Characterization of crystallized LiMn2O4 thin films grown by pulsed laser deposition

LiMn₂O₄ thin films were grown on stainless steel substrates at 625°C and 100?mTorr of oxygen by pulsed laser deposition. The deposited film was highly crystallized with an average crystal size of about 260?nm. The initial discharge capacity of the film was about 53.8?µAh?cm^?2?µm^?1 and the capacity decayed at an average rate of about 0.29% per cycle when the film was cycled between 3.0 and 4.5?V vs. Li/Li⁺, with a current density of 20?µA?cm^?2. It was observed that the grains became smaller and the boundaries of grains became obscure after 100 cycles, indicating that manganese dissolution via loss of MnO may be the main factor leading to the capacity fade in pure thin film LiMn₂O₄ electrodes. The apparent diffusion coefficient of Li ions, obtained from cyclic voltammetry scans, was of the order of 10^?12?cm²?s^?1. High charge-transfer resistance was observed at high potentials. Ex-situ X-ray diffraction (XRD) and Raman spectroscopy were used to investigate the structure changes of LiMn₂O₄ thin film with intercalation/de-intercalation of lithium. XRD results revealed a relatively small lattice change with the removal of lithium in crystallized thin film, compared to that of powder LiMn₂O₄ cathode.     

Characterization of ZnO-SnO2 thin film composites prepared by pulsed laser deposition

Thin films of ZnO-SnO₂ composites have been deposited on Si(1 0 0) and glass substrates at 500 °C by pulsed laser ablation using different composite targets with ZnO amount varying between 1 and 50 wt%. The effect of increasing ZnO-content on electrical, optical and structural properties of the ZnO-SnO₂ films has been investigated. X-ray diffraction analysis indicates that the as-deposited ZnO-SnO₂ films can be both crystalline (for ZnO <1 wt%) and amorphous (for ZnO ≥ 10 wt%) in nature. Atomic force microscopy studies of the as-prepared composite films indicate that the surfaces are fairly smooth with rms roughness varying between 3.07 and 2.04 nm. The average optical transmittance of the as-deposited films in the visible range (400-800 nm), decreases from 90% to 72% for increasing ZnO concentration in the film. The band gap energy (E_g) seems to depend on the amount of ZnO addition, with the maximum obtained at 1 wt% ZnO. Assuming that the interband electron transition is direct, the optical band gap has been found to be in the range 3.24-3.69 eV for as-deposited composite films. The lowest electrical resistivity of 7.6 × 10⁻³ Ω cm has been achieved with the 25 wt% ZnO composite film deposited at 500 °C. The photoluminescence spectrum of the composite films shows a decrease in PL intensity with increasing ZnO concentration.     

Epitaxial ZrC thin films grown by pulsed laser deposition

ZrC thin films were grown on (0 0 1)Si, (1 1 1)Si and (0 0 0 1)sapphire substrates by the pulsed laser deposition (PLD) technique. X-ray diffraction, X-ray reflectivity and Auger electron spectroscopy investigations were used to characterize the structure and composition of the deposited films. It has been found that films grown at temperatures higher than 700 °C under very low water vapor pressures were highly textured. Films deposited on (0 0 1)Si grew with the (0 0 1) axis perpendicular to the substrate, while those deposited on (1 1 1)Si and (0 0 0 1)sapphire grew with the (1 1 1) axis perpendicular to the substrate. Pole figures investigations showed that films were epitaxial, with in-plane axis aligned to those of the substrate.     

Electrical conductivity of YSZ film grown by pulsed laser deposition

Yttria-stabilized zirconia (YSZ) thin films, 0.6–1.5 μm, were deposited on Pt and sapphire substrates by a pulsed laser deposition (PLD) method. Their structural and transport properties have been studied by means of X-ray diffraction and electrical conductivity measurements. The in-plane and the perpendicular-to-plane conductivities (hereafter, “across-plane” conductivity) of thin films were measured and compared to that of bulk sample. X-ray diffraction and electron microscopy results showed that the films on Pt and sapphire were polycrystalline cubic with a columnar structure. Both the across-plane and the in-plane conductivities of YSZ thin film were close to that of bulk specimens. Thus no conductivity enhancement was found for the present nano-crystalline YSZ films (grain or column size, 60∼100 nm).     

