Intense ion bombardment has been necessary so far to produce cubic boron nitride thin films independent of the deposition technique used. Unfortunately, residual stress is one of the consequences of ion–surface interactions, leading to low adhesion and limited film thickness. In this study, boron nitride thin films were deposited by r.f.magnetron sputtering of a hexagonal boron nitride target combined with r.f. argon ion bombardment. The films were characterized by X-ray reflectivity analysis, X-ray Auger electron and infra-red spectroscopy as well as stress analysis. Stress reduction mechanisms are discussed: (1) deposition at higher substrate temperatures, (2) post-annealing, (3) post-ion implantation, (4) addition of a third alloying component, (5) multilayer concept, and (6) optimization of the deposition parameters.

Cubic boron nitride thin films were deposited by unbalanced r.f. magnetron sputtering of a hexagonal boron nitride target in a pure argon discharge in combination with r.f. argon ion bombardment. At a flux ratio of the argon ions relative to the film forming boron and nitrogen atoms of 20, and an argon ion energy of 87 eV, the total content of sp3-bonds of a 300 nm film amounts to 92.8%, according to infrared analysis. This film has a hexagonal interface between the silicon substrate and the cubic top layer which is estimated to be 15.6 nm on the basis of infrared spectroscopy as well as X-ray reflectivity. From the infrared investigations of the film thickness dependence it can be concluded that 72% of the sp2-bonds in the 300 nm c-BN film are formed in the hexagonal interface region, and only 18% between the cubic crystallites in the top layer. Consequently, the content of the cubic phase in the top layer amounts to 98.6%, which is in agreement with the density of 3.502 g/cm3 as determined by X-ray reflectivity measurements.

We present a combined experimental and theoretical study of the electron-impact ionization of helium at 44.6 eV incident energy. The absolute coplanar triple differential cross sections (TDCS) are measured in different geometrical arrangements, with the excess energy being equally shared between the two outgoing electrons. The measurements are compared with the convergent close-coupling (CCC) theory. The measured angular distributions of the TDCS are well reproduced by the calculations. Good agreement in magnitude is also obtained after the CCC results have been multiplied by a single factor derived from the comparison of the CCC and estimated true single differential cross sections. This suggests that the CCC theory yields accurate angular and, after rescaling, absolute distributions for all in- and out-of-plane geometries.

Exploiting the high brilliance of synchrotron radiation, we performed surface-sensitive and depth-resolved x-ray scattering experiments on thin films of boron nitride grown on Si(001) substrates. In-plane strains of different structural phases, namely turbostratic and cubic, grain sizes and textures were determined. Annealing the films up to temperatures of 1000 °C leads to large strain relaxation of about 70%, while the grain size stays constant at 80 Å.

We present a combined experimental and theoretical study of 32.6-eV electron-impact ionization of helium. The measured absolute coplanar triply differential cross sections are in the equal-energy-sharing (E-A=E-B=4 eV) kinematical region, and have been obtained in the fixed theta(A), fixed theta(B)-theta(A), and symmetric geometries. The convergent close-coupling calculations are in excellent agreement with experiment.

Nitrogenated and hydrogenated amorphous carbon (a-C:H:N) films have been deposited by a plasma beam source using a gas mixture of C2H2, Ar and N2. The Ar/C2H2 ratio is kept constant at a ratio of 3, with the nitrogen flow allowed to vary. Nonnitrogenated films, with Ar/C2H2 ratios of 3 and 6 were also deposited and analyzed before attempting to identify the modifications to the microstructural properties due to nitrogen doping. The nitrogenated and hydrogenated a-C (a-C:H:N) films deposited in this study reveal interesting properties with regard to their optical gap, electrical conductivity, and mobility of the charge carriers. The optical E04 gap passes through a maximum of 2.7 eV as a function of incorporated nitrogen. The electrical conductivity, too, reaches a peak value of 10−3(Ω cm)−1 with increasing optical gap and remains constant for higher N2 flows. The electrical conductivity process is thermally activated with activation energies in the range 0.1–0.3 eV. This is discussed in terms of the mobility of the charge carriers (determined by Hall measurements) and electronic doping. The defect density (measured by electron spin resonance) is found to decrease with increasing nitrogen incorporation. The films have also been characterized by infrared spectroscopy, photo thermal deflection, and Raman spectroscopy. The microstructure of the deposited a-C:H:N films is discussed in terms of the electronic density of states.

