C.A. Carosella

Pulsed laser deposition of epitaxial BaFe12O19 thin films

Epitaxial thin films of barium hexaferrite (BaFe12O19) have been fabricated by the pulsed laser deposition technique on basal plane sapphire. Structural studies reveal the films to be predominantly single phase and crystalline, with the c axis oriented perpendicular to the film plane. The magnetic parameters deduced from vibrating sample magnetometer and ferromagnetic resonance (FMR) measurements are close to the parameters associated with bulk materials. Post annealing of the films reduced the FMR linewidth by more than a factor of 3 so that it compares reasonably well with single‐crystal films. The derivative FMR linewidth was measured to be 66 Oe at 58 GHz and 54 Oe at 86 GHz. Spin‐wave‐like modes have been observed for the first time in barium ferrite films. The deduced exchange stiffness constant of 0.5×10−6 ergs/cm is in reasonable agreement with recent calculations.

Near infrared rugate filter fabrication by ion beam assisted deposition of Si (1− X ) NX films

The rugate filter employs a sinusoidal refractive index depth profile to produce high reflection in a narrow band of wavelengths. Fabrication relies on a continuously variable index of refraction in the wavelength regime of interest. The near IR refractive index of amorphous silicon-nitrogen films decreases continuously as the composition varies from pure silicon to stoichiometric silicon nitride (Si(3)N(4)). Ion implantation was found unsuitable as a fabrication method for rugate filters. Homogeneous and inhomogeneous films up to 5 microm in thickness have been produced by simultaneous deposition of electron beam evaporated silicon and of energetic nitrogen particles arising from an ion beam. The relative fluxes of beam and evaporant are found to determine the ratio of nitrogen to silicon in the films and therefore to determine the index. Single-band reflection filters of the rugate design of high peak optical density were fabricated under computer control using a quartz crystal oscillator shielded from the beam to monitor the silicon evaporation and three suppressed Faraday cups to monitor the ion beam current.

Fundamentals of ion‐beam‐assisted deposition. II. Absolute calibration of ion and evaporant fluxes

A method is given to obtain an absolute calibration of the ion and evaporant fluxes in an ion‐beam‐assisted deposition system based upon a Kaufman ion source and an electron beam vapor source. The nitrogen‐ion silicon‐vapor material system is used for the calibration; Rutherford backscattering is used for measurement of composition and thickness of Si1−x Nx films deposited on C and Si substrates. It is shown that quantitative predictions of the ion‐to‐atom impingement ratio, film composition, and film thickness can be obtained when sputtering, reflection, charge exchange neutralization of the ions, and species content of the nitrogen beam are considered.

Ion implantation studies of (SN)x and (CH)x

Abstract We report the results of the initial investigation of the application of ion implantation for the “doping” of the electroactive polymers, (SN) x and (CH) x . Increases in conductivity have been measured for some (CH) x samples after being implanted. Evidence for the formation of a discrete chemical species has been observed in the case of (CH) x implanted with Br + ions. Advantages and drawbacks associated with this technique are discussed.

Oriented barium hexaferrite thin films prepared by pulsed laser deposition

Oriented thin films of barium hexaferrite, BaFe/sub 12/O/sub 19/, were grown in situ on (0001) sapphire substrates utilizing a pulsed laser deposition technique. X-ray diffraction, elastic backscattering spectrometry, ferrimagnetic resonance, and vibrating sample magnetometry confirm that the structure, composition, and magnetic parameters are consistent with films prepared by other techniques such as liquid phase epitaxy. >

Physical aspects of ion beam assisted deposition

Abstract Progress toward obtaining an understanding of the physical processes that are active during ion beam assisted deposition (IBAD) is reviewed. A model is presented that includes the effects of sputtering, reflection of ions, multiple species beam. charge exchange neutralization, and incorporation of ambient gas atoms. Good agreement is found with data for the composition of silicon nitride. boron nitride and titanium nitride films as a function of the arrival ratio of nitrogen ions to evaporant atoms. Calculations based upon collision cascade simulation are reviewed which predict the energy dependence of the critical arrival ratio to achieve low intrinsic stress in deposited films. Factors which influence the choice of IBAD system geometry, the choice of ion beam energy, and applications of the films are also discussed.

