Study of defect evolution by TEM with in situ ion irradiation and coordinated modeling

The paper describes a novel transmission electron microscopy (TEM) experiment with in situ ion irradiation designed to improve and validate a computer model. TEM thin foils of molybdenum were irradiated in situ by 1?MeV Kr ions up to ～0.045 displacements per atom (dpa) at 80°C at three dose rates ?5?×?10^?6, 5?×?10^?5, and 5?×?10^?4?dpa/s – at the Argonne IVEM-Tandem Facility. The low-dose experiments produced visible defect structure in dislocation loops, allowing accurate, quantitative measurements of defect number density and size distribution. Weak beam dark-field plane-view images were used to obtain defect density and size distribution as functions of foil thickness, dose, and dose rate. Diffraction contrast electron tomography was performed to image defect clusters through the foil thickness and measure their depth distribution. A spatially dependent cluster dynamic model was developed explicitly to model the damage by 1?MeV Kr ion irradiation in an Mo thin foil with temporal and spatial dependence of defect distribution. The set of quantitative data of visible defects was used to improve and validate the computer model. It was shown that the thin foil thickness is an important variable in determining the defect distribution. This additional spatial dimension allowed direct comparison between the model and experiments of defect structures. The defect loss to the surfaces in an irradiated thin foil was modeled successfully. TEM with in situ ion irradiation of Mo thin foils was also explicitly designed to compare with neutron irradiation data of the identical material that will be used to validate the model developed for thin foils.     

Surface morphology of siloxane block copolymer crystals: (Tetramethyl-p-silphenylenejsiloxane—dimethylsiloxane

The metal decoration technique was applied to solution grown crystals and cast thin films of (tetramethyl-p-silphenylene) siloxane and dimethylsiloxane (DMS) block copolymers in order to elucidate their surface textures as a function of copolymer composition. Electron diffraction and microscopy studies were used. Metal-free zones are observed at surface steps of single crystals, and decorating particles occasionally form spiral growths in the inner regions of crystals. However, the decorating particles form regular patterns, particularly on the copolymer crystal surfaces. In the case of solution-cast thin films, deposition of metallic particles occurs along lamellar crystal edges or where a fibrillar morphology occurs. The nucleation density of metallic particles depends on the copolymer composition and increases with increasing crystallinity of the samples. Probable models are suggested to account for this surface texture. The propensity for screw-dislocations crystal growths on the crystal surfaces decreases as the noncrystallizable DMS component increases.     

Front- and rear-face X-ray emission from laser-irradiated Al foils

Summary We studied theK-shell X-ray emission from plasmas produced by laser irradiation of Al foils. Electron temperature and density of the emitting region were estimated from line ratio measurements. Spectra obtained from the rear face of the foils showed that X-ray transmission is influenced by energy transport in the foil.     

Particle Sampling and Real Time Size Distribution Measurement in H2/O2/TEOS Diffusion Flame

Growth characteristics of silica particles have been studied experimentally using in situ particle sampling technique from H₂/O₂/Tetraethylorthosilicate (TEOS) diffusion flame with carefully devised sampling probe. The particle morphology and the size comparisons are made between the particles sampled by the local thermophoretic method from the inside of the flame and by the electrostatic collector sampling method after the dilution sampling probe. The Transmission Electron Microscope (TEM) image processed data of these two sampling techniques are compared with Scanning Mobility Particle Sizer (SMPS) measurement. TEM image analysis of two sampling methods showed a good agreement with SMPS measurement. The effects of flame conditions and TEOS flow rates on silica particle size distributions are also investigated using the new particle dilution sampling probe. It is found that the particle size distribution characteristics and morphology are mostly governed by the coagulation process and sintering process in the flame. As the flame temperature increases, the effect of coalescence or sintering becomes an important particle growth mechanism which reduces the coagulation process. However, if the flame temperature is not high enough to sinter the aggregated particles then the coagulation process is a dominant particle growth mechanism. In a certain flame condition a secondary particle formation is observed which results in a bimodal particle size distribution.     

Mössbauer conversion electron studies of tantalum metal surface layers

Conversion electrons following the Mössbauer absorption of the 6.2 keV -rays of¹⁸¹Ta were observed in backscattering geometry. Mössbauer spectra for tantalum single crystal and foil surfaces (mean-depth 330 Å) are compared with normal transmission spectra for tantalum foils (bulk). While no broadening of lines is observed for carefully polished single crystal furfaces, foil surfaces show considerably broader lines than bulk spectra. The linewidth and isomer shift indicate an increase of the concentration of absorbed residual gases at the foil surfaces. The observed dispersion term arising from the interference between photo- and conversion electrons for this E1-transition, depends only on the absorber thickness.     

