Ionized Cluster Beam Technique Research Articles

Growth of CdTe on Si(100) surface by ionized cluster beam technique: Experimental and molecular dynamics simulation

II–VI semiconductor CdTe was grown on the Si(100) substrate surface by the ionized cluster beam (ICB) technique. In the ICB method, when vapors of solid materials such as CdTe were ejected through a nozzle of a heated crucible into a vacuum region, nanoclusters were created by an adiabatic expansion phenomenon. The clusters thus obtained were partially ionized by electron bombardment and then accelerated onto the silicon substrate at 473K by high potentials. The cluster size was determined using a retarding field energy analyzer. The results of X-ray diffraction measurements indicate the cubic zinc blende (ZB) crystalline structure of the CdTe thin film on the silicon substrate. The CdTe thin film prepared by the ICB method had high crystalline quality. The microscopic processes involved in the ICB deposition technique, such as impact and coalescence processes, have been studied in detail by molecular dynamics (MD) simulation.

Admittance spectroscopy of metal–semiconductor interfaces prepared by ionized cluster beam technique

Analysis of the Ag/p-Si(1 0 0) metal–semiconductor interface prepared by the ionized cluster beam (ICB) technique using admittance spectroscopy is given. The observed peak in the imaginary part of the complex dielectric function spectra indicates the presence of the interface states at the metal–disordered layer and disordered layer–semiconductor interfaces. The frequency dependence of the zero-bias measured conductance and capacitance of the ICB m/s interface is well described assuming the distribution of electronic states in the semiconductor bandgap, and the frequency response of the conductance is related to the hopping conductivity and the tunnelling current to the interface states.

Correlation between magnetic properties and carrier concentration in Ge1−xMnxTe

The dependence of magnetic properties on the carrier concentration for Ge1−xMnxTe films prepared by ionized-cluster beam technique has been studied to clarify the mechanism of carrier-induced ferromagnetism. The experimental results suggest that the cluster of spins aligned by short-range ferromagnetic interaction tends to be formed for samples with the lower carrier concentration than the critical value for the occurrence of homogeneous ferromagnetic order. With increasing carrier concentration, the long-range ferromagnetic interaction grows. The magnetotransport properties of Ge1−xMnxTe films are found closely related to its magnetic properties, indicating carrier-enhanced ferromagnetic effects.

Fermi Level Pinning in Ag/Si Schottky Structures Prepared by Ionized Cluster Beam Technique

The observed variation of the Schottky barrier height in ionized-cluster-beam (ICB)-deposited Ag/Si Schottky structures is described within the framework of the disorder-induced gap stated theory (DIGS). The physical mechanisms determining the position of the Fermi level in ICB Schottky structures under different regimes of acceleration voltage are suggested, emphasizing the role of the local electronic structure.

Carrier-enhanced ferromagnetism in Ge1−xMnxTe

We have studied the dependence of magnetic properties on the carrier concentration of IV–VI diluted magnetic semiconductor Ge1−xMnxTe prepared by ionized-cluster beam technique. With increasing carrier concentration, the magnetic properties drastically change; saturation magnetization increases and coercive field decreases in hysteresis loop, and the Curie temperature increases. These results obviously show carrier-enhanced ferromagnetic order. The similar effect is also observed in magnetoresistance behavior.

Film growth of Ge 1− xMn xTe using ionized-cluster beam technique

IV–VI diluted magnetic semiconductor Ge 1− x Mn x Te of NaCl crystal structure is successfully obtained with the Mn concentration x up to x=0.96 using ionized-cluster beam technique. The (1 1 1) plane of Ge 1− x Mn x Te is grown epitaxially parallel to the (1 1 1) plane of BaF 2 substrate. The lattice constant of Ge 1− x Mn x Te decreases with the increase of Mn concentration. At the Curie temperature ( T c), ferromagnetic phase transition occurs as the result of Runderman–Kittel–Kasuya–Yoshida (RKKY) interaction. The highest T c in this study is 140 K for x=0.51. Temperature dependence of spontaneous magnetization suggests the existence of multiple exchange interactions. The distinct magnetic anisotropy is not observed in the magnetization curves applying the magnetic field parallel and perpendicular to the plane. The obtained demagnetizing factor is 0.52, which was smaller than that of the thin film. It can be ascribed to the non-uniform magnetization state.

Photocatalytic decomposition of NO on titanium oxide thin film photocatalysts prepared by an ionized cluster beam technique

Transparent TiO2 thin film photocatalysts were prepared on transparent porous Vycor glass (PVG) by an ionized cluster beam (ICB) method. The UV‐VIS absorption spectra of these films show specific interference fringes, indicating that uniform and transparent TiO2 thin films are formed. The results of XRD measurements indicate that these TiO2 thin films consist of both anatase and rutile structures. UV light (λ > 270 nm) irradiation of these TiO2 thin films in the presence of NO led to the photocatalytic decomposition of NO into N2, O2 and N2O. The reactivity of these TiO2 thin films for the photocatalytic decomposition of NO is strongly dependent on the film thickness, i.e., the thinner the TiO2 thin films, the higher the reactivity.