SnO2 thin films grown by pulsed Nd:YAG laser deposition

SnO₂ thin films have been deposited on glass substrates by pulsed Nd:YAG laser at different oxygen pressures, and the effects of oxygen pressure on the physical properties of SnO₂ films have been investigated. The films were deposited at substrate temperature of 500°C in oxygen partial pressure between 5.0 and 125 mTorr. The thin films deposited between 5.0 to 50 mTorr showed evidence of diffraction peaks, but increasing the oxygen pressure up to 100 mTorr, three diffraction peaks (110), (101) and (211) were observed containing the SnO₂ tetragonal structure. The electrical resistivity was very sensitive to the oxygen pressure. At 100 mTorr the films showed electrical resistivity of 4×10⁻² Ω cm, free carrier density of 1.03×10¹⁹ cm⁻³, mobility of 10.26 cm² V⁻¹ s⁻¹ with average visible transmittance of ∼87%, and optical band gap of 3.6 eV.     

Observation of multiferroic properties in a CdTe:Mn thin film grown by pulsed laser deposition techniques

We report multiferroic properties in a 3% Mn-doped CdTe (CdTe:Mn or CTM) thin film grown in a co-deposition system constituting pulsed laser deposition and radio frequency (RF) sputtering, in which the Mn concentration was tuned by the sputtering rate of Mn. We observed a clear ferroelectric hysteresis loop in the CTM thin film with remanent polarization of 3.5 μC/cm² and ferromagnetism in the film at a temperature lower than the Curie temperature of 15 K. Both features show direct evidence of multiferroics in the CTM thin film.     

CuGaO2 thin film synthesis using hydrogen-assisted pulsed laser deposition

Phase formation, crystallinity, and orientation of CuGaO₂ thin films is reported in which hydrogen gas is utilized as a reducing reactant during growth to drive the valence state of Cu to +1. At relatively low growth temperatures, the films are a mixture of CuGaO₂, Cu₂O, and CuGa₂O₄. At higher temperatures, the majority phase is CuGaO₂. The use of H₂ during film growth facilitated the formation of the delafossite phase. Phase purity is further improved via high temperature annealing. The formation of the delafossite phase via post-annealing treatment is in agreement with the thermodynamic equilibrium studies of the Cu-Ga-O system, showing that the CuGaO₂ phase is thermodynamically stable under the conditions considered. With the post-annealing process, we achieved phase-pure CuGaO₂ films with p-type resistivity on the order of 30 Ω cm and carrier density of mid-10¹⁷ cm^-3. PACS 71.20.Nr; 73.61.Le; 81.15.-z     

Superhydrophobicity of polytetrafluoroethylene thin film fabricated by pulsed laser deposition

Superhydrophobic polytetrafluoroethylene (PTFE) thin films were obtained by pulsed laser deposition (PLD) technique carried out with KrF excimer laser (λ = 248 nm) of about 1 J/cm² at a pressure of 1.33 Pa. The samples exhibit high water contact angle of about 170° and the sliding angle smaller than 2°. From studying the surface morphology of the prepared films, it is believed that the nano-scale surface roughness has enhanced the hydrophobic property of the PTFE. The increase of trapping air and reducing liquid-solid contact area due to the rough surface, as suggested by the Cassie-Baxter's model, should be responsible for superhydrophobicity of the PLD prepared films. This study thus provides a convenient one-step method without using wet-process to produce a superhydrophobic surface with good self-cleaning properties.     

Characterization of nitrogen-doped ZnO thin films grown by plasma-assisted pulsed laser deposition on sapphire substrates

The crystalline, optical and electrical properties of N-doped ZnO thin films were measured using X-ray diffraction, photoluminescence and Hall effect apparatus, respectively. The samples were grown using pulsed laser deposition on sapphire substrates coated priorly with ZnO buffer layers. For the purpose of acceptor doping, an electron cyclotron resonance (ECR) plasma source operated as a low-energy ion source was used for nitrogen incorporation in the samples. The X-ray diffraction analyses indicated some deterioration of the ZnO thin film with nitrogen incorporation. Temperature-dependent Van der Pauw measurements showed consistent p-type behavior over the measured temperature range of 200–450 K, with typical room temperature hole concentrations and mobilities of 5×10¹⁵ cm⁻³ and 7 cm²/V s, respectively. Low temperature photoluminescence spectra consisted of a broad emission band centered around 3.2 eV. This emission is characterized by the absence of the green deep-defect band and the presence of a band around 3.32 eV.     

