Design study of hard X-ray tomography system to obtain a spatial resolution of 100 nm

An optic-based X-ray tomography system of a high spatial resolution using a conventional X-ray tube was proposed. The system had several X-ray optics: multilayer mirror for monochromatic X-ray, capillary optic for focusing X-ray onto a sample, and objective zone plate. The X-ray tomography system was designed for obtaining a spatial resolution of 100 nm. Design parameters for each optic were determined and optimized by ray tracing in considering X-ray intensity and reflectivity. The X-ray tomography system with a spatial resolution of 100 nm will provide a good inspect tool in bio-medical field and semiconductor applications.     

New directions in X-ray microscopy

The development of high brightness X-ray sources and high resolution X-ray optics has led to rapid advances in X-ray microscopy. Scanning microscopes and full-field instruments are in operation at synchrotron light sources worldwide, and provide spatial resolution routinely in the 25–50 nm range using zone plate focusing elements. X-ray microscopes can provide elemental maps and/or chemical sensitivity in samples that are too thick for electron microscopy. Lensless techniques, such as diffraction microscopy, holography and ptychography are also being developed. In high resolution imaging of radiation-sensitive material the effects of radiation damage needs to be carefully considered. This article is designed to provide an introduction to the current state and future prospects of X-ray microscopy for the non-expert.     

Magnetic microstructures and their dynamics studied by X-ray microscopy

Full-field soft X-ray microscopy in combination with X-ray magnetic circular dichroism as contrast mechanism is a powerful technique to image with elemental specificity magnetic nanostructures and multilayered thin films at high lateral resolution down to 15nm by using Fresnel zone plates as X-ray optical elements. Magnetization reversal phenomena on a microscopic level are studied by recording the images in varying external magnetic fields. Local spin dynamics at a time resolution below 100ps can be addressed by engaging a stroboscopic pump-and-probe scheme taking into account the time pattern of synchrotron storage rings. Characteristic features of magnetic soft X-ray microscopy are reviewed and an outlook into future perspectives with regard to increased lateral and temporal resolution is given.     

Studying nanomagnets and magnetic heterostructures with X-ray PEEM at the Swiss Light Source

Polarization dependent X-ray absorption spectroscopy and microscopy enables the element selective investigation of magnetic systems at the nanoscale. At the Swiss Light Source a photoemission electron microscope is used for the study of a broad variety of systems. Here, a review of recent activities is presented with a focus on instrumental and analytical developments. A new procedure for the 3 dimensional determination of the magnetization vector has been developed, and is demonstrated for GdFeCo microstructures displaying in-plane and out-of-plane domains, and sub-20 nm Fe nanoparticles. The recent progress for measurements in applied magnetic fields is presented and a new set-up for time-resolved measurements employing femtosecond laser pulses is described.     

Femtosecond spectroscopic imaging by time-of-flight photoemission electron microscopy

Advances in electron optics and fast-pulsed light sources have enabled the imaging of nanoscale structures with simultaneous energy and time resolutions. We present the results obtained from a time-resolved time-of-flight photoemission electron microscopy (TR-TOF-PEEM) system. This system combined the spatial resolution of conventional PEEM with the time resolution of a femtosecond-pulsed laser and the energy resolution of a TOF energy analyzer. The TOF-PEEM system consists of three electrostatic lenses in front, a drift tube for the measurement of TOF, and a delay line detector (DLD) at the end of the optics. The excitation source is femtosecond pulses from a cavity-dumped Ti:sapphire oscillator that is frequency-doubled to 400 nm using a β-barium borate (BBO) crystal. Using a pump-probe two-photon photoemission technique, we demonstrate an example of sub-100 nm space-resolved ultrafast time evolution of the electron energy spectra for the plasmon resonance of an Ag-coated Si nanostructure, which exhibited unexpectedly intense high energy photoemission signals that show different time evolution between bright and dark regions in a PEEM image.     

Single-shot extreme ultraviolet laser imaging of nanostructures with wavelength resolution

We have demonstrated near-wavelength resolution microscopy in the extreme ultraviolet. Images of 50 nm diameter nanotubes were obtained with a single ~1 ns duration pulse from a desktop-size 46.9 nm laser. We measured the modulation transfer function of the microscope for three different numerical aperture zone plate objectives, demonstrating that 54 nm half-period structures can be resolved. The combination of near-wavelength spatial resolution and high temporal resolution opens myriad opportunities in imaging, such as the ability to directly investigate dynamics of nanoscale structures.     

