Miko Marinov

Effect of ion bombardment on the initial stages of thin film growth

Abstract The influence of ion bombardment on the initial stages of silver deposition onto amorphous substrates was investigated. Pronounced adatom-depleted zones arise around larger crystallites, and coalescence begins earlier in the deposition process. A defined crystal orientation appears from the beginning of the condensation. The results are explained using the assumption of enhanced surface mobilities of both adatoms and crystallites. The possibility of application of ion bombardment for surface decoration is qualitatively investigates and discussed.

The change in the structure of vacuum-condensed hexagonal close-packed metal films on ion bombardment

Abstract Grazing electron diffraction showed that vacuum-condensed cadmium and cobalt thin films change their crystallographic structure on ion bombardment with 10 keV argon ions. Cadmium films show a 〈11 2 0〉 orientation of the crystals after bombardment; this orientation does not depend on their initial orientation and corresponds to the direction of minimum loss of energy per unit distance of the incident particles. The bombardment of cobalt films results in the transformation of the initial h.c.p. crystal structure to an f.c.c. modification. The f.c.c. crystals show a 〈110〉 orientation, i.e. they are once again oriented in the direction of the minimum loss of energy per unit distance of the impinging ions. The observed phenomena are discussed in terms of the existing concepts of the effect of bombardment of solids by charged particles in relation to its dependence on crystal structure.

Ferromagnetic Nanomaterials Obtained by Thermal Decomposition of Ferrocene

Ferromagnetic micro and nano particles that are chemically resistant have been obtained by thermal decomposition of ferrocenes in a tightly closed chamber at high pressures. The investigation is focused on the influence of decomposition temperature, work atmosphere, temperature-change rate and process duration. According to the conditions, Fe3C, Fe3O4 and pure α-Fe particles have been created. Their composition and structure have been studied by Mössbauer spectroscopy, Scanning and Transmission Electron Microscopy, Electron Probe X-ray Micro Analysis and Energy Dispersive X-ray Spectrometry. In a tightly closed chamber, all components obtained during the decomposition process remain there. This difference to the widely-used Chemical Vapor Deposition method is very important. It inhibits the decomposition process and growth of ordered structures, preventing the end materials to be separated from each other. During the process, iron is liberated from the ferrocene molecule. Experiments have shown that it is highly chemically active to carbon and oxygen. For example, creation of carbide occured in conditions that are not allowed according to the iron-carbon phase diagram valid for bulk iron. Parallel to the reaction of iron with carbon (according to work atmosphere), the surplus of carbon atoms causes emerging of carbon nanoparticles.

Fullerene macro structures

Abstract At an arc discharge with CH 4 present in the gas ambient, conditions were created stimulating the simultaneous formation of single layer fullerene structures, which after being covered by many layers, yield multiple layer structures. As a result well formed regions containing numerous spherical, conical and polyhedral macro forms of the order of several micrometers were grown. Also obtained were regions containing large quantities of nanotubes over 10 μm in length. A model is proposed to explain the structure built up. To aid in the pyrolytic growth of cover layers the temperature of the deposit was maintained high by the “inverse method”.

Carbon macrostructures obtained at AC arc discharge

The differences in arc discharge specifics at various locations on the inside of the plasma cord lead to the growth of different carbon structures. Amorphous and low order structures with many defects were observed along the periphery of the deposits. Radially directed layers containing very small size graphite crystals predominate in the regions close to the periphery of the deposit. Conditions favor bucky-tube growth in the deposit center regions, the carbon macrostructures formed represent columns separated well apart, a diverse range of bucky tubes oriented at random have been observed in the spaces between the columns. After etching it was found that graphite crystals directed perpendicular to the axis of the deposit are contained in the column structures. It is shown that due to discharge fluctuations there arise layers that terminate the process of deposit growth. In the periodic process of resublimation, at some locations the layer structure breaks up and multiple-layer spherical perfect formations are synthesized at high temperatures. A wide pore carbon material suitable as a catalyst has been grown.

Fullerene structure synthesis by DC arc discharge in ferrocene vapours

Abstract The DC discharge between carbon electrodes in Ar and ferrocene gas mixture ambient was used to obtain fullerene structures (FS) and FS with incorporated iron atoms. The used method has been developed by the authors and it supplies the electrode deposit growth with carbon from the ferrocene mainly. In contrast to the classical method for iron in fullerenes incorporation when iron or its compounds are inserted into the sublimated electrode and are supplied from there during electrode consummation, in the concerned method iron is provided to a substantial degree from the ferrocene, too. The existence of five already structured carbon atom rings in the ferrocene corresponds to the method when naphthalene is used for fullerene synthesis. This makes fullerene creation easier and increases the fabricated product quantity. The proposed gas mixture peculiarities and advantages are discussed. The differences and the advantages of the produced electrode deposits and the FS are pointed out and clarified.

Morphology and structure of gold, silver and copper layers obtained by sputtering during ion bombardment of targets from these metals

Abstract The mechanism by which gold, silver and copper layers are formed by sputtering during the ion bombardment of targets of these metals has been investigated experimentally. Empirical evidence is given to show that, during the bombardment of metal foils with an appropriate thickness under certain conditions with argon ions, sputtering on both sides of the target occurs, namely forward and transmission sputtering. Transmission electron microscopy, scanning electron microscopy and transmission high energy electron diffraction were used to study the morphologies and structures of the layers obtained by both types of sputtering. Some possible applications of such layers are suggested.

Ion bombardment in electron microscopy investigations

Abstract Transmission electron microscopy, transmission high energy electron diffraction, reflection high energy electron diffraction and scanning electron microscopy were employed to evaluate the possibilities of ion bombardment used in the preparation of electron microscope specimens. The experimental results show that the uncontrolled use of ion bombardment for thinning of metal foils, cleaning layers or crystal surfaces etc. may often lead to incorrect interpretation of the electron microscopy investigations. In contrast, it is stressed that controlled ion bombardment directly in the column of the electron microscope is a very useful method for the observation and study of some very interesting phenomena which occur to the structure of the specimens during ion bombardment.

Influence of ion bombardment on the surface structure of silicon single crystals

Abstract The structural changes in silicon single-crystal surfaces under ion bombardment were investigated using reflection high energy electron diffraction and gold decoration. It is established that the ion bombardment leads to complete amorphization of the initially single-crystal surface. With more intensive ion bombardment circularly symmetrical zones with higher densities of gold particles appear.

Specifics at obtaining buckytubes in an arc discharge

Due to a diversity of physical processes taking place during arc discharge burning, the conditions at different locations within the discharge space are not the same. The analyses conducted address above all the temperature differences that arise on the electrode surfaces. The question of how to manage the processes of sublimation and condensation is discussed.