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A simple 1-D model has been developed for the velocity of flyers in vacuum generated by laser-induced forward transfer (LIFT) with a dynamic release layer (DRL). It is an extension of a laser ablation model for metal flyer plates based on the Gurney model of explosive output for driving metal fragments. The model has been extended to the bilayer system of a DRL overlain with a transfer layer. The suitability of the model has been checked with experimental velocity data obtained from shadowgraphy. The experiments used bilayer samples of triazene polymer/aluminium, ablated from the backside through the substrate at reduced pressure (5 × 10−2 mbar). The results suggest that the Gurney energy approach provides the basis of a viable, physically relevant, algebraic model for LIFT, but other loss mechanisms still need be incorporated, particularly thermal loss into the fused silica substrate.

Pulsed laser deposition is often used to grow multi-elemental thin films from stoichiometric targets. The growth process is influenced by a wide variety of parameters like the target composition, background gases, laser wavelength, laser fluence, or spot size. The changes these parameters induce in the film growth also affect the plasma plume and species formed during laser ablation. For oxide growth O2, and sometimes N2O, is utilized as background gas to achieve the required oxygen composition for the as-grown film. Mass spectrometry combined with time- and space resolved emission spectroscopy is used to investigate the behavior and evolution of plasma species in the plasma plume during the ablation process of LuMnO3 dependent on the background gas.

Patterned deposition of polymer light-emitting diode (PLED) pixels is a challenge for electronic display applications. PLEDs have additional problems requiring solvent orthogonality of different materials in adjacent layers. We present the fabrication of a PLED pixel by the sequential deposition of two different layers with laser-induced forward transfer (LIFT), a "dry" deposition technique. This novel use of LIFT has been compared to "normal" LIFT, where all the layers are transferred in a single step, and a conventional PLED fabrication process. For the sequential LIFT, a 50-nm film of an alcohol-soluble polyfluorene (PFN) is transferred onto a receiver with a transparent anode, before an aluminum cathode is transferred on top. Both steps use a triazene polymer dynamic release layer and are performed in a medium vacuum (1 mbar) across a 15 μm gap. The rough morphologies of the single-layer PFN pixels and the PLED device characteristics have been investigated and compared to both bilayer Al/PFN pixels fabricated by normal LIFT and conventionally fabricated devices. The functionality of the sequential LIFT pixels (0.003 cd/A, up to 200 mA/cm(2), at 30-40 V) demonstrates the suitability of LIFT for sequential patterned printing of different thin-film layers.

We report on low energy muon measurements performed on 100 nm and 28 nm thin epitaxial, highly strained and twin free TbMnO3 films grown on (110) YAlO3 substrates by pulsed laser deposition (λ = 248 nm, ν = 2 Hz, T S = 760°C). These investigations were done at the LEM beamline at the PSI, Switzerland which allowed for depthdependent analysis of the muon spin relaxation rate as a function of temperature. A clear decrease of the relaxation rates could be observed in regions near the substrate/thin film interface compared to measurements at the surface or in the middle of the films. This behavior could be attributed to a straininduced change of the Tb spin dynamics. Furthermore, it could be shown that the films are fully magnetic below a temperature of 40 – 50 K, which agrees well with susceptibility measurements performed on these films as well as with the bulk literature value of TN,Mn = 41 K.

LaTiO 3− x N x films with high nitrogen contents ( x ≈ 0.4–0.8) have been grown on (0 0 1)-oriented MgO and LaAlO 3 substrates by pulsed reactive crossed-beam laser ablation from a La 2 Ti 2 O 7 target in a one-step process. These films have a perovskite-type structure, similar to bulk polycrystalline LaTiO 2 N. The nitrogen content in the films can be changed by selecting the nitriding source, i.e. NH 3 or N 2 gas pulse, and by varying the substrate temperature. Films deposited on MgO show a preferential (0 0 1) and (1 1 2) orientation, whereas films on LaAlO 3 are predominantly (0 0 1) oriented. N(2 p ) orbitals contribute to the top of the valence band, leading to a considerable decrease in the band gap energy from ∼4.0 eV for the parent LaTiO 3.5 to ∼2.4–2.9 eV for LaTiO 3− x N x ( x ≈ 0.4–0.8) films. This results in a strong visible light absorption at wavelengths below ∼500 nm. The band gap energies in LaTiO 3− x N x films decrease with increasing nitrogen content. The values of the band gap energies for LaTiO 3− x N x as a function of the N content agree well with other titanate-based perovskite-type oxynitrides, which confirms the proposed band gap model.

Recent developments in European supercomputing are reviewed covering both the latest hardware trends and the increasing difficulties faced by scientists in utilising these machines to perform large-scale numerical simulations. These challenges are reflected in the large number of international initiatives which have come into being over the last few years, founded in anticipation of exascale hardware which is foreseen within the next decade. The role of a key institution in supercomputing within these programmes is described using the example of the Julich Supercomputing Centre (JSC), and progress in setting up its own community-oriented support units for scientific computing – Simulation Laboratories – is reported on. Finally, an assessment is made of some common grand challenges and their suitability for scaling to exaflop-scale computation.

