Using a novel ultrahigh vacuum (UHV) transmission electron microscope with in-situ UHV sputtering attachment we have studied the sintering of copper and silver nanoparticles with single crystal copper substrates. Copper and silver particles deposited on (001) copper initially assume random orientations. Upon annealing, however, the particles reorient and assume an epitaxial orientation with the substrate. In the case of copper on copper, homoepitaxy occurs by a process involving sintering and grain growth. In the case of silver on copper, we have observed the particles to wet the substrate surface and sinter to form a thin epitaxial film with the orientation relationship (111)Ag // (001)Cu, [110]Ag // [110]Cu.

Transition metal particles dispersed oxide ceramic nanocomposites A12O3/Co and ZrO2/Ni, in which metal content is less than 20 vol%, have been fabricated by the reduction and sintering of composite powders. These powder mixtures were prepared by solution chemical processes to obtain suitable structure for ceramic/metal nanocomposites. Nickel or cobalt nitrate, as a source of metal dispersion, was dissolved into alcohol and mixed with alumina or zirconia powder. These powders were reduced by hydrogen and successively hot press sintered. Nanometer-sized Co or Ni particles were mainly dispersed at the matrix grainboundaries. Fracture strength was improved by dispersing metal particles due to microstructural refinement, whereas toughness was increased by incorporating large metals. Ferromagnetic responses with enhanced coercive force were also observed for these composites.

The physics of particle adhesion is a complex subject and depends on the interaction mechanisms and the mechanical properties of the contacting materials. These interactions, which tend to be caused by van der Waals and electrostatic interactions, generate stresses that, in turn, result in deformations of the contacting materials. Most of today's understanding of particle adhesion is based on theories that assume that the adhesion-induced strains are small. However, for small particles, the strains can be quite large, resulting in yielding and plastic deformations. In some instances, the entire particle can become engulfed by the substrate. This paper discusses the nature of the deformations, as are presently known, and extrapolates today's understanding of particle adhesion, which is based on the micrometer-size scale, to nanometer-size particles.

Grain size and strain distribution functions of polycrystals of SiC with nanosize grains were examined based on X-ray diffraction data and ab initio calculations of scattered intensity from Debye functions. A tentative model of distribution of strain induced under high isostatic pressure in nanoparticles with different grain size is presented. Nanocrystalline SiC powders with grains down to 80Å in diameter were examined. In situ high pressure diffraction experiments were performed in cubic anvil cell MAX80 (up to 6 GPa) and in Diamond Anvil Cell (DAC) (up to 45 GPa) at HASYLAB, Hamburg, Germany. Shape of the Bragg lines was analysed with the use of two methods: (i) calculation of theoretical diffraction patterns based on modeling of one-dimensional disordering and ab initio calculation of scattered intensity starting from Debye functions and, (ii) approximation of the experimental shape of Bragg reflections by a combination of two functions: Gaussian (G) and Lorentzian (L).

In this paper we present an overview of two very different approaches to the synthesis of composite particulates which result in a “core-shell” type structure. It is shown that both these synthesis approaches result in very characteristic interface structures between the outer coating and the host particles. One synthesis strategy is to use laser ablation deposition on individual particles and the other is to “coat” particles ‘in-situ’ by taking advantage of solid state diffusional transformations. Examination of the interface between the outer shell and the core of the particle shows that textured or toptactical growth occurs and it is suggested that this unique crystallographic characteristic may be responsible for the properties offered by these engineered particulates. The applications of such engineered particulates is also discussed.

A sparingly soluble model drug, phenytoin (5,5-diphenyl-hydantoin, denoted as PT), was added during hydrolysis and polycondensation of tetra orthoethyl silicate (TEOS). The average size of the composite primary particles after in situ recrystallization of PT and gelation of silica was 2–3nm. The extent of hydrogen bond (HB) in PT was reduced after the complex formation (CF), while many PT molecules were attached by HB on the surface of silica gel. The apparent solubility to ethanol decreased to 29%∼18% by CF. The firstorder rate constant of dissolution of PT into H20 increased by CF up to 40 times. Addition of acrylamide also enhanced the dissolution rate. Mechanisms of faster dissolution were discussed in terms of the hydrogen bond reformation and microstructure.

