Formation of Charged Particle Tracks in Solids

A criterion for formation of etchable tracks in solids is suggested using the well-known concepts of ionization and thermal spikes, diffusion process with useful and justified assumptions, and present or published experimental and theoretical investigations on the same subject. The suggested criterion is useful for a wide spectrum of researchers including development and applications of track recording materials, ions implantation, sputtering and other areas, which include interactions of charged particles with solids.     

Manipulation of nanoparticles using dynamic force microscopy: simulation and experiments

82 , M = Sc, Y, La) are discussed. The first ¹³C hyperfine structure has been analyzed in detail and at least seven electronically different groups of carbon atoms could be assigned by simulations of the ESR spectra. The strong similarity of the ¹³C satellite structure suggests the preference of one cage isomer for the scandium group C₈₂ endohedrals. The geometric structure and the electronic structure of all nine fullerene cage isomers of La@C₈₂ were studied by approximate density-functional-based theoretical calculations. A C_3v isomer was found as the most stable one. The manifold of ¹³C hyperfine coupling constants could be interpreted on the basis of the calculated spin density distributions. Received: 15 September 1997/Accepted: 16 October 1997     

Fabrication and characterization of In2O3 nanowires

In₂O₃ nanowires were successfully fabricated through a simple gas-reaction route in argon atmosphere. These nanowires have diameters ranging from 20 nm to 50 nm and lengths up to tens of micrometers. High-resolution transmission electron microscopy observations and the electron-diffraction (ED) pattern reveal that the In₂O₃ nanowires are formed by the stacking of (2) planes along the [1] direction, which is parallel to the wire axis. A strong and wide ultraviolet (UV) emission band centered at around 392 nm is observed for the first time in the room-temperature photoluminescence measurement in addition to the usual blue emission (468 nm). Moreover, five discrete fine peaks (372 nm, 383 nm, 406 nm, 392 nm and 413 nm) are further identified in this broad UV band. Received: 10 April 2002 / Accepted: 12 April 2002 / Published online: 19 July 2002     

Atomic layer deposition coating of ZnO shell for GaN-ZnO core-sheath heteronanowires

We have synthesized GaN-core/ZnO-shell nanowires and investigated effects of the ZnO coating. The X-ray diffraction pattern showed that as-synthesized samples are composed of GaN and ZnO. Transmission electron microscopy indicated that the deposited ZnO shell layer is poly-crystalline. The photoluminescence (PL) spectrum of GaN has been changed by the ZnO coating, where emission bands centered at roughly 1.9 eV, 2.5 eV, and 3.3 eV were newly added to the emissions from core GaN nanowires. We found that overall PL intensity has been significantly increased by coating the ZnO shell layers.     

GaN nanotweezers

A new form of GaN nanomaterial (nanotweezers) has been obtained by chemical vapor deposition on an etched cubic MgO (100) plane. The nanotweezers consist of a bottom rod and two arms. The bottom rods have diameters of about 100–150 nm and lengths of about 200–500 nm, on which two arms grow out. The bottoms of the arms are about 40–70 nm and the tops are about 15–30 nm in diameter, and 0.8–1.5 μm in length. X-ray and electron diffractions indicate the nanotweezers are zinc blende gallium nitride. We infer that the fabrication of the GaN nanotweezers is associated with small convex hillocks on the surface of the etched cubic MgO (100) single-crystal substrates and that the nanotweezers grow by a growth mechanism that is similar to vapor-phase heteroepitaxy. Received: 23 April 2002 / Accepted: 25 April 2002 / Published online: 10 September 2002 RID="*" ID="*"Corresponding author. Fax: +86-10/8264-9531, E-mail: xlchen@aphy.iphy.ac.cn     

Effects of organic acids on the size-controlled synthesis of rutile TiO2 nanorods

Size-controlled synthesis of pure rutile-phase TiO₂ nanorods was carried out by a hydrothermal method using different organic acids as modifiers, and metatitanic acid and concentrated sulfuric acid as raw materials. The synthesized rutile TiO₂ nanorods were characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The effects of organic acid modifiers on the sizes of rutile TiO₂ nanorods were investigated. It was found that the steric effect occurred by the organic modifiers and non-polarity of organic acids were beneficial to the formation of small-sized rutile TiO₂ nanorods. The strongly coordinative interaction between the carboxyl (or hydroxyl) group of the modifier and the surface of TiO₂ nanoparticles effectively inhibited the crystal growth.     

Investigation of Ni/Ta contacts on 4H silicon carbide upon thermal annealing

Nickel and Tantalum thin films with 3:5 thickness ratios were deposited in succession onto 4H-SiC substrate at room temperature. The samples were then heated in situ in vacuum at 650, 800 or 950 °C for 30 min. Glancing angle X-ray diffraction (XRD), Auger electron spectroscopy (AES) and current-voltage (I-V) technique were used for characterising the interfacial reactions and electrical properties. Amorphous Ni-Ta can be formed by solid-state reaction at 650 °C. The minor dissolved Ni in the Ta metal promotes the reaction between Ta and SiC. With increasing annealing temperature up to 950 °C, the dominant carbide changes from Ta₂C to TaC and a layer structure is developed. Electrical measurements show that ohmic contact is formed after annealing at or above 800 °C.     

Surface chemical functionalized single-walled carbon nanotube with anchored phenol structures: Physical and chemical characterization

Surface functionalization of single-walled carbon nanotube was carried out by introducing ylides groups containing anchored phenol structures. The functionalized nanotube is characterized using elemental analysis, Fourier transform infrared spectroscopy, field emission scanning electron microscopy, thermogravimetric analysis, Raman spectroscopy and zeta potential measurements. Elemental and FT-IR analysis reveal the successful functionalization of azomethine ylides. Raman spectroscopic studies corroborates that the surface functionalization does not affect the basic crystal domain size of the nanotubes. Functionalized carbon nanotubes exhibit higher zeta potential values showing its higher dispersant ability in water and acetone solvent in comparison to pure carbon nanotube.     

Scattering study of vitrifying Cr-Ti solutions

The configurations involved in the spontaneous vitrification of quenched Cr-Ti -phase alloys were investigated by X-ray diffraction and elastic neutron scattering. The two methods yield complementary information: X-rays are sensitive to the topology whereas neutrons emphasize the chemical fluctuations. The results show the presence of two simultaneous but opposing processes, the formation of CsCl-type chemical short range order on one hand and progressive structural disordering on the other. The latter ultimately leads to amorphization. The probable reason for this behavior is that at the temperature in question only the chromium atoms are mobile.     

Limiting fragmentation from scale-invariant merging of fast partons

Exploiting the idea that the fast partons of an energetic projectile can be treated as sources of colour radiation interpreted as wee partons, it is shown that the recently observed property of extended limiting fragmentation implies a scaling law for the rapidity distribution of fast partons. This leads to a picture of a self-similar process where, for fixed total rapidity Y  , the sources merge with probability varying as 1/y$1/y$.