Cross-sectional Transmission Electron Microscopy Observations Research Articles

Co-deposited layers on gap surfaces of bulk tungsten divertor tiles in JET ITER-like wall: Directional effects and nanostructures

Co-deposited layers on surfaces of bulk tungsten divertor tiles (W lamellae) from the first campaign of JET with the ITER-Like Wall (JET-ILW, 2011–2012) were examined by means of a cross-sectional transmission electron microscope observation. The focus was on geometrical effects in impurity deposition, mainly beryllium (Be), on surfaces located in the poloidal gap separating adjacent lamellae. The study was carried out on the sides (gap surfaces) of two W lamellae from Stack C (located on the outboard part of the horizontal section of the lower divertor), from the region most exposed to the plasma (lamella C23) and in the magnetic shadow of the upstream divertor module (lamella C3). The tile manufacturing process (cold rolling) left shallow grooves, i.e. structures classified as convex (hill) and concave (valley) regions. These regions are decisive for the deposition structure. The main results were: (i) two kinds of impurity deposition features, “homogeneous” and “directional”, have been distinguished; (ii) the directional ones were characterized by nanoscale inclined vertical stripes in the deposition layer; (iii) homogeneous deposition without directional features were in the valley region. The results clearly indicate the impact of the surface finish, even in the tile gaps, on the qualitative and quantitative aspects of deposition.

Local strain distribution analysis in strained SiGe spintronics devices

This paper reports nanobeam X-ray diffraction (nanoXRD) measurement results for strained SiGe spintronics devices grown by MBE. A quantitative nanoXRD analysis verifies that in-plane strain is properly exerted on the SiGe spin channel layer in the device showing enhanced spin diffusion length, whereas overall strain relaxation and local change in crystallinity occur in the sample with unclear spin signals. Crystal defects such as dislocations and stacking faults found in cross-sectional transmission electron microscopy observations are correlated with the results of nanoXRD analysis and their influence on spin transport properties are discussed. The present results demonstrate the capability of the nanoXRD based method for quantitative nondestructive analysis of strain distribution and crystallinity in real device structures.

MBE growth of SnTe films on GaAs substrates with ZnTe buffer layers

SnTe (100) single-domain thin films have been previously grown on GaAs substrates by molecular beam epitaxy but obtaining excellent crystallinity can be difficult. In this paper, ZnTe buffer layers are introduced to improve the crystallinity of SnTe films. The effects of the molecular beam flux ratio (JTe/JSn) and growth temperature (Tg) on the crystallinity are investigated to achieve high-quality layers. The surface morphology and electrical properties of the SnTe thin films are also evaluated in addition to the conventional X-ray diffraction (XRD)measurements. The crystallographic properties of the grown samples are shown to be significantly improved by introducing a ZnTe buffer layer. XRD (θ–2θ) full width at half maximum of the lowest value obtained so far is about 0.14°. It is also found that lowering JTe/JSn to 0.6 results in a reduced growth rate, and an increased growth temperature (Tg = 220 °C) promotes the migration of atoms at the growth front. Both effects contribute to improvement in the crystallographic quality, including the layer surface smoothness. The cross-sectional transmission electron microscopy observation of the sample indicates the abrupt interface formation with different lattice structures. It is also found that low growth temperatures (below 200 °C) are not favorable for the SnTe layer growth, which is confirmed by the surface morphology.

Microstructure and Magnetism of Heavily Helium-Ion Irradiated Epitaxial Iron Films

This study reports on the microstructure and magnetism of pure iron irradiated with high doses of helium ions. Iron alloys are important structural materials used as components in fusion reactors, and a comprehensive database of their various properties has been developed. But little has been investigated on magnetic properties, in particular, the effects of high doses and helium cavities are lacking. Single-crystal iron films, with a thickness of 200 nm, were prepared using the ultra-high vacuum evaporation method. These films were then irradiated with 30 keV He+ ions at room temperature up to a dose of 18 dpa. X-ray diffraction measurements and cross-sectional transmission electron microscope observations revealed significant microstructural changes, including a large lattice expansion perpendicular to the film plane and the formation of high-density cavities after irradiation. However, the saturation magnetization and the shape of the magnetization curve showed almost no change, indicating the robustness of the magnetic properties of iron.

