Pulsed Laser Ablation Deposition Research Articles

Growth of Al:ZnO nano-flowers by pulsed laser ablation deposition

Aluminium-doped (3%) zinc oxide thin films (AZO) were prepared, using pulsed laser deposition, with varying deposition times. The target was fabricated from compacted aluminium-doped zinc oxide nano-powder produced by sol–gel. The films had a growth consisting of nanostructures in the form of columns with sharp ends which, for certain deposition times, resemble nano-flowers or nano-leaves. The small spheroid-like particles created during columnar growth act as a seed for other AZO needles, resulting in the appearance of lotus-like flowers and even smaller needles growing from the petals. The deposition time was found to have a significant effect on the properties of the ZnO films. Specifically, the thickness of the films increased monotonically with deposition time until it reached a maximum value at 30 min. X-ray diffraction analysis revealed that the films were composed of polycrystalline ZnO with a hexagonal wurtzite structure. The preferred orientation and crystallite size also exhibited a similar trend with deposition time; thus, grain size shows a maximum at 30 min of deposition, where the preferred orientation changes from 103 to 002. Regarding optical properties, the bandgap energy of the ZnO films displayed a non-monotonic trend with deposition time, increasing for the sample deposited for 20 min but above this deposition time, although the obtained value exhibits a slight tendency to decrease, taking into account the confidence interval, the bandgap remains similar. This study demonstrates that careful control of deposition time is critical for achieving desirable properties of Al doped ZnO films. These observations have important implications for potential applications of the ZnO films in solar cells, antibacterial, and photocatalytic activities. The findings of this work pave the way for the design and optimization of ZnO-based materials for various applications.

Structural, Optical and Electrical Properties of (PbS: Co) Nanostructured Thin Films Synthesized by Pulsed Laser Ablation Deposition Tech

Structural, Optical and Electrical Properties of (PbS: Co) Nanostructured Thin Films Synthesized by Pulsed Laser Ablation Deposition Tech

Role of the interfaces in the crystallization and hysteresis mechanisms of amorphous Fe-B thin films

In this work we study the crystallization processes of two sets of amorphous Fe80B20 films fabricated by Pulsed Laser Ablation Deposition on substrates with different nature, Corning glass® and MgO(001). We analyze their magnetic hysteresis mechanisms by means of magneto-optic techniques and Transmission Electron Microscopy. The as-deposited amorphous films present a highly homogeneous uniaxial magnetic anisotropy with the easy axis orientation dependent on the type of substrate and much weaker than that of bulk alloys with similar composition. The onset of crystallization for the films deposited on glass and MgO appears, respectively, at temperatures 150 °C and 250 °C below that of their bulk counterparts. We study the role of the substrate in the crystallization mechanism and the resulting nanostructure of the magnetic films. While the crystallization of the MgO-deposited films proceeds in a broad front growing from the substrate to the surface, that of the glass-deposited films takes place through the nucleation and growth of isolated crystallites. We analyze the evolution of the coercivity during the crystallization of the films. It follows a similar trend for both types, remaining in values close to those of the amorphous precursors until it rises steeply at a given annealing temperature. The threshold of the steep coercivity increase of the glass-deposited films is shifted to lower temperatures with respect to the MgO ones, in spite of the higher crystallization onset temperature of the former. The coercivity mechanisms have been analyzed, correlated to the films interfacial characteristics and compared to those of bulk alloys.

Optical reflectivity of heat-treated nanofibrous silicon thin-films induced by high energy picosecond laser pulses

In this study, selective optical properties of Si/SiO2 thin films and their dependence on heat treatment were investigated. Samples were synthesized by pulsed-laser ablation deposition of c-Si on glass substrates and annealed at different temperatures (400 °C, 1000 °C). Nanofabrication parameters were chosen to produce significantly different nanostructures ranging from agglomerated particles to nanofibers. Morphology, crystalline, and elemental characterization techniques were employed to explore the variations in visible range reflection measurements. The adverse effect of annealing temperatures on Vis-range reflection spectra to increase and decrease the intensity was confirmed. These improvements are attributed to crystalline and amorphous lattice structures and elemental composition supported by the X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) method results.

A Review of the Effect of a Nanostructured Thin Film Formed by Titanium Carbide and Titanium Oxides Clustered around Carbon in Graphitic Form on Osseointegration.