Thickness-dependent magnetic domain structures of Co ultra-thin film investigated by scanning transmission X-ray microscopy

Thickness-dependent magnetic domain structure of ultrathin Co wedge films (0.3 nm–1.0 nm) sandwiched by Pt layers was investigated by scanning transmission x-ray microscopy (STXM) employing X-ray magnetic circular dichroism (XMCD), utilizing elliptically polarized soft x-rays and electromagnetic fields, with a spatial resolution of 50 nm. The magnetic domain images measured at the Co L₃ edge showed the evolution of the magnetic domain structures from maze-like form to the bubble-like form as the perpendicular magnetic field was applied. The asymmetric domain expansion of a 500 nm-scale bubble domain was also measured when the in-plane and perpendicular external magnetic field were applied simultaneously.     

Investigating the magnetic properties of soft magnetic composites based on mechanically alloyed nanocrystalline Fe-5 wt% Ni powders

In this work, the soft magnetic composites (SMCs) of the nanocrystalline Fe-5 wt% Ni powders coated with phenolic resin were studied. The nanocrystalline powders with an average diameter of 10 nm were obtained by mechanical alloying up to 96 h milling in a high-energy planetary ball mill. The microstructure and magnetic properties of the milled powders were characterized by X-ray diffraction, energy dispersive X-ray spectroscopy and a vibrating sample magnetometer. The results of X-ray diffraction showed that the bcc Fe(Ni) solid solution is formed after 24 h milling. Magnetic measurements indicated that the 96 h milled powders with a steady-state grain size of 10 nm have the highest saturation magnetization and the lowest coercivity. The SMCs based on nanocrystalline powders showed higher electrical resistivity and magnetic permeability up to 1 MHz, as compared with the pure iron-based composites. Besides, the nanocrystalline-based SMCs exhibited higher relaxation frequency and a significantly lower loss factor up to 1 MHz.     

Sub-38 nm resolution tabletop microscopy with 13 nm wavelength laser light

We have acquired images with a spatial resolution better than 38 nm by using a tabletop microscope that combines 13 nm wavelength light from a high-brightness tabletop laser and Fresnel zone plate optics. These results open a gateway to the development of compact and widely available extreme-ultraviolet imaging tools capable of inspecting samples in a variety of environments with a 15-20 nm spatial resolution and a picosecond time resolution.     

X-ray diffraction microscopy of magnetic structures

We report the first proof-of-principle experiment of iterative phase retrieval from magnetic x-ray diffraction. By using the resonant x-ray excitation process and coherent x-ray scattering, we show that linearly polarized soft x rays can be used to image both the amplitude and the phase of magnetic domain structures. We recovered the magnetic structure of an amorphous terbium-cobalt thin film with a spatial resolution of about 75 nm at the Co L3 edge at 778 eV. In comparison with soft x-ray microscopy images recorded with Fresnel zone plate optics at better than 25 nm spatial resolution, we find qualitative agreement in the observed magnetic structure.     

Magnetic studies on ZnTe:Cr film grown on glass substrate by thermal evaporation method

ZnTe and ZnTe:Cr films were prepared on glass substrate by using thermal evaporation method. X-ray diffraction analysis revealed the presence of ZnCrTe phase. X-ray photoelectron spectroscopy was used to estimate the composition of as-prepared films. The valence state of Cr in ZnTe:Cr film is determined to be +2 by using electron spin resonance spectroscopy. Magnetic moment data as a function of magnetic field was recorded by using superconducting quantum interference device magnetometry at 300 K. The result showed a clear hysteresis loop with coercive field of 48 Oe. Magnetic domains were observed by using magnetic force microscopy and the average value of domain size was 3.7 nm.     

Magnetic and structural studies on CoFe2O4 nanoparticles synthesized by co-precipitation,normal micelles and reverse micelles methods

Cobalt ferrite nanoparticles were synthesized by the chemical co-precipitation, normal micelles and reverse micelles methods of iron and cobalt chlorides. X-ray diffraction analysis, Fourier Transform Infrared (FTIR) and Vibrating Sample Magnetometer were carried out at room temperature to study the structural and magnetic properties. X-ray patterns revealed the production of a broad single cubic phase with the average particle sizes of ∼12 nm, 5 nm and 8 nm for co-precipitation, normal micelles and reverse micelles methods, respectively. The FTIR measurements between 400 and 4000 cm⁻¹ confirmed the intrinsic cation vibrations of spinel structure for each one of the three methods. Moreover, the average particle sizes were lower than the single domain size (128 nm) and higher than the super-paramagnetic size (2–3 nm) at room temperature. The results revealed that the magnetic properties depend on the particle size and cation distribution, whereas the role of particle size is more significant.     