A mechanical route plays an important role in particulate coatings and synthesis. A type of particulate surface modification, i.e., oriented coating of fine particles onto the surface of a core particle, is proposed. For achieving this concept, the author has developed a two-step process involving mechanical and chemical methods. As an example, needle-like dicalcium phosphate fine particles were coated, in a standing-up state, onto the surface of nylon-12 core particles (avg 50um). The effect of the crystal structure of dicalcium phosphate on the particulate oriented coating was investigated.

A novel dry coating technique called magnetically assisted impaction coating (MAIC) to synthesize engineered particulates with controlled surface coatings has been developed. In this method, the impaction of magnetic particles, core particles and secondary particles results in dry coating on the surface of the core particle. The attachment of particles to surfaces and factors affecting the efficiency of the process have been discussed.

Microstructure control of ceramics is expected to produce novel functions or to improve properties. Nanocomposite powders of functional ceramics were fabricated by vapor, solid and liquid phase reactions, respectively. Superconducting bulk materials were fabricated by thermal plasma method and mist pyrolysis method. Microstructure control of powders for sintering contributed to improve the microstructure at grain boundaries and to introduce magnetic flux pinning centers, both resulted in the improvement of superconducting transport current property. On the other hand, a magnetic nanocomposite for the remote sensing of stress in structural ceramics was fabricated by sol-gel method and solid state reaction. Successfully introduced nano-dispersoids of ferromagnetic materials by the sintering of nanocomposite powders resulted in the harmonization of added functionality and proper mechanical properties. Magnetic response to applied stress in structural ceramic matrix was detected as the result of amplified magnetostriction caused by the nano-size effect on ferromagnetic dispersoids.

Nanostructured powders, with particle sizes in the range 1 to 100 nm, have shown great promise in the forming of advanced films and coatings for a variety of applications including tribological, high surface area supports for catalysts, chemical gas sensors, and optoelectronics. This paper is a summary of two major classes of powder synthesis techniques: (1) precipitation from aqueous salt solutions, and (2) condensation from vapor phase. The solution approach leads to powder particles that are spherical shells consisting of nanograins. The powder is milled with melting point lowering compounds and reagglomerated to make it suitable for thermal spraying. In contrast, the vapor condensation approach yields powder particles that are discrete, and loosely agglomerated. In a variation of the process, the heated clusters or nanoparticles are allowed to sinter on a heated substrate, forming porous or dense coatings. Films/coatings with thicknesses between 0.5 μm and 20.0 μm at rates in excess of 1 μm/min. are formed by the in situ deposition process. The synthesis techniques, powder and coating characteristics, and applications of the technologies, are described in this paper.

Particulate coatings have wide ranging applications in several new technologies such as flatpanel displays, sintering of advanced ceramics, rechargeable batteries, etc. In this paper, we show the feasibility of the pulsed laser ablation technique to make very thin, uniformly distributed and discrete coatings in particulate systems so that the properties of the core particles can be suitably modified. Presently, laser ablation techniques have been primarily applied to deposit thin films on flat substrate materials. To deposit discontinuous particulate coatings, the laser induced plume from the target comes in contact with an agitated bed of core particles (size 1–800μm). The pressure and nature of the background gas (inert or active) controls the cluster size of the particles in the laser plume. Experiments were conducted for laser deposition of silver particles on alumina core particles by excimer laser (wavelength = 248 nm and pulse duration = 25 nanosecond) irradiation of silver targets. The surface coverage and the coating of the film wasf found to depend on the laser parameters (energy density and number of laser pulses) as well as the residence time of the core particles in the plume regime. The films were characterized by wavelength and energy dispersive x-ray spectroscopy and x-ray photoelectron spectroscopy techniques.

