Cross-beam Pulsed Laser Deposition Research Articles

Growth of epitaxial TiN (111) thin films with low resistivity on Si (111) by crossed-beam pulsed laser deposition

Titanium nitride (TiN) thin films were grown epitaxially on Si (111) substrates by reactive pulsed laser deposition. Substrate temperatures ranged from 550 to 950 °C while plume kinetic energies ranged from 46 to 154 eV. Quality of the grown films depended strongly on kinetic energy of the films than the growth temperatures. High quality film was grown at 750 °C with a laser plume kinetic energy of ~ 92 eV. Full width at half maximum for a ω-scan around the TiN (111) peak and a φ-scan through the TiN (002) peak were 0.3° and 0.43 °, respectively. The resistivity of the films was increased with increased temperatures and a room temperature resistivity of 3.8 μΩ-cm was obtained.

Room Temperature Synthesis of Mixed Platinum and Tin Oxide Nanocomposite Catalyst with Enhanced Mass Activity and Durability for Ethanol Electrooxidation in an Acidic Medium

Pt-transition metal oxides are emerging as new class of electrodes for alcohol oxidation reactions. We prepare at room temperature Pt-SnO2 nanocomposites of various surface morphologies onto carbon nanotubes for enhanced ethanol oxidation reaction (EOR) by cross-beam pulsed laser deposition technique. Synthesized nanocomposites are characterized by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), XRD, Raman spectroscopy, and transmission electron microscopy (TEM). It is observed that the interaction of SnO2 with Pt modifies the electronic structure of the latter inducing the formation of ionized Pt2+ and Pt4+ while Sn revealed mixed Sn4+ and Sn2+ cations. An optimum electrocatalytic performance toward EOR is obtained with a Pt-SnO2 grown under 0.5 Torr of He atmosphere. Versus a CNT/Pt electrode, this CNT/Pt-SnO2 electrode (i) oxidizes ethanol at much lower potentials (86 mV negative), and (ii) displays a superior specific mass activity of 1.6 times and 2.2 times by cyclic voltammetry and long-term stability, respectively. Such performance is ascribed to a combination of: (i) SnO2 has abundant hydroxyls on the surface and decrease the CO poisoning based on a bifunctional mechanism; (ii) modification of the electronic structure of Pt (electronic effect) and (iii) a semi-porous surface morphology favorable for the mass transfer of ethanol molecules.

Cross-beam pulsed laser fabrication of Free-Standing Nanostructured Carbon Nanotubes-Pt-Ceria Anode with unprecedented electroactivity and durability for ethanol oxidation

Owing to its inherent properties such as great capacity to store and release oxygen, lattice oxygen that has a key role in removing the CO poisoning effect, non-toxicity, abundance, low cost and low temperature processing, CeO2 is emerging as a unique class of electrode material for low temperature polymer electrolyte fuel cells such as direct ethanol fuel cells (DEFCs). However, the maximal exploitation of its functional properties is strictly reliant on the availability of optimized synthesis routes that allow tailor-designing, architecturing and manipulation of CeO2 in a precise manner when it is combined with other functional materials. Here we use the cross-beam pulsed laser deposition (CBPLD) technique to synthesize free-standing (binderless) Pt–CeO2 nanostructured thin films onto carbon nanotubes as anodes for ethanol oxidation reaction. Further significance of this work is that it establishes the importance in the design of the catalyst layer architecture. Indeed, we demonstrate here that when CeO2 material is beneath or when it is mixed with Pt, the interactions between Pt with CeO2 are not similar leading inevitably to different electrocatalytic performances. Given proper tailoring synthesis conditions, CBPLD-developed Pt–CeO2 thin films are remarkably stable and provide electrochemical performance much greater than the layer onto layer CeO2/Pt architecture.

Kinetically stable PtxIr100-x alloy thin films prepared by pulsed laser deposition: Oxidation of NH3 and poisoning resistance