Plasma-activated high-strength non-isothermal anodic bonding for efficient fabrication of the micro atomic vapor cells

Microfabricated alkali metal vapor cells are the core components for miniaturizing quantum devices, such as atomic clocks, atomic gyroscopes, and atomic magnetometers. Alkali metals are prone to thermal migration at the bonding interface during the sealing of the vapor cell, which leads to bonding failure. In this study, a non-isothermal anodic bonding process based on plasma activation was developed to achieve high-strength bonding at low temperatures using the temperature gradient to keep the alkali metal away from the bonding interface. This procedure eliminates interference from the alkali metal and significantly increases the success rate of anodic bonding of vapor cells. Simulation results for the temperature field and the residual stresses during anodic bonding demonstrate that the procedure is theoretically feasible. The effect of plasma treatment on the contact angle and roughness of the bonding surface revealed a mechanism for improving the bond strength. In addition, the construction of an integrated processing platform made it possible to perform non-isothermal anode bonding, injection of alkali metal, filling of inert gases, and recovery and recycling of noble gases. The high strength and good hermeticity of the bonding interface were demonstrated by the bond strength, cross-sectional high-resolution transmission electron microscopy observations, and leakage rate tests. Finally, the absorption spectrum and free-induction decay signal of the fabricated vapor cell were measured.

Observation of comet-shaped defect as killer defect in halide vapor phase epitaxial (001) β-Ga2O3 and its impact on Schottky barrier diodes

We observed killer defects that served as reverse leakage current paths for halide vapor phase epitaxial (001) β-Ga2O3 Schottky barrier diodes, which resulted in a leakage current of −0.46 μA at reverse bias of −100 V. Synchrotron X-ray topography revealed comet-shaped contrasts extending along [010] which are induced from the strain field surrounding the defects. They consisted of perfect (100)-cracks and horizontal-oriented (001) cracks. The cross-sectional scanning transmission electron microscopy observation showed (100)-cracks on the surface and dislocations along [100] beneath the surface. This defect was speculated to be generated from damage during the chemical-mechanical polishing.

Single crystal-single crystal bonding of langasite exhibited high strength of 23.28 MPa

Langasite (LGS, La3Ga5SiO14) is a promising material in high-temperature piezoelectric devices due to its excellent thermal stability, piezoelectricity, and electrical property. A major challenge in the development of LGS-based devices is to form high-strength bonding of the brittle LGS. Here, we report that the single crystal-single crystal (dual-SC) bonding of LGS is realized through thermal activation under a low compression of 50 kPa for the first time. A record bonding strength of 23.28 MPa is achieved within the dual-SC bonded LGS/LGS structure (with a high bonding ratio exceeding 93%), which is 5 times higher than that of the recent reported LGS/LGS bonding structure (in which a relatively fragile amorphous interface layer is formed between the two LGS samples). The smooth and void-free dual-SC bonding interface of LGS is verified via the cross-sectional transmission electron microscopy (TEM) observations.

Nb–Nb direct bonding at room temperature for superconducting interconnects

Superconducting devices with high-density integration are required for applications, such as high-performance detectors and quantum computing. Here, the direct bonding of Nb electrodes at room temperature using a surface activated bonding method was investigated. We directly bonded Nb bonding pads and then performed current–voltage measurements in a 3He cryostat. A superconducting current of 1–5 mA was confirmed for the bonded interconnect. The transition temperature was 7.3–9.3 K. These values are affected by the quality of the bonding interface. According to cross-sectional transmission electron microscopy observations and energy-dispersive x-ray spectroscopy analysis of the bonding interface, the Nb layers were bonded with a 3-nm-thick intermediate layer made of Si and Nb between them. The Si sources were the bonding substrate and the bonding jig in the bonding apparatus.

