Modification of diamond single crystals by chromium ion implantation with sacrificial layers

Single-crystal diamond surfaces were implanted with chromium ions. Ion energies chosen were 120 and 180 keV. Ion doses of 1x10(17) cm(-2) were applied at a substrate temperature of 750 degrees C. Reduced lattice damage could be obtained by deposition of a titanium sacrificial layer with a thickness of 10 and 50 nm before implantation. Depth profiles of the elemental binding states were taken by photoelectron spectroscopy. The effect of the sacrificial layer thickness on diamond lattice damage was investigated by infrared spectroscopy.     

Array-orderly single crystalline silicon nano-wires

Array-orderly single crystal silicon nano-wires (SiNWs) using self-organized nano-holes of anodically oxidized aluminum were fabricated. By field emission scanning electron microscope (FESEM) and transmission electron microscope (TEM), the well-orderly single crystal SiNWs arrays were observed. The interval of the SiNWs is excellent symmetrical and consentaneous. The diameter and the length are around 35 nm and 4 μm, respectively. Furthermore, the energy dispersive X-ray spectroscopy analysis (EDX) indicated that the SiNWs consist of silicon core and silicon oxide sheath mainly. The Raman scattering was also carried out to analyze the structure of the oriented SiNWs. Finally, the growth mechanism of the SiNWs was discussed.     

The mechanism responsible for extraordinary Cs ion selectivity in crystalline silicotitanate

Combining information from time-resolved X-ray and neutron scattering with theoretical calculations has revealed the elegant mechanism whereby hydrogen crystalline silicotitanate (H-CST; H2Ti2SiO7 x 1.5 H2O) achieves its remarkable ion-exchange selectivity for cesium. Rather than a simple ion-for-ion displacement reaction into favorable sites, which has been suggested by static structural studies of ion-exchanged variants of CST, Cs(+) exchange proceeds via a two-step process mediated by conformational changes in the framework. Similar to the case of ion channels in proteins, occupancy of the most favorable site does not occur until the first lever, cooperative repulsive interactions between water and the initial Cs-exchange site, repels a hydrogen lever on the silicotitanate framework. Here we show that these interactions induce a subtle conformational rearrangement in CST that unlocks the preferred Cs site and increases the overall capacity and selectivity for ion exchange.     

Highly stable redox-active molecular layers by covalent grafting to conductive diamond

We demonstrate a modular "click"-based functionalization scheme that allows inexpensive conductive diamond samples to serve as an ultrastable platform for surface-tethered electrochemically active molecules stable out to ～1.3 V vs Ag/AgCl. We have cycled surface-tethered Ru(tpy)(2) to this potential more than 1 million times with little or no degradation in propylene carbonate and only slightly reduced stability in water and acetonitrile.     

Role of projectile and surface temperatures in the energy transfer dynamics of protonated peptide ion collisions with the diamond {111} surface

The effects of temperature on energy transfer during collisions of protonated diglycine ions, Gly(2)-H(+), with a diamond {111} surface were investigated by chemical dynamics simulations. The simulations were performed for a collision energy of 70 eV and angle of 0 degrees with respect to the surface normal. In one set of simulations the initial surface temperature, T(surf), was varied from 300 to 2000 K, while the Gly(2)-H(+) vibrational and rotational temperatures were maintained at 300 K. For the second set of simulations the Gly(2)-H(+) vibrational temperature, T(vib), was varied from 300 to 2000 K, keeping both the Gly(2)-H(+) rotational and surface temperatures at 300 K. Increasing either the surface temperature or Gly(2)-H(+) vibrational temperature to values as high as 2000 K has, at most, only a negligible effect on the partitioning of the incident collision energy to the surface and to the vibrational and rotational modes of Gly(2)-H(+). To a good approximation, the initial surface and peptide ion energies are nearly adiabatic during the collisional energy transfer. This adiabaticity of the initial peptide ion energy agrees with experiments (J. Phys. Chem. A 2004, 108, 1). A more quantitative analysis of the effects of T(vib) and T(surf) shows there are small, but noticeable, effects on the energy transfer efficiencies. Namely, increasing the vibrational or surface temperature results in a near-linear decrease in the energy transfer to the degrees of freedom associated with this temperature.     

