Through control of the grain-boundary structure, principally in the nature of the nanoscale intergranular films, a silicon carbide with a fracture toughness as high as 9.1 MPa.m1/2 has been developed by hot pressing β-SiC powder with aluminum, boron, and carbon additions (ABC-SiC). Central in this material development has been systematic transmission electron microscopy (TEM) and mechanical characterizations. In particular, atomic-resolution electron microscopy and nanoprobe composition quantification were combined in analyzing grain boundary structure and nanoscale structural features. Elongated SiC grains with 1 nm-wide amorphous intergranular films were believed to be responsible for the in situ toughening of this material, specifically by mechanisms of crack deflection and grain bridging. Two methods were found to be effective in modifying microstructure and optimizing mechanical performance. First, prescribed post-annealing treatments at temperatures between 1100 and 1500°C were seen to cause full crystallization of the amorphous intergranular films and to introduce uniformly dispersed nanoprecipitates within SiC matrix grains; in addition, lattice diffusion of aluminum at elevated temperatures was seen to alter grain-boundary composition. Second, adjusting the nominal content of sintering additives was also observed to change the grain morphology, the grain-boundary structure, and the phase composition of the ABC-SiC. In this regard, the roles of individual additives in developing boundary microstructures were identified; this was demonstrated to be critical in optimizing the mechanical properties, including fracture toughness and fatigue resistance at ambient and elevated temperatures, flexural strength, wear resistance, and creep resistance.

The Metal Induced Growth (MIG) of nanowires has the potential to alter the conventional lithographic techniques to provide an easier fabrication method in nanoelectronics. Our group has studied the MIG technique to synthesize poly-silicon and nano size structures. This work gave silicon nanowires of 20∼200 nm diameter, 3∼10νm length and single crystal structure. Until now, the growing of silicon nanowires has been understood by two models. One is an oxide- assisted mechanism and the other is a metal catalyst assisted mechanism. Both cases need higher growth temperatures above 900°C. We are now proposing the repeatable growth of silicon nanowires at a low processing temperature, 550∼600°C, which is the lowest silicon nanowire growth temperature without using a gas type silicon source (silane).

This novel method to grow silicon nanowires has several advantages: (1) low processing temperature; (2) straight line growth; (3) single crystal structure and (4) repeatability. This Si nanowire growing mechanism is based on NiSi formation.

Surface-functionalized polymeric nanoparticles (NP) are a versatile medium for drug delivery and imaging. The surface functionality is typically exploited to introduce molecules such as polymers and biomolecules to improve cellular localization, DNA binding and circulation. NP bearing surface functionality are typically prepared from polymers possessing functionalizable backbones or by layer-by-layer assembly of polyelectrolytes onto unmodified particles. We have developed a process to produce functionalized polymeric NP in a single step using non-functionalized polymers. This is achieved by the entrapment of polymeric functional moieties from an aqueous phase in a rapidly solidifying polymer core. NP were characterized using light scattering, scanning electron microscopy, zeta potential (ζ) measurement, fluorescent microscopy, and X-ray photoelectron spectroscopy (XPS). Stable NP ranging in diameter from 70 to 400nm with narrow polydispersity (PDI) can be produced by this process. The presence of functional moieties on the NP surface was verified by isoelectric point measurement and XPS. We foresee a number of uses for these functionalized nanoparticles, including drug delivery and modification of hard and soft material surfaces (both synthetic and biological) for tissue engineering.

A method to generate line pattern structures in thin organic films with embedded gold and silver nanoparticles is introduced. The films are irradiated with ultrashort, linearly polarized laser pulses. As we find out from electron microscopy (TEM, SEM), periodically arranged line-like structures are formed after the irradiation. We have used so far three different laser wavelengths (266 nm, 400 nm, 800 nm). The resulting structure periods in the range of 170 nm to 600 nm indicate a linear correlation of the period length of the line structures and the wavelength of the incident laser light. The direction of the particle lines corresponds to the linear polarization of the laser pulses. The anisotropic structure modification is mirrored in corresponding anisotropic optical film properties.