Evaluation of Damage in Crystalline Silicon Substrate Induced by Plasma Enhanced Chemical Vapor Deposition of Amorphous Silicon Films

We evaluated damage to crystalline silicon (c-Si) induced by plasma enhanced chemical vapor deposition (PECVD) of hydrogenated amorphous silicon (a-Si:H). The damaged layer +-on the c-Si surface under the a-Si:H film was evaluated by lifetime measurements using the photoconductance method in conjunction with step etching. This damaged layer is approximately 2.8 nm and did not disappear by annealing at 200 °C for 30 min in the air atmosphere. The image from cross-sectional transmission electron microscope (TEM) observation also shows an area of contrast on the c-Si surface approximately 2.8 nm thick, which appears to be a damaged layer. Photoluminescence (PL) measurements revealed that this damage is a non-luminescent defect. We verified that the difference in H2 flow rate during the a-Si:H deposition has an effect on the depth of the damage penetration into the c-Si. We concluded that the H atom is the main cause of the damage introduced into c-Si during a-Si:H deposition by PECVD.

Structural Defects and Ferromagnetic Signature of V-Doped Sb2Te3 Thin Films Grown on SrTiO3(001) Produced by RF-Magnetron Sputtering.

Thin films of V-doped Sb2Te3 compounds were fabricated by co-deposition of Sb2Te3 and V using rf-magnetron sputtering onto SrTiO3(001) substrates kept at 570 K. The microstructures of the films were characterized using transmission electron microscopy (TEM) and electron diffraction. The crystal structure of the sputtered film (Sb38V2Te60) is the Bi2Te3-type structure with lattice parameters of a = 0.44 ± 0.03 nm and c = 3.02 ± 0.02 nm. A combination of cross-sectional and plan-view TEM observations revealed the preferential orientation of the c axis in the film's normal direction. A thin amorphous layer exists between the Sb2Te3 thin film and the SrTiO3 substrate. The interfacial amorphous layer relaxes the strain between the thin film and the substrate, and hence, it should promote the growth of a low-index atomic plane with a low surface free energy (i.e., (0001) of the Sb2Te3). The onset of ferromagnetic order was detected at temperatures below 70 K. A remarkable increase in magnetization was detected in the film's normal direction, which corresponds to the magnetic easy axis (i.e., c axis of the Sb2Te3). V3+ ions substituting Sb sites should contribute to ferromagnetism at low temperatures.

Molecular beam epitaxy of stoichiometric tin–telluride thin films

Tin–telluride (SnTe) thin films were grown on (001)-oriented GaAs substrates using molecular beam epitaxy. Samples were grown with various molecular beam intensity ratios at substrate temperatures of 225 °C and 240 °C. The crystallinity of the SnTe thin films was studied using X-ray diffraction θ–2θ measurements. Stoichiometric SnTe layers were achieved by tuning both molecular beam intensity ratio and substrate temperature. It was also found that the excess Te remained in films when the molecular beam intensity ratio was Te rich. The (111)-oriented domain was confirmed when the substrate temperature was 240 °C. Continuous film formation was confirmed from cross-sectional transmission electron microscopy (TEM) observation. The segregation of Te for certain samples were also confirmed from the TEM energy dispersive x-ray mapping.

The restricted random dislocation distribution model to describe ensembles of dislocations with a screw component in ZnO layers with a mosaic structure

By applying the restricted random dislocation distribution model, solved using a discrete Hankel transform approach, it is shown that the shapes and characteristics of the ω-scans of the ZnO 00.2 reflection are mainly determined by the strain field introduced by dislocations with a screw component. On the other hand, no clear evidence of mosaicity or interfacial region contributions is found despite the layers exhibiting a c axis oriented residual columnar structure and a highly defective interface being present. The applied model not only permits a more precise estimation of the densities of dislocations, which present a screw component with respect to methods based on the analysis of the 00.2 peak ω-scan FWHM, but also gives an indication of their distribution characteristics with the extracted values, as well as their homogeneous/quasi-regular spacing, being confirmed by cross-sectional transmission electron microscopy observations.

