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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.

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.

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 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.

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.

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.

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

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.

Inefficient Mg-induced p-type doping has been remained a major obstacle in the development of GaN-based electronic devices for solid-state lighting and power applications. This study reports comparative structural analysis of defects in GaN layers on freestanding GaN substrates where Mg incorporation is carried out via two approaches: ion implantation and epitaxial doping. Scanning transmission electron microscopy revealed the existence of pyramidal and line defects only in Mg-implanted sample whereas Mg-doped sample did not show presence of these defects which suggests that nature of defects depends upon incorporation method. From secondary ion mass spectrometry, a direct correspondence is observed between Mg concentrations and location and type of these defects. Our investigations suggest that these pyramidal and line defects are Mg-rich species and their formation may lead to reduced free hole densities which is still a major concern for p-GaN-based material and devices. As freestanding GaN substrates offer a platform for realization of p-n junction-based vertical devices, comparative structural investigation of defects originated due to different Mg incorporation processes in GaN layers on such substrates is likely to give more insight towards understanding Mg self-compensation mechanisms and then optimizing Mg doping and/or implantation process for the advancement of GaN-based device technology.

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.

Phase shifting electron holography is a transmission electron microscope technique that a number of holograms with different initial phases are acquired by changing the angle of the incident electron beam, and the intensity variation at a certain point on the holograms is fitted by sinusoidal curve to retrieve the object wave passing through a specimen. In reality, however, Fresnel fringes caused by the electrostatic biprism modulates the electron wave, limits the fitting accuracy and results in phase errors in phase reconstruction. In this study, we suggest a modified phase reconstruction method for phase shifting electron holography. The intensity variations at a certain point on each hologram are fitted not by sinusoidal curve, but by Fresnel diffraction affected curve to retrieve the object wave. This would provide better fitting accuracy, and has a potential to improve the precision of phase shifting electron holography. Simulations demonstrated the improvements of this method comparing with conventional phase shifting holography method.

The demand for nanoscale strain mapping is increasing with the spread of nanotechnologies. Traditional macroscale strain measurement methods do not have the required spatial resolution, and well-known transmission electron microscopy methods often encounter difficulties that limit their practical application. We evaluate a stage-scan strain mapping method based on nanosized selected area electron diffraction. Two-dimensional scanning of the sample and simultaneous acquisition of diffraction patterns at fixed beam conditions enable the comparison of interplanar distances measured at different places. Accurate determination of the lattice constant changes becomes possible owing to the two-dimensional Gaussian fitting used to determine the exact position of diffraction spots. The results obtained by stage-scan mapping agree well with the reference X-ray diffraction data, and are not affected by elliptical distortion of the diffraction pattern. The simplicity and stability of the stage-scan strain mapping method make it complementary to other transmission electron microscopy based methods for strain mapping.

Energy-filtered scanning confocal electron microscopy (EF-SCEM) is a technique that uses the reduced depth of field of an aberration-corrected transmission electron microscope to provide three-dimensional (3D) compositional information. Using a silicon sample in the orientation, we show that EF-SCEM image data can be recorded that shows lattice resolution in the plane perpendicular to the incident beam direction. The confocal effect is demonstrated through the reduction of the mean intensity as the confocal plane is displaced from the sample mid-plane, unlike optical sectioning in high-angle annular dark-field scanning transmission electron microscopy (STEM). Simulations of the EF-SCEM data show agreement with the experimental data, and allow the interpretability of the data to be explored. The effects of channelling, absorption and delocalisation complicate the quantitative and qualitative interpretation of the data, highlighting the need for matching to simulations. Finally the effects of the finite detector pin-hole aperture size are explored, and we show that the EF-SCEM contrast in the plane perpendicular to the beam direction starts to resemble that of a STEM spectrum imaging experiment as the aperture size increases. © 2013 Elsevier B.V.