A series of kinetically stable PtxIr100-x thin film alloys have been synthesized by crossed beam pulsed laser deposition and physically characterized by X-ray diffraction and X-ray photoelectron spectroscopy. It is shown that a metastable solid solution between Pt and Ir is formed over the whole composition range, with the lattice parameter of the fcc phase increasing steadily between 3.84 and 3.92Å as the Pt content is increased from 0 to 100 at.%. The surface composition of all samples follows closely the bulk composition, indicating there is no surface segregation of either element. A detailed analysis of the Pt and Ir 4f core level peaks shows that the binding energy of the Pt 4f7/2 and Ir 4f7/2 core level peaks both decrease with increasing Pt concentration, from 71.6 to 71.2eV as the bulk Pt content increases from ca 65% to 100%, and from 61.1 to 60.6eV as the bulk Pt content increases from 0 to 90 at.%, respectively. Such behaviour was recently shown to reflect a change in the center of gravity of the occupied states, where the d-band level of both Pt and Ir shift to higher energy as the Pt bulk content is decreased. Both the surface composition and surface electronic structure are not altered following all the electrochemical analyses. The electrocatalytic properties of these PtxIt100-x alloys for the anodic oxidation of NH3 in aqueous alkaline media were investigated. Voltammetric and chronoamperometric studies on these alloys show improved poison tolerance for NH3 oxidation as compared to pure polycrystalline platinum, with optimal results observed with Pt89Ir11 alloys. Such improvement for long term stability is associated with the electronic effect and bifunctional mechanism at the PtIr surface alloys.

Photocatalytic Degradation of Malachite Green Dye and Pharmaceuticals Using Co:TiO<sub>2</sub> Thin Films

The crossed beam pulsed laser deposition technique was successfully used to prepare Co:TiO2 thin films with different cobalt concentrations and a band gap as low as 2.0 eV. The aim of this work is to report the application of TiO2 thin films modified with different amounts of cobalt (Co:TiO2) as catalysts in the degradation of a malachite green (MG) solution as well as in solutions containing pharmaceutical wastes such as the analgesics diclofenac and naproxen. For catalyst activation an UV lamp with emission at 254 and 404 nm was used as the energy source. It was followed the decrease in the characteristic absorption band of the different polluted solutions over the reaction time. In general terms, the obtained results showed that samples containing cobalt exhibited better photocatalytic performance than the undoped TiO2 films. An optimal cobalt content in the film was found that provided the highest degradation for the different solutions.

Effect of aluminum plasma parameters on the physical properties of Ti-Al-N thin films deposited by reactive crossed beam pulsed laser deposition

This work reports on the preparation and characterization of Ti-Al-N thin films deposited by reactive crossed beam pulsed laser deposition (RCBPLD). The elemental composition, vibrational properties and hardness of the deposited films were investigated as a function of the plasma parameters, that is, the Al+ mean kinetic energy and plasma density. The composition of the thin films was determined from X-ray photoelectron spectroscopy (XPS) measurements as well as by Rutherford backscattering spectroscopy (RBS). The structural modifications of the deposited materials due to Al incorporation were characterized by Raman spectroscopy. The hardness of the deposited films was determined by nanoindentation. It was found that by using this experimental configuration the aluminum content in the deposited films was incorporated in a controlled way, from 2.2 to 31.7at.% (XPS measurements), by varying the Al+ mean kinetic energy and the plasma density. Raman results suggest that at low aluminum concentrations a solid solution of Ti(Al, N) is produced, whereas at higher aluminum concentrations a nanocomposite formed of TiAlN and AlN is obtained. Ti-Al-N films with hardnesses up to 28.8GPa, which are suitable for many mechanical applications, were obtained. These results show that the properties of the deposited material are controlled, at least partially, by the aluminum plasma parameters used for thin film growth.

The cobalt oxide/hydroxide nanowall array film prepared by pulsed laser deposition for supercapacitors with superb-rate capability

The aluminum doped cobalt oxide thin film was prepared through crossed-beam pulsed laser deposition (PLD) of aluminum and cobalt metals in the low-pressure O2/H2 atmosphere. The thin film was etched by NaOH to remove aluminum oxide and then cobalt oxide/hydroxide nanowall array film was obtained. The pseudocapacitive performances of the nanowall array film are tested by cyclic voltammetry (CV) and galvanostatic charge–discharge measurements in 1M KOH aqueous solution. When deposited in the atmosphere of O2:H2=2:1, the thin film displays a high specific capacitance (690Fg–1) and a superb rate capability (75% capacitance retention from 1Ag–1 to 120Ag–1). In addition, excellent cycling stability is achieved for the film electrode and the specific capacitance degradation is only 0.3% after 1000 cycles.

