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Garnet-type Li

Ultra-thin silicon nitride (SiN) membranes are critical in microfabrication-based liquid cells (LCs) for transmission electron microscopy (TEM). This study used a homemade LC with a 50-nm SiN membrane to study the dynamics of 2.58-nm platinum (Pt) nanoparticles (NPs) in approximately 200-nm-deep water. When a strong beam with electron flux ranging from 2.5 × 103 to 1.4 × 106 e−/(nm2 s) was applied to resolve the NPs, the beam caused NP aggregation and even drilled a hole on the top membrane. The hole drilling was prevented by coating a 1–4-nm-thick amorphous carbon layer on both sides of the membrane. The NP aggregation rate also decreased with increasing carbon thickness. After overcoming the aforementioned issues, lattice fringes of the Pt NPs were visible when the NPs were attached to the membrane of the 4-nm-carbon-coated LC containing a thin liquid layer. The effects of the electron beam and carbon on the LC and Pt NPs were investigated and discussed. This work provides a reference for LC-TEM research using strong electron beams.

Diffraction patterns contain useful information about the materials. Recent developments in four-dimensional scanning transmission electron microscopy and the acquisition of the spatial distribution of diffraction patterns have produced significant results. The acquisition of a temporal series of diffractions is achieved for a stationary beam. However, the acquisition of spatiotemporal distribution of diffraction patterns has only been established under limited conditions. In this study, we developed a simple method that enables the recording of the spatiotemporal distribution of diffraction patterns and applied it to the relaxation time measurement that is robust to sample drift.

For decades, it has been reported that some organic crystals suddenly crack, break, or jump when they are heated from room temperature. Recently, such crystals have been intensively studied both in fundamental science and for high-speed mechanical device applications. According to these studies, the sudden crystal motions have been attributed to structural phase transitions induced by heating. Stress created by the phase transition is released through the sudden and rapid motion of the crystals. Here we report that single crystal nanofibers of coronene exhibit a new type of ultrafast motion when they are cooled from room temperature and subsequently heated to room temperature. The nanofibers make centimeter-scale jumps accompanied by surprisingly unique behaviors such as sharp bending and wriggling. We found that the motions are caused by a significantly fast structural phase transition between two polymorphs of coronene. A theoretical investigation revealed that the sudden force generated by the phase transition together with the nanoscale dimensions and elastic properties create dynamical instability in the nanofibers that results in the motions. Our finding demonstrates the novel mechanism that leads to ultrafast, large deformation of organic crystals.

Heterointerfaces with an epitaxial relationship, self-assembled nanocomposites of Pt(111)/CeO2(111) 60°, were successfully formed by simple oxidation of Pt5Ce alloy. Oxygen dissolution into the alloy causes spacial periodic compositional perturbation by atomic segregation, specifically, by local diffusion of Pt and Ce atoms. A striped pattern of Pt and CeO2 with a 4–5 nm periodicity formed through phase transformation of the Pt-rich alloy and oxidation of the Ce-rich alloy, respectively. Notably, a fully epitaxial relationship between the Pt and CeO2 phases was observed even in the initial stage. With continued annealing, the crystals rotated into an energetically favorable orientation with respect to the remaining (111)Pt//(111)CeO2. The alloy oxidation and its resulting nanoscale phase-separation behavior were verified in an ex situ annealing experiment of an alloy specimen, which had been first thinned by a focused ion beam. Changing the oxygen partial pressure to the reaction interface may alter the orientation relationship between the hexagonal close-packed Pt5Ce structure and face-centered cubic Pt/CeO2 structure, thereby altering the growth direction of the separated phases. These findings present a pathway for the self-assembly of epitaxial Pt(111)/CeO2(111) interface and are expected to assist the structural design of metal–oxide nanocomposites.

