Laser Deposition Technique Research Articles

An efficient urea biosensor based on laser ablated ZnO thin film

ABSTRACTZinc oxide (ZnO) thin film deposited onto indium tin oxide (ITO) coated Corning glass substrates using pulsed laser deposition (PLD) technique has been used as a matrix for realization of an efficient urea biosensor after immobilization of urease (Urs) enzyme onto the surface of ZnO. The bioelectrode (Urs/ZnO/ITO/glass) is found to be exhibiting an enhanced sensitivity of 22μΑmΜ−1cm−2 towards urea over a wide detection range of 5-200 mg/dl. The relatively low value of Michaelis menten constant (Km= 0.94mM) indicates high affinity of the immobilized urease towards the analyte (urea). The prepared biosensor retains 90% of its activity for more than 10 weeks. The observed enhanced response characteristics of bioelectrode are attributed to the growth of the matrix (highly c-axis oriented ZnO thin film) with desired surface morphology and high electron communication feature. The results confirm the promising application of PLD grown ZnO thin film as an efficient matrix for urea detection.

Enhanced thermoelectric properties of Al-doped ZnO thin films

ABSTRACTWe have prepared 2% Al doped ZnO (AZO) thin films on SrTiO3 and Al2O3 substrates by Pulsed Laser Deposition (PLD) technique at various deposition temperatures (Tdep = 300 °C – 600 °C). Transport and thermoelectric properties of AZO thin films were studied in low temperature range (300 K - 600 K). AZO/STO films present superior performance respect to AZO/Al2O3 films deposited at the same temperature, except for films deposited at 400 °C. Best film is the fully c-axis oriented AZO/STO deposited at 300 °C, with electrical conductivity 310 S/cm, Seebeck coefficient -65 μV/K and power factor 0.13 × 10-3 Wm-1K-2 at 300 K. Its performance increases with temperature. For instance, power factor is enhanced up to × 10-3 Wm-1K-2 at 600 K, surpassing the best AZO film previously reported in literature.

Influence of Momentary Annealing on the Nanoscale Surface Morphology of Room Temperature Pulsed Laser Deposited NiO(111) Epitaxial Thin Films on Atomically Stepped Sapphire (0001) Substrates

ABSTRACTWe examined the influence of momentary annealing on the nanoscale surface morphology of NiO(111) epitaxial thin films deposited on atomically stepped sapphire (0001) substrates at room temperature in O2 at 1.3 × 10−3 and 1.3 × 10−6 Pa using a pulsed laser deposition (PLD) technique. The NiO films have atomically flat surfaces (RMS roughness: approximately 0.1–0.2 nm) reflecting the step-and-terrace structures of the substrates, regardless of the O2 deposition pressure. After rapid thermal annealing (RTA) of the NiO(111) epitaxial film deposited at 1.3 × 10−3 Pa O2, a periodic straight nanogroove array related to the atomic steps of the substrate was formed on the film surface for 60 s. In contrast, the fabrication of a transient state in the nanogroove array formation was achieved with RTA of less than 1 s. However, when the O2 atmosphere during PLD was 1.3 × 10−6 Pa, random crystal growth was observed and resulted in a disordered rough surface nanostructure after RTA.

Room Temperature Ferromagnetism in PLD Grown Zn1-xLixO1-yNy Thin Films

Zn1-xLixO1-yNy (ZnO:(N,Li)) thin films grown by Pulsed Laser Deposition (PLD) technique are found to exhibit intrinsic ferromagnetic behavior at room temperature (RT). XRD reveals that the grown Zn1-xLixO1-yNy thin films (x = 0.05, y = 0.08) are single phase and preferred oriented along c-axis. In contrast to pure ZnO thin films, ZnO thin films doped with non-magnetic nitrogen (ZnO:N) result in good M-H hysteresis loop at RT. Co-doping of ZnO:N with Li is found to enhance the saturation magnetization (Ms) appreciably. The room temperature ferromagnetic behavior and semiconducting property of Zn1-xLixO1-yNy thin film could be promising for spin injection based functional devices.