Simulation of channelled ion ranges in crystalline silicon

We present results from a channelled ion range simulation model based on separation of ion trajectories into three different categories known as random, channelled, and well-channelled. We present this for boron projectiles incident along the Si 〈1 0 0〉 direction. Stopping powers for channelled particles, well-channelled, and random particles are determined using experimental ratios of random and channelled stopping powers for a boron/silicon system. We have found the particle range distributions and the mean range of particles in crystalline channels. A new program code has been developed for the implementation of the presented model. The results are compared with experimental data as well as Crystal-transport and range of ions in matter, stopping and ranges of ions in matter, and projected range algorithm programs. We have found good agreement between our calculations and experiment, with an average discrepancy of 7%. Our model is also able to simulate the observed shift towards larger depths for the main ion distribution under channelling conditions.     

Shape control of single crystalline bismuth nanostructures

A synthesis approach for shape control of single crystalline Bi nanostructures has been developed. By controlling the molar ratio of PVP and Bi in a polyol process, Bi nanocubes with an edge length of approximately 60-80 nm, triangular nanoplates with an edge length of 200-500 nm, and nanospheres with an average diameter of 75 nm have been successfully synthesized. In the same synthetic process, Bi nanobelts with lengths of up to 80 microm and widths of up to 0.6 microm were synthesized in large quantities by introducing a trace amount of Fe3+ species into the reaction system. These single crystalline nanostructure Bi materials are expected to find potential applications in a variety of areas including high efficiency thermoelectric devices.     

High sensitivity of diamond resonant microcantilevers for direct detection in liquids as probed by molecular electrostatic surface interactions

Resonant microcantilevers have demonstrated that they can play an important role in the detection of chemical and biological agents. Molecular interactions with target species on the mechanical microtransducers surface generally induce a change of the beam's bending stiffness, resulting in a shift of the resonance frequency. In most biochemical sensor applications, cantilevers must operate in liquid, even though damping deteriorates the vibrational performances of the transducers. Here we focus on diamond-based microcantilevers since their transducing properties surpass those of other materials. In fact, among a wide range of remarkable features, diamond possesses exceptional mechanical properties enabling the fabrication of cantilever beams with higher resonant frequencies and Q-factors than when made from other conventional materials. Therefore, they appear as one of the top-ranked materials for designing cantilevers operating in liquid media. In this study, we evaluate the resonator sensitivity performances of our diamond microcantilevers using grafted carboxylated alkyl chains as a tool to investigate the subtle changes of surface stiffness as induced by electrostatic interactions. Here, caproic acid was immobilized on the hydrogen-terminated surface of resonant polycrystalline diamond cantilevers using a novel one-step grafting technique that could be also adapted to several other functionalizations. By varying the pH of the solution one could tune the -COO(-)/-COOH ratio of carboxylic acid moieties immobilized on the surface, thus enabling fine variations of the surface stress. We were able to probe the cantilevers resonance frequency evolution and correlate it with the ratio of -COO(-)/-COOH terminations on the functionalized diamond surface and consequently the evolution of the electrostatic potential over the cantilever surface. The approach successfully enabled one to probe variations in cantilevers bending stiffness from several tens to hundreds of millinewtons/meter, thus opening the way for diamond microcantilevers to direct sensing applications in liquids. The evolution of the diamond surface chemistry was also investigated using X-ray photoelectron spectroscopy.     