The similar crystalline structure of diamond and cubic boron nitride suggests the synthesis of superhard thin films containing boron, carbon and nitrogen. BCN thin films have been prepared by reactive r.f.-magnetron sputtering of a hexagonal boron nitride target in an argon/acetylene atmosphere of a constant pressure of 2 × 10−2 mbar. A deposition temperature of 600 °C leads to nearly hydrogen-free BCN films. At a flow ratio of 0.05% C2H2/Ar, the composition of the deposited BCN films is close to B5CN3 as a result of energy dispersive X-ray (EDX) and elastic recoil detection (ERD) measurements. By applying a r.f.-substrate bias, the ion energy has been varied at a constant ratio of ions to film-forming particles of 4. The BCN films show a maximum in stress at an ion energy of 110 eV due to knock-on subplantation of argon ions and a phase separation into carbon, boron and cubic boron nitride regions as a result of X-ray diffraction investigations. Auger electron- and infra-red spectroscopy.

Superhard amorphous boron carbide films with a film thickness of about 2 μm have been prepared by r.f.-magnetron sputtering of a boron carbide target in a pure argon discharge at a gas pressure of 1.6 × 10−3 mbar. The flux ratio of the argon ions to boron and carbon atoms has been kept constant at 3.5, while the energy of the argon ions is varied by applying a d.c.-substrate bias. The effect of argon ion implantation measured by Rutherford back scattering is discussed. When the argon ion energy is increased, the mechanical properties show extreme values at an argon ion energy of 74 eV, which can be explained quantitalively by knock-on subplantation. Stress up to 6.7 GPa and a micro-hardness up to 72 GPa are obtained. The hardness enhancement is correlated with the increase of stress. The influence of preferential sputtering of boron or carbon from the deposited B4C film can be neglected.

Amorphous carbon films with high sp3 content were deposited by magnetron sputtering and intense argon ion plating. Above a compressive stress of 13 GPa a strong increase of the density of the carbon films is observed. We explain the increase of density by a stress-induced phase transition of sp2 configured carbon to sp3 configured carbon. Preferential sputtering of the sp2 component in the carbon films plays a minor role compared to the sp2⇒sp3 transition at high compressive stress formed during the deposition process. Transmission electron microscopy shows evidence of graphitic regions in the magnetron sputtered/Ar plated amorphous carbon thin films. Differences in the microstructure of the tetrahedral amorphous carbon (ta–C) films deposited by filtered arc and mass selected ion beam; and those films deposited using magnetron sputtering combined with intense ion plating can be used to explain the different electronic and optical properties of both kinds of ta–C films.

ion=100 eV. Above E*ion the average density (deduced from X-ray reflectivity) shows a strong increase, indicating the sudden appearance of the cubic boron nitride phase consistent with the sp3 concentration deduced from IR absorption spectroscopy. The in-plane X-ray diffraction shows that this cubic phase consists of small nanocrystals of 70 Å linear size.

We present a combined experimental and theoretical study of double differential cross sections (DDCS) for electron-impact ionization of helium. Relative DDCS have been measured in a crossed-beam apparatus for primary energies 200, 100, 64.6, 50, 40, 32.6 and 28.6 eV. These are put on the absolute scale using the convergent close-coupling (CCC) calculations at 100 eV. The absolute data are found to be in good agreement with the CCC calculations except for the cases where the secondary electron energy is close to the half excess energy. In these cases, particularly at smaller energies, the CCC theory still predicts similar profiles, but gives substantially smaller magnitudes than the present measurements, which are consistent with the earlier measurements of Pichou et al.

Superhard materials such as nanocrystalline cubic boron nitride (c-BN) and β-silicon carbide (β-SiC) as well as amorphous boron carbide (B4C) and highly tetrahedral amorphous carbon (ta-C) are produced by radio frequency (RF) unbalanced magnetron sputtering in combination with intense ion plating in a pure argon discharge. As a result of energy and mass analysis the film-forming fluxes Φn consist of sputtered atomic target components and the plating flux ΦAr+ of argon ions. Subplantation, ion-plating-induced increase of surface mobility and substrate-temperature-induced crystallisation are the three main parameters affecting the formation of superhard phases with strong covalent bonding. Knock-on subplantation allows the formation of B4C with hardness up to 72GPa at a flux ratio ΦAr+/Φn of 3 for a plating energy of 75eV. Also c-BN and ta-C can be produced with similar parameters. In the case of SiC, densification is diminished by preferential sputtering of Si and consequently stochiometry and hardness are adversely affected. However, intense ion plating with a low ion energy of 25eV and small film-forming fluxes shift the temperature of the phase transition from amorphous to nanocrystalline β-SiC from the usual value of >900°C to about 420°C. Furthermore, investigations of the formation of superhard materials in the ternary system boron–carbon–nitrogen are reported.

Absolute triply differential (e,2e) cross section measurements are presented for He at incident energies and 104.6 eV with equal energy sharing and the configuration. Results of distorted partial-wave calculations agree with the measurements; those of convergent close-coupling calculations agree with the relative angular distributions, and with absolute values after rescaling by consideration of the singly differential cross section.