Zinc sulphide (ZnS) particles are efficient phosphors for application in flat-panel displays. Spherical ZnS particles were prepared by precipitation from a homogeneous solution. Nanoparticles of 20 to 40 nm having a very narrow size distribution could be synthesized by using complexing chelates such as acetate and acetylacetonate. Complexing of the precipitating cation with the anions present in the system lead to a limited concentration of free cations in the solution. This strongly influences the kinetics of the primary particle agglomeration/growth, resulting in nanometer-sized ZnS particles. Nanostructured ZnS synthesized in this way are polycrystalline particles composed of crystallites of 5–10 nm. The synthesis of very small, non-agglomerated, nanocrystalline particles in the 5–10 nm size range was also possible, making use of a strong complexing ligand (thioglycerol) during the synthesis. The synthesis of controlled monosized ZnS particles will be presented and discussed. The photoluminescence characteristics of ZnS make this material a suitable candidate as phosphor for application in low voltage display technology. The effect of Mn2+ doping on the luminescence characteristics of ZnS will also be discussed.

The use of nanoparticle colloids for spray deposition of Cu-In-Se precursor films and subsequent thermal treatment to form CuInSe2 (CIS) films has been investigated. In the present study, the metathesis reaction between Na2Se in methanol and metal salts (i.e., Cu(BF4)2 and/or InI3) in pyridine produced CuSe, In2Se3, and CuInSe2.5 nanoparticle colloids. Purified colloid was sprayed onto heated molybdenum-coated sodalime glass substrates to form CuInSe2.5/Mo and In2Se3/CuSe/Mo precursor films. These precursor films were subjected to various thermal treatments in an effort to produce large-grained CIS films from the nano-sized precursors. The annealed CIS films were characterized by scanning electron microscopy (SEM) and x-ray diffraction (XRD). Results of this continuing effort will be discussed.

The influence of nano-thick hydrophilic or hydrophobic films on adhesion properties of particles to surfaces has been investigated. Al2O3 and Ag layers were deposited on Ag and Al2O3 core particles, respectively by a modification of pulsed laser deposition technique. The as-received and surface-modified particles were further coated by a secondary process with submicron Al2O3 particles. We observe that deposition of hydrophobic or hydrophilic surfaces affects the surface coverage of secondary particles on core particles and hence the adhesion characteristics.

Chemical mechanical polishing (CMP) is a critical step in the fabrication of integrated circuits. Each layer of deposited material must be planarized before the next layer of circuitry can be formed. In CMP, a chemically active solution is used to modify the substrate so that a particulate abrasive may polish more efficiently. Modification of the surface often requires high oxidizer concentrations or pH extremes. Under these circumstances the stability of the polishing slurry and prevention of particulate attachment to the substrate is a difficult problem. In this study, atomic force microscopy (AFM) has been used to directly measure the forces between surfaces that simulate those in CMP. Initial investigation has focused on modeling the polishing of tungsten interconnect material by alumina slurries at acidic pH and evaluating the role surfactants can play in the stabilization of the polishing slurry and CMP processes.

The surfaces of insulating alumina particles have been coated with high temperature superconducting, Yba2Cu3O7-x, and colossal magnetoresistive, Pr0.65Ba0.05 Ca0.3 Mn03-x, films. These coatings on particulate surfaces have been realized using a new technique which is based on laser assisted generation of homogeneous flux of ablated materials in front of a fluidized bed of host particles. The coated particulates have been characterized using scanning electron microscopy (SEM), energy dispersive x-ray (EDX) analysis, Auger electron spectroscopy (AES), and superconducting quantum interference device (SQUID) magnetometer.

In laser cleaning of micro-particles from solid surface, the adhesion force between the particles and the substrate surface and the thermal expansion of both particles and substrate play important roles in determining the threshold laser fluence. Taking Van der Waals force and cleaning force due to fast thermal expansion of particles and substrate surface induced by pulsed laser irradiation into account, a cleaning model was established for removal of tiny particles from substrate surfaces. The cleaning condition and cleaning threshold can be obtained from this model. This model can qualitatively and quantitatively predict how the laser cleaning process depending on laser incident direction, laser wavelength, particle size, particle material and substrate material. Theoretical predictions have been verified by the experimental results. Laser cleaning of micro-particle has wide applications in microelectronics and magnetic recording industries.