Characterization and field-emission property of aligned porous carbon nanotube film by hydrogen-ion implantation

To enhance the field emission of carbon nanotube (CNT) films, a novel technique that combines hydrogen-ion implantation used in the silicon-on-insulation smart-cut process and plasma-enhanced chemical vapor deposition was developed to produce an aligned porous carbon nanotube (AP-CNT) film on a Si substrate. All steps in the AP-CNT synthesis were carried out in vacuum, which reduced possible contamination. The morphology and the field-emission properties of the CNT films were investigated and results show that CNT holes with a diameter of 5 m and a depth of 30 m were produced in the AP-CNT film. The alignment of the CNTs is visibly improved. Due to the implantation treatment, the turn-on field of the CNT films decreased from 1.5 to 0.8 V/m, and the emission-current (and dot) density obviously increased. This field-emission improvement may mainly arise from the holes formed in the AP-CNT films. The edges of these holes not only intensified the electron emission but also increase the emission site density of the CNT films. PACS 81.05.Uw; 61.72.Tt; 85.45.Db     

Pulsed laser crystallization of hydrogen-free a-Si thin films for high-mobility poly-Si TFT fabrication

The possibility to fabricate high-mobility polysilicon TFTs by nanosecond pulsed laser crystallization of unhydrogenated amorphous Si thin films has been investigated. Two types of lasers have been used: a large area ( 1 cm²) single ArF excimer laser pulse and a small diameter ( 100 m) frequency-doubled Nd:YAG laser beam, working in the scanning regime. Processed films have been characterized in detail by different optical and microscopic techniques. Device performances indicate that the best results are achieved with the excimer laser leading to high mobility values (up to 140 cm²/Vs) which are much larger than in polysilicon TFTs fabricated onto the same quartz substrates by low-temperature thermal (630° C) crystallization of amorphous Si films (_fe55 cm²/Vs).     

A Compact Sol-Gel Laser with Dynamic Distributed Feedback

Lasing in dynamic-distributed-feedback (DDFB) laser on the basis of a modified sol-gel matrix activated with Rhodamine 4C is reported. The lasing is achieved in the range of 590 nm with a wavelength tuning of about 20 nm. The slope efficiency of the sol-gel DDFB laser excited by the second harmonic radiation of a YAG:Nd³⁺ laser with a pulse duration of 40 ns is 16.5% at a lasing wavelength of 593 nm. The DDFB laser is also characterized by a threshold pumping energy of 90 J and a pumping energy density up to 40 mJ/cm². The typical spectral width of the laser line is 0.025 nm.     

Excimer-laser-induced ablation of the high-T c superconductor Bi-Ca-Sr-Cu-O

The ablation of ceramic Bi-Ca-Sr-Cu-O by XeCl-excimer-laser projection has been investigated. In both air and vacuum, etching commences at about 2.4 J/cm² and then increases with fluence within the regime investigated ( <) 20 J/cm²). At 10 J/cm² the respective etch rates are around 1 m/pulse and 1.6 m/pulse.     

Micro-Raman spectroscopy in polycrystalline CuInSe2 formation

The crystalline formation of CuInSe₂ thin films has been investigated using micro-Raman spectroscopy and AES composition analysis. It is confirmed that the Raman peaks are stongly dependent on the surface morphology and the Cu:In:Se ratio. In the films annealed at 315°C, crystalline grains larger than 2 m show Raman peaks at 174 cm^–1 and 258 cm^–1. The In content is very low and the Cu:Se ratio is about 1:1 in these grains. The low In concentration is thought to be due to the formation of In₂O₃ on the surface. On the other hand, random structures of 1–2 m grains found in films annealed at temperatures below 305°C show peaks at 174 cm^–1 and 186 cm^–1 instead of 258 cm^–1 and have a Cu:In:Se ratio of 1:1:3–4. Thus the 186 cm^–1 peak is thought to be related to a Cu, In-deficient phase when compared to stoichiometric CuInSe₂. The optimum annealing condition was found by analyzing the Raman spectra and composition of different crystalline CuInSe₂ grains. Films annealed under this condition exhibited a clear Raman peak at 174 cm^–1 and consisted of clusters of crystals less than 1 m in size.     

