RBS analysis of ions implanted in light substrates exposed to hot plasmas laser-generated at PALS

Ge and Ta ion implantation of silicon and carbon substrates has been obtained at PALS Research Laboratory in Prague by using laser pulses of 400 ps duration, 438 nm wavelength, 10^14?16 W/cm² intensity. Substrates were exposed in vacuum at different distances from the target and at different angles with respect to the normal to the target surface. ‘On line’ measurements of ion energy were obtained with time-of-flight techniques by using an electrostatic deflector as ion energy analyzer. ‘Off line’ measurements of ion energy were obtained by Rutherford backscattering spectrometry (RBS) of 2.25 MeV He²⁺ beam at CEDAD Laboratory of Lecce University. The RBS spectra have given the depth profiles of the ion-implanted species and the implanted doses as a function of the laser intensity, angular position and target distance. A spectra deconvolution method based on the ion stopping power in the substrate matrix was applied in order to evidence the energy of the implanted ions. Measurements indicate that ions with energy ranging between 100 keV and 10 MeV and dose of the order of 10^14?16/cm² are implanted and that the process of ion implantation occurs mainly in substrates placed at little angles with respect to the normal to the target surface. Only a thin film deposition occurs for substrates placed at large angles with respect to the normal direction. Results indicate that the ion energies measured with the ‘on line’ and the ‘off line’ techniques are in good agreement.     

Comparative study on low energy ion beam modification of thermoplastic polymers

ABSTRACT

Polycarbonate (PC) and polyethylene terephthalate (PET) thermoplastic polymer films were irradiated by low energy ion beams such as 100 keV Hydrogen (H⁺) ions and 350 keV Nitrogen (N⁺) ions at varied fluence from 1?×?10¹³ ions/cm² to 5?×?10¹⁴ ions/cm². The depth profile concentration of ions was calculated using Stopping and Range of Ions in Matter (SRIM) software code. Fourier Transform Infrared (FTIR) technique shows decrement in the intensity of peaks and disappearance of peaks mainly related to carbonyl stretching at 1770?cm^?1 and C–C stretching at 1500?cm^?1. Scanning electron microscopy (SEM) of irradiated polymers showed the formation of pores. X-ray diffraction (XRD) analysis has showed decrease in the intensity indicating the decrease in crystallinity after irradiation. Mechanical studies revealed that the molecular weight and microhardness decrease with increase in ion fluence due to increase in chain scission. The contact angle increased with increase in ion fluence indicating the hydrophobic nature of polymer after irradiation. Antibiofilm activity test of irradiated films shows resistance to Salmonella typhi (S. typhi) pathogen responsible for typhoid. The study shows that Nitrogen ion induces more damage compared to Hydrogen ions and PC films get more modified than PET films.     

Synthesis and optical properties of silver nanoparticles in ORMOCER

Experimental results on synthesis of metal nanoparticles in ORMOCER by ion implantation are presented. Silver ions were implanted into organic/inorganic matrix at an accelerating energy of 30?keV and doses in the range of 0.25?10¹⁷ to 0.75?10¹⁷?ion/cm². The silver ions form metal nanoparticles, which demonstrate surface plasmon absorption at the wavelength of 425?C580?nm. The nonlinear absorption of new composite materials is measured by Z-scan technique using 150?fs laser pulses at 780?nm wavelength. ORMOCER matrix shows two-photon nonlinear absorption, whereas ORMOCER with silver nanoparticles demonstrates saturated absorption. Some optical applications of these composite materials are discussed.     

Experimental study and computer simulations of the implantation of laser plasma ions in pulsed electric fields

Results are presented from experimental studies of pulsed plasma flows generated by nanosecond laser pulses with an intensity of 7 × 10⁸ W/cm² from a solid-state target in a strong electric field. The current pulses through the laser target and the depth distributions of the iron ions implanted in a silicon substrate to which a negative high-voltage pulse was applied are measured. The physical processes occurring in laser plasma with an initial iron ion density of 6 × 10¹⁰ cm⁻³ are simulated numerically by the particle-in-cell method for different delay times and different shapes of the accelerating high-voltage pulse. The model developed allows one to calculate the ion flows onto the processed substrate, the electron flows onto the target, and the energy spectra of the implanted ions. The results from computer simulations are found to be in good agreement the experimental data.     

Retrieval of currents of multiply charged ions emitted from laser-produced carbon plasma

The emission of ions from laser-produced carbon plasmas is investigated by a deconvolution of ion collector signals. The deconvolution is based on the use of Kelly and Dreyfus function expressing the time-resolved ion current to recover hidden peaks in an ion collector signal. The parameters of recovered C ^q+ (1?≤?q?≤?6) currents make possible the quantification of properties of laser-produced plasmas. The drift and peak velocities of C ^q+ ions, the abundance of ions and the plasma temperature are presented in the dependence on focused laser beam energy. The carbon plasma was generated employing either single 9-ns pulses of second harmonics (532 nm) of Nd:YAG laser or pulses repeated at a stable repetition rate of 30 Hz.     