We study the role of a strong electron confinement on the surface-enhanced Raman scattering from molecules adsorbed on small noble-metal nanoparticles. We describe a novel enhancement mechanism which originates from the different effect that confining potential has on s-band and d-band electrons. We demonstrate that the interplay between finite-size and screening efects in the nanoparticle surface layer leads to an enhancement of the surface plasmon local field acting on a molecule located in a close proximity to the metal surface. Our calculations show that the additional enhancement of the Raman signal is especially strong for small nanometer-sized nanoparticles.

Ni nanowires were fabricated by electrochemical deposition in the pores of alumina filtration membranes, with the diameter around 200nm. To study the magnetic and electrical properties of Ni nanowires, individual nanowire was selected and connected with metal electrodes. Single and multiple constrictions were formed on the nanowires by focused ion beam (FIB). The wires were further thinned using oxygen plasma oxidation. Magnetoresistance curves were studied and compared before and after FIB trimming and oxidization.

Crystalline semiconductor nanoparticles are of interest for a variety of electronic and opto-electronic applications. We report experimental studies of the synthesis and characterization of crystalline silicon nanoparticles using a constricted-mode capacitive RF plasma in continua- tion of results reported earlier from an RF inductively coupled plasma [1]. The constricted-mode discharge is based on a thermal plasma instability yielding a high-density plasma filament, which rotates at a high frequency. Silane is dissociated, leading to particle nucleation and growth. Particles are extracted by passing the particle-laden gas through an orifice to form a beam and col- lected by inertial impaction.

We are able to reproducibly synthesize highly oriented freestanding single-crystal silicon nanoparticles. Monodisperse particle size distributions centered at a 35nm particle diameter with a geometric standard deviation of 1.3 are obtained. Transmission electron microscope (TEM) studies show uniformly shaped cubic particles. Selected-area electron diffraction patterns indi- cate the particles have the diamond-cubic silicon structure. To study the electrical properties of these particles, metal-semiconductor-metal structures were fabricated and analyzed.

Nonvolatile nanoscale memories with ultra-long retention times have been demonstrated for both binary and multilevel applications. These devices were based on nanowires functionalized with a self- assembled monolayer of redox active molecular wires, where the bit was represented by the charge stored in the redox molecules and the nanowire conductance was used as the readout. Our devices exhibited reliable operation, on/off ratios ∼ 104 and retention times ∼ one month, one of the longest retention times ever achieved with nanoscale devices. These devices were further tailored for multilevel data storage with appreciable noise margins, representing a new concept for functional devices. Our work clearly demonstrates the potential of combining nanowires and molecular wires for superior performance.

An array of copper nanowires (50-110 nm in diameters) was deposited by the electrolysis of CuSO4-H2SO4 solution at room temperature using DC current. The array was created by forcing deposited copper to follow a pattern of nano tunnels. These nano tunnels were formed with two different methods: anodizing an aluminum film that coated on a silicon wafer to form nano holes within oxidized alumina, and etching the ion-tracked polycarbonate membrane.

The difference in top morphologies of the Cu nanowires in these templates is very marked. The copper nano wires deposited in anodized alumina template form the separate spherical balls with diameter of about 10 νμ on the surface of the alumina film, in spite of the template thickness of only 0.5 νm. In contrast, no such Cu agglomeration was formed with copper nano wires deposited in holes of polycarbonate. This variance in copper morphologies is likely due to the difference of the interface energy between Cu and anodic alumina and that of Cu and polycarbonate.

Multiple branched SnO2 nanowire junctions have been synthesized by thermal evaporation of SnO powder. Their nanostructures were studied by transmission electron microscopy and field emission scanning electron microcopy. It was observed that Sn nanoparticles generated from decomposition of the SnO powder acted as self-catalysts to control the SnO2 nanojunction growth. Orthorhombic SnO2 was found as a dominate phase in nanojunction growth instead of rutile structure. The branches and stems of nanojunctions were found to be an epitaxial growth by electron diffraction analysis and high resolution electron microscopy observation. The growth directions of the branched SnO2 nanojunctions were along the orthorhombic [110] and [1 1 0]. The growth of SnO2 nanojunction is controlled by a self-catalytic vapor-liquid-solid growth using Sn nanoparticle catalysts.