A study of thermal and mechanical effects on materials induced by pulsed laser drilling

Holes drilled in metals and silicon using different short-pulse lasers (copper vapour, Nd : YLF and titanium: sapphire) were characterized under optical and electron microscopy. The aim was to analyze and compare the thermal and mechanical effects on materials induced by laser drilling with a wide range of pulse widths (50 ns to 200 fs) and power densities (10⁸ W/cm² to 10¹⁵ W/cm²).Heat affected structural zones around micro-holes drilled in cold-rolled copper were revealed by analyzing ion-polished hole sections in the scanning electron microscope using electron channelling contrast. The heat affected zones were found to have a maximum width of 5 m to 10 m, independent of the duration of the pulses. Mechanically and thermally induced deformations and slip phenomena, including prismatic punching, were observed in laser-drilled molybdenum monocrystals. The dislocation arrangement which developed during laser drilling of silicon monocrystals was visualized by transmission electron microscopy.The microscopic studies showed that for percussion drilling in the high fluence range characterized by high ablation rates of a few micrometres per pulse the use of shorter pulses (_H < 50 ns) did not lead to any appreciable reduction in the melt component, material re-deposition or thermal load on the wall of the hole. In addition, the increasing mechanical loads on the material due to the higher pressure in the drill channel becomes a limiting factor for the precision of the processing.     

Tailoring of the functional properties of sol–gel films on Pt/TiO2/SiO2/(100)Si substrates: (Pb,La)TiO3/(Pb,Ca)TiO3 multilayer heterostructures

Preferentially oriented sol–gel (Pb,Ca)TiO₃/(Pb,La)TiO₃/(Pb,Ca)TiO₃ and (Pb,La)TiO₃/(Pb,Ca)TiO₃/(Pb,La)TiO₃ multilayer heterostructure thin films deposited on silicon-based substrates have been studied and compared with identically prepared (Pb,La)TiO₃ (PTL) and (Pb,Ca)TiO₃ (PTC) films. The existence in their texture of two components that contribute to the net polarization in the direction normal to the plane of the film, 001 and 111, results in significant ferroelectric and pyroelectric properties. P_r=26 Ccm^-2 and =28.5×10^-9 Ccm^-2K^-1, and P_r=17 Ccm^-2 and =22.8×10^-9 Ccm^-2K^-1, have been achieved, respectively, in the PTL/PTC/PTL and PTC/PTL/PTC heterostructures. The surface roughness of these films provides a high specific surface that can be interesting for infrared detectivity. An increase of the dielectric permittivity in the whole temperature interval up to the transition temperature has been observed for both heterostructures with respect to the PTL and PTC films. This effect is due to a release of stress in the heterostructures that is revealed by the increase of the tetragonal distortion, c/a, of these films. PACS 68.55.Jk; 77.80.-e; 77.84.Dy     

Effects of catalysts on the internal structures of carbon nanotubes and corresponding electron field-emission properties

Using a chemical vapor deposition (CVD) method, multi-walled carbon nanotubes with uniform diameters of approximately 10 nm were synthesized on silicon substrates by the decomposition of acetylene using Fe, Co and Ni as the catalysts. Catalyst effects on the internal structures of the carbon nanotubes were evident in the Fe, Co and Ni catalyzed nanotubes. Although these nanotubes demonstrated similar morphologies, due to the variety of internal structures, the nanotubes synthesized from different catalysts demonstrated various electron field-emission characteristics including turn-on field, threshold field and field enhancement factor. Compared with carbon nanotubes from Ni catalyst, nanotubes from Fe and Co with the same diameters have better field-emission properties. Graphite layers in nanotubes from Fe and Co are much straighter and more parallel to the tube axis with fewer defects. For instance, the turn-on field and threshold field for nanotubes from Ni are 5 V/m and 9 V/m, respectively. These electric fields are much higher than those for nanotubes from Fe, which are 0.35 V/m and 2.8 V/m, respectively. This could be due to the effect of catalysts on the work function of nanotubes, since the catalyst particle usually terminates the free end of the nanotube, and the influence of internal structure on electron transportation along the nanotube axis. Therefore, this study suggests that besides a small diameter, good graphitization (crystallization) is an important prerequisite for a good carbon nanotube emitter. PACS 79.70.+q; 68.37.Lp; 81.07.De     

