Biaxially textured Ag films by grazing ion beam assisted deposition

The effect of grazing incidence 4 keV Ar⁺ ion irradiation on the early stage of Ag thin film growth on amorphous Si was investigated. The double effect of axial and surface channeling resulted in grains oriented along the 〈110〉 axis in-plane, while the (111) out-of-plane texture was maintained. A slight average tilt of the (111) out-of-plane texture axis towards the ion beam direction is proposed to result from the difference between terrace and step edge sputtering yield. The observed tilt is consistent with a minimum erosion orientation of the surface profile.     

Enhancement of wettability and antibiotic loading/release of hydroxyapatite thin film modified by 100 MeV Ag ion irradiation

The effect of swift heavy 100 MeV Ag⁷⁺ ions irradiation was studied on hydroxyapatite (HAp) thin film prepared by pulsed laser deposition technique (PLD). The GIXRD analysis confirmed the absence of any phase in the HAp phase due to irradiation. In addition, there was a considerable decrease in crystallinity and crystallite size on irradiation. There was no significant variation in the stoichiometry of the irradiated films. Irradiation seemed to decrease the optical band gap energy of HAp thin films. The surface roughness, wettability and bioactivity were improved on irradiation of the samples. Amount of amoxicillin loading/release increased (10%) in ion beam irradiated (1 × 10¹² ions cm⁻²) sample. Irradiated sample showed fast rate of amoxicillin (AMX) release than the pristine. Bactericidal effect was found to increase on irradiation. Surface modified and antibiotics incorporated HAp coated titanium implants may be used to prevent post-surgical infections and to promote bone-bonding of orthopedic devices.     

Angular dependence of sputtering effects by ethanol cluster ion irradiation on solid surfaces

In order to clarify the interactions of ethanol cluster ions with solid surfaces such as Si(100), SiO₂ and Au surfaces, sputtering effects were investigated by changing the acceleration voltage and incident angle (θ) of the cluster ions. The sputtered depth at a normal incidence of θ = 0° increased with an increase of the acceleration voltage. The sputtering ratio of Si to SiO₂ was approximately 10, which suggested that chemical reactions between Si and ethanol produced silicon hydride as a dominant etching material. Furthermore, the sputtered depth of Si surfaces by ethanol cluster ion irradiation had a maximum value at an incident angle between 10° and 60°, and the angle corresponding to the maximum peak increased with an increase of the acceleration voltage. On the other hand, for the physical sputtering of Au surfaces by ethanol cluster ion irradiation, the sputtered depth decreased with the increase of the incident angle, and the change was in accordance with cos θ.With regards to the angular distribution of sputtered particles, Si surface atoms were ejected by ethanol cluster ion irradiation according to a cosine law distribution. This indicated that the Si surfaces were chemically sputtered by ethanol cluster ion irradiation. On the other hand, for the case of Au surfaces, the ejection of the sputtered particles changed to the under-cosine law. This was ascribed to the lateral sputtering effect of ethanol cluster ion irradiation.     

Metal cluster complex primary ion beam source for secondary ion mass spectrometry (SIMS)

To develop a solution-type ion beam source utilizing a wide variety of metal cluster complexes that are stable only in organic solvents, we have investigated an electrospray method for transferring ions from solutions to gas phase. As initial experiments, we have studied electrospray characteristics of ethanol solutions containing a room-temperature molten salt (i.e., an ionic liquid) and acetic acid as alternatives to solutions of metal cluster complexes. In electrospray experiments, we used a stainless-steel capillary with an inner diameter of 30 μm. Experimental results showed that electrosprayed currents increased with applied voltage in both positive-ion and negative-ion modes. In addition to positive currents, stable negative currents were also confirmed to be produced. Current exceeding 250 nA was produced at 2 kV with a flow rate of 2 μL/min at a concentration of 1 × 10⁻³ mol/L. It was confirmed that several nA out of electrosprayed currents were delivered through an orifice (120 μm internal diameter) into a vacuum chamber. Experimental results indicate that the electrospray method seems to be applicable to an ion beam source for utilizing massive metal cluster complexes in solutions.     

