Effects of stress on the structure of indium-tin-oxide thin films grown by pulsed laser deposition

The effects of stress in pulsed laser deposited (PLD) indium-tin-oxide (ITO) films formed on glass substrate at 200 °C and oxygen pressures (P_{o 2}) ranging from 0.1 to 2.7 Pa are discussed. Grazing incidence X-ray diffraction (GIXRD) investigations of the ITO films show splitting of the diffraction peaks and significant changes in the lattice constants for films deposited at low P_{o 2} and when the thickness of the films is larger than 150 nm. These features were due to intrinsic stress caused by the incidence of energetic particles on the substrate during growth. The splitting of the peaks only occurred in the bulk of the films, while near the surface, single peaks were evidenced, indicating the existence of two layers. No apparent splitting of the diffraction peaks or shifts in peak positions occurred in the ITO layers with thickness less than 100 nm. In spite of the presence of stress in the ITO films, resistivity less than 3 10, ^-4 cm was obtained. © 2001 Kluwer Academic Publishers     

Reshaping the tips of ZnO nanowires by pulsed laser irradiation

Vertically aligned ZnO nanowires have been synthesized by a hydrothermal method. After being irradiated by a short laser pulse, the tips of the as-synthesized ZnO nanowires can be tailored into a spherical shape. Transmission electron microscopy revealed that the spherical tip is a single-crystalline piece connected to the body of the ZnO nanowire, and that the center of the sphere is hollow. The growth mechanism of the hollow ZnO nanospheres is proposed to involve laser-induced ZnO evaporation immediately followed by re-nucleation in a temperature gradient environment. The laser-irradiated ZnO nanowire array shows hydrophobic properties while the original ZnO nanowire array shows hydrophilicity. The as-grown ZnO nanowire arrays with hollow spherical tips can serve as templates to grow ZnO nanowire arrays with very fine tips, which may be a good candidate material for use in field emission and scanning probe microscopy.      

Direct-write patterning of indium-tin-oxide film by high pulse repetition frequency femtosecond laser ablation

Ablation of indium oxide doped with tin oxide (ITO) from glass substrates is described. Laser pulse energy and focus spot size were varied in single-pulse, single-spot ablation tests and for ablation of linear features with scanned multiple pulses. The single-pulse ablation threshold of ITO was smaller than that of the glass substrate so the entire thickness of ITO could be removed in a single pulse or with overlying multiple pulses without the possibility of substrate ablation. Linear features could be created at much higher scanning speeds using a high repetition frequency (100 kHz) Yb fiber amplified laser as compared to a lower repetition frequency (2 kHz) laser. An analysis showed that incubation effects lowered ITO ablation thresholds when pulse frequency was high relative to scanning speed, contributing to large feasible scanning speeds for high pulse frequency lasers.     

ZnO nanowires by pulsed laser vaporization: synthesis and properties

We report a new pulsed-laser vaporization (PLV) technique to synthesize nanowires of single-crystal ZnO having a wurtzite structure by using colloidal gold nanoparticles as seeding catalysts. The average diameter of the nanowires is approximately 13 nm, with a very narrow range of 7 to 25 nm. The nanowires are straight for the most part, with the axes parallel to the [0001] growth direction. Raman and photoluminescence spectra from the nanowires and bulk ZnO are similar except for a approximately 510 nm band in the nanowires due to oxygen vacancies. The bulk-like vibrational and electronic properties of the nanowires is due to the diameter being larger than the threshold below which quantum confinement-induced effects are expected.     