We present a method that allows us to produce aligned metallic nanowires on almost any material. This method recently enabled us to produce interconnected platinum nanowire networks on polymeric Nafion® or gold nanowires on Teflon AF. We will explain the principle of this method by means of a reference material, the so called layered transition metal dichalcogenides (TMDC) crystals. The method is based on producing cracks in thin films as templates, using large sticking coefficient differences and long diffusion lengths. The underlying mechanism that forms the template cracks is mechanical stress. In the case of the TMDC crystals this stress is introduced in the substrate by an electronic interaction between the metal used for the nanowires and the TMDC-crystal. The large difference in the condensation coefficient is an immanent property of layered crystals for many different adsorbates. Obtained by cleavage along a so called “Van-der-Waals-gap”, surfaces of such crystals are atomically flat over hundreds of microns. As a consequence of their layered character the surfaces have no reconstruction and almost no step edges or other defects, which is the basis for the long diffusion length. In contrast, the rare defects have a very high sticking coefficient and act as excellent nucleation centers. Therefore, after metal evaporation on such surfaces in UHV, various structures can be formed in a self organized processes. We observed, e.g., clusters in fractal or geometric arrangements or large nanowire networks on the surfaces [1]. In order to understand, why the different structures form, a systematic study of the growth parameters, (nucleation, diffusion length, evaporated metal, influence of the substrate-crystal), is necessary. Therefore, we first carried out diffusion studies on these surfaces. We could show that in extreme cases (Cu on metallic TaS2) diffusion length of more than 50νm could be observed combined with a nucleation probability of almost zero. This is evident from a growth mode showing similarities with the DLA (Diffusion Limited Aggregation) growth process. In contrast, metal diffusion (Cu) on the geometrically similar surfaces on the semiconducting (WSe2) surface shows much a shorter diffusion length and no DLA growth. We suggest a model to explain the different diffusion behavior as a key to understand the different self organized structures. Learning from the TMDC crystals, we show the application on technological more important materials.

Well oriented vertical ZnO nanowires (NWs) are grown on c-plane sapphire via a vapor- phase transport process using an Au thin film as a catalyst. This new finding is unexpected due to the fact that the lattice mismatch between the zinc oxide and the underlying substrate is 18%. X- ray diffraction (XRD) analysis shows that single-crystal, wurtzite NWs grow in the [0001] direction normal to the basal sapphire plane, which proves that a-plane sapphire is not essential for growth of vertical ZnO NWs, as has been previously stated.[1] We have found that by controlling the thickness of the Au-film and pre-growth annealing of the Au/sapphire substrate NWs can be grown either tilted or vertical. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) studies on Au films with thicknesses ranging from 1 to 10 nm show that in the absence of film annealing, NWs can be grown 32° tilted from the surface normal, whereas pre-annealed Au films result in growth of NWs in the surface normal direction. We attribute the formation of the normal and tilted growth directions to the surface concentration of O and Al ions on sapphire.

It is well documented that buried layers in quantum dot (QD) superlattices influence the position of quantum dots in the subsequently grown layers through strain field interactions (e.g.1,2, 3,4). Using the Focused Ion Beam (FIB) tomographic technique we have reconstructed the 3D relationship of successive layers of coherent Ge QDs separated by epitaxial Si capping layers - a “QD superlattice”.

Techniques such as Atomic Force Microscopy (AFM) and Scanning Tunneling Microscopy (STM) can only look at a single surface layer of QDs or, in the case of Transmission Electron Microscopy (TEM), look at a two-dimensional projection of a three-dimensional volume so that 3D relationships need to be inferred. Since the strain interactions are complex, an enhanced fundamental understanding of these self-organization mechanisms can more directly be obtained from full 3D reconstructions of these structures.