Improving the biocompatibility of implants is an extremely important step towards improving their quality. In this review, we recount the technological and biological process for coating implants with thin films enriched in titanium carbide (TiC), which provide improved cell growth and osseointegration. At first, we discuss the use of a Pulsed Laser Ablation Deposition, which produced films with a good biocompatibility, cellular stimulation and osseointegration. We then describe how Ion Plating Plasma Assisted technology could be used to produce a nanostructured layer composed by graphitic carbon, whose biocompatibility is enhanced by titanium oxides and titanium carbide. In both cases, the nanostructured coating was compact and strongly bound to the bulk titanium, thus particularly useful to protect implants from the harsh oxidizing environment of biological tissues. The morphology and chemistry of the nanostructured coating were particularly desirable for osteoblasts, resulting in improved proliferation and differentiation. The cellular adhesion to the TiC-coated substrates was much stronger than to uncoated surfaces, and the number of philopodia and lamellipodia developed by the cells grown on the TiC-coated samples was higher. Finally, tests performed on rabbits confirmed in vivo that the osseointegration process of the TiC-coated implants is more efficient than that of uncoated titanium implants.

Nucleation and growth of Si nanoparticles under different pulse repetition rates without the baffle for nanosecond pulsed laser-ablated deposition

AbstractIn this article, Si nanoparticle (NP) films were prepared by pulsed laser ablation (PLA) in the argon atmosphere of 10 Pa at room temperature under different pulse repetition rates from 1 to 40 Hz without the baffle. Different from the conventional PLA method, the substrates were placed below and parallel to the ablated plume axis. The obtained films containing NPs were characterized by scanning electron microscopy and Raman spectrometer. The experimental results under constant laser fluence demonstrate the strong dependence of the mean size and the area number density of NPs on the repetition rate. Specifically, with the increase of pulse repetition rate, the mean size of the NPs in the film first decreases and reaches its minimum at 20 Hz, and then increases after 20 Hz, and decreases again till 40 Hz. The area number density shows the contrary trend versus mean size. The in situ diagnostic results of Langmuir probe denote the ablated Si ion density increases monotonously with the increase of repetition rate, while the temperature is almost constant. Combining with the nucleation probability, the growth/aggregation duration of NPs in the “nucleation region” and the effect of the baffle, the influence of pulse repetition rate on the formation of NPs is addressed. It is found that the repetition rate impacts the growth modes of NPs (i.e., growth and aggregation). 1–20, 20–30, and 30–40 Hz, respectively, correspond to growth-, aggregation-, and growth-controlled rate ranges without the baffle; however, 1–10, 10–20, and 20–40 Hz, respectively, correspond to growth-controlled, aggregation/growth-coexisted, and aggregation-controlled rate ranges with the baffle.

Phase transformation in ultrathin Y–Ba–Cu–O films by high-pressure oxygen annealing

To examine the thermodynamic phase stability of Y–Ba–Cu–O superconductors in ultrathin film form, we study the effects of high-pressure oxygen annealing and Cu enrichment on YBa2Cu3O[Formula: see text] films ranging from 8 nm to 15 nm in thickness. The films are grown epitaxially on SrTiO3 substrates by pulsed laser-ablated deposition, and post-annealed in 475 atm of oxygen at 800[Formula: see text]C while subjected to varying concentrations of excess CuO. X-ray diffraction (XRD) on the annealed films shows evidence for suppression of YBa2Cu3O[Formula: see text] and formation of Y2Ba4Cu8O[Formula: see text]. This structural transformation towards a higher-oxidation phase is expectedly correlated with film thinness and Cu enrichment.

Ultra-low palladium catalysts for phenylacetylene semihydrogenation: Synthesis by modified pulsed laser ablation–deposition

Pulsed laser ablation–deposition (PLA–PLD) in inhomogeneous electrical and electromagnetic fields was used to synthesise supported Pd catalysts. A modified PLA–PLD method opens up opportunities for obtaining Pd nanoparticles with the size from 2 to 5nm by varying the deposition conditions. The catalysts were investigated by transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The content of metal in catalysts was ultra-low (0.011–0.016wt%). The catalysts demonstrated unexpectedly high activity for phenylacetylene semihydrogenation (TOFv 18–55s−1, TOFs 41–224s−1) at the Pd/substrate molar ratio less than 1/100000 and styrene selectivity up to 93%.

