Wide Range Of Fluences Research Articles

Strain propagation in nanolayered perovskites probed by ultrafast x-ray diffraction

Strain propagation in a perovskite heterostructure grown on a ${\mathrm{SrTiO}}_{3}$ (STO) substrate is studied by ultrafast x-ray diffraction. Femtosecond displacive phonon excitation in a ${\mathrm{PbZr}}_{0.2}{\mathrm{Ti}}_{0.8}{\mathrm{O}}_{3}∕{\mathrm{SrRuO}}_{3}$ (PZT/SRO) film launches acoustic strain waves propagating into the STO substrate. We demonstrate a two-step time evolution of diffracted x-ray intensity which originates from different interfering contributions to the (004) Bragg peak of the STO substrate. Analysis by dynamical x-ray diffraction theory gives the absolute strain $\mathrm{\ensuremath{\Delta}}a∕{a}_{0}$ in a wide range of optical pump fluences. Ultrafast transient strain as small as $\mathrm{\ensuremath{\Delta}}a∕{a}_{0}=2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}$ is determined in this way.

Barrier height modification of Au/n-Si Schottky structures by swift heavy ion irradiation

Influence of 120 MeV 107Ag 7+ ion irradiation on current–voltage ( I– V) characteristics of Au/n-Si(1 0 0) Schottky diodes as a function of fluence is investigated. The irradiation fluence was varied from 5 × 10 10 to 1 × 10 13 ions cm −2. By systematically varying the ion fluence we can control the variations in various parameters of the Schottky diodes. The ideality factor increases from a value 1.1 to 1.3 with increasing fluence upto 5 × 10 11 ions cm −2. After this as fluence increases to 5 × 10 12 ions cm −2, ideality factor becomes 1.28. The Schottky barrier height (SBH) decreases from a value of 0.82 eV for the unirradiated diode to 0.72 eV for the diode irradiated with a fluence of 5 × 10 10 ions cm −2. After this SBH increases to a value 0.77 eV and then remain constant upto a fluence 1 × 10 13 ions cm −2. The basic energy loss mechanism of swift heavy ion (SHI) at the metal–semiconductor (MS) interface is used to explain the change in Schottky diode parameters. After an initial fluence of 5 × 10 10 ions cm −2, the role of electronic energy loss in modification of interface states has been envisaged in relation to the immunity of SBH over a wide fluence range.

Efficiency of silicon micromachining by femtosecond laser pulses in ambient air

Femtosecond lasers have proven to be effective tools for precise micromachining. Taking advantage of the reduced heat diffusion and the sharp ablation threshold at comparatively low energy densities, subdiffraction limit sized craters have been machined on silicon wafers by single near infrared Ti:sapphire laser pulses using a high numerical aperture objective lens. Two different ablation regimes have been identified by varying the laser fluence. While two-photon absorption dominates in the low fluence regime, electronic diffusion is a major energy transport mechanism at higher laser fluences. Time-resolved pump-and-probe side-view imaging has been performed to investigate the energy coupling to the target specimen over a wide range of fluences (up to around 1000J∕cm2) at lateral beam dimensions of the order of micrometers. The decrease of the ablation efficiency in the high fluence regime (>10J∕cm2) is attributed to the strong interaction of the laser pulse with the laser-induced plasma.

Stability and luminescence studies of Tm and Er implanted ZnO single crystals

Zinc oxide single crystals were implanted with Tm and Er ions in a wide range of fluences. For both types of ions RBS/channeling shows for the as-implanted state the same minimum yield as for the host. Damage recovery becomes significant for annealing above 750°C and is almost complete at 1050°C. Implantation damage decreases for implantations at mild temperatures (450°C) and is also highly reduced for 〈0001〉 aligned implantations: under this condition the measured minimum yield is about one order of magnitude lower compared to the random implantations. The RE ions start to diffuse towards the surface above 900°C and about 80% of them have segregate to the surface after 90min annealing at 1050°C. A small fraction of the ions retained in the implanted region is located in regular lattice sites. In the as-implanted state the optical activity of the RE ions is highly quenched by the implantation defects. For all the RE studied, diffusion to the surface destroys the luminescence. Photoluminescence (PL) studies for Er implantations reveal in the as-implanted and annealed samples the presence of a weak emission near 1.54μm due the 4I13/2→4I15/2 transition of the Er3+ ions.

