Pressed Powder Targets Research Articles

Crystal Al-Doped ZnO Thin-Film Preparation by Sputtering Deposition using a Mixed-Powder Target

Al-doped ZnO films were prepared by sputtering deposition using mixtures of Al2O3 and ZnO powder targets. The film quality depended on the conditions of the target powder. The deposition rate, crystallinity, and transparency of films prepared with new, pressed powder targets were higher than those prepared with used, nonpressed powder targets. In addition, we found that pressurizing the new-powder target and increasing the substrate temperature resulted in thin films with high transparency and electrical conductivity

The potential of transparent sputtered NaI:Tm[formula omitted], CaBr[formula omitted]:Tm[formula omitted], and CaI[formula omitted]:Tm[formula omitted] thin films as luminescent solar concentrators

The parameters governing the performance of a luminescent solar concentrator (LSC) are determined for sputtered thin-films of NaI:Tm2+, CaBr2:Tm2+, and CaI2:Tm2+. These parameters are determined by using six gradient thin film material libraries, combinatorially sputtered from metallic and pressed powder targets. These films show strong 4f13→4f12d1 absorption of maximally 752cm−1 at.%−1 for NaI:Tm2+, 31cm−1 at.%−1 for CaBr2:Tm2+, and 473cm−1 at.%−1 for CaI2:Tm2+. This absorption covers the entire visible spectrum and does not overlap with the infrared 4f-4f emission at 1140nm. Decay measurements are used to estimate the quantum yields of the thin-films. These quantum yields can be as high as 44% for NaI:Tm2+, when doped with 0.3at.% Tm. Even at doping percentages as low as 0.3at.%, the films appear to show luminescence quenching. The concentration-dependent absorption and quantum yield are combined with the index of refraction, resolved from transmission measurements, to simulate the optical efficiency of a thin film Tm2+-doped halide LSC. These simulations show that LSCs based on Tm2+ can display excellent color rendering indices of up to 99%, and neutral color temperatures, between 4500K and 6000K. Under optimal conditions, thin-films constrained to a thickness of 10μm and 80% transmission of the visible spectrum, would be able to display optical efficiencies of 0.71%. This optical efficiency compares favorably to the maximally achievable 3.5% under these constraints. This efficiency is largely independent of the size of LSC itself.

Characterization and device application of indium doped ZnO homojunction prepared by RF magnetron sputtering

Undoped and Indium doped Zinc Oxide (IZO) nanocrystalline thin films were synthesized via RF magnetron sputtering techniques using home-made cold pressed powder targets. The morphology, crystal structure, elemental analyses were studied using FESEM, AFM, XRD, EDS and XPS techniques. All the films showed hexagonal wurtzite structure, and revealed appreciable variations in (100), (002) and (101) peak intensities with indium doping. The incorporation of In into the ZnO films was confirmed by both EDS and XPS measurements. XPS and Photoluminescence (PL) studies of doped films demonstrated significant reduction of oxygen vacancies (Vo) after incorporation of indium in ZnO lattice at substitutional sites. PL spectra showed convoluted peaks, which correspond to band to band transitions and defect level emissions. The optical studies showed high transmittance of over 90% in the UV–vis region and exhibited the absorption edge near 380 nm. The band gap energy of the films increased from 3.27 eV to 3.42 eV, with In content. In addition, typical rectifying I–V characteristics of SZO/IZO homojunction layers were demonstrated.

Formation of ErAs Nanoparticles by Pulsed Laser Ablation of Pressed Powder Targets

We investigate the optimal growth conditions for ErAs nanoparticle powders by nanosecond pulsed laser ablation in a He environment from elemental pressed powder targets. Incongruent ablation of the target due to differences in vaporization enthalpies is observed, and compensation for these differences is explored through altering target composition. The preferential ablation of As from the Er-As pressed powder targets appears to diminish over time, resulting in the reduced impact of differing vaporization enthalpies. Additionally, the influence of collection distance is investigated as a means to control crystallite size and powder composition. Particle size is shown to increase with collection distance and appears to reach a plateau as the beaker diameter becomes much larger than the plume size.

