Scanning X-ray microscopy based on Kumakhov optics and a raster X-ray source

The concept of scanning X-ray microscopy has been practically implemented for the first time using a cylindrical polycapillary structure of the Kumakhov X-ray optics and a scanning microfocus X-ray source. The scanning X-ray microprobe is provided by electron-beam scanning of a focal spot over the target in a transmission X-ray tube equipped with an output cylindrical polycapillary structure.     

High-intensity X-ray microbeams obtained using a cylindrical polycapillary structure

High-intensity quasi-parallel X-ray microbeams with a radiation flux density on the order of 10¹⁰ photon/(s mm²) and a divergence of several milliradians, which is close to the parameters of synchrotron radiation, were obtained using a microfocus source based on a transmission-type X-ray tube. The divergent X-ray radiation was converted into a quasi-parallel beam using a cylindrical structure of Kumakhov polycapillary optics with a micron channel diameter.     

Optic parameters of a middle-focus Kumakhov lens for hard X-rays

Middle-focus Kumakhov polycapillary lenses for hard X-ray optic systems are created for the first time. The performance of such a lens has been studied for X-rays in the 20–65 keV range. The radiation energy density amplification coefficient of the lens in this energy range falls within four to two orders of magnitude. Thus, the upper boundary of the energy range for effective use of the Kumakhov polycapillary X-ray optics has been increased to over 60 keV.     

External focusing of nanosecond pulsed X-ray radiation

The feasibility of efficient focusing of high-power pulsed X-ray radiation generated by explosive electron emission from carbon nanoclusters is shown by direct experiments with the use of polycapillary X-ray optics. It is shown that the X-ray spot in the focus of the polycapillary lens can be reduced to 1/20 of its initial size.     

Microscopic X-ray sources imaged using high-resolution enlargement Kumakhov optics

A substantially new direction in X-ray microscopy is developed. X-ray images of a microscopic X-ray source representing a focal spot of a microfocus X-ray tube have been obtained with a spatial resolution on the level of 1 μm. This possibility is provided by a cone-shaped polycapillary high-resolution Kumakhov optical structure.     

Broadband Filtering of an X-Ray Spectrum by Transmission through a Polycapillary Structure

Technical Physics Letters - The efficiency of broadband filtering of a polychromatic X-ray spectrum by a polycapillary structure in the region of photon energies E > 10 keV was demonstrated....     

Pulsed operation of low-power plasma thruster

Integral and local characteristics of the laboratory model of a low-power plasma thruster operating in a pulsed regime have been experimentally studied. Rectangular pulses of discharge current with the leading and trailing fronts not exceeding 1 ms have been obtained. At an average supplied electric power of ∼150 W, the propulsion efficiency amounted to 35%. The plasma concentration, electron temperature, and potential distributions in the output plasma jet have been measured using an electric probe. These measurements showed that a well formed plasma jet with a small divergence angle exists behind the thruster edge.     

Wavelength dispersive X-ray fluorescence imaging

A new wavelength-dispersive X-ray fluorescence (WD-XRF) imaging spectrometer equipped with a two-dimensional X-ray detector was developed in the laboratory. Straight polycapillary optics was applied instead of a soller slit, which is used in conventional WD-XRF spectrometers. X-rays were guided through the straight polycapillary to the exit of the optics by X-ray external total reflections. X-ray fluorescence was dispersed by an analyzing crystal (LiF(200)), keeping the information of elemental distribution on the surface of the sample. The energy resolution of the developed spectrometer was 130-152 eV at the Zn Kα peak. X-ray elemental images of Cu Kα and Ni Kα were successfully obtained by an X-ray CCD detector at the corresponding diffraction angles. The analytical performance of this technique, and further improvements are discussed.     

Obtaining X-ray shadow images using high-resolution enlargement Kumakhov optics

X-ray shadow images have been obtained using cone-shaped polycapillary structures of high-resolution Kumakhov optics. The proposed method develops a substantially new direction in X-ray microscopy. This technique does not require using expensive microfocus X-ray sources employed in the traditional X-ray imaging systems characterized by spatial resolution on a level of 5–6 μm. The images obtained in this study show resolution on a level of 1 μm.     

Modification-scanning X-ray microscopy of semiconductor structures using Kumakhov optics

A modification variant of scanning X-ray microscopy using Kumakhov optics has been realized for the first time. Using the proposed device, radiation tests of pressure sensors based on silicon-on-sapphire structures were performed under laboratory conditions. The source of ionizing radiation in the new device is an X-ray tube with a middle-focus polycapillary Kumakhov lens.     

Comparative study of X-ray fluorescence signal collection by collimators of two types

The response signal collection functions in a confocal setup of the X-ray fluorescence (XRF) tomography have been modeled for a polycapillary collimator and a multichannel collimator fabricated by means of microelectronic technology (MT). The dimensions of the effective collection region for the two types of collimators are compared. For the MT-fabricated device, a fraction of X-ray photons transmitted due to the total external reflection from channel walls has been evaluated. It is shown that, for a proper choice of parameters, the contribution of these photons to the collection function is negligibly small.     