Analysis of the accuracy of several methods for determining the concentration of 11B+ implanted silicon

The concentration of 11B+ in silicon has been determined by a number of different analytical techniques. Several commercial vendors provided silicon wafers implanted with 11B+ ions over a wide range of fluence (4×1013– 3×101611B/cm2) and energy (300eV–10keV) for evaluation. The techniques used in this evaluation included the following: Elastic recoil detection (ERD) using 12MeV F4+ ions, nuclear reaction analysis (NRA) using the 11B(p,α)8Be* reaction and secondary ion mass spectroscopy (SIMS). The accuracy and potential drawbacks of each of these techniques is discussed.

Electron paramagnetic resonance characterization of defects produced by ion implantationinto silicon

Many of the defects created by ion implantation into silicon can be detectedby electron paramagnetic resonance (EPR). The main defects observed areisolated point defects such as Si-P3 centres (neutral 4-vacancies), silicondangling bonds in amorphous silicon and defects associated with the so-calledΣ resonance—a single broad anisotropic line; particular attention is paid to the latter defectsas they have the highest population over a wide fluence range. This paper reports theeffects on the nature and population of these defects of changing the fluence, mass andenergy of the implanted ions as well as the effects of changing the implantationtemperature.

Dependence of the structural relaxation of amorphous silicon on implantation temperature

The structural relaxation of amorphous silicon, created by ion implantation, was investigated by in situ differential scanning nanocalorimetry. Nanocalorimetry provided the possibility to measure the heat released by relaxation during annealing, for a wide range of implantation fluences and beginning at cryogenic temperatures. Ion implantation was first carried out for fluences between ${10}^{\ensuremath{-}5}$ and 0.8 displacements per atom (DPA) at 133 K and 297 K, and then for temperatures ranging from 118 K to 463 K for fluences of 0.0185 and 0.37 DPA. A heat release saturation occurred above 0.1 DPA, and was found to depend on implantation temperature. The saturation level was extrapolated to 0 K, leading to an estimate of $28\ifmmode\pm\else\textpm\fi{}3\phantom{\rule{0.3em}{0ex}}\mathrm{kJ}∕\mathrm{mol}$ for the maximum enthalpy that can be stored in $a\text{\ensuremath{-}}\mathrm{Si}$, relative to crystalline Si.

Polymer jacket stripping of optical fibres by laser irradiation

Laser jacket stripping of the two-layer polymer jacket coating of Corning SMF-28 silica fibres has been studied as an alternative approach to chemical and mechanical techniques. These polymer outer layers, although chemically similar, become discernable through laser ablation and depth per pulse experiments. Etch rate measurements using nanosecond UV excimer laser sources (F2, ArF, KrF and XeCl lasers) reveal that, as expected, the threshold fluence (energy per unit area) for significant material removal drops as the laser wavelength becomes shorter. For some wavelengths and fluences, spontaneous cone formation has been observed, thus providing additional threshold data through apex angle determination. The possible occurrence of deleterious damage to the silica cladding has been assessed using electron microscopy and optical transmission measurements. A wide fluence range over which damage was not observed characterised all the interactions. Irradiation techniques for producing apertures in the polymer coating or complete jacket removal are demonstrated and discussed. Briefly, polymer jacket stripping using a femtosecond laser source (800 nm) has been demonstrated.

Energy balance of pulsed laser ablation: thermal model revised

We present the results of modeling of nanosecond laser ablation of graphite, niobium, YBa2Cu3O7 superconductor, and silicon performed on the basis of a modified thermal model which includes a thorough calculation of the solid–melt interface. The model is based on experimental data on mass removal and takes into account plasma absorption. The numerical results of the laser energy balance are presented over a wide range of laser fluences. The probable critical temperatures for the materials studied have been estimated on the basis of the modeling.

Comprehensive device Simulation modeling of heavily irradiated silicon detectors at cryogenic temperatures

Radiation hardness is a critical design concern for present and future silicon detectors in high energy physics. Tracking systems at the CERN Large Hadron Collider (LHC) are expected to operate for ten years and to receive fast hadron fluences equivalent to 10/sup 15/cm/sup -2/ 1-MeV neutrons. Recently, low temperature operating conditions have been suggested as a means of suppressing the negative effects of radiation damage on detector charge collection properties. To investigate this effect, simulations have been carried out using the ISE-TCAD DESSIS device simulator. The so-called "three-level model" has been used. A comprehensive analysis of the influence of the V/sub 2/, C/sub i/O/sub i/ and V/sub 2/O capture cross sections on the effective doping concentration (N/sub eff/) as a function of temperature and fluence has been carried out. The capture cross sections have been varied in the range 10/sup -18/-10/sup -12/ cm/sup 2/. The simulated results are compared with charge collection spectra obtained with 1064-nm laser pulses on devices irradiated with 23-GeV protons as a function of detector bias voltage. To validate the model, a wide range of temperature and fluence has been studied using a one-dimensional (1-D) simplified structure. Thousands of simulation results have been cross checked with the experimental data. The data between 190 K (the lower limit for simulations due to computational difficulties) and 290 K are well reproduced for all of the fluences considered. We conclude that the three-level model can be successfully used to predict irradiated detector behavior down to a temperature of at least 190 K.