Wear resistance of ZrC/TiN and ZrC/ZrN thin multilayers grown by pulsed laser deposition

ZrC/TiN and ZrC/ZrN multilayers thinner than 350 nm were grown on (100) Si substrates at a temperature of 300 °C by the pulsed laser deposition (PLD) technique using a KrF excimer laser (λ=248 nm, pulse duration τ=25 ns, 8.0 J/cm2 fluence and 40 Hz repetition rate). Cross-sectional transmission electron microscopy, Auger electron spectroscopy depth profiling and simulations of X-ray reflectivity curves indicated that there was intermixing between the deposited layers at the interfaces as well as between the first layer and the substrate. Nanoindentation investigations found hardness values between 35 and 38 GPa for the deposited multilayers. Linear unidirectional sliding wear tests were conducted using a ball-on-plate tribometer under 1 N normal force. Wear tracks were produced in a Hysitron nanoindenter with 1 μm radius diamond tip under a 500 μN load. High-resolution cross-sectional transmission electron microscopy studies of the wear tracks showed that the multilayers withstood these tests without significant damage. The results could be explained by the use of a high laser fluence during deposition that resulted in very dense and strongly adherent nanocrystalline layers.

Pulsed laser deposition of uniform semiconductor nanodot arrays

Uniform arrays of silicon (Si), gallium arsenide (GaAs) and zinc oxide (ZnO) nanodots have been deposited using Pulsed Laser Deposition (PLD) technique combined with a contact mask consisting of nano-holes fabricated by E-beam lithography (EBL). These nanocrystalline semiconductor nanodots have been deposited by PLD on Si and GaAs substrates at room temperature. Characterization of the nanodots has been carried out using different techniques including X-ray diffraction (XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), Auger Electron Spectroscopy (AES), and Raman spectroscopy. This work demonstrates a novel technique for deposition of uniform array of semiconductor nanostructures using a contact mask at room temperature for photonic applications.

Flux-pinning properties of YBa2Cu3O7−x multilayered films with Y2O3 and ZnO nanoparticle inclusions

We investigated the flux-pinning properties of YBa2Cu3O7−x (YBCO) films in which Y2O3 and ZnO nanoparticles were uniformly embedded by using the pulsed laser deposition (PLD) technique. Y2O3 and ZnO nanoparticles with average sizes of 10–30 nm and with different densities by changing the number of nanoparticle layers were introduced in a YBCO matrix in the form of a multilayered structure. The total thickness of the YBCO superconducting layers was kept to be 250 nm. Dilute doping was found to be effective for both Y2O3 and ZnO nanoparticles. For Y2O3 doping, critical current density (Jc) enhancements over a wide range of fields were obtained in 1- and 5-layer doped samples, while weak Jc enhancements and a better field dependence of Jc were found in the YBCO film with 1 layer of ZnO. Based on an analysis of surface morphology, the transition temperature (Tc), and Jc, we discuss the difference between the two types of nanoparticles as flux-pinning centers.

Microstructural Characterization of La- and Ti-Codoped Multiferroic BiFeO$_{3}$ Epitaxial Thin Films

La- and Ti-codoped multiferroic BiFeO3 (BLFTO) epitaxial thin films were grown on (001) SrTiO3 (STO) substrates by pulsed laser deposition (PLD) technique. The microstructure of BLFTO thin film had been intensively studied by using transmission electron microscopy (TEM). It was found that La-and Ti-codoping can reduce leakage current and improve ferroelectric behavior of BiFeO3 without changing its structure. The correlation of microstructure with electrical property is discussed.

Study of Matching Fields in Kagomé Patterned YBCO Thin Films

Superconducting YBCO thin films have been prepared by the pulsed laser deposition (PLD) technique. YBCO films have been patterned by kagome antidot lattice. The optical lithography technique has been used to get the required pattern. We have studied the variation of the critical current with magnetic field in kagome patterned YBCO films. The longitudinal critical current exhibits jumps which are found to be asymmetrically positioned in magnetic field. These steps are found mainly at nonmatching fields. Around the zero field limit the critical current remains independent of magnetic field. The impact of the DC current and ac-superposition in controlling the vortex motion in patterned film has been discussed.

