Electrons emission from laser induced metallic plasmas

Localized behavior of laser induced metallic plasmas has been investigated using Langmuir probe as an electrostatic diagnostic tool. A Q-switched Nd:YAG pulsed laser (1064 nm, 12 ns, 1.1 MW) is tightly focused on metal targets (Cu, Zn, Cd, Ag, Pt and Au) having dimensions 2 × 2 × 0.2 cm³ under vacuum ∼10⁻³ torr. The varying biasing voltages are applied to Langmuir probe. The electric signals are recorded on two channel 200 MHz digital storage oscilloscope (UNI T - UTT 2202). A comparison shows strong dependence of electron parameters (temperature, density, Debye length, plasma frequency and number of particles in Debye sphere) in plasmas on target materials' properties (atomic number, surface binding energy etc.). The maximum values for electron density (8.08502 × 10¹⁷ m⁻³), Debye length (8.07066 × 10⁻⁴ m), plasma frequency (5.19627 × 10¹⁰ Hz) are found for silver and copper metals, respectively, where as the electron temperature shows variation in this trend i.e. maximum value (1.36581 × 10⁶ K) for cadmium and minimum value is for gold (1.0008 × 10⁵ K). the maximum value of number of particles in Debye length at +15 V (1.47 × 10²⁶) for Pt and that minimum for Ag (2.1355 × 10⁷).     

Role of transverse magnetic field in the capacitive discharge

The influence of magnetic field on the plasma which is one of the oldest problems in plasma physics and remains of great interest in plasma fusion studies, recently has been an important problem in many plasma discharge used in processing semiconductor materials, because the application of a magnetic field results in enhancement of some desirable features of specific plasma sources. In this paper, the transverse magnetic field effects on the radio frequency capacitive discharge of low and intermediate gas pressure (1.33 Pa∼40.00 Pa) are reviewed to clarify the role of the magnetic field in the capacitive discharge. Lots of physical phenomena induced by transverse magnetic field, such as power dissipation mode transition, low energy electron heating/cooling, axial variation of electron density and temperature and E × B drift are presented and analyzed. This article is expected to provide qualitative insight to understand the role of magnetic field in the capacitive discharges.     

Catalytic oxidation of carbon monoxide over radiolytically prepared Pt nanoparticles supported on glass

Platinum nanoparticles have been prepared by radiolytic and chemical methods in the presence of stabilizer gelatin and SiO₂ nanoparticles. The formation of Pt nanoparticles was confirmed using UV-vis absorption spectroscopy and transmission electron microscopy (TEM). The prepared particles were coated on the inner walls of the tubular pyrex reactor and tested for their catalytic activity for oxidation of CO. It was observed that Pt nanoparticles prepared in the presence of a stabilizer (gelatin) showed a higher tendency to adhere to the inner walls of the pyrex reactor as compared to that prepared in the presence of silica nanoparticles. The catalyst was found to be active at ≥150 °C giving CO₂. Chemically reduced Pt nanoparticles stabilized on silica nanoparticles gave ∼7% CO conversion per hour. However, radiolytically prepared Pt nanoparticles stabilized by gelatin gave ∼10% conversion per hour. Catalytic activity of radiolytically prepared platinum catalyst, coated on the inner walls of the reactor, was evaluated as a function of CO concentration and reaction temperature. The rate of reaction increased with increase in reaction temperature and the activation energy for the reaction was found to be ∼108.8 kJ mol⁻¹. The rate of CO₂ formation was almost constant (∼1.5 × 10⁻⁴ mol dm⁻³ h⁻¹) at constant O₂ concentration (6.5 × 10⁻³ mol dm⁻³) with increase in CO concentration from 2 × 10⁻⁴ mol dm⁻³ to 3.25 × 10⁻³ mol dm⁻³. The data indicate that catalytic oxidation of CO takes place by Eley-Rideal mechanism.     

Characteristics of monopole antenna plasmas for TEOS PECVD

Silicon dioxide film was deposited on Si substrate by plasma-enhanced chemical vapor deposition using a monopole antenna plasma source. Electron density was measured by a plasma absorption probe with and without a grounded plate close to monopole antennas. A high electron density was obtained with the grounded plate. The typical electron density of the monopole antenna plasma source was ∼ 3 × 10¹⁰ cm^− 3 at a position of 13 mm away from the antenna in oxygen plasma. The electron density rapidly decreased along the distance from the monopole antenna. Since the deposition rate and breakdown field were improved with the higher electron density, the grounded plate improved the performance of the SiO₂ film deposition.     