Liquid cell transmission electron microscopy (LCTEM) enables imaging of dynamic processes in liquid with high spatial and temporal resolution. The widely used liquid cell (LC) consists of two stacking microchips with a thin wet sample sandwiched between them. The vertically overlapped electron-transparent membrane windows on the microchips provide passage for the electron beam. However, microchips with imprecise dimensions usually cause poor alignment of the windows and difficulty in acquiring high-quality images. In this study, we developed a new and efficient microchip fabrication process for LCTEM with a large viewing area (180 µm × 40 µm) and evaluated the resultant LC. The new positioning reference marks on the surface of the Si wafer dramatically improve the precision of dicing the wafer, making it possible to accurately align the windows on two stacking microchips. The precise alignment led to a liquid thickness of 125.6 nm close to the edge of the viewing area. The performance of our LC was demonstrated by in situ transmission electron microscopy imaging of the dynamic motions of 2-nm Pt particles. This versatile and cost-effective microchip production method can be used to fabricate other types of microchips for in situ electron microscopy.

The development of lithium-ion batteries (LIBs) with high-energy densities faces challenges to meet the ever-growing market demands. Tungsten oxide (WO3) with high theoretical capacity and low cost...

The threshold voltage (V TH) stability in GaN fat field-effect transistors (FATFETs) with a large channel area of ∼6.2 × 104 μm2 was studied using drain current vs gate voltage (I D–V G) characteristics. Each measurement was found to positively shift the previous I D–V G curve, and V TH eventually saturated with increasing number of measurements. The saturated V TH was ∼0.8 V for measurements in which V G ranged from −10 to 25 V and was ∼8 V for measurements in which the V G ranged from −10 to 40 V. Moreover, the positive gate bias stress increased V TH to 12.3 V. These shifts of V TH can be explained by electron trapping; according to charge-pumping measurements, the traps cannot exist in the oxide or the oxide/p-GaN interface but can exist near the surface region in p-GaN layers in GaN FATFETs. Scanning transmission electron microscopy and electron energy-loss spectroscopy analyses revealed the presence of oxygen within several atomic layers of p-GaN from the oxide/p-GaN interface. This intermixed oxygen might be the origin of the n-type behavior of the p-GaN surface; furthermore, the oxygen is speculated to be related to the traps. Surprisingly, similar incorporated oxygen was observed even in the surface region of as-grown p-GaN layers.

In this work, a planar electron emission device based on a graphene/hexagonal boron nitride (h-BN)/n-Si heterostructure is fabricated to realize highly monochromatic electron emission from a flat surface. The h-BN layer is used as an insulating layer to suppress electron inelastic scattering within the planar electron emission device. The energy spread of the emission device using the h-BN insulating layer is 0.28 eV based on the full-width at half-maximum (FWHM), which is comparable to a conventional tungsten field emitter. The characteristic spectral shape of the electron energy distributions reflected the electron distribution in the conduction band of the n-Si substrate. The results indicate that the inelastic scattering of electrons at the insulating layer is drastically suppressed by the h-BN layer. Furthermore, the maximum emission current density reached 2.4 A/cm2, which is comparable to that of a conventional thermal cathode. Thus, the graphene/h-BN heterostructure is a promising material for planar electron emission devices to obtain a highly monochromatic electron beam and a high electron emission current density.

This paper reports the electrode performance of a Si anode composed of nanoparticles prepared by spray deposition in a solid-state cell. Upon lithiation, the Si nanoparticles undergo volume expansi...