Argon ion beam and electron beam-induced damage in Cu(In,Ga)Se2 thin films

Ar ion beam and electron beam-induced damages in Cu(In,Ga)Se₂ thin films are investigated by transmission electron microscopy and X-ray energy-dispersive spectroscopy. We find that a high-energy Ar ion beam can cause severe damage in Cu(In,Ga)Se₂ surface regions by preferentially depleting Se and In. The depletion can occur with an Ar ion beam at energy as low as 0.5 keV. High-energy electron beams also cause damage in Cu(In,Ga)Se₂ thin films by preferentially depleting In and Ga. Our results imply that special care must be taken for measurements involving surface treatments using high-energy Ar ion beams or electron beams.     

Diffusion-induced step decoration of Co on Ag(001)

We have investigated submonolayers of Co deposited on a Ag(001) surface with ultra low energy ion deposition and a deposition energy ranging from 5 to 30 eV. The sites of nucleation, the island densities and heights were determined with scanning tunneling microscopy. Next to randomly distributed islands on the terraces observed for every deposition energy, preferential nucleation on the upper side of the Ag steps was observed only for 5 and 15 eV. We found that for increasing characteristic length between the islands on a terrace, the number of islands per unit step length increases. This implies that step decoration is related to enhanced diffusion of Co atoms on the Ag surface during nucleation.     

A combined In situ grazing incidence small angle X-ray scattering and grazing incidence X-ray diffraction study of the growth of Ge Islands on pit-patterned Si(001) substrates

The growth of Ge islands on a pit-patterned Si(001) template is investigated in situ, combining grazing incidence diffraction, multiple wavelength anomalous diffraction, and small angle scattering. This allows monitoring in situ the detailed structural and morphological evolutions of the pits, of the wetting-layer and of the nucleated islands on the pit-patterned Si(001) substrate. It is shown that after Si regrowth, the Si substrate displays {107} and {1 1 11} facets. During the very first stages of Ge growth, the preliminary facets of the Si substrate are energetically unfavourable, and the pit facets break up into a rather complex pattern of {10n} and {11m} facets with n > 7 and m > 11. At 5 and 6 ML, intensity rods from {105} and {113}-type facets appear in the GISAXS images revealing the formation of pyramids and domes, respectively. The degree of ordering, the shape, strain and composition of the islands are characterized during the growth process to provide a detailed evolution of their structure and morphology.     

Structure of ultrathin MgO films on Mo(001)

We have studied the structure of ultrathin MgO films grown on a single crystal Mo(001) surface. Scanning tunneling microscopy (STM) and low energy electron diffraction (LEED) were used to investigate the effect of substrate temperature and oxygen partial pressure on the growth and morphology of these films. LEED indicates the growth of (100) films with MgO 〈110〉 directions oriented along 〈100〉 directions of the substrate. Despite the insulating nature of bulk MgO, films up to 25-Å thick are sufficiently conducting to perform STM measurements. STM reveals Mg deposition in an oxygen ambient at substrate temperatures from 300 to 900 K produces uniform films. Films as thick as eight atomic layers typically have only three layers exposed. These films consist of small domains between 20 and 60 Å in diameter. The domain shapes are random and the perimeters show no preferred orientation. In contrast, films grown at temperatures in excess of 1000 K exhibit larger three-dimensional MgO islands (Volmer-Weber growth). Steps on these high temperature films orient preferentially along thermodynamically favored MgO 〈100〉 directions. STM images of films deposited at high temperature exhibit a checkerboard pattern. The dimensions and symmetry of this pattern are consistent with the coincidence arising from the mismatch of the MgO(100) and Mo(001) lattice. Annealing room temperature deposited films results in island coalescence and produces uniform films with domains in excess of 100 Å. The perimeters of these domains are oriented along MgO 〈100〉 directions.     