We fabricated micrometer-scale optical ring resonators by micromanipulation of thiacyanine (TC) dye nanofibers that propagate exciton polaritons (EPs) along the fiber axis. High mechanical flexibility of the nanofibers and a low bending loss property of EP propagation enabled the fabrication of microring resonators with an average radius (r(ave)) as small as 1.6 μm. The performances of the fabricated resonators (r(ave) = 1.6-8.9 μm) were investigated by spatially resolved microscopy techniques. The Q-factors and finesses were evaluated as Q ≈ 300-3500 and F ≈ 2-12. On the basis of the r(ave)-dependence of resonator performances, we revealed the origin of losses in the resonators. To demonstrate the applicability of the microring resonators to photonic devices, we fabricated a channel drop filter that comprises a ring resonator (r(ave) = 3.9 μm) and an I/O bus channel nanofiber. The device exhibited high extinction ratios (4-6 dB) for its micrometer-scale dimensions. Moreover, we successfully fabricated a channel add filter comprising a ring resonator (r(ave) = 4.3 μm) and two I/O bus channel nanofibers. Our results demonstrated a remarkable potential for the application of TC nanofibers to miniaturized photonic circuit devices.

We present an electron holography technique to acquire an interferogram, that is, cosine image of phase distribution. The interferogram is constructed by shifting the specimen in one direction with a stage-scanning system and acquiring line intensities of holograms. Taking line intensities eliminates the carrier fringes in the holograms and yields the interferogram. Under phase object approximation, the object phase can be readily obtained from the interferogram without any reconstruction procedure. The spatial resolution of phase is determined independently of the fringe spacing, overcoming the limitation of conventional techniques based on the Fourier transformation method.

We fabricated a micron-sized ring resonator channel drop filter by micromanipulation of nanofibers of thiacyanine dye that propagate exciton polaritons along the fibers. The device consisted of a microring with a radius of r ≈ 4 μm and a straight nanofiber that functioned as an I/O bus channel. The performance of the device was evaluated using spatially resolved fluorescence microscopy. The device exhibited an extinction ratio of re = 2-4 dB for the visible wavelength region of 490-540 nm. Our results demonstrate that thiacyanine nanofibers are promising building blocks for exciton polariton-based photonic circuits, which can be highly miniaturized compared with conventional waveguide-based photonic circuits.

A new method is proposed for mapping of phase distribution in electron holography. A stage-scanning system was used for moving the specimen to obtain a series of holograms with different specimen positions in a fixed electron-optics configuration. By applying a digital aperture which selects an area on holograms with different specimen positions, an interferogram of the specimen can be obtained directly without a complex reconstruction method such as the one using Fourier transformation. Experimental results for a Co particle demonstrated the practicability of this method.

Manipulation of light using subwavelength waveguides is a key technology in the development of miniaturized photonic circuits, which possess various advantages over their electronic counterparts. The novel approach presented for such waveguiding involves the propagation of exciton polaritons (EPs), which are quasi-particles formed by strong exciton–photon coupling, along organic dye nanofibers. A self-assembled nanofiber of thiacyanine (TC) with a width of ≈200 nm propagates the EPs created by an optical excitation over a submillimeter-scale distance and passes through a bend with a micrometer-scale radius with low bending loss. To demonstrate the remarkable potential of EP-based miniaturized photonic circuits, asymmetric Mach–Zehnder interferometers (AMZIs) are fabricated with TC nanofibers by micromanipulation. The AMZIs with a footprint of ≈20 μm × 20 μm exhibit a visibility of nearly unity and function as channel drop filters with the considerably high extinction ratio of up to ≈15 dB. Such high-performance and ultracompact channel drop filters operating in the visible wavelength region have rarely been developed with other waveguide technologies. The coherent properties of the EPs in the nanofibers are investigated using time-resolved experiments. The coherent properties provide useful information for designing EP-based photonic circuits and for understanding EP dynamics in a nanofiber.