All-solid-state lithium-ion batteries (ASSLIBs) with oxide-based solid electrolytes are a promising candidate for next generation of rechargeable batteries, due to their reliability and high-energy density. The formation of well-defined electrode/solid electrolyte interfaces with an excellent ionic conductivity by co-sintering is one of the key challenges to develop oxide-based ASSLIBs.1 Electrode materials and solid electrolytes often react with each other to form a resistive substance at their interface during co-sintering.2-4 Thus, optimization of the co-sintering conditions is important to control the interfacial structure which governs the ionic conductivity. However, the effect of the interfacial structure on the ionic conductivity remains unclear. In this study, we co-sintered the composites of LiCoPO4 (LCP) electrode material and Li1.3Al0.3Ti1.7(PO4)3 (LATP) oxide-based solid electrolyte and investigated the interfacial structure by using X-ray diffraction (XRD), X-ray absorption fine structure (XAFS) and scanning transmission electron microscopy combined with electron energy loss spectroscopy and an energy-dispersive X-ray spectroscopy (STEM-EELS/EDX). Figure 1(a) shows the XRD patterns of the LCP/LATP composites before and after sintering at 800°C. The diffraction patterns are almost identical to each other and all the diffraction peaks are attributed to the LCP and LATP with an exception of AlPO4 impurity. However, the Co K-edge XANES is slightly changed after sintering as shown in Figure 1(b). These results suggest that a small amount of LCP and LATP react with each other. Figure 1(c) shows a typical STEM image of the LCP/LATP composites after sintering at 800°C. According to EDX analysis, light and dark gray domains correspond to LCP and LATP, respectively. Apart from LCP and LATP, there are two types of LCP/LATP interfaces: interface A and B. Line profile STEM-EELS/EDX analysis revealed that LCP and LATP directly bound to each other at the interface A. On the other hand, a thermally reacted thin layer, possibly cobalt oxide (CoO) and/or cobalt phosphide (Co2P), is formed at interface B. The effect of such thermally reacted interlayer on the ionic conductivity will be discussed in detail. References: R. Chen, Q. Li, X. Yu, L. Chen and H. Li, Chemical Reviews, 2020, 120, 6820-6877. M. Gellert, E. Dashjav, D. Grüner, Q. Ma and F. Tietz, Ionics, 2017, 24, 1001-1006. C.-Y. Yu, J. Choi, V. Anandan and J.-H. Kim, The Journal of Physical Chemistry C, 2020, 124, 14963-14971. L. Miara, A. Windmuller, C. L. Tsai, W. D. Richards, Q. Ma, S. Uhlenbruck, O. Guillon and G. Ceder, ACS Applied Materials and Interfaces, 2016, 8, 26842-26850. Figure 1

The planar type electron emission devices using atomic layered materials of graphene and hexagonal boron nitride (h-BN) were developed to suppress inelastic electron scattering within the device structure. High emission efficiency of more than 40 % and high emission current density of more than 100 mA/cm2 were achieved by the suppression of the inelastic electron scattering within the topmost gate electrode using graphene,. In addition, highly monochromatic electron emission with an energy spread of 0.18 eV in the full width at half maximum were realized by the suppression of the inelastic electron scattering within the topmost gate electrode and insulating layer using the graphene/h-BN heterostructure. These results would lead to several practical applications of planar type electron emission devices.

We previously reported highly monochromatic electron emission from the planar-type electron emission devices based on a graphene/hexagonal boron nitride (h-BN) heterostructure. In this paper, the electron energy distribution (EED) of these devices is examined to clarify the mechanism of monochromatic electron emission. We find that the monochromaticity of the electron beam depends significantly on the electronic structure of the substrate material; for the devices with an n-type silicon substrate, the narrowest FWHM of the electron beam is 0.18 eV, whereas that of devices with a metallic (Nb) substrate is 0.33 eV. At the same time, simulations considering the electron scattering by phonons acceptably reproduced the shape of each EED spectrum considering the small energy loss due to out-of-plane acoustic phonon modes in h-BN. Thus, the monochromatic electron emission from the $\mathrm{graphene}/h$-$\mathrm{BN}/n$-$\mathrm{Si}$ device is ascribed to a combination of the narrow energy distribution of electrons at the conduction band of the n-$\mathrm{Si}$ substrate and small phonon energy of the h-BN insulating layer. These features also realize the excellent emission properties in addition to the monochromaticity of the beam, such as a high emission current density of $9.3{\mathrm{A}/\mathrm{cm}}^{2}$, insensitivity to environmental pressure up to 10 Pa, and long lifetime of more than 7 days with little decay.