Positron mobility in anthracene

We have measured the positron mobility in a sample of scintillation grade anthracene at two temperatures. We obtain at 300 K: =(26.0±0.9±2.6) cm²V^–1s^–1 and at 77 K: =(33.4±1.1±3.3) cm²V^–1s^–1, where the first error estimate is statistical and the second is systematic. We have also made preliminary measurements on a highly purified sample that yields =(130±3±20) cm² V^–1 s^–1 at 300 K. The data are consistent with the hypothesis that the positron is scattered from both impurities and acoustic phonons in the first sample, and predominantly from photons in the second. It appears that positrons in pure anthracene crystals are delocalized and have a mean free path of about 85 Å at room temperature.     

Laser-reactive ablation deposition of silicon-nitride films

Silicon-nitride films were deposited on silicon waters by XeCl (308 nm) excimer-laser ablation of silicon in low-pressure (0.05–5 mbar) ammonia atmospheres. Series of 10 000 pulses at the repetition rate of 8 Hz were directed to the target surface. The fluence was set at about 5 J/cm². Pulse duration was about 30 ns. The deposited films were characterized by different techniques (X-ray diffraction, X-ray photoelectron spectroscopy, Auger electron spectroscopy, Rutherford backscattering spectrometry, scanning electron microscopy, profilometry). Silicon-nitride films with thickness close to 1 m were obtained under specific experimental conditions.     

Field emission from nitrogen-implanted CVD diamond film grown on silicon wafer

Nitrogen was implanted into chemical vapor deposition (CVD) diamond films and the electron field emission properties of the nitrogenated diamond films were investigated. Nitrogen implantation was carried out using 10 keV in the dose range from 1×10¹⁶ to 5×10¹⁷ cm^-2 at room temperature. Raman and X-ray photoelectron spectroscopy measurements revealed that nitrogen implantation damaged the structure of the diamond film and promoted the formation of sp² C–C and sp² C–N bondings. Increasing the implantation dose could lower the threshold field of the emission of the diamond film from 18 V/m to 4 V/m. The effective work function of the nitrogen-implanted CVD diamond films was estimated to be in the range of 0.01–0.1 eV. The enhancement of field emission for nitrogen-implanted CVD diamond films was attributed to the increase of the sp² C bonds fraction and the formation of defect bands within the bulk diamond band gap induced by nitrogen implantation, which could alter the work function and elevate the Fermi level. Consequently, the energy barrier for electron tunneling was reduced.     

Fabrication and characteristics of double-fused vertical-cavity lasers

We discuss the fabrication process and characteristics of three consecutive runs of double-fused 1.5-m vertical-cavity lasers. We have measured light-current characteristics of over three hundred lasers with ten different diameters between 6 and 60 m and observe a yield of over 95%. The process and design improvements resulted in a low pulsed threshold current of 3 mA on a number of 6- and 8-m-diameter devices and threshold current density of 2 kA cm^–2 on 60-m-diameter devices at room temperature.     

High quality,high-<Emphasis Type="Italic">k</Emphasis> gate dielectric: amorphous LaAlO<Subscript>3</Subscript> thin films grown on Si(100) without Si interfacial layer

High-k dielectric amorphous LaAlO₃ thin films have been grown on n-type Si(100) substrates by laser molecular beam epitaxy. The interfacial characteristics of the LaAlO₃ films on Si were measured by high-resolution transmission electron micrography and X-ray photoemission spectroscopy. A sharp interface without a silica inter-layer between the LaAlO₃ film and Si substrate was observed. Atomic force microscopy measurements indicated that the root-mean-square surface roughness within a 2m×2m area of the LAO films was 0.12 nm. The flatband voltage and fixed charge density of the 8 nm thickness LaAlO₃ films were about 0.355 V and 1.8×10¹²/cm², respectively. The leakage currents of the LaAlO₃/Si(100) samples with different film thicknesses of 5, 8 and 12 nm were 0.45, 0.23 and 0.05 mA/cm², respectively, at a +1 V dc bias voltage. LaAlO₃ appears to be one of the most promising high dielectric constant materials for use in future ultra large scale integrated devices. PACS 77.55+f; 77.84.Bw; 73.40.Qv     

Slow and monoenergetic (3Heμ−)+ beam production and novel applications

Based upon the recent discovery at UT MSL/KEK, a new idea is proposed for producing a slow and monoenergetic (3.2 keV) (³He^–)⁺ ion beam by using particle decay of the (d³He) muon molecule formed during the (d) to³He transfer reaction. The proposed intense (³He) beam as well as the less intense (⁴He) beam will open up way to various new types of important CF experiments.     

