Search

We used the mechanically controllable break junction technique to discriminate between the electric field and temperature effects in the process of surface modification. The electric field strength at the surface of electrodes was accurately determined using the field emission resonance spectra and was gradually raised to the point where surface modification starts. We found that only a limited number of metals with large values of the work function, >=4.5–5 eV, and evaporation fields, <=1.5–2 V/Å, can be modified in this way. Adsorption of He on the surface drastically increases the local work function of material and enables the field induced nanostructuring of the electrode surface practically for all metals. [ABSTRACT FROM AUTHOR]

High magnetic fields were used for the alignment of J-aggregates of cyanine dyes in solution leading to strongly polarized optical properties, yielding a maximum dichroic ratio of 13. The aligned aggregates were fixed by gelation resulting in samples that are stable at room temperature and exhibit strongly polarized absorption and emission spectra. [ABSTRACT FROM AUTHOR]

Presents information on a study conducted which investigated the growth temperature and magnetic magnetic properties of epitaxial Fe layers on MgO(001). Characteristics of MgO(001); Examination of the low-energy electron diffraction of the Fe layers; How the Fe layers were grown; Assessment of the magnetic properties of the films; Methods of the study; Results of the study.

Examines the edge effects in the magnetoconductance of macroscopic samples of near-intrinsic germanium near room temperature as a model system for an ambipolar conductor. Cause of the spatial variation of the density of charge carriers; Estimates for the surface recombination velocity and the bulk recombination rate; Relation between the ratio of the two four-terminal resistance and proportionality factors.

Spin-polarized scanning tunneling microscopy has produced a great amount of images presenting magnetic contrast between different magnetic domains with an unsurpassed spatial resolution but getting values like the surface polarization has proven to be a difficult task. We will discuss in detail how to extract this information for the case of manganese layers grown on Fe(001) whiskers. Mn layers adopt a body-centered-tetragonal (bct) structure when they are grown on the Fe(001) surface at room temperature. The Mn layers show an antiferromagnetic coupling between the layers. Comparing our spin-polarized scanning tunneling spectra measured with Fe-coated W tips with spin-resolved band structure calculations, we are able to find the value of the sample surface polarization. Also discussed is a method to change the tip magnetization. Finally, the magnetic structure around a screw dislocation on the surface is reviewed. Microsc. Res. Tech. 66:93-104, 2005. © 2005 Wiley-Liss, Inc. [ABSTRACT FROM AUTHOR]

We have designed and built a low-temperature (1.3-4.2 K) scanning-tunneling microscope which is capable of collecting light that is generated in the tunneling region. Light collection is done by means of two fibers whose cleaved front is in close proximity (approx. 1 mm) to the tunneling region. The whole system can be operated in high magnetic fields (11 T) without loss of optical signal strength. As a demonstration, we measured the electroluminescence spectra of an InGaAs quantum well at various temperatures. At 4.2 K, we found an electron-to-photon conversion factor that is three orders of magnitude higher than at room temperature. © 2001 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Presents an accurate method for calibration of the relative displacement of mechanically controllable break junction electrodes and determination of the metal work function using oscillating behavior of tunnel conductance in a field emission region. Junction conductivity in the field emission region; Accuracy of the method.

Reports on an adaptation of the mechanically controllable break junction technique using thin metallic films to create point contacts and tunnel junctions. Presentation of point-contact spectra of some materials and tunneling data to illustrate the possibilities offered by the method.

Presents a sensitive capacitance thermometer at low temperature for use in magnetic fields. Temperature range; Sensitivity of the thermometer at low temperatures; Reproducibility of the thermometer.

Describes the design and performance of a low temperature scanning tunneling microscope (STM) setup that can be used in magnetic fields. Sensitivity of the instrument to external vibrations; Influence of external magnetic fields on the performance of the STM; Spectroscopic capability.

A scanning tunneling microscope (STM) has been developed, dedicated for use on artificially fabricated nanostructures at low temperatures. With this STM mesoscopic phenomena can be studied, combining the unique possibilities of scanning tunneling microscopy and artificially fabricated nanostructures for investigating the physics in this regime. The STM is vibration insensitive, has reliable coarse approach mechanisms in three dimensions, and operates at low temperatures. In order to be able to position the tip above the structure of interest, also a searching strategy has been developed. In this article we describe design and operation of the STM and demonstrate searching. [ABSTRACT FROM AUTHOR]

We investigated the behavior of piezoelectric elements used in an STM for fine positioning of the tip. Special attention was paid to the influence of hysteresis. We found that the expansion coefficient of the elements depends on the magnitude of the displacements they produce. If the range is limited to several nanometers, the sensitivity can be taken constant and hysteresis can be neglected. However,if displacements of about a micron are involved, the sensitivity is about 40% higher and the hysteresis will significantly disturb the image. We also compared different calibration methods. An inductive displacement transducer yields results which correspond to those obtained with the known height of steps on a flat gold surface. A Michelson interferometer yields results which are valid for large displacements which cannot be used if small-scale structures are imaged. [ABSTRACT FROM AUTHOR]

We have constructed a double point-contact system for use at liquid-helium temperatures which is adjustable from the outside. Both point-contact wires can be independently displaced vertically with a travel of 5 mm and horizontally with a travel of 4 mm. Displacements of 5 μm can be achieved. The sample table is rotatable over 360° and can be translated over 2 mm, which implies that point-contact wires can be placed at any desired position of a sample. Moreover, the point-contact wires and the sample can be viewed from the outside to check positions and a magnetic field up to 1.2 T can be applied. The point contacts obtained with this system are both mechanically and electrically stable, also in a magnetic field. The instrument is of great use for transverse electron focusing studies of transport properties of metals, surfaces, and interfaces. Because of versatility, the instrument is also suitable for single point-contact experiments to study interfaces of normal metals and superconductors or to perform point-contact spectroscopy experiments. [ABSTRACT FROM AUTHOR]

We have constructed a scanning tunneling microscope for operation under UHV conditions (10-8 Pa). With this instrument topographic measurements can be made on metal and semiconductor surfaces by means of a scanning tip electrode, driven by piezoelectric ceramic elements. The maximum area covered ranges up to 4000×4000 Å2 with a resolution better than 10 Å laterally and 0.15 Å rms perpendicular to the plane. Because of its compact design, the scan unit is very insensitive to vibrations and has a response time down to 0.3 ms. This allows a high scan rate to be used. In order to minimize temperature effects, special attention is paid to the geometry of the construction and the materials used, resulting in a drift ≤4 Å/min along the surface and 0.5 Å/min perpendicular. [ABSTRACT FROM AUTHOR]

Holographic transmission electron microscopy showed that magnetic flux does not diverge from the top of an Fe-coated W tip indicating the in-plane magnetization at the apex of successful spin-polarized tips. A dependence of differential conductivities of GaAs with Fe-coated W tips on the helicity of illuminating laser light was confirmed at negative sample bias where partially spin-polarized electrons in the conduction band of p-GaAs tunnel into spin-dependent Fe empty states while no dependence of those with nonmagnetic W tips. [ABSTRACT FROM AUTHOR]