The dynamics of Pt nanoparticles (NPs) in water are observed by high-resolution scanning transmission electron microscopy with a home-made static sandwich-type liquid cell (LC). Carbon is coated on both sides of the membrane windows of the LC to make them conductive. The slow motion of Pt NPs in thin water droplets enables us to acquire high-resolution scanning transmission electron microscopy images. Using a dose rate of 3 × 105 e nm−2s, some Pt NPs with a diameter of less than 2 nm disappear into the water, some move around, and others repeatedly attach to and detach from each other. The density of Pt NPs larger than 2 nm remains unchanged with further observation. However, by increasing the dose rate to 5.3 × 105 e nm−2s, the Pt NPs gather at the beam illumination area, and then form aggregates with chain network structures. It is also determined that the NPs attach to each other at their {111} surfaces.

We have systematically studied the strain relaxation processes in GaSb heteroepitaxy on GaAs(111)A using thin InAs interlayers. The growth with 1 ML- and 2 ML-InAs leads to formation of an InAsSb-like layer, which induces tensile strain in GaSb films, whereas the GaSb films grown with thicker InAs layers (≥3 ML) are under compressive strain. As the InAs thickness is increased above 5 ML, the insertion of the InAs layer becomes less effective in the strain relaxation, leaving residual strain in GaSb films. This leads to the elastic deformation of the GaSb lattice, giving rise to the increase in the peak width of X-ray rocking curves.

Polycrystalline NASICON-type Li-ion conductor LiZr2(PO4)3 (LZPO) with different ratios of Li isotopes, namely 6LiZr2(PO4)3 (6-LZPO), 7LiZr2(PO4)3 (7-LZPO), and LZPO with the natural Li isotope ratio (n-LZPO), has been synthesized by a conventional solid state reaction. The phase transformation as a function of temperature between the low-temperature triclinic phase, which exhibits lower Li-ion conductivity, and high-temperature rhombohedral phase, which exhibits higher Li-ion conductivity, has been evaluated by powder X-ray diffraction (XRD), electron diffraction, and differential scanning calorimetry (DSC) measurements. According to XRD and DSC measurements, the phase transition temperature decreases in the order 6-LZPO > n-LZPO ≈ 7-LZPO. The dependence of phase transition temperature on the Li isotope implies that Li ions have a strong effect on phase stability. The phase transition is primarily related to the change in configuration entropy of Li ions in LZPO.

In this study, the lithium tracer diffusion coefficient (DLi∗) in spinel-type LiMn2O4 thin films is measured by secondary ion mass spectroscopy (SIMS) in the temperature range from 200 to 550 °C. An ion-exchange method is employed to prepare diffusion couples consisting of the stable isotopes 6Li and 7Li. The isotope profiles were measured by SIMS analysis to determine DLi∗ in the LiMn2O4 films. The DLi∗ value was 1.4 × 10−10 cm2/s at 300 °C and the activation energy was 0.52 eV, which is consistent with that of bulk LiMn2O4. The extrapolated value of DLi∗ at 25 °C was on the order of 10−14 cm2/s, which is smaller than the chemical diffusion coefficient of LixMn2O4 measured by electrochemical methods. The temperature dependence of DLi∗ can be explained by the vacancy diffusion model, in which the extrinsic and intrinsic regions of diffusion exist in the low- and high-temperature regions, respectively.

We investigate the carrier transfer in stacked droplet epitaxially grown GaAs quantum dots (QDs) in experiments and calculations. While in the Stranski-Krastanov growth mode, QDs align due to stain propagation, droplet epitaxy QDs pose a difficulty for achieving coupled stacked QDs due to their random positioning. We demonstrate that carrier transfer is possible in such structures by designing their size and areal density. We achieve a significant geometrical overlap between stacked QDs by employing an areal density of 3.9×1010 dots/cm2 and an average QD diameter of 45.5 nm. A clear redshift in the position of the photoluminescence peak is observed when the separation layer’s thickness is reduced from 16 nm to 2.5 nm. Theoretical calculations of the electronic states of the stacked QDs with varying degrees of misalignment confirm that this red-shift is mainly caused by a lowering of the ground state energy due to coupling. To separately analyze the effect of vertical carrier transfer between QDs, we investigate samples with two layers of stacked QDs of different sizes. We demonstrates in photoluminescence experiments that carriers readily transfer to the larger QD when the barrier thickness is reduced to a degree where tunneling is possible.

