We report here on applying electric fields and dielectric media to achieve controlled alignment of single-crystal nickel silicide nanowires between two electrodes. Depending on the concentration of nanowire suspension and the distribution of electrical field, various configurations of nanowire interconnects, such as single, chained, and branched nanowires were aligned between the electrodes. Several alignment mechanisms, including the induced charge layer on the electrode surface, nanowire dipole-dipole interactions, and an enhanced local electrical field surrounding the aligned nanowires are proposed to explain these novel dielectrophoretic phenomena of one-dimensional nanostructures. This study demonstrates the promising potential of dielectrophoresis for constructing nanoscale interconnects using metallic nanowires as building blocks.

We demonstrate the directed assembly and integration of ZnO nanobridges into working devices on silicon-on-insulator substrates. The “pick and place” method of nanowire integration is avoided and metal catalysts are not used. ZnO nanowires (NWs) were grown selectively via a vapor-solid method using a patterned ZnO thin-film seed layer that was deposited on Si trench sidewalls via atomic layer deposition. ZnO NWs grew to span the trench and self-terminate on the opposing surface, effectively forming electrically accessible horizontal ZnO nanobridge devices. Vertical bridge devices were also constructed using undercut islands. Directly grown horizontal ZnO nanobridge devices were operated as gas and UV sensors, demonstrating that this method represents a significant step towards practical large-scale integration of nanodevices into Si microelectronics.

We demonstrate selective growth of vertically aligned ZnO nanowires on a (100) Si substrate using a patterned thin film ZnO seed layer. Metal catalysts, which can be a source of contamination, were not used. A single-crystalline structure with c-axis preferred orientation and a strong intrinsic near band edge photoluminescence peak at 380 nm with no detectable visible photoluminescence indicate a lack of defects and the high quality of the ZnO nanowires.

Multiwalled carbon nanotubes ͑CNTs͒ were coated, using atomic layer deposition, with a thin layer of ZnO and subsequently annealed. Studies of the morphologies of the ZnO-coated CNTs revealed no significant change in the internal structures ͑multiwalled graphite sheets͒ and the diameters of the CNTs, but the ZnO appeared to form bead-shaped single crystalline particles attaching to the surface of the nanotubes. The electron field-emission properties of the ZnO-coated CNTs were dramatically improved over both uncoated CNTs and ZnO nanowires. It is reasoned that numerous ZnO "nanobeads" on the surface of the nanotubes serve as additional emission sites, in addition to the tips of CNTs, and result in the enhancement of electron field emission.

We present a floating-potential dielectrophoresis method used for the first time to achieve controlled alignment of an individual semiconducting or metallic single-walled carbon nanotube (SWCNT) between two electrical contacts with high repeatability. This result is significantly different from previous reports, in which bundles of SWCNTs were aligned between electrode arrays by a conventional dielectrophoresis process where the results were only collected from the control electrode regions. In this study, our alignment focus is not only on the regions of the control electrodes but also on those of the floating electrodes. Our results indicate that bundles of carbon nanotubes along with impurities were first moved into the region between two control electrodes while individual nanotubes without impurities were straightened and aligned between two floating electrodes. The measurements for the back-gated nanotube transistors made by this method displayed an on-off ratio and transconductance of 10(5) and 0.3 microS, respectively. These output and transport properties are comparable with those of nanotube transistors made by other methods. Most importantly, the findings in this study show an effective way to separate individual nanotubes from bundles and impurities and advance the processes for site-selective fabrication of single-SWCNT transistors and related electrical devices.

Photoionization efficiency (PIE) data for (CO)+2, (N2)+2, and (NO)+2 have been obtained near the thresholds using the molecular beam method. The ionization energies (IE) for (CO)2, (N2)2, and (NO)2 were measured to be 13.05±0.04 eV (950±3 Å), 14.69±0.05 eV (844±3 Å), and 8.736±0.002 eV (1419.2±0.3 Å), respectively. Using these values, the known IE’s for CO, N2, and NO, and the estimated binding energies for (CO)2, (N2)2, and (NO)2, the bond dissocations energies for CO+⋅CO, N+2⋅N2, and NO+⋅NO were deduced to be 0.97±0.04, 0.90±0.05, and 0.598±0.006 eV, respectively. From the analysis of the PIE curve for (NO)+2, the IE’s of (NO)2 to NO+(?1S+, v = 1)⋅NO and NO+(?1S+,v = 2)⋅NO were determined to be 8.997±0.007 eV (1 378±1 A°) and 9.253±0.013 eV (1 340±2 A°), respectively. This measurement supports the conclusion that the bonding of NO+ in NO+⋅NO is stronger than that of NO, but weaker than that of NO+. The IE’s for (CO)3, (N2)3, and (NO)n = 3–6 were also measured.

No abstract

Thin HfO 2 films have been deposited on silicon via atomic layer deposition using anhydrous hafnium nitrate ͓Hf(NO 3) 4 ͔. Properties of these films have been investigated using x-ray diffraction, x-ray reflectivity, spectroscopic ellipsometry, atomic force microscopy, x-ray photoelectron spectroscopy, and capacitance versus voltage measurements. Smooth and uniform initiation of film growth has been detected on H-terminated silicon surfaces. As-deposited films were amorphous, oxygen rich, and contained residual NO 3 and NO 2 moieties from the nitrate precursor. Residual nitrates were desorbed by anneals Ͼ400°C, however, the films remained oxygen rich. Crystallization of thin films (Ͻ10 nm) occurred at roughly 700°C. For films less than ϳ10 nm thick, the effective dielectric constant of the film and any interfacial layer ͑neglecting quantum effects͒ was found to be in the range of kϳ10Ϫ11. From a plot of electrical thickness versus optical thickness, the dielectric constant of the HfO 2 layer was estimated to be k HfO 2 ϳ12 Ϫ14. Leakage current was lower than that of SiO 2 films of comparable equivalent thickness. The lower than expected dielectric constant of the film stack is due in part to the presence of an interfacial layer ͑likely HfSiO x). Excess oxygen in the films may also play a role in the reduced dielectric constant of the HfO 2 layer.