Knowledge about the crystallization and grain growth characteristics of metal oxide thin films is essential for effective microstructural engineering by thermal post-annealing and the integration to Si-based miniaturized electroceramic devices. Finite size and interface effects may cause fundamentally different behavior compared to three dimensional macroscopic systems. This work presents a comprehensive investigation of the crystallization kinetics and microstructural evolution upon thermal post-annealing of amorphous 200 nm and 1.2 μm thin films of 8 mol% yttria-stabilized zirconia grown by pulsed laser deposition (PLD) using ex- and in-situ X-ray diffraction, Raman spectroscopy, and electron microscopy techniques. The layers exhibit a remarkably low crystallization temperature of 200–250 °C while exposure to energetic electrons induces the formation of randomly dispersed ~ 20 nm sized crystallites already at ambient temperature. The isothermal amorphous to crystalline phase transformation kinetics can be described quantitatively by the Johnson–Mehl–Avrami–Kolmogorov model. They reveal characteristics of a three dimensional growth under cation bulk diffusion control with heterogeneous nucleation that changes from continuous to instantaneous initial seeding at temperatures above 300 °C. Large (> 100 nm) equiaxed grains are formed rapidly without a stabilization of transient nanocrystals during the thermally induced phase transformation. A stagnation of normal grain growth resulting in a logarithmic normal size distribution is observed once the average grain dimensions approach the film thickness. The results on the crystallization and grain growth of the PLD-grown YSZ films are evaluated with regards to the fabrication of YSZ solid electrolyte membranes for Si-supported micro solid oxide fuel cells and gas sensors.

Ultrathin crystalline films of 10 mol% gadolinia-doped ceria (CGO10) are grown on MgO (100) substrates by pulsed laser deposition at a moderate temperature of 400°C. As-deposited CGO10 layers of approximately 4 nm, 14 nm, and 22 nm thickness consist of fine grains with dimensions ≤∼11 nm. The films show high density within the thickness probed in the X-ray reflectivity experiments. Thermally activated grain growth, density decrease, and film surface roughening, which may result in the formation of incoherent CGO10 islands by dewetting below a critical film thickness, are observed upon heat treatment at 400°C and 800°C. The effect of the grain coarsening on the electrical characteristics of the layers is investigated and discussed in the context of a variation of the number density of grain boundaries. The results are evaluated with regard to the use of ultrathin CGO10 films as seeding templates for the moderate temperature growth of thick solid electrolyte films with improved oxygen transport properties.

Sub-micron thick yttria-stabilized zirconia (YSZ) layers (t = 400–700 nm) containing 3 (3YSZ) or 8 mol.% (8YSZ) Y2O3 with microstructures ranging from isotropic amorphous to columnar polycrystalline and a variable porosity can be grown by pulsed laser deposition (PLD) varying the substrate temperature and oxygen background pressure. The dependence of the mechanical and optical properties on the film microstructure and chemical composition was investigated by nanoindentation experiments and transmission spectrophotometry. Dense amorphous YSZ layers exhibit a higher optical transmissivity, 0.2 eV lower band gap energy (5.5 vs. 5.7 eV), and up to 25% lower hardness (11.9 vs. 16.0 GPa) and reduced elastic moduli (231 vs. 278 GPa) compared with crystalline films, irrespective of the dopant level. High refractive indices, n600 nm, in the range 2.18–2.23, i.e. close to single crystal reference data, are obtained for the low pressure PLD regime. Within these boundaries the index decreases with increasing Y2O3 content and is consistently slightly smaller for amorphous layers compared with crystalline films of the same composition, due to a lower atomic packing density. The gradual decrease in the refractive index for YSZ layers grown at background pressures above 1.0 Pa marks the development of pores in the form of inter-columnar voids and can be used for sensitive quantification of the film porosity. The lattice order affects the fracture behaviour, as amorphous coatings show plastic deformation mediated by shear bands, while the crystalline layers yield hoop and surface cracks upon indentation. The crystalline 3YSZ films exhibit an enhanced fracture toughness compared with 8YSZ, which is related to the stress-induced transformation to the monoclinic phase in partially stabilized zirconia.

A simple and effective method to functionalize glass surfaces that enable polymer micropatterning and subsequent spatially controlled adhesion of cells is reported in this paper. The method involves the application of laser induced forward transfer (LIFT) to achieve polymer patterning in a single step onto cell repellent substrates (i.e. polyethyleneglycol (PEG)). This approach was used to produce micron-size polyethyleneimine (PEI)-patterns alternating with cell-repellent areas. The focus of this work is the ability of SH-SY5Y human neuroblastoma cells to orient, migrate, and produce organized cellular arrangements on laser generated PEI patterns.

