B. Enders

Carbon nitride thin films formed by low energy ion beam deposition with positive and negative ions

Abstract Carbon nitride became an attractive system for the search of new functional materials since the existence of crystalline carbon nitride was predicted in 1989. Up to now the research in this field is focused mainly on the realization of the hexagonal phase of C3N4, whose properties have been proposed to be of low-compressibility, having a high thermal conductivity, a high optical band gap and insulating character. Ion beam deposition with mass analyzed positive and negative ions is a new technique for depositing thin films under well characterized conditions. With the Positive And Negative ion Deposition Apparatus (PANDA) the simultaneous deposition of low energy carbon and nitrogen ions under ultrahigh vacuum conditions is possible. Depositions were performed on silicon wafers under change of ion species and transport ratios. Rutherford backscattering was used as well as infrared and Raman spectroscopy in order to get compositional and structural information of the deposited thin films. The results are presented together with an overview of carbon nitride solids reported in the literature.

Optical properties of carbon and carbon nitride films prepared by mass-separated energetic negative carbon and carbon nitrogen ions

Carbon and carbon nitride (CN) films were prepared under ultrahigh vacuum condition by ion beam deposition using isotopically mass-separated, energetic (50–400 eV) negative 12C2− and 12C14N− ions, respectively. The optical properties as well as structures and chemical composition of the films have been characterized and discussed as a function of the kinetic energy of C2− and CN− ions. The structures of carbon and CN films in this study were hydrogen-free amorphous carbon (a-C) like. The N/C composition ratio of the CN films was N/C∼0.4, although the arrival ratio of N/C was N/C=1. The CN film properties depended weakly on kinetic energy of CN− ions, while on a-C films there were kinetic energy dependence of C2− ions of optical constant observed.

Kinetic energy influence of hyperthermal dual ion beams on bonding and optical properties of carbon nitride films

Carbon nitride films were produced by simultaneous irradiation of well-defined hyperthermal (50–400 eV), isotopically mass-separated 12C2− and 14N+ ions with various kinetic energy combinations. It was found that the intensity of CN-triple bonds normalized by the amount of nitrogen atoms in the films and the complex refraction index (n,k) are correlated with the energy combination of 12C2− and 14N+ ions.

Corrosion properties of ion beam modified fullerene thin films on iron substrates

The corrosion behavior of fullerene coated iron samples was investigated by using electrochemical techniques. Fullerene was deposited on iron substrates via thermal evaporation under high vacuum conditions. Subsequent sample preparation included heat treatment as well as Ar+ ion irradiation under various conditions, which were carried out to modify the fullerene coatings. Changes in the structure of the films due to the treatment were analyzed by Raman spectroscopy. To reveal the samples’ corrosion behavior, cyclovoltammetric measurements were performed in a weakly acidic aqueous medium particularly with regard to possible corrosion protective properties. As the results show, Ar-ion treatment of the fullerene films leads to considerably increased corrosion resistance, which is due to formation of a dense amorphous carbon network. In contrast, heat treatment of the fullerene films increases the corrosion rates, presumably due to formation of iron carbide, which leads to galvanic corrosion.

Ion beam assisted deposition under off-normal ion incidence : an experimental and analytical study of re-sputtering effects

Abstract Ion beam assisted deposition (IBAD) is a coating technique which combines the condensation of a material and ion bombardment. Ion bombardment strongly affects not only the features of the growing film such as composition or microstructure but it also leads via re-sputtering processes to a loss of condensating material. This mostly undesirable effect reduces the film growth velocity and may become critical when the ion impact angle deviates from the substrate surface normal. Because material modification processes including deposition and ion bombardment are more and more transferred into industrial application, the knowledge of angular-dependent re-sputtering yields is of utmost importance for applicability of the process to component parts or workpieces. In the present study cylindrical samples were coated with several monoelemental films by means of ion bombardment during electron beam evaporation and also the decoupled process of bombardment after deposition. Thickness losses for the ‘dynamic’ and ‘static’ process are determined with Rutherford Backscattering Spectroscopy. An analytical equation is applied which describes the thickness reduction over all angles of ion incidence including an expression for the angular dependence of the re-sputtering yield with only three adjustable parameters. A correlation is found between these parameters and the film’s atomic number and surface binding energy. Furthermore, the results are discussed in terms of whether a ‘dynamic’ re-sputtering yield exists or the ‘static’ process gives an appropriate description of ion beam-induced re-sputtering during deposition.

