Yuriy Halahovets

Annealing behaviour of structural and magnetic properties of evaporated Co thin films

Cobalt thin films of 50 nm nominal thickness were e-beam evaporated on silicon substrates covered with thermal oxide. Two series of independent and cumulative vacuum annealings up to 600 ◦ C and 650 ◦ C, respectively, were performed. The x-ray diffraction, specular and non-specular x-ray reflectivity and longitudinal magneto-optical Kerr effect measurements were applied to probe the annealing behaviour of the film structure and magnetic properties. A gradual transition from the hexagonal close-packed (hcp) to the face-centred cubic (fcc) structure was observed. Evolution of the in-plane magnetic anisotropy is dominated by residual stresses which relax during the structural transformation. The coercivity follows the stress behaviour in the hcp phase up to 300 ◦ C and increases abruptly above 400 ◦ C due to improving the magneto-crystalline anisotropy in the growing fcc crystallites and enhanced surface/interface roughness. (Some figures in this article are in colour only in the electronic version)

Scanning magneto-optical Kerr microscope with auto-balanced detection scheme

We have developed a scanning magneto-optical Kerr microscope dedicated to localization and measurement of the in-plane magnetization of ultra-thin layered magnetic nanostructures with high sensitivity and signal-to-noise ratio. The novel light detection scheme is based on a differential photodetector with automatic common mode noise rejection system with a high noise suppression up to 50 dB. The sensitivity of the developed detection scheme was tested by measurement of a single Co layer and a giant magnetoresistance (GMR) multilayer stack. The spatial resolution of the Kerr microscope was demonstrated by mapping an isolated 5×5 μm spin-valve pillar.

In Situ X-Ray Reciprocal Space Mapping for Characterization of Nanomaterials

Definition of Topic In this chapter, we will focus on the small-angle X-ray scattering (SAXS) technique performed on planar samples in the grazing-incidence small-angle X-ray scattering (GISAXS) geometry. This particular method of SAXS allows a fast, nondestructive analysis of the near-surface electron density variations on the lateral length scale ranging from several angstroms up to several hundreds of nanometers with adjustable in-depth sensitivity down to several nanometers. Special emphasis will be given to GISAXS experiments with laboratory X-ray sources as these are much more easily accessible as compared to synchrotron facilities.

Nano-machining for advanced X-ray crystal optics

We present our recent technological achievements in development of the nano-machining of active X-ray crystal optics surfaces. This technique uses a single crystal diamond tool with extremely precise and temperature stabilized positioning system. We can prepare various simple (flat, spherical, cylindrical) as well as more complex free-form surfaces (including aspherical ones). The objective is to prepare high-quality surfaces of the desired shape with sub-nanometer surface roughness and low sub-surface damage of the crystal lattice. The final surface roughness of a flat Ge surface below 0.4 nm (RMS) was achieved for a very slow regime of the processing using feed rates≤0.25 mm/min. At such a slow feed rate, a parasitic surface grating formed due to rastering the diamond tool along the surface was minimized. Surface roughness Ra was reached well below the level of 3 nm stated by the machining device manufacturer in specifications, which is a very good result. The sub-surface damage varied periodically and ...

In-situ GISAXS monitoring of ultrashort period W/B4C multilayer x-ray mirror growth

Ultrashort period multilayer X-ray mirrors with the layer thickness down to 1 nm or less represent a technological challenge. Here, the layer thickness becomes comparable to the interface roughness and discontinuous layers producing strong diffuse scattering may appear. The grazing-incidence small-angle X-ray scattering (GISAXS) is a unique nondestructive technique to probe the mirror quality in terms of the statistical interface roughness and its correlation properties. We present the first in-situ laboratory GISAXS experiments of monitoring the multilayer mirror growth in order to better understand and optimize the deposition process. A microfocus X-ray source IμS with focusing Montel optics (Incoatec) and 2D X-ray detector Pilatus 200K (Dectris) were mounted on a custom-designed dual-ion beam sputtering apparatus (Bestec). Two W/B4C mirrors with 15 periods of 1.8 nm and 2.1 nm were prepared as determined from the post-deposition specular X-ray reflectivity measurements. The in-situ GISAXS tracking was done by a fast repeated collection of the GISAXS frames with the integration time of 8 s at the incidence angle of 0.25 degree. Two distinct features along qz at qy = 0, namely Yoneda and Bragg-like (BL) multilayer peaks evolved in the GISAXS pattern. Oscillatory behavior of the latter in terms of intensity and FWHM was observed after the initial stage. Lateral cuts of the diffuse scattering concentration stripes surrounding BL peaks in particular GISAXS frames provided temporal evolution of the correlation and fractal interface parameters. Their potential for tailoring the multilayer properties is discussed.

