Mass-separated Ion Beam Deposition Research Articles

Chemical bond analysis of amorphous carbon films

Hydrogen-free carbon films with the various sp 3 bond fractions between 83% and 40% were prepared by mass-separated ion beam deposition (MSIBD). These sp 3 bond fractions were obtained by electron energy loss spectroscopy (EELS). Chemical bond analysis of these carbon films was performed by x-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), and Raman spectroscopy, and the comparison of these methods was examined. XPS C1s spectra of carbon films show two contributions at the energies of 284.5 and 285.5 eV, which are originated from sp 2-bonds and sp 3 bonds, respectively. The sp 3 bond fractions obtained by XPS are in good agreement with the values given by EELS. The fine structure of AES spectra at the kinetic energy region between 245 and 265 eV reflects the sp 3 bond fraction. AES spectra are changed from the diamond-like feature to the graphite-like one with decreasing the sp 3 bond fraction. Raman spectra show two broad peaks of G band and D band, the ratio of two peak intensities is independent on the sp 3 bond fraction of films. The shift of G peak position has a correlation with the sp 3 bond fraction in the sp 3 bond rich region.

Characterization of Ion Beam Deposited 107Ag Thin Films on Si(111) Surface by means of Rutherford Backscattering Spectroscopy and Reflection High Energy Electron Diffraction

The crystalline quality of the 107Ag films on Si(111) surface grown by mass-separated low energy ion beam deposition (IBD) has been studied by means of combined techniques of reflection high energy electron diffraction (RHEED), low energy electron diffraction, and Rutherford backscattering spectroscopy (RBS). Although crystalline quality of the films hardly depends on Ag ion energy in the range of 30-100 eV for RHEED patterns, the RBS-channeling spectra clearly show the difference in the minimum channeling yield Xmin and the increasing rate of the channeling yield dx(z)/dz. The Ag ion energy to obtain a well-crystallized Ag film is found to be 30-50 eV. In addition, it is shown that excellent quality of the Ag films grown at elevated temperature can be obtained by means of IBD.

低エネルギー質量分離イオンビーム照射装置を用いた金の堆積率の測定

Au deposition rates were measured as a function of Au ion injection energy with the use of a low-energy mass separated ion beam deposition apparatus. Unlike similar measurements reported earlier, in the present experiments, the quality of ion beams (i.e., their mass and energy spectra) was also examined. In the deposition experiments, the Au ion beam was injected into a gold-coated quartz crystal microbalance (QCM), which measures the mass of deposited Au atoms for the given ion beam current. The measured deposition rates in the energy range of 40-200 eV are consistent with those reported in earlier works.

Characterization of Ion Beam Deposited 107Ag Thin Films on Si(111) Surface by means of Rutherford Backscattering Spectroscopy and Reflection High Energy Electron Diffraction

The crystalline quality of the 107Ag films on Si(111) surface grown by mass-separated low energy ion beam deposition (IBD) has been studied by means of combined techniques of reflection high energy electron diffraction (RHEED), low energy electron diffraction, and Rutherford backscattering spectroscopy (RBS). Although crystalline quality of the films hardly depends on Ag ion energy in the range of 30-100 eV for RHEED patterns, the RBS-channeling spectra clearly show the difference in the minimum channeling yield Xmin and the increasing rate of the channeling yield dx(z)/dz. The Ag ion energy to obtain a well-crystallized Ag film is found to be 30-50 eV. In addition, it is shown that excellent quality of the Ag films grown at elevated temperature can be obtained by means of IBD.