Unique properties of polyaniline in the presence of applied magnetic field and ferric chloride

Fe-contained polyaniline (abbreviated as PANI–Fe) was prepared by chemical oxidation of aniline with ammonium peroxydisulfate oxidant in 0.5 mol dm⁻³ HCl and an adequate content of FeCl₃·6H₂O solution in the presence of an applied magnetic field at room temperature. The X-ray photoelectron spectroscopy (XPS) and UV–vis and FTIR spectra suggest that there is an interaction between FeCl₃ and PANI chains, but PANI–Fe backbone is essentially identical with that of parent polyaniline. The electron paramagnetic resonance (EPR) spectrum shows that there were unpaired electrons in PANI–Fe synthesized in the presence of an applied magnetic field, the spin density and the conductivity of which are 7.308 × 10²⁰ spins g⁻¹ and 0.891 S cm⁻¹, respectively. The plot of magnetization (M) vs. the applied magnetic field (H) displays that the PANI–Fe possesses soft ferromagnetic behavior at room temperature. The results of cyclic voltammogram show that the PANI–Fe film is of excellent electrochemical activity.     

Plasma and antenna characteristics of a linearly extended inductively coupled plasma system using multi-polar magnetic field

A novel internal-type linear inductive antenna, referred to as a “double comb-type antenna”, was used as a large-area plasma source with a substrate area of 880 mm × 660 mm. This study investigated the effect of a multi-polar magnetic field on plasma confinement. High density plasma in the order of 3.2 × 10¹¹ cm^− 3, which is 50% higher than that obtained for a source without a magnetic field, with good plasma stability was obtained at a pressure of 15 mTorr Ar and an RF power of 5000 W. Plasma uniformity < 3% within the substrate area was also obtained.     

Effect of post-deposition annealing on phase formation and properties of RF magnetron sputtered PLZT thin films

In this work, we report the preparation of lanthanum-modified lead zirconate titanate (PLZT) thin films by RF magnetron sputtering on platinized silicon (Pt/Ti/SiO₂/Si) substrate. Sputtering was done in pure argon at 100 W RF power without external substrate heating. X-ray diffraction studies were performed on the films to study the effect of post-deposition furnace annealing temperature and time on the perovskite phase formation of PLZT. Annealing at 650 °C for 2 h was found to be optimum for the preparation of PLZT films in pure perovskite phase. The effect of different annealing conditions on surface morphology of the films was examined using AFM. The dielectric, ferroelectric and electrical properties of these films were also investigated in detail as a function of different annealing conditions. The pure perovskite film exhibits better properties than the other films which have some fraction of unwanted pyrochlore phase. The remanent polarization for pure perovskite film was found to be ∼29 μC/cm² which is almost double compared to the films having mixed phases. The dc resistivity of the pure perovskite film was found to be 7.7 × 10¹⁰ Ω cm at the electric field of ∼80 kV/cm.     

Room temperature deposited vanadium oxide thin films for uncooled infrared detectors

We demonstrate the room temperature deposition of vanadium oxide thin films by pulsed laser deposition (PLD) technique for application as the thermal sensing layer in uncooled infrared (IR) detectors. The films exhibit temperature coefficient of resistance (TCR) of 2.8%/K implies promising application in uncooled IR detectors. A 2-D array of 10-element test microbolometer is fabricated without thermal isolation structure. The IR response of the microbolometer is measured in the spectral range 8-13 μm. The detectivity and the responsivity are determined as ∼6×10⁵ cm Hz^1/2/W and 36 V/W, respectively, at 10 Hz of the chopper frequency with 50 μA bias current for a thermal conductance G∼10-3 W/K between the thermal sensing layer and the substrate. By extrapolating with the data of a typical thermally isolated microbolometer (G∼10⁻⁷ W/K), the projected responsivity is found to be around 10⁴ V/W, which well compares with the reported values.     

