Search

Femtosecond laser-induced breakdown spectroscopy (fs-LIBS) is employed to detect tiny amounts of mass ablated from macroscopic specimens and to measure chemical images of microstructured samples with high spatial resolution. Frequency-doubled fs-pulses (length 400 fs, wavelength 520 nm) are tightly focused with a Schwarzschild microscope objective to ablate the sample surface. The optical emission of laser-induced plasma (LIP) is collected by the objective and measured with an echelle spectrometer equipped with an intensified charge-coupled device camera. A second fs-laser pulse (1040 nm) in orthogonal beam arrangement is reheating the LIP. The optimization of the experimental setup and measurement parameters enables us to record single-pulse fs-LIBS spectra of 5 nm thin metal layers with an ablated mass per pulse of 100 femtogram (fg) for Cu and 370 fg for Ag films. The orthogonal double-pulse fs-LIBS enhances the recorded emission line intensities (two to three times) and improves the contrast of chemical images in comparison to single-pulse measurements. The size of ablation craters (diameters as small as 1.5 µm) is not increased by the second laser pulse. The combination of minimally invasive sampling by a tightly focused low-energy fs-pulse and of strong enhancement of plasma emission by an orthogonal high-energy fs-pulse appears promising for future LIBS chemical imaging with high spatial resolution and with high spectrochemical sensitivity.

We report on femtosecond (130 femto second) laser pulse removal and modification in Copper Boron Oxide thin films (CuBO2) deposited on silicon substrate. The samples were irradiated with 100 to 500 number of laser pulses at room temperature. Micro-size constructions on the surface of exposed CuBO2 thin films were produced and was observed using Scanning Electron Microscope (SEM). Self-prepared shapes like wrinkles, cellular erections, group of spots and cracks are observed by SEM studies. The small particles produced at initial laser pulses agglomerate into microspheres of Copper Boron Oxide. The optical properties show the high transmission value in (CuBO2) thin films when the number of laser pulses is increased. The optical band gap energy also decreases as compared to as deposited film up to 300 number of pulses and then increases up to 500 number of pulses. The results show that femtosecond laser irradiation considerably modifies the optical properties and surface morphology of (CuBO2) thin films.

The angular dependence of magnetic-field commensurability effects in thin films of the cuprate high-critical-temperature superconductor YBa$_{2}$Cu$_{3}$O$_{7-\delta}$ (YBCO) with an artificial pinning landscape is investigated. Columns of point defects are fabricated by two different methods of ion irradiation -- scanning the focused 30 keV ion beam in a helium ion microscope or employing the wide-field 75 keV He$^+$ beam of an ion implanter through a stencil mask. Simulations of the ion-target interactions and the resulting collision cascades reveal that with both methods square arrays of defect columns with sub-$\mu$m spacings can be created. They consist of dense point-defect clusters, which act as pinning centers for Abrikosov vortices. This is verified by the measurement of commensurable peaks of the critical current and related minima of the flux-flow resistance vs magnetic field at the matching fields. In oblique magnetic fields the matching features are exclusively governed by the component of the magnetic field parallel to the axes of the columnar defects, which confirms that the magnetic flux is penetrated along the defect columns. We demonstrate that the latter dominate the pinning landscape despite of the strong intrinsic pinning in thin YBCO films., Comment: 8 pages, 6 figures

In this contribution, we show CH3NH3PbI3–xClx perovskite solar cells (PSCs) processed in ambient air from a solution containing the diketone, acetylacetone (AA) solvent as an additive. PSCs with the AA additive show enhanced photovoltaic properties. The optimized PSC with 10 vol % AA additive shows an average open-circuit voltage (VOC) of about 1.02 V, short-circuit current density (Jsc) of around 18.7 mA/cm2, fill factor of about 76%, and power conversion efficiency of around 14.5%. Atomic force microscopy topographic imaging depicts that the addition of AA into the MAPbI3–xClx solution enhances the crystal growth with comparable improvement in the surface smoothness. Electrochemical impedance spectroscopy and intensity modulated photovoltage spectroscopy investigations show that incorporation of AA resulted in the improvement of charge carrier dynamics in the bulk and across interfaces, and reduction of recombination pathways. Moreover, MAPbI3–xClx films with the AA additive exhibit stronger photoluminescence compared to the pristine MAPbI3–xClx films. This appears to confirm that the AA solvent additive plays a vital role to reduce the trap states and recombination conduits across the film, which boosts the enhancement of radiative recombination pathways. We believe that this additive is highly practical and a viable option to fabricate and optimize large-area, stable, thin film PSCs in ambient environment.

Thin films of the high-temperature superconductor HgBa$_2$CaCu$_2$O$_{6+\delta}$ have been prepared on SrTiO$_3$ substrates by pulsed-laser deposition of precursor films and subsequent annealing in mercury-vapor atmosphere. The microstructural properties of such films can vary considerably and have been analyzed by x-ray diffraction and atomic force microscopy. Whereas the resistivity is significantly enhanced in samples with coarse-grained structure, the Hall effect shows little variation. This disparity is discussed based on models for transport properties in granular materials. We find that, despite of the morphological variation, all samples have similar superconducting properties. The critical temperatures $T_c \sim 121.2$ K $\dots 122.0$ K, resistivity, and Hall data indicate that the samples are optimally doped. The analyses of superconducting order parameter fluctuations in zero and finite magnetic fields yield the in-plane $\xi_{ab}(0) \sim 2.3$ nm $\dots 2.8$ nm and out-of-plane $\xi_{c}(0) \sim 0.17$ nm $ \dots 0.24$ nm Ginzburg-Landau coherence lengths at zero temperature. Hall measurements provide estimates of carrier scattering defects in the normal state and vortex pinning properties in the superconducting state inside the grains., Comment: 9 pages, 5 figures

Femtosecond laser-induced breakdown spectroscopy (fs LIBS) experiences a growing number of applications. We used a fs double pulse (DP) laser system to enhance the line intensities and we quantified the major mechanisms responsible for intensity enhancement in fs DP LIBS. The laser-induced plasma was excited by a 400 nm pulse and a delayed 800 nm pulse focused on metallic and oxide materials. The 400 nm pulses were produced by frequency doubling of the fundamental laser pulses at 800 nm. The laser radiation not converted by second harmonic generation was used as the 800 nm pulses. The LIBS spectra and the time-resolved plasma parameters were measured as function of pulse energies and correlated to the volume of ablation craters and the amount of nanoparticles formed in the process. Our results showed that the fs LIBS line intensities measured with double pulse excitation IDP were much higher than with single pulse excitation ISP. The intensity enhancement on metallic Cu was IDP/ISP = 2–30 depending on the energy of the first fs pulse. The dominating mechanisms of DP intensity enhancement were the increased number of atoms in plasma N and the higher plasma temperature T. The increase of N was due to the larger volume of DP ablation craters. The atomization of nanoparticles by laser-plasma-particle interaction contributed much less. The intensity enhancement was highest at lowest energy of the first pulse. Fs DP LIBS may thus enable elemental imaging with improved lateral resolution, higher sensitivity and increased elemental contrast.