Dynamics of femtosecond laser-produced plasma ions

We investigated the ion laser-produced plasma plume generated during ultrafast laser ablation of copper and silicon targets in high vacuum. The ablation plasma was induced by ≈50 fs, 800 nm Ti:Sa laser pulses irradiating the target surface at an angle of 45°. An ion probe was used to investigate the time-of-flight profiles of the emitted ions in a laser fluence range from the ablation threshold up to ≈10 J/cm². The angular distribution of the ion flux and average velocity of the produced ions were studied by moving the ion probe on a circle around the ablation spot. The angular distribution of the ion flux is well described by an adiabatic and isentropic model of expansion of a plume produced by laser ablation of solid targets. The angular distribution of the ion flux narrows as the laser pulse fluence increases. Moreover, the ion average velocity reaches values of several tens of km/s, evidencing the presence of ions with kinetic energy of several hundred eV. Finally, the ion flux energy is confined in a narrow angular region around the target normal.     

Laser ablation loading of a radiofrequency ion trap

The production of ions via laser ablation for the loading of radiofrequency (RF) ion traps is investigated using a nitrogen laser with a maximum pulse energy of 0.17?mJ and a peak intensity of about 250?MW/cm². A?time-of-flight mass spectrometer is used to measure the ion yield and the distribution of the charge states. Singly charged ions of elements that are presently considered for the use in optical clocks or quantum logic applications could be produced from metallic samples at a rate of the order of magnitude 10⁵ ions per pulse. A linear Paul trap was loaded with Th⁺ ions produced by laser ablation. An overall ion production and trapping efficiency of 10^?7 to 10^?6 was attained. For ions injected individually, a dependence of the capture probability on the phase of the RF field has been predicted. In the experiment this was not observed, presumably because of collective effects within the ablation plume.     

Rutherford backscattering studies of surface density reduction in ion-implanted and excimer-laser-annealed Ge

Rutherford backscattering (RBS) with 17MeV ¹⁹F is used to obtain depth profiles of ion-implanted Ge both before and after pulsed excimer (XeCl) laser annealing. The as-implanted Ge samples show a reduction of at least a factor of two in the Ge density to a depth of ≈ > 0.3 /gmm, and dopant profiles of similar width following room-temperature implantations of In, Sb and Bi at 350 keV. The heavy ion projectile provides distinct kinematic advantages in the present work with a high mass substrate and deep dopant distributions. Annealing with several ≈ 15 nsec laser pulses (λ = 308 nm) restores the surface Ge density and produces epitaxial regrowth. For Sb implants the dopant incorporation exceeds the equilibrium solubility limit by a factor of 50.     

Observation of highly ionised species in plasma produced by picosecond laser pulses

Results are presented which show that in the case of the light elements highly ionised species can be detected in laser produced plasmas using a normal incidence spectrograph, the plasmas being formed by picosecond pulses from a high power Nd: glass laser. In particular hydrogenic ions of carbon, oxygen and fluorine have been observed when the incident laser flux density onto a solid target was about 3×10¹⁴W/cm².     

The near surface changes in boron implanted 4145 steel

Boron implanted 4145 steel was evaluated for changes in the near-surface region property such as microhardness. The surfaces when implanted with ¹¹B⁺ ions at 135 keV energy to a dose 1 × 10¹⁷ ions cm^?2 resulted in increase of microhardness for 10 to 40 gms of applied load. An increase upto 40% in microhardness could be observed in the specimen when annealed at 310δC for 3 hours. Furthermore, the effect of ion-beam induced intermixing of 250Å thin carbon film due to boron implantation was also studied for different doses ranging from 1 × 10¹⁷ to 3 × 10¹⁷ boron ions cm^?2. An increase in microhardness with applied load was observed for 1 × 10¹⁷ ions cm^?2 concentration, while hardest layer was formed at 3 × 10¹⁷ ions cm^?2 dose which practically had very little effect to 10 and 20 gms of load.     

Study of porous carbon thin films produced by pulsed laser deposition

Amorphous carbon is an interesting material and its properties can be varied by tuning its diamond-like (sp³) fractions. The diamond-like fractions in an amorphous carbon films depends on the kinetic energy of the deposited carbon ions. Porous amorphous carbon thin films were deposited onto silicon substrates at room temperature in a vacuum chamber by Glancing Angle Pulsed Laser Deposition (GAPLD). Krypton fluoride (248 nm) laser pulses with duration of 15 ns and intensities of 1-20 GW/cm² were used. In GAPLD, the angles between the substrate normal and the trajectory of the incident deposition flux are set to be almost 90°. Porous thin films consisting of carbon nanowires with diameters less than 100 nm were formed due to a self-shadowing effect. The kinetic energies of the deposited ions, the deposition rate of the films and the size of the nanowires were investigated. The sp³ fraction of the porous carbon films produced at intensity around 20 GW/cm² were estimated from their Raman spectra.     