Growth of SiO(x) nanowires by laser ablation

Amorphous SiO(x) nanowires (NWs) were synthesized using laser ablation of silicon-containing targets. The influence of various parameters such as target composition, substrate type, substrate temperature and carrier gas on the growth process was studied. The NWs were characterized using high resolution scanning and transmission electron microscopes (HRSEM and HRTEM) with their attachments: electron dispersive spectroscopy (EDS) and energy electron loss spectroscopy (EELS). A metal catalyst was found essential for the NW growth. A growth temperature higher than 1000?°C was necessary for the NW formation using an Ar-based carrier gas at 500?Torr. The use of Ar-5%H(2) instead of pure Ar resulted in a higher yield and longer NWs. Application of a diffusion barrier on top of the Si substrate guaranteed the availability of metal catalyst droplets on the surface, essential for the NW growth. Ni was found to be a better catalyst than Au in terms of the NW yield and length. Two alternative sequences for the evolution of the amorphous SiO(x) NWs were considered: (a)?the formation of Si NWs first and their complete oxidation afterwards, which seems to be doubtful, (b)?the direct formation of SiO(x) NWs, which is more likely to occur. The direct formation mechanism was proposed to advance in three stages: preferential adsorption of SiO(x) clusters on the catalyst surface first, a successive surface diffusion to the catalyst droplet lower hemisphere, and finally the formation and growth of the NW between the catalyst and the substrate.     

Physical consequences of the equivalence of conditions for the steady-state growth of nanowires and the nucleation on triple phase line

A new theoretical model describing the steady-state growth and crystalline structure of semiconductor nanowires (NWs) is proposed and its physical consequences are considered. It is demonstrated that the Nebol’sin-Shchetinin condition (nonwetting of the NW side surface by the liquid drop) necessary for the steady-state growth of NWs according to the vapor-liquid-solid (VLS) mechanism is equivalent to the Glas condition of nucleation on the triple phase line for the monocentric NW growth. An energy criterion for the steady-state growth of NWs is formulated in the general case of faceted NW side surface. Effective surface energies are found that determine the activation barrier for nucleation at the NW top. Based on the proposed model, the issue of determining the III–V semiconductor NW crystal structure (cubic zinc blende type versus hexagonal wurtzite type) is considered. In particular, it is shown that a decrease in the surface energy of a catalyst must lead to the predominant formation of a cubic phase, which is confirmed by experimental data on the growth of GaAs nanowires according to the VLS mechanism with Au and Ga catalysts.     

Effect of the growth conditions on the spatial features of Re nanowires produced by directional solidification

The effects of the solidification parameters, such as growth rate and temperature gradient, on the distance and diameter of Re nanowires have been examined. Both the spacing and diameter increase with decreasing growth rate and temperature gradient, respectively. The ratio of fiber spacing to diameter is 9.1. In addition, it was demonstrated that the temperature gradient influences interface undercooling in the same way as the growth rate and may be used as an additional parameter to control fiber spacing and diameter.     

Characterizations of Ga-doped ZnO nanowires depending on growth temperature and target-substrate distance in hot-walled pulsed laser deposition

Using a hot-walled pulsed laser deposition (HW-PLD), nanowires (NWs) comprising 3 weight% Ga-doped ZnO (3GZO) have been successfully grown on a sapphire substrate. The structural and optical properties of 3GZO nanostructures have also been systematically investigated with respect to the target-substrate (T-S) distance and the growth temperature. The morphology transformations of nanostructures such as nano-horns, NWs, and clusters are strongly affected by growth temperatures due to different thermal energy. Also, the morphologies of nanostructures--including length, diameter, and density--are strongly affected by the T-S distance, illustrating a close correlation between the growth kinetics and the position in the plume formed by the particles from the GZO target. Also, the exciton that is bound to the neutral donor (D(0)X) peak of the 3GZO nanostructures is found at the low temperature PL spectra, indicating successful Ga-doping into ZnO NWs.     

Hardness of titanium carbide films deposited on silicon by pulsed laser ablation

Hardness of titanium carbide films deposited on silicon (111) substrate by pulsed laser ablation is evaluated in dependence on laser beam fluence and the film thickness. Measurements were performed with the use of a common microhardness testing equipment, the indenter penetartion depth being more than thickness of the coating. Two methods based both on a law-of-mixtures approach were employed to calculate the film hardness from the measured hardness of the composite film-substrate system. One of them accounts for the indentation size effect. The hardness is revealed to reduce significantly with an increase of the film thickness and the laser beam fluence.     