Scanning confocal electron microscopy (SCEM) is a new imaging technique that is capable of depth sectioning with nanometer-scale depth resolution. However, the depth resolution in the optical axis direction (Z) is worse than might be expected on the basis of the vertical electron probe size calculated with the existence of spherical aberration. To investigate the origin of the degradation, the effects of electron energy loss and chromatic aberration on the depth resolution of annular dark-field SCEM were studied through both experiments and computational simulations. The simulation results obtained by taking these two factors into consideration coincided well with those obtained by experiments, which proved that electron energy loss and chromatic aberration cause blurs at the overfocus sides of the Z-direction intensity profiles rather than degrade the depth resolution much. In addition, a deconvolution method using a simulated point spread function, which combined two Gaussian functions, was adopted to process the XZ-slice images obtained both from experiments and simulations. As a result, the blurs induced by energy loss and chromatic aberration were successfully removed, and there was also about 30% improvement in the depth resolution in deconvoluting the experimental XZ-slice image.

The imaging properties of bright field and annular dark field scanning confocal electron microscopy (BF-SCEM and ADF-SCEM) are discussed based on their point spread functions (PSFs) in comparison with multislice simulations. Although the PSFs of BF-SCEM and ADF-SCEM show similar hourglass shapes, their numerical distributions are quite different: BF-SCEM PSF is always positive and shows a center of symmetry whereas the ADF-SCEM PSF is complex and has Hermitian symmetry. These PSF properties explain the large elongation effect in BF-SCEM for laterally extended object and almost no-elongation in ADF-SCEM, illustrating the importance of the numerical analysis of PSFs. The Hermitian symmetry of the ADF-SCEM PSF results in an interesting “edge enhancement effect” at the interface. Simulation using the PSF and the multislice method verified this effect at GaAs surfaces and InAs interfaces embedded in GaAs. This unique feature of ADF-SCEM can potentially be useful for depth sectioning. It is also pointed out that a PSF imaging model cannot be applicable for BF-SCEM of a phase object, when the system is symmetric and aberration free.

Scanning confocal electron microscopy (SCEM) offers a mechanism for three-dimensional imaging of materials, which makes use of the reduced depth of field in an aberration-corrected transmission electron microscope. The simplest configuration of SCEM is the bright-field mode. In this paper we present experimental data and simulations showing the form of bright-field SCEM images. We show that the depth dependence of the three-dimensional image can be explained in terms of two-dimensional images formed in the detector plane. For a crystalline sample, this so-called probe image is shown to be similar to a conventional diffraction pattern. Experimental results and simulations show how the diffracted probes in this image are elongated in thicker crystals and the use of this elongation to estimate sample thickness is explored.

A H-terminated surface conductive layer of B-doped diamond on a (111) surface was used to fabricate a metal–oxide–semiconductor field-effect transistor (MOSFET) using an electron beam evaporated SiO2 or Al2O3 gate insulator and a Cu-metal stacked gate. When the bulk carrier concentration was approximately 1015/cm3 and the B-doped diamond layer was 1.5 μm thick, the surface carrier mobility of the H-terminated surface on the (111) diamond before FET processing was 35 cm2/Vs and the surface carrier concentration was 1.5 × 1013/cm2. For the SiO2 gate (0.76 μm long and 50 μm wide), the maximum measured drain current at a gate voltage of −3.0 V was −75 mA/mm and the maximum transconductance was 24 mS/mm, and for the Al2O3 gate (0.64 μm long and 50 μm wide), these features were −86 mA/mm and 15 mS/mm, respectively. These values are among the highest reported direct-current (DC) characteristics for a diamond homoepitaxial (111) MOSFET.

