Combination Of Pulsed Laser Deposition Research Articles

Fabrication of laser deposited high-quality multilayer zone plates for hard X-ray nanofocusing

Abstract Recently, we demonstrated unprecedented sub-5 nm point focusing of hard X-rays (at 7.9 keV) based on the combination of a high gain Kirkpatrick–Baez (KB) mirror system and a high resolution W/Si multilayer zone plate (MZP). This MZP was prepared by the combination of pulsed laser deposition (PLD) and focused ion beam (FIB). Despite the small focus size, the MZP's quality suffered from sufficient but comparatively low efficiency (2%). In this paper we discuss how to overcome limitations of MZP fabrication by PLD by investigating the material systems W/Si, W/ZrO2, and Ta2O5/ZrO2. We give a detailed description on the optimization processes for the deposition of smooth multilayers with highly precise layer thicknesses on a rotating wire. Furthermore, we present our latest results regarding a Ta2O5/ZrO2 MZP, which has been proven already to be a system of high potential in the very first experiments as the efficiency reached 6.9% (at 18 keV).

Relaxor Ferroelectricity and Magnetoelectric Coupling in ZnO–Co Nanocomposite Thin Films: Beyond Multiferroic Composites

ZnO-Co nanocomposite thin films are synthesized by combination of pulsed laser deposition of ZnO and Co ion implantation. Both superparamagnetism and relaxor ferroelectricity as well as magnetoelectric coupling in the nanocomposites have been demonstrated. The unexpected relaxor ferroelectricity is believed to be the result of the local lattice distortion induced by the incorporation of the Co nanoparticles. Magnetoelectric coupling can be attributed to the interaction between the electric dipole moments and the magnetic moments, which are both induced by the incorporation of Co. The introduced ZnO-Co nanocomposite thin films are different from conventional strain-mediated multiferroic composites.

Deposition of nonpolar m-plane InGaN/GaN multiple quantum wells on LiGaO2(100) substrates

High-quality nonpolar m-plane InGaN/GaN multiple quantum wells (MQWs) have been deposited on LiGaO2(100) substrates by the combination of pulsed laser deposition (PLD) and molecular beam epitaxy (MBE) technologies. This work opens up a new prospect for achieving high-efficiency nonpolar m-plane GaN-based devices.

A new system for achieving high-quality nonpolar m-plane GaN-based light-emitting diode wafers

High-quality nonpolar m-plane GaN-based light-emitting diode (LED) wafers have been deposited on LiGaO2(100) substrates by a combination of pulsed laser deposition and molecular beam epitaxy technologies.

Development of laser deposited multilayer zone plate structures for soft X-ray radiation

As a novel approach, the combination of pulsed laser deposition and focused ion beam was applied to fabricate different types of multilayer zone plate structures for soft X-ray applications. For this purpose, high quality non-periodic ZrO 2/Ti multilayers were deposited by pulsed laser deposition on planar Si substrates and on rotating steel wires with layer thicknesses according to the Fresnel zone plate law. Linear focusing optics were fabricated by cutting slices out of the multilayers by focused ion beam and placing them directly over pinholes within Si 3N 4 substrates. Additionally, it was shown that laser deposition of depth-graded multilayers on a wire is also a promising way for building up multilayer zone plates with point focus. First experiments using a table-top X-ray source based on a laser-induced plasma show that the determined focal length and spatial resolution of the fabricated multilayer Laue lens corresponds to the designed optic.

Nanoporous MnO x thin-film electrodes synthesized by electrochemical lithiation/delithiation for supercapacitors

Nanoporous MnO x thin-film electrodes are synthesized using a combination of pulsed laser deposition (PLD) and electrochemical lithiation/delithiation methods. A dense Mn 3O 4 thin-film deposited by PLD can transform into a nanoporous MnO x thin-film after electrochemical lithiation/delithiation. A nanoporous MnO x thin-film electrode exhibits significantly improved supercapacitive performance compared with an as-deposited Mn 3O 4 thin-film electrode. A MnO x thin-film finally transforms into a MnO 2 thin-film through an electrochemical oxidation process during continuous cyclic voltammetry scanning.