A Tale of Two Stabilities: How One Boron Atom Affects a Switch in Bonding Motifs in CeO2B x- ( x = 2, 3) Complexes.

Boronyl (B≡O) ligands have garnered much attention as isoelectronic and isolobal analogues of CO and CN-, yet successful efforts in synthesizing metal boronyl complexes remain scarce. Anion photoelectron (PE) spectroscopy and density functional theory calculations were employed to investigate two small CeO2B x- ( x = 2, 3) complexes generated from laser ablation of a mixed Ce/B pressed powder target. The spectra reveal markedly different bonding upon incorporation of an additional B atom. Most interestingly, CeO2B2- was found to have a Ce(I) center coordinated to two monoanionic boronyl ligands in a bent geometry. This result was unexpected as previous studies suggest electron-rich metals are most suitable for stabilizing such ligands; furthermore, it is one of the first examples of an experimental metal-polyboronyl complex. Introducing another boron atom, however, favors a much different geometry in which Ce(II) coordinates an O2B33- unit through both the O and B atoms, which was evident in the markedly different PE spectra.

Preparation of tris(8-hydroxyquinolinato)aluminum thin films by sputtering deposition using powder and pressed powder targets

Tris(8-hydroxyquinolinato)aluminum (Alq3) thin films, for use in organic electroluminescence displays, were prepared by a sputtering deposition method using powder and pressed powder targets. Experimental results suggest that Alq3 thin films can be prepared using powder and pressed powder targets, although the films were amorphous. The surface color of the target after deposition became dark brown, and the Fourier transform infrared spectroscopy spectrum changed when using a pressed powder target. The deposition rate of the film using a powder target was higher than that using a pressed powder target. That may be because the electron and ion densities of the plasma generated using the powder target are higher than those when using pressed powder targets under the same deposition conditions. The properties of a thin film prepared using a powder target were almost the same as those of a film prepared using a pressed powder target.

Growth of ErAs Nanoparticles by Pulsed Laser Ablation in an Inert Environment

The incorporation of ErAs nanoparticles into III–V semiconductor films has been shown to dramatically alter the properties of the resulting nanocomposite, while maintaining an epitaxial relationship throughout the film. Even though these composites have been extensively studied, little work has been done on the particles themselves, absent of the host matrix. In this paper, we demonstrate ErAs nanoparticle growth outside of a host matrix by laser ablation in an inert environment. Rietveld refinement was used to determine the compositions of ablation targets and resulting powders to better understand the requirements for the growth of binary nanoparticles from pressed powder targets and the limiting factors for particle growth. Powders with an ErAs concentration of 67.1% were obtained, and higher concentrations are expected to be achieved with higher purity targets.

High entropy alloy thin films deposited by magnetron sputtering of powder targets

High entropy alloys (HEA) contain at least five principal elements in equimolar or near-equimolar ratios. These materials crystallize typically as a face-centered cubic (FCC), body-centered cubic (BCC) solid solution or as a mixture of these two crystal structures. AlCoCrCuFeNi thin films were deposited by magnetron sputtering of homemade pressed powder targets. Four targets with different compositions were sputtered under various conditions to modify the alloy composition. Scanning electron microscopy and energy-dispersive X-ray spectroscopy were used to study the surface morphology and composition whereas X-ray diffraction and X-ray reflectivity provided information regarding the phase formation and density of the films. It is suggested that, when taking into account the atomic radii of the constituent elements, the sputter deposited alloy thin films can be topologically regarded as binary alloys of the form Al-(CoCrCuFeNi). If the concentration of the largest atom (Al) increases, a transition from FCC to BCC is noticed. This structure transition could be attributed to a critical lattice distortion.

The influence of target surface morphology on the deposition flux during direct-current magnetron sputtering

The effect of the target surface morphology on the sputter deposition flux and the energy flux is investigated by comparing solid targets to pressed powder targets. A significant, material dependent difference of the effective sputter yield between both target types is noticed. This difference is explained by combining two effects: a local increase of the elemental sputter yield and the redeposition of sputtered atoms onto the target. Both effects strongly depend on the target surface morphology. The experimental trends are reproduced by Monte Carlo simulations. This allows a description of the angular distribution of the sputtered atoms which is an important parameter to define the particle flux and the energy distribution of the atoms arriving on the substrate. Using the previously developed particle trajectory code simtra, the latter is demonstrated for the studied materials (Al, Ag, Cu, and Ti).