Microstructure and electrical properties of Ba0.5Sr0.5TiO3 thin films prepared on copper foils with La2O3 buffer layers

Ba_0.5Sr_0.5TiO₃ (BST) thin films were deposited on copper foils via sol-gel method with La₂O₃ as a buffer layer. The films were processed in almost inert atmosphere so that the substrate oxidation was avoided while allowing the perovskite film phase to crystallize. The existence of a La₂O₃ buffer layer between the BST thin film and Cu foil improved the dielectric constant and reduced the leakage current density of the BST thin film. Meanwhile, the BST thin film exhibited ferroelectric character at room temperature, which was contrast to the para-electric behavior of the film without the buffer layer. Effects of La₂O₃ buffer layer on the crystallizability and microstructure of BST thin films were also investigated.     

连续离子层吸附反应沉积后硫化法制备柔性铜锌锡硫薄膜太阳电池

在柔性钼箔衬底上采用连续离子层吸附反应法(successive ionic layer absorption and reaction)制备ZnS/Cu2SnSx叠层结构的预制层薄膜,预制层薄膜在蒸发硫气氛、550 C温度条件下进行退火得到Cu2ZnSnS4吸收层.分别采用EDS,XRD,Raman,SEM表征吸收层薄膜的成分、物相和表面形貌.结果表明,退火后薄膜结晶质量良好,表面形貌致密.用在普通钠钙玻璃上采用相同工艺制备的CZTS薄膜表征薄膜的光学和电学性能,表明退火后薄膜带隙宽度为1.49 eV,在可见光区光吸收系数大于104cm 1,载流子浓度与电阻率均满足薄膜太阳电池器件对吸收层的要求.用上述柔性衬底上的吸收层制备Mo foil/CZTS/CdS/i-ZnO/ZnO:Al/Ag结构的薄膜太阳电池得到2.42%的效率,是目前报道柔性CZTS太阳电池最高效率.     

New features from transparent thin films of EuTiO3

ABSTRACT

The almost multiferroic perovskite EuTiO₃ (ETO) has been prepared as films on substrates of SrTiO₃. For all prepared film thicknesses highly transparent insulating films with atomically flat surfaces and excellent orientation have been grown. They were characterized by X-ray diffraction, magnetic susceptibility and birefringence measurements and found to exhibit bulk properties, namely an antiferromagnetic transition at T_N = 5.1 K and a structural transition at T_S = 282 K. The latter could only be identified due to the high transparency of the samples since the optical band gap is of the order of 4.5 eV and larger than observed before for any bulk and thin film samples.     

Nanoscale Analysis of Multilayer Interfaces of W/Al2O3/Ti/Cu

W, Al₂O₃ and Ti films were deposited onto a Cu substrate by means of the rf magnetron sputtering method. After deposition, the foils were annealed at various temperatures in vacuum and the interfaces of the films were observed by a field-emission transmission electron microscopy (FE-TEM), after preparing a cross-sectional thin foil using a focused ion beam (FIB) machine. After annealing the foil at 473 and 623 K, no reaction phases were identified at each interface of W/Al₂O₃, Al₂O₃/Ti and Ti/Cu-substrate. However, from the results of compositional analysis at the interface of Al₂O₃/Ti bilayer, after heat-treatment at 623 K, the formation of an oxide layer was suggested even though it was not clearly observed. On the other hand, after heat-treatment at 823 K, the formation of CuTi₂, Cu₃Ti₂ and Cu₄Ti phases were identified at the interface of Ti/Cu bilayers from the compositional analysis of reaction layers after heat-treatment at different temperatures, and the diffusion coefficients and activation energies in the phases were evaluated. In this paper, the influence of heat-treatment on the interfacial behavior of multilayer are discussed on the basis of nanoscale analysis by EDS and HRTEM images.     