Field emission studies of Te nanorods grown on Si (111) substrate

Tellurium nanorods were grown on silicon (111) substrates by thermal evaporation. The synthesized Te nanorods were characterized by scanning electron microscope (SEM) and transmission electron microscope (TEM), prior to the field emission investigations. The TEM image revealed that the nanorods are needle-like having diameter less than 20 nm and length in the range of 200-400 nm. The selected area electron diffraction (SAED) pattern and high resolution TEM micrographs clearly reveal the crystalline nature of the Te nanorods. The field emission studies were carried out in a planar diode (close proximity) configuration at background pressure of ∼1 × 10⁻⁹ mbar. An emission current density of ∼8.5 μA/cm² has been drawn at an applied field of ∼3.2 V/μm. The Folwer-Nodhiem plot, showed a non-linear behaviour. The high value of field enhancement factor (β ∼ 1 × 10⁴), estimated from the slope of the F-N plot, suggests that the emission is indeed from the nanometric tips of the Te nanorods. The emission current stability studied at the preset value ∼3.5 μA over duration of more than 3 h is found to be very good, suggesting the use of Te nanorods as promising electron source for field emission based micro/nano-electronic devices.     

Field emission from oriented tin oxide rods

Tin oxide (SnO₂) films were grown on silicon substrates by a wet chemical route. It was found from scanning electron microscopy investigations that oriented SnO₂ rods normal to the substrates were obtained. Field emission studies were carried out in diode configuration in an all metal ultra high vacuum chamber at a base pressure ∼ 1.33 × 10^− 8 mbar. The ‘onset’ field required to draw 0.1 μA/cm² current density from the emitter cathode was found to be ∼ 3.4 V/μm for SnO₂ rods. The field emission current and applied field follows the Folwer-Nordheim relationship in low field regime. The observed results indicate that the field emission characteristics of chemically grown SnO₂ structures are comparable to the vapor grown nanostructures.     

O density measurements in the pulsed-DC reactive magnetron sputtering of titanium

Using eclipse laser photo-detachment in conjunction with Langmuir probing, the density of O⁻ ions in a reactive pulsed magnetron (100 kHz, 55% duty) plasma has been determined at different times during the pulse period at a set of positions along the centre line axis of the discharge. The magnetron was operated at a fixed average power of 400 W with an oxygen partial pressure of 10% of the total pressure 1.33 Pa. The results show the plasma is weakly electro-negative, with a negative ion-to-electron density ratio α up to a maximum of 0.63.During the plasma on-phase (at all chosen measurement positions) the O⁻ density was found to reach a maximum directly after initiation of the voltage pulse decreasing weakly during the rest of the on-phase. On the transition from on-to-off phases of the pulse the negative ion density was found to fall (by 60% both close and far from the target but only 10% near the discharge centre), with the O⁻ density remaining almost constant during the rest of the afterglow.The spatial structure of the O⁻ density reveals a distinct peak 75 mm from the target close to but not at the position of the null in the magnetic field, falling by a factor of eight for increasing distances up to 30 mm both towards and away from the target. The highest O⁻ density recorded at this position was 1 × 10¹⁶ m⁻³, at a time of 2.12 μs into the pulse. From a comparison between on- and off-phase densities and using an intuitive model of the plasma, the results indicate that most negative ions are created in the bulk plasma. The density of target-borne O⁻ ions is estimated to be about 1 × 10¹⁵ m⁻³ varying little with position, possibly forming a beam-like structure.     

High current, high energy proton beams accelerated by a sub-nanosecond laser

The sub-nanosecond laser system available at PALS facility in Prague has been used in order to produce MeV proton beams with typical current density approaching 1 A/cm² at few tens of centimeters from the target surface. In spite of the relatively long pulse duration (0.3 ns) and low intensity (∼10¹⁶ W/cm²), far away from the forefront laser facilities used for advanced proton beam acceleration in the recent years (from tens of femtoseconds to few picoseconds), the obtained results are promising both in terms of maximum proton energy and fast proton current. Real-time diagnostics systems, mainly in time-of-flight (TOF) configuration, have been used in order to estimate maximum and peak energy of the plasma fast proton component, peak current density, total number of fast protons and conversion efficiency of laser energy into accelerated fast proton total energy. Optimization of the maximum attainable proton energy and current has been carried out by irradiating targets of different composition as well as varying the laser energy and the focal spot diameter. Experimental results, as well as possible applications in material science and nuclear physics, are discussed and compared with literature data.     