Deposition of thin films by sputtering cold isostatically pressed powder targets: A case study

AbstractPowders of copper and aluminium with a maximum grain size of 50 µm are mixed in different ratios. The mixtures are cold isostatically pressed into two‐inch circular targets which are mounted in a conventional magnetron set‐up and used to deposit both metallic Cu–Al as well as oxygen rich Cu–Al–O thin films. In both cases the thin film composition is analysed and related to the target composition. Crystallographic properties of the deposited films are presented as well. The influence of the target composition on the reactive behaviour is studied by hysteresis measurements. Furthermore, the effective sputter yields of elemental powder targets were measured. Depending on the material, the sputter yields of the powder target either increased or decreased compared to the sputter yields of solid targets. This can be qualitatively explained by an analysis of the target roughness. For the fast scanning of the compositional influence on material properties, the use of powder targets shows to be a suitable and valuable approach.

Tunable optical and nano-scale electrical properties of WO3 and Ag-WO3 nanocomposite thin films

WO3 and Ag-WO3 nanocomposite thin films have been synthesized from pure WO3 and Ag-WO3 composite pressed powder targets submitted to pulses generated by a frequency quadrupled Nd:yttrium aluminium garnet (YAG; λ = 266 nm, τ ~ 5 ns, ν = 10 Hz) laser source. The irradiations were performed in low pressure oxygen atmosphere. The obtained results proved the possibility to tailor the synthesized thin films optical properties in the UV–Visible spectral region and their nano-scale electrical characteristics through the process parameters, as ambient oxygen pressure value during the thin films deposition and Ag concentration of the Ag-WO3 composite targets. The tunable optical and electrical features allow for the creation of new materials for future applications as photocatalysts, transparent conducting electrodes, electrochromic or chemical and biological sensor devices.

Growth and characterization of nitrogen–doped TiO 2 thin films prepared by reactive pulsed laser deposition

Nitrogen–doped titanium dioxide (TiO 2) thin films were grown on (001) SiO 2 substrates by reactive pulsed laser deposition. A KrF* excimer laser source ( λ = 248 nm, τ FWHM ≅ 10 ns, ν = 10 Hz) was used for the irradiations of pressed powder targets composed by both anatase and rutile phase TiO 2. The experiments were performed in a controlled reactive atmosphere consisting of oxygen or mixtures of oxygen and nitrogen gases. The obtained thin film crystal structure was investigated by X-ray diffraction, while their chemical composition as well as chemical bonding states between the elements were studied by X-ray photoelectron spectroscopy. An interrelation was found between nitrogen concentration, crystalline structure, bonding states between the elements, and the formation of titanium oxinitride compounds. Moreover, as a result of the nitrogen incorporation in the films a continuous red-shift of the optical absorption edge accompanied by absorption in the visible spectral range between 400 and 500 nm wavelength was observed.

Plasma plume photography and spectroscopy of Fe—Oxide materials

Time-resolved photography was employed to study plasma dynamics and particle ejection of laser-irradiated iron oxide materials. Nano-particle powder, pressed powder pellets and sintered ceramics were ablated in air and Ar gas background by means of short laser pulses (Nd:YAG laser wavelength λ = 1064 nm and pulse duration τ L ≈ 6 ns; KrF laser λ = 248 nm and τ L ≈ 20 ns). Plasma plume dynamics significantly depended on sample morphology. The ejection of non-luminous particles up to several hundreds of microseconds after the laser pulse was observed for powder and pressed powder target materials. Laser-induced breakdown spectroscopy (LIBS) was employed for element analysis of iron oxide powders, pressed pellets and sintered ceramics. LIBS spectra of the different targets were comparable to each other and qualitatively independent of target morphology.