Cubic boron nitride thin film growth by boron and nitrogen ion implantation

Cubic boron nitride $(c\text{\ensuremath{-}}\mathrm{B}\mathrm{N})$ thin films were deposited on silicon substrates using mass separated ion beam deposition (MSIBD). In order to investigate the influence of the ion energy on the growth of $c\text{\ensuremath{-}}\mathrm{B}\mathrm{N}$ films, $^{11}\mathrm{B}^{+}$ and $^{14}\mathrm{N}^{+}$ ions were implanted into $c\text{\ensuremath{-}}\mathrm{B}\mathrm{N}$ with ion energies ranging from $5\phantom{\rule{0.3em}{0ex}}\mathrm{keV}\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}43\phantom{\rule{0.3em}{0ex}}\mathrm{keV}$ and substrate temperatures $({T}_{S})$ from room temperature (RT) to $250\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$. A systematic study on the interplay of ${E}_{\mathit{\text{ion}}}$ and ${T}_{S}$ has revealed a characteristic energy-dependent temperature threshold for $c\text{\ensuremath{-}}\mathrm{B}\mathrm{N}$ growth. This behavior is explained by dynamic annealing of defects caused by a penetrating ion in a collison cascade. In this picture, the suppression of defect accumulation that is crucial for maintaining cubic phase formation is attributed to temperature-driven back diffusion and subsequent annihilation of B and N interstitial recoils. The model is confirmed by analyzing the depth profile of implanted, isotopically pure $^{10}\mathrm{B}$, and its application for both $c\text{\ensuremath{-}}\mathrm{B}\mathrm{N}$ nucleation and growth is discussed.

Ion accelerator facilities at the University of Göttingen

The accelerators at the II. Physikalisches Institut of the University of Göttingen were reinstalled in a new building during the summer of 2003. They cover a wide energy range and are used for many different applications. The highest energies are obtained with the 3MV Pelletron MaRPel, which is preferentially used for ion beam analysis. Ions in the energy range from 30keV to 1000keV are delivered by the 500kV heavy ion implanter IONAS which is used for analysis, implantation and ion beam modification. ADONIS and STRINGER are mass-separated ion beam deposition (MSIBD) systems which produce 30keV mass separated beams which can be decelerated to 20eV to synthesize isotopically pure hard coatings like cubic BN, tetrahedral bounded amorphous C (ta-C) and BxC. The low energy implanter IOSCHKA delivers ions of 10keV maximum, which can be slowed down to a few eV. The targets can be transferred in UHV to an STM set-up to investigate surface modifications after single ion impacts or the development of surface ripple patterns.

Field emission studies on swift heavy ion irradiated tetrahedral amorphous carbon

We investigate the feasibility of electrically structuring flat films by swift heavy ion irradiation to create durable field emitters. Using mass separated ion beam deposition amorphous carbon films, doped with H and F to influence sp 3-fraction and dielectric properties, were grown on highly conducting Si substrates. After deposition, the films were irradiated with 350 MeV 197Au ions creating embedded graphitic channels along their trajectories with diameters only a few nanometers. Those channels were examined using an atomic force microscope (AFM) with a conducting cantilever by applying a bias voltage to the substrate. The channels exhibit conductivities several orders of magnitude higher than the host matrix. Field emission was observed for the F doped samples, and field emission current characteristic and turn-on fields of 30 V/μm were measured. Using field emission energy distribution (FEED) analysis defect states at or near the Fermi level of the track could be identified as the emission source. Computer calculations were performed to approximate the geometric field enhancement of the ion tracks, which was found to be largely reduced by dielectric screening of the amorphous carbon host matrix.

Diffusion in diamond-like carbon

The diffusion of carbon and five other elements in amorphous carbon (a-C) films was studied. One set of samples were sp 2 dominated a-C and the other set of samples were sp 3 dominated tetrahedral amorphous carbon (ta-C). The films were deposited using mass separated ion beam deposition under UHV conditions. The diffusion of 13C as well as that of hydrogen and deuterium was studied using high resolution elastic recoil detection analysis. No apparent self-diffusion could be detected using this technique. The diffusion of hydrogen was found to start at temperatures between 600 and 800 °C. For deuterium, activation energies of 3.34(5) and 3.39(5) eV were found for diffusion in ta-C and a-C, respectively. Tungsten, copper and silver were used to study the diffusion of metals in ta-C. Up to annealing temperatures of 1000 °C no diffusion took place in the samples. During annealing at 1200 °C the ta-C is converted into graphite, making diffusion into the carbon matrix possible. The fact that there is no diffusion of copper in ta-C at temperatures below 1200 °C shows that ta-C is a possible diffusion barrier between copper and silicon.