High-resolution X-ray imaging—a powerful nondestructive technique for applications in semiconductor industry

The availability of high-brilliance X-ray sources, high-precision X-ray focusing optics and very efficient CCD area detectors has contributed essentially to the development of transmission X-ray microscopy (TXM) and X-ray computed tomography (XCT) with sub-50 nm resolution. Particularly, the fabrication of high aspect ratio Fresnel zone plates with zone widths approaching 15 nm has contributed to the enormous improvement in spatial resolution during the previous years. Currently, Fresnel zone plates give the ability to reach spatial resolutions of 15 to 20 nm in the soft and of about 30 to 50 nm in the hard X-ray energy range. X-ray microscopes with rotating anode X-ray sources that can be installed in an analytical lab next to a semiconductor fab have been developed recently. These unique TXM/XCT systems provide an important new capability of nondestructive 3D imaging of internal circuit structures without destructive sample preparation such as cross sectioning. These lab systems can be used for failure localization in micro- and nanoelectronic structures and devices, e.g., to visualize voids and residuals in on-chip metal interconnects without physical modification of the chip. Synchrotron radiation experiments have been used to study new processes and materials that have to be introduced into the semiconductor industry. The potential of TXM using synchrotron radiation in the soft X-ray energy range is shown for the nondestructive in situ imaging of void evolution in embedded on-chip copper interconnect structures during electromigration and for the imaging of different types of insulating thin films between the on-chip interconnects (spectromicroscopy).     

Improvement of the magnetic properties of Nd9.5Fe81Zr3B6.5 nanocomposite magnets by semi-melt spinning

Nd_9.5Fe₈₁Zr₃B_6.5 ribbons are prepared by single roller melt-spinning technique at 1150 °C which is in the solid and liquid coexistence zone. The phase evolution and magnetic properties were studied by X-ray diffraction, differential scanning calorimetry, transmission electron microscopy observations, and magnetization measurements. The experimental results show that in comparison to the ribbons quenching at higher temperature, the thickness of ribbons prepared at 1150 °C are insensitive to the wheel speed and an uniform nanoscale structure with fine grains can be obtained directly from the semi-melt and the exchange coupling interaction between the grains was enhanced for the nanocomposite permanent alloy which can contributed to excellent magnetic properties.     

Application of citrate-stabilized gold-coated ferric oxide composite nanoparticles for biological separations

Gold-coated magnetic nanoparticles were synthesized with size ranging from 15 to 40 nm using sodium citrates as the reducing agent. Oxidized magnetites (Fe₃O₄) fabricated by co-precipitation of Fe²⁺ and Fe³⁺ in strong alkaline solution were used as magnetic cores. The structures of gold (Au) shell and magnetic core (Au–Fe) were studied by transmission electron microscopy (TEM) image and energy dispersive spectroscopy (EDS) spectrum. Results from high-resolution X-ray diffraction (HR XRD) show that the Au–Fe oxide nanoparticles have a face-centered cubic shape with the crystalline faces of {1 1 1}. The Au-coated magnetic nanoparticles exhibited a surface plasmon resonance peak at 528 nm. The nanoparticles are well dispersed in distilled water. A 3000 G permanent magnet was successfully used for the separation of the functionalized nanoparticles. Magnetic properties of the nanoparticles were determined by magnetic force microscope (MFM) in nanometric resolution and vibrating sample magnetometer (VSM). Magnetic separation of biological molecules using Au-coated magnetic oxide composite nanoparticles was examined after attachment of protein immunoglobulin G (IgG) through electrostatic interactions. Using this method, separation was achieved with a maximum yield of 35% at an IgG concentration of 400 ng/ml.     