Isotope-selective ionization utilizing molecular alignment and non-resonant multiphoton ionization

We demonstrate laser nitrogen isotope separation, which is based on field-free alignment and angular-dependent ionization of ¹⁴N₂ and ¹⁵N₂ isotopologues. A linearly polarized short laser pulse (???~?795?nm, ?????~?60?fs) creates rotational wave packets in the isotopologues, which periodically revive with different revival times as a result of different moments of inertia. Another linearly polarized short laser pulse (???~?795?nm, ?????~?60?fs) ionizes one of the isotopologues selectively as a result of their different angular distributions. In the present experiments, the ion yield ratio R [=I(¹⁵N₂ ⁺)/I(¹⁴N₂ ⁺)] can be changed in the range from 0.85 to 1.22, depending on the time delay between the two laser pulses.     

Investigation of energetic ion-induced mixing in Bi/Ge system

The present study is carried out for the investigation of energetic ion beam mixing in the Bi/Ge system, induced by electronic excitation. The system Ge/Bi/C was deposited on Si substrate at room temperature in the high vacuum deposition system and irradiated using Au ions of 120?MeV at the fluences 1?×?10¹³, 5?×?10¹³ and 1?×?10¹⁴?ions/cm². The top layer of carbon was deposited as the protecting layer to avoid oxidation. The swift heavy ions (SHI)-induced interface mixing was studied by Rutherford backscattering spectroscopy (RBS) for depth profiles and compositions, grazing incidence X-ray diffraction (GIXRD) for phase identification and atomic force microscopy (AFM) for surface roughness. We have calculated the mixing rate, mixing efficiency and inter-diffusion coefficient for the Bi/Ge system. We observed that the thickness of the mixed region increased with increasing fluence. In the GIXRD pattern, no new crystalline phase formation was observed after irradiation, the mixed region may be in an amorphous form. The mixing effect is explained in the framework of the thermal spike model.     

Control of cluster multielectron ionization in ultraintense laser fields

We performed classical molecular dynamics simulations to explore the controllability of the inner ionization process in Xe_n clusters (n = 2?2171), driven by ultraintense infrared Gaussian laser fields (peak intensity I _M = 10¹⁵?10¹⁸ W cm^?2, temporal pulse length τ = 10?100 fs, and frequency ν = 0.35 fs^?1). Controllability of ion charge abundances and of their spatial distributions inside the cluster emerges from the different pulse length dependences of classical barrier suppression ionization (BSI) and of electron impact ionizations (EII), as well as from the time scale of the Coulomb explosion (CE). For large clusters (Xe₂₁₇₁), low intensities (10¹⁵ W cm^?2), and long pulses (τ = 100 fs), EII is the dominating ionization channel, which favors the formation of maximum charged ions (Xe¹⁰⁺, Xe¹¹⁺) in the cluster center. In contrast, BSI forms an inverse radial charge ordering with the highest charges in the exterior cluster shells. This suggests that the production of the two inverse radial charge distributions with an equal average ion charge can be forced by the choice of multiple pulses with different intensities and pulse lengths. At high intensities (10¹⁷?10¹⁸ W cm^?2), where EII is insignificant and CE sets in much earlier, the BSI radial charge ordering and the enhancement of the ion charges beyond the single-atom limit by the ignition effect is observed only for short pulses.     

Tungsten ions produced by infrared pulsed laser irradiation

Energetic ions have been obtained irradiating a tungsten target with a Q-switched Nd:Yag laser, 1064?nm wavelength, 9?ns pulse width, 900?mJ maximum pulse energy and power density of the order of 10¹⁰?W/cm². The laser-target interaction induces a strong metal etching with production of plasma in front of the target. The plasma contains neutrals and ions with high charge state. Time-of-flight measurements are presented for qualitative analysis of the ion production. A cylindrical electrostatic ion analyzer permits measuring of the yield of emitted ions, the charge state of detected ions and the ion energy distribution. Measurements indicate that, at a laser fluence of the order of 100?J/cm², the charge state may reach 9+ and the ion energy reaches about 5?keV. The ion energy distribution is given as a function of the charge state. Experimental results indicate that an electrical field is developed along the normal to the plane of the target surface, which accelerates the ions up to high velocity. The ion velocity distributions follow a “shifted Maxwellian distribution”, which the author has corrected for the Coulomb interactions occurring inside the plasma.     