The shockwave propagation and aerosol formation during femtosecond laser ablation (fs-LA) of dielectric materials (Li2B4O7, Y:ZrO2) in ambient air were monitored using shadowgraphy and light scattering. Three independent shockwave fronts were observed originating from (i) the instantaneous compression of ambient gas during the initial stage of fs-LA, (ii) a secondary compression caused by material ejection, and (iii) an air breakdown well above the target surface. In addition, particle size distributions were found to be multimodal implying the co-existence of condensational growth and supplementary particle production pathways such as phase explosion or critical point phase separation (CPPS). As a consequence, fs-LA of Li2B4O7 resulted in the formation of primary aggregates reaching diameters of > 10 μm. In contrast, aggregates formed during fs-LA of Y:ZrO2 covered a size range < 1 μm. Our data, furthermore, indicate the existence of a breakdown channel in the ambient atmosphere being capable to carry plasmatic, i.e. non-condensed matter beyond the primary shockwave barrier which may occasionally causes a spatial separation of material released. Assuming the Taylor-Sedov model of explosion to be valid the over-all energy dissipated in acoustic transients was found to exceed values of 50%.

Electrical characterization of 10 mol% gadolinia doped ceria (CGO10) films of different thicknesses prepared on MgO(100) substrates by pulsed laser deposition is presented. Dense, polycrystalline and textured films characterized by fine grains (grain sizes < 18 nm and < 64 nm for a 20-nm and a 435-nm film, respectively) are obtained in the deposition process. Grain growth is observed under thermal cycling between 300 and 800°C, as indicated by X-ray-based grain-size analysis. However, the conductivity is insensitive to this microstructural evolution but is found to be dependent on the sample thickness. The conductivity of the nanocrystalline films is lower (7.0×10−4 S/cm for the 20-nm film and 3.6×10−3 S/cm for the 435-nm film, both at 500°C) than that of microcrystalline, bulk samples ( $6\times 10^{-3}$ S/cm at 500°C). The activation energy for the conduction is found to be 0.83 eV for the bulk material, while values of 1.06 and 0.80 eV are obtained for the 20-nm film and the 435-nm film, respectively. The study shows that the ionic conductivity prevails in a broad range of oxygen partial pressures, for example down to about 10 −26 atm at 500°C.

ISSN:2196-7350

This paper presents polymer pixel printing for applications in chemoselective sensors where nanosecond laser direct transfer methods, with a triazene polymer (TP) acting as a Dynamic Release Layer (DRL), are used. A sys- tematic study of laser fluence, donor film morphology and both single- and multiple-pixel deposition were optimized with the final goal to obtain continuous pixels of sensi- tive polymers, polyethylenimine (PEI) and polyisobutylene (PIB), on SAW surfaces. Morphology characterization after the laser transfer has been performed by Optical Microscopy and Scanning Electron Microscopy (SEM). The responses of the coated transducers were measured after deposition with different laser fluences and it was found that a fluence under 625 mJ/cm 2 was required in order to prevent damage of the interdigital transducers (IDT) of the sensor devices. The sen- sitivity of the polymer coated devices to acetone concentra- tions gives an indication that LIFT can be used for printing sensitive polymer pixels onto transducer devices.

This paper presents a comparative study of polymer pixel on sensors obtained by Laser Induced Forward Transfer (LIFT) assisted by a triazene polymer as Dynamic Release Layer (DRL). Polyisobutylene (PIB) was selected as model for chemoselective polymers which could be used as hydrogen-bond acidic polymer for vapor sensors. PIB films deposited on fused silica, respectively, on triazene polymer coated fused silica substrates were used as targets. Both targets were prepared by Matrix Assisted Pulsed Laser Evaporation (MAPLE). The parameters related to a regular, well-defined transfer were analyzed and compared for the substrates with and without the DRL. The morphological characterization of the transferred PIB was performed by Atomic Force Microscopy (AFM), Optical Microscopy, and Scanning Electron Microscopy (SEM). It was found that a minimal thickness of the dynamic release layer, i.e. 100 nm is required to protect the sensitive PIB polymer in a clean laser transfer process.

Laser-induced forward transfer (LIFT) using a triazene polymer as dynamic release layer was used for the transfer of polyethyleneimine (PEI) pixels for microsensors applications. A XeCl laser was used to transfer the PEI pixels from a thin film coated onto the triazene layer. The PEI films were either in direct contact with the receiver or a gap was maintained between the donor film and the receiver. An optimization of the process was carried out by changing the laser fluences, the ratio between the thickness of the PEI and of the triazene layer, and the transfer distance. Welldefined, regular PEI pixels were obtained on the receiver. The morphology of the patterns was characterized using optical microscopy and scanning electron microscopy (SEM). The transfer onto surface acoustic wave (SAW) devices suggests that LIFT is a promising technique for the fabrication of microsensors with polymers as active layer.

The patterned deposition of thin films is essential for many technological applications. One promising material deposition technique is laser-induced forward transfer (LIFT), where a thin layer coated on a transparent substrate is ablated by a laser pulse passing through the substrate. The ablated material is collected on a nearby receiver substrate in a pattern defined by the laser. The technique can be applied to heat and light sensitive materials, provided that they are not directly irradiated by the laser pulse. For this application, a sacrificial layer is introduced between the substrate and the transfer layer so that the laser energy is converted into mechanical propulsion while protecting the sensitive layer from radiation. In this work, the application of a triazene polymer as a sacrificial layer for LIFT has been studied with the final goal of transferring organic light-emitting diode (OLED) pixels. Donor films made of a stack of triazene polymer, metal, and optionally an electroluminescent polym...