In Situ Transmission Electron Microscopy Study of Shrinkage Kinetics of CH4N-Molecular-Ion-Implantation-Induced Extended Defects

The thermal stability of end-of-range (EOR) defects formed in a CH4N-molecular-ion-implanted epitaxial silicon (Si) wafer was studied by transmission electron microscopy (TEM) observation. By plan-view TEM observation, we found that the density and size of the CH4N-ion-implantation-induced EOR defects negligibly changed upon heat treatment at temperatures below 1000 °C, whereas the EOR defect density was drastically reduced by heating at 1100 °C. This result suggests that almost all CH4N-ion-implantation-induced EOR defects were sufficiently thermally stable to maintain their size at temperatures below 1000 °C, and that above 1100 °C, most of the EOR defects lost their stability, shrank and finally dissolved. Additionally, by in situ cross-sectional TEM observation during heat treatment, we found a large difference in the shrinkage rates of the EOR defects between at the beginning of heat treatment and the last minute of just before defect disappearance. We found that the EOR defects began to gradually shrank at the beginning of heat treatment (1st stage), and then the shrinkage rate rapidly increased (2nd stage), finally resulting in the dissolution of the defects. The activation energies for the shrinkage of EOR defects in the 1st and 2nd stages (E D-1 and E D-2) were found to be 7.55 ± 1.03 and 4.57 ± 0.32 eV, respectively. The shrinkage behavior in the 1st stage is likely to be due to the thermally activated desorption of C and N species that segregated along the edge of an EOR defect. On the other hand, from the E D-2 value, the shrinkage behavior in the 2nd stage is deduced to be due to the desorption of interstitial Si atoms. These findings suggest that this two-stage shrinkage behavior is peculiar to the EOR defects formed in the CH4N-ion-implanted epitaxial Si wafer, and that the interaction between the EOR defect and the impurities segregated at the edge of the defect affects the thermal robustness of the molecular-ion-implantation-induced EOR defects.

Surface nanostructures on Nb-doped SrTiO3 irradiated with swift heavy ions at grazing incidence

A single crystal of SrTiO3 doped with 0.5 wt% niobium (Nb-STO) was irradiated with 200 MeV Au32+ ions at grazing incidence to characterize the irradiation-induced hillock chains. Exactly the same hillock chains are observed by using atomic force microscopy (AFM) and scanning electron microscopy (SEM) to study the relation between irradiation-induced change of surface topography and corresponding material property changes. As expected, multiple hillocks as high as 5–6 nm are imaged by AFM observation in tapping mode. It is also found that the regions in between the adjacent hillocks are not depressed, and in many cases they are slightly elevated. Line-like contrasts along the ion paths are found in both AFM phase images and SEM images, indicating the formation of continuous ion tracks in addition to multiple hillocks. Validity of preexisting models for explaining the hillock chain formation is discussed based on the present results. In order to obtain new insights related to the ion track formation, cross-sectional transmission electron microscopy (TEM) observation was performed. The ion tracks in the near-surface region are found to be relatively large, whereas buried ion tracks in the deeper region are relatively small. The results suggest that recrystallization plays an important role in the formation of small ion tracks in the deep region, whereas formation of large ion tracks in the near-surface region is likely due to the absence of recrystallization. TEM images also show shape deformation of ion tracks in the near-surface region, suggesting that material transport towards the surface is the reason for the absence of recrystallization.

Homoepitaxial overgrowth of (111) diamond films on Au-coated and Ni-coated substrates

Homoepitaxial growth of (111)-oriented diamond films on the Au-coated and Ni-coated diamond substrates by microwave plasma chemical vapor deposition (CVD) has been investigated. The process is involved with overgrowth of CVD diamond on Au and Ni islands formed by hydrogen plasma annealing of the 20 nm Au and Ni film coatings on diamond substrates. Cross-sectional transmission electron microscopy (TEM) observations show that both of the Au and Ni islands as single crystallites are in epitaxy with diamond substrate and no diamond growth occurs on top of those islands in the early stage of diamond deposition. The overgrowth of diamond over the metal islands results in excellent coalescence to form a continuous film with a lower defect density than the film without the metal coating. With such Au and Ni islands, the film stress can be further relaxed as shown with Raman spectroscopy.