Preparation of Co:TiO2 thin films by crossed-beam pulsed laser deposition

Co:TiO2 thin films were deposited using two interacting plasmas produced from different targets, TiO2 and cobalt. By keeping constant the laser ablation conditions on the TiO2 target and changing them on the Co target, it was possible to vary in a controlled way the Co content in the films. The cobalt plasma parameters, such as the ion kinetic energy and plasma density, were determined for each deposition condition in an attempt to correlate them with the material’s properties. The cobalt ion mean kinetic energy was varied from 36 to 789 eV, resulting in films with Co content from 1.2 up to 5.1 at.%, respectively, revealing that the cobalt content can be controlled by the Co+ kinetic energy. The study of the optical properties showed that the optical band gap decreased from 2.9 to 2.0 eV as the Co content increased. Raman spectroscopy was used to characterize the microstructure of the deposits, and the obtained results suggest the formation of two coexisting phases: TiO2 in its rutile phase and CoTiO3. It was found that as the Co+ energy increases, the CoTiO3 phase develops in a greater quantity. XPS measurements confirm the Raman spectroscopy results.

Metastable AuxRh100–x Thin Films Prepared by Pulsed Laser Deposition for the Electrooxidation of Methanol

Metastable AuxRh100–x thin films were prepared by crossed beam pulsed laser deposition on two different substrates. High kinetic-energy deposition conditions were used (0.1 Torr He, 5.5 cm target-to-substrate distance). The films were characterized by X-ray diffraction and X-ray photoelectron spectroscopy, and their electrocatalytic activities for the electrooxidation of methanol were assessed by linear sweep voltammetry in 1 M NaOH. All films are made of a single fcc phase compound. For 40 < x < 85 at %, the lattice parameter deviates slightly from that expected from Vegard’s law. The XRD patterns of AuxRh100–x/C and AuxRh100–x/Si did not evolve over a period of 1 year, indicating that the solid solution is kinetically stable. However, as expected from the Au–Rh binary phase diagram, heat treatment of Au50Rh50/C at 500 °C in Ar during 24 h leads to decomposition of the metastable fcc phase and the formation of Rh and Au. X-ray photoelectron spectroscopy revealed that the Au surface composition closely fo...

Microstructural characterization of Ti–C–N thin films prepared by reactive crossed beam pulsed laser deposition

In this work, Raman spectroscopy has been used to characterize Ti–C–N thin films in order to obtain information about the microstructure of the deposited materials, and in particular to study the effects due to the carbon incorporation into the TiN lattice. Ti–C–N thin films were prepared using a crossed plasma configuration in which the ablation of two different targets, titanium and carbon, in a reactive atmosphere was performed. With this configuration, the carbon content in the films was varied in an easy way from 5.0 at% to 40.0 at%. Thin film composition was determined from Non-Rutherford Backscattering Spectroscopy (NRBS) measurements. X-ray photoelectron spectroscopy and X-Ray diffraction measurements were also carried out in order to characterize the films in more detail, with this being used to give support to the interpretation of the Raman spectra. The Raman results revealed that at lower carbon concentrations a solid solution Ti(C, N) is formed, whilst at higher carbon concentrations a nanocomposite, consisting of nanocrystalline TiCN and TiC immersed in an amorphous carbon matrix is obtained.

Modified crossed-beam PLD method for the control of ion energy spectrum

The modified crossed-beam pulsed laser deposition method, which allows wide-range variations in the energy of deposited particles, is presented for the first time. Time-of-flight curves (TFCs) of silicon ions that are formed by the crossed plumes from two silicon targets and the erosion plume from one silicon target are measured using the Langmuir probe technique. It is demonstrated that the TFCs of ions from the erosion plume are approximated by sums of the one-dimensional Maxwell velocity distributions. Variations in the ion concentrations that result from the interaction are measured. Transformations of the energy spectrum of the plasma beam formed by crossed plumes are determined using variations in the angle between the plumes.

Specific character of the 119Sn thin films growth on amorphous Si by the CBPLD method

The research of the 119Sn thin films growth on amorphous Si that is important for the multilayer periodical spin-tunnel nanostructures creation have been investigated in this paper. The 119Sn mono-isotopic thin films on the silicon substrates (100) had been received by crossed-beam pulsed laser deposition method (CBPLD). Similarly the [Fe/Si/Sn/Si] multilayer periodical structures have been deposited. The received samples were investigated by atomic-force microscopy, electronic microscopy and X-ray reflectometry methods. It has been established that at 119Sn film thickness up to 3 nm it is possible to received atomic-smooth surfaces with 0.5 nm roughness.

Ion energy spectrum control in modified cross-beam pulsed laser deposition method

The time-of-flight curves of the ion current to a probe in a plasma beam formed by crossing plumes from two laser-ablated silicon targets have been measured using the Langmuir probe technique. It is established for the first time that the ion energy spectrum of the plasma beam formed by the two laser erosion plumes and oriented in the direction of the bisector of the angle between the initial plumes can be modified by changing the angle between them (i.e., between the erosion plume). A modified cross-beam pulsed laser deposition method is proposed, which allows the energies of deposited particles to be controlled in a broad range.