The study of carbon nanotubes as conductive additives of cathode in lithium ion batteries

Carbon nanotubes (CNTs), including multi-walled CNTs (MWCNTs) and single-walled CNTs (SWCNTs), are employed as conductive additives in lithium ion batteries. The effects of MWCNTs’ carbon precursors, diameter, and weight fraction on the electrochemical behavior of MWCNTs/LiCoO₂ composite cathode are investigated. Meanwhile, a comparison is made between SWCNTs /LiCoO₂ and MWCNTs/LiCoO₂. Among the three kinds of carbon precursors: CH₄, natural gas, and C₂H₂, MWCNTs prepared from CH₄ are very fit for acting as conductive additives due to their better crystallinity and lower electrical resistance. MWCNTs with smaller diameter favor improving the electrochemical behavior of MWCNTs/LiCoO₂ composite cathode at higher charge/discharge rate owing to their advantage in primary particle number in unit mass. To make full use of LiCoO₂ at higher rate, it is necessary to add at least 5 wt.% of MWCNTs with a diameter 10~30 nm. However, SWCNTs are not expected to be added into LiCoO₂ composite cathode since they tend to form bundles.     

Oxygen-18 surface exchange and diffusion in Li2O-deficient single crystalline lithium niobate

¹⁸O/¹⁶O isotope exchange in combination with SIMS depth profiling was used to investigate oxygen transport in Li₂O-deficient single crystalline LiNbO₃ in the temperature range 983 ≤ T/K ≤ 1188 at 200 mbar oxygen. Within the limit of experimental error and for the investigated range of temperatures no significant differences between transport parallel and transport perpendicular to the c-axis were found. The following temperature dependencies were determined: for oxygen tracer diffusion D = 6.4 × 10⁻³exp[−333 kJ/mol/(RT)] m²/s; and for oxygen surface exchange k = 7.8 × 10²exp[−288 kJ mol⁻¹/(RT)] m/s. The activation enthalpy obtained for tracer diffusion can be interpreted as the enthalpy of migration of extrinsic oxygen vacancies induced by impurities with lower valency on niobium sites.     

Thermodynamic surface properties of single crystal faces of xenon calculated by employing the Einstein model of crystalline solids

By broadening the scope of the Einstein statistical-mechanical treatment of a crystalline solid to cover also low-index faces, and using the Lennard-Jones interaction potential and, in addition, adopting an approximate monolayer-nearest-neighbor model, we have calculated the thermodynamic properties of (100) and (111) single crystal faces of Xe(s) in the temperature range 20–80 K. The reversible cleavage work (that corresponds to the Gibbs σ-quantity of interfaces) was found to be on the order of 20–30 mJ m⁻² and is largely due to reduction of the pair-wise dispersion interactions for monolayer atoms as compared with the atoms in the bulk of the crystal. For an unstrained crystal, σ diminishes slightly with temperature for both energetic as well as entropic reasons. On the other hand, the differential work of stretching a solid interface, γ, is a negative quantity (−5 to −30 mN m⁻¹), corresponding to surface pressure, the main reason being that upon (elastic, homogeneous) stretching, the vibration energy levels of the top monolayer are shifted upward, at the same time becoming more closely spaced. It is shown that such a stretching operation causes the T × surface excess entropy term to increase at a faster rate than the corresponding surface energy term, which accounts for the negative sign found for γ. On the same basis, we can also verify that the general, though sometimes questioned, Shuttleworth relation, is necessarily fulfilled for an ideally terminated (metastable) Xe crystal face with a filled monolayer of immobile Xe atoms. As a matter of fact, this equation merely represents an alternative mathematical disguise of the basic energy differential expression for the monolayer.     

A highly conductive and crystalline graphite-like polymer from 2,4-hexadiyn-1,6-diol

Poly-(2,4-hexadiyn-1,6-diol) (PHDO), prepared by NbCl₅/(n-Bu)₄Sn catalyzed metathesis of HDO, was pyrolyzed at various temperatures and electrical and structural properties of resulting polymers were investigated by FT-IR, Laser Raman, CP/MAS ¹³C-NMR and X-ray diffraction methods. The polymer obtained by pyrolysis of PHDO at 800°C showed a conductivity of about 10 S/cm at room temperature. The structure of the polymer seems to be a graphite-like crystal consisting of condensed aromatic layers. © 1994 John Wiley & Sons, Inc.     