Exfoliation Resistance, Microstructure, and Oxide Formation Mechanisms of the White Oxide Layer on CP Ti and Ti-Nb-Ta-Zr Alloys.

We found that specific biomedical Ti and its alloys, such as CP Ti, Ti–29Nb–13Ta–4.6Zr, and Ti–36Nb–2Ta–3Zr–0.3O, form a bright white oxide layer after a particular oxidation heat treatment. In this paper, the interfacial microstructure of the oxide layer on Ti–29Nb–13Ta–4.6Zr and the exfoliation resistance of commercially pure (CP) Ti, Ti–29Nb–13Ta–4.6Zr, and Ti–36Nb–2Ta–3Zr–0.3O were investigated. The alloys investigated were oxidized at 1273 or 1323 K for 0.3–3.6 ks in an air furnace. The exfoliation stress of the oxide layer was high in Ti–29Nb–13Ta–4.6Zr and Ti–36Nb–2Ta–3Zr–0.3O, and the maximum exfoliation stress was as high as 70 MPa, which is almost the same as the stress exhibited by epoxy adhesives, whereas the exfoliation stress of the oxide layer on CP Ti was less than 7 MPa, regardless of duration time. The nanoindentation hardness and frictional coefficients of the oxide layer on Ti–29Nb–13Ta–4.6Zr suggested that the oxide layer was hard and robust enough for artificial tooth coating. The cross-sectional transmission electron microscopic observations of the microstructure of oxidized Ti–29Nb–13Ta–4.6Zr revealed that a continuous oxide layer formed on the surface of the alloys. The Au marker method revealed that both in- and out-diffusion occur during oxidation in Ti–29Nb–13Ta–4.6Zr and Ti–36Nb–2Ta–3Zr–0.3O, whereas only out-diffusion governs oxidation in CP Ti. The obtained results indicate that the high exfoliation resistance of the oxide layer on Ti–29Nb–13Ta–4.6Zr and Ti-36Nb-2Ta-3Zr-0.3O are attributed to their dense microstructures composing of fine particles, and a composition-graded interfacial microstructure. On the basis of the results of our microstructural observations, the oxide formation mechanism of the Ti–Nb–Ta–Zr alloy is discussed.

Growth of Metastable α-Ga<sub>2</sub>O<sub>3</sub> Epitaxial Thin Film on Flexible Synthetic Mica by Insertion α-Fe<sub>2</sub>O<sub>3</sub> Buffer Layer

Metastable α-Ga2O3 thin films with a corundum structure were grown epitaxially on flexible synthetic mica. The κ-Ga2O3 thin films were grown in a temperature range of 450‒600 °C, without a buffer layer. In contrast, the α-Ga2O3 thin films were grown in a wider temperature range of 350‒600 °C, by inserting corundum-structured α-Fe2O3 buffer layers. X-ray diffraction (XRD) rocking curve measurements revealed that the α-Ga2O3 thin film grown at 425 °C had the highest degree of crystallinity. Cross-sectional transmission electron microscopy (TEM) observations and an XRD φ scan revealed that the epitaxial relationship between the thin film and the substrate via the buffer layer was (0001) α-Ga2O3 [11‒20] || (001) synthetic mica [100]. Furthermore, when TEM observation was performed close to the surface of the α-Ga2O3 thin film at a high magnification, a lattice image derived from the out-of-plane (0001)-plane orientation was observed. However, it was also revealed that the α-Ga2O3 thin films did not have a single crystal structure but rather an in-plane domain structure. By conducting selected area electron diffraction (SAED) at the interface area, it was determined that the α-Fe2O3 buffer layer was polycrystalline. This implies that α-Ga2O3 thin films were epitaxially grown while forming the in-plane domains on the polycrystalline buffer layers. The results of this study indicate the flexible applications of α-Ga2O3 thin films, which have significant potential for use as power sources and deep-ultraviolet devices.