Structure of carbon nitride films prepared by mass-separated low-energy ion beam deposition

Carbon nitride films were prepared on Si(1 0 0) wafers by alternating irradiation with mass-separated ion beams of C + and N + at the ultra-high vacuum pressure 10 −7 Pa. The ion energy of both ion species was 50 eV. The Si substrate was kept at room temperature (rt), 460, 800 or 1130 K during deposition, and the effects of the substrate temperature on the film structure and chemical bonds formed were investigated. The films were characterized by transmission electron microscopy, X-ray diffraction, electron energy-loss spectroscopy, and X-ray photoelectron spectroscopy. The CN film prepared at rt was amorphous. The nitrogen content decreased from 27 at.% in the film prepared at rt, to 20 at.% in the film prepared at 1130 K. The amorphous CN film prepared at rt consisted of sp 2 CN, sp 3 CN, sp 2 CC, and sp 3 CC bonds, whose bond angles were distorted. This distortion of the chemical bonds decreased, and the structure of the CN film changed to a graphite-like one on increasing the growth temperature. The graphite-like film has a highly preferential crystal orientation, and the c-axis of the graphite basal plane is parallel to the film growth surface. The basal plane is also curved and interlinked because of the presence of in-plane sp 2 CN and 3D sp 3 CN bonds.

Tribological properties of diamond-like carbon films prepared by mass-separated ion beam deposition

Carbon films were prepared by mass-separated ion beam deposition (MSIBD) with a high ion beam current density of 0.2 mA/cm2 under a ultra-high vacuum pressure of 10−7 Pa. The dependence of the sp3 bond fraction and the tribological properties on the ion beam energy was investigated. The maximum value of the sp3 bond fraction was 84%, which was obtained at the ion energy between 75 and 100 eV. The hardness and the Young's modulus of the carbon films were determined by a nanoindentation test, and these properties showed the same dependence of the sp3 bond fraction on the ion energy. A maximum hardness of 80 GPa and a modulus of 740 GPa were obtained at the ion energy of 100 eV. The friction coefficient was not dependent on the ion energy and showed a low value between 0.08 and 0.1. The low friction coefficient of obtained films was due to the homogeneous amorphous structure and very smooth surface of films. The wear rate showed the same dependence of the sp3 bond fraction on the ion energy and a minimum value of 6.01×10−9 mm3/Nm at the ion energy of 100 eV. The wear resistance was related to the sp3 bond fraction and the hardness of films.

The sp 3 bond fraction in carbon films prepared by mass-separated ion beam deposition

Amorphous carbon films were prepared by mass-separated ion beam deposition (MSIBD), and the sp 3 bond fraction was examined by electron energy loss spectroscopy. In previous studies, the carbon ion current was low, and the vacuum pressure during deposition was insufficient. There seems to be an influence of residual hydrogen gas, and damage to the film by the high-speed neutral species produced by the charge exchanging with residual gas molecules during ion transportation. In this study, an MSIBD system was developed with a high ion current density under ultra-high vacuum conditions. Typical carbon ion beam density was 0.2 mA/cm 2 at an energy of 100 eV under a vacuum pressure of 6×10 −7 Pa. The sp 3 bond fraction of the carbon film, which was prepared under a vacuum pressure of 10 −5 Pa during deposition, was 34%. However, that of the film prepared under 10 −7 Pa reached 83%. It was thought that the impact of the high-speed neutral carbon species on the films accounts for the degradation of the sp 3 bond fraction. The dependence of the sp 3 bond fraction on the carbon ion energy was examined. The maximum sp 3 bond fraction of 84% is obtained at an ion energy between 75 and 100 eV.