Chemical composition of ZrC thin films grown by pulsed laser deposition

ZrC films were grown on (1 0 0) Si substrates by the pulsed laser deposition (PLD) technique using a KrF excimer laser working at 40 Hz. The nominal substrate temperature during depositions was set at 300 °C and the cooling rate was 5 °C/min. X-ray diffraction investigations showed that films deposited under residual vacuum or under 2 × 10⁻³ Pa of CH₄ atmosphere were crystalline, exhibiting a (2 0 0)-axis texture, while those deposited under 2 × 10⁻² Pa of CH₄ atmosphere were found to be equiaxed and with smaller grain size. The surface elemental composition of as-deposited films, analyzed by Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS), showed the usual high oxygen contamination of carbides. Once the topmost 2-4 nm region was removed, the oxygen concentration rapidly decreased, down to around 3-8% only in bulk. Simulations of the X-ray reflectivity (XRR) curves indicated a smooth surface morphology, with roughness values below 1 nm (rms) and films density values of around 6.30-6.45 g/cm³, very close to the bulk density. The growth rate, estimated from thickness measurements by XRR was around 8.25 nm/min. Nanoindentation results showed for the best quality ZrC films a hardness of 27.6 GPa and a reduced modulus of 228 GPa.     

Chalcogenide-based thin film sensors prepared by pulsed laser deposition technique

One advantage of the pulsed laser deposition (PLD) method is the stoichiometric transfer of multi-component target material to a given substrate. This advantage of the PLD determined the choice to prepare chalco-genide-based thin films with an off-axis geometry PLD. Ag-As-S and Cu-Ag-As-Se-Tetargets were used to deposit thin films on Si substrates for an application as a heavy metal sensing device. The films were characterized by means of Rutherford backscattering spectrometry (RBS), transmission electron microscopy (TEM), and electrochemical measurements. The same stoichiometry of the films and the targets was confirmed by RBS measurements. We observed a good long-term stability of more than 60 days and a nearly Nernstian sensitivity towards Pb and Cu, which is comparable to bulk sensors.     

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.     

Characterization of polymer thin films obtained by pulsed laser deposition

The development of laser techniques for the deposition of polymer and biomaterial thin films on solid surfaces in a controlled manner has attracted great attention during the last few years. Here we report the deposition of thin polymer films, namely Polyepichlorhydrin by pulsed laser deposition. Polyepichlorhydrin polymer was deposited on flat substrate (i.e. silicon) using an NdYAG laser (266 nm, 5 ns pulse duration and 10 Hz repetition rate).The obtained thin films have been characterized by atomic force microscopy, scanning electron microscopy, Fourier transform infrared spectroscopy and spectroscopic ellipsometry.It was found that for laser fluences up to 1.5 J/cm² the chemical structure of the deposited polyepichlorhydrin polymer thin layers resembles to the native polymer, whilst by increasing the laser fluence above 1.5 J/cm² the polyepichlorohydrin films present deviations from the bulk polymer.Morphological investigations (atomic force microscopy and scanning electron microscopy) reveal continuous polyepichlorhydrin thin films for a relatively narrow range of fluences (1-1.5 J/cm²).The wavelength dependence of the refractive index and extinction coefficient was determined by ellipsometry studies which lead to new insights about the material.The obtained results indicate that pulsed laser deposition method is potentially useful for the fabrication of polymer thin films to be used in applications including electronics, microsensor or bioengineering industries.     

Characterization of zirconium thin films deposited by pulsed laser deposition

Zirconium(Zr) thin films deposited on Si(100) by pulsed laser deposition(PLD) at different pulse repetition rates are investigated. The deposited Zr films exhibit a polycrystalline structure, and the X-ray diffraction(XRD) patterns of the films show the α Zr phase. Due to the morphology variation of the target and the laser–plasma interaction, the deposition rate significantly decreases from 0.0431 /pulse at 2 Hz to 0.0189 /pulse at 20 Hz. The presence of droplets on the surface of the deposited film, which is one of the main disadvantages of the PLD, is observed at various pulse repetition rates. Statistical results show that the dimension and the density of the droplets increase with an increasing pulse repetition rate. We find that the source of droplets is the liquid layer formed under the target surface. The dense nanoparticles covered on the film surface are observed through atomic force microscopy(AFM). The root mean square(RMS) roughness caused by valleys and islands on the film surface initially increases and then decreases with the increasing pulse repetition rate.The results of our investigation will be useful to optimize the synthesis conditions of the Zr films.     