Sol-gel synthesis of nanocomposite crystalline HMX/AP coated by resorcinol-formaldehyde

This work aims to improve the performance of composite explosive by using the sol-gel method to mix high explosive and oxidizer in nanoscale. Nanocomposite materials of HMX and AP were prepared by using resorcinol-formaldehyde (RF) as binder. Its structure was characterized by scanning electron microscopy (SEM), BET method, X-ray powder diffraction (XRD), and DSC. SEM images indicate that HMX/AP/RF aerogel has a laminate-like structure with uniform pores. The XRD results show that the mean crystal size of HMX is less than 100 nm; HMX and AP are mixed uniformly in nanoscale. The specific surface area of HMX/AP/RF is 27 m²/g and much less than that of RF aerogel. The mesopores and micropores of HMX/AP/RF aerogel mainly focus in the range of 2-20 and 0.6-1.6 nm, respectively. DSC analysis indicates that the thermal decomposition temperature of HMX/AP/RF is reduced compared to that of original HMX.     

Scanning Hall probe microscopy of vortex matter

Scanning Hall probe microscopy (SHPM) is a novel scanned probe magnetic imaging technique whereby the stray fields at the surface of a sample are mapped with a sub-micron semiconductor heterostructure Hall probe. In addition an integrated scanning tunnelling microscope (STM) or atomic force microscope (AFM) tip allows the simultaneous measurement of the sample topography, which can then be correlated with magnetic images. SHPM has several advantages over alternative methods; it is almost completely non-invasive, can be used over a very wide range of temperatures (0.3–300 K) and magnetic fields (0–7 T) and yields quantitative maps of the z-component of magnetic induction. The approach is particularly well suited to low temperature imaging of vortices in type II superconductors with very high signal:noise ratios and relatively high spatial resolution (>100 nm). This paper will introduce the design principles of SHPM including the choice of semiconductor heterostructure for different measurement conditions as well as surface tracking and scanning mechanisms. The full potential of the technique will be illustrated with results of vortex imaging studies of three distinct superconducting systems: (i) vortex chains in the “crossing lattices” regime of highly anisotropic cuprate superconductors, (ii) vortex–antivortex pairs spontaneously nucleated in ferromagnetic-superconductor hybrid structures, and (iii) vortices in the exotic p-wave superconductor Sr₂RuO₄ at milliKelvin temperatures.     

Magnetic properties and heating effect in bacterial magnetic nanoparticles

A suspension of bacterial magnetosomes was investigated with respect to structural and magnetic properties and hyperthermic measurements. The mean particle diameter of about 35 nm was confirmed by transmission electron microscopy (TEM), X-ray and magnetic analysis. The X-ray powder diffraction peaks of magnetosomes fit very well with standard Fe₃O₄ reflections. The found value for specific absorption rate (SAR) of 171 W/g at 5 kA/m and 750 kHz means that magnetosomes may be considered as good materials for the biomedical applications in hyperthermia treatments. Moreover, they have biocompatible phospholipid membrane.     

Experimental system for X-ray magnetic diffraction under extreme conditions

An experimental system for X-ray magnetic diffraction (XMD) under extreme conditions was constructed on the beamline BL39XU at SPring-8. This system aims at studying magnetic properties of ferromagnets through the measurements of magnetic form factors under the conditions of low temperature (5 K), high magnetic field (6 T) and high pressure (10 GPa). This system consists of a superconducting magnet (SCM), a diamond anvil cell (DAC), a two-axis manipulator for the DAC, a five-axis goniometer for the SCM, and an X-ray polarizer with a phase plate. Details of this system are presented. Experimental results on uranium telluride are shown as a performance test with this instrumentation.     

Synthesis and magnetic characterization of Zn0.6Ni0.4Fe2O4 nanoparticles via a polyethylene glycol-assisted hydrothermal route

Zn-doped nickel ferrite nanoparticles (Zn_0.6Ni_0.4Fe₂O₄) have been prepared via a surfactant, polyethylene glycol assisted hydrothermal route. X-ray powder diffractometry (XRD), Fourier transform infrared spectroscopy, transmission electron microscopy (TEM), and vibrating scanning magnetometry (VSM) were used for the structural, morphological, and magnetic characterizations of the product, respectively. TEM analysis revealed that the nanoparticles have a narrow size distribution, with average particle size of 15±1 nm, which agrees well with the XRD based estimate of 14±2 nm. The absence of saturation and remanent magnetization, and coercivity in the high temperature region of the M-H curve and non-zero magnetic moments indicate superparamagnetism of the nanoparticles with a canted spin structure. The appearance of a peak on the temperature-dependent zero-field cooling magnetization curve at ∼190 K indicates the blocking temperature of the sample.