Nonlinear Conductivity Fluctuations in Fe-Chalcogenide Superconductors

Electric transport and voltage-noise measurements on FeTe0.5Se0.5 epitaxial thin films are reported. The films were grown by pulsed laser ablation deposition on lanthanum aluminate single crystal substrates, and subsequently patterned by ion beam etching. Several configurations, with different voltage contacts distances and different strip widths, have been measured. At low temperature and current bias, the measured low frequency 1/f noise behaves according to the standard resistance fluctuations model. Conversely, an excess unconventional 1/f noise is observed in the high-temperature region (T >; 70 K). The experimental results indicate the existence of an electric field threshold, above which nonlinear fluctuation processes are activated. The results of noise measurements correlate well with the already reported change in sign of the Hall resistance in the same temperature range. Possible correlation between the hole contribution to the electrical transport and nonlinear noise effects observed is discussed.

Overview and development of metallic photocathodes prepared by laser ablation

The development of photocathodes materials has become an important task for X-ray free electron laser and new generation of particle accelerator. The choice of the op- timum cathode type and its further improvement is a funda- mental issue for the progress in radio-frequency photoinjec- tors. Metallic photocathodes offer several advantages over the semiconductor ones, e.g. long lifetime and prompt re- sponse time on the photoemission. This paper reviews the requirements and the current status of metallic photocath- odes prepared by pulsed laser ablation deposition technique. Magnesium, yttrium and lead are proposed as good alterna- tive to copper photocathode which is generally used in radio- frequency photoinjectors. Parametric studies of the irradia- tion conditions are demanded to optimize the metallic thin film deposition. The main achievements on the morphology and structure characterization as well as photoemission test- ing of metallic photocathodes are presented and discussed.

Hybrid heterostructure with a nanolayer of diluted GaIn(Mn)AsSb compound in a type II broken-gap heterojunction

Nanotechnology of obtainment of diluted magnetic semiconductors based on the GaInAsSb compounds is developed using the pulsed laser ablation deposition of Mn atoms on the surface of the epitaxial layer of a quaternary alloy obtained by liquid phase epitaxy. Fabricated heterostructures were studied using high-resolution X-ray diffraction for the Bragg and grazing diffraction geometries, and the depth profiling analysis was performed by secondary ion mass spectrometry. It was established that the nanoscale region of the Ga0.96In0.04As0.11Sb0.89 epilayer near the deposition surface of atomic Mn exhibits the presence of a quinary compound with Mn atoms in the lattice of the solid solution layer.

Modelling and Experimentation of Solid Lubrification with Powder MoS<sub>2</sub> through Self-Repairing and Self-Replenishing

Molybdenum disulphides (MoS2), which belong to the family of transition metal dichalcogenides, are well known for their solid lubricating behaviour. Thin films of MoS2 exhibit extremely low coefficient of friction in dry environments, and are typically applied by mixed in oil, grease or impregnated into porous matrix of powdered materials, sputter deposition, pulsed laser ablation, evaporation or chemical vapour deposition and, which are essentially either line-of-sight or high temperature processes. Solid lubricant coatings are attractive because they can reduce friction-generated heat. MoS2 is a common solid lubricant. However, the use of MoS2 can limited by excessive wear, as well as a friction coefficient. Several studies on solid lubricant coatings demonstrated success in lubricating dry sliding contacts over very long periods in tribometer tests or reciprocating sliding experiments.Several pellet-on-disk and pad-on-disk tribometer tests were conducted to study the lubrication characteristics of third-body particles of MoS2 powder. The tests consisted of simultaneous pellet-on-disk and pad-on-disk sliding contacts. Results from the tests show the self-repairing, self-replenishing, oil-free lubrication mechanism of MoS2. A theoretical control volume fractional coverage (CVFC) model was developed to predict: - (1) the friction coefficient at the pad-on-disk interface and - (2) the wear coefficient for the lubricated pellet-on-disk sliding contact. The fractional coverage varies with time and quantifies the amount of third-body film covering the disk asperities. Results from the model capture the tribological behaviour of the experimental sliding contacts reasonably well. The aim of this paper is modeling and experimentation of solid lubrification with MoS2 particles through self-repairing and self-replenishing and through the comparision between theoretical and experimental results obtained in the process of friction and wear by tribological tests.