Owing to its high theoretical capacity of ~4200 mAh g−1 and low electrode potential (+/Li), utilising silicon as anode material can boost the energy density of rechargeable lithium batteries. Nevertheless, the volume change (~300%) in silicon during lithiation/delithiation makes stable cycling challenging. Since some of the capacity fading mechanisms do not function in solid electrolytes, silicon anodes exhibit better cycling performance in solid electrolytes than liquids. Nonetheless, capacity can fade rapidly because of the difficulties in maintaining mechanical integrity in thick/bulky electrodes, especially when high active material loading is employed to deliver practically useful areal capacity. By contrast, silicon nanostructures can relieve deformation-induced stress and enhance cycling performance. Here we report enhanced cycling performances achieved using nanostructured silicon films and inorganic solid electrolyte and show that amorphous porous silicon films maintain high capacity upon cycling (2962 mAh g−1 and 2.19 mAh cm−2 after 100 cycles).

Photocatalytic splitting of water under solar light has proved itself to be a promising approach toward the utilization of solar energy and the generation of environmentally friendly fuel in a form of hydrogen. In this work, we demonstrate highly efficient solar-to-hydrogen conversion efficiency of 7.7% by photovoltaic–photoelectrochemical (PV–PEC) device based on hybrid MAPbI3 perovskite PV cell and WO3/BiVO4 core–shell nanorods PEC cell tandem that utilizes spectral splitting approach. Although BiVO4 is characterized by intrinsically high recombination rate of photogenerated carriers, this is not an issue for WO3/BiVO4 core–shell nanorods, where highly conductive WO3 cores are combined with extremely thin absorber BiVO4 shell layer. Since the BiVO4 layer is thinner than the characteristic carrier diffusion length, the photogenerated charge carriers are separated at the WO3/BiVO4 heterojunction before their recombination. Also, such architecture provides sufficient optical thickness even for extremely thin BiVO4 layer due to efficient light trapping in the core–shell WO3/BiVO4 nanorods with high aspect ratio. We also demonstrate that the concept of fill factor can be used to compare I–V characteristics of different photoanodes regarding their optimization for PV/PEC tandem devices.

Lithium-ion conductors with a crystal structure classified as Na super ion Conductors (NASICON) exhibit high ionic conductivity at room temperature that may be used in next-generation batteries. This study finds unusual ionic conduction of Li1.3Al0.3Ti1.7(PO4)3 (LATP): hysteresis on temperature and atmosphere dependence. The precise conductivity analyses (a wide frequency range, a wide temperature range, and a narrow temperature interval) reveal that the unusual conductivity is attributed to grain boundary conductivity enhanced by moisture. From the detailed studies on bulk (crystal structure) and grain boundary (microcracks, segregation, and impurities) of LATP pellets, it is concluded that the unusual ionic conduction results from adsorbed water on microcracks of LATP pellets. It is also confirmed that at high humidity, grain boundary resistance is further reduced by condensed water in the microcracks. This study reveals the high moisture sensitivity of conductivity of LATP for the first time, which is explained by the concerted influence of microstructure and humidity on ionic conductivity across grain boundaries. The results point out the importance of atmosphere control in scientific studies and for quality control of this class of solid electrolytes in advanced batteries like all-solid-state batteries, Li-air batteries, and others.

Unlike X-ray diffraction or Raman techniques, which suffer from low spatial resolution, transmission electron microscopy can be used to obtain strain maps of nanoscaled materials and devices. Convergent-beam electron diffraction (CBED) and nanobeam electron diffraction (NBED) techniques detect the deviation of a lattice constant (i.e. an indicator of strain) within 0.01%; however, their use is restricted to beam-insensitive samples. Selected-area electron diffraction (SAED) does not have such limitations but has low spatial resolution and precision. The use of a spherical aberration corrector and a nanosized selected-area aperture improves the spatial resolution, but the precision is still low. In this study, a two-dimensional stage-scanning system is used to acquire arrays of diffraction patterns at different positions of the sample under fixed beam conditions. Data processing with iterative nonlinear least-squares fitting enabled the spot displacement for each point of the scan area to be measured with precision comparable to that of the CBED or NBED technique. The precise strain determination, in combination with the simplicity of the measurement process, makes the nanosized SAED technique competitive with other methods for strain mapping at nanoscale dimensions.

