Effect of irradiation on the laws of annealing of impurity hardening of NaCl crystals

Studies were carried out on crystals containing various types of impurity: Ca²⁺, a hole-acceptor impurity, which dissolves well in NaCl; and Pb²⁺, an electronacceptor impurity, which dissolves poorly in NaCl. For the first time when doped crystals were annealed softening was observed to occur as a result of irradiation with soft x-rays prior to the annealing. The microhardness of irradiated doped NaCl crystals drops below the value that corresponds to the unannealed unirradiated sample. This effect is more pronounced in NaCl:Pb. It is postulated that the weakening effect is due to the breakup of impurity complexes. This assumption is supported by the results of studies on the laws governing the annealing of dislocation structures about the imprints of an indenter. These laws are shown to depend on the type of impurity: processes of dislocation polygonization were observed in NaCl:Ca crystals and the dislocation distribution was random in NaCl:Pb crystals. Pre-irradiation of the latter caused dislocations to be built in and polygonization to appear. Evidently, by breaking up impurity complexes in NaCl:Pb crystals x-ray irradiation brings the state of the impurity in them closer to that in NaCl:Ca.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 57–62, August, 1988.     

X-Ray Luminescence of Defects in Spinel Single Crystals

The flareup of x-ray luminescence in spinel single crystals (MgAl₂O₄) depending on the time of x-ray irradiation and the decay of fluorescence depending on the time elapsed after the termination of irradiation have been investigated. These dependences were measured at different powers of the irradiation dose (power of the x-ray tube) and at different temperatures of the samples. The experimental results suggest the existence of large-size complexes of defects, which include antisite defects and impurity ions, the exchange of charge carriers between which during and after irradiation leads to luminescence of the impurity ions. Transfer of charge carriers between isolated elements of the pairs of antisite defects (not interacting with the impurity ions) leads to the formation of a competing channel of recombination luminescence in the UV region of the spectra. The decay of fluorescence attributable to transitions in the Mn²⁺ and Cr³⁺ ions depending on the time elapsed after the termination of x-ray irradiation points to the existence of various combinations of antisite defects in the surroundings of these ions.     

Ablation process of silica glass induced by laser plasma soft X-ray irradiation

Silica glass can be machined by irradiation with laser plasma soft X-rays on nano- and micrometer scale. We have investigated the ablation process of silica glass induced by laser plasma soft X-ray irradiation. We observed ionic and neutral species emitted from silica surfaces after irradiation. Dominant ions and neutrals are O⁺ and Si⁺ ions and Si, O, SiO and Si₂ neutrals, respectively. The ions have kinetic energies of 13 and 25 eV, which are much higher than those of particles emitted by evaporation. The energy of laser plasma soft X-rays absorbed to silica glass at a fluence of 1.4 J/cm² is estimated to be 380 kJ/cm³, which is higher than the binding energy of SiO₂ of 76 kJ/cm³. These results suggest that the most of the bonds in silica glass are broken by absorption of laser plasma soft X-rays, that several percent of the atoms are ionized, and that neutral atoms are emitted together with repulsive ions. The process possibly enables us to fabricate nano structures.     

Spectroscopic study of plasmons in ion-irradiated single-walled carbon nanotubes

The electronic structure of single-walled carbon nanotubes was experimentally investigated using x-ray photoelectron spectroscopy, reflection electron energy-loss spectroscopy, and Auger electron spectroscopy. A shake-up satellite structure observed near the C 1s core-level lines in the x-ray photoelectron spectra at high binding energies in the range 284–330 eV due to excitation of π and π + σ plasmons was studied. The effect of irradiation by 1-keV argon ions on the shape of the spectra was analyzed. The shape of the C 1s satellite spectra was found to be sensitive to Ar⁺ irradiation in the electron energy loss range 10–40 eV corresponding to excitation of π + σ plasmons. Auger spectroscopy revealed the presence of argon on the surface of ion-irradiated samples. The argon content increased to ～4 at. % with increasing irradiation dose. An analysis of the results obtained and their comparison with the data available in the literature led to a qualitative conclusion that the bond angles of the carbon atoms making up the walls of single-walled carbon nanotubes are distorted at sites exposed to Ar⁺ irradiation.     