Microstructures and Interface Magnetic Moments in Mn2VAl/Fe Layered Films Showing Exchange Bias.

Heusler alloys are a material class exhibiting various magnetic properties, including antiferromagnetism. A typical application of antiferromagnets is exchange bias that is a shift of the magnetization curve observed in a layered structure consisting of antiferromagnetic and ferromagnetic films. In this study, a layered sample consisting of a Heusler alloy, MnVAl and a ferromagnet, Fe, is selected as a material system exhibiting exchange bias. Although the fully ordered MnVAl is known as a ferrimagnet, with an optimum fabrication condition for the MnVAl layer, the MnVAl/Fe layered structure exhibits exchange bias. The appearance of the antiferromagnetic property in the MnVAl is remarkable; however, the details have been unclear. To clarify the microscopic aspects on the crystal structures and magnetic moments around the MnVAl/Fe interface, cross-sectional scanning transmission electron microscope (STEM) observation, and synchrotron soft X-ray magnetic circular dichroism (XMCD) measurements were employed. The high-angle annular dark-field STEM images demonstrated clusters of MnVAl with the L2 phase distributed only around the interface to the Fe layer in the sample showing the exchange bias. Furthermore, antiferromagnetic coupling between the Mn- and Fe-moments were observed in element-specific hysteresis loops measured using the XMCD. The locally ordered L2 phase and antiferromagnetic Mn-moments in the MnVAl were suggested as important factors for the exchange bias.