脉冲激光气相沉积法制备钴纳米薄膜实验研究

采用脉冲激光沉积技术制备了钴纳米薄膜,分析和讨论了不同背景气压和脉冲频率对钴纳米薄膜表面形貌的影响及纳米微粒的形成机理。实验结果表明：在低背景气压下,等离子体羽辉自身粒子之间的碰撞占主导作用,容易形成液滴;在较高背景气压下,等离子体羽辉边缘粒子和背景气体粒子之间的碰撞占主导作用,容易形成小岛并凝聚成微颗粒;在4Hz的脉冲重复频率和5Pa背景气压下生长出单分散性良好的钴纳米颗粒。     

Electrical characterisation of phosphorus-doped ZnO thin films grown by pulsed laser deposition

Phosphorus-doped ZnO films were grown by pulsed laser deposition using a ZnO:P₂O₅-doped target as the phosphorus source with the aim of producing p-type ZnO material. ZnO:P layers (with phosphorus concentrations of between 0.01 to 1 wt%) were grown on a pure ZnO buffer layer. The electrical properties of the films were characterised from temperature dependent Hall-effect measurements. The samples typically showed weak n-type conduction in the dark, with a resistivity of 70 Ω cm, a Hall mobility of μ_n0.5 cm² V ⁻¹ s⁻¹ and a carrier concentration of n3×10¹⁷ cm⁻³ at room temperature. After exposure to an incandescent light source, the samples underwent a change in conduction from n- to p-type, with an increase in mobility and decrease in concentration for temperatures below 300 K.     

Non-stoichiometry-induced metal-to-insulator transition in nickelate thin films grown by pulsed laser deposition

While controlling the cation contents in perovskite rare-earth nickelate thin films, a metal-to-insulator phase transition is reported. Systematic control of cation stoichiometry has been achieved by manipulating the irradiation of excimer laser in pulsed laser deposition. Two rare-earth nickelate bilayer thin-film heterostructures with the controlled cation stoichiometry (i.e. stoichiometric and Ni-excessive) have been fabricated. It is found that the Ni-excessive nickelate film is structurally less dense than the stoichiometric film, albeit both of them are epitaxial and coherent with respect to the underlying substrate. More interestingly, as a temperature decreases, a metal-to-insulator transition is only observed in the Ni-excessive nickelate films, which can be associated with the enhanced disproportionation of the Ni charge valence. Based on our theoretical results, possible origins (e.g. anti-site defects) of the low-temperature insulating state are discussed with the need of future work for deeper understanding. Our work can be utilized to realize unusual physical phenomena (e.g. metal-to-insulator phase transitions) in complex oxide films by manipulating the chemical stoichiometry in pulsed laser deposition.     

Oxygen incorporation in ZnTe thin films grown by plasma-assisted pulsed laser deposition

We studied oxygen incorporation into ZnTe thin films with nitrogen and oxygen plasma during a plasma-assisted pulsed laser deposition (PA-PLD). It was shown that ZnTe:O layer formed with oxygen plasma exhibits an enhancement of optical transparency in visible spectral region due to the formation of amorphous TeO_x. Especially, the ZnTe:NO deposited by PA-PLD under nitrogen and oxygen partial pressures with N₂:O₂ of 10:3 sccm showed p-type semiconducting characteristics and the formation of intermediate band at about 0.5–0.8 eV below the ZnTe band edge. These results for oxygen incorporation in ZnTe thin film such as the enhancement of optical transparency in visible spectral region and the intermediate band formation will be useful for optoelectronic devices or intermediate band solar cells.     

Structural and morphological properties of thin ZnO films grown by pulsed laser deposition

The pulsed laser deposition technique was used to produce zinc oxide thin films onto silicon and Corning glass substrates. Homogeneous surfaces exhibiting quite small Root Mean Square (RMS) roughness, consisting of shaped grains were obtained, their grain diameters being 40-90 nm at room temperature and at 650 °C growth respectively. Films were polycrystalline, even for growth at room temperature, with preferential crystallite orientation the (0 0 2) basal plane of wurtzite ZnO. Temperature increase caused evolution from grain to grain agglomeration structures, improving crystallinity. Compressive to tensile stresses transition with temperature was found while the lattice constant decreased.     

Role of vanadium content in ZnO thin films grown by pulsed laser deposition

Vanadium-doped ZnO films (Zn_1−xV_xO, where x = 0.02, 0.03, 0.05 and 0.07), were formed from ceramic targets on c-cut sapphire substrates using pulsed laser deposition at substrate temperature of 600 °C and oxygen pressure of 10 Pa. In order to clarify how the vanadium concentration influences the films’ properties, structural and magnetic investigations were performed. All films crystallised in wurtzite phase and presented a c-axis preferred orientation at low concentrations of vanadium. The results implied that the doping concentration and crystalline microstructure influence strongly the system's magnetic characteristics. Weak ferromagnetism was registered for the film with the lowest doping concentration (2 at.%), which exhibited a ferromagnetic behavior at Curie temperature higher than 300 K. Increasing the vanadium content in the film caused degradation of the magnetic ordering.