Concentration dependence of Fe segregation near the surface in V-Fe alloys after V+ ion irradiation

The effect of Fe segregation near the free surface of V model alloys containing 2, 5, or 7 at % Fe is investigated by x-ray photoelectron spectroscopy. Segregation is induced by 50-keV V⁺ ion irradiation at a temperature of 30–40°C with fluences ranging from 10¹⁹ to 10²¹. Young’s moduli in these alloys are measured by the torsion pendulum method. The degree of Fe segregation is estimated, and its dependence on the irradiation dose and iron concentration in these alloys is analyzed. Correlation is found between the behavior of Young’s moduli and the degree of iron surface segregation as functions of the Fe concentration in the alloys.     

Helium-like recombination pumped soft x-ray lasers

Experimental studies on recombination pumped soft x-ray lasers with helium-like ions are presented. The four-beam multi-TW neodymium-doped phosphate glass laser system at the Institute for Solid State Physics of the University of Tokyo was used in this work. From simultaneous time- and space-resolved spectra of the resonance lines of helium-like aluminium ions, population inversions between the n=3 and 2 levels were observed. Details on the first observation of amplification in a recombination-pumped helium-like soft x-ray laser, exhibiting a time-resolved small-signal gain of 3.3±0.5 cm^-1 for the 3 ¹D-2 ¹P transition of helium-like nitrogen, are also given.     

Stable and fully controlled long-time operation of a soft X-ray laser for user application experiments

Irradiation of user-supplied samples with pulsed 18.9 nm radiation originating from a molybdenum soft x-ray laser pumped in a double-pulse, single-beam (DGRIP) configuration is described. Stable operation at 10 Hz during up to 50,000 pulses is demonstrated with an average on-sample pulse energy of 200 nJ. The ability of the irradiation device to precisely deliver high photon doses with good spatial uniformity is confirmed. This constitutes to our knowledge the first demonstration of a laser-pumped soft x-ray laser as a stable and fully characterized irradiation source running automatically over exposure times of several hours.     

The effect of injected-charge spatial distribution on the x-ray induced electron emission intensity in ferroelectric electrets

The nonmonotonic behavior of electron emission intensity induced in a surface layer of a ferroelectric electret by soft x-ray irradiation with an injected charge depth is predicted using a model of an accelerating electric field. The predicted behavior is in agreement with the results of the model experiments.     

Observations of surface modifications induced by the multiple pulse irradiation using a soft picosecond x-ray laser beam

To study the interactions between picosecond soft x-ray laser (SXRL) beams and material surfaces, gold (Au), copper (Cu), and silicon (Si) surfaces were irradiated with SXRL pulses having a wavelength of 13.9 nm and a duration of ～7 ps. Following irradiation, the surfaces of the substrates were observed using a scanning electron microscope and an atomic force microscope. With single pulse irradiation, ripple-like structures were formed on the Au and Cu surfaces. These structures were different from previously investigated conical structures formed on an Al surface. In addition, it was confirmed that the development of modified structures, i.e., growth of hillocks on the Au and Cu surfaces, was observed after multiple SXRL pulse exposures. However, on the Si surface, deep holes that seemed to be melted structures induced by the accumulation of multiple pulses of irradiations were found. Therefore, it was concluded that SXRL beam irradiation of various material surfaces causes different types of surface modifications, and the changes in the surface behaviors are attributed to the differences in the elemental properties, such as the attenuation length of x-ray photons.     

Homogeneous focusing with a transient soft X-ray laser for irradiation experiments

We report the work done on a transient soft X-ray laser (SXRL) beam to deliver a proper extreme UV irradiation source for applications. The same optical tool was first demonstrated on a quasi stationnary state (QSS) soft X-Ray laser at the PALS Institute in Prague. The problem set by the transient soft X-Ray laser developed by the LIXAM at the LULI installation in Palaiseau is more crucial, first because the beam spatial profile is more irregular secondly because high repetition rate soft X-ray laser facilities in the future are based on this SXRL type. The spots obtained show a 20 micron average diameter and a rather homogeneous and smooth profile that make them a realistic irradiation source to interact with targets requiring relatively high fluence (near 1 J/cm²) or intensity (near 10¹¹ W/cm²) in the extreme UV domain.     