Structural and Electrochemical Properties of Nanocrystalline PtRu Alloys Prepared by Crossed-Beam Pulsed Laser Deposition

Mixed Pt−Ru thin films were prepared by crossed-beam pulsed laser deposition. The depositions were performed at different He background gas pressures, and the composition was varied over the whole composition range. X-ray diffraction patterns and X-ray photoelectron spectroscopy were used to assess the structure, the surface composition, and the electronic structure of the catalysts. The electrochemical properties of the films were assessed through cyclic voltammetry and CO stripping measurements in acidic solution. Consistent with the binary Pt−Ru phase diagram, it is shown that fcc Pt(Ru) is formed for [Pt]bulk ≥ 40 atom %, whereas hcp Ru(Pt) is obtained for [Pt]bulk ≤ 20 atom %. Likewise, X-ray photoelectron spectroscopy revealed that the Pt surface composition of PtxRu100−x thin films closely follows the bulk Pt concentration. There is a ca.0.8 eV difference in the value of Δ(Ru 3d5/2−Pt 4f7/2) as the [Pt]bulk is increased from 0 to 100 atom %, indicating that the alloy is present at the surface of th...

TiCN thin films grown by reactive crossed beam pulsed laser deposition

In this work, we used a crossed plasma configuration where the ablation of two different targets in a reactive atmosphere was performed to prepare nanocrystalline thin films of ternary compounds. In order to assess this alternative deposition configuration, titanium carbonitride (TiCN) thin films were deposited. Two crossed plasmas were produced by simultaneously ablating titanium and graphite targets in an Ar/N2 atmosphere. Films were deposited at room temperature onto Si (100) and AISI 4140 steel substrates whilst keeping the ablation conditions of the Ti target constant. By varying the laser fluence on the carbon target it was possible to study the effect of the carbon plasma on the characteristics of the deposited TiCN films. The structure and composition of the films were analyzed by X-ray Diffraction, Raman Spectroscopy and non-Rutherford Backscattering Spectroscopy. The hardness and elastic modulus of the films was also measured by nanoindentation. In general, the experimental results showed that the TiCN thin films were highly oriented in the (111) crystallographic direction with crystallite sizes as small as 6.0 nm. It was found that the hardness increased as the laser fluence was increased, reaching a maximum value of about 33 GPa and an elastic modulus of 244 GPa. With the proposed configuration, the carbon content could be easily varied from 42 to 5 at.% by changing the laser fluence on the carbon target.

Oxygen Reduction Kinetics on PtxNi100 − x Thin Films Prepared by Pulsed Laser Deposition

Mixed Pt–Ni thin films were prepared by crossed beam pulsed laser deposition. The depositions were performed at high kinetic energy conditions in the presence of 0.1 Torr He. X-ray diffraction patterns and X-ray reflectometry measurements showed that all films are made of a single face-centered cubic phase compound whose lattice parameter and density vary linearly with the bulk Pt composition. Likewise, X-ray photoelectron spectroscopy revealed that the Pt surface composition of thin films closely follows the bulk Pt concentration. The electrochemical active surface area (EASA) was evaluated by estimating , the hydrogen desorption charge in the potential region of ca. 0.05–0.35 V (where UPD stands for underpotential deposited). is almost constant for with but increases steadily for lower values of . This is thought to reflect the fact that dissolution of Ni atoms occurs, leading to an increase in the EASA and Pt enrichment at the surface of the films, as determined by XPS measurements. A positive potential shift (60 mV) of the half-wave current potential for oxygen reduction is observed as the Pt content is reduced from to . This effect is mostly related to an increase in the EASA as the intrinsic ORR activity of thin films, as determined from normalized kinetic current density values, is constant and does not vary with the bulk Pt content of the film.

Structure and giant magnetoresistance of granular Co–Cu nanolayers prepared by cross-beam pulsed laser deposition

A series of CoxCu100−x (x=0, 40–75, 100) layers with thicknesses between 13 and 55 nm were prepared on silicon substrates using cross-beam pulsed laser deposition. Wide-angle x-ray diffraction (WAXRD), transmission electron microscopy (TEM), and electrical transport measurements revealed a structure consisting of decomposed cobalt and copper grains with grain sizes of about 10 nm. The influence of cobalt content and layer thickness on the grain size is discussed. Electron diffraction indicates the presence of an intermetallic Co–Cu phase of Cu3Au structure type. Thermal treatment at temperatures between 525 and 750 K results in the progressive decomposition of Co and Cu, with an increase of the grain sizes up to about 100 nm. This is tunable by controlling the temperature and duration of the anneal, and is directly observable in WAXRD patterns and TEM images. A careful analysis of grain size and the coherence length of the radiation used allows for an accurate interpretation of the x-ray diffraction patterns, by taking into account coherent and noncoherent scattering. The alloy films show a giant magnetoresistance of 1%–2.3% with the maximum obtained after annealing at around 725 K.