Comparative analysis of the implantation-induced structural modifications in GaAs and Ge

Raman spectroscopy was used to analyze disorder evolution, crystalline to amorphous phase transformations as well as modifications of amorphous phase beyond the amorphous threshold in representative compound and elemental tetrahedral semiconductors when implanted in a very wide range of ion fluences (1 × 10 12–3 × 10 16/cm −1). The particular goal of this study was to separate the effects of the microstructural modifications due to the implantation-induced damage from the effects arising from the incorporation of foreign species into the lattice, which was expected to be important when dealing with very high doses. We have studied monocrystalline GaAs-implanted with Si ions, GaAs samples implanted with equal doses of Ga and As ions to preserve stoichiometry, and Ge samples implanted with Ge ions in the same range of doses. It was found that the evolution of morphology with implantation is very similar in every aspect for both types of GaAs samples, either Si-implanted or Ga + As-implanted. This implies that energy deposition by energetic ions strongly predominates in the process of damage accumulation, making it much more important than the possible influence of chemical effects.

Time-resolved laser-induced incandescence of soot: the influence of experimental factors and microphysical mechanisms.

We present a data set for testing models of time-resolved laser-induced incandescence of soot. Measurements were made in a laminar ethene diffusion flame over a wide range of laser fluences at 532 nm. The laser was seeded to provide a smooth temporal profile, and the beam was spatially filtered and imaged into the flame to provide a homogeneous spatial profile. The particle incandescence was imaged onto a fast photodiode. The measurements are compared with the standard Melton model [Appl. Opt. 23,2201 (1984)] and with a new model that incorporates physical mechanisms not included in the Melton model.

The damage process induced by swift heavy ion in polycarbonate

To describe the damage process of polymer in the energetic heavy ion tracks by thermal spike model, polycarbonate (PC, Makrofol KG) foil stacks were irradiated with various swift heavy ions (1.158 GeV Fe 56, 1.755 GeV Xe 136 and 2.636 GeV U 238) in a very wide electronic stopping power range (from 1.9 to 17.1 keV/nm) and fluence range from 1 × 10 10 to 3 × 10 12 ions/cm 2. The amorphous processes and chemical degradation in the irradiated PC were studied by X-ray diffraction and Fourier transform infrared spectroscopy measurements. By applying the saturated track model, the mean damage radii of tracks of the amorphous and alkyne formation process were obtained for Fe, Xe and U ion irradiation, respectively. The results were validated by the thermal spike model. The analysis of the irradiated PC films shows that the predictions of the thermal spike model of Szenes are basically in quantitative agreement with the experimental results.

Understanding and predicting the temporal response of laser-induced incandescence from carbonaceous particles

This paper describes a model for analyzing and predicting the temporal behavior of laser-induced incandescence (LII) from combustion-generated soot, carbon black, and other carbonaceous particles on a nanosecond time scale. The model accounts for particle heating by absorption of light from a pulsed laser and cooling by sublimation, conduction, and radiation. The model also includes mechanisms for oxidation, melting, and annealing of the particles and nonthermal photodesorption of carbon clusters from the particle surface. At fluences above 0.1 J/cm2, particle temperatures during the laser pulse are determined by the balance between absorption and sublimation, whereas at lower fluences particle temperatures do not reach the sublimation temperature, and temperatures are predominantly controlled by absorption and conduction. After the laser pulse, temperatures are predominantly controlled by conductive cooling rates. Oxidative heating may compete with conductive cooling on these time scales. Annealing of the particles to a more ordered phase of carbon is predicted to occur at fluences as low as 0.02 J/cm2. Annealing may strongly influence sublimation rates, and changes in emissivity during annealing are predicted to increase signal decay rates. Supersonic expansion of the carbon clusters sublimed from the surface is calculated to occur at fluences above 0.12 J/cm2. When compared with LII measurements recorded in a flame at atmospheric pressure, the model reproduces the shapes and relative magnitudes of LII temporal profiles over a wide range of laser fluences. Comparisons between model predictions and experimental observations suggest that the particles do not melt at laser fluences that lead to melting of bulk graphite. These comparisons also indicate that the energy released during particle annealing is much smaller than that released during annealing of neutron- or electron-irradiated graphite. Despite good agreement between model and experimental results, large uncertainties exist for input parameters used to calculate annealing rates and rates of oxidation, conduction, absorption, emission, and photolytic desorption of carbon clusters for both the initial and annealed particles.