Laser-induced breakdown spectroscopy (LIBS) is a rapidly developing technique for chemical materials analysis. LIBS is applied for fundamental investigations, e.g., the laser plasma matter interaction, for element, molecule, and isotope analysis, and for various technical applications, e.g., minimal destructive materials inspection, the monitoring of production processes, and remote analysis of materials in hostile environment. In this review, we focus on the element analysis of industrial materials and the in-line chemical sensing in industrial production. After a brief introduction we discuss the optical emission of chemical elements in laser-induced plasma and the capability of LIBS for multi-element detection. An overview of the various classes of industrial materials analyzed by LIBS is given. This includes so-called Technology materials that are essential for the functionality of modern high-tech devices (smartphones, computers, cars, etc.). The LIBS technique enables unique applications for rapid element analysis under harsh conditions where other techniques are not available. We present several examples of LIBS-based sensors that are applied in-line and at-line of industrial production processes.

We investigate femtosecond laser-induced breakdown spectroscopy (fs-LIBS) for the spectrochemical imaging of thin films with high spatial resolution. Chemical images are obtained by recording LIBS spectra at each site of 2D raster-scans across the samples employing one fs-laser pulse per site. The diffraction images of the Echelle spectrometer are binned to reduce the read-out time of the intensified CCD detector and to increase the stability of the emission signals against peak drifts in the echellograms. For copper thin films on glass the intensities of Cu I emission lines and the size of ablation craters vary non-monotonously with the film thickness h Cu = 5–500 nm. The emission efficiency, defined as the Cu I line intensity per ablated volume, strongly decreases for films thicker than the optical penetration depth. The Na I line intensity from glass increases exponentially with decreasing Cu film thickness. For yttrium barium copper oxide (YBCO) thin films on MgO various atomic and molecular emission lines of the laser-induced plasma are measured (film thickness h YBCO = 200–1000 nm). The obtained element (Y, Ba, Cu, Mg) and molecular (Y-O) fs-LIBS images match the structure of the micro-patterned YBCO films very well. The achieved lateral resolution δr = 6 μm is among the best values reported for spectrochemical LIBS imaging.

Laser-induced breakdown spectroscopy (LIBS) for composition analysis of polymer materials results in optical spectra containing atomic and ionic emission lines as well as molecular emission bands. In the present work, the molecular bands are analyzed to obtain spectroscopic information about the plasma state in an effort to quantify the content of different elements in the polymers. Polyethylene (PE) and a rubber material from tire production are investigated employing 157 nm F2 laser and 532 nm Nd:YAG laser ablation in nitrogen and argon gas background or in air. The optical detection reaches from ultraviolet (UV) over the visible (VIS) to the near infrared (NIR) spectral range. In the UV/VIS range, intense molecular emissions, C2 Swan and CN violet bands, are measured with an Echelle spectrometer equipped with an intensified CCD camera. The measured molecular emission spectra can be fitted by vibrational-rotational transitions by open access programs and data sets with good agreement between measured and fitted spectra. The fits allow determining vibrational-rotational temperatures. A comparison to electronic temperatures Te derived earlier from atomic carbon vacuum-UV (VUV) emission lines show differences, which can be related to different locations of the atomic and molecular species in the expanding plasma plume. In the NIR spectral region, we also observe the CN red bands with a conventional CDD Czerny Turner spectrometer. The emission of the three strong atomic sulfur lines between 920 and 925 nm is overlapped by these bands. Fitting of the CN red bands allows a separation of both spectral contributions. This makes a quantitative evaluation of sulfur contents in the start material in the order of 1 wt% feasible.

The Hall effect in the mixed state of thin films of the high-temperature superconductor YBa2Cu3O 7 − δ (YBCO) that were patterned with a square array of regions with suppressed superconducting order parameter is investigated. Cylindrical defect columns penetrating the entire thin YBCO film along its crystallographic c − axis have been created by irradiation with He + ions through a silicon stencil mask. Distinct peaks of the critical current at commensurate arrangements of magnetic flux quanta with the artificial defect lattice confirm enhanced vortex pinning. Vortex motion not only leads to a dissipative voltage along the current direction but also to a transverse voltage, termed vortex Hall effect. We report on the observation of a novel commensurability effect in the transverse Hall signal. A sign change and a positive peak of the Hall coefficient appear in a narrow magnetic field range around the matching field. The feature appears in the temperature range below the critical temperature, where the Hall effect usually is negative in underdoped and optimally-doped cuprate superconductors. The results indicate that the Hall matching effect originates from enhanced pinning of the vortices along the regular defect columns.