Charge trapping memory devices employing multi-layered Ge/Si nanocrystals for storage fabricated with ALD and PLD methods

The Ge/Si nanocrystals on ultra thin high-k tunnel oxide Al2O3 were fabricated to form the charge trapping memory prototype with asymmetric tunnel barriers through combining the advanced atomic layer deposition (ALD) and pulse laser deposition (PLD) techniques. Charge storage characteristics in such memory structure have been investigated using capacitance-voltage (C-V) and capacitance-time (C-t) measurements. The results prove that both the two-layered and three-layered memory structures behave relatively qualified for the multi-level cell storage. The results also demonstrate that compared to electrons, holes reach a longer retention time even with an ultra thin tunnel oxide owing to the high band offset at the valence band between Ge and Si.

Fabrication of Nanocomposite Thermoelectric Materials by a Pulsed Laser Deposition Method

We applied a pulsed laser deposition (PLD) technique to fabricate nanocomposite half-Heusler thermoelectrics by employing two different methods: a dry process and a wet process. First, we tried to obtain nanosized thermoelectric particles by using PLD in a liquid solvent. Nanosized (<100 nm) spherical and crystalline half-Heusler particles containing Ti, Zr, Hf, Ni, and Sn elements were obtained by this method, showing good controllability of stoichiometry. The key is to select a solvent that prevents oxidation. Second, the dry PLD process was employed to coat the thermoelectric powder with metal oxides. To this end, we developed a PLD coating apparatus. After sintering the coated powder using the spark plasma sintering (SPS) technique, we confirmed that a nanosized layer of the metal oxides was uniformly formed at the grain boundaries of the half-Heusler matrix. With these two examples, the capability of the PLD techniques to fabricate well-controlled nanocomposite thermoelectric materials is demonstrated.

Improvement of resistive switching in Ti/Pr0.7Ca0.3MnO3/La0.67Sr0.33MnO3/Pt heterostructures

Ti/Pr0.7Ca0.3MnO3/Pt and Ti/Pr0.7Ca0.3MnO3/La0.67Sr0.33MnO3/Pt heterostructures are prepared using a pulsed laser deposition (PLD) technique, and the resistive switching of the heterostructures is investigated. The Ti/Pr0.7Ca0.3MnO3/La0.67Sr0.33MnO3/Pt heterostructure, which has a La0.67Sr0.33MnO3 modulation layer, shows superior characteristics of resistive switching. In particular, the switching ratio and the fatigue properties are improved greatly in this heterostructure. The mechanism of resistive switching in Ti/Pr0.7Ca0.3MnO3/La0.67Sr0.33MnO3/Pt heterostructure is also discussed in this paper.

Influence of O2 Pressure on the Structure and Surface Morphology of YSZ Layer for YBCO Coated Conductor Deposited by PLD on Ni-W Tape

Yttria-stabilized ZrO2 (YSZ) buffer layers were prepared on Ni-5%W tapes coated with CeO2-seed layers by a pulsed laser deposition (PLD) technique. The influences of oxygen pressure on the structure and surface morphology of YSZ buffer layers for YBCO coated conductors was investigated. X-ray diffraction (XRD), scanning electron microscopy (SEM) and Atomic Force Microscope (AFM) were used to characterize YSZ films. It was found that the structure and surface morphology were sensitive to the oxygen pressure. When the O2 pressure was higher than 1 mTorr, the YSZ film had mixed orientation and rugged surface. When the oxygen pressure was reduced to 0.5 mTorr, YSZ film had the pure (001) orientation. The surface became smooth as the oxygen pressure decreased. However, when the pressure was low to 0.1 mTorr, X-ray diffraction peaks form YSZ (002) were weak and the rough surface appeared again. The results could be explained either by plume stoichiometric changes, gas and ions interaction, or atomic rearrangement on the substrate.