The ns-laser ablation characteristics of tetragonal 3YSZ versus cubic 8YSZ have been investigated to minimize a transfer of particulates in the pulsed laser deposition process. 3YSZ is significantly less prone to the exfoliation of μm-sized fragments than 8YSZ due to its enhanced fracture toughness, which allows the deposition of particulate-free films in a fluence range of 1.2–1.5 J/cm 2 . The influence of the PLD process parameters on the film microstructure and stoichiometry have been investigated with respect to the growth of dense 3YSZ layers with adequate adhesion to the c -cut sapphire single crystals. Dense 3YSZ films are obtained below a threshold pressure of ∼0.025 mbar. At 600 °C polycrystalline layers with a preferential (1 0 1) and (0 0 1) orientation and a columnar microstructure are formed while deposition at room temperature yields uniform amorphous layers. Strongly oxygen deficient films of the metastable t ′′ phase are obtained at a low background pressure of 10 −3 mbar. The meta phase films exhibit a low activation energy of 0.77 ± 0.02 eV and an enhanced d.c. electrical conductivity, e.g. 9 × 10 −5 S/cm at 400 °C, comparable or even higher than for 8YSZ films and bulk at temperatures up to 500 °C.

Computational simulations and thus scientific computing is the third pillar alongside theory and experiment in todays science. The term e-science evolved as a new research field that focuses on collaboration in key areas of science using next generation computing infrastructures (i.e. co-called e-science infrastructures) to extend the potential of scientific computing. During the past years, significant international and broader interdisciplinary research is increasingly carried out by global collaborations that often share a single e-science infrastructure. More recently, increasing complexity of e-science applications that embrace multiple physical models (i.e. multi-physics) and consider a larger range of scales (i.e. multi-scale) is creating a steadily growing demand for world-wide interoperable infrastructures that allow for new innovative types of e-science by jointly using different kinds of e-science infrastructures. But interoperable infrastructures are still not seamlessly provided today and we argue that this is due to the absence of a realistically implementable infrastructure reference model. Therefore, the fundamental goal of this paper is to provide insights into our proposed infrastructure reference model that represents a trimmed down version of ogsa in terms of functionality and complexity, while on the other hand being more specific and thus easier to implement. The proposed reference model is underpinned with experiences gained from e-science applications that achieve research advances by using interoperable e-science infrastructures.

Over the last 20 years, the open-source community has provided more and more software on which the world’s high-performance computing systems depend for performance and productivity. The community has invested millions of dollars and years of effort to build key components. Although the investments in these separate software elements have been tremendously valuable, a great deal of productivity has also been lost because of the lack of planning, coordination, and key integration of technologies necessary to make them work together smoothly and efficiently, both within individual petascale systems and between different systems. A repository gatekeeper and an email discussion list can coordinate open-source development within a single project, but there is no global mechanism working across the community to identify critical holes in the overall software environment, spot opportunities for beneficial integration, or specify requirements for more careful coordination. It seems clear that this completely uncoordinated development model will not provide the software needed to support the unprecedented parallelism required for peta/exascale computation on millions of cores, or the flexibility required to exploit new hardware models and features, such as transactional memory, speculative execution, and GPUs. We believe the community must work together to prepare for the challenges of exascale computing, ultimately combing their efforts in a coordinated International Exascale Software Project.

Laser-induced forward transfer is a powerful technique for the patterned deposition of thin layers. Sensitive materials can be transferred using an intermediate sacrificial layer, which protects the material from direct laser irradiation. Among various materials, triazene polymers are very promising sacrificial layers, and therefore, their ablation behavior has a particular importance for the transfer. The ablation behavior of a single sacrificial layer of a specific triazene polymer was investigated using time-resolved shadowgraphy to understand and optimize the deposition process. We analyzed the evolution of the shock wave generated by the decomposition of the triazene polymer to estimate the thermodynamics of the process. The energy balance shows that a large part of the energy is released into the shock wave but that thermal and mechanical losses predominate. On the other hand, the kinetic energy of the flyer corresponds only to a few percent of the total energy. We also observed a difference in the ...

Nitrogen was successfully incorporated into the surface of a SrTiO3(1 1 1) single crystal by exposing it to a microwave-induced glow discharge plasma of ammonia (NH3). The layers generated by the flux of active species in the plasma varied in composition and structure depending on the treatment time, t. Substitution of oxygen by nitrogen along with the reduction of the crystal surface was observed by X-ray photoelectron spectroscopy. The 0–150 nm thick top layer showed Sr and O deficiencies and was identified as a mixture of nanocrystalline cubic rocksalt-type TiN, perovskite-type SrTiO3−δ–SrTiO3−xNy and amorphous phases. Deeper nitrogen diffusion into the crystal yielded perovskite-type nitrogen-doped strontium titanate. The diffusion of N into the perovskite structure was characterized by the diffusion coefficient D = (2.1 ± 0.4) × 10−15 cm2 s−1. The growth of the N-containing perovskite layers showed the time dependency L [ μ m ] = 6.3 t [ min ] . Examination of the electronic properties revealed metallic-like electrical conductivity, superconductivity with Tc of up to 5 K, and negative Seebeck coefficients of up to S = −465 μV K−1 at room temperature.