Fabrication of multilayer Laue lenses by a combination of pulsed laser deposition and focused ion beam

X-ray diffractive techniques using Fresnel zone plate lenses of various forms are of great technical interest because of their ability to form images at very high spatial resolution, but the zone plates are unfortunately very hard to produce by lithography. Alternatively, multilayer Laue lenses (MLLs) and multilayer zone plates are used due to the higher and easily adjustable aspect ratio necessary for different wavelengths. In this paper, the fabrication of a MLL by a combination of pulsed laser deposition and focused ion beam machining is described. All steps of the production of a Ti/ZrO(2) microlens test structure with focal length of 220 microm (for a wavelength of 2.88 nm in the "water window" regime) are explained in detail. It is shown that this combination of two powerful techniques is very effective for the fabrication of MLL. All steps can be done in a very precise and controlled way without introducing damage to the grown multilayer structures.

Hydrogen storage characteristics of nanograined free-standing magnesium–nickel films

Free-standing magnesium–nickel (Mg–Ni) films with extensive nanoscale grain structures were fabricated using a combination of pulsed laser deposition and film delaminating processes. Hydrogen sorption and desorption properties of the films, free from the influence of substrates, were investigated. Oxidation of the material was reduced through the use of a sandwiched free-standing film structure in which the top and bottom layers consist of nanometer-thick Pd layers, which also acted as a catalyst to promote hydrogen uptake and release. Hydrogen storage characteristics were studied at three temperatures, 296, 232, and 180°C, where multiple sorption/desorption cycles were measured gravimetrically. An improvement in hydrogen storage capacity over the bulk Mg–Ni target material was found for the free-standing films. As shown from a Van’t Hoff plot, the thermodynamic stability of the nanograined films is similar to that of Mg2Ni. These results suggest that free-standing films, of which better control of material compositions and microstructures can be realized than is possible for conventional ball-milled powders, represent a useful materials platform for solid-state hydrogen storage research.

Pulsed laser deposition of hydroxyapatite thin films on Ti–6Al–4V: Effect of heat treatment on structure and properties

Hydroxyapatite (HA) is an attractive biomaterial that has been widely used as a coating for dental and orthopedic metal implants. In this work, HA coatings were deposited on Ti–6Al–4V substrates by laser ablation of HA targets with a KrF excimer laser. Deposition was performed at ambient temperature under different working pressures that varied from 10 −4 to 10 −1 torr of oxygen. The as-deposited films were amorphous. They were annealed at 290–310 °C in ambient air in order to restore the crystalline structure of HA. The coatings morphology, composition and structure were investigated by scanning electron microscopy, atomic force microscopy, energy-dispersive X-ray spectroscopy and X-ray diffraction techniques. Mechanical and adhesive properties were examined using nanoindentation and scratch tests, respectively. The stability of the HA coatings was tested under simulated physiological conditions. This study reveals that the combination of pulsed laser deposition and post-deposition annealing at 300 °C have the potential to produce pure, adherent, crystalline HA coatings, which show no dissolution in a simulated body fluid.

Epitaxial growth and surface metallic nature of LaNiO3 thin films

In situ epitaxial growth control of LaNiO3 (LNO) films at high oxygen pressure has been successfully achieved using a combination of pulsed laser deposition and high-pressure reflection high-energy electron diffraction (RHEED). RHEED oscillations, indicative of epitaxial layer-by-layer growth, were clearly observed during LNO deposition under optimal conditions. The film surfaces were composed of atomically flat terraces and steps. Detailed photoelectron spectroscopy analysis of LNO grown at the optimal oxygen pressure revealed that Ni ions assume a uniform Ni3+ high-valence state and that the resultant metallic properties are preserved even at the surface and in the interface region between LNO and the LaAlO3 substrate.

Metal-supported Solid Oxide Fuel Cell Operated at 400~600{degree sign}C

Metal-supported SOFCs potentially offer many advantages compared to conventional technology, such as low operating temperatures, reduced cost, and increased reliability. They are also a promising choice for applications that require quick start-up, good stability against thermal cycles and mechanical shock resistance such as Auxiliary Power Units (APU) for the automotive industry. The National Research Council of Canada's Institute for Fuel Cell Innovation (NRC-IFCI) has been working on the development of metal supported SOFCs since 2004. In this paper, a metal-supported SOFC with a samarium doped ceria (SDC)/scandia-stabilized zirconia (ScSZ) bilayer electrolyte was fabricated by a combination of pulsed laser deposition (PLD) and wet chemistry processing. The cell performance and aging characteristics were analyzed by AC impedance spectroscopy and current-voltage measurements during operation in the temperature range from 400oC to 600oC. The power generation characteristics at low temperatures of this metal- supported SOFC will be beneficial for quick start-up and is expected to alleviate the performance deterioration. These results at such an early stage of research is very promising for the future development of this technology.

