The group's research interests are quite diverse; problems which are important from fundamental science point of view and also those which are technologicaly important are addressed. Attempts are being continuously made to modify existing techniques, whenever required to meet specific aims, for example ESR-STM attempts to exploit atomic resolution capability of STM to detect single spin centers. Another example is the attempt to use AFM in the fabrication of submicron and nano devices.

Running Projects

* ESR-STM

* SPM fabrication of submicron and nano devices

* SPM investigations of partially disordered structures

* Microscopy of Heterogenous corrosion

ESR-STM
The main characteristic of the tunnel junction in the scanning tunneling microscope is its extremely small size - that leads to atomic resolution. We found that when this extremely small tunneling junction is placed in the neighbourhood of precessing paramagnetic spin centers, a small time dependent periodic rf component at the Larmor frequency is detected in the tunneling current. These components were found to be spatially localised and dependent on the type of spin center which is detected. For example, we could distinguish between silicon and iron spin centers according to their (different) frequencies. The frequency of the signals are modulated by magnetic field modulation, and as a result sensitivity enhancement with phase sensitive detection is possible. We are currently working on detection of the signal in time domain, with an emphasis on: (i) measuring the phenomenon in paramagnetic molecules, (ii) measuring spin-spin interactions and (iii) the capability of the technique to get spectroscopic information.

SPM fabrication of submicron and nano devices
It is generally accepted that the top-down approach for device fabrication (refining processes used to fabricate large devices in order to produce smaller ones) is not going to work as the size of devices continues to shrink. In such cases a new and novel approach would be required. SPM techniques are amongst the most promising candidates for nanodevice fabrication. We were able to fabricate nanosized diodes and transistors using the process of thermally assisted electromigration in semionic materials. When a semionic material is heated to a temperature of few hundred degrees Celsius, the ions start to diffuse. By approaching the surface of such a material with a (conducting) tip of an AFM, it is possible to repel (or attract) the doping atoms or ions by applying an electrical pulse. The pulse creates local heating because of energy dissipation, and the electric field induces a directional diffusion away from or towards the tip. In this way extremely small bipolar transistors were fabricated (down to 60 nm) which are smaller than existing ones. We are currently working on the reproducibility of this fabrication method. Future directions are to use this method for different materials and to connect the device to external pads in order to investigate the correlation between device structure and performance.

SPM investigations of partially disordered structures
The ability of the STM to provide structural information on a surface with atomic resolution in real space makes it independent of the translational periodicity which is essential for diffraction techniques. Therefore the information the STM can provide on partially disordred structures is unique. There is a lot of interest, both from the scientific and the technological point of view, in the stochastic kinetic processes which lead to the formation of unique random structures on the surface. For example covering the surface with submonolayer coverage leads to the formation of vacancy islands. Upon heating, these islands grow and diffuse to the step which gets a random shape. Analyzing this shape by models of random deposition of particles with increasing size on a one dimensional interface led to an explanation of this structure as well as to a complete characterisation of the diffusion of vacancy islands. Other random structures are being analyzed in a similary way. We are also interested in partially amorphous surfaces and in the correlation between the amorphous structure and the physical characteristics (such as electronic structure) of different regions on the surface.

Microscopy of Heterogenous corrosion
The kinetics of the reaction of gases (for example hydrogen) with heavy (rare-earth) metal surfaces is studied. The reaction with different parts of the surface (point defects, grain boundaries, dislocations, etc.) will be studied in detail with atomic resolution. The stresses developed on the surface as a result of the accumlation of the reaction products inside the metallic matrix and the affect of such stresses on the continuation of the reaction will be explored. In addition reacting samples with different grain boundaries will be imaged and the affect of grain size as well as the affect of surface impurities such as oxides will be explored. We shall study these processes also on samples on which external stresses will be applied. These studies are performed in different temperatures with a UHV-STM, UHV-AFM and a scanning auger microscope which we have in our laboratory.

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