Nitrogen-substituted cubic perovskite-type SrTiO 3 thin films were deposited in a one-step process using pulsed reactive crossed beam laser ablation (PRCLA) and RF-plasma assisted pulsed laser deposition (RF-PLD). Both techniques yield preferentially oriented films on SrTiO 3 (001), LaAlO 3 (001) and MgO(00 1) substrates with the unit cell parameters within 0.390(5) < a < 0.394(9) nm. The nitrogen content is higher in films deposited by PRCLA (0.84-2.40 at.%) as compared to films deposited by RF-PLD with nitrogen plasma (0.10-0.66 at.%). PRCLA with an ammonia gas pulse leads to a higher nitrogen content compared to the films grown with a nitrogen gas pulse, while films deposited by RF-PLD with ammonia plasma reveal only minor nitrogen contents (

The ability to control cell placement and to produce idealized cellular constructs is essential for understanding and controlling intercellular processes and ultimately for producing engineered tissue replacements. We have utilized a novel intra-cavity variable aperture excimer laser operated at 193 nm to reproducibly direct write mammalian cells with micrometer resolution to form a combinatorial array of idealized cellular constructs. We deposited patterns of human dermal fibroblasts, mouse myoblasts, rat neural stem cells, human breast cancer cells, and bovine pulmonary artery endothelial cells to study aspects of collagen network formation, breast cancer progression, and neural stem cell proliferation, respectively. Mammalian cells were deposited by matrix assisted pulsed laser evaporation direct write from ribbons comprised of a UV transparent quartz coated with either a thin layer of extracellular matrix or triazene as a dynamic release layer using CAD/CAM control. We demonstrate that through optical imaging and incorporation of a machine vision algorithm, specific cells on the ribbon can be laser deposited in spatial coherence with respect to geometrical arrays and existing cells on the receiving substrate. Having the ability to direct write cells into idealized cellular constructs can help to answer many biomedical questions and advance tissue engineering and cancer research.

Microfuel cells are a possible replacement for batteries as energy sources in portable devices. At PSI a micropolymer electrolyte fuel cell was developed, whose flow fields consist of micro-structured glassy carbon plates. Micro-structuring of glassy carbon is carried out in a multi-step process. A sputtered aluminum mask is selectively removed by single pulse laser ablation from glassy carbon thereby defining micro-channels subsequently etched by reactive ion etching. A pulsed XeCl excimer laser (308 nm) is used for the single pulse patterning of a metal mask on the glassy carbon. The influence of the excimer laser typical pulse to pulse energy fluctuations on the micro-structuring process must be known to minimize defects during RIE etching of the micro-channels. To obtain a better understanding of the processes occurring during ablation, ns-shadowgraphy was performed. The formation of a shockwave was observed, followed by a similar but much slower perturbation, and the subsequent release of fragments. The calculated velocities can be correlated with the energy release during ablation. The post-ablation examination of the samples by profilometry, optical microscopy, SEM and EDX is used to measure the amount of removed material, the quality of the aluminum mask edges and aluminum residues on the glassy carbon surface. Such criteria allow us to classify the laser irradiation as a function of laser fluence: no ablation, partial ablation, complete ablation, and over-ablation.

Thin films of a photodecomposible triazene polymer are used as sacrificial layer for the micro-deposition of sensitive materials by laser-induced forward transfer. To understand the ablation process of this sacrificial layer, the ultraviolet laser ablation of triazene films was investigated by time-resolved shadowgraphy. Irradiation from the film side shows a complete decomposition into gaseous fragments, while ablation through the substrate causes ejection of a solid flyer of polymer. The occurence of the flyer depends on the film thickness as well as on the applied fluence, and a compact flyer is obtaind when these two parameters are optimized.

Tunneling between different topological sectors with dynamical chiral fermions is difficult because of a poor mass scaling of the pseudo-fermion estimate of the determinant. For small fermion masses it is virtually impossible using standard methods. However, by projecting out the small Wilson eigenvectors from the overlap operator, and treating the correction determinant exactly, we can significantly increase the rate of topological sector tunneling and reduce substantially the auto-correlation time. We present and compare a number of different approaches, and advocate a method which allows topological tunneling even at low mass with little addition to the computational cost., Comment: 17 pages; v2 as accepted in computer Physics Communications