室温生长MgO底层诱导(001)取向FePt薄膜的有序化过程对FePt成分的依赖

室温下通过磁控溅射在表面热氧化的Si基片上生长了MgO/Fe_xPt_100-x双层膜和Fe_xPt_100-x单层膜系列样品，Fe_xPt_100-x的原子成分x=48—68.研究了热处理前后不同成分FePt薄膜的晶体结构和磁性的变化，尤其是MgO底层的引入对FePt的晶体结构和磁性的影响 关键词： FePt(001)薄膜 0相')" href="#">L1₀相     

The elastic potential energy of a thin foil deformed by an in-plane 60° dislocation

An explicit expression of the elastic potential energy, W ^p, stored in a thin foil by a dissociated dislocation running parallel to the free surfaces is obtained in isotropic elasticity. It is used to discuss the metastable elastic equilibrium of a 60° dislocation in an ultrathin silicon foil when the fault plane is slightly inclined with respect to the free surfaces. The energy W ^p depends in particular on the positions of the two partials in the foil and on the thickness h, a situation not fully considered previously. For such ultrathin foils, propitious to the observation of partial dislocations cores at near atomic resolution, the theory predicts rapid changes with h of the separation distance S. This result is in accordance with previous experimental observations of S realized with the so-called “forbidden-reflection lattice imaging” technique.     

Gold coatings on polyethyleneterephthalate nano-patterned by F2 laser irradiation

In this work we present periodic surface structures generated by linearly polarized F₂ laser light (157 nm) on polyethyleneterephthalate (PET). Atomic force microscopy was used to study the topological changes induced by the laser irradiation. The laser irradiation induces the formation of periodic ripple structures with a width of ca 130 nm and a height of about 15 nm in the fluence range 3.80-4.70 mJ/cm² and the roughness of the polymer surface increases due to the presence of these periodic structures. Subsequently, the laser modified PET foils were coated with a 50 nm thick gold layer by sputtering. After Au deposition on the PET foils with ripple structure, the roughness of surface decreases in comparison to PET with ripples without Au coating. For 50 nm thick Au layers, the ripple structure is not directly transferred to the gold coating, but it has an obvious effect on the grain size of the coating. With considerably thinner Au layers, the ripple structures are smoothened but preserved.     

Study of latent and etched tracks by a charged particle transmission technique

A recently suggested technique for non-destructive investigation of inhomogeneities in thin objects, which is based on the measurement of the energy spectra of charged particles transmitted through the object, is used for the study of thermal annealing of 10–20 μm thick polyethylene terephtalate, polypropylene and polycarbonate foils irradiated with 1–10 MeV/amu heavy ions. At elevated temperature a foil linear contraction is observed on pristine and irradiated material. Also the foil roughness increases with increasing temperature. On the same foils with etched pores 0.5–1.0 μm in diameter, the thermal annealing results in gradual closing of the pores up to about 30% of their initial diameter at the temperatures of 150–175°C. At higher temperatures the pore diameter increases and achieves its initial value.     

Fabrication of atomically smooth SrRuO3 thin films by laser molecular beam epitaxy

High-quality SrRuO₃ (SRO) thin films and SrTiO₃/SRO bilayer were grown epitaxially on SrTiO₃ (STO)(001) substrates by laser molecular beam epitaxy. The results of in situ observation of reflection high-energy electron diffraction and ex situ X-ray diffraction ϑ-2ϑ scan indicate that the SRO thin films have good crystallinity. The measurements of atomic force microscopy and scan tunneling microscopy reveal that the surface of the SRO thin film is atomically smooth. The resistivity of the SRO thin film is 300 μΘ·cm at room temperature. Furthermore, the transmission electron microscopy study shows that the interfaces of STO/SRO and SRO/STO are very clear and no interfacial reaction layer was observed. The experimental results show that the SRO thin film is an excellent electrode material for devices based on perovskite oxide materials. Supported by the National Natural Science Foundation of China (Grant No. 10334070)     

Plastic deformation of a monoclinic Al13Fe4 at 300 ∼ 873 K

The plasticity of monoclinic Al₁₃Fe₄ particles grown in a spray-formed Al–Fe alloy is examined after being submitted to two deformation modes between 300 and 873 K by specially designed semi-in situ compression tests; one is uniform and the other is by indentation. In the uniform mode, cracks propagate through the Al₁₃Fe₄ particles along the pentagonal column planes, leaving extremely thin and heavily deformed plastic zones along the cracked faces at 300 and 473 K. In contrast, the generation of isolated dislocations and their motion govern the plastic deformation at 673 and 873 K. In the indentation mode, local deformation is achieved exclusively by individual dislocations over the whole range of temperature explored. A possible mechanism of dislocation motion in monoclinic Al₁₃Fe₄ is discussed based on Burgers vector analyses coupled with the three-dimensional observation of dislocation configurations.     

