High-energy Ti Research Articles

Dual roles of [NCN]2- on anatase TiO2: A fully occupied molecular gap state for direct charge injection into the conduction band and an interfacial mediator for the covalent formation of heterostructured g-C3N4/a-TiO2 nanocomposite

When low density of melamine is calcined with a-TiO2 at 550 °C, two FT-IR peaks observed at 2048 and 2066 cm−1 are assigned to NCN2- covalently attached to a five-coordinated Ti atom and an oxygen vacancy, respectively, complemented by DFT computation. Admixture of NCN2- HOMO(π2p, 87.5 %) with the high energy Ti(3d, 12.5 %) destabilizes and upshifts the NCN2- HOMO into the a-TiO2 bandgap. A five-line EPR pattern derived from 71 % of atomic spin density localized on two equivalent 14N nuclei, observed under sub-bandgap excitation, verifies the presence of a molecular gap-state. The NCN2--a-TiO2 exhibits excellent H2 production at a rate of 5101 μmol.h-1.g-1. Upon increasing melamine concentration, the rapid and simultaneous decreases of NCN2- FT-IR and NCN1- EPR signals accompanied by transitions of other spectroscopic data to those characteristic of tri-s-triazine demonstrate that the formation of heterostructured g-C3N4/a-TiO2 proceeds via the intermediacy of NCN2--a-TiO2, thereby a mechanism is proposed.

High-energy hybrid femtosecond laser system demonstrating 2 × 10 PW capability

Abstract We report on a two-arm hybrid high-power laser system (HPLS) able to deliver 2 × 10 PW femtosecond pulses, developed at the Bucharest-Magurele Extreme Light Infrastructure Nuclear Physics (ELI-NP) Facility. A hybrid front-end (FE) based on a Ti:sapphire chirped pulse amplifier and a picosecond optical parametric chirped pulse amplifier based on beta barium borate (BBO) crystals, with a cross-polarized wave (XPW) filter in between, has been developed. It delivers 10 mJ laser pulses, at 10 Hz repetition rate, with more than 70 nm spectral bandwidth and high-intensity contrast, in the range of 1013:1. The high-energy Ti:sapphire amplifier stages of both arms were seeded from this common FE. The final high-energy amplifier, equipped with a 200 mm diameter Ti:sapphire crystal, has been pumped by six 100 J nanosecond frequency doubled Nd:glass lasers, at 1 pulse/min repetition rate. More than 300 J output pulse energy has been obtained by pumping with only 80% of the whole 600 J available pump energy. The compressor has a transmission efficiency of 74% and an output pulse duration of 22.7 fs was measured, thus demonstrating that the dual-arm HPLS has the capacity to generate 10 PW peak power femtosecond pulses. The reported results represent the cornerstone of the ELI-NP 2 × 10 PW femtosecond laser facility, devoted to fundamental and applied nuclear physics research.

339 J high-energy Ti:sapphire chirped-pulse amplifier for 10 PW laser facility.

We report on the laser pulse output of 339J centered at 800nm from a chirped-pulse amplification (CPA) Ti:sapphire laser system at the Shanghai Superintense Ultrafast Laser Facility. The experimental results demonstrated that the parasitic lasing as well as the transverse amplified spontaneous emission of the homemade 235-mm-diameter Ti:sapphire final amplifier were suppressed successfully via the temporal dual-pulse pumped scheme and the index-matching liquid cladding technique. The maximum pump-to-signal conversion efficiency of 32.1% was measured for the final amplifier. With a compressor transmission efficiency of 64% and a compressed pulse duration of 21fs obtained for the sample light at a lower energy level, this laser system could potentially generate a compressed laser pulse with a peak power of 10.3PW. The experimental results represent significant progress with respect to the CPA laser.

Narrowband terahertz generation with chirped-and-delayed laser pulses in periodically poled lithium niobate.

We generate narrowband terahertz (THz) radiation in periodically poled lithium niobate (PPLN) crystals using two chirped-and-delayed driver pulses from a high-energy Ti:sapphire laser. The generated frequency is determined by the phase-matching condition in the PPLN and influences the temporal delay of the two pulses for efficient terahertz generation. We achieve internal conversion efficiencies up to 0.13% as well as a record multicycle THz energy of 40μJ at 0.544THz in a cryogenically cooled PPLN.