Magnetic fields penetrate a type-II superconductor as magnetic flux quanta, called vortices. In a clean superconductor they arrange in a hexagonal lattice, while by adding periodic artificial pinning centers many other arrangements can be realized. Using the focused beam of a helium ion microscope we have fabricated periodic patterns of dense pinning centers with spacings as small as 70 nm in thin films of the cuprate superconductor YBa$_{2}$Cu$_{3}$O$_{7-\delta}$. In these ultradense kagom\'e-like patterns, the voids lead to magnetic caging of vortices, resulting in unconventional commensurability effects that manifest themselves as peaks in the critical current and minima in the resistance versus applied magnetic field up to $\sim 0.4\,$T. The various vortex patterns at different magnetic fields are analyzed by molecular dynamics simulations of vortex motion, and the magnetic field dependence of the critical current is confirmed. These findings open the way for a controlled manipulation of vortices in cuprate superconductors by artificial sub-100 nm pinning landscapes., Comment: Minor additions

The properties of natural and synthetic rubber critically depend on the concentration of the vulcanizing system, among others. Sulfur and zinc oxide are typically used as cross-linking and activating agents for the vulcanization reaction (0-3 wt %). We present an advanced spectroscopic method to chemically analyze the vulcanizing system in rubber under ambient conditions, and we demonstrate a novel application to measure the elements in-line of industrial rubber production. The laser-induced breakdown spectroscopy (LIBS) technique is optimized to ablate material from the surface of produced rubber sheets and to measure the optical emission of S and Zn from the rubber plasma in air. The sulfur lines in the near-infrared range are masked by molecular emission bands of the C-N radical and spectrally interfered by atomic lines of O. Plasma excitation in collinear double-pulse geometry and detection of plasma emission with time-gated detectors suppresses the spectroscopic overlays and enables to resolve the sulfur lines. For the determination of ZnO the weak Zn lines in the ultraviolet range are measured due to their superior intensity stability compared to the much stronger lines in the deeper UV. S and ZnO are quantified in three different rubber materials prepared from the most important polymers used in rubber production. The mean error of prediction of concentrations RMSEP is ≤0.07 wt % for S and ≤0.33 wt % for ZnO for all polymer types. Our results demonstrate that the vulcanizing system of rubber can be quantified under ambient conditions with LIBS. Other chemical elements could be analyzed also and the rubber production could be controlled employing this multielement detection technique as process analytical sensor.

The improved Monte-Carlo (MC) method for standard-less analysis in laser induced breakdown spectroscopy (LIBS) is presented. Concentrations in MC LIBS are found by fitting model-generated synthetic spectra to experimental spectra. The current version of MC LIBS is based on the graphic processing unit (GPU) computation and reduces the analysis time down to several seconds per spectrum/sample. The previous version of MC LIBS which was based on the central processing unit (CPU) computation requested unacceptably long analysis times of 10's minutes per spectrum/sample. The reduction of the computational time is achieved through the massively parallel computing on the GPU which embeds thousands of co-processors. It is shown that the number of iterations on the GPU exceeds that on the CPU by a factor > 1000 for the 5-dimentional parameter space and yet requires > 10-fold shorter computational time. The improved GPU-MC LIBS outperforms the CPU-MS LIBS in terms of accuracy, precision, and analysis time. The performance is tested on LIBS-spectra obtained from pelletized powders of metal oxides consisting of CaO, Fe2O3, MgO, and TiO2 that simulated by-products of steel industry, steel slags. It is demonstrated that GPU-based MC LIBS is capable of rapid multi-element analysis with relative error between 1 and 10's percent that is sufficient for industrial applications (e.g. steel slag analysis). The results of the improved GPU-based MC LIBS are positively compared to that of the CPU-based MC LIBS as well as to the results of the standard calibration-free (CF) LIBS based on the Boltzmann plot method.

Tomography of a laser-induced plasma in air is performed by inverse Radon transform of angle-resolved plasma images. Plasmas were induced by single laser pulses (SP), double pulses (DP) in collinear geometry, and by a combination of single laser pulses with pulsed arc discharges (SP-AD). Images of plasmas on metallurgical steel slags were taken at delay times suitable for calibration-free laser-induced breakdown spectroscopy (CF-LIBS). Delays ranged from few microseconds for SP and DP up to tens of microseconds for SP-AD excitation. The white-light and the spectrally resolved emissivity e(x,y,z) was reconstructed for the three plasma excitation schemes. The electron number density Ne(x,y,z) and plasma temperature Te(x,y,z) were determined from Mg and Mn emission lines in reconstructed spectra employing the Saha-Boltzmann plot method. The SP plasma revealed strongly inhomogeneous emissivity and plasma temperature. Re-excitation of plasma by a second laser pulse (DP) and by an arc discharge (SP-AD) homogenized the plasma and reduced the spatial variation of e and Te. The homogenization of a plasma is a promising approach to increase the accuracy of calibration-free LIBS analysis of complex materials.

Slag from secondary metallurgy in industrial steel production is analyzed by laser-induced breakdown spectroscopy (LIBS). The major oxides CaO, Al2O3, MgO, SiO2, FeO, MnO, and TiO2 are determined by calibration-free LIBS (CF-LIBS) method. For the minor oxide P2O5 calibration curves are established and the limits of detection (LOD) and the root-mean squared errors of prediction (RMSEP) are determined. The optical emission of the laser-induced plasma is measured for different detection geometries and varying sample position relative to the focal plane of the laser beam. LIBS spectra, plasma parameters, and analytical results are very similar for light collection with optical fibres close to the plasma (“direct detection”) and at remote position (“collinear detection”). With collinear detection, the CF-LIBS calculated oxide concentrations are insensitive to sample position along the optical axis over wide range. The detection limits and the prediction errors of minor P2O5 depend on the major slag element used for signal normalization. With Mg and Si as internal reference elements the LOD values are 0.31 wt% and 0.07 wt%, respectively. The RMSEP values are lowest for signal normalization to Si. Calculations of the optical emission of ideal plasma support the experimental preference for Si as reference element in the phosphorous calibration.

In our previous work Siraj et al (J Alloys Comp 563:280, 2013), the electron beam irradiation at high energies (6–15 MeV) at constant dose of 30 Gy produced Zinc oxide elongated nanostructures and modified the optical band gap energies accordingly. In present work, those nanostructures are fractured to smaller sizes by increasing the electron doses to 100 and 200 Gy. The very high temperature gradient induced stresses are responsible for further fracturing of ZnO nanostructures. The optical properties such as refractive index, extinction coefficient and optical band gap energy have also modified when higher cumulative electron doses are used. The optical band gap energies are found to decrease by increasing electron doses at all used electron energies, which is attributed to the production of different defects like vacancies, unpaired bonds, nanovoids, nanocavities, nanocracks and high strains. The electron beam irradiation of ZnO thin films at used parameters (doses and energies) is found to be plausible technique to produce nanostructures of different sizes and accordingly modify the optical band gap energies. The results can be beneficial for optical and optoelectronic industries.