Three-dimensional trace element analysis by confocal X-ray microfluorescence imaging

A three-dimensional (3D) variant of scanning micro X-ray fluorescence (XRF) is described and evaluated at the ID18F instrument of the European Synchrotron Radiation Facility (ESRF). The method is based on confocal excitation/detection using a polycapillary half-lens in front of the energy-dispersive detector. The experimental arrangement represents a significant generalization of regular two-dimensional (2D) scanning micro-XRF and employs a detector half-lens whose focus coincides with that of the focused incoming beam. The detection volume defined by the intersection of the exciting beam and the energy-dependent acceptance of the polycapillary optics is 100-350 mum(3). Minimum detection limits are sub-ppm, and sensitivities are comparable with regular scanning XRF. Next to the reduction of in-sample single/multiple scattering, the setup provides the possibility of sample depth scans with an energy-dependent resolution of 10-35 mum in the energy range of 3-23 keV and the possibility of performing 3D-XRF analysis by simple XYZ linear scanning. This provides a suitable alternative to X-ray fluorescence tomography. The method is illustrated with results of the analysis of solid inclusions in diamond and fluid inclusions in quartz.     

Optimization of a silicon X-ray phase plate

We report that X-ray phase plates give optimal performance when operated, not at the exact Bragg angle but at the angle for which the phase shift is reduced by π. This operating point maximizes the output of circular polarization by accepting larger beam divergence.     

LEDs based on InAs/InAsSb heterostructures for CO<Subscript>2</Subscript> spectroscopy (λ = 4.3 μm)

Light-emitting diodes (LEDs) operating in a 4.1–4.3 μm wavelength range have been created on the basis of InAs/InAsSb heterostructures grown by metalorganic vapor-phase epitaxy. The output radiation power of LEDs is increased using flip-chip design. Investigation of the electrolumuinescent properties of LEDs with smooth and profiled output edge surface showed that the latter LEDs possess a greater efficiency, which is related to an increase in the radiation yield due to multiply repeated reflection from the curved surface. The output power of LED operating in a quasi-continuous wave mode was 30 μW at a current of 200 mA and that in a pulse mode was 0.6 mW at a current pulse amplitude of 2 A.     

Harmonic mode-locking in quantum dot lasers with tunnel-coupled waveguides

Passive mode-locking has been studied in the lasers with tunnel-coupled waveguides with the active region based on InAs/InGaAs quantum dots emitting in the range of 1.3–1.31 μm. Specific optical mode formation in this composite waveguide reduces the output beam divergence and raises the temperature stability of the lasing wavelength. The reduced optical confinement factor facilitates obtaining passive modelocking regimes. High response rate of the saturable absorber associated with the carrier escape time shorter than 20 ps allows generating a third harmonic with the frequency as high as 46.1 GHz.     

A micro X-ray fluorescence analysis method using polycapillary X-ray optics and grazing exit geometry

Grazing exit X-ray fluorescence (GE-XRF), which has unique advantages in surface and film analysis, is a development of XRF related to total reflection XRF. The combination of polycapillary X-ray optics with total reflection geometry in the detection path allows micro analysis in thin layer characterization. This technique was applied to analyze a series of titanium and iron layers which were deposited on GaAs single crystal by metal vapor vacuum arc ion sources. Thickness and density of the layers result from fitting the experimental data to model calculations, and the information of layer uniformity can be acquired by two-dimensional scan analysis. The GE-XRF method has application for complete layer characterization and process control during the layer deposition.     

Magnetic Properties of GaGdN Studied by SX-MCD and XAFS

The element-selected magnetic circular dichroism (MCD) between Gd core states is observed in the soft X-ray region (1150–1250 eV). The dichroism intensity for the transition from the 3d to 4f orbital of the Gd atomic state is very strong and reaches up to about 30% at 15 K. The temperature dependence of the MCD intensity shows a ferromagnetic phase around 50–80 K in addition to the room temperature ferromagnetic phase. Its X-ray absorption near edge structure is different from those of other Gd compounds. It seems to be related to the strength of the ferromagnetic behavior.     

Influence of the type of cathode on the dynamic characteristics of ionization waves

The influence of different types of cathodes on the dynamic characteristics of ionization waves is determined experimentally. It is established that when the discharge is initiated by negative pulses, the maximum wave propagation velocity is observed for a cold cathode while the maximum peaking of the output pulse leading edge is observed for a heated cathode. The mechanism for this effect is discussed. Pis’ma Zh. Tekh. Fiz. 24, 39–42 (July 12, 1998)     

TiO<Subscript>2</Subscript>/graphene composite from thermal reaction of graphene oxide and its photocatalytic activity in visible light

In this study, the P25 TiO₂ nanoparticles and graphene sheets (GSs) composite were prepared from a facile thermal reaction of graphene oxide. Its microstructures and photocatalytic properties were characterized and measured using X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), Brunauer–Emmett–Teller (BET) specific area analysis, X-ray photoelectron spectroscopy (XPS), FT-IR spectra, and ultraviolet–visible (UV–vis) diffuse reflectance spectroscopy. Compared with pure P25 nanoparticles, the results reveal that (1) there is a red shift about 20 nm in the absorption edge of the P25/graphene composite; (2) the photocurrent of the composite is about 15 times higher than that of pure P25; (3) the visible light photocatalytic activity of the composite is enhanced greatly on decomposition of methylene blue (MB). The photocatalytic mechanism of the P25/graphene composite is also discussed.