Structural and Electrochemical Characterization of Metastable PtAu Bulk and Surface Alloys Prepared by Crossed-Beam Pulsed Laser Deposition

Crossed-beam pulsed laser deposition in a moderate He background gas pressure was used to prepare PtAu thin films. The Pt bulk content was determined by neutron activation analysis, whereas X-ray diffraction and X-ray photoelectron spectroscopy were used to assess the bulk and the surface structure of the films, respectively. It is shown that metastable PtAu alloys with a unique fcc structure are formed over the whole composition range. The surface composition of the films closely follows the bulk content, and X-ray photoelectron spectroscopy reveals that the surface of the films is also made of a PtAu alloy. These films are stable under ambient conditions. The electrochemical properties of these films were determined by cyclic voltammetry in H2SO4 electrolyte, and their reactivity toward the electrooxidation of CO and the electroreduction of O2 was assessed. The CO stripping peak potential value increases with the Au content, indicating an increased binding energy in comparison with polycrystalline Pt. S...

Physico-Chemical and Electrochemical Properties of Platinum−Tin Nanoparticles Synthesized by Pulsed Laser Ablation for Ethanol Oxidation

Mixed Pt−Sn catalysts were prepared by crossed beam pulsed laser deposition. Five catalyst compositions were investigated, namely, Pt100Sn0, Pt90Sn10, Pt75Sn25, Pt50Sn50, and Pt30Sn70. The depositions were performed either under vacuum or in the presence of 2 Torr He. The pressure in the deposition chamber has a strong influence on the surface structure and morphology of the catalytic particles, as determined from scanning electron micrographs (SEM) and atomic force microscopy (AFM). For catalysts prepared under He, X-ray diffraction (XRD) patterns show an expansion of the fcc lattice, indicating that Sn atoms are dissolved in it. Up to 13 atom % Sn can be dissolved in the Pt fcc structure. In contrast, less than 3 atom % of Sn can be dissolved in Pt when the catalysts are prepared under vacuum. X-ray photoelectron spectroscopy has revealed that the surface composition of PtxSn100-x catalysts prepared under 2 Torr He closely follows the bulk concentration. Catalysts with the same composition prepared under vacuum exhibit a surface enrichment with Pt atoms. In these catalysts, tin is highly oxidized and the mean [O]/[Sn] surface ratio is 2.35. In contrast, tin in catalysts prepared under 2 Torr He is less oxidized and the mean [O]/[Sn] surface ratio is 1.37. Cyclic voltammogram curves reveal that mixing Sn with Pt lowers the onset oxidation potential of ethanol. This effect is more pronounced for catalysts prepared under 2 Torr He, and Eonset = 0.31 V vs RHE is reached for [Pt]bulk = 75 atom %. Similarly, chronoamperometric measurements conducted at +0.5 V vs RHE also demonstrated that Pt75Sn25 catalyst prepared under 2 Torr He is the most active after 1 h of electrolysis. The reasons underlying these differences are discussed.

Ethanol Electrooxidation on Pt-Sn Catalysts Deposited by Pulsed Laser Ablation

Pt3Sn catalysts were prepared from pure Pt and Sn targets by crossed beam pulsed laser deposition. The deposition was performed either under vacuum or in the presence of a He background pressure (1, 2, 3, 4 and 5 Torr). The pressure in the deposition chamber influences the surface structure and the morphology of the catalytic nanoparticles, as determined from scanning electron microscopy. Cyclic voltammogram curves reveal that Pt3Sn catalysts deposited under He lower the onset oxidation potential of ethanol compared to Pt3Sn electrodes synthesized under vacuum. This effect is particularly evident for Pt3Sn elaborated at 2 Torr He which provides a high current density value close to 20 mA.cm-2 at 0.7 V vs. RHE. Chronoamperometric measurements conducted at + 0.5 V vs. RHE also demonstrated that Pt3Sn deposited at 2 Torr He is the most active electrocatalyst after 1 hour of electrolysis.