Microstructure Characterization of Electrodeposited Invar Fe–Ni Alloy

In Fe–Ni alloys, coefficients of thermal expansion (CTEs) of Fe–Ni alloys with 30 to 40 mass% Ni are small compared to that of Fe (CTE = 12 ppm/K) or Ni (CTE = 13 ppm/K) at near room temperature. In particular, the Fe–Ni alloys with 36 mass% Ni exhibit the lowest CTE (approximately 1 ppm/K) among the Fe–Ni alloys. These Fe–Ni alloys with 30 to 40 mass% Ni are called “Invar alloys.” An Fe–Ni alloy electroplating can be used as the high-throughput Invar alloy fabrication process, furthermore, an Fe–Ni alloy electroforming process can provide precise micrometer-sized three-dimensional structures of Invar alloys with excellent thermal dimensional stability, e.g., MEMS (microelectromechanical systems).We already have prepared electrodeposited Invar Fe–Ni alloys with 36 mass% Ni from plating baths containing saccharin as a stress reducer and containing Fe2+ and Ni2+ ions with various concentration ratios. The electrodeposited Invar Fe–Ni alloys contained of small amount of S (~0.02 mass%) which was originated from saccharin.It was confirmed that as-deposited Invar Fe–Ni alloys were mainly composed of metastable bcc phases, resulting in larger CTEs. When the alloys were annealed at 400°C or above, the equilibrium fcc phases became the predominant phases, accompanied by a drastic decrease of the CTEs. The bcc-to-fcc transformation led to a decrease of the CTEs.In general, electrodeposited fcc Ni and Ni-rich Fe–Ni alloys containing small amounts of S are often embrittled upon annealing. An S (sulfide) in the as-deposited fcc films is dispersed at grain boundaries (2). During recrystallization and grain growth of the fcc grains by heat treatment, the S (sulfide) is extruded into recrystallized an fcc grain boundary with segregating as a thin layer form. The S thin layer coats the fcc grain boundaries and causes grain boundary weakening; therefore, distinct embrittlement occurs, and the embrittlement is promoted by rapid grain growth during annealing (3).With respect to our electrodeposited Invar Fe–Ni alloys with S, in contrast, ductile behavior was confirmed, irrespective of whether the alloys were heat-treated. Upon heat treatment at 400 to 500°C, the Invar Fe–Ni alloys exhibited high strength with good ductility, consistent with their low CTE (1). Moreover, we observed that the S in the Invar Fe–Ni alloys heat-treated at 600°C existed not as a filmy sulfide but as a granular sulfide at grain boundaries. However, the microstructures containing the granular sulfide generated in the film during heat treatment have not been sufficiently explored.In this study, we investigated microstructure of the electrodeposited Invar alloys with and without heat treatment in detail. In particular, morphology and composition of the sulfide were evaluated in the Invar alloys with changing of microstrucutre during an annealing.A galvanostatic electrolysis was conducted for preparation of the Invar Fe–Ni alloy film with 36 mass% Ni from the plating bath (1).A transmission electron microscopy (TEM) was are used for microstructure characterization of the obtained films. A focused-ion-beam (FIB) system have given choice to fabricate cross-sectional TEM specimen.From the results of cross-sectional TEM observation of the electrodeposited Invar Fe- 36 mass%Ni alloys with and without heat treatment at 300 to 600°C, it was found that the as-deposited bcc electrodeposited Invar alloys exhibited a columnar microstructure composed of micrometer-sized coarse grains and submicrometer-sized grains.After the heat treatment at 300 to 400°C, where the proportion of fcc phase increased, the columnar structure became indistinct and the fraction of the submicrometer-sized fine grains increased. Furthermore, no substantial segregated sulfide was detected at the Fe–Ni alloy from elemental mapping by energy dispersive spectroscopy (EDS) in TEM.Heat treatment at 500°C led to grain growth; the alloys treated at this temperature were fully composed of the fcc phase, accompanied by a decrease in the CTE.Our TEM results suggest that S in the Invar Fe-36 mass%Ni alloy became highly concentration upon heat treatment at 500°C and formed granular Fe-rich Fe–Ni–S in grain-boundary triple-points.In our research, the formation of granular sulfide in the film after heat treatment at 500 ° C and its composition were confirmed for the first time.Upon heat treatment at 600°C, Fe-Ni matrix grains grew up as recrystallized grains, accompanied by grain growth of the Fe–Ni–S compound in the matrix grains or grain-boundary triple-points. T. Nagayama, T. Yamamoto and T. Nakamura, Electrochim. Acta, 205, 178 (2016). I. Tabakovic, S. Riemer, K. Tabakovic, M. Sun and M. Kief, J. Electrochem. Soc., 153, C586 (2006). Y. M. Wang, S. Cheng, Q. M. Wei, E. Ma, T. G. Nieh and A. Hamza, Scripta Mater., 51, 1023 (2004).

Scanning probe-based nanolithography: nondestructive structures fabricated on silicon surface via distinctive anisotropic etching in HF/HNO3 mixtures

HF/HNO3 mixtures were typical isotropic etching systems for processing silicon (Si) surface, and still suffer from difficulties in controllably fabricating nanostructures. Here, fast and anisotropic etching approach with HF/HNO3 mixtures was developed to overcome this challenge. An atomic force microscope diamond tip was used for the preparation of friction-induced hillocks, mainly consisting of amorphous Si, through reciprocating sliding of Si surfaces below critical contact pressure. The hillock acted as a mask against HF/HNO3 mixtures etching, forming nanostructures through subsequent distinctive anisotropic etching. The effects of volume ratio of HF/HNO3 mixtures, sliding cycle, normal load, and etching time on anisotropic etching were systematically investigated to optimize fabrication parameters. Further analysis suggested that lower average dangling bond density in scanned regions may retard the breakup of Si–H bonds and polarized Si–Si backbonds, leading to lower dissolution rates compared to original Si surface. Cross-sectional high-resolution transmission electron microscope observations revealed defect-free nanostructures fabricated by the anisotropic etching. Also, several nondestructive nanostructures with different patterns were realized on Si surfaces by programming tip scanning traces. In sum, the proposed method is promising for the fabrication of controllable nano-sized functional devices by HF/HNO3 mixtures. Nanofabrication of nondestructive structures on silicon surface via distinctive anisotropic etching in HF/HNO3 mixtures