Protection of cylinders by ion-beam sputter deposition: corrosion of carbon-coated aluminium tubes

In application, cylinders and tubes may chemically fail when they are exposed to aggressive media. As for other objects, coating with a protective film may improve the situation. However, coating the inner walls of hollow objects, such as tubes, by means of physical vapour deposition techniques is not feasible, because the material to be deposited has to enter the tube under very flat angles to the surface normal of the walls, depending on the ratio of the inner diameter to the tube length. This problem can be overcome when the source of the material to be deposited is located inside the tube. This is possible when sputter deposition is performed with an ion beam. A sputter target is located inside the tube; energetic ions are accelerated into this tube and impinge onto the target. Thus, material is sputtered from the target onto the inner walls of the tube. With this technique, aluminium tubes were coated inside with thin, amorphous carbon films. The corrosion performance in an aqueous chloride-containing environment, where aluminium suffers from pitting corrosion, was evaluated by means of electrochemical polarisation measurements. These showed that the films exhibited low microporosity with a good corrosion protection effect when appropriate deposition process parameters were used.

Electrochemical porosity evaluation of thin films on iron base materials

Corrosion properties of bulk materials coated with thin protective films are not only dependent on the electrochemical properties of the bulk materials and the intrinsic corrosion properties of thin protective films but also to a high degree on the films porosity. It is therefore necessary to know about the porosity in order to be able to control and optimize it with the deposition process. In this contribution we introduce a technique to measure the porosity by means of an electrochemical technique. Model systems are chosen, i.e. thin iron films deposited on silicon wafers were coated with tungsten and carbon thin protective films. The depositions were done with coaxial arc deposition, evaporation, and plasma immersion ion assisted sputter deposition. Raman measurements, Rutherford backscattering spectroscopy, raster electron microscopy, atomic force microscopy and electrochemical measurements were carried out to characterize the films.

Ion-beam deposition with positive and negative ions

Abstract Recently, we have developed a new apparatus for low-energy, mass-analysed, dual-ion-beam direct deposition. The facility has two sets of ion sources, sector-type 90 ° mass analysing magnets and beam lines including deceleration lenses for the positive and negative ions. Positive and negative ions merge at the substrate surface with incident angles of 30 ° and −30 ° with respect to the surface normal. The ion-beam energy can be varied between 10 eV and 20 keV. Because of this wide energy range of about three orders of magnitude, the apparatus allows ion-beam deposition and ion implantation experiments to be conducted under ultrahigh vacuum (UHV) conditions. A typical ion-beam current is 10 μA or more depending on the ion species and energy; the beam size is 10 mm or more in diameter. The base pressure of the deposition chamber is of the order of 10 −8 Pa and the pressure during operation is about 10 −6 Pa. The machine enables positively and negatively charged ions to be deposited simultaneously or separately. In such a way, it is possible to form high-purity binary compound films on conducting and insulating substrates. Furthermore, the facility is useful for studying the fundamental processes of ion-beam deposition and/or ion-surface interactions. The machine is called TAOTRON; its nickname is PANDA which stands for positive and negative ion deposition apparatus. In this paper, the construction and characteristics of the facility are reported, together with a concise historical view of its background. Preliminary results obtained by this new technique are presented.

Low energy ion beam deposition with positive and negative ions – experiments to and modeling of subsurface growth

Ion beam deposition with mass-analyzed positive and negative ions is a new technique for depositing thin films under well-characterized conditions. With Positive And Negative ion Deposition Apparatus (PANDA) the simultaneous deposition of positive and negative ions under ultra-high vacuum conditions as well as the use of single beams is possible. In the present contribution we present a subplantation model for low-energy ion species including sputtering and decoverage during sputtering. With the related program code it is possible to get composition profiles as well as a comparison between the arrival ion fluence and the subplanted amount. The results of the model are compared to carbon and gold depositions on silicon wafers. It is shown, that in both cases of carbon and gold subplantation an almost linear deposition behaviour is found for fluences less than 1018 ions/cm2. For carbon depositions that nearly linear behaviour arises from the similar and moderately low self-sputtering yields and for gold subplantations it is due to surface silicon which protects the underlying gold from being sputtered.

Characterization of carbon nitride films produced by simultaneous low energy dual ion beams irradiation

Abstract CN films were deposited using simultaneously positive 14 N + and negative 12 C 2 − ions (50–400 eV) under high vacuum condition. The film structure and the C-N bonding states in the films were investigated as a function of kinetic energy combinations of C 2 − and N + through Rutherford backscattering spectrometry (RBS), Fourier transform infrared absorption spectroscopy (FTIR) and Raman scattering results. The film structure was amorphous carbon-like. The order of carbon network and a fraction of various kinds of C-C and C-N bonds in the films were found to be correlated with the kinetic energy of N + ions.