Laser photoelectron projection microscopy of insulating samples with sub-wavelength spatial resolution

Operation of a laser-driven photoelectron projection microscope is analyzed in the case of low-conductivity samples. Under certain conditions, even with “perfectly” insulating samples, one can obtain photoelectron images with a high magnification factor and spatial resolution smaller than the laser wavelength owing to the effect that the diple field of a sample polarized by a strong external electric field has on the motion of emitted photoelectrons. The experimental investigation of lithium fluoride and glass samples reported in this paper can be considered a qualitative confirmation of the suggested model. Zh. éksp. Teor. Fiz. 112, 1273–1284 (October 1997)     

Low energy electron point source microscopy

The setup of the LEEPS (low energy electron point source) microscope is described and images of carbon fibres and nanotubes are shown and compared to simulated images. We used a Kirchhoff-Helmholtz type transform to reconstruct the (wave front at the) object. We also showed that this transform can be used to reconstruct optical in-line holograms.     

Field electron emission images of multi-walled carbon nanotubes

Field electron emission microscope images from multi-walled carbon nanotubes can typically be characterized by the presence of five pentagons surrounding a sixth central pentagon. The observations of bright line centered interference patterns between adjacent pentagons in the field electron emission microscope images of multi-walled carbon nanotubes have been reported in the literature. We have observed a shift from bright to dark line centered interference patterns and associated this with the presence of surface adsorption. In order to identify the origin of the contaminant, multi-walled carbon nanotubes were dosed with H₂, H₂O, CO and O₂ and then imaged in the field electron emission microscope. Only the samples exposed to O₂ showed a shift from a bright line centered pattern between adjacent pentagons of a clean surface to a dark line centered pattern when one pentagon was contaminated or a bright line centered pattern when both adjacent pentagons become contaminated. The results of the experimental studies and the modeling of the changes in the field emission pattern as phase shifts in the wave function of the tunneling electrons due to modifications in the surface work function are presented.     

Preparation of nanosized ZnO using α brass

Nanosized ZnOs were synthesized on the surface of α brass coated a film of nickel catalyst at 500-700 °C under atmosphere of O₂ and CH₄ gases. The nanosized ZnOs have shapes including pillar, leaf, sheet and rod, which were determined by the synthesis temperature and the flow rates of O₂ and CH₄ gases. The nanosized ZnOs were characterized by electron microscopy including transmission electron microscope for crystal structure, morphology and high resolution images, both field emission scanning electron microscope and scanning electron microscope for morphology, and energy dispersive X-ray spectroscope equipped in electron microscope for chemical composition. A mechanism was proposed for the growth of nanosized ZnO obtained in this work.     

Size of the localized electron emission sites on a closed multiwalled carbon nanotube

We have measured the size of the localized electron emission sites on multiwalled carbon nanotubes (MWNTs) with caps closed by a fullerenelike structure. MWNTs were individually mounted on tungsten support tips and imaged with a field emission microscope (FEM). The magnification of the FEM was calibrated using electron ray tracing and verified by comparing transmission electron microscope images. The FEM image was also tested for effects of the lateral energy spread. We found ring-shaped emission areas with three flattened sides, of a radius of 1.7±0.3 nm, and separated by 5±1 nm.     

Photon emission from adsorbed C60 molecules with sub-nanometer lateral resolution

We present the first experimental demonstration of spatially resolved photon emission of individual molecules on a surface. A scanning tunneling microscope (STM) was used as a local electron source to excite photon emission from hexagonal arrays of C₆₀ molecules on Au(110) surfaces. Specifically, we show that in maps of photon emission intensities, C₆₀ fullerenes appear as arrays of individual light emitters 4 Å in diameter and separated by 10 Å. Comparison with simultaneously recorded STM images reveals, that most intense emission is detected when the STM tip is centered above a molecule. The results demonstrate the highest spatial resolution of light emission to date using a scanning probe technique.     

Observation of the pre-explosion state and of the initial moment of an explosion of a field emission center in a field emission microscope

Never-before-observed emission images corresponding to a transition from intense field emission to explosive electron emission are obtained in a Muller field emission microscope with short (∼2 ns)high-voltage pulses. These images are much brighter than ordinary field emission images. Moreover, the images have a characteristic multi-brightness structure with ring-shaped frames around regions of different brightness. Analysis of the experimental data points to a field emission nature of these images. The appearance of such emission images can be explained by emission from a liquid phase which arises immediately prior to the explosion of a microemitter. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 4, 280–285 (25 February 1998)     

Laser photoelectron projection microscopy of an organic conducting polymer

A conducting organic polymer is visualized on a laser photoelectron projection microscope, which is based on Letokhov’s concept and has a nanometer spatial resolution. Photoelectron images of polyaniline (which is the most promising representative of conducting polymers) with a magnification of ∼10⁵ have been obtained when a 100-nm quartz capillary coated with a film of this material was irradiated by femtosecond laser pulses. The projection photoelectron method using 400- and 800-nm laser radiation has made it possible to directly reveal the existence of the redox heterogeneity of the organic polymer, which is due to the contact of the sections of polyaniline with different oxidation degrees and strongly affects the electric conductivity of the sample.     