Thermal stability of silicon nitride coatings produced by ion assisted deposition

Abstract Amorphous Si-N alloy films containing from about 20 to 60 at.% N were deposited by combined e-beam evaporation of Si and ion bombardment of N. A Kaufman-type ion gun produced the 500-eV nitrogen ion beam. Films up to 1-μm thick were deposited on single-crystals of silicon and sapphire in a vacuum of about 2 × 10 −4 Torr. The as-deposited films were characterized by Rutherford backscattering spectroscopy for composition, visible and near-infrared spectrophotometry to measure index of refraction and absorption bands from Si-N bond vibrations, and X-ray diffraction for crystal structure. Subsequently, samples were annealed in a thermogravimetric analyzer at temperatures up to 1350°C to ascertain their thermal stability against crystallization, oxidation, and reaction with the substrate. Postanneal examination by Rutherford backscattering, spectrophotometry. X-ray diffraction, and optical and scanning electron microscopy provided detailed information on the thermally induced changes in the films. Crystallization of Si occurred in N-poor samples, while α Si 3 N 4 crystallized in N-rich samples after 1200°C anneals. Blisters sometimes also appeared following 1200°C anneals of N-rich samples. For anneals up to 1200°C, no reactions with sapphire or Si substrates were observed and minimal oxidation was found.

Ion beam assisted deposition of metal nanoclusters in silica thin films

Abstract Gold and silver nanoclusters in silica were deposited by coevaporation of gold and silicon or silver and silicon under simultaneous oxygen bombardment. The noble metal concentration, the linear absorption coefficient and the cluster size can be controlled by variation of the process parameters. The position of the absorption peak was shifted from 400 to 700 nm by the choice of the cluster metal and the dielectric matrix.

ION-BEAM-ASSISTED DEPOSITION OF AU NANOCLUSTER/NB2O5 THIN FILMS WITH NONLINEAR OPTICAL PROPERTIES

Abstract Gold nanocluster thin films (∼ 200 nm thickness) consisting of metal clusters ∼ 5 nm in size embedded in a matrix of Nb2O5 were deposited by ion beam-assisted deposition (IBAD) by coevaporation of Au and Nb with O2+ ion bombardment. The microstructure and optical characteristics of these films were examined as-deposited and after annealing at 600°C. Annealing crystallized the amorphous oxide matrix and ripened the nanoclusters. A strong linear absorption at the wavelength of the surface plasmon resonance for Au developed as a result of annealing. The linear optical behavior was modeled using Mie scattering theory. Good agreement was found between the nanocluster sizes predicted by the theory and the particle sizes observed experimentally using transmission electron microscopy (TEM). The nonlinear optical (NLO) properties of the nanocluster films were probed experimentally using degenerate four wave mixing and nonlinear transmission. The wavelength was near the peak of the surface plasmon resonance as measured by VIS/UV spectroscopy. Values of |χxxxx(3)| were 7.3 × 10−8 and 3.0 × 10−10 esu for annealed and unannealed samples, respe The dominant mechanism for the nonlinear response was change in dielectric constant due to the generation of a distribution of hot, photoexcited electrons.

Ion beam effects on the formation of Ge and Si nanoclusters in silica thin films

Abstract We have observed that ion-beam-assisted deposition (IBAD) has important effects on the optical properties of nanoclusters of Si or Ge in silica thin films. Si or Ge nanocluster(nc)-containing, thin silica films were prepared both by evaporation (PVD) and ion-beam-assisted deposition (IBAD), along with post-deposition annealing. Ge-nc IBAD films contain smaller nanoclusters (3.8± 0.5 nm) with a much tighter size distribution than the PVD films (13±6 nm). The difference in cluster size leads to a shift of the peak position of photoluminescence (PL). Furthermore, X-ray diffraction (XRD) from Ge-nc containing silica films reveals that IBAD promotes the crystallization of semiconductor ncs at lower annealing temperatures and inhibits further growth with increasing annealing temperature. For the Si-system, a decreasing Si-nc size was observed for an increasing ion energy, which weakens the PL and produces an observable small blue shift in the peak of the PL.