The extreme computational costs of calculating the sign of the Wilson matrix within the overlap operator have so far prevented four dimensional dynamical overlap simulations on realistic lattice sizes, because the computational power required to invert the overlap operator, the time consuming part of the Hybrid Monte Carlo algorithm, is too high. In this series of papers we introduced the optimal approximation of the sign function and have been developing preconditioning and relaxation techniques which reduce the time needed for the inversion of the overlap operator by over a factor of four, bringing the simulation of dynamical overlap fermions on medium-size lattices within the range of Teraflop-computers. In this paper we adapt the HMC algorithm to overlap fermions. We approximate the matrix sign function using the Zolotarev rational approximation, treating the smallest eigenvalues of the Wilson operator exactly within the fermionic force. We then derive the fermionic force for the overlap operator, elaborating on the problem of Dirac delta-function terms from zero crossings of eigenvalues of the Wilson operator. The crossing scheme proposed shows energy violations which are better than O($\Delta\tau^2$) and thus are comparable with the violations of the standard leapfrog algorithm over the course of a trajectory. We explicitly prove that our algorithm satisfies reversibility and area conservation. Finally, we test our algorithm on small $4^4$, $6^4$, and $8^4$ lattices at large masses., Comment: v2 60 pages; substantial changes to all parts of the article; v3 minor revsions

Detection efficiencies of laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), defined as the ratio of ions reaching the detector and atoms released by LA were measured. For this purpose, LA of silicate glasses, zircon, and pure silicon was performed using nanosecond (ns) as well as femtosecond (fs) LA. For instance, ns-LA of silicate glass using helium as in-cell carrier gas resulted in detection efficiencies between approximately 1E-7 for low and 3E-5 for high mass range elements which were, in addition, almost independent on the laser wavelength and pulse duration chosen. In contrast, the application of argon as carrier gas was found to suppress the detection efficiencies systematically by a factor of up to 5 mainly due to a less efficient aerosol-to-ion conversion and ion transmission inside the ICP-MS.

Laser plasma thrusters are a new kind of propulsion system for small satellites, and work with the thrust created by the laser ablation of a target. Liquid polymer solutions are very promising fuels for such systems, provided that no splashing of the target occurs, because ejection of droplets strongly decreases the performances of the system. We have investigated the nanosecond infrared laser ablation of glycidyl azide polymer solutions containing carbon nanoparticles as absorber. Shadowgraphy imaging revealed two cases, namely splashing regime and solid-like behavior. The transition between both regimes depends on the viscosity of the solution and on the laser fluence, and is explained by the recoil force acting on the target. Appropriate conditions to avoid splashing were identified, showing that this liquid polymer solution is a suitable fuel for laser plasma thrusters.

The mass distributions of the species generated by laser ablation from a La0.6Ca0.4MnO3 target using laser irradiation wavelengths of 193nm, 266nm and 308nm have been investigated with and without a synchronized gas pulse of N2O. The kinetic energies of the species are measured using an electrostatic deflection energy analyzer, while the mass distributions of the species were analyzed with a quadrupole mass filter. In vacuum (pressure 10−7mbar), the ablation plume consists of metal atoms and ions such as La, Ca, Mn, O, LaO, as well as multiatomic species, e.g. LaMnO+. The LaO+ diatomic species are by far the most intense diatomic species in the plume, while CaO and MnO are only detected in small amounts. The interaction of a reactive N2O gas pulse with the ablation plume leads to an increase in plume reactivity, which is desired when thin manganite films are grown, in order to incorporate the necessary amount of oxygen into the film. The N2O gas pulse appears to have a significant influence on the oxidation of the Mn species in the plume, and on the creation of negative ions, such as LaO−,O− and O 2 −

Thin films of a tailor-made photodecomposible aryltriazene polymer were applied in a modified laser-induced forward transfer (LIFT) process as sacrificial release layers. The photopolymer film acts as an intermediate energy-absorbing dynamic release layer (DRL) that decomposes efficiently into small volatile fragments upon UV laser irradiation. A fast-expanding pressure jet is generated which is used to propel an overlying transfer material from the source target onto a receiver. This DRL-assisted laser direct-write process allows the precise deposition of intact material pixels with micrometer resolution and by single laser pulses. Triazene-based photopolymer DRL donor systems were studied to derive optimum conditions for film thickness and laser fluences necessary for a defined transfer process at the emission wavelength of a XeCl excimer laser (308 nm). Photoablation, surface detachment, delamination and transfer behavior of aryltriazene polymer films with a thickness from 25 nm to ∼400 nm were investigated in order to improve the process control parameters for the fabrication of functional thin-film devices of microdeposited heat- and UV-sensitive materials.