Atomic resolution imaging of oxygen atoms close to heavy atoms by HRTEM and ED,using the superconductor SmFeAsO0.85F0.15 as an example

Imaging of light atoms has always been a challenge in high-resolution electron microscopy. Image resolution is mainly limited by lens aberrations, especially the spherical aberration of the objective lens. Image deconvolution could correct for the image distortion by lens aberrations and restore the structure projection, the resolution of which is limited by the information limit of the microscope. Electron diffraction unrestricted by lens aberrations could overcome this resolution limit. Here we show a combination of electron diffraction and image deconvolution to reveal simultaneously the atomic columns of O and considerably heavier Sm at a very close distance (1.17 Å) in iron-based superconductor SmFeAsO_0.85F_0.15 using a conventional 200 kV electron microscope. The approach used here, starting from an image and an electron diffraction pattern, has an advantage for those radiation-sensitive samples. Besides, it can be applied to simultaneously imaging light and heavy atoms, even though they have a big difference in atomic number and a much smaller atomic distance than the microscope resolution.     

Growth of β-Ga<Subscript>2</Subscript>O<Subscript>3</Subscript> nanoparticles by pulsed laser ablation technique

This work investigates pulsed laser ablation for Ga₂O₃ nanoparticles. Nanoparticles with diameters of 10 to 500 nm were deposited on silicon substrates in large quantities, by KrF excimer laser ablation of a GaN (99.99% purity) target in high purity nitrogen (99.9995%) background gas at room temperature, without a catalyst. The particle size and phase structure of the as-deposited nanoparticles are examined by X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM), transmission electron microscope (TEM), and selected-area electron diffraction (SAD). FE-SEM images show that the nanoparticles aggregate to form micron-size nanoclusters at chamber pressures of 1 and 5 Torr. On the other hand, nanoparticles aggregate with chain-like nanostructures, are synthesized at high chamber pressures (10 Torr). TEM images further reveal that chain-like nanostructures are formed by the aggregation of individual spherical and ellipsoidal nanoparticles. Photoluminescence measurement shows stable and broad blue emission at 445 nm. PACS 81.20.-N; 81.15.Fg; 75.50.Vv     

Synthesis and structural characterization of perovskite 0.65Pb(Mg1/3Nb2/3)O3-0.35PbTiO3 nanotubes

We report the synthesis and structural characterization of 0.65Pb(Mg_1/3Nb_2/3)O₃-0.35PbTiO₃ (PMN-PT) nanotubes prepared by a novel sol-gel template method. X-ray diffraction (XRD) and selected-area electron diffraction (SAED) investigations demonstrated that the postannealed (650 °C for 1 h) PMN-PT nanotubes were polycrystalline with perovskite crystal structure. The field emission scanning electron microscope (FE-SEM) shows that as prepared PMN-PT nanotubes were hollow with diameter to be about 200 nm. High resolution transmission electron microscope (HRTEM) analysis confirmed that the obtained PMN-PT nanotubes made up of nanoparticles (10-20 nm) which were randomly aligned in the nanotubes. Energy-dispersive X-ray spectroscopy (EDX) analysis confirmed the stoichiometric 0.65Pb(Mg_1/3Nb_2/3)O₃-0.35PbTiO₃. The possible formation mechanism of PMN-PT nanotubes was proposed at the end.     

适用于激光聚变实验的短焦距高放大倍率Wolter显微镜设计

围绕内爆压缩及阻滞阶段相关物理实验的诊断需求,提出了一种满足阿贝正弦条件的短焦距高放大倍率Wolter-Ⅲ型X射线显微镜的光学设计。详细介绍了Wolter-Ⅲ型显微镜的结构特点和设计方法,与Wolter-Ⅰ型相比可以通过将主平面向靠近物点方向移动的方式减小系统焦距,从而获得更大的放大倍数,实现显微镜与探测器的像质匹配,提高诊断系统的空间分辨。由光线追迹可以得出,在±190 μm的视场范围内,空间分辨率优于3 μm;在±240 μm范围内分辨率优于5 μm;在±300 μm范围内分辨率优于8 μm,几何集光立体角约为5×10?6 sr。     

时间分辨电子显微镜的数值模拟

对时间分辨电子显微镜进行了数值模拟。通过求解从样品透射出来的电子在静态磁场和动态电场的混合场中的运动,评价时间分辨电子显微镜的动态时空特性。根据该数值模拟,时间分辨电子显微镜能够在荧光屏上获得样品在不同时刻的6幅显微分幅图像。     

Energy distribution of field emission electrons from carbon nanocrystals

Using a field electron microscope and a field electron dispersion energy analyzer, carbon nanocrystals contained in polyacrylonitrile (PAN) fibers are studied. Transition of the emitting nanocrystals into the second stable state has been discovered, corresponding to an emission current and field electron energy distribution of magnitudes lower by nearly an order of magnitude, with an additional low-energy peak. Heating the samples at 750° C restores the initial characteristics of the field electron energy distribution and current-voltage characteristics of the nanocrystals. The forbidden bandwidth of the nanocrystals has been determined.     