A Detailed Study of the Synthesis of Bismuth Thin Films by PVD-Methods and their Structural Characterization

ABSTRACTA comprehensive and rather complete study for the synthesis of Bismuth thin-films using physical vapor deposition (PVD) techniques aimed at identifying key features of their crystallographic structure and morphology/topography, as a function of the synthesis method is presented. These films were deposited on oxidized and non-oxidized polished silicon substrates, glass-plates and polyimide flexible films, by thermal evaporation (resistive boat and e-beam) DC- and RF-magnetron assisted sputtering, and pulsed laser (ablation) deposition (PLD). The synthesis was performed controlling the main deposition parameters of these methods.XRD-spectra conclusively indicate that the films can be preferentially oriented along the [003] or [012] Bi-structure’s directions, depending on the source-to- substrate (STS)-distance, sputtering power, substrate’s temperature and PLD ion’s kinetic energy. It is also concluded that a relatively short STS-distance results in a rather polycrystalline structure, near independent to the used sputtering power.

Scanning tunneling spectroscopy study ofc-axis proximity effect in epitaxial bilayer manganite/cuprate thin films

Recent experimental studies have indicated novel superconducting proximity effects in thin-film heterostructures comprising ferromagnetic manganites and superconducting cuprates. To look for such effects microscopically, we performed scanning tunneling spectroscopy on La${}_{2/3}$Ca${}_{1/3}$MnO${}_{3}$/YBa${}_{2}$Cu${}_{3}$O${}_{7\ensuremath{-}\ensuremath{\delta}}$ (LCMO/YBCO) bilayer thin films. $c$-axis-oriented films of varying thickness were grown on SrTiO${}_{3}$ substrates using pulsed laser-ablated deposition. Heteroepitaxiality of the films was confirmed by cross-sectional transmission electron microscopy. Tunneling spectra were measured at 4.2 K and analyzed for signatures of a pairing gap on the LCMO layer. For bilayer samples with LCMO thickness down to 5 nm, asymmetric conductance spectra characteristic of single-layer LCMO films were observed, showing no clear gap structures. These observations are consistent with a very short-range proximity effect involving spin-singlet pairs, and difficult to reconcile with longer-range proximity scenarios involving spin-triplet pairs.

Detailed studies of aluminum thin films morphology deposited by pulsed laser ablation

In the present paper we report the investigations by scanning electron microscopy of Al thin films prepared by pulsed laser ablation deposition experiments in vacuum. Laser parametric studies show that the poor thickness uniformity of Al films arises from surface roughening and structure formation on the irradiated Al target surface. Moreover, it has been confirmed that the plume deflection effect, the morphological changes of the irradiated target surfaces and of the deposited films strongly depend on the laser fluence (4.6–14.7 J/cm 2). At low laser fluence, plume deflection angles up to 12° and columnar structures on the target surface have been observed. The variation in the target morphology and in the droplets density of the deposited films can be associated with competitive ablation processes related to different values of local incident laser fluence. Systematic profilometric investigations of the deposited Al films revealed a strong asymmetry during the deposition process. These results confirm once again our previous achievements obtained with Si laser ablation experiments.

Metallic photocathodes prepared by pulsed laser ablation deposition for application to bright electron sources

AbstractWe present the results of our investigation on metallic films as suitable photocathodes for the production of intense electron beams in radio frequency (RF) photoinjector guns. Pulsed laser ablation deposition (PLAD) technique was used for growing Mg and Y thin films onto Si and Cu substrates in high vacuum of 10−5 Pa and at room temperature. The morphology, the structure, the thickness and the contamination level of thin films surface deposited on Si were deduced by using different diagnostic techniques. Thin films deposited on Cu have been tested as photocathodes in an ultrahigh vacuum photodiode chamber at 10−7 Pa. Relatively high‐quantum efficiencies have been obtained for the deposited films, comparable to those of corresponding bulks. Samples could stay for several months in open air before being tested in a photodiode cell.The deposition process and the role of the gas absorption on the photocathode surface and its influence on the photoelectron performances are also presented and discussed. Copyright © 2010 John Wiley & Sons, Ltd.

T c = 21 K in epitaxial FeSe0.5Te0.5 thin films with biaxial compressive strain

Epitaxial FeSe0.5Te0.5 thin films with different thickness were grown by pulsed laser ablation deposition on different substrates. High purity phase and fully epitaxial growth were obtained. By varying the film thickness, superconducting transition temperatures up to 21 K were observed, significantly larger than the bulk value 16.2 K. Structural analyses indicated that the c-axis is smaller than the bulk value but it is almost independent of the film thickness and the a-axis changes significantly with the film thickness and is linearly related to the Tc. The latter result indicates the important role of the compressive strain in enhancing Tc. Tc is also related to both the Fe–(Se,Te) bond length and angle, suggesting the possibility of further enhancement.