The effect of high iron-ion implantation doses on the X-ray emission spectra of silicon

X-ray emission spectroscopy (Si L _{2, 3} spectra, 3d3s → 2p electronic transition) was employed to study p-and n-type silicon samples implanted with Fe⁺ ions in a pulse mode (the implantation energy was 30 keV, the pulse current was varied up to 0.5 A, the pulse duration was 400 μs, and the ion irradiation doses ranged from 10¹⁴ to 10¹⁷ cm⁻²). The x-ray emission spectra were found to be dependent on the ion irradiation dose and the electron-accelerating voltage that was used in the x-ray studies. By comparing the Si L spectra with the spectra of reference materials and by modeling the former spectra, it was revealed that, as the ion-irradiation dose increases, there occur disordering of the structure, partial amorphization of the sample in a surface layer approximately 7200-? thick, and its subsequent recrystallization (under high irradiation doses). It was shown that this effect is most pronounced in a layer at a depth of ∼1000 ? and is not associated with the formation of iron silicide FeSi in the bulk of the sample but rather is due to the breakage of Si-Si bonds caused by ion implantation under the irradiation doses used. Original Russian Text ? D.A. Zatsepin, E.S. Yanenkova, é.Z. Kurmaev, V.M. Cherkashenko, S.N. Shamin, S.O. Cholakh, 2006, published in Fizika Tverdogo Tela, 2006, Vol. 48, No. 2, pp. 204–209.     

Investigations of the mega-ampere multiwire X pinch

The results of experimental investigations into the dynamics of a plasma produced in the multiwire X pinch at currents up to 2.3 MA are presented. The materials, diameters, and the number of wires are varied. At such currents, the power of the soft x-ray radiation with the photon energy from 1 to 2 keV increases to 120 GW, and, since the size of a hot spot is less than 20 μm, it corresponds to a source brightness of ～10¹⁵ W/(cm² sr). The energy recorded in lines of neon-like molybdenum (in the range of 2.5–3 keV) is higher than 10 J. Hard x-ray radiation detected in experiments with tungsten and molybdenum X pinches has the photon energy ≥800 keV.     

Study of sawtooth oscillations on the HT-7 tokamak using 2D tomography of soft x-ray signal

It is the first time so far as we know that two arrays of multi-channel soft x-ray detectors are used to generate twodimensional （2D） images of sawtooth oscillation on the HT-7 tokamak using the Fourier-Bessel harmonic reconstruction method, and using the singular value decomposition to analyse the data from soft x-ray cameras. By these two arrays, 2D image reconstruction of soft x-ray emissivity can be obtained without assumption of plasma rigid rotation. Tomographic reconstruction of the m=1 mode structure is obtained during the precursor oscillation of the sawtooth crash. The crescent-shaped mode structure appearing on the contour map of the soft x-ray emissivity is consistent with the quasiinterchange mode. The characteristics of the m=1/n=1 mode structure observed in the soft x-ray tomography are as follows： the magnetic surface is made up of the crescent-shaped “hot core” and the circular “cold bubble”. The structure of the magnetic surface rotates in the direction of the electron diamagnetic drift and the rotation frequency is the oscillation frequency of soft x-ray signals.     

Matrix assisted growth of nanoparticles and nanoporous films

Since the inception of matrix assisted pulsed laser evaporation (MAPLE), a large body of research has focused on the structure and property preservation of soft materials. Departing from this precedent, a variation of MAPLE to grow complex inorganic nanoparticles and nanoporous thin films from acetate precursors is presented. While some aspects of MAPLE are retained, a weakly absorbing matrix solvent is used to promote absorption by the precursors, leading to photothermal decomposition. The diffusion of ions within the laser interaction volume results in the formation of nanoparticles, which are then ejected by subsequent pulses. The acetate precursors were processed into colloidal suspensions in deionized water and frozen to form solid targets, followed by irradiation with a pulsed excimer laser at fluences ranging from 0.25 to 0.75 J/cm². Nanoparticles and nanoporous films of unary, binary, and ternary metallic and oxide systems were deposited at room temperature onto substrates of Si and electron-transparent grids. Size distributions varied between different material systems with negligible pressure and energy effects, with distribution extrema ranging from 2 to 100 nm in diameter. Characterization of the nanoparticles was performed by high resolution scanning and transmission electron microscopy, and energy dispersive x-ray spectroscopy.     