Dependence of the Silica Glass Parameters on the Fluence of Fast Neutrons

The results of comprehensive investigations into the influence of fast-neutron fluences on the silica glass parameters are presented. In particular, the dose dependences of the parameters are measured by optical (luminescence, absorption, EPR, IR, and refraction), dielectric, and x-ray spectroscopy methods over a wide range of fluences from 1017 to 1021 cm–2. It is concluded that the specific features in the formation of radiation-induced defects and silica damages are most likely due to the neutron-induced phase transition.

Effect of the Dose of Irradiation by Fast Neutrons on the Optical Properties of Vitreous Silicon Dioxide

The influence of neutron irradiation on some parameters of vitreous silicon dioxide was investigated by optical, dielectric, and x-ray spectroscopy. The laws governing the change in the spectral characteristics, structure parameters, polarizability, and refractive index of vitreous silicon dioxide in a wide range of fluences of fast neutrons are determined. It is assumed that the revealed species of the corresponding dose dependences of some characteristics are caused by the radiation-stimulated change in the structure of the substance. The effect of large doses is considered.

Fluorescence spectra of Rhodamine 6G for high fluence excitation laser radiation

Fluorescence spectral changes of Rhodamine 6G in ethanol and glycerol solutions and deposited as a film on a silica surface have been studied using a wide range of pumping field fluence at 532 nm at room temperature. Blue shift of the fluorescence spectra and fluorescence quenching of the dye molecule in solution are observed at high excitation fluence values. Such effects are not reported for the film sample. The effects are interpreted as the result of population redistribution in the solute–solvent molecular system induced by the high fluence field and the fluence dependence of the radiationless decay mechanism.

Non-linear effect of gold cluster ion induced damage in silicon

We observed as much as 50% more damage for Au-cluster ion implantation in Si as compared with that of the Au monomer in the energy range of 6 keV/atom. This is contrary to the literature where the linear damage result was reported. In this experiment, small gold clusters Au n with n from 1 to 4 were used. Energy of 6 keV per Au atom was applied to bombard the Si single-crystal surface. The radiation damage was characterized by Rutherford backscattering spectrometry/channeling in the number of Si atom displacements per Au atom. We have also studied this non-linear effect in a wide range of fluences from 8×10 12 to 1.2×10 15 Au-atoms/cm 2 and observed a fluence-dependent effect. At higher fluence, sputtering and overlapping of the damage will reduce the damage efficiency, therefore reducing the non-linear effect. This could be the reason that earlier publication did not observe the non-linear effect.

Ion beam induced changes in electrical resistivity of polymer films: the case of unplasticized poly(vinyl chloride)

Electrical resistivity of the unplasticized poly(vinyl chloride) copolymer (UPVC) films irradiated with high-energy proton beams was studied with reference to a control sample, as a function of both ion energy and ion dose. Upon irradiation with beam energy ranging from 25 up to 37 MeV and at a beam fluence of 0.225×1010 ion cm-2, the room-temperature resistivity of the insulating films decreased by four orders of magnitude from its original value. Furthermore, using 25 MeV proton beams over a wide range of fluence (1011-1015 cm-2), the room-temperature resistivity of the films decreased by only three orders.Then, the dependence of the resistivity ρ(T) on the ion energy and fluence was also observed as the temperature T was progressively increased up to 373 K. The observed behaviour of ρ(T) agrees with the charge transport model, consistent with a hopping mechanism in the polymer. In addition, the changes in the ac electrical resistivity of the irradiated UPVC films have been measured within the temperature range (293-373 K) and at different frequencies (100 kHz-3 MHz).

Investigation of the Periodic Microstructure Inducedby a 355 nm UV Polarized Laser on a Polyimide Surface

We investigate a periodic microstructure induced by a 355 nm ultravioletpolarized laser on a polyimide surface and the dependence of the structures onlaser parameters. Laser-induced periodic surface structures (LIPSS) ofsub-micrometre size were generated on three kinds of polyimide films by apolarized Nd:YAG laser of 355 nm within a wide range of laser fluence. Thechemical structure of the polyimide, the film-making process, the number of laserpulses and the laser fluence greatly influenced the formation of LIPSS. Theperiodicity of LIPSS was decided by the wavelength, the incidence angle ofthe laser beam and the apparent refractive index of the material.