Growth of diborides thin films on different substrates by pulsed laser ablation

The growth of scandium, titanium and zirconium diborides thin films by pulsed laser ablation technique on different substrates has been studied. In situ reflection high energy electron diffraction and ex situ X-ray diffraction analyses indicate that the films are strongly c-axis oriented on all the substrates and also epitaxial, apart from Si(111), where the in plane orientation is poor. Atomic force microscopy imaging reveals a flat surface in all the epitaxial samples, with roughness lower than 1 nm. The results on silicon carbide and sapphire are very promising for using these materials as buffer layers in magnesium diboride thin films growth, especially to improve epitaxy and to prevent oxygen diffusion from the substrate, and also to study the influence of lattice strain on MgB₂ critical temperature.     

Carbon nitride films deposited by reactive sputtering and pulsed laser ablation

Carbon nitride films were deposited by reactive sputtering process and by pulsed laser ablation process with substrate bias. By applying the RF bias, it enables the ion irradiation on to the depositing film surface continuously. ECR plasma source was used for reactive sputtering. Nd:YAG laser (λ=532 nm, 210 mJ) was used to ablate a graphite target in the nitrogen atmosphere. The film properties were examined by XPS, Raman, nanoindentation measurement, and FE-SEM. It was shown that the films deposited by reactive sputtering had smooth surface and its hardness of approximately 30 GPa. However, the films deposited by pulsed laser ablation had uneven surface and low hardness. Both processes, the atomic composition ratio of N/C and sp³ bonding ratio increased with ion bombardment energy up to 100-150 eV, and level off above it. The maximum atomic composition ratio of N/C was 0.35 for reactive sputtering and 0.24 for laser ablation.     

Effect of aging on copper nanoparticles synthesized by pulsed laser ablation in water: structural and optical characterizations

Effect of aging on copper nanoparticles synthesized by pulsed laser ablation of copper plate in water was studied. By characterization studies of the aged nanoparticles, it is found that copper nanoparticles converted into Cu@Cu₂O nanostructure. The synthesized nanomaterial is characterized with UV-Visible absorption, transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) and Raman and photoluminescence (PL) spectroscopic techniques. TEM image shows that the aged nanoparticles get assembled into cactus like structure and are spherical in shape with average diameter 7 nm and dispersion 2 nm. XRD and FTIR spectrum confirm the formation of Cu@Cu₂O in the aged sample. Raman spectrum also confirms the presence of Cu₂O nanoparticles. PL spectrum of the aged nanoparticles shows a direct allowed transition with bandgap energy of 2·24 eV. The mechanism for synthesis of core-shell nanoparticles and formation of self-assembly of nanoparticles is also discussed.     

Optical measurement in carbon nanotubes formation by pulsed laser ablation

Carbon nanotubes (CNTs) were produced by laser ablation of a graphite composite target in argon and nitrogen ambient gas. To investigate the effect of nitrogen gas on CNTs formation, the plasma plume was examined using optical emission spectroscopy. The vibrational temperature of C₂ molecules was estimated by fitting of a Swan band spectrum. The temperature in N₂ ambient gas is lower than that in Ar ambient gas. In a nitrogen atmosphere, the spectrum intensity of C₂ Swan band was enhanced and CN violet system was also observed. Soot collected in the reaction tube was observed using FE-SEM and TEM. The soot deposited in the nitrogen gas contained more bundled CNTs than those in Ar ambience.     