We investigate the effect of 700 keV Ni +2 ions irradiation at different ion fluences (1 × 10 13 , 1 × 10 14 , 2 × 10 14 , 5 × 10 14 ions/cm 2 ) on the structural, surface, magneto-optic and optical properties of ZnO thin films. The X-ray diffraction (XRD) results show improved crystallinity when ion fluence is increased to 2 × 10 14 ions/cm 2 , while deterioration is observed at the highest ion fluence of 5 × 10 14 ions/cm 2 . Scanning electron micrographs (SEM) show the formation of small grains at ion fluence 1 × 10 13 ions/cm 2 , micro-rods at fluences 1 × 10 14 and 2 × 10 14 ions/cm 2 and ultimate fracturing of thin film surface at ion fluence 5 × 10 14 ions/cm 2 . Faraday rotation measurements are also performed and show a decrease in Verdet constant from 53 to 31 rad/(T-m) when irradiated at 1 × 10 13 ions/cm 2 , increasing up to 45 rad/(T-m) at 2 × 10 14 ions/cm 2 , and then decreasing again to 36 rad/(T-m) at 5 × 10 14 ions/cm 2 . The optical band gap energy of the films is determined using spectroscopic ellipsometry, which shows an increase in optical band gap energy ( E g ) from 3.04 eV to 3.19 eV when the fluence increases to 2 × 10 14 ions/cm 2 and a decrease to 3 eV at fluence 5 × 10 14 ions/cm 2 . We argue that these properties can be explained using ion heating effect of thin films.

Laser ablation - spark discharge - optical emission spectroscopy (LA-SD-OES) and Laser-induced breakdown spectroscopy (LIBS) are applied for the analysis of minor elements Manganese (Mn) and Chromium (Cr) in steel and for the chemical imaging of micro-patterned photoresist layers. In LA-SD-OES a weak laser pulse (typical energy 50 μJ to 5 mJ) triggers an electric discharge between a high voltage electrode and the laser ablated spot on the sample surface. Intense emission lines of neutral and singly-ionized atoms are observed with both spectroscopic techniques. However, lines of doubly-ionized atoms are detected with LA-SD-OES only. The line intensities of C III and Al III increase with decreasing laser pulse energy, surprisingly. The appearance of intense doubly-ionized lines indicates that the mechanisms of plasma excitation are different in LA-SD-OES compared to LIBS and that the combined plasma is not in local thermodynamic equilibrium at low laser energy. The calibration curves of Mn and Cr in industrial steel reveal steeper slope (higher sensitivity) for the Mn II and Cr II lines measured with LA-SD-OES and for the Mn I and Cr I lines measured with LIBS. Chemical imaging of the photoresist layer with LA-SD-OES at the atomic lines of C I and C III and the molecular band of CN reveals all details of the sample. Similar images are obtained for C I and CN using LIBS, however, no image contrast is obtained at the C III line. The very low pulse energy in LA-SD-OES enables soft sampling and may be beneficial also for the analysis and imaging of sensitive material.

Chemical imaging by Laser ablation – spark discharge – optical emission spectroscopy (LA-SD-OES) is presented. A low-energy laser pulse triggers an electric spark between a metal electrode tip and a sample and the excited plasma is analyzed by OES. Without a laser pulse the spark is suppressed as the applied electric field strength is below the self-breakdown threshold in air. The laser-triggered discharge is spatially confined to a plasma channel between tip and ablated spot on the sample. This localization of the electric spark enables for element imaging with high spatial resolution not feasible with spark-OES. Human fingerprints, mesoscopic layered samples, and micro-patterned polymer layers are spectrochemically imaged. The image contrast defined as signal to background ratio of the analyte emission line intensity is higher for LA-SD-OES than for Laser-induced breakdown spectroscopy (LIBS) at low laser energy. We also measure the lag time between laser pulse and spark depending on the applied electrode voltage and the distance between tip and sample and discuss the results in terms of avalanche ionization in air. The optical spectra measured by LA-SD-OES and LIBS in the same experimental setup are similar. Higher ionized emission lines are detected with LA-SD-OES only.

In superconductors with a periodic pinning potential, the vortices can lock into a commensurate arrangement, where each pin is filled by one vortex. Then, an intriguing duality between conduction electrons in a normal metal and mobile vortices in a superconductor arises. While the mutual repulsion of electrons can evoke a Mott insulator, the interaction between mobile and commensurably trapped vortices can lead to a vortex Mott metal-to-insulator transition with vanishing resistance. The authors report on a hitherto unknown manifestation of such a state, uncovered by measurements of the voltage orthogonal to the injected current. This vortex Hall effect exhibits a sharp peak and a change of sign when the number of vortices exactly matches that of the pins.

Aluminum doped ZnO (AZO) and pure ZnO thin films are grown on polymer substrates by pulsed-laser deposition and the optical, electrical, and structural film properties are investigated. Laser fluence, substrate temperature, and oxygen pressure are varied to obtain transparent, conductive, and stoichiometric AZO layers on polyethylene terephthalate (PET) that are free of cracks. At low fluence (1 J/cm2) and low pressure (10− 3 mbar), AZO/PET samples of high optical transmission in the visible range, low electrical sheet resistance, and high figure of merit (FOM) are produced. AZO films on fluorinated ethylene propylene have low FOM. The AZO films on PET substrates are used as electron transport layer in inverted organic solar cell devices employing P3HT:PCBM as photovoltaic polymer-fullerene bulk heterojunction.