Optimization of a High-Energy Ti–Al–B Nanopowder Fuel

Sonochemically generated reactive metal nanopowders containing Ti, Al, and B represent a new class of high-energy-density nanopowder fuels with superior energy content and air stability as compared to nano-aluminum. In this work, we optimize the energy density of a Ti–Al–B reactive metal nanopowder fuel by varying the Ti:Al:B ratios using a sonochemically mediated decomposition of a complex metal-hydride. After heating the recovered solids under vacuum to temperatures in the range between 150 to 300 °C, the powder’s air stability is significantly improved so that it can be handled in air. Variable-temperature vacuum heat treatment was used to produce fuels tuned to be stable with a gravimetric energy density exceeding that of pure bulk Al (>31 kJ/g). The density of the powder was found to be 2.62 g/cm3 by helium pycnometry, which translates to an impressive volumetric energy content of 89 kJ/cm3. In poly(methyl methacrylate)-protected bomb calorimetry tests commercial nano-aluminum (SkySpring Nanomaterial...

Combustion characteristics of high energy Ti–Al–B nanopowders in a decane spray flame

Boron-based fuels theoretically offer significantly higher volumetric energy densities than conventional liquid fuels. High-energy, amorphous, reactive mixed-metal (Ti–Al–B) nanopowders (RMNPs), produced by a sonochemical reaction, have shown exceptional air stability and greater energy density than nano-aluminum. In this work, we examine the combustion behavior of suspensions created using these high-energy RMNPs suspended in n-decane with a non-ionic surfactant to aid dispersion. Measurements were taken in a reacting spray plume, created using a flow-blurring atomizer and piloted with a surrounding annular propane-air flat-flame burner. Flame spectra were collected and used to identify chemiluminescence of relevant gas-phase intermediate species (BO2, AlO) and to calculate the temperature of reacting particles using multi-wavelength pyrometry. Fluctuations in the nanopowder content delivered to the spray flame were tracked by in situ sampling of the suspensions at the point of entry into the atomizer fuel tube and determining a correlation between additive concentration and flame luminance. This correlation was used to relate the condensed-phase temperature to additive concentration. The combustion characteristics of these suspensions were compared with neat n-decane fuel, as well as suspensions of commercially sourced aluminum nanopowder. Although temperature increased with concentration for both additives, the temperature measured for suspensions with nano-Al were shown to have a much stronger dependence on additive concentration than those with RMNPs. X-ray powder diffraction of the RMNP combustion products showed the fully oxidized TiO2, B(OH)3, and Al2O3 phases, along with TiB2 and TiC phases. Thermogravimetric analyses of the residual powders showed a mass gain corresponding to 2–4% residual active metal content, suggesting the combustion of the intermetallic RMNPs in the spray flame was nearly complete. These results show that these amorphous, sonochemically-generated, high-energy intermetallic RMNPs combust well in a hydrocarbon spray flame, but poor suspension stability and adverse effects on spray behavior remain technical barriers that must be improved.

A high-flux high-order harmonic source

We develop and implement an experimental strategy for the generation of high-energy high-order harmonics (HHG) in gases for studies of nonlinear processes in the soft x-ray region. We generate high-order harmonics by focusing a high energy Ti:Sapphire laser into a gas cell filled with argon or neon. The energy per pulse is optimized by an automated control of the multiple parameters that influence the generation process. This optimization procedure allows us to obtain energies per pulse and harmonic order as high as 200 nJ in argon and 20 nJ in neon, with good spatial properties, using a loose focusing geometry (f#≈400) and a 20 mm long medium. We also theoretically examine the macroscopic conditions for absorption-limited conversion efficiency and optimization of the HHG pulse energy for high-energy laser systems.