Metal-supported solid oxide fuel cell operated at 400–600 °C

A metal-supported SOFC with a samarium doped ceria (SDC)/scandia-stabilized zirconia (ScSZ) bilayer electrolyte was fabricated by a combination of pulsed laser deposition (PLD) and wet ceramic processes. The cell performance and aging characteristics during operation were analyzed by both AC impedance spectroscopy and current-voltage measurements in the temperature range from 400 °C to 600 °C. The power generation characteristics of this metal-supported SOFC at low temperatures should allow for rapid start-up and help to reduce the performance deterioration seen in high temperature SOFCs due material oxidation and instability. In this paper, our early research results are presented.

Cover Picture: Formation of Metal Nano- and Micropatterns on Self-Assembled Monolayers by Pulsed Laser Deposition Through Nanostencils and Electroless Deposition (Adv. Funct. Mater. 10/2006)

The cover illustrates two-step fabrication of metal micro- and nanostructures on self-assembled monolayers (SAMs) by pulsed laser deposition and electroless deposition. Metal–SAM–metal junctions are a key component of molecular electronic devices. Pt was deposited in a micropattern by pulsed laser deposition through a stencil. XPS maps show how the Pt pattern is developed into a Cu pattern using electroless deposition as reported by Ravoo, Brugger, Reinhoudt, Blank, and co-workers on p. 1337. The Cu pattern can also be observed by optical microscopy (background). Patterns of noble-metal structures on top of self-assembled monolayers (SAMs) on Au and SiO2 substrates have been prepared following two approaches. The first approach consists of pulsed laser deposition (PLD) of Pt, Pd, Au, or Cu through nano- and microstencils. In the second approach, noble-metal cluster patterns deposited through nano- and microstencils are used as catalysts for selective electroless deposition (ELD) of Cu. Cu structures are grown on SAMs on both Au and SiO2 substrates and are subsequently analyzed using X-ray photoelectron spectroscopy element mapping, atomic force microscopy, and optical microscopy. The combination of PLD through stencils on SAMs followed by ELD is a new method for the creation of (sub)-micrometer-sized metal structures on top of SAMs. This method minimizes the gas-phase deposition step, which is often responsible for damage to, or electrical shorts through, the SAM.

Formation of Metal Nano- and Micropatterns on Self-Assembled Monolayers by Pulsed Laser Deposition Through Nanostencils and Electroless Deposition

Patterns of noble-metal structures on top of self-assembled monolayers (SAMs) on Au and SiO2 substrates have been prepared following two approaches. The first approach consists of pulsed laser deposition (PLD) of Pt, Pd, Au, or Cu through nano- and microstencils. In the second approach, noble-metal cluster patterns deposited through nano- and microstencils are used as catalysts for selective electroless deposition (ELD) of Cu. Cu structures are grown on SAMs on both Au and SiO2 substrates and are subsequently analyzed using X-ray photoelectron spectroscopy element mapping, atomic force microscopy, and optical microscopy. The combination of PLD through stencils on SAMs followed by ELD is a new method for the creation of (sub)-micrometer-sized metal structures on top of SAMs. This method minimizes the gas-phase deposition step, which is often responsible for damage to, or electrical shorts through, the SAM.

Fabrication of hollow spheres composed of nanosized ZSM-5 crystals via laser ablation

Zeolite spheres with a core-shell structure were fabricated by a combination of pulsed laser deposition (PLD) and vapor-phase crystallization. Spherical mesoporous DAM-1 or SBA-15 was used as the silicon source and substrate. After vapor phase treatment hollow spherical shells consisting of nanosized ZSM-5 crystals were formed. In addition, the size of the ZSM-5 crystals in the shell ranges from 5 to 500 nm which can be adjusted by changing the crystallization time (3–5 days) or the PLD coating thickness. The deposition rate was 13 nm/min at 120 mJ and 6.5 nm/min at 70 mJ. The ZSM-5 core–shell structure was characterized by XRD, IR, SEM and N 2 absorption. The dissolution of the mesoporous silica substrate and transport of the resulting silica species to the growing ZSM-5 film during vapor-phase crystallization is discussed in terms of a solution mediated transport mechanism.