All-solid-state batteries (ASSBs) have various problems associated with their usage that are normally not encountered in conventional lithium-ion batteries. Stress on interfaces between solid electrolytes and active materials is one of the key issues because the active materials change their volume during charging/discharging. In this work, first, we reveal that garnet-type solid electrolytes, Li 6.5 La 3 Zr 1.5 Ta 0.5 O 12 (LLZT), prepared by the spark plasma sintering (SPS) technique, exhibit a residual tensile stress of more than 100 MPa in the direction of the SPS pressure. Then, the influence of the strain on ionic conduction is investigated in detail. It is demonstrated that the strain causes no change in the bulk resistance, while the grain boundary resistance increases in both the pre-exponential factor and the activation energy. The results suggest the importance of the strength of grain boundaries (including interfaces) for the practical application of ASSBs.

Garnet-type solid electrolytes are one of key materials to enable practical usage of lithium metal anode for high-energy-density batteries. However, it suffers from lithium growth in pellets on charging, which causes short circuit. In this study, grain boundaries of Li6.5La3Zr1.5Ta0.5O12 (LLZT) pellets are modified with Li2CO3 and LiOH to investigate the influence of the microstructure of grain boundaries on lithium growth and to study the mechanism of the lithium growth. In spite of similar properties (relative density of ca. 96% and total ionic conductivity of 7 × 10−4 S cm−1 at 25 °C), the obtained pellets exhibit different tolerance on the short circuit. The LLZT pellets prepared from LiOH-modified LLZT powders exhibit rather high critical current density of 0.6 mA cm−2, at which short circuit occurs. On the other hand, the LLZT pellets without grain boundary modification short-circuited at 0.15 mA cm−2. Microstructural analyses by means of SEM, STEM and EIS suggest that lithium grows through interconnected open voids, and reveal that surface layers such as Li2CO3 and LiOH are not only plug voids but also facilitate the sintering of LLZT to suppress the lithium growth. The results indicate a strategy towards short-circuit-free lithium metal batteries.

For applications such as the fabrication of plasmonic waveguides we developed a patterning technique to fabricate an array of nanoparticles on a substrate using focused electron beams (Noriki, T.; Abe, S.;.Kajikawa, K.; Shimojo, M. Beilstein J. Nanotechnol. 2015, 6, 1010–1015). This technique consists of three steps: Firstly, nanoparticles are placed over the entire surface of a substrate. Secondly, the nanoparticles are fixed on the substrate by focused electron beam irradiation. The electron beam decomposes the organic molecules located around the particle into amorphous carbon. The amorphous carbon immobilizes the particle on the substrate. Finally, the unfixed nanoparticles are removed. However, in this original technique, the area in which the nanoparticles were fixed was wider than the electron-probe size of a few nanometers. To understand this widening mechanisms, the effects of accelerating voltage, particle size and substrate material are investigated by means of both experiments and simulation. It is demonstrated that the fixing area is greatly affected by the electrons back-scattered by the substrate. The back-scattering leads to an increase in line width and thus reduces the resolution of this patterning technique.

We measured the local composition and thickness of SiO2-based glass material from diffraction. By using four dimensional scanning transmission electron microscopy (4D-STEM), we obtained diffraction at each scanning point. Comparing the obtained diffraction with simulated diffraction patterns, we try to measure the local composition and thickness. Although this method requires some constraints, this method measured local composition and thickness with 1/10 or less electron dose of EELS., Comment: 15 pages, 10 figures, 6 supporting figures

Scientific instruments for material characterization have recently been improved to yield big data. For instance, scanning transmission electron microscopy (STEM) allows us to acquire many diffraction patterns from a scanning area, which is referred to as four-dimensional (4D) STEM. Here we study a combination of 4D-STEM and a statistical technique called non-negative matrix factorization (NMF) to deduce sparse diffraction patterns from a 4D-STEM data consisting of 10,000 diffraction patterns. Titanium oxide nanosheets are analyzed using this combined technique, and we discriminate the two diffraction patterns from pristine TiO2 and reduced Ti2O3 areas, where the latter is due to topotactic reduction induced by electron irradiation. The combination of NMF and 4D-STEM is expected to become a standard characterization technique for a wide range materials.