Effects of Ca/Al ratio and extrusion process on Mg–Al–Ca alloys to produce a high toughness in-situ composite

The microstructures and tensile properties of Mg–Al₂Ca–Mg₂Ca in situ composites (Mg–17Al–8Ca, Mg–14Al–11Ca and Mg–12.5Al–12.5Ca) with different Ca/Al ratios have been studied in both as-cast and extruded conditions. The results indicated that by increasing Ca/Al ratio, new Mg₂Ca intermetallic introduces to the Al₂Ca phase in eutectic structure. Computer-aided cooling curve analysis confirmed the formation of these phases during solidification. Extrusion process not only altered the size of large bulk Al₂Ca intermetallic, but also changed the size and morphology of intermetallics in eutectic structure considerably. The results showed that with increasing Ca/Al ratio, tensile properties of cast composites changes slightly, but significant enhancement is observed after extrusion process. The strength and elongation values of Mg–12.5Al–12.5Ca (Ca/Al = 1) alloy improved from 166 MPa and 2% in as-cast condition to 465 MPa and 12% in hot-extruded condition. The reason for the improved toughness may be attributed to the formation of finer and well-dispersed distribution of hard (Al₂Ca) and ductile (Mg₂Ca) phases. It was found that hot extrusion easily deforms ductile Mg₂Ca phase in comparison with Al₂Ca phase. In as-extruded condition, there are more very fine dimples than as-casted condition because extrusion process leads to formation of fragmented tiny particles and more uniformity distribution of Al₂Ca particles.     

Transition radiation,Cerenkov radiation and energy losses of relativistic charged particles traversing thin foils at oblique incidence

Semiclassical relativistic energy losses and the transition radiation are calculated for fast charged particles (e.g. electrons) traversing a thin dielectric foil at oblique incidence. The transition radiation formula is generalized for foils with spatial dispersion. This formula for oblique electron incidence is of particular interest for the observation of Cerenkov radiation, emitted from a dielectric foil. The emission of Cerenkov radiation is discussed for varying electron incidence angle and foil thickness by the aid of numerical computations.     

Chemical and catalytic effects of ion implantation

Energetic particles are used for inducing chemical reactions as well as for modifying the properties of materials with regard to their bulk and surface chemical behavior. The effects are partly caused by radiation damage or phase intermixing, partly by the chemical properties of the individual bombarding particles. In this contribution a survey of relevant applications of these techniques is presented:

1) Chemical reactions of implanted and recoil atoms and their use for syntheses, doping and labeling of compounds.

2) The formation of thin films by decomposing chemical compounds with ion beams.

3) Catalytic effects on substrates treated by sputtering or ion implantation. Recent results with nonmetallic substrates are reviewed. Mainly hydrogenation reactions at a solid/gas interface or redox reactions at an electrified solid/liquid interface are mentioned.

The present status and future prospects of these kinds of investigations will be discussed.     

Interaction of H_2~+ molecular beam with thin layer graphene foils

The interaction of MeV H_2~+ molecular ions with thin layer graphene and graphite foils was studied by using a highresolution electrostatic analyzer.A large number of fragment protons were observed at zero degree(along the beam direction) when the H_2~+ beam was passing through the monolayer graphene foil, which indicates that the electron of the H_2~+ molecular ions can be stripped easily even by the monolayer graphene foil.More trailing than leading protons were found in the energy spectrum, which means significant wake effect was observed in the monolayer graphene foil.The ratio of the numbers of trailing protons over leading protons first increased with the thickness for the much thinner graphene foils, and then decreased with the thickness for the much thicker graphite foils, which indicates that the bending effect of the wake field on the trailing proton varied with the foil thickness.     

High voltage electron microscopy observations of the growth of interstitial loops in an iron-nitrogen alloy

Precipitation of interstitial loops and iron nitride in an iron nitrogen alloy, has been examined in the temperature range 30 °C to 300 °C using a High Voltage Electron Microscope. The use of thick foils has enabled the direct observation of iron nitride precipitation. Observations confirm both theoretical and indirect experimental studies of the hardening behaviour of α-iron alloys following neutron irradiation.

Many of the interstitial loops are of {100} type. In certain cases, the unfaulted ½{110} type are observed. The precipitation of iron nitride at the edge of the loop, effectively prevents further growth thus inhibiting void swelling.