Hot electrons produced from long scale-length laser-produced droplet plasmas

Microplasmas produced from 15 μm methanol droplets irradiated by 100 fs laser pulses in the intensity range 10¹⁴–10¹⁶ W cm^?2 are investigated via measurements of the hot electron temperature and x-ray yields under different conditions of intensity, polarization state, and plasma scale-length. The scale length of the drop-let plasma is increased with an intentional prepulse that is 10 ns ahead of the main pulse. Hot electron temperatures up to 48 keV have been measured at intensities of 2.5 × 10¹⁵W cm^?2 and the scaling of temperature as a function of intensity is determined for a long scale-length droplet plasma. The polarization and ellipticity dependence of the hard x-ray yield from the microdroplet plasmas are used to probe the shape of the droplet after irradiation by a prepulse.     

Effect of point defect concentration in NaCl and LiF crystals on the saturation field of the magnetoplastic effect

The effect is studied of the calcium impurity concentration in NaCl crystals and of preliminary x-ray irradiation of NaCl and LiF crystals on the magnetic saturation field B₀ characterizing the transition from the conventional proportionality of the dislocation mean path length l to the magnetic induction B squared(l∝B²) to saturation (l=const). B₀ is shown to increase with the calcium concentration in NaCl crystals and with the dose of x-ray irradiation of NaCl and LiF. This finding indicates that the dislocation breakaway from local defects in weak magnetic fields is controlled by the mechanism of longitudinal spin relaxation in a system of radical pairs that form due to interaction between dislocation cores and paramagnetic centers.     

Soft x-ray PHA measurement of the long pulse discharge in HT-7 tokamak

By analyzing the soft x-ray energy spectrum measured by the soft x-ray pulse height analysis (PHA) system, the electron temperature (Te) and the effective charge number (Zeff) of the ultra-long pulse discharge driven by lower hybrid wave (LHW) were obtained in the HT-7 tokamak. Moreover, the information of medium-Z impurities such as Ti, Cr, Fe, and Ni intrinsic to HT-7 tokamak can also be inspected. The accuracy of the electron temperature derived from the soft x-ray energy spectrum measurements is verified by comparing with the temperature measured by the Thomson scattering system for various plasmas and electron cyclotron emission diagnostic system for ohmic plasmas. The bulk electron temperature of about 1 keV and Zeff≈2 were achieved for long pulse plasma. The appreciable Kα lines of Ti, Cr, Fe and Ni metallic impurities released from the antennas of radio frequency wave and/or the first wall and Ar injected into plasma can be observed, and they kept stable during the long duration discharges. As a result, the longest pulse discharge with relatively high temperature of Te(0)∼1 keV, and ne(0)∼0.5×¹⁰¹⁹ m−3 has been achieved with a duration of 400 s in the HT-7 experimental campaign in 2008.     

A soft X-ray laser utilizing charge exchange

A scheme for a soft x-ray laser utilizing electron pickup in an excited state of a multiply ionized species is presented. Using a current source of 10 to 20 mA, we estimate a yield of ≈ 10⁶ x-ray quanta per pulse. The present scheme seems to be well within the realm of modern technology.     

Detection and switching of the oxidation state of Fe in a self-assembled monolayer

A self-assembled monolayer of ferrocene-capped alkanethiols is produced in two stable oxidation states of Fe (Fe²⁺ and Fe³⁺). These oxidation states are detected with sub-monolayer sensitivity by the fine structure of the Fe2p absorption edge. The native Fe²⁺ ferrocene layer is converted chemically to Fe³⁺, and the Fe³⁺ layer can be transformed back to Fe²⁺ or possibly Fe⁰ by irradiation with soft X-rays. The results have implications on switching mechanisms in molecular electronics.     

Control of the properties of Pb(TixZr1-x )O3 solid solutions by external disturbances

The influence of x-ray irradiation to absorbed radiation doses D = (0.5?12) × 10⁸ rad on the properties of ferroelectric ceramic Pb(Ti_xZr_1?x )O₃ solid solutions with compositions close to the morphotropic phase boundary was studied. The effects of x-ray radiation on the electrical conductivity of ferroelectric ceramics are shown to differ with x ranging from 0.42 to 0.60. Using empirical equations and numerical techniques, quantitative relations are established between the composition, absorbed radiation dose, and electrical conductivity for Pb(Ti_xZr_1?x )O₃.