Grain size-dependent electrical transport properties in La0.75Sr0.25Mn1−xMgxO3±δ ceramics

The role of GB in Mg-substituted lanthanum-strontium manganite ceramics is studied with microstructural details. At higher concentrations of Mg (x>0.05), where the average grain size is ∼1 μm, the M-I transition is shifted from 348 to 110 K. Annealing in lower p_O2 (10⁻⁶ atm) at 1375 K for 1 h obliterates the M-I transition and brings in insulating behaviour throughout the temperature of measurement. Re-annealing in oxygen atmosphere for 10-25 min reintroduces the M-I transition, indicating that the electrical transport properties depend on the chemical inhomogeneity introduced by the in- or out-diffusion of oxygen through the GB regions. Samples with larger grain size (∼35 μm) do not exhibit major modifications in electrical resistivity on annealing in different p_O2. The insulating manganites display non-linear J-E characteristics below the magnetic transition temperature at electric field strengths <50 V/cm. The non-linear behaviour is explained on the basis of the inelastic tunnelling through the multiple localised states in the insulating GB regions. The external magnetic field lowers the voltage at which the non-linearity sets in. The tunnelling therefore may be not only through independent defect centres of oxygen vacancies (V_O), but possibly from defect complexes such as Mn³⁺-V_O or Mn²⁺-V_O, where spin-dependent tunnelling can take place.     

Magnetization studies on ?-Fe2.4Co0.6N nanoparticles

?-Fe_2.4Co_0.6N nanoparticles are prepared by nitridation of ultrafine iron-cobalt oxide in NH₃ gas atmosphere at 873 K for 3 h. Their magnetic properties are studied using ac and dc magnetization techniques. Two peaks at 69 and 151 K are found in ac susceptibility study. The former peak is assigned to superparamagnetic blocking temperature (T_B ∼ 69 K), whereas the origin of the latter one could not be ascertained since it is observed only from imaginary part of ac susceptibility study. The positions of peaks are found to be dependent on the applied fields and frequencies. Also, dc magnetization studies corroborate T_B. Anisotropy constant (K_a) is found to be 2.3 × 10⁵ erg/cm³. The peaks disappear at high-applied field due to the overcome of applied filed over anisotropic energy. Ferromagnetic domains rotate incoherently. At low temperature, Bloch law cannot be applied, but Curie law can be applied above T_B. Interestingly, spin relaxation is faster at 10 K as compared to that at 70 K indicating the presence of frustration of spins at lower temperature.     

Fabrication and dielectric property of ferroelectric PLZT films grown on metal foils

We have grown ferroelectric Pb_0.92La_0.08Zr_0.52Ti_0.48O₃ (PLZT) films on platinized silicon and LaNiO₃-buffered nickel substrates by chemical solution deposition using a sol-gel process based on acetic acid chemistry. The following measurements were obtained under zero-bias field: relative permittivity of ≈960 and dielectric loss of ≈0.04 on the PLZT film grown on Pt/Si substrates, and relative permittivity of ≈820 and dielectric loss of ≈0.06 on the PLZT film grown on LNO-buffered Ni substrates. In addition, a relative permittivity of 125 and dielectric loss of 0.02 were measured at room temperature under a high bias field of 1 × 10⁶ V/cm on PLZT deposited on LNO-buffered nickel substrate. Furthermore, a steady-state leakage current density of ≈8.1 × 10⁻⁹ A/cm² and mean breakdown field strength of 1.7 × 10⁶ V/cm were measured at room temperature. Finally, remanent polarization (P_r) of ≈2.0 × 10⁻⁵ C/cm², coercive electric field (E_c) of ≈3.4 × 10⁴ V/cm, and energy density of ≈45 J/cm³ were determined from room-temperature hysteresis loop measurements on PLZT/LNO/Ni film-on-foil capacitors with 250-μm-diameter platinum top electrodes.     