Slag from secondary metallurgy in industrial steel production is analyzed by calibration-free laser-induced breakdown spectroscopy (CF-LIBS). The slag pieces are homogenized by ball milling and sintering. LIBS spectra are measured under ambient conditions using nanosecond Nd:YAG laser pulses (1064 nm) for ablation. A fiber-coupled Echelle spectrometer with two separate detection arms in the UV range (190 to 360 nm) and in the VIS range (298 to 864 nm) and one ICCD camera is used for detection. The UV and VIS spectra are measured sequentially and combined to one spectrum to increase the number of highly resolved emission lines for the calculation of oxide concentrations in slags. The combination of spectra requires an adaption procedure including independent radiometric calibration, the de-convolution of spectrometer functions, baseline corrections, and intensity scaling. More than 60 emission lines of elements Ca, Al, Mg, Si, Fe, Mn, and Ti are evaluated. The electron density is derived from Stark broadening of a Mg line, and the plasma temperature is determined from Saha–Boltzmann plots of Ca, Mn, or Ti lines. With the combined LIBS spectra, the CF-LIBS calculated concentrations C CF are closer to the nominal concentrations C N determined by x-ray fluorescence spectrometry. Significantly reduced relative errors of concentration e r = | C CF − C N | / C N are observed for the oxides CaO, Al 2 O 3 , MgO, SiO 2 , and MnO, and no reduction was found for FeO and the minor phase TiO 2 . The improved accuracy of concentrations is attributed to a better detection of the major elements Ca, Al, and Si in the combined LIBS spectra.

Spintronics is not the only alternative to traditional electronics. The $f\phantom{\rule{0}{0ex}}l\phantom{\rule{0}{0ex}}u\phantom{\rule{0}{0ex}}x\phantom{\rule{0}{0ex}}o\phantom{\rule{0}{0ex}}n$ (magnetic flux quantum) could be used as a vehicle for ultralow-energy data processing and storage, in fluxonic devices. First, though, we need to figure out how to create circuitry. The authors demonstrate a technique for fabricating submicrometer patterns over a wide area in a cuprate superconductor, where fluxons are carried by nanoscale magnetic vortices. Being able to create these ``pinning centers'' at will allows for trapping and manipulating vortices in a controlled fashion.

Electronic stopping of slow protons in ZnO, VO2 (metal and semiconductor phases), HfO2, and Ta2O5 was investigated experimentally. As a comparison of the resulting stopping cross sections (SCS) to data for Al2O3 and SiO2 reveals, electronic stopping of slow protons does not correlate with electronic properties of the specific material such as band gap energies. Instead, the oxygen 2p states are decisive, as corroborated by density functional theory calculations of the electronic densities of states. Hence, at low ion velocities the SCS of an oxide primarily scales with its oxygen density., Financial support of this work by the FWF (FWF-Project No. P22587-N20 and FWF-Project No. P25704-N20) is gratefully acknowledged. M. A. and J. I. J. acknowledge financial support by the Gobierno Vasco-UPV/EHU Project No. IT756-13, and the Spanish Ministerio de Economía y Competitividad (Grants No. FIS2013-48286-C02-02-P and FIS2016-76471-P). Fabrication and characterization of VO2 films at Vanderbilt University (CMG and RFH) was supported by a grant from the National Science Foundation (DMR-1207507). A research infrastructure fellowship of the Swedish Foundation for Strategic Research (SSF) under Contract No. RIF14-0053 supporting accelerator operation is acknowledged.

The halogen chlorine is hard to detect in laser-induced breakdown spectroscopy (LIBS) mainly due to its high excited state energies of 9.2 and 10.4 eV for the most intense emission lines at 134.72 nm and 837.59 nm, respectively. We report on sensitive detection of Cl in industrial iron oxide Fe 2 O 3 powder by single-pulse (SP) and dual-pulse (DP) LIBS measurements in the near infrared range in air. In compacted powder measured by SP excitation (Nd:YAG laser, 532 nm) Cl was detected with limit of detection LOD = 440 ppm and limit of quantitation LOQ = 720 ppm. Orthogonal DP LIBS was studied on pressed Fe 2 O 3 pellets and Fe 3 O 4 ceramics. The transmission of laser-induced plasma for orthogonal Nd:YAG 1064 nm and ArF 193 nm laser pulses showed a significant dependence on interpulse delay time (ipd) and laser wavelength (λ L ). The UV pulses (λ L = 193 nm) were moderately absorbed in the plasma and the Cl I emission line intensity was enhanced while IR pulses (λ L = 1064 nm) were not absorbed and Cl signals were not enhanced at ipd = 3 μs. The UV laser enhancement of Cl signals is attributed to the much higher signal/background ratio for orthogonal DP excitation compared to SP excitation and to the increased plasma temperature and electron number density. This enabled measurement at a very short delay time of t d ≥ 0.1 μs with respect to the re-excitation pulse and detection of the very rapidly decaying Cl emission with higher efficiency.

We report on measurements of the magnetoresistance and of the critical current in thin films of the high-temperature superconductor YBa 2 Cu 3 O 7 - δ (YBCO). A square array of regions with suppressed superconducting order parameter has been created in these films by introducing point defects via irradiation with He + ions through a silicon stencil mask. In such a structure distinct peaks of the critical current can be observed at commensurate arrangements of magnetic flux quanta with the artificial defect lattice. Concurrently, the magnetoresistance shows pronounced minima. Both observations demonstrate that the strong intrinsic pinning in YBCO can be overcome by a periodic array of ion-damage columns with 300 nm spacing.

We report on laser-induced breakdown spectroscopy (LIBS) of chlorine containing waste polymers in-line of an industrial materials sorting plant. Material from municipal waste plastic collection containing different types of plastic pieces and impurities is measured without pre-treatment directly on the conveyor belt (conveyor speed 2 m/s). The encapsulated LIBS system mounted to the conveyor comprises a fast Nd:YAG laser and spectrometer with charge-coupled device (CCD) detector, a distance sensor, and a software for quasi real-time evaluation of measured LIBS spectra. Approximately 800,000 spectra are collected during the in-line measurement series using one laser pulse per spectrum. The optical plasma emission of Cl I at 837.6 nm is detected to identify waste polymers with high Cl content such as polyvinylchloride (PVC). The LIBS spectra are evaluated employing a fast linear correlation algorithm. The correlation histogram for more than 20,000 spectra shows three distinct peaks that are associated to different materials containing high amount of Chlorine (>20 wt %), Titanium, and low amount of Cl (

We investigate the influence of sample temperature on the dynamics and optical emission of laser induced plasma for various solid materials. Bulk aluminum alloy, silicon wafer, and metallurgical slag samples are heated to temperature TS ≤ 500 °C and ablated in air by Nd:YAG laser pulses (wavelength 1064 nm, pulse duration approx. 7 ns). The plasma dynamics is investigated by fast time-resolved photography. For laser-induced breakdown spectroscopy (LIBS) the optical emission of plasma is measured by Echelle spectrometers in combination with intensified CCD cameras. For all sample materials the temporal evolution of plume size and broadband plasma emission vary systematically with TS. The size and brightness of expanding plumes increase at higher TS while the mean intensity remains independent of temperature. The intensity of emission lines increases with temperature for all samples. Plasma temperature and electron number density do not vary with TS. We apply the calibration-free LIBS method to determine the concentration of major oxides in slag and find good agreement to reference data up to TS = 450 °C. The LIBS analysis of multi-component materials at high temperature is of interest for technical applications, e.g. in industrial production processes.