Calcium phosphate thin film processing by pulsed laser deposition and in situ assisted ultraviolet pulsed laser deposition

Calcium orthophosphates (CaP) and hydroxyapatite (HA) were intensively studied in order to design and develop a new generation of bioactive and osteoconductive bone prostheses. The main drawback now in the CaP and HA thin films processing persists in their poor mechanical characteristics, namely hardness, tensile and cohesive strength, and adherence to the metallic substrate. We report here a critical comparison between the microstructure and mechanical properties of HA and CaP thin films grown by two methods. The films were grown by KrF* pulsed laser deposition (PLD) or KrF* pulsed laser deposition assisted by in situ ultraviolet radiation emitted by a low pressure Hg lamp (UV-assisted PLD). The PLD films were deposited at room temperature, in vacuum on Ti–5Al–2.5Fe alloy substrate previously coated with a TiN buffer layer. After deposition the films were annealed in ambient air at 500–600 °C. The UV-assisted PLD films were grown in (10^–2–10^–1 Pa) oxygen directly on Ti–5Al–2.5Fe substrates heated at 500–600 °C. The films grown by classical PLD are crystalline and stoichiometric. The films grown by UV-assisted PLD were crystalline and exhibit the best mechanical characteristics with values of hardness and Young modulus of 6–7 and 150–170 GPa, respectively, which are unusually high for the calcium phosphate ceramics. To the difference of PLD films, in the case of UV-assisted PLD, the GIXRD spectra show the decomposition of HA in Ca₂P₂O₇, Ca₂P₂O₉ and CaO. The UV lamp radiation enhanced the gas reactivity and atoms mobility during processing, increasing the tensile strength of the film, while the HA structure was destroyed.     

铜纳米棒和纳米线控制生长的条件研究

利用CuSO4·5H2O和NaOH为原料，一种六元脂肪族醇为还原剂，X射线衍射（XRD）和扫描电镜（SEM）为主要表征手段，研究了不同水热条件下铜的还原。结果表明，水热条件变化时，可以得到形貌各异的氧化亚铜和金属铜。其中，当n（OH）：n（Cu^2＋）=4，加入醇的物质的量等于Cu^2＋的物质的量，水热温度为180℃，反应时间为20h时，得到产物经X射线衍射分析确定为金属铜，扫描电镜照片显示在产物中有纳米棒和纳米线形成，纳米棒的直径在100-500nm不等，长径比在50以上，而纳米线比纳米棒更细，蜿蜒曲折，柔韧性较好。     

Nanoparticles of antimony sulfide by pulsed laser ablation in liquid media

In the present article, antimony sulfide nanoparticles have been synthesized by pulsed laser ablation of an antimony sulfide pellet in distilled water and isopropyl alcohol. The target was irradiated by 1064 and 532 nm from a pulsed Nd:YAG laser operated at 10 Hz and pulse width of 10 ns at room temperature. Analysis of the morphology, crystalline phase and elemental composition were done using transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDX), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The optical band gap energies of these colloidal nanoparticles were evaluated from UV–Visible absorption spectra. It was observed that the morphology, size, and optical properties of the antimony sulfide nanoparticles depend on the wavelength of the laser and the liquid media.     

Fabrication of PDPhSM matrix nanocomposite thin films by pulsed laser ablation

We have developed a new method to fabricate poly(diphenylsilylenemethylene) (PDPhSM) matrix nanocomposite thin films containing copper nanoparticles produced by pulsed laser ablation in this paper. First of all, 1,1,3,3-tetraphenyl-1,3-disilacyclobutane (TPDC) films were deposited on 4 cm² silicon substrates cut from c-Si wafers by conventional vacuum evaporation under a pressure of 3.0 × 10⁻⁵ Torr; then copper nanoparticles were deposited onto the TPDC films by pulsed laser ablation; finally the TPDC films with copper nanoparticles were heated in an electric furnace in an air atmosphere at 553 K for 10 min to induce ring-opening polymerization of TPDC. The results indicated that it is possible to fabricate PDPhSM matrix nanocomposite thin films using copper nanoparticles produced by laser ablation. The morphology and size distribution of copper nanoparticles can be controlled by pulsed laser ablation conditions. Also, the polymerization efficiency depends on the size and chemical state of copper nanoparticles.