Polytetrafluoroethylene (PTFE) films prepared by F2-laser deposition

Thin films of polytetrafluoroethylene (PTFE) were prepared by pulsed-laser deposition (PLD) from bulk PTFE targets using 157 nm F 2 -laser radiation. The films were analyzed by means of optical polarization microscopy, stylus profilometry, XPS, XRD, FTIR spectroscopy, and by capacitance measurements. The effect of substrate temperature, T s , on the morphology and crystallinity of the films was studied. Films treated at sufficiently high T s consist mainly of spherulite-like crystallites. Films with a thickness of more than about 155 nm are continuous, pinhole-free, well adherent to the substrate, and have a composition which is similar to that of the target material. The minimum film thicknesses and deposition rates are much lower than those achieved with pressed PTFE powder targets using 248 nm KrF-laser ablation. This is related to the different deposition mechanisms. Film formation based on KrF-laser ablation of pressed powder targets is mainly related to the condensation of large particulates transferred in a particle jet from the target to the substrate. F 2 –laser ablation and film formation seems to be based on the ablation and condensation of small fragments. Correspondingly, the morphology, crystallinity, and the optical and dielectrical properties of films significantly differ from each other.

Picosecond pulsed laser deposition at high vibrational excitation density: the case of poly(tetrafluoroethylene)

The availability of tunable, picosecond free-electron lasers operating with high efficiency in the mid-infrared opens a materials-processing regime qualitatively distinct from that accessed by femtosecond Ti:sapphire lasers, one which is characterized by a high spatio-temporal density of vibrational, rather than electronic, excitation. As an example of this novel materials-processing regime, we present new results on pulsed laser deposition of thin poly(tetrafluoroethylene) films. Films of poly(tetrafluoroethylene) were deposited by resonant (4.2 and 8.26 μm) and non-resonant (7.1 μm) infrared picosecond laser ablation from either a pressed powder target or a commercial bulk target. The films were smooth and crystalline and largely free of particulates without annealing. Infrared and X-ray photoelectron spectra indicated that the films retained the chemical properties of the starting material. Observations of the film properties are consistent with a steady-state ablation mechanism, possibly enhanced by non-linear absorption due to the high photon flux in the free-electron laser micropulses.

Microstructure Development and Tribological Behavior in AlCuFe Quasicrystalline Thin Films

A series of AlCuFe films were deposited by magnetron sputtering and subjected to X-ray diffraction and tribological testing to elucidate the correlation between quasicrystalline phase content and coefficient of friction. The sputter target was a pressed powder target comprised of a mixture of elemental powders combined in the ratio Al65Cu23Fe12 and pressed at 400°C. This target was designed to produce film compositions within the single-phase icosohedral quasicrystalline regime. X-ray diffraction performed on the as-deposited coatings showed that they were comprised of a nanoscale/amorphous precursor phase with broad X-ray diffraction maxima. Anneals of the as-deposited films were performed at 450 or 500°C in argon for various times to cause partial or full development of the quasicrystalline microstructure, and films were tribo-tested in two separate systems. The first of these was an oscillating pin-on-flat system, in which a coated 2 mm diameter pin was used to test as-deposited films at temperatures of up to 220°C under vacuum and a 15 g load. The second system used a 0.25″ diameter alumina ball and a load of 100 g to test films in air at temperatures of 25, 150, and 300°C. Various anneal conditions were also tested. For an as-deposited coating, a coating annealed for 2 h at 450°C, and a coating annealed for 1h at 500°C, the observed coefficients of friction were 0.45, 0.23, and 0.17, respectively. Correlation between quasicrystalline phase content, room temperature friction coefficient, and appearance of the wear track clearly showed that annealing to the fully developed quasicrystalline structure resulted in a harder film with a lower coefficient of friction.