Highly oriented La2/3Ca1/3MnO3 films grown on silicon-on-insulator substrates by pulsed laser deposition

High quality La2/3Ca1/3MnO4(LCMO) thin films have been deposited on silicon-on-insulator (SOI) substrates only buffered by yt tria-stabilized zirconia (YSZ) by using the pulsed laser deposition (PLD) technique. The results obtained from X-ray diffraction (XRD), reflection high energy electron diffraction (RHEED), scanning electron microscopy (SEM) and magnetization investigations indicate that the LCMO films are highly oriented both in-plane and out-of-plane. The Curie temperature Tc is close to 260 K and the insulator–metal (I–M) transition appears around 220 K. The conducting mechanism at low temperatures is dominated by the electron–magnon scattering. A tensile stress from the film–substrate lattice mismatch results in magnetic ‘easy axes’ in the film plane and the magnetic anisotropy energy increases with cooling. A maximum magnetoresistance (MR) is observed near 190 K, with the external magnetic field either parallel or vertical to the LCMO film plane. Moreover, the large intrinsic high-field magnetoresistance (HFMR) and the very small extrinsic low-field magnetoresistance (LFMR) again reveal that the LCMO films on SOI substrates are highly oriented thin films of good crystallinity.

Optical Analysis of Germanium Carbide Thin Films Deposited by Reactive Pulsed Laser Ablation

We deposited germanium carbide (GeC) thin films by Pulsed Laser Deposition (PLD) technique. Plasma plume created in PLD makes it possible to grow GeC thin film at room temperature. Thick-ness and optical constants were measured using spectroscopic ellipsometer (SE) in Ultraviolet-Visible range. Relationship between optical constants with methane gas pressure was analyzed. X-ray Photoelectron Spectroscopy (XPS) was used for compositional analyses. It is observed that higher pressure of methane gas for the growth of GeC by PLD is responsible for carbon agglomera-tion at the surface of the film. Moreover, the tunability of the band gap was observed from 1.6 to 2.8 eV with the pressure of methane gas.

Bulk nickel–carbon nanotube nanocomposites by laser deposition

Nickel–carbon nanotube (CNT) nanocomposites have been processed in a bulk form using a laser deposition technique, commercially known as the laser engineered net shaping (LENS) process. Mechanical milling of the powder feedstock consisting of nickel powders and CNTs before laser deposition has resulted in not only a more homogeneous distribution of the nanotubes in the nickel matrix, but also two distinct scales of reinforcements within the composite. The larger reinforcement scale consists of submicrometre to micrometre sized bundles of CNTs while the smaller scale consists of individual (or cluster of a few) CNTs within the nickel matrix. High resolution transmission electron microscopy studies indicate that the nickel/CNT interface is well bonded without the presence of any significant interfacial reaction product. The degree of disorder and defects in the CNT bundles in the nickel matrix varied as a function of bundle size as revealed by Raman spectroscopy results.

The effect of different gas atmospheres on luminescent properties of pulsed laser ablated SrAl2O4:Eu2+,Dy3+ thinfilms

Abstract SrAl2O4:Eu2+,Dy3+ thin films were grown on Si (1 0 0) substrates using the pulsed laser deposition (PLD) technique to investigate the effect of vacuum, oxygen (O2) and argon (Ar) deposition atmospheres on the structural, morphological, photoluminescence (PL) and cathodoluminescence (CL) properties of the films. The films were ablated using a 248 nm KrF excimer laser. Atomic force microscopy (AFM), scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS) and fluorescence spectrophotometry were used to characterize the thin films. Auger electron spectroscopy (AES) combined with CL spectroscopy were employed for the surface characterization and electron-beam induced degradation of the films. Better PL intensities were obtained from the unannealed films prepared in Ar and O2 atmospheres with respect to those prepared in vacuum. A stable green emission peak at 515 nm, attributed to 4f65d1→4f7 Eu2+ transitions were obtained with less intense peaks at 619 nm, which were attributed to transitions in Eu3+. After annealing the films prepared in vacuum at 800 °C for 2 h, the intensity of the green emission (520 nm) of the thin film increased considerably. The amorphous thin film was crystalline after the annealing process. The CL intensity increased under prolonged electron bombardment during the removal of C due to electron stimulated surface chemical reactions (ESSCRs) on the surface of the SrAl2O4:Eu2+, Dy3+ thin films. The CL stabilized and stayed constant thereafter.