Two new triazene monomers, such as (1-( para methoxy-phenyl)-3-(2 acryloyloxyethyl)-3-methyl triazene-1, M 1 ) and (1-( para chloro-phenyl)-3-(2 acryloyloxyethyl)-3-methyl triazene-1, M 2 ) were synthesized and further employed as reaction partners with methyl methacrylate (MMA) in order to investigate the substituent effect of the triazene moiety on the polymeric properties. The synthesized monomers and polymers (PA1, molar fraction of M 1 = 0.16; PA2, molar fraction of M 2 = 0.11) were characterized by analytical and spectroscopic methods, while the surface morphology of polymers was visualized by atomic force microscopy (AFM) and optical microscopy. The photosensitivity of these copolymers was evaluated upon UV exposure, in solution and in film state, following the decreasing value of the π–π * absorption band corresponding to the triazene group centered at 290 nm and 320 nm. For both copolymers, the kinetic data indicated a first-order photoprocess, as evidenced from the determined constant rate in film state (PA1, k = 2.3 × 10 −3 s −1 ; PA2, k = 2.7 × 10 −4 s −1 ). Moreover, the ablation characteristics achieved at low fluence for an irradiation wavelength of 308 nm, quality structuring with no any debris and the absence of carbonization of the irradiated areas suggest that such photolabile polyacrylates could offer new possibilities in printing techniques and nanostructures on surfaces. In addition, the triazene functions introduced as side groups may be used for the tailoring of special polymeric architectures.

Epitaxial thin films of LaCo1� xNixO3 were deposited on MgO (100) substrates by pulsed reactive crossed-beam laser ablation (PRCLA). The electrical transport and thermopower of the epitaxial La(Co,Ni)O3 thin films were measured in a broad temperature range and their thermoelectric activity was compared with bulk samples. The measured films show positive Seebeck coefficient values indicative of p-type conduction. The thin films display a better thermoelectric performance at high temperatures compared to the polycrystalline samples. 2008 Elsevier Masson SAS. All rights reserved.

Geothermal and solar heat can be directly converted into electricity by using thermoelectric generators. Perovskite-type metal oxides are potential materials to improve the efficiency of these devices. Cobaltates with p -type conductivity and n -type manganates are considered for the development of a ceramic thermoelectric converter. Sintered pellets and thin PLD films with the composition La 1− x Ca x MO 3−δ ( x =0, 0.3, 0.4) (M = Co, Mn) were synthesised and characterised concerning their thermoelectric properties in a broad temperature range. It was found that similar to polycrystalline samples the electrical conductivity of LaCoO 3 increases significantly with 40% Ca-substitution due to the formation of Co 4+ ions while the thermopower decreases. The thermopower values of the La 0.8 Ca 0.2 MnO 3−δ films have a negative sign, but become large and positive at temperatures of 1000 K.

Laser ablation of a homologous series of four tailor-made UV-sensitive aryltriazene polymers with an increasing content of photodecomposible chromophore units has been studied with a XeCl excimer laser (emission wavelength 308 nm). Irradiation induces a photolytic cleavage of the aryltriazene chromophores which then leads to a fragmentation of the polymer main chain. Resulting effects of different chromophore densities on the ablation parameters of thin films were investigated by profilometry analysis of the ablated spots. No relevant influence of the chromophore density was found for the threshold fluence of laser ablation (∼25 mJ/cm2) of the four polymers for single-pulse experiments. In the same way, ablation depths per pulse at a given laser fluence and with the same film thickness showed no significant differences. Remarkable differences were found for the resulting surface morphology of ablated spots at laser fluences near the ablation threshold. Homogeneous ablation resulting in a flat and smooth bottom surface of the ablated pits were observed mainly for laser fluences above the range of two times the ablation threshold (>∼50 mJ/cm2). Investigating the ablation behaviour of such triazene-based photopolymers allows to derive photophysical key parameters necessary for the optimization of application processes where the designed polymers are used as sacrificial absorbing release layers in advanced laser-induced forward transfer (LIFT) applications.

Laser induced backside wet etching combined with the diffractive gray tone phase mask has been used for the fabrication of a micro-lens array with a single lens diameter of 1 mm and a micro-prism in quartz. The micro-lens array was tested as beam homogenizer for high power XeCl excimer laser yielding a clear improvement in the quality of the laser beam. The optimum fluence range for fabrication of micro-lenses by laser induced backside wet etching using 1.4 M pyrene in THF solution and 308 nm irradiation wavelength is 1–1.6 J/cm2. The etching mechanisms of LIBWE are based on a combination of pressure and temperature jumps at quartz–liquid interface.

The deposition of metal and polymer patterns was achieved with a laser forward transfer method involving a sacrificial release layer. Aluminum, gelatine and methylcellulose pixels were precisely transferred from a donor to a receiver substrate using the UV-laser decomposition of an intermediate triazene polymer layer. The roughness and edge sharpness of the pixels are found to be very dependent on the transfer material. For aluminum, a thick layer of triazene has to be used to get a clean transfer, which remains unclear yet. The applied fluence as well as the triazene thickness are strongly interdependent on the mechanical properties of the transfer layer. This work endeavours some important aspects of the transfer mechanism, and opens the way to further investigations, which are necessary to get a clear understanding of the process.

The laser ablation of a photosensitive triazene polymer was investigated with a ns XeCl excimer laser over a broad range of thicknesses (10–400 nm). We found that the ablation threshold fluence increased dramatically with decreasing film thickness for films thinner than 50 nm. Ablation on substrates with different thermal properties (sapphire, fused silica, PMMA) was investigated as well, and a clear influence of the substrate material was obtained. A mathematical model combining thermal diffusion and absorption effects was used to explain the experimental data. The model is in good agreement with the experimental data and shows that heat diffusion into the substrate plays a crucial role for the ablation process of very thin films.