The present work deals with the formation of nanostructures and tuning of optical band gap of ZnO thin films by high energy electron bombardment. In first step, Zinc Oxide (ZnO) thin films were deposited on silicon (1 0 0) substrates by pulsed laser deposition (PLD) technique using KrF Excimer laser. In second step, ZnO thin films were irradiated by electron beam of energy 6, 9, 12 and 15 MeV at constant dose. The surface morphology was studied by Atomic Force Microscope (AFM), whereas the optical properties were determined by Spectroscopic Ellipsometry (SE). Atomic force micrographs showed the formation of nanoscale structures on the surface of ZnO thin film. The nanostructures grew in size and reached its maximum size at 12 MeV electron energy. SE analysis revealed the increase in refractive index, appearance of broad absorption peak in visible region, and increase in optical band gap energy of ZnO thin film by 12 MeV electron bombardment. From the results, it can be concluded that the size of nanostructures and the optical band gap energy of ZnO thin films can be tuned by electron irradiation at various energies.

Aluminum and gallium doped zinc oxide thin films with negative dielectric permittivity in the near infrared spectral range are grown by pulsed laser deposition. Composite ceramics comprising ZnO and secondary phase Al2O3 or Ga2O3 are employed as targets for laser ablation. Films deposited on glass from dense and small-grained ceramic targets show optical transmission larger than 70 % in the visible and reveal an onset of metallic reflectivity in the near infrared at 1100 nm and a crossover to a negative real part of the permittivity at approximately 1500 nm. In comparison to noble metals, doped ZnO shows substantially smaller losses in the near infrared.

Laser-induced breakdown spectroscopy (LIBS) is a promising method for fast and quantitative element analysis of complex materials. We report on LIBS measurements of multi-component oxide materials and the compositional analysis of materials by a calibration-free (CF) method. This CF-LIBS method relies on modeling of the optical emission of laser-induced plasma assuming local thermodynamic equilibrium. Various materials are investigated and the calculated concentration values (CCF) of oxides CaO, Al2O3, MgO, SiO2, FeO, and MnO are in agreement with nominal concentration values (CN) from reference analysis. The relative error in oxide concentration er=|CCF−CN|/CN decreases with increasing concentration. The quantification is limited to major oxides (CN≥1 wt%). Slag samples from industrial steel production are analyzed on site by means of a mobile measurement system. LIBS measurements are performed at different sample temperatures. The results obtained show that CF-LIBS is applicable to fast compositional analysis of complex materials in harsh environments.

Double-pulse laser-induced breakdown spectroscopy (LIBS) is an emerging technique for accurate compositional analysis of many different materials. We present results of collinear double-pulse LIBS for analysis of the trace elements aluminum, phosphorus and boron in sintered iron oxide targets. The samples were ablated in air by double-pulse Nd:YAG laser radiation (6 ns pulse duration, laser wavelength of 532 nm) and spectra were recorded with an Echelle spectrometer equipped either with a CCD (charge coupled device) or an ICCD (intensified charge coupled device) camera. For the trace elements aluminum and phosphorus, the use of the CCD detector system resulted in considerable higher signal-to-noise ratios and/or better limits of detection compared to the results achieved with the ICCD detector. The use of CCD double-pulse LIBS enables to detect low concentrations of phosphorus with a limit of detection of 10 ppm by evaluating the UV line at 214.91 nm, which overlaps with a Fe I line. Compared to the ICCD system, the CCD system requires the accumulation of a higher number of laser double-pulses to achieve acceptable signal quality. This can be disadvantageous for elements showing pronounced depletion effects as for the trace element boron in sintered iron oxide targets.

The resistivity and the Hall effect as a function of current density and temperature in the normal state of very thin films of YBa2Cu3O6+x are measured with a fast pulsed-current technique. The in-plane longitudinal and transverse (Hall) conductivities are reduced in intense current densities up to several $\mathrm{MA\,cm}^{-2}$ . In optimally-doped samples, this non-ohmic effect is limited to temperatures below 100 K. In a moderately underdoped sample, however, the non-linearity extends to the temperature range from T c =53 K to ∼150 K. The non-linear part of the Hall conductivity does not scale with a critical exponent, thus excluding classical amplitude fluctuations of the superconducting order parameter as possible origin.

Irradiation of thin films of the cuprate high-temperature superconductor YBa 2 Cu 3 O 7 - δ (YBCO) with 75 keV He + ions leads to an exponential increase of the resistivity and a non-linear decrease of the critical temperature. At a fluence above 3 × 10 15 cm - 2 the material becomes semiconducting. Calculations of ion-target interactions using the MARLOWE code indicated that these effects are due to the creation of point defects, primarily by displacing oxygen atoms, and that the lateral broadening of the ion’s collision cascades is smaller than 10 nm in a 100 nm thick YBCO film. Irradiating a YBCO film through a silicon stencil mask with minimum aperture of 125 nm placed on top of the sample results in a local modification of its electrical properties. We demonstrate that this technique can be used to produce patterns of sub-100 nm size, visualized by scanning electron microscopy and conductive atomic force microscopy. This simple one-step process does not require the removal of target material and avoids the contamination problems associated with chemical etching and focused ion beam techniques.