Properties of MgB/sub 2/ films with very high transport critical current densities

Magnesium diboride, MgB/sub 2/, thin films are fabricated through two different kinds of process. One is an in-situ process by using electron beam deposition and the other is an ex-situ process by using the combination of pulsed laser deposition and heat treatment. The critical current density, J/sub c/, is investigated as a function of external magnetic field in the range of 0-7 T and/or temperatures ranging from 4.2 K to the critical temperature by using dc 4-probe transport method. The in-situ processed film shows very high J/sub c/, e.g., 7.1/spl times/10/sup 6/, 1.2/spl times/10/sup 6/, and 1.4/spl times/10/sup 5/ A/cm/sup 2/ in 0, 4, and 7 T (perpendicular fields), respectively. Angular dependence of J/sub c/ is much different between the two kinds of films. J/sub c/-angle (magnetic field) curves of the in-situ processed film show two peaks; one is around the field perpendicular to the film surface and the other is around the parallel field. On the contrary, the curves of the ex-situ processed film have only one peak around the parallel field. Microstructure analyses show that the in-situ film has columnar grains aligned perpendicular to the film surface and that the ex-situ one has granular grains with random orientations. These results indicate that the grain boundaries between columnar grains act as effective pinning centers and enhance J/sub c/ in the perpendicular fields.

Selective epitaxial growth of submicron complex oxide structures by amorphous SrTiO3

A chemical-free technique for fabricating submicron complex oxide structures has been developed based on selective epitaxial growth. The crystallinity and hence the conductivity of the complex oxide is inhibited by amorphous SrTiO3 (STO). Using a combination of pulsed laser deposition and electron-beam lithography, amorphous STO barriers are first deposited on a single-crystal substrate. A thin film is then deposited on the patterned substrate with the amorphous STO barriers acting to electrically and physically isolate different regions of the film. Since no chemical or physical etchants come in contact with the deposited film, its integrity and stability are preserved. This technique has produced submicron YBa2Cu3O7−δ and La2∕3Ca1∕3MnO3 structures.

Combinatorial approach to material synthesis and screening of hydrogen storage alloys

The development of a practical fuel cell powered automobile is now the focus of intense competition. Full exploitation of the advantages of a fuel cell will require the development of a practical hydrogen storage medium. We introduce the use of thin-film combinatorial methods to synthesize hydrogen storage alloys and demonstrate the use of spatially resolved infrared imaging as a high throughput hydrogen storage candidate screening technique. Using a combination of pulsed laser deposition and magnetron sputtering, multi-compositional samples were produced for hydrogen sorption studies. Analysis is presented of a sample that consists of 16 separate Mg–Ni–Fe ternary pads and 32 Mg–Ni or Mg–Fe binary pads. Hydrogen sorption related emissivity changes observed indicate a substantial decrease in hydriding temperatures, which sensitively depend on composition.

Study of nanocrystalline diamond film growth in rf hybrid laser deposition systems in O2, H2 and H2+Ar ambients

Pulsed laser deposition (PLD) and hybrid pulsed laser deposition (HPLD) systems were used for nanocrystalline diamond (NCD) film growth on Si(100) and sapphire(0001) substrates. The PLD system was based on a KrF excimer laser (λ=248 nm,20 ns), which ablated a graphite target in pure oxygen or hydrogen ambient. The HPLD system was based on a combination of PLD and additional capacitively coupled radio-frequency discharges (13.56 MHz) in argon–hydrogen ambient. Radio-frequency power was applied to two plane parallel electrodes or directly to the substrate holder. The working atmosphere pressure was varied from 1 Pa to 220 Pa and the substrate temperature was varied from 20 °C to 660 °C. X-ray diffraction analysis, Raman spectroscopy and a profilometer were used to study the deposited film properties. A band around 1180 cm-1, which can be attributed to NCD, occurred in the Raman spectra. A characteristic diamond peak at 1332 cm-1 was not observed. Films prepared by HPLD showed better compositional homogeneity (from Raman analysis) than films created by PLD.

Fabrication of long-Y123 coated conductors by combination of IBAD and PLD

Continuous deposition of Gd 2Zr 2O 7 films were carried out on 10 mm width Hastelloy tapes by ion-beam-assisted deposition (IBAD). They were uniformly deposited with the in-plane mosaic spread (Δ φ) of 10–14° in the 50 m long and of 16–18° in the 60 m long, at a production rate of 0.5–1.0 m/h. The 6 cm sample with the I c value of 141 A and the J c value of 1.25 MA/cm 2 were obtained by 6 repeated depositions using pulsed laser deposition (PLD). Continuous deposition of Y-123 films were performed by PLD on long IBAD template tapes at a tape speed of 4.0 m/h. The I c value of 40 A and the J c value of 0.8 MA/cm 2 were obtained at the length of 30 m. Furthermore, the 46 m YBCO coated tape with the I c value of 74 A and the n value of 32 was formed uniformly.