Applied Physics A, 89 (4), ISSN:0947-8396, ISSN:1432-0630, ISSN:0340-3793

A novel, simplified concept for polymer electrolyte micro-fuel cells is introduced that combines several functions in fewer parts. It consists only of three elements; two glassy carbon sheets with micro-structured flow fields and a catalyst-coated membrane. The micro-structures are prepared in a sequence of three processing steps, i.e. sputtering, laser ablation, and reactive ion etching. Fuel cell tests were carried out with different flow fields, and a maximum power density of ∼415 mW/cm2 at a cell voltage of 425 mV was obtained up to now. Keywords: Micro-structuring, Micro polymer electrolyte fuel cell, Glassy carbon, Catalyst-coated membrane, Flow field structure

The micro-laser plasma thruster (μ-LPT) is a micropropulsion device, designed for steering and propelling of small satellites (1–10 kg). A laser is focused onto a polymer layer on a substrate to form a plasma, which produces the thrust that is used to control the satellite motion. Three different polymers were tested to understand the influence of their specific properties on the thrust performance: poly(vinyl chloride) (PVC) as a low-energetic material, a glycidyl azide polymer (GAP), and poly(vinyl nitrate) (PVN) as high-energetic polymers. Different absorbers (carbon nanoparticles or an IR dye) were added to the polymer to achieve absorption at the irradiation wavelength (1064 nm). The influence of the material and dopant properties on the decomposition characteristics and the energy release were investigated by thrust measurements and ns-shadowgraphy. Mass spectrometry and time- and space-resolved plasma emission spectroscopy in air and vacuum were used to analyze the degree of fragmentation as function of the material properties. The kinetic energies of selected fragments were calculated from the spectra. GAP + C showed the best performance in all measurements at high fluences, while at low fluences PVN + C revealed the best performance.

It has been shown recently that diamond-like carbon (DLC) with a sp 3 fraction above 60% is a better wall coating material for ultracold neutron applications than beryllium. We report on results of Raman spectroscopic and XPS measurements obtained for diamond-like carbon coated neutron guides produced in a new facility, which is based on pulsed laser deposition at 193 nm. For diamond-like carbon coatings on small stainless steel substrates we find sp 3 fractions in the range from 60 to 70% and showing slightly increasing values with laser pulse energy and pulse repetition rate.

UV-Laser ablation of polymers is a well-established method to structure and deposit polymers, but the mechanisms of ablation are still controversial, i.e. photothermal or photochemical processes. An approach to probe the ablation mechanisms and to improve ablation is to incorporate photoactive groups into the polymer structure. The investigation of the ablation behavior of designed triazene polymers showed that the ablation mechanism is always a combination of both photothermal and photochemical processes, but the ratio can be changed by using different polymers and irradiation wavelengths. Also the quality of structures in the triazene polymers is superior at an irradiation wavelength of 308 nm compared to commercially available polymers. Polymers can be designed not only for UV irradiation, but also for applications in the IR range, but with different requirements. One application for designed polymers in the near-IR range is as fuel for the laser plasma thruster, which is used as propulsion system for small satellites. With commercially available polymers the necessary thrust could not be achieved. A specially designed polymer-absorber system for this application produce more energy in the form of thrust, than the laser delivered.

The ablation products of various polymers (triazene polymers, polyimides and glycidyl azide polymer) with 157 nm F2 laser irradiation were studied with time-of-flight mass spectroscopy, ion probe and white-light interferometry. In contrast to the ablation with longer UV wavelengths, 157 nm irradiation results in non-preferential bond-breaking and a much more pronounced fragmentation into fragments with masses

A novel method for the fabrication of complex 3 dimensional structures, such as plano-convex microlens arrays in quartz, is presented. This technique is applied for precise micromachining of UV transparent materials, e.g. quartz, by using a conventional XeCl excimer laser and an organic solution which is in contact with the substrate. Strong absorption of the intense laser light results in the formation of the high pressure and temperature jumps at the quartz-liquid interface, which are the key elements in this process. A combination of laser assisted wet etching with the projection of a Diffractive Gray Tone Phase Mask is applied to fabricate diffractive and refractive micro-lens arrays in quartz. A quartz micro-lens array, which consists of 10 × 10 plano-convex microlenses is tested as a beam homogenizer for the quadrupled Nd:YAG laser.

An improved synthesis of photosensitive homopolymers containing aryltriazene chromophores covalently incorporated into the polymer backbone is reported. Such photopolymers proved to have promising properties for novel UV-laser applications. A homologous series of new aryltriazene polymers with increasingly branched side chains (R = Me, Et, iPr, tBu) was synthesized and characterized. Homogeneous thin films with thicknesses from ≈15 to >150 nm were prepared by spin-coating. Photodecomposition was studied in solution and on thin films. Polymers with increasingly branched and bulky substituents showed decreasing photodissociation rates. NMR studies suggested an enhanced hindrance of the N(2)–N(3) bond rotation in the aryltriazene moiety with increasing steric demand of the substituents.