Characteristics of a magnetron cold cathode gauge

The discharge characteristics of a cold-cathode gauge of the non-inverted magnetron type were studied in ultra-high vacuum. The experimental magnetron cell of length 56 mm and diameter 32 mm was made of stainless steel. The cathode with a diameter of 6 mm was placed along the anode axis. The diameter of the anode was 25 mm and the length was 50 mm. Discharge current versus voltage and magnetic field was measured in the pressure range between 1×10⁻⁸ and 1×10⁻⁶ mbar. It was found that the current at first slowly increased with increasing voltage, reached a maximum at a certain voltage, and decreased rapidly with further increase of the voltage. The voltage, at which the current reached the maximum, depended on the magnetic field density and slightly on the pressure. A novel type of a cold cathode gauge with a self-adjusting power supply is suggested.     

Magnetic and dielectric study of R0.5Sr0.5MnO3 (R = Gd, Tb and Dy)

Magnetic and dielectric properties of perovskite manganites R_0.5Sr_0.5MnO₃ (R = Gd, Tb and Dy) have been investigated. DC and AC magnetic measurements showed short-range glassy magnetic ordering at T_g ∼ 40 K. Such ordering was observed by neutron diffraction and is ascribable to the size mismatch of R³⁺ and Sr³⁺ settled randomly at the same crystallographic site. Dielectric constants for each material were ∼1000-10,000 between ∼50 and ∼300 K and showed broad maximums above T_g. Dielectric dispersion showed poor coherency of the motion of polar regions, plausibly because of the size-mismatch effect; both the magnetic and dielectric properties of this system are governed by the randomness at the R/Sr site. The tan δ and EXAFS data suggest that the dielectric response is rooted in a transfer of the Mn-3d electrons.     

Magnetic behavior of arrays of nickel nanowires: Effect of microstructure and aspect ratio

Arrays of nickel nanowires with aspect ratio of ∼1200 and diameters ranging between 25 and 100 nm have been fabricated by electrodeposition in etched ion track templates. Samples with different areal densities ranging from 1 × 10⁶ cm⁻² to 1 × 10⁸ cm⁻² have been prepared for this study. Magnetic measurements were performed at room temperature for different aspect ratios and diameters of the wires. Coercivity of the wires showed a strong dependence on aspect ratio (l/d), diameter and microstructure. In the case of parallel applied field coercivity of the wires has maximum value at ∼40 nm diameter. The wires with high areal densities showed relatively lower coercivities as compared to the low density samples. The results have been discussed by taking into account various magnetic anisotropies originating from the shape and crystalline nature of the wires, and the magnetostatic interactions among the wires.     

Effect of ion bombardment on the optical properties of LDPE/EPDM polymer blends

Ion bombardment is a suitable tool to improve the physical properties of polymers. In the present study, the effect of ion bombardment on the optical properties of low density polyethylene (LDPE)/Ethylene propylene diene monomer (EPDM) blend (LDPE/EPDM) was studied. Polymer samples was bombarded with 130 keV He and 320 keV Ar ions at fluencies levels ranging from 1 × 10¹³ to 2 × 10¹⁶ ions/cm². The untreated and ion beam bombarded samples were investigated using ultraviolet-visible (UV-Vis) spectrophotometry. The optical band gap (E_g), was decreased from ∼2.9 eV for the pristine sample down to 1.7 eV for the samples bombarded with He and Ar ions at the highest fluences. Change in the optical gap indicates the presence of a gradual phase transition for the polymer blends. Activation energy has been investigated as a function of the ion fluences. With increasing ion fluence, a decrease in both the energy gap and the activation energy was observed. The number of carbon atoms (N) in a formed cluster is determined according to the modified Tauc's equation.     

Development of a dedicated ion injector for accelerator-based nanoprobe facilities

The paper discusses possible ways of increasing beam brightness in ion injectors. The argon/helium ion injector comprising a newly designed RF ion source and, a Wien filter has been designed for use in accelerator-based nanoprobe facilities. The phase set degradation due to aberrations in the injector ion-optic system was simulated with allowance for multipole and fringing fields. The RF ion sources with different permanent magnet systems were tested. Experiments were performed with argon and helium. A plasma density of up to 3×10¹¹ cm⁻³ and beam brightness of ∼100 A/(m² rad² eV) were obtained. The ion current density inside an extracting electrode in the source was 10 mA/cm² for an emission hole diameter of 0.6 mm. Measurements of the current value and emittance were performed with ion source testing equipment permitting measurements of the ion beam current, emittance, mass composition, and RF power input into the plasma.