Lithium ion induced stabilization of the liquid crystalline DNA

A comparative study of the effects of alkali metal ions Li(+), Na(+), K(+), Rb(+), and Cs(+) on the liquid crystalline organization of high-molecular-weight calf thymus DNA using polarized light microscopy was performed. Major differences in the behavior of Li(+) as compared to the other ions were found. Critical DNA concentration expected to exhibit anisotropic behavior was found to be the same for all the monovalent ions, except for Li(+). DNA initially showed cholesteric textures, which later changed to higher ordered columnar phase for all ions, with the cholesteric-columnar transition facilitated upon increasing the size of the counterion. For Li(+) ion, a nematic schlieren-like texture was formed initially, which after a few days changed to a highly stable (for more than 2 months) biphasic cholesteric-columnar arrangement. The observed differences between Li(+) and other alkali metal ions could be rationalized on the basis of the higher number of hydration water molecules of Li(+) and its complexation behavior. Highly stable DNA mesophases may find applications in the field of nanoelectronics, in designing biosensing units, and in DNA chips.     

Orientation of water molecules by the diamond surface

The properties of water in suspensions of diamond powders with particle sizes from 125–160 μm to 2–10 nm were studied. The dielectric constant of water in these suspensions changed from 1.3 × 10³ to 2.6 × 10⁶. The particle sizes correlated with the dielectric constants. The sound velocity of “diamond” water exceeded the initial velocity by 15–20 m/s. The crystals isolated from “diamond” water after prolonged storage had specific diffraction patterns and IR spectra. Their composition was not determined.     

Fractional surface termination of diamond by electrochemical oxidation

The crystalline form of sp(3)-hybridized carbon, diamond, offers various electrolyte-stable surface terminations. The H-termination-selective attachment of nitrophenyl diazonium, imaged by AFM, shows that electrochemical oxidation can control the fractional hydrogen/oxygen surface termination of diamond on the nanometer scale. This is of particular interest for all applications relying on interfacial electrochemistry, especially for biointerfaces.     

Experimental evaluation of single ion activities

When an ion-exchange membrane separates two electrolyte solutions having two different co-ions and a common counterion a bi-ionic potential (bi-co-ionic potential) appears across the membrane. If the membrane is ideally permselective for counterions and the activities of counterions on both sides of the membrane are equal to each other, the membrane potential Δψ becomes zero. We selected KCl as a reference electrolyte because of a symmetrical electrolyte in aqueous solutions. Then, the mean activity of ions in KCl may be assumed to be equal to each single ion activity at low molalities. Single ion activity in a test electrolyte containing K⁺ ion or Cl⁻ ion was estimated from the molality of KCl at Δψ=0 by interpolating bi-co-ionic potential to zero for KCl/membrane/LiCl, NaCl, C₆H₅COOK, or p-CH₂CHC₆H₄SO₃K systems. The values of single ion activity coefficients estimated in this work were fairly different not only from the mean activity coefficients of ions but also from the single ion activity coefficients estimated by Debye–Hückel formula.     

Optical recognition of surface chirality at Au(hkl) single crystalline surfaces by second harmonic generation rotational anisotropy

Two-dimensional chirality at naturally chiral gold single crystalline surfaces was detected and characterized using optical second harmonic generation (SHG) measurements. SHG rotational anisotropy (SH-RA) patterns at Au(643)S and Au(643)R surfaces were mirror symmetric to each other. Systematic SH-RA measurements at chiral Au(hkl) surfaces with the same step and kink structures but different (111) terrace widths showed a linear correlation between surface step density and SH-RA fitting parameters arising from defects. These results indicate that SH-RA measurements provide information not only on surface chirality but also on density of surface defects.