Laser ablation of AgSbS2 and cluster analysis by time‐of‐flight mass spectrometry

Thin films of AgSbS(2) are important for phase-change memory applications. This solid is deposited by various techniques, such as metal organic chemical vapour deposition or laser ablation deposition, and the structure of AgSbS(2)(s), as either amorphous or crystalline, is already well characterized. The pulsed laser ablation deposition (PLD) of solid AgSbS(2) is also used as a manufacturing process. However, the processes in plasma have not been well studied. We have studied the laser ablation of synthesized AgSbS(2)(s) using a nitrogen laser of 337 nm and the clusters formed in the laser plume were identified. The ablation leads to the formation of various single charged ternary Ag(p)Sb(q)S(r) clusters. Negatively charged AgSbS(4) (-), AgSb(2)S(3) (-), AgSb(2)S(4) (-), AgSb(2)S(5) (-) and positively charged ternary AgSbS(+), AgSb(2)S(+), AgSb(2)S(2) (+), AgSb(2)S(3) (+) clusters were identified. The formation of several singly charged Ag(+), Ag(2) (-), Ag(3) (-), Sb(3) (+), Sb(3) (-), S(8) (+) ions and binary Ag(p)S(r) clusters such as AgSb(2) (-), Ag(3)S(-), SbS(r) (-) (r = 1-5), Sb(2)S(-), Sb(2)S(2) (-), Sb(3)S(r) (-) (r = 1-4) and AgS(2) (+), SbS(+), SbS(2) (+), Sb(2)S(+), Sb(2)S(2) (+), Sb(3)S(r) (+) (r = 1-4), AgSb(2) (+) was also observed. The stoichiometry of the clusters was determined via isotopic envelope analysis and computer modeling. The relation of the composition of the clusters to the crystal structure of AgSbS(2) is discussed.

Optical properties of ITO/TiO 2 single and double layer thin films deposited by RPLAD

Indium tin oxide (ITO) and titanium dioxide (TiO 2) single layer and double layer ITO/TiO 2 films were prepared using reactive pulsed laser ablation deposition (RPLAD) with an ArF excimer laser for applications in dye-sensitized solar cells (DSSCs). The films were deposited on SiO 2 substrates either at room temperatures (RT) or heated to 200–400 °C. Under optimized conditions, transmission of ITO films in the visible (vis) range was above 89% for films produced at RT and 93% for the ones deposited at higher temperatures. Increasing the substrate temperature from RT to 400 °C enhances the transmission of TiO 2 films in the vis-NIR from about 70% to 92%. High transmission (≈90%) was observed for the double layer ITO/TiO 2 with a transmission cut-off above 900 nm. From the transmission data, the energies gaps ( E g), as well as the refractive indexes ( n) for the films were estimated. n ≈ 2.03 and 2.04, respectively for ITO films and TiO 2 film deposited at 400 °C in the visible region. Post-annealing of the TiO 2 films for 3 h at 300 and 500 °C was performed to enhance n. The refractive index of the TiO 2 films increases with the post-annealing temperature. The direct band gap is 3.6, 3.74 and 3.82 eV for ITO films deposited at RT, 200, and 400 °C, respectively. The TiO 2 films present a direct band gap of 3.51 and 3.37 eV for as deposited TiO 2 films and when annealed at 400 °C, respectively. There is a shift of about 0.1 eV between ITO and ITO/TiO 2 films deposited at 200 °C. The shift decreases by half when the TiO 2 film was deposited at 400 °C. Post-annealing was also performed on double layer ITO/TiO 2.

Aligned growth of ZnO nanowires by NAPLD and their optical characterizations

Not only vertically aligned ZnO nanowires but also horizontally aligned ZnO nanowires have been successfully grown on the annealed (0 0 0 1) c-cut and (1 1 2 0) a-cut sapphire substrates, respectively using catalyst-free nanoparticle-assisted pulsed-laser ablation deposition (NAPLD). The as-synthesized ZnO nanowires exhibit an ultraviolet emission at around 390 nm and the absent green emission under room temperature. The single ZnO nanowire was collected in the electrode gap by dielectrophoresis (DEP). Under the optical pumping, the single ZnO nanowire exhibited UV emission at around 390 nm with several sharp peaks whose energy spacings are almost constant, which greatly differs from the broad UV emission of the film with many nanowires, suggesting ZnO nanowires as candidates for laser media. The single ZnO nanowire showed polarized photoluminescence (PL). The as-synthesized ZnO nanowires could find many interesting applications in short-wavelength light-emitting diode (LED), laser diode and gas sensor.