深紫外激光光发射与热发射电子显微镜在热扩散阴极研究中的应用

对热扩散阴极表面微区发射状态进行原位观察和分析一直是热阴极研究的重要课题.本文着重介绍深紫外激光光发射电子/热发射电子显微镜的基本原理及其在热扩散阴极研究中的典型实例.系统配备了高温激活所用的加热装置,样品可被加热至1400℃.系统具有光发射电子、阴极热发射电子、光发射电子和阴极热发射电子联合三种电子成像模式.应用表明,对于热扩散阴极而言,深紫外激光光发射电子像适于呈现阴极表面的微观结构形貌;热发射电子像适于反映阴极表面的本征热电子发射及均匀性;光电子和热电子联合成像适于对阴极表面的有效发射点做出精确定位.     

Design of a mirror aberration corrector and a beam separator for LEEM

A SPLEEM (spin polarized low energy electron microscope) has been designed with a numerical simulation of electrostatic and magnetic field distributions and electron ray trajectories. Highly (more than 90%) spin polarized electron source has been used. A Wien type spin manipulator and a magnetic lens type spin rotator are used to align spin direction. A magnetic field free objective lens is designed to observe magnetic domain structure of magnetic materials. High or low magnification mode can be selected by using a combined electrostatic and magnetic objective lens for a high spatial resolution and a wide imaging area observation. An electrostatic mirror aberration corrector is installed after the image forming objective lens. A double deflection 45° beam separator is used to bend the direction of electrons from the source to the objective lens and from the objective lens to the mirror aberration corrector.     

Extracting domain wall patterns from SEM magnetic contrast images

The magnetic contrast images of a soft magnetic metallic glass Fe₇₉Si₆B₁₄Cu₁ subjected to a periodic magnetic field were recorded with a scanning electron microscope by using a stroboscopic technique. An image processing method for the extraction of domain patterns from these images is presented. By this technique, delicate details of the dynamic magnetization process can be investigated and differences in the local magnetisation and domain wall movement can be analysed.     

Microstructure and microhardness analysis of the hexagonal oxides formed on the surface of the AISI 304 stainless steel after Nd:YAG pulsed laser surface melting

The laser surface melting (LSM) technique was adopted to modify the surface layer microstructure of the AISI 304 stainless steel in this paper. The results showed that the hexagonal morphologies have been successfully fabricated on the surface after LSM. These hexagons had side lengths of about 0.5-1 μm and were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), field emission scanning electron microscope (FESEM) and high resolution transmission electron microscope (HRTEM). It was proved by the XRD that the stainless steel surface mainly consisted of γ-Fe, Cr₂O₃, Fe₂O₃ and some manganese oxides. The FESEM micrographs showed that the hexagonal oxides were regular hexagons in geometry. The HRTEM micrographs also indicated the presence of the hexagons on the surface of the stainless steel. The spacing values were calculated from the HRTEM micrograph and the SAED pattern, and the hexagonal oxide phases determined by these spacing values were consistent with those verified by the XRD. After LSM, the microhardness of the stainless steel was significantly improved.     

Secondary electron emission from solid HD and a solid H2-D2 mixture

Secondary electron emission from solid HD and a solid 0.6 H₂ + 0.4 D₂ mixture has been studied for electron and hydrogen ion bombardment at primary energies from 0.5 to 3 keV and 2 to 10 keV/amu, respectively. The yield for solid HD is well explained by a simple stoichiometric model of the low-energy stopping power for the internal secondaries. The secondary electron yield from the mixture is somewhat larger than the expected value, but lies between the values for pure solid H₂ and D₂. The secondary electron emission coefficient for solid tritium may be determined from a linear extrapolation of the present data.     

Synthesis of flower-shape clustering GaN nanorods by ammoniating Ga2O3 films

Flower-shape clustering GaN nanorods are successfully synthesized on Si（111） substrates through ammoniating Ga2O3/ZnO films at 950℃. The as-grown products are characterized by x-ray diffraction （XRD）, scanning electron microscope （SEM）, field-emission transmission electron microscope （FETEM）, Fourier transform infrared spectrum （FTIR） and fluorescence spectrophotometer. The SEM images demonstrate that the products consist of flower-shape clustering GaN nanorods. The XRD indicates that the reflections of the samples can be indexed to the hexagonal GaN phase and HRTEM shows that the nanorods are of pure hexagonal GaN single crystal. The photoluminescence （PL） spectrum indicates that the GaN nanorods have a good emission property. The growth mechanism is also briefly discussed.