Deposition of diamond like carbon (DLC) and C-N films using ion beam assisted deposition (IBAD) technique and evaluation of their properties

Diamond like carbon films and C-N films were prepared using ion beam assisted deposition technique (IBAD). Tribological properties were studied by subjecting DLC coated films to the accelerated wear tests. These tests indicated a significant improvement in the mechanical surface properties of glass by DLC coating. Better wear features were obtained for thinner DLC coating as compared to the thicker ones. We also studied the optical properties and obtained a band gap of 1·4 eV for these films. An attempt was made to prepare C₃N₄ films by using IBAD. We observed variation in the nitrogen incorporation in the film with the substrate temperature.     

MBE方法在GaAs(001)衬底上外延生长GaSb膜

利用分子束外延方法(MBE)在GaAs(001)衬底上外延生长了GaSb薄膜,利用高分辨透射电子显微镜(HRTEM)、原子力显微镜(AFM)、Hall效应(HallEffect)和低温光荧光谱(LTPL)等手段对薄膜的晶体质量、电学性能和光学质量进行了研究。发现直接生长的GaSb膜表面平整,空穴迁移率较高。引入GaSb/AlSb超晶格可有效阻断进入GaSb外延层的穿通位错,对应的PL谱强度增强,材料的光学质量变好。     

Optical properties of GaN epilayers grown on Si (111) and Si (001) substrates

We report the observation of bright photoluminescence (PL) emission from two types of GaN epilayers grown by molecular beam epitaxy (MBE). Wurtzite phase GaN/Si (111) epilayers are grown by gas source MBE process, whereas cubic phase GaN epilayers are grown on (001) Si covered by thin SiC film in the process of Si annealing in propane prior to the GaN growth. PL emissions are identified based on the results of detailed PL and time-resolved PL investigations. For the wurtzite phase GaN we observe an efficient up in the energy transfer from bound to free excitons. This process is explained by a large difference in the PL decay times for two types (free and bound (donor, acceptor)) of excitonic PL emissions. For cubic phase GaN we confirm recent suggestion that acceptors have smaller thermal ionization energies than those in the wurtzite phase GaN.     

Growth, structure and epitaxy of ultrathin NiO films on Ag(001)

NiO ultrathin films have been grown on Ag(001) by Ni deposition in an O₂ atmosphere. The thickness range 5–50 ML has been investigated. X-ray photoelectron spectroscopy has been used to study the stoichiometric composition and chemical purity of the oxide films. We found completely oxidized stoichiometric NiO films. Their contamination has been found to be limited to the topmost layers. Photoelectron diffraction has given information concerning the local crystal structure of the films. The film atomic geometry has been found to be the same independent of thickness in the 0–50 ML range. The films have the expected (001) rock-salt structure with the same in plane orientation as the Ag(001) substrate. Specular X-ray reflectivity has allowed a very accurate thickness evaluation and has given information on the width of the density gradients at the film–substrate and vacuum–film interfaces, found to be of the order of a few atomic layers.     

Effect of the oxygen flow on the properties of ITO thin films deposited by ion beam assisted deposition (IBAD)

ITO films were deposited onto glass substrates by ion beam assisted deposition method. The oxygen ions were produced using a Kaufman ion source. The oxygen flow was varied from 20 until 60 sccm and the effect of the oxygen flow on properties of ITO films has been studied. The structural properties of the film were characterized by X-ray diffraction and atomic force microscopy. The optical properties were characterized by optical transmission measurements and the optical constants (refractive index n and extinction coefficient k) and film thickness have been obtained by fitting the transmittance using a semi-quantum model. The electrical properties were characterized by Hall effect measurements. It has been found that the ITO film with low electrical resistivity and high transmittance can be obtained with 40 sccm oxygen flow (the working pressure is about 2.3 × 10^− 2 Pa at this oxygen flow).     

