Zhong-Lie Wang

Empirical formulae for energy loss straggling of ions in matter

Abstract A detailed survey of the currently available data for the energy loss straggling of hydrogen, helium and heavy ions in matter has been undertaken. An empirical formula based on Chus calculation has been obtained for the energy loss straggling of hydrogen ions. Using this formula with the effective charge and the scaling of straggling, similar to the scaling of stopping powers, good estimates have been made for He and heavy ions. The empirical formulae represent the available data accurately and permit reliable estimates for combinations of projectile and target where currently no data is available.

Preparation and characterization of Bi2Ti2O7 thin films by chemical solution deposition technique

Abstract Transparent and crack-free Bi 2 Ti 2 O 7 thin films with strong (111) orientation were successfully prepared on n-Si(100) by chemical solution deposition (CSD) using bismuth nitrate and titanium butoxide as starting materials. The structural properties were studied by X-ray diffraction. The dielectric constant at 100 kHz at room temperature was 118 and loss factor was 0.074, for a 0.4-μm-thick film annealed at 500°C for 30 min. The leakage current density was 4.06×10 −7 A/cm 2 at an applied voltage of 15 V.

Influences of substrates and substrate temperatures on characteristics of epitaxial La0.5Sr0.5CoO3 thin films

Abstract Epitaxial growth of La 0.5 Sr 0.5 CoO 3 (LSCO) film has been achieved by pulsed laser deposition. Widely used substrates, MgO, SrTiO 3 and LaAlO 3 were chosen to examine the effect of the substrates on the growth of LSCO films. The influence of the substrate temperatures ( T s ) on the characteristics of the LSCO films was studied in a temperature range of 500–850°C. The LSCO films deposited at substrate temperatures of T s =800–850°C show good epitaxial features, better than that of the films deposited at lower T s . The experimental results reveal that the lattice mismatch and the difference of the expansion coefficients between the substrates and the LSCO films are important in the growth process of the LSCO films.

Ion-induced crystallization and amorphization at crystal/amorphous interfaces of silicon

Abstract New empirical equations describing the rate of ion-induced crystallization at a Si crystal/amorphous interface have been developed. In our model, crystallization/amorphization at the interface arises from formation of hot spots and of knock-ons in the collision cascades. It is presumed that the hot spots induce amorphous-to-crystal transformation which lowers the free energy, similarly to heating to high temperatures, and that the bond rearrangement by a series of displacements by knock-ons and recombination to the original lattice point in collision cascades can lead to both crystal-to-amorphous and amorphous-to-crystal transformations. In both hot-spot and knock-on effects, the presence of di-vacancies under irradiation with ion beams is assumed to prohibit crystallization. The model can explain the experimental observation that the crystallization/amorphization rate is scaled by X = o 1 2 exp (C v /2kT) , the product of the root of the flux and the inverse of root of the Boltzmann factor for the motion of the di-vacancies. Crystallization rate in the hot-spots derived assuming that an incident ion induces spontaneous crystallization within a characteristic volume along the track reveals that the radius is 10 atomic distances and the thickness of is about 0.3 monolayer for 1.5 MeV Xe ions. The calculated crystallization/amorphization rate fits to experimental results over a wide temperature range.

Strain analysis of PbTiO3 fine particles and films prepared by sol-gel method

Abstract The micro-strain as well as the grain size in PbTiO3 fine particles and films was determined by x-ray diffraction. For isolated particles, the micro-strain supposedly resulting from non-equilibrium defects decreases monotonically with the increase in sintering temperature. The micro-strain in films is higher than that in isolated particles because there are many defects accumulated at the grain boundary. As the sintering temperature increases the micro-strain in films first decreases and then increases. The decrease in micro-strain at lower sintering temperatures can be attributed to the thermally induced defect-elimination, while the increase in micro-strain at higher sintering temperatures is supposed due to the extension of the transition region at the surface and interface.

Surface analysis of PbTiO3 films prepared by the sol‐gel method

The surface of PbTiO3 films prepared by the sol‐gel method was analyzed by the use of x‐ray photoelectron spectra combined with secondary‐ion mass spectra and infrared absorption spectra. The results suggested that traces of organic materials still existed at least in the surface layer of the films. The outmost surface was partly covered by adsorbed oxygen. The surface layer of the film deviated from stoichiometry because of the shortage of Ti; the thickness of it was estimated about 400 A.

Reduction of secondary defects in MeV ion‐implanted silicon by means of ion beam defect engineering

A new concept of ion beam defect engineering is proposed. Reduction of secondary defects in 1 MeV As ion‐implanted Si(100) has been investigated by Rutherford backscattering/channeling and high resolution electron microscopy. It is found that the additional irradiation of 1.6 MeV Si ions prior to two‐step thermal annealing leads to a noticeable reduction of secondary defects. Good recrystallization of a buried amorphous layer is also obtained by irradiation of 1.6 MeV, 2×1015 Si/cm2 into the implanted Si sample held at elevated temperatures.

Ion-beam-assisted deposition of ferroelectric PbTiO3 films

Ferroelectric PbTiO3 films were deposited by ion‐beam‐assisted deposition (O2+Ar 75–150 eV). The effects of ion bombardment on the Pb/Ti ratio and the structures of the film are discussed. For a given target‐substrate distance and substrate temperature, the Pb/Ti ratio decreased with increasing bombarding beam energy. Compared with the films deposited without ion bombardment, the deposition rate was increased under ion bombardment, which is attributed to an increase in the surface reaction rate. The crystal grains are larger for films deposited under ion bombardment, which implies that ion bombardment enhances the surface mobility of adatoms and hence the growth kinetics of the growing films. Dielectric and ferroelectric properties of the as‐deposited films are also reported.

Lattice disorder in LiNbO3 crystals induced by MeV Cu+ implantation

The effects of 1 MeV Cu ion implantation in LiNbO3 crystals have been investigated using the Rutherford backscattering/channeling technique. The samples have been implanted with doses ranging from 5×1014 ions/cm2 to 2×1015 ions/cm2. The damage profiles have been deconvoluted from Rutherford backscattering spectra after considering the energy spreading due to difference of stopping power between nonchanneled and channeled particles. The energy dependence of the scattering cross section and stopping power have also been taken into account. The damage profiles have compared with TRIM’89 (Transport of Ions in Matter, version 1989) code calculation. For the lowest dose (5×1014 ions/cm2) implantation, the damage profile is in agreement with the defect profile calculated using the trim code. The damage peak is located shallower than the theoretical ion mean projected range, but the damage spread is larger than the ion spread. For higher dose implantations, a broadening of the damage profiles is observed, probabl...

Radiation damage behavior of LiNbO3 crystal by MeV F ion implantation

X, Y, and Z crystalline cut LiNbO3 crystals were implanted by 1.0 MeV F ions with a dose of 1×1015 ions/cm.2 The virgin and implanted LiNbO3 crystals were investigated using the Rutherford backscattering/channeling technique. The obtained minimum yields of virgin crystals were 4%, 8%, and 6% for X‐, Y‐, and Z‐cut LiNbO3 crystals, respectively, because of their different arrangements of lattice sites in channeling direction. The measured damage profiles are also influenced by the arrangement of lattice sites in channeling measurements. The damage profiles of X‐cut LiNbO3 crystal induced by 1.0 MeV F+ at a fluence range of 1×1014–3×1015 ions/cm2 have been studied and compared with the Transport of Ions in Matter, version 1990 calculation. It has been found that not only the nuclear energy deposition but also the electronic energy deposition influences the defect production.