Irradiation of high-temperature superconducting (HTS) YBa2Cu3O7-d (YBCO) thin films with 75 keV He + ions leads to a quasi-exponential increase of the in-plane (ρab) and the out-of-plane (ρc) resistivity in the normal state and to a non-linear decrease of the critical temperature Tc with ion dose. In situ electrical measurements at room temperature reveal an irradiation-induced reduction of resistivity anisotropy ρc/ρab and a slight relaxation of film resistivity after the ion irradiation is stopped. Ex situ measurements show a stretched-exponential relaxation of Tc and normal state resistivity that continues for several weeks after the ion irradiation. Irradiation of YBCO thin films by low-energy He + ions through stencil masks results in local modification of the electrical and superconducting properties of the HTS material. We demonstrate that masked ion-beam lithography enables to produce structures smaller than 100 nm in size that have potential for applications in future superconducting nano-electronics.

Double-pulse laser-induced breakdown spectroscopy (LIBS) is an emerging technique for accurate compositional analysis of many different materials. We present a systematic study of collinear double-pulse LIBS for analysis of the trace and side elements boron, manganese, copper, aluminum, titanium, silicon, chromium, nickel, potassium, and calcium in sintered iron oxide targets. The samples were ablated in air by single-pulse and double-pulse Nd:YAG laser radiation (6 ns pulse duration, laser wavelength of 532 nm) and spectra were recorded with an Echelle spectrometer equipped with an ICCD camera. We investigated the evolution of atomic and ionic line emission intensities for different interpulse delay times between the laser pulses (from 100 ns to 50 μs) and gate delays after the second laser pulse. We also varied the energy partition between the first and second laser pulse and the size of the irradiated spot at the sample surface. For the trace and side elements, we observed double-pulse LIBS signals that were enhanced as compared to single-pulse measurements depending on the interpulse delay time, the energy partition between the pulses, and the spot size. For the elements boron, copper, aluminum, titanium, chromium, potassium, and calcium limits of detection below 10 ppm were achieved.

Laser-induced breakdown spectroscopy method is modified using an external radiofrequency (RF) plasma jet that overlaps spatially with the laser-induced plasma. Short UV laser pulses (wavelength 193 nm) are employed to ablate iron oxide ceramics, zinc oxide ceramics and polyethylene pressed pellets in ambient air background. An RF generator (frequency 13.56 MHz, power ≤1 kW) and a gas nozzle system are employed to generate a continuous jet of argon and nitrogen plasma expanding into air. The optical emission of the overlapped plasma is analyzed using an Echelle spectrometer equipped with an intensified CCD camera. The time dependence of optical emission intensities and of plasma parameters is investigated by varying the spectrometer delay time with respect to the laser pulse. The emission intensities of major (Fe, Zn) and minor (Mn, Al) elements are moderately increased with the RF plasma jet (≤2×). The intensities of atomic lines and molecular bands from ablated polymer material are increased also.

Laser induced breakdown spectroscopy (LIBS) is an emerging technique for fast and accurate compositional analysis of many different materials. We present a systematic study of collinear double-pulse LIBS on different technical polymers such as polyamide, polyvinyl chloride, polyethylene etc. Polymer samples were ablated in air by single-pulse and double-pulse Nd:YAG laser radiation (8 ns pulse duration) and spectra were recorded with an Echelle spectrometer equipped with an ICCD camera. We investigated the evolution of atomic and ionic line emission intensities for different delay times between the laser pulses (from 20 ns to 500 μs) at a laser wavelength of 532 nm. We observed double-pulse LIBS signals that were enhanced as compared to single-pulse measurements depending on the delay time and the type of polymer material investigated. LIBS signals of polymer materials that are enhanced by double-pulse excitation may be useful for monitoring the concentration of heavy metals in polymer materials.

Surface planarization and masked ion-beam structuring (MIBS) of high-Tc superconducting (HTS) YBa2Cu3O7-δ (YBCO) thin films grown by pulsed-laser deposition (PLD) method is reported. Chemical–mechanical polishing, plasma etching, and oxygen annealing of YBCO films strongly reduce the particulate density (~ 10–2 ×) and surface roughness (~ 10–1 ×) of as-grown PLD layers. The resistivity, critical temperature Tc ≈ 90 K and critical current density Jc (77 K) > 1 MA/cm2 of films are not deteriorated by the planarization procedure. The YBCO films are modified and patterned by irradiation with He+ ions of 75 keV energy. Superconducting tracks patterned by MIBS without removal of HTS material and, for comparison, by wet-chemical etching show same Tc and Jc(T) values. Different micro- and nano-patterns are produced in parallel on planarized films. The size of irradiated pattern depends on the mask employed for beam shaping and features smaller than 70 nm are achieved.

The quantitative determination of oxide concentration by laser-induced breakdown spectroscopy is relevant in various fields of applications (e.g.: analysis of ores, concrete, slag). Calibration free laser-induced breakdown spectroscopy and the multivariate calibration are among the methods employed for quantitative concentration analysis of complex materials. We measured the intensity of neutral and ionized atomic emission lines of oxide materials by laser-induced breakdown spectroscopy and we modified the calibration free laser-induced breakdown spectroscopy method to increase the accuracy. The concentration of oxides was obtained by using stoichiometric relations. Sample materials were prepared from oxide powder (Fe 2 O 3 , MgO, CaO) by mixing and pressing. The concentration was 9.8–33.3 wt.% Fe 2 O 3 , 7.6–33.3 wt.% MgO and 33.3–81.2 wt.% CaO for different samples. Nd:YAG laser (wavelength 1064 nm, pulse duration ≈ 6 ns) ablation was performed in air. The laser-induced plasma emission was measured by an Echelle spectrometer equipped with a sensitivity calibrated ICCD camera. The numerical calibration free laser-induced breakdown spectroscopy algorithm included the fast deconvolution of instrumental function, and the correction of self-absorption effects. The oxide concentration C CF calculated from calibration free laser-induced breakdown spectroscopy results and the nominal concentration C N were very close for all samples investigated. The relative error in concentration, | C CF – C N |/ C N , was 2 O 3 , MgO, and CaO, respectively. The results indicate that this method can be employed for the analysis of major elements in multi-component technical materials.

Aluminum doped Zinc Oxide (AZO) and Lithium doped Zinc Oxide (LZO) thin films are obtained by Pulsed Laser Deposition (PLD) method. These films are characterized by using Spectroscopic Ellipsometry (SE), X-ray Diffraction (XRD) and Photoluminescence (PL). By modeling the ellipsometry spectra we get the dielectric functions, the optical band gap Eg, and the electrical properties. Our results show the influence of the processing parameters on the optical and structural properties of doped ZnO thin films. The post-annealing treatment applied to AZO thin films, changes strongly the optical properties, by lowering the resistivity and red-shifting the band gap.