By capping with Si at 300°C we were able to grow QD superlattices with QDs tens of nanometers in height. This places them within the resolution of the FIB tomographic technique to reconstruct. Using the FIB we performed in-situ serial sectioning of the QD superlattice and then reconstructed the QD superlattice. The reconstruction was then analyzed to investigate the ordering of the QDs.

Results from a reconstruction of a superlattice matrix will be presented with analysis of the self-ordering of the QDs. Observations of a novel self-limiting (in height) morphology, the quantum mesa, associated with the capping technique used will also be discussed.

We have developed a new pulsed laser deposition technique using two Nd:YAG laser beams for the nucleation of silicon carbide (SiC) crystalline nano-particles and single crystalline SiC thin films. Transmission electron microscopy and atomic force microscopy observation suggest that several nanometer size SiC particles can be prepared by the new pulsed laser deposition (PLD) method using two Nd:YAG laser beams (1064nm and 532nm). X ray photoelectron spectroscopy measurements suggest that the silicon/carbon composition ratio of the prepared SiC thin films can be controlled by laser fluence and wavelength.

We present a theoretical study of the optical properties of one-dimensional (1-D) metal nanostructures including nanorods and nanotubes. Although the optical properties of gold nanotubes are similar to that of gold nanorods, both the longitudinal and transverse plasmon resonances of gold nanotubes show much larger red-shifting and narrower. The E-field calculations indicate that the 1-D gold nanostructures, particularly gold nanotubes have great potential for applications to SERS.

Surfaces of ceria (CeO2) particles have been studied by electron energy-loss spectroscopy in a field-emission gun scanning transmission electron microscope. All the ceria particles analyzed contained Ce3+ at the surface. Rare-earth impurities such as La were enriched at the surface and were observed for particles ranging from tens to hundreds of nanometers in size. The oxidation state of the cerium ion is measured from the Ce M5/M4white-line intensity ratio.

Zinc oxide (ZnO) nanorods were fabricated directly on silicon substrate with diameters in the range of 70-350 nm and up to 15 νm long using pulsed-laser deposition at a relatively low processing temperature (450°C) without any catalytic template. The influences of substrate temperatures and the oxygen pressures on the formation of ZnO nanorods were investigated. The Raman scattering studies and scanning electron microscopy results indicated that the ZnO nanorods were well aligned along c-axis and isolated from each other. The additional Raman modes at ∼ 477 cm−1 and 574 cm−1 were observed in the c-axis oriented ZnO nanorods which attributed to the activation of the upper and lower surface phonon modes respectively.

Scanning transmission electron microscopy (STEM) coupled with electron energy loss spectroscopy (EELS) was used to determine the distribution of ZnS shell material on colloidal core-shell CdSe/ZnS quantum dots (QDs). A sub-nm electron probe was placed at various locations on core-shell QDs to ascertain the chemical distribution of the shell material. While a definite shell of ZnS was detected surrounding the CdSe core, the integrated EELS signals from positions around the QD suggest the distribution of the shell material may not be uniform. A non-uniform shell implies a reduced quality of the QD surface passivation.

The synthesis of water soluble nanomagnetic conducting polyaniline with an average particle size of 8nm ±1nm is presented. The particle growth morphology during reaction kinetics was controlled by using polyelectrolyte mediated dual oxidant-dopant system. The synthesis was carried out in a single reactor and the entire synthetic approach follows the principles of green chemistry. Dual oxidant-dopant system offers a solvent less chemical route for the synthesis of nanomagnetic polyaniline with maximum yield production.

We studied the self-assembly of nanoscopic building blocks comprised of polymer-tethered nanoparticles using computer simulation and predict that these building blocks can assemble into mono- and multi-layer sheets and shells. The simulations further demonstrate that for some nanoparticle geometries and tethered nanoparticle topologies, ideas from block copolymers, surfactants and liquid crystals can be used to predict the ordered morphologies attained via self- assembly and that for specific cases the morphologies are consistent with Israelachvili packing rules.