Mass spectrometry diagnostics of short-pulsed HiPIMS discharges

Time-resolved mass spectrometry (MS) study of a high-power impulse magnetron sputtering discharge (HiPIMS) operating in the ‘short-pulse’ regime (5 µs) at 1 kHz of the repetition frequency is undertaken. Several time-resolved effects related to both Ti+ and Ar+ ion energy distribution functions (IEDF) are found. In particular, the dynamics of both the low- (0–5 eV) and high- (5–30 eV) energy regions presented in Ti+ IEDFs is clarified. According to our results the sputtered and ionized Ti arrive at the virtual substrate position in the form of two waves, with the first one representing the high-energy Ti+, and the second one responsible for the low-energy Ti+. An essential decrease in the population of the energetic Ti+ group is observed at the moment of the arrival of the low-energy group, which is explained by the charge exchange processes, as well as by the refilling process afterwards. The role of Ar metastables presumably generated at the end of the plasma pulse for further Ti ionization is stressed as well. The time-averaged IEDFs for Ti+ and Ar+ are additionally analysed. The effective ion temperatures are calculated for these species for the above-mentioned energy ranges. A considerable increase in the effective ion temperature for the high-energy Ti+ is found, which is directly related to the elevation of the high-energy tail in the time-averaged IEDFs with increasing discharge voltage. Possible mechanisms for such an elevation are discussed.

Influence of amplified spontaneous emission on gain lifetime in high-aperture Ti:sapphire amplifiers

We demonstrate that by lowering gain lifetime, transverse amplified spontaneous emission imposes practical limit on usable aspect ratio of large-aperture amplifiers in a high-energy Ti:sapphire system.

Using hybrid ionized physical vapor deposition to control interface reaction during titanium deposition onto aluminum under-layer

For via structures landed on aluminum (Al) lines, ionized metal plasma (IMP) titanium (Ti) liner deposition can induce high via resistance as a result of the reaction between high energy Ti ions and the Al under-layer. The scale of the interface reaction is a function of the energy of the incoming Ti ions. A method to minimize the Ti/Al interface reaction is to introduce a thin protection layer over the Al under-layer prior to IMP Ti liner deposition. A convenient way to implement this method is to use a hybrid process, in which a Ti protection layer is first deposited in non-ionized mode prior to IMP Ti deposition. Hybrid ionized physical vapor deposition has been confirmed to be effective in minimizing the Ti/Al interface reaction during titanium deposition onto the aluminum under-layer.

ASE suppression in a high energy Titanium sapphire amplifier

The energy required to generate ultrashort pulses with petawatt peak power from a Ti:sapphire laser system is a few tens of joules. To achieve this, the final amplifier must have a gain region of around 5 cm diameter that is uniformly pumped at high fluence. The high level of amplified spontaneous emission (ASE) in such an amplifier will seriously degrade its performance unless care is taken to minimise the transverse gain and the internal reflections from the crystal edges. In developing the amplifiers for the Astra Gemini laser system, we have combined the techniques of beam homogenisation and double-pass pumping of a lightly-doped crystal with a new index-matched absorber liquid. Our results demonstrate that this combined approach successfully overcomes the problem of gain depletion by ASE in a high-energy Ti:sapphire amplifier.

Insights into the radiation response of pyrochlores from calculations of threshold displacement events

We have used molecular-dynamics simulations to examine the displacement threshold energy (Ed) surface for cations and anions in Gd2Ti2O7 and Gd2Zr2O7 pyrochlores. In both pyrochlores, the Ed surface is highly anisotropic and it requires less energy to displace anions than cations. Both anion and cation Ed values are higher in the titanate compared to the zirconate. Titanium displacement energies are in excess of 170eV for all directions examined, because cation exchange is less energetically favorable in Gd2Ti2O7 compared to Gd2Zr2O7. These high-energy Ti displacements result in the formation of defect clusters that may prevent efficient defect recovery. This provides an explanation for the difference in susceptibility to amorphization between titanate and zirconate pyrochlores.

Highly efficient second-harmonic nanosource for near-field optics and microscopy.

A nanometric source of second-harmonic (SH) light with unprecedented efficiency is demonstrated; it exploits the grazing-incidence illumination of a metal tip, which is conventionally used for atomic force microscopy, by 25-fs laser pulses of a high-energy Ti:sapphire oscillator. Tip scanning around the beam focus shows that the SH generation is strongly localized at its apex. The polarization dependence of the SH light complies with the model of an on-axis nonlinear oscillating dipole.