Ion bombardment as the initial stage of diamond film growth

It is believed that during the initial stage of diamond film growth by chemical-vapor deposition (CVD), ion bombardment is the main mechanism in the bias-enhanced-nucleation (BEN) process. To verify such a statement, experiments by using mass-separated ion-beam deposition were carried out, in which a pure carbon ion beam, with precisely defined low energy, was selected for investigating the ion-bombardment effect on a Si substrate. The results are similar to those of the BEN process, which supports the ion-bombardment-enhanced-nucleation mechanism. The formation of sp3 bonding is based on the presumption that the time of stress generation is much shorter than the duration of the relaxation process. The ion-bombarded Si is expected to enhance the CVD diamond nucleation density because the film contains amorphous carbon embedded with nanocrystalline diamond and defective graphite.

Effect of ambient vacuum pressure on the corrosion properties of pure iron films formed by the ion beam deposition method

High purity iron films deposited on Si substrates by the low-energy, mass-separated ion beam deposition (IBD) method showed the highest corrosion resistance against NaCl solution than any other iron materials. The corrosion properties of the films depend on the ambient vacuum conditions during film formation. High pressure surroundings seem to bring gaseous compounds into the films, which make the surfaces unstable owing to a high density of defects in the films. Surface observations by transmission electron microscopy indicate the presence of a stable iron oxide layer on the IBD iron film which had formed under suitable vacuum conditions. The presence of fewer defects in IBD iron film seems to be a prerequisite of this protective oxide layer.

Low energy ion assisted carbon film growth: methods and mechanisms

Hydrogen-free amorphous carbon films (a-C) prepared by different ion assisted methods (i) ion assisted evaporation (IAE), (ii) unbalanced magnetron sputtering (MS), (iii) mass separated ion beam deposition (MSIBD) and (iv) filtered vacuum cathodic arc evaporation (VA) in the optimum energy range of about 100 eV were compared. Density data, Raman spectra and surface topography images show a different behaviour of the films. The different growth processes were discussed in connection with results from ion implantation experiments into IAE a-C and computer calculations of the ion-solid interactions by use of the TRIM-code. Self-interstitials in the sub-surface region of the carbon matrix created due to pure carbon ion beam bombardment (MSIBD and VA) are the key for the understanding of the densification process. The lower number of self-interstitials created during the noble-gas ion assisted processes can be compensated by extremely high argon-ion to carbon-neutral arrival ratios in the case of MS. Furthermore, the sputtered carbon atoms with energies in the range of a few eV should assist this deposition process. Without energetic carbon particles (thermal carbon atoms from the evaporation process) as in the case of neon ion assisted evaporation, it is also possible to prepare dense a-C, however with lower density (2.7 g/cm 3).

Thin film growth using a high-current, mass-separated low energy ion beam deporstion system

A high-current, mass-separated low energy ion beam deposition system with dual ion sources, which utilizes acceleration-deceleration method, has been developed to create new functional materials, especially those having multi-layered structure. In this system, the maximum ion currents obtained at the ion energy of 100 eV are 5.1 mA for Ar + ions and 5.3 mA for Ca + ions. The deceleration characteristics in the high current region at the ion energy below 100 eV are described. Epitaxial growth of α-Fe film on the Si(111) substrate has been also carried out at room temperature using this system. The dependence of beam diameter on Fe + ion current and the dependence of the film quality on Fe + ion energy are discussed.

Correlation of Raman spectra with carbon ion energy for amorphous diamond-like films produced with a mass-separated ion beam

The Raman spectra of hydrogen-free amorphous diamond-like films prepared using a mass-separated carbon ion beam and different deposition energies are investigated. The correlation between the numerical parameters of the Raman spectra in the 100 to 2100 cm −1 range and the deposition energy, and consequently the sp 3 fraction, is demonstrated.

