:10.1116/1.585585

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

A novel approach based on scanning tunneling microscopy controlled field emission with microlens to form an exceptionally high brightness electron source and low aberration electron probe forming system has been explored. Electron optical studies of such a microsource have shown it to have a brightness two to three orders of magnitude greater than conventional field emission sources at energies in the low keV range and the ability to form an ultrahigh resolution probe with diameter in the 1 to 10 nm range in conjunction with additional microlenses. Encouraging preliminary experimental results have been obtained.

ISSN:0734-211X    

DOI:10.1116/1.585586

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

We have fabricated III–V semiconductor quantum wires which display a variety of novel transport and optical phenomena. For the definition of structures with widths down to 40 nm high resolution electron beam lithography and dry etching have been used. For the observation of dimensionality dependent effects in optical spectra buried quantum wires have been developed by overgrowth of dry etched structures and implantation induced intermixing. The physical properties of the nanometer structures have been analyzed by magnetotransport studies and emission spectroscopy.

ISSN:0734-211X    

DOI:10.1116/1.585587

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

Scanning tunneling microscopy observations of homoepitaxial growth on vicinal Si(001) and of coarsening of Si islands are used to develop a model of growth based on a configuration‐dependent activation energy to hopping. In the model four contributions to this energy barrier are proposed: the activation energy to surface diffusionEs, the dimer formation energyEdand two directional interaction energies between neighboring atoms not forming a dimer,E∥andE⊥. Monte Carlo simulations are employed to compare experimental results with the results of the tested model and to deduce the atomic interaction energies:Es=(1.15±0.1) eV,Ed=(0.45±0.10) eV,E∥=(0.20+0.2−0.14) eV,E⊥=(0.10+0.1−0.07) eV. Preliminary results of simulations, including anisotropic diffusion, are presented.

ISSN:0734-211X    

DOI:10.1116/1.585588

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

Insituelectrochemical scanning tunneling microscopy (STM) was applied to single‐crystal platinum(111), rhodium(111), and palladium(111) surfaces in an aqueous sulfuric acid solution. Atomically flat surfaces of Pt(111) are roughened in solutions by the electrochemical oxidation–reduction cycle. It is shown that a single potential cycle causes the formation of many adatoms and very small clusters on the Pt(111) terrace. A steady‐state surface structure can be clearly observed after applying a few potential cycles. The STM image is composed of regularly arrayed islands whose diameter and height are in the ranges of 2–3 and 0.5–0.75 nm, respectively. Atomically flat terrace‐step structures can be also observed on Rh(111) and Pd(111) surfaces. The effect of oxidation–reduction cycle on these surfaces is also discussed.

ISSN:0734-211X    

DOI:10.1116/1.585589

出版商:American Vacuum Society    

年代:1991

数据来源: AIP

摘要:

The ability of scanning force microscopy to detect minute forces at high spatial resolution offers the possibility to systematically map the ever‐present van der Waals (VDW) forces between probe and sample. Rigorously based on macroscopic quantum field theory the presented analysis involves anabinitiocalculation of VDW forces in close relation to the experimental situation. It is shown that VDW forces directly reflect surface dielectric properties of the sample under investigation. Highly polar immersion liquids present between probe and sample are shown to significantly reduce VDW forces in magnitude. Additionally, some immersion media are found to cause a transition from attractive to repulsive interactions. The lateral resolution of VDW microscopy is estimated to be in the sub‐100 nm range. First experimental aspects concerning VDW force detection are presented.

ISSN:0734-211X    

DOI:10.1116/1.585590

出版商:American Vacuum Society    

年代:1991

数据来源: AIP