Nucleation of Ge quantum dots on the C-alloyed Si(001) surface

Carbon pre-deposition onto the bare Si(001) surface has been shown to alter the (2×1) surface structure by formation of c(4×4) reconstructed domains containing a high C-concentration. Here we studied by ultra-high vacuum scanning tunneling microscopy the effect of this restructured surface on the initial stages of Ge nucleation by molecular beam epitaxy. Ge is found to form three-dimensional (3D) islands already at sub-monolayer coverage, resulting in a Volmer–Weber growth mode. Strain effects repel Ge adatoms from the C-rich domains, leading to enhanced Ge island formation on the C-free surface regions in between the c(4×4) areas. At a low growth temperature of 350°C, very small three-dimensional islands (3–5 nm in diameter, height 3–4 ML) with a density of nearly 1×10¹² cm⁻² are obtained for only 0.5 ML of Ge. At higher substrate temperatures of approximately 500°C this three-dimensional growth mode is less pronounced, but still evident. The initially nucleated three-dimensional islands define the positions of the larger quantum dots at higher Ge coverage, that exhibit enhanced photoluminescence (PL) properties.     

Formation of iron silicide on Si(001) studied by high resolution Rutherford backscattering spectroscopy

The initial stage of the formation of iron silicides has been investigated by high resolution Rutherford backscattering spectroscopy (HRBS). Just after Fe is deposited on Si(001) at room temperature, the deposited Fe atoms dig themselves into subsurface ejecting Si atoms into outer surface. Upon annealing at 300-400 °C, significant number of Si atoms are displaced from their lattice position near the interface between the crystalline Si and the Fe-Si mixing layer. Such displaced Si diffuses into the Fe-Si mixing layer and forms the layer with the composition of Fe:Si≈1:2. This layer is considered to be a precursive state of FeSi₂.     

Photoluminescence characterization of β-FeSi2 prepared by ion beam sputter deposition (IBSD) method

Photoluminescence (PL) measurement technique was found to be effective in revealing the unique characteristics of β-FeSi₂ film formation on Si substrates by means of ion beam sputter deposition (IBSD) method. A strong photoluminescence peak at around 0.8 eV was observed for β-FeSi₂ samples and also for Si substrates that were sputter etched by Ne⁺, and then thermally annealed in air at elevated temperature. Comparison with literature data indicated that the PL peak at 0.8 eV observed in this study was mainly from D1 emission bands in Si substrate, whose intensity was enhanced by the sputter etching and the subsequent annealing of the substrate. Furthermore, comparison between CZ-Si and FZ-Si results indicated that the energy of 0.8 eV peak observed in this study was affected by the presence of oxygen in the Si bulk as well.     

Atomic force microscopy and scanning tunneling microscopy studies of large-scale unstable growth formed during GaAs(001) homoepitaxy

Atomic force and scanning tunneling microscopy studies have been performed on GaAs(001) films grown by molecular beam epitaxy. Multilayered mounds are seen to evolve when the growth conditions favor island nucleation. As the epilayer thickness is increased, these features grow in all dimensions but the angle of inclination remains approximately constant at 1°. The mounding does not occur on surfaces grown in step flow. We propose that the multilayered features are due to an unstable growth mode which relies on island nucleation and the presence of a step edge barrier.     

Impact of dose and energy of argon (Ar) and fluorine (F) ion implantation on uniformity of silicon oxidation

Oxidation rate of silicon was altered by implanting argon (⁴⁰Ar⁺) and fluorine (¹⁹F⁺) ions at doses ranging from 5×10¹³ to 1×10¹⁶ ions/cm² and energies ranging from 20 to 70 keV. Silicon wafers were oxidized using a rapid thermal oxidation system to retain post-implant conditions of the wafers until onset of oxidation cycle. Dramatic change in the uniformity of grown oxide was observed as a function of implantation dose and energy. Uniformity was found improving with increased implantation dose, whereas, it deteriorated with increased implantation energy. Two phenomenological models are proposed to explain the improvement in uniformity of the grown oxide films.