Thin superconducting YBa$_{2}$Cu$_{3}$O$_{7-\delta}$ films are patterned with a vortex-pin lattice consisting of columnar defect regions (CDs) with 180 nm diameter and 300 nm spacing. They are fabricated by irradiation with 75 keV He$^+$ ions through a stencil mask. Peaks of the critical current reveal the commensurate trapping of vortices in domains near the edges of the sample. Upon ramping an external magnetic field, the positions of the critical current peaks are shifted from their equilibrium values to lower magnetic fields in virgin and to higher fields in field-saturated down-sweep curves, respectively. Based on previous theoretical predictions, this irreversibility is interpreted as a nonuniform, terrace-like critical state, in which individual domains are occupied by a constant number of vortices per pinning site. The magnetoresistance, probed at low current densities, is hysteretic and angle dependent and exhibits minima that correspond to the peaks of the critical current. The minima's positions scale with the component of the magnetic field parallel to the axes of the CDs, as long as the tilted vortices can be accommodated within the CDs. This behavior, different from unirradiated films, confirms that the CDs dominate the pinning., Comment: 9 pages, 7 figures

Double-layers of lithium doped ZnO (LZO) and aluminum doped ZnO (AZO) are grown on r-cut sapphire (r-Al 2 O 3 ) crystal substrates by pulsed-laser deposition. The epitaxial double-layers are a-axis lattice oriented to the substrate. The LZO/AZO/r-Al 2 O 3 samples have high optical transmission in the visible range and a bandgap energy of E g =3.28 eV according to the absorption edge of ZnO. The AZO bottom layers are electrically conductive (resistivity at room temperature ρ∼10 ―3 Ω cm) and LZO top layers are highly resistive (ρ ≥ 10 5 Ω cm). Acoustic shear mode resonances in r-Al 2 O 3 are excited by employing electric fields to the piezoelectric LZO layer (frequency interval 1.5-3 GHz). For biological applications, Madin-Darby canine kidney cells are cultivated on Platinum coated LZO/AZO/r-Al 2 O 3 samples. Osmotic pressure applied to the cells increases or reduces the cell volume depending on the osmolarity of the medium.

Laser-induced breakdown spectroscopy (LIBS) in the vacuum ultraviolet range (VUV, λ < 200 nm) is employed for the detection of trace elements in polyethylene (PE) that are difficult to detect in the UV/VIS range. For effective laser ablation of PE, we use a F2 laser (wavelength λ = 157 nm) with a laser pulse length of 20 ns, a pulse energy up to 50 mJ, and pulse repetition rate of 10 Hz. The optical radiation of the laser-induced plasma is measured by a VUV spectrometer with detection range down to λ = 115 nm. A gated photon-counting system is used to acquire time-resolved spectra. From LIBS measurements of certified polymer reference materials, we obtained a limit of detection (LOD) of 50 µg/g for sulphur and 215 µg/g for zinc, respectively. The VUV LIBS spectra of PE are dominated by strong emission lines of neutral and ionized carbon atoms. From time-resolved measurements of the carbon line intensities, we determine the temporal evolution of the electronic plasma temperature, Te. For this, we use Saha–Boltzmann plots with the electron density in the plasma, Ne, derived from the broadening of the hydrogen H-α line. With the parameters Te and Ne, we calculate the intensity ratio of the atomic sulphur and carbon lines at 180.7 nm and at 175.2 nm, respectively. The calculated intensity ratios are in good agreement with the experimentally measured results.

Time-resolved photography was employed to study plasma dynamics and particle ejection of laser-irradiated iron oxide materials. Nano-particle powder, pressed powder pellets and sintered ceramics were ablated in air and Ar gas background by means of short laser pulses (Nd:YAG laser wavelength λ = 1064 nm and pulse duration τ L ≈ 6 ns; KrF laser λ = 248 nm and τ L ≈ 20 ns). Plasma plume dynamics significantly depended on sample morphology. The ejection of non-luminous particles up to several hundreds of microseconds after the laser pulse was observed for powder and pressed powder target materials. Laser-induced breakdown spectroscopy (LIBS) was employed for element analysis of iron oxide powders, pressed pellets and sintered ceramics. LIBS spectra of the different targets were comparable to each other and qualitatively independent of target morphology.

Thin films of complex oxides have been obtained by pulsed-laser deposition (PLD) from glass targets belonging to the system Li 2 O–Al 2 O 3 –P 2 O 5 –(RE) 2 O 3 , with RE = Nd, Pr, Er. The films were deposited on quartz, silicon and ITO/glass substrates using a F 2 laser ( λ = 157 nm, ι ≈ 20 ns) for ablation in vacuum. The structural, morphological and optical properties of the oxide films were investigated through IR and UV–VIS spectroscopy, Atomic Force Microscopy (AFM), Scanning Electron Microscopy, Energy Dispersive X-ray Spectroscopy (SEM-EDX) and Spectroscopic Ellipsometry. The laser wavelength was found to be the key parameter to obtain thin films with very smooth surface. In this way new possibilities are opened to grow multilayer structures for photonic applications.

Multi-component oxide ceramics and epitaxial oxide thin films are analyzed by laser-induced breakdown spectroscopy (LIBS). Furthermore, pulsed-laser deposition (PLD) of thin films is investigated by long-term monitoring of the optical plasma emission. Both nano-composite high-temperature superconductors (HTS) consisting of YBa2Cu3O7 − δ bulk and Y2Ba4MCuOx (M-2411, M = Ag, Nb) nano-particles, and semiconducting ZnO doped with Aluminum and Lithium are ablated by nano-second laser pulses. The plasma emission is recorded using grating spectrometers with intensified gated detectors. The LIBS signals of nano-particles correlate with the nominal content of the M-2411 phase (0–15 mol%) and reveal a strong signal of Ytterbium impurity (3–35 ppm). In situ monitoring of the PLD process shows element signals that are stable for more than 10,000 laser pulses for both HTS and ZnO ceramics. The relative concentration of elements in thin films and ceramics as determined by LIBS is almost the same.