Diamond crystallites up to 40 nm in size have been grown from a highly ionised plasma beam of acetylene for ion energies close to 100 eV per C atom and substrate temperatures above 450°C. This shows that diamond can be grown by physical vapour deposition from an ion-rich plasma as well as by chemical vapour deposition from a radical-rich plasma. The formation mechanism is argued to be one of nucleation and growth rather than a stress-induced transformation from graphite.

Electron-impact ionization of the ground state of helium is measured and calculated for the case of 64.6 eV incident electrons with coplanar outgoing 20 eV electrons. Various geometries are considered: symmetric, fixed and fixed . The method of calculation is the convergent close-coupling theory. This theory is able to reproduce the angular profiles in essentially all of these geometries, yet it yields cross sections which are a constant factor of approximately two lower than experiment.

The properties of hydrogenated carbon films deposited from a highly ionized hydrocarbon plasma beam are studied as a function of deposition temperature. At low temperatures, the films have high sp3 bonding, density, and compressive stress and are very smooth. Two transition temperatures are observed, a lower transition T1 around 250 °C, dependent on ion energy, due to graphitization of C–C bonds, and a higher one T2 at about 450 °C due to the loss of hydrogen. The roughness rises at T1 and falls above T2. These transitions are used to understand the subplantation deposition mechanism. The optical gap varies differently, decreasing gradually across T1 due to ordering of sp2 sites. We also report the temperature dependence of the x-ray diffraction, Raman spectrum, elastic modulus, hardness, substrate adhesion, friction coefficient, refractive index, and paramagnetic defect density. The friction coefficient of ta-C:H is low (0.05–0.1), and is maintained at ambient humidities, unlike for a-C:H. The friction mechanism is attributed to shear-induced graphitization. The spin density is found to decline with deposition temperature and the spin resonance line is argued to be exchange narrowed.

Silicon carbide thin films were deposited by unbalanced radio frequency (RF) (13.56 MHz) magnetron sputtering from a silicon carbide target in a pure argon discharge. Deposition parameters were 80 W RF target power, 1.6 × 10−3 mbar argon pressure and 6 cm target substrate distance. As determined with energy and mass analysis, the flux of the film-forming particles (ΦSi + ΦC ≈ 0.6 × 1015 cm−2 s−1) consists of mainly neutral silicon and carbon atoms with typical energies of a few electronvolts. The flux of the plating particles (ΦAr + ≈ 1.5 × 1015 cm−2 s−1) is composed of argon ions with a well-defined energy of 24 eV. The low film growth rate, in combination with a high flux ratio of plating argon ions to film-forming particles ΦAr +/(ΦSi + ΦC) of about 2.5, shifts the temperature of the phase transition from amorphous silicon carbide to nanocrystalline silicon carbide from normally 1000 °C in the case of plasma-enhanced chemical vapour deposition (PECVD) or chemical vapour deposition (CVD) deposition techniques down to 420 °C. The films were characterized by measurements of the mechanical properties, e.g. hardness and stress, as well as X-ray diffraction (XRD) and Auger electron spectroscopy (AES). Due to the crystallization at 420 °C the stress of the films is reduced from 6.3 GPa (at 60 °C and for the amorphous phase) to approximately 0.8 GPa. The hardness is between 53 and 37 GPa. At higher plating energies (> 85 eV) the ion-plating-induced densification is diminished by preferential sputtering of silicon and consequently stoichiometry and hardness are negatively affected.

To investigate the effect of radiation damage on the stability and the compressive stress of cubic boron nitride (c-BN) films, samples either prepared by r.f. magnetron sputtering or ion beam-assisted sputter deposition (IBAD) were irradiated at room temperature with 350 keV inert ions (Kr+). FTIR spectra taken before and after each irradiation step clearly demonstrate that c-BN is stable under this medium energy bombardment. Furthermore, additional AES measurements show that the average film stoichiometry is not affected by the ion fluences used in the present experiments. While the observed broadening of the different lines in the IR spectra with increasing ion fluences points to a build-up of disorder and/or a decreasing average grain size due to the bombardment, the additionally found significant shift of the line related to the c-BN TO-mode towards smaller wave numbers, indicates a strong relief of the compressive stress present in the as-prepared films. This irradiation-induced stress relief could be independently confirmed by profilometer measurements yielding post-bombardment values of 5.1 GPa as compared to 20.5 GPa before irradiation. (C) 1997 Elsevier Science S.A.

The different kinematical and geometrical arrangements that may be used in (e,2e) studies are briefly reviewed. The ionization of H(1s) is considered, and within the confines of a relatively simple theoretical model, it is shown how to define experimental setups where one may extract information on the role of Coulomb three-body effects in the incident and final channels. Theoretical and experimental results are pre sented for coplanar constant geometry where the focus is primarily on incident channel effects.