Numerical Analysis of the Nucleation Process for Metallic Clusters in the Ionized Cluster Beam Technique

The nucleation process in the ionized cluster beam technique is numerically analyzed to clarify the condition for producing metallic clusters. The mean free path of monomers in the crucible and the Knudsen number are calculated under experimental conditions to judge the magnitude of the collision rate of monomers. The steady-state nucleation rate is calculated as a function of the crucible temperature and the Mach number to evaluate the effects of crucible conditions and nozzle geometry on the nucleation rate. The numerical results for various metals are consistent with the existing experiments.

Raman characteristics of hard carbon-nitride films deposited by reactive ionized cluster beam techniques

Raman spectroscopy was used to investigate the effect of nitrogen pressure on the structure of carbon-nitride films deposited by the reactive ionized cluster beam (RICB) technique. It is noted that a peak centered at about 1248 cm−1 emerges in the Raman spectra and becomes more pronounced when nitrogen pressure is increased. This peak can be attributed to the covalent NC single bonds. Moreover, the structure of the deposited films changes from DLC to diamond, and finally to carbon-nitride with the increase of nitrogen pressure. The results of Knoop hardness tests show the films have rather high hardness up to 6200 kg f/mm2.

Preparation of GaN Thin Films by Reactive Ionized Cluster Beam Technique

GaN thin films were prepared by reactive ionized cluster beam technique at relatively low substrate temperature about 400°C. The composition, structure and morphology of the films were characterized by x-ray photoelectron spectroscopy, transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The binding energy of N 1s electron in the film is 397.85 eV which shows the formation of Ga-N bonding. The film has a polycrystalline structure revealed by the measurement results of TEM and SEM. It was found that raising nitrogen ion ratio in the beam is helpful to decrease oxygen content in the film.

Structural and tribological characteristics of carbon nitride films deposited by the reactive ionized-cluster beam technique

Abstract A reactive ionized-cluster beam deposition system was used to synthesize carbon nitride films. Raman scattering analysis shows the existence of a characteristic peak due to covalent C–N single bonds. This is consistent with the results of Fourier transform infrared and X-ray photoelectron spectroscopic measurements. The deposited films exhibit an extremely high hardness of 6200 kgf mm −2 . The friction and wear behavior of these films without any lubrication were measured by a reciprocating-motion ball-on-disk tribometer. It is noted that the deposited films have low initial and steady-state friction coefficients in the range 0.08–0.14. The wear rates of carbon nitride films are significantly lower than that of carbon thin films prepared by the same deposition system and evaluated under similar test conditions. These results are very encouraging for the tribological applications of carbon nitride films.

Low-Temperature Deposition of CuIn(SxSe1-x)2 Thin Films by Ionized Cluster Beam Technique

CuIn(SxSe1-x)2 thin films were prepared on Mo-coated soda-lime glass substrates by the ionized cluster beam (ICB) technique, in which Cu, In2S3 and Se vapors were ionized and accelerated. The substrate temperature was kept at Ts=400°C. The films were characterized using X-ray diffraction (XRD), a scanning electron microscope (SEM), and an electron-probe microanalyzer (EPMA). It was found that polycrystalline films with improved grain size were obtained when the substrate temperature exceeded 250°C. Using the ICB technique, thin film solar cell devices based on these CuIn(SxSe1-x)2 films were fabricated. The photovoltaic effect was confirmed in substrate-type structure solar cells with the low-temperature deposition of ICB-grown CuIn(SxSe1-x)2 thin films.

Carbon nitride films synthesized by the reactive ionized cluster beam technique

Carbon nitride thin films were deposited by the reactive ionized cluster beam (RICB) technique. Fourier transform infrared (FTIR) transmission analysis shows that no marked IR peak exists for the film deposited without nitrogen, whereas a broad peak in the range 1000- and a peak due to the C3pt- 1pt- -1pt-N triple bonds are present for the films deposited with nitrogen. Both FTIR and Raman measurements obviously suggest that C1pt-N single bonds exist when nitrogen is introduced. The intensity of this band rises with increasing nitrogen pressure. The above results are also supported by x-ray photoelectron spectroscopy (XPS) analysis.

