C. Weissmantel

Structure and properties of quasi-amorphous films prepared by ion beam techniques

Abstract Ion beam deposition techniques offer interesting possibilities for the preparation of metastable quasi-amorphous films owing to a high local activation and rapid quenching on an atomic scale. This is demonstrated in the context of new results obtained with the following materials: (1) i-carbon with diamond-like properties; (2) hard BN coatings;(3) hydrogenated dopable a-Si. The film-forming processes and the layer properties observed are interpreted by a first approximation model based on the concept of rapidly collapsing thermal spikes.

Preparation and properties of hard i-C and i-BN coatings

Abstract The state of the art in preparing and investigating hard i-C films is discussed in the context of new experimental results. Such films, which are characterized by unusual hardness and high electrical resistivity, can be produced by using deposition techniques, such as plasma, ion beam or ion plating methods, in which ionized film-forming and/or inert species of sufficient energy are involved. Although crystalline fractions may occur, the basic structure of the layers was found to be amorphous. The results of electron diffraction analysis and electron energy loss spectrometry in conjunction with the relatively low mass density of the films suggest a structural model consisting of puckered n -fold carbon rings (where n = 3−8) with presumably tetrahedral cross-links. The physical properties of i-C coatings are reviewed with particular emphasis on microhardness, frictional behaviour, wear and corrosion protection. First results obtained for BN deposits indicate that similar i-BN structures can be prepared. Widespread applications of i-C and i-BN coatings, eventually in the form of composite layers together with other hard materials, are anticipated.

Preparation of hard coatings by ion beam methods

Abstract The activated growth of surface coatings under the influence of impinging ionized species has been investigated by beam techniques operating in high vacuum. A brief survey of the operating parameters using one or several beam bundles of ions or neutrals is given. Some results and problems are discussed in connection with the following processes: (1) nitriding of iron by low energy ion bombardment; (2) dual beam synthesis of silicon nitride and of hard carbon; (3) preparation of chromium-carbon and of hard carbon layers by ion beam plating from organic vapours. It is concluded that beam techniques can contribute to a better understanding of activated film growth at high rates of deposition. Moreover, ion beam methods offer interesting prospects for the preparation of special layer structures, particularly unusual film phases such as the hard i-carbon.

Ion-based growth of special films: Techniques and mechanisms☆

Abstract The effects of ion-solid interaction offer specific possibilities for the preparation and modification of thin solid films. Following a survey of experimental configurations some aspects of elementary mechanisms, in particular atomic mixing and the role of thermal spikes, are discussed. Recent results are presented under the following headings: (1) ion beam sputter deposition of epitaxial silicon; (2) ion beam sputter deposition of amorphous silicon and graphoepitaxy; (3) the ion-based formation of hard carbon layers by different ion beam techniques. Further trends and applications are outlined.

Structure and properties of transparent and hard carbon films

Abstract Hard, electrically insulating and optically transparent carbon layers have been deposited by condensing ionized molecular species, i.e. benzene. These layers exhibited macroscopic properties that could be described as “diamondlike”. High resolution electron microscopy revealed that these films can be interpreted as extremely fine-crystalline phases with coherently scattering regions of about 0.8 nm in diameter. The intensity functions obtained by electron diffraction are not consistent with those of a known carbon phase, but they may be represented by a superposition of the functions corresponding to diamond and graphite phases.

Preparation and characterization of ion-plated boron nitride

Abstract After reviewing techniques for the ion-enhanced deposition of BN, we describe an ion plating apparatus consisting of an electron beam evaporator, an ionization chamber and a substrate holder. The processes involved in the evaporation of boron and the ionization of NH3, especially the generation rate of ions, are calculated. A concept for the analysis of the coatings is outlined. Chemical reaction between boron and NH3 occurs readily without ion support leading to a polymer-like deposit with a hydrogen content of 30 at.% and a low cross-linkage of boron and nitrogen bonds. The observed effects of ion enhancement are (i) a reduction in the hydrogen content to as low as 7 at.%, depending on the deposition parameters, and (ii) an increase in structure of the hexagonal BN type including cross-linkages. For substrate temperatures below 280 K, however, no significant ion effects with respect to the incorporation of hydrogen could be detected. Details of the predominantly amorphous structure could be obtained from electron diffraction and vibrational spectroscopy data. The films were found to exhibit compressive stresses which were reduced on annealing.

On the influence of residual stresses and density fluctuations on the crystallization of amorphous carbon films

Abstract Carbon films deposited from the vapour phase are often initially amorphous. Relaxation processes result in subsequent crystallization. The nucleation of crystalline phases is investigated in carbon films prepared by laser pulse vapour deposition as well as by ion plating. Residual compressive stress and a high local mass density favour nucleation.

Nitride film deposition by reactive ion beam sputtering

Abstract Ion beam sputtering has been employed for reactive film preparation and investigations of the mechanism of reactive film formation in the pressure range of 10-3 Pa. The growth rate, composition and resistivity of the films were studied as functions of the ion energy and sputtering yield. Particular attention was given to the location of the reaction zone and to the kinetics. Si3N4 and AlN were chosen as model substances and were synthesized by sputtering silicon and aluminum with an N2+ ion beam. The results indicate that the reaction takes place on the target and that the film composition depends on the sputtering yield of the target materials. By means of two ion beams, the first consisting of Ar+ ions which sputter the target and the second consisting of N2+ ions which are directed onto the growing film, an ion-induced synthesis of the compound was achieved on the substrate. In the case of Si3N4 formation, the same reaction yield of 0.32 has been found for both the target and the substrate reaction.

Hard films of unusual microstructure

Abstract Investigations of the ion-activated formation of hard carbon (i-C) films have demonstrated that the condensation of energetic particles may result in the growth of deposits with unusual more or less amorphous microstructure. In this context the question arises whether metastable “i phases” can also be prepared from other materials, and preliminary results obtained for metal-carbon and B-N coatings are presented. It is concluded that intensified research in this field could lead to a better understanding of metastable film structures and offer new ways of applying them.

Ion beam techniques for thin and thick film deposition

Abstract Film deposition techniques in which a considerable fraction of ionised species are involved, have found growing interest for applications on laboratory and industrial scale. Investigations using ion beams or mixed fluxes of ions and neutrals can contribute to a better understanding of plasma deposition, and they offer new possibilities for the preparation of special layer structures. This is outlined in connection with recent work on ion beam sputtering, ion beam condensation and ion beam plating.