A. Barna

Amorphisation and surface morphology development at low-energy ion milling

Abstract Amorphisation and surface morphology development of Si and GaAs was studied by means of XTEM after ion bombarding at various low energies in our novel ion milling unit. In this device, the specimen is rotated and the ion energy can be reduced down to 0.12 keV. It was shown that the thickness of the amorphised layer is about 1 nm for Si/0.25 keV, and not observed for GaAs/0.25 keV and Si/0.12 keV. This amorphisation is much thinner than those measured at higher energies, e.g. 5 nm, 2.1 nm for Si/3 keV, GaAs/1.6 keV. Dynamic TRIM simulation could be successfully applied for the description of amorphisation. It will be shown for the first time that the interface roughness also decreases with decreasing ion energy.

FORMATION PROCESSES OF VACUUM-DEPOSITED INDIUM FILMS AND THERMODYNAMICAL PROPERTIES OF SUBMICROSCOPIC PARTICLES OBSERVED BY IN SITU ELECTRON MICROSCOPY

The formation of vacuum-deposited In thin films was studied by in situ electron microscopy. The dependence of melting point and crystallization temperature on particle size was measured. A preferred orientation was found to develop at a given crystallite size depending on the substrate temperature and on the ratio of impinging oxygen molecules to film atoms (K factor).

Crystallization processes in a-Ge thin films

Abstract The authors studied the nucleation rate and the rate of crystal growth in a-Ge films, paying particular attention to the effects of residual gases. Activation energies for the relevant processes were obtained.

TEM sample preparation by ion milling/amorphization

Abstract Artefacts evolved during TEM sample preparation by ion milling are discussed. Possibilities are given to minimise the amorphization/damage of the ion milled samples. A new type of low energy ion gun is applied in the ion milling device; ion beam induced artefacts are minimised, as shown for samples of GaAs and Si.

Ultrahard coatings from Ti-BN multilayers and by co-sputtering

Abstract Two new techniques for the preparation of very hard Ti-B-N coatings are presented. The first method is accomplished in two steps: (i) the deposition of a multilayer coating of the sequence Ti-BN by reactive or non-reactive sputtering from a titanium and a hexagonal BN target respectively; (ii) a subsequent thermal treatment of the multilayer to induce a diffusion-activated mixing process between the titanium and BN layers with consequent phase transformations. The coatings were characterized with respect to stoichiometry by X-ray photoelectron spectroscopy with respect to structure by glancing angle X-ray diffractometry and with respect to hardness and residual stress by micro-indentation and the substrate-bending method respectively. Hardness values up to 6000 HV were observed at a concentration ratio [ Ti ]:[ B ]:[ N ] = 1:0.5:0.4. The coting with this compositional ratio is assumed to comprise a mixture of two solid solutions of the type Ti(B x ,N x ) and TiN 1-x (B y . Thsi new technique has the advantage that almost stress-free coatings with good adhesion to metallic and non-metallic substrates are obtained. The second method is a co-sputtering process from a titanium and BN target. With this method coatings of considerable compressive stress are obtained.

Computer simulation of the post-nucleation growth of thin amorphous germanium films

Abstract The very early stage of formation of amorphous germanium films by vapour deposition is simulated. A simplified model is considered. In the post-nucleation stage particles are formed by an atom-by-atom building process. Re-evaporation of adatoms and migration along the edge of already formed particles are taken into account. An upper limit is obtained for the maximum edge migration distance for which irregularly shaped particles can still be formed within our model. From the results it is concluded that, during the formation of thin evaporated amorphous germanium films which show a supernetwork with irregularly shaped particles of high density, self-surface diffusion or diffusion along the edge of a particle cannot be significant.

In situ electron microscopy of thin film growth

Corresponding to the demands in the investigation of different thin film phenomena, the in situ electron microscopic technique has been developed in different directions. A review of such development is given. Furthermore, experimental conditions ensuring reliable quantitative results are discussed. The phase transitions occuring during thin film growth, i.e. liquid-crystal-line, and amorphous-crystalline transitions are dealt with, demonstrations being given by the examples of In, Ge and Sb films. The discussion is focused on the effect of gaseous contamination on the processes.

Analysis of the development of large area surface topography during ion etching

Abstract The model, considering the lateral displacement and collective behaviour (annihilation) of surface macrosteps together with the dependence of the local etching rate on the material properties, is proved to be able to predict the development of the surface topography at various etching parameters (incidence angle of the ion beam, static or rotating sample, sputtering gas) 1,2 . The model has been applied for single crystalline (Si, Al) and polycrystalline (Ti, Cu) materials. The effect of sample rotation and rocking on the topographical development is discussed in dependence on the ion beam incidence angle. It is shown that surface polishing can be achieved for all kinds of samples using adequate parameters; however, there is a limit for the smoothness depending on the sample material and sputtering gas.

Design of a new vacuum deposition specimen holder for an electron microscope operating at 10−8 torr

Abstract The authors have developed a specimen holder for in situ vacuum deposition of thin films in the pressure region of 10−8 torr. Substrate temperatures can be measured to ±4°C over a range of —150°C to +400°C. The residual pressure can be measured during operation by a cold-cathode ionization vacuum gauge in the vicinity of the specimen. UHV is achieved by surrounding the specimen with a cooled cartridge pumped by the gauge working as a getter ion pump.

Hardness, stress relaxation and microstructure of TiBN multilayer coatings

Abstract Multilayer coatings of a TiBN layer sequence have been prepared by sequential sputtering from a Ti cathode and a h-BN cathode. These layers were subjected to thermal treatment at 400°C by which a hardening process as consequence of interdiffusion was observed. Hardness values of up to 60 GPawere obtained. In contrast to most other hard coatings these TiBN coatings display only small macroscopic stress of the order of ±1 GPa as measured by the substrate bending method. Tensile or compressive stress can be engineered by correctly choosing the repeat thickness and the individual layer ratio. TEM investigations suggest that these low stress values are due to an internal stress relaxation process. The individual multilayers are subjected to a high microscopic internal stress resulting in fragmentation into very small pieces of about 50 nm. This is supported by the strong bending of these fragments as observed in the TEM micrographs.