Thin Film Growth of Group III Nitrides by Mass Separated Ion Beam Deposition

ABSTRACTWe have grown gallium nitride (GaN), aluminum nitride (AIN) and boron nitride (BN) thin films by mass separated ion beam deposition. All deposited films were found to be almost stoichiometric. AIN and GaN films are crystalline even after room temperature deposition whereas for the formation of crystalline boron nitride temperatures above 150°C are necessary. The influence on the phase formation and the film structure of ion energy and substrate temperature on the one hand, and bond ionicity on the other hand, was investigated for these three systems.

Characterization of cubic boron nitride films grown by mass separated ion beam deposition

We have prepared BN films by ion beam deposition of mass separated low energy 11B + and 14N + ions with energies between 100 and 500 eV. The silicon substrates were kept at room temperature or heated up to 350°C. The films were characterized with Auger electron spectroscopy and Rutherford backscattering. The influence of ion energy, ion flux and substrate temperature on the c-BN formation will be discussed. Successful synthesis of cubic boron nitride (c-BN) with a phase purity up to 80% is confirmed by infrared absorption spectroscopy, transmission electron microscopy (TEM) and transmission electron diffraction (TED). For a film with high c-BN content TEM revealed a growth sequence of an amorphous interface layer, followed by few nm of highly oriented hexagonal BN (h-BN) and a layer of nanocrystalline c-BN. We were also able to produce a textured h-BN layer in between two c-BN layers.

Conduction processes in boron- and nitrogen-doped diamond-like carbon films prepared by mass-separated ion beam deposition

Boron- and nitrogen-doped diamond-like amorphous carbon (DLC) films were prepared by alternating direct deposition of low energy mass-separated 12C+ and dopant ions. Concentration vs. depth profiles for N and B dopants were determined by neutron depth profiling. The measured current-voltage characteristics of these films, which were deposited on polished stainless steel, are explained best by Frenkel-Poole emission for high electric fields. Two different trap states Φ1 and Φ2 were found to contribute to the conduction process. At low electric fields our results suggest that conduction is due to variable-range hopping via localized states at the Fermi level. The doped DLC films show a higher electrical conductivity, indicative of an increased density of localized states, rather than a shift in the Fermi level. A diode-like device was prepared, but the measured I-V curves did not indicate that a p-n junction had formed. DLC/Si heterojunctions were also prepared and their current-voltage characteristics are presented and discussed.

Doping and growth of diamond-like carbon films by ion beam deposition

Hydrogen-free amorphous carbon films produced by direct deposition of low energy carbon ions exhibit diamond-like properties such as extreme hardness, large band gap and high index of refraction. Using mass separated ion beam deposition, high purity diamond-like carbon (DLC) films were grown under vacuum conditions better than 10 −5 Pa on Si substrates kept at room temperature. The deposition parameters such as the ion energy, vacuum conditions, substrate temperature and ion species can be controlled independently, and thus used to modify the film properties and composition. In this paper we present the first results of doping of DLC films during growth by alternating deposition of 100 eV 12C + ions and dopant ions such as 63Cu +, 27Al +, 11B + or 14N +. For beam currents of up to 100 μA cm −2, DLC films with a thickness of several micrometers were produced. Undoped films were characterized by Raman spectrometry, ellipsometry, electrical measurements, Rutherford backscattering spectrometry (RBS) and proton induced X-ray emission. For these films an energy gap of 2.6 eV, a Vickers hardness of 4500 kg mm −2, an index of refraction n > 2, a resistivity of 10 9 Ω cm and an electrical breakdown strength greater than 10 9 V m −1 were measured. Dopant concentration profiles of copper-doped films were analyzed by RBS. Homogeneous dopant concentrations of several atomic per cent are easily achieved.