The correlation of XPS analysis with electrochemical history in aqueous corrosion

The response of the surface composition of aluminium brass to electrochemical polarization is sea water has been studied by XPS in an attempt to elucidate the behaviour of condenser tube surfaces in marine environments. Individual specimens were polarized at 100 mV intervals between +100 and ?1200 mV (SHE) for a charge transfer of 500 mA s. The rather complex spectra were normalised using Jorgenson's factors to permit meaningful discussion of the surface chemistry. In addition an ion etching was used to remove the high surface coverage of carbon molecules picked up from solution. The validity of each of these techniques, necessary for examination of samples removed from the aqueous phase, is discussed. In the present case they permit the observation of a strong correlation between the Mg⁺⁺/Cl^? ratio and the surface potential. The movement of the ratio gives a nice demonstration of cathodic basicity and anodic acidity in accord with electrochemical concepts. This result may be of practical use in ascertaining whether corrosion pits on industrial plant are still active.     

Radiation effects and pulsed laser deposition of titanium by Nd:Yag laser

A study of Ti laser irradiation and thin film deposition produced by an Nd:Yag pulsed laser is presented. The laser pulse, 9?ns width, has a power density of the order of 10¹⁰?W/cm². The titanium etching rate is of the order of 1?µg/pulse, it increases with the laser fluence and shows a threshold value at about 30?J/cm² laser fluence. The angular distribution of ejected atoms (neutrals and ions) is peaked along the normal of the target surface. At high fluence, the fractional ionization of the plasma produced by the laser is of the order of 10%. Time-of-flight measurements demonstrate that the titanium ions, at high laser fluence, may reach kinetic energies of about 1?keV. Obtained results can be employed to produce energetic titanium ions, to produce coverage of thin films of titanium and to realize high adherent titanium-substrate interfaces. The obtained results can be employed to produce energetic titanium ions, to produce a coverage of thin titanium films on polymers, and to realize highly adherent titanium–substrate interfaces.     

Application of snow nanograin targets for the generation of fast ions in femtosecond laser plasma

We have measured the energy of the directed motion of multiply charged ions produced when solid targets are exposed to low-contrast (10^?3–10^?2) femtosecond laser pulses with intensities 10¹⁵–10¹⁶ W cm^?2. The measurements are based on the recording of spatially resolved X-ray spectra for H-and He-like oxygen ions in the target plane. Analysis of the He_β and Ly_α line profiles has revealed fractions of accelerated ions in plasma with energies from several to several tens of kiloelectronvolts. We show that using a layer of frozen nanometer-size water droplets as the targets leads to an effective absorption of laser pulses and a twofold rise in the energy (to 0.1 MeV) of He-like oxygen ions compared to the use of solid targets.     

Gas mixture effects on ion‐beam flux characteristics from dense plasma focus device: Investigation by the Vlasov–Maxwell equations and experiments

The Vlasov–Maxwell equations were numerically solved to calculate the ion‐beam flux from the plasma of argon and the plasma of mixtures of argon and neon. Some experiments were performed to measure the ion beam from the Amirkabir plasma focus (APF) device. The calculations have shown that the argon ion‐beam flux peaked up to 1.928 × 10³⁰ ions m^?2 s^?1 at the optimum pressure of 1.866 mbar while the neon‐argon mixture's ion‐beam flux reached a maximum of 4.301 × 10³⁰ ions m^?2 s^?1 for 15% neon admixture at the optimum pressure of 1.866 mbar. The calculated kinetic energy of the ion beam has shown a maximum value of 708.7 J for the mixture of 85% argon‐15% neon at the mentioned optimum pressure.     

Non-equilibrium plasma production by pulsed laser ablation of gold

A gold target has been irradiated with a Q-switched Nd:Yag laser having 1064?nm wavelength, 9?ns pulse width, 900?mJ maximum pulse energy and a maximum power density of the order of 10¹⁰?W/cm². The laser–target interaction produces a strong gold etching with production of a plasma in front of the target. The plasma contains neutrals and ions having a high charge state. Time-of-flight (TOF) measurements are presented for the analysis of the ion production and ion velocity. A cylindrical electrostatic deflection ion analyzer permits measurement of the yield of the emitted ions, their charge state and their ion energy distribution. Measurements indicate that the ion charge state reaches 6⁺ and 10⁺ at a laser fluence of 100?J/cm² and 160?J/cm², respectively. The maximum ion energy reaches about 2?keV and 8?keV at these low and high laser fluences, respectively. Experimental ion energy distributions are given as a function of the ion charge state. Obtained results indicate that electrical fields, produced in the plume, along the normal to the plane of the target surface, exist in the unstable plasma. The electrical fields induce ion acceleration away from the target with a final velocity dependent on the ion charge state. The ion velocity distributions follow a “shifted Maxwellian distribution”, which the authors have corrected for the Coulomb interactions occurring inside the plasma.