Molecular Beam Deposition of Nanoscale Ionic Liquids in Ultrahigh Vacuum

We propose a new approach to nanoscience and technology for ionic liquids (ILs): molecular beam deposition of IL in ultrahigh vacuum by using a continuous wave infrared (CW-IR) laser deposition technique. This approach has made it possible to prepare a variety of "nano-IL" with the given composition on the substrate: a nanodroplet, on one hand, the volume of which goes down to 1 aL and, on the other hand, an ultrathin film with a thickness to several 100 nm or less. The result of fractional distillation of a binary mixture of ILs, investigated by nuclear magnetic resonance as well as electrospray ionization time-of-flight mass spectrometry, indicates that this deposition process is based on the thermal evaporation of ILs, and thus this process also can be used as a new purification method of ILs in vacuum. Furthermore, the fabrication of binary mixture droplets of two ILs on the substrate by alternating deposition of two ILs was demonstrated; the homogeneity of the composition was confirmed even for one single droplet by high-spatial-resolution Raman spectroscopy.

Tailoring of Multiferroic Properties of BiFeO&lt;sub&gt;3&lt;/sub&gt; Thin Films by Cation Substitution

Mn-doped multiferroic BiFeO3 (BFMO) thin films were deposited on LaNiO3(LNO)/SrTiO3(STO)/Si(100) substrates by pulsed laser deposition (PLD) technique. X-ray diffraction (XRD) showed that films were bicrystalline single phase with (110) preferential orientation. Multiferroic top layer and oxide bottom electrode (LNO) epitaxially followed the buffer layer (STO). Oxygen partial pressure during deposition proved to be critical for phase formation, crystallinity and resistivity of the films. Atomic force microscopic (AFM) studies revealed the smooth, dense and crack free surfaces of the films. Cross-section view of the multilayers by field emission scanning electron microscope (FE-SEM) gave their thickness. Mn substitution resulted in the increase of magnetization saturation, coercive field and clarity of hysteresis loop. The magneto-electric (ME) effect was demonstrated by measuring the dielectric response in a varying magnetic field. Optimally deposited BFMO films show saturated P-E loop.

Dielectric Tunable Properties of Ba&lt;sub&gt;0.6&lt;/sub&gt;Sr&lt;sub&gt;0.4&lt;/sub&gt;TiO&lt;sub&gt;3&lt;/sub&gt; Thin Films with and without LSCO Buffer Layer

Barium strontium titanate Ba0.6Sr0.4TiO3 (BST) thin films were fabricated by pulsed laser deposition (PLD) technique on Pt/TiO2/SiO2/Si substrate with and without high (100) oriented LSCO buffer layer. Crystal structure and surface morphology of BST thin films with and without LSCO buffer layer were characterized by X-ray diffraction (XRD) and atom force microscope (AFM). The dielectric measurements were conducted on metal-insulator-metal capacitors at the frequency from 100 Hz to 1M Hz and at room temperature. It was found that the LSCO buffer layer was beneficial for BST films to decrease surface roughness, dielectric loss and to increase grain size, dielectric constant, tunability and figure of merit (FOM). The influence of LSCO buffer layer on the microstructure, dielectric and tunable properties of BST thin films were analyzed. At 1M Hz, the dielectric constants of BST films with and without LSCO buffer layer are 684 and 592, respectively. The tunability of BST thin film with LSCO buffer layer was about 65.48%, which was higher than that (about 41.84%) of BST thin film without LSCO buffer layer.