イオンクラスタービーム法で作製したFe-Cuグラニュラー合金膜の磁性と巨大磁気抵抗

イオンクラスタービーム法で作製したFe-Cuグラニュラー合金膜の磁性と巨大磁気抵抗

Homogeneous nucleation in nozzle in the ionized cluster beam technique

Homogeneous nucleation in nozzle in the ionized cluster beam technique

高速粒子による衝突活性化

Collisional activation of the matter induced by the bombardment of the fast particle is summarized. The particle with the velocity higher than the Bohr velocity (transit time through 5A shorter than 2.5×10-16s) experiences the electronic stopping power when it passes through the matter and induces dense electronic excitations and ionizations which results in the heavy sputtering of the matter. This kind of activation is usefully applied in the PDMS. When the particle velocity becomes lower than the Bohr velocity, the energy is mainly deposited to the matter by the nuclear stopping power, i.e., energy loss is governed by the screened Coulombic collisions of the atoms giving rise to the momentum transfer to the target nuclei. When the transit time of the particle through 5A is between 2.5×10-16-10-14 s, the electronic excitation and ionization take place by the collision. These phenomena are fully utilized in the FAB/SIMS and CID techniques. With the transit time in the range of 10-14-2.5×10-13s, the velocity is not high enough for the electronic excitation and the particle loses its energy mainly by the vibrational and phonon excitation of the target. This range of the velocity corresponds to that of the massive cluster impact ionization. With the velocity equal to or lower than 2.5×10-13s, the energy of the incident particle is consumed mainly by the phonon excitation and the collision results in the modest heating of the colliding interface between the projectile and the target. This range of the velocity is successfully used in the ionized cluster beam technique developed by Takagi of the Kyoto University.

Microstructure and domain configurations in ferroelectric PbTiO3 and Pb(Zr,Ti)O3 thin fims

Ferroelectric domain configurations in PbTiO3 and Pb(ZrxT1−x)O3 (PZT, x = 0.3 or 0.5) thin films have been studied by transmission electron microscopy. The PbTiOg and PZT thin films have been deposited by the ionized cluster beam technique and radio frequency sputtering, respectively. The grain size in these thin films is typically less than 0.5 μm. Lamellar 90°-domain features have been observed in both PbTiO3 and PZT (30/70) samples. The domain walls correspond to the {011} twin boundaries. La-doping and Ca-modification are shown to affect the microstructure of the PZT films. No clear domain feature occurs in the PZT thin film that has composition near the morphotropic phase boundary. The effects of grain sizes are briefly discussed.

ICB deposition and epitaxial growth of GaAs thin films

The hetero- and homoepitaxial deposition of GaAs films by the ionized cluster beam technique in connection with subsequent neutral beam deposition forming a double layer structure have been studied. It is found that ICB-deposited films have superior quality in comparison with conventional ion beam deposited films and comparable quality like MBE or MOCVD-deposited films. By the fabrication of device structures, it has been proved that the start of film growth from an interface formed by an ICB-deposited As layer is advantageous. Additionally, surface cleaning by low-energy ionized cluster beams has been studied. For the first time, defect-free surface cleaning by low-energy cluster ion beams has been realized.

Industrial applications of ICB deposition for the fabrication of electronic devices

Technologies for forming functional layers are required to increase functions and to achieve miniaturization of devices. Ionized cluster beam (ICB) deposition is suitable for these needs and has been used to form thin films with unique characteristics compared to films formed by other techniques. Here, the ICB technique for forming a TiN Ti layer at the bottom of contact holes in DRAMs is discussed. A simple deposition model predicted that the narrow angular distribution of evaporated species and deposition at low vacuum pressure are essential conditions for sufficient coverage of the contacts. The bottom coverage of TiN Ti films has been improved by over 10 times by using the ICB technique in comparison with films produced by conventional sputtering methods. Other applications of ICB to high reflective optical mirrors with an atomically flat surface and high-temperature superconductors with high critical current density within a wide range are also discussed.

Gold and zinc thin films deposited by the ionized cluster beam technique

Thin film deposition from beams of atom clusters, some of which are ionized and accelerated to the growing surface, was first proposed in 1972. This idea created interest because it was fundamentally different from other deposition methods and was expected to have unique capabilities. Development of a suitable cluster source has been difficult, and large clusters of zinc (about 2000 atoms per cluster) have only recently been produced. Two source parameters were change to accomplish this. The crucible pressure was increased from 2 Torr to over 1000 Torr, and a converging-diverging nozzle 18 mm long and 0.4 mm in diameter at the throat was used in place of the older nozzle with dimensions of 1 mm × 1 mm. To separate the pressure and nozzle effects, gold thin films are being deposited with the new converging-diverging nozzle. The vapor pressure of gold is much lower than that of zinc at a given temperature. Cluster size measurements show no significant numbers of gold clusters. The effect of the crucible pressure on the formation of the large cluster is much more significant than that of the nozzle geometry. The effects of varying ion energy bombardment on film microstructure are also evaluated using atomic force microscopy.