LiCoO2 is epitaxially grown on SrTiO3 (100) substrates with (104) orientation. Because the LiCoO2 film is grown with its c-axis parallel to four equivalent 〈111〉 axes of the SrTiO3, the (104)-oriented film exhibits four-domain structure on the SrTiO3 (100) substrate. Introducing off-cut angle to the substrate surface breaks the equivalency between the four 〈111〉 axes of the SrTiO3 substrate to induce preferential growth of specific orientation with the c-axis in a descending direction of off-cut surface. Increasing off-cut angle and lowering deposition rate promote the preferential growth, because they facilitate step-flow growth mode, and finally align the c-axes in the domains completely into one 〈111〉 direction of the SrTiO3 substrate. The LiCoO2 film delivers a discharge capacity of 90 mAh g−1 at a low discharge rate of 0.01 C, and 25% of capacity is kept even at a high rate of discharge with 100 C.

We have successfully grown high quality InxGa1-xAs metamorphic layer on GaAs (111)A using molecular beam epitaxy. Inserting a thin 3.0-7.1 monolayer (ML) InAs interlayer between the In0.25Ga0.75As and GaAs allowed the formation of a nearly lattice-relaxed In0.25Ga0.75As with a very flat upper surface. However, when the thickness of the inserted InAs is thinner or thicker than these values, we observed degradation of crystal quality and/or surface morphology. We also revealed this technique to be applicable to the formation of a high quality metamorphic InxGa1-xAs layer with a range of In compositions (0.25 ≤ x ≤ 0.78) on GaAs (111)A. Cross-sectional scanning transmission electron microscope studies revealed that misfit dislocations formed only at the interface of InAs and GaAs, not at the interface of In0.25Ga0.75As and InAs. From the dislocation density analysis, it is suggested that the dislocation density was decreased by growing In0.25Ga0.75As on InAs, which effectively contribute the strain relaxation of In0.25Ga0.75As. The InGaAs/InAlAs quantum wells that were formed on the metamorphic layers exhibit clear photoluminescence emissions up to room temperature.

It is found that cooling dramatically changes the waveguiding properties of organic nanofibers of thiacyanine (TC), which function as active waveguides. At liquid nitrogen temperature (T = 83 K), nanofibers with a width of less than 100 nm efficiently propagate fluorescence (λ = 460–480 nm) over their entire length of ∼100 μm, whereas they propagate no fluorescence at room temperature. Moreover, the fluorescence is observed to be transmitted through sharply bent nanofibers with a bend radius of a few hundred nanometers at T = 83 K. We show that these waveguiding properties result from a modulation of the light–matter interaction in the nanofibers by cooling, which leads to a high refractive index and a low extinction coefficient. Our result demonstrates that nanoscale light manipulation with sub-100-nm-width waveguides is possible by simply cooling TC nanofibers to liquid nitrogen temperature, which can be easily accessed.

By using a focused-ion-beam (FIB) method with Ga ions, we prepared quasi-one-dimensional (q-1D) In/Mo specimens with widths of ≈ 200 nm and ≈ 500 nm from two dimensional (2D) films deposited on a SiO2/Si substrate. We observed the superconducting transition of q-1D In/Mo, whose transition temperature Tc is higher than T c ≈ 3.6 K of a 2D In/Mo specimen on a glass substrate. For specimens fabricated using the FIB method, the element distributions analyzed by energy dispersive x-ray spectroscopy reveal Ga invasion into the q-1D In/Mo region. The gradually changing resistance of q-1D In/Mo at temperatures below Tc can be well explained by the thermal activation phase-slip model with T c = 5.1 K and coherence length ξ ( 0 ) ≈ 9.5 nm .