A cluster calculation of the muon hyperfine field in nickel

We have performed a partially self-consistent, first-principles calculation of the hyperfine field at a ⁺ at the octahedral interstitial site in ferromagnetic nickel. Using a package of programs made available by the Department of Theoretical Chemistry of the University of Mexico, various calculations were performed of the spin-dependent charge density in the central region of a spherically averaged superposition of atomic charge densities. In this way it was found that: (1) The electronic configuration of bulk Ni contains a significant amount of 4p-states, in agreement with other calculations¹. (2) The ⁺ produces only a weak perturbation on its nearest-neighbor Ni atoms. (3) The hyperfine field at the ⁺ is opposite to the bulk magnetization and has the value –590 G, in good agreement with the measured² value of –641 G.     

Observation of plastic deformation in TiAlCN/a -C ceramic nanocomposite coating

Extensive plastic deformation of titanium aluminum carbonitride/amorphous carbon nanocomposite coating at room temperature was observed in this study. Nanoindentation measurement showed that the coating hardness was 24.4 GPa with the plasticity of 57.6%. The critical load of 1.3 m coating in scratch test was beyond 100 N. The depth of the 100 N scratch track identified by microstylus profilometer was 6.7 m, while the thickness of the coating in the center of the scratch track observed by scanning electron microscopy was 0.4 m, which is only about one third of that for the as-deposited coating. The amorphous carbon with sp² hybrid and -bonding is proposed to account for this unique plasticity. PACS 81.15.Gh; 81.07.Bc     

Photo-chemical vapor deposition of hydrogenated amorphous silicon films

A photo-chemical vapor deposition, using ultraviolet light excitation and a mercury photo-sensitization, was investigated for depositing hydrogenated amorphous silicon films from SiH₄. The photoelectric and structural properties were examined to characterize the deposited films. Those properties were depended strongly on substrate temperature, and the films which were deposited at a substrate temperature more than 200°C contained dominant SiH configurations. A relatively large single crystalline grain size of about 0.5 m was observed in a 1.0 m thick film, which was obtained at a substrate temperature as low as 200°C. Phosphorus impurity doping into the films and Pt-Schottky diode fabrication were also attempted.     

Topographical and surface chemical characterization of nanosecond pulsed-laser micromachining of titanium at 532-nm wavelength

Electropolished titanium was micromachined by single, 5-ns pulses from a frequency-doubled (532 nm) Nd:YAG laser. The focal spot size was varied from 10 to 100 m and the applied fluences varied from the melting threshold (1 J/cm²) to more than 100 J/cm². The resulting craters were imaged by optical microscopy, topographically characterized by interferometry and chemically characterized on the surface by small-spot depth-profiling Auger electron spectroscopy and small-spot X-ray photoelectron spectroscopy. The prevailing ablation regime for the studied fluences and focal spot sizes was found to be melt ejection. The surface chemical characterization showed growing oxide thickness in the heat-affected zone (around the center spot) for increasing fluence but no difference inside the crater. Titanium nitride formation was found inside the crater. PACS 81.65; 87.80Mj     

UV laser-induced grating formation in PDMS thin films

Excimer laser (193 nm and 157 nm) induced ablation and structure formation in poly-dimethylsiloxane (PDMS) thin films is demonstrated. Ellipsometric measurements provide values of the optical constants of the films as well as their thicknesses, which are below 1 m. At fluences above 160 mJ/cm² two pulses of UV light induce gratings with at minimum 1-m periods and crossed gratings with 4-m periods. The structure heights are between 10 nm and 20 nm with ridge widths of several hundred nanometres. The ablation occurs after a single incubation pulse with a threshold that increases logarithmically with the ablation wavelength increasing from 157 nm to 1064 nm. At 193 nm the ablation rate for 2 J/cm² is 127 nm/pulse. PACS 79.20.La; 34.50.Dy; 68.55.Jk