Investigation of sputtered HfF 4 films and application to interference filters for thermophotovoltaics

The optical properties of sputter deposited hafnium fluoride films and their use in fabricating a front surface, interference filter for thermophotovoltaic energy conversion were investigated. In particular, HfF 4 films were being considered for the low index component in a multilayer interference filter that will selectively transmit photons in the wavelength range of 1.0–2.4 μm, and strongly reflect all other wavelengths. Processes were developed for sputter depositing HfF 4 films with an index of refraction between 1.5 and 1.6, and an extinction coefficient below 0.001 in the 1.0–2.4 μm wavelength range. All HfF 4 coatings were deposited by RF reactive magnetron sputtering with pressed powder targets. Chamber pressure during depositions ranged from 0.27 to 1.33 Pa, and RF power ranged from 50 W (0.91 W/cm 2) to 150 W (2.73 W/cm 2). Deposition rates depended primarily on target power and ranged from 0.03 to 0.1 nm/s. All depositions were performed with Ar as the sputtering gas. Resputtering effects due to plasma and adatom bombardment and neutral Ar atoms reflected off the target played an important role in sputter deposition of hafnium fluoride. Film thickness and composition varied strongly with substrate distance from the target axis. Resputtering of growing films by energetic argon atoms also resulted in strongly absorptive, fluorine-deficient films on the substrate platform near the target axis. However, films became increasingly more stoichiometric and transmissive as one moves away from the target axis. The films were found to be amorphous or weakly crystalline. Nine-layer interference filters were fabricated utilizing HfF 4 and an Si:H alloy for the low- and high-index components, respectively. Physisorbed water in the HfF 4 layers and SiH bond stretching were the primary sources of absorption between 1 and 12 μm wavelengths.

Structural comparison of gadolinium and lanthanum silicate films on Si(1 0 0) by HRTEM, EELS and SAED

High-resolution transmission electron microscopy (HRTEM), electron energy loss spectroscopy (EELS) and selected area electron diffraction (SAED) were used to study gadolinium and lanthanum silicate films deposited on Si(1 0 0) substrates using electron-beam evaporation from pressed-powder targets. As-deposited films consist of an amorphous silicate layer without an interfacial layer. After annealing at 900 °C in oxygen for 2 min, an interfacial SiO 2 layer is formed in the gadolinium silicate film, while this interfacial layer is a SiO 2-rich lanthanum silicate layer in the lanthanum silicate film. The formation of interfacial silicate layers is thermodynamically more favorable for the lanthanum films than for the gadolinium films. The gadolinium silicate films crystallize at a temperature between 1000 and 1050 °C, while the crystallization temperature for the lanthanum silicate films is between 900 and 950 °C.

Characterization of gadolinium and lanthanum oxide films on Si (100)

High-resolution transmission electron microscopy, electron energy loss spectroscopy, and Auger electron spectroscopy, were used to study gadolinium and lanthanum oxide films deposited on Si (100) substrates using electron-beam evaporation from pressed-powder targets. As-deposited films consist of a crystalline oxide layer and an amorphous interfacial layer. A complicated distinct multilayer structure consisting of oxide layers, silicate layers, and SiO2-rich layers in thick (∼30 nm) annealed films has been observed for both gadolinium and lanthanum films. For thinner annealed films (∼8 nm), there is no longer a crystalline oxide layer but an amorphous gadolinium or lanthanum silicate layer and an interfacial SiO2-rich layer. The formation of the lanthanum silicate by annealing lanthanum oxide is found to be thermodynamically more favorable than the formation of gadolinium silicate.

Sm-doped CdWO4 thin films synthesized by pulsed laser deposition

Samarium doped CdWO4 (Sm-CdWO4) thin films were synthesized by pulsed laser deposition (PLD) using pressed powder targets composed of Sm2O3, CdO, and WO3 mixtures. Congruent, stoichiometric, and crystalline thin films were obtained on glass substrates at 873 K using targets with 0.01 at. % Sm. The x-ray activated photoluminescence (x-ray PL) spectra were redshifted by about 40 nm at 298 K. Changes of the PL component at 2.85 eV into those at 2.20 and 2.52 eV were typical in their convolutions. These PL components showed very similar dependencies on excitation wavelengths, indicating that CdWO4 related PL emissions in the Sm-doped PLD films are relaxed from the same midband excited state. The PL peaks characteristic to Sm3+ had two sidebands shifted to both lower and higher energy sides as much as 0.03 eV. Plume emission spectra were analyzed to elucidate effects of Sm on our PLD processes. It was interpreted that energy transfer should occur between excited neutral Cd to the excited state of Sm3+ in laser plume.