Energy and mass spectroscopy studies during triode ion plating of TiN films in two different layouts

Abstract Plasma properties are compared in two triode ion-plating systems using a low-voltage arc discharge. The systems differ in the configuration of the chamber and magnetic field. Mass and energy distributions of positive ions during deposition of TiN films were measured by an energy-resolved mass spectrometer. Plasma parameters were determined also by Langmuir probe diagnostics. In both systems, single and multiple charged ions of Ar and N2 gas and the evaporated Ti were detected. The system with a strong magnetic field confinement exhibits a higher plasma potential (Up=55 V) under standard deposition conditions, the peak ion energy is higher and the energy distribution is narrower than in the system without magnetic confinement (Up=12 to 35 V). The probability for the multiple charged ions in this system is much higher than in the system without the magnetic confinement, so the population of Ti++ in this system is even higher than that of Ti+. The presence of high-energy neutral Ti is also observed.

Investigation of depth distributions of defects in Si created by high energy Ti ions

Defect distributions in Si created by high energy MeV Ti ions were studied as a function of the irradiation angle and energy using Rutherford backscattering/channeling. A silicon crystal of 〈100〉 direction was irradiated at room temperature by 1.0–2.0 MeV Ti ions under tilted angles with a dose of 5 × 10 14 ions cm −2. It is found that the damage peak produced by 1.0 MeV Ti + is higher than one produced by 2.0 MeV Ti + at the same dose. The defect distributions extracted from the present experiment are compared with TRIM '89 calculations. The results show that the shape and depth of the damage profile under tilted angle implantation are qualitatively describe by TRIM '89.

Thermally stable, buried high-resistance layers in p-type InP obtained by MeV energy Ti implantation

High-energy Ti+ ions ranging from 1 to 5 MeV were implanted into p-type InP:Zn (for two different zinc concentrations) at both room temperature and 200 °C. The range statistics for Ti implanted at various energies were calculated by analyzing the as-implanted profiles determined by secondary-ion mass spectrometry. Ti did not redistribute during post-implantation annealing except for a slight indiffusion, irrespective of the implant or annealing temperatures used. This behavior is different from the behavior of other implanted transition metals (Fe and Co) in InP, which redistributed highly when the implants were performed at room temperature. In the MeV Ti-implanted InP:Zn the background Zn showed a small degree of redistribution. Rutherford backscattering measurements showed a near virgin lattice perfection for 200 °C implants after annealing. Buried layers with intrinsic resistivity were obtained by MeV Ti implantation in InP:Zn (p=5×1016 cm−3).

Nitrogen sorption on titanium: Reconstruction of the subsurface composition profile using low- and high-energy Auger data

Although Auger electron spectroscopy (AES) is the most widely used technique for surface analysis, there are many problems associated with its application to TiN, a technologically important material. The N and high-energy Ti peaks overlap completely and there is no elemental N standard available at ambient temperature. TiN standards can be used and the overlap problem can be overcome by computer simulation of the high-energy spectrum. Furthermore, the computer simulation technique can also be applied to the low-energy TiNx spectrum to give quantitative analysis with increased depth resolution. A procedure is proposed for deconvolution of the low- and high-energy AES data during nitrogen sorption on titanium to determine the composition profile based on a simple adsorption–diffusion model. Nitrogen sorption at various pressures has been followed at sample temperatures in the range 300–900 K. For a given nitrogen pressure, the experimentally observed escape depth averaged N/Ti ratios x̄ increase with sample temperature, pass through a maximum at Tm, and then decrease. At Tm the diffusion coefficient attains a value such that the diffusion rate and nitrogen gas arrival rates balance. For T<Tm the surface concentration x0 will be close to saturation, whereas for T>Tm, x0 will decrease rapidly. The concentration profiles obtained by computer deconvolution of the high- and low-energy Auger data confirm this model. As would be expected, Tm increases with increasing nitrogen pressure which increases the supply rate to the surface. The diffusion coefficients determined by computer deconvolution agree well with literature values for higher temperature studies. Prebombardment of the surface with Ar+ ions greatly increases the amount of nitrogen sorbed at room temperature and reduces Tm. The effect on the concentration profile is equivalent to an increase in diffusion coefficient caused by the excess defect concentration, viz., radiation enhanced diffusion.