P3HT:PCBM Based Organic Solar Cells: Structure Optimization and Improving External Quantum Efficiency by Plasmonic Nanoparticles Incorporation

We optimized morphology of the active layer of organic solar cells based on poly(3-hexylthiophene-2,5-diyl) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) bulk heterojunction. The optimization process includes a 20 min solvent annealing followed by a 5 min thermal annealing at 110 ∘C. After such a procedure a ∼ 3 % power conversion efficiency (PCE) was achieved. Adding of gold plasmonic nanoparticles (0.1 wt %) resulted in external quantum efficiency improvement.

Correlation between x-ray reciprocal space maps and magnetic properties of current-induced magnetization switching pseudospin valve structures

A thorough study of x-ray diffuse scattering from the spin valve structures suitable for current induced magnetization switching is presented. We used complete reciprocal space maps of diffusely scattered x rays to show the effect of bottom Au electrode on the morphology of buried spin valve interfaces. The thickness and roughness of each layer, as well as vertical and lateral roughness correlation lengths, were obtained. The impact of interfaces morphology on the magnetic properties, especially on the increase of spin valve coercivity, was measured and simulated within the frame of Neel magnetostatic coupling model based on the parameters from the x-ray diffuse scattering data. Measurement of x-ray diffuse scattering presents a rapid and nondestructive technique for in-depth and self-contained analysis of spin valve layers and interfaces.

Control of interparticle distance of ordered iron-oxide nanoparticle assemblies by means of surfactant design

Effect of the nanoparticle effective size on interparticle distance in ordered nanoparticle films was investigated. To obtain different interparticle distance, the iron oxide nanoparticles (IONPs) with the size of 6.5 nm were functionalized by three kinds of surfactants: mixture of oleic acid/oleylamine, polybutylacrylate and polystyrene. Both hydrodynamic diameter and size distribution of nanoparticles in colloidal solution were measured by dynamic light scattering (DLS) in range from 8 to 17 nm. The ordering and homogeneity of the prepared Langmuir monolayers on solid surface was studied by scanning electron microscope (SEM) and atomic force microscopy (AFM). Method of pair correlation function was used for calculation of interparticle distance ensuing from SEM images. The distances from center to center of particles varied in the range from 6.75 to 11.75 nm. From the results it follows that we are able to change of interparticle distance on a solid substrate using of nanoparticles with different surfactant size.Effect of the nanoparticle effective size on interparticle distance in ordered nanoparticle films was investigated. To obtain different interparticle distance, the iron oxide nanoparticles (IONPs) with the size of 6.5 nm were functionalized by three kinds of surfactants: mixture of oleic acid/oleylamine, polybutylacrylate and polystyrene. Both hydrodynamic diameter and size distribution of nanoparticles in colloidal solution were measured by dynamic light scattering (DLS) in range from 8 to 17 nm. The ordering and homogeneity of the prepared Langmuir monolayers on solid surface was studied by scanning electron microscope (SEM) and atomic force microscopy (AFM). Method of pair correlation function was used for calculation of interparticle distance ensuing from SEM images. The distances from center to center of particles varied in the range from 6.75 to 11.75 nm. From the results it follows that we are able to change of interparticle distance on a solid substrate using of nanoparticles with different surfac...

Cyclopean gauge factor of the strain-resistance transduction of indium oxide films

The resistance of indium-oxide covered polyethylene terephthalate foils (IO-PET) shows an extreme sensitivity to tensile strain. In terms of the deformation-resistance transduction, the gauge factor as high as about 60 000 was recorded upon the relative elongation up to 1%. Except the onset of deformation, the nearly exponential dependence of the resistance on strain suggests that the conductivity of the strained films is governed by tunnelling mechanism; this notion is supported by the formation of scattered cracks in the IO- PET film. The cracks are oriented perpendicularly to the strain vector and are characterized by a rather similar and uniform width. Appropriateness of the standard definition of the gauge factor for strain sensors, which are governed by tunnelling conductance, is critically discussed.