Imaging properties of scanning confocal electron microscopy (SCEM) were studied by calculating simple model systems using the multislice method. A simple geometrical explanation was given, particularly for the difference between bright field (BF) and annular dark field (ADF) SCEM. It is demonstrated that the BF-SCEM image contrast consists of two features. One gradually changes over a wide defocus range and depends on the lateral size of the object. Another appears only near the focus and is independent of sample size. On the contrary, ADF-SCEM image contrast does not depend on the lateral size of the object. Therefore, the ADF-SCEM will provide more readily interpretable image contrast.

We report on the fabrication of a lattice-matched GaAs/AlGaAs quantum dot solar cell (QDSC) in which a ten-stacked QD layer is embedded. The GaAs QDs were grown by droplet epitaxy. Photocurrent originating from the QDs was confirmed. Cross-sectional scanning transmission electron microscopy (TEM) revealed no apparent dislocation in the QD layers.

We investigated the self-assembly of GaAs/AlGaAs quantum dots (QDs) on GaAs (3 1 1)A substrates by droplet epitaxy. High-density Ga droplets were formed on the (3 1 1)A surfaces due to the short surface migration distance of Ga atoms. The maximum area density exceeded 10 11 /cm 2 . These Ga droplets were crystallized into dot-shaped nanostructures (QDs) even by the irradiation of low As 4 flux intensity. The capped GaAs QDs exhibited efficient, narrow PL emission at 5 K, indicating their high quality and uniformity.

A stage-scanning system is composed of a specially designed transmission electron microscopy specimen holder equipped with a piezo-driven specimen stage, power supplier and control software. This system enables the specimen to be scanned three-dimensionally, and therefore confocal scanning transmission electron microscopy (STEM) can be performed with a fixed electron-optics configuration. It is demonstrated that stage-scanning confocal STEM images can be obtained with the lateral atomic resolution and the specimen can be moved three-dimensionally with high precision.

Nanowires for measuring the electronic transport property of a self-assembled quantum dot and a quantum ring were fabricated by electron beam induced deposition (EBID), and cross-sectional transmission electron microscopy (TEM) observations were conducted for the first time for the nanowires. TEM observations revealed that an amorphous layer existed between the substrate and the W deposit, showing a low W deposition rate at the early stage of deposition, and confirmed that the layer was an amorphous carbon layer. The layer growth mechanism was discussed using a phenomenological theory considering two different precursors and assuming one of the precursors covers the entire surface initially. It was shown that the layer manner growth happens in a wide range of parameters. From high-resolution TEM, obvious signs of irradiation damage during the deposition were not observed, and the amorphous layer thickness was about 5 nm, which should not affect much transport property measurement, indicating that EBID is quite promising for nanowire fabrication for transport measurements of a single self-assembled nanostructure.

Electrons with energies of 20, 200, and 400 keV were used in electron-beam-induced deposition (EBID) to investigate deposition on both the top and bottom surfaces of a film substrate when an electron beam is injected into the top surface. Tungsten tips were successfully fabricated on the-bottom surface of the film substrate using 200 and 400 keV electrons. The microstructure as-deposited at a different electron energy,is a mixture of nanocrystallites and amorphous materials. The nanocrystallites of the structure deposited using 20 keV electrons (1-2 nm) were smaller than those of the structures deposited using 200 keV (2-4 nm) and 400 keV electrons (3-5 nm). The proportion of amorphous materials in the as-deposited structure was reduced using high-energy electrons. There was no difference in microstructure between the top and bottom tips simultaneously deposited on the film substrate using high-energy electrons.

We investigated the effects of post-growth annealing on structural and optical properties of self-assembled ring-shaped GaAs quantum dots (QDs) by photoluminescence (PL) measurements and cross-sectional high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM). Marginal structural changes of the QDs were observed after the annealing process up to 800 °C while the intensity of PL emission increased drastically. The annealed laser structure with three layers of the ring-shaped QDs showed photo-pumped laser action with clear threshold at 77 K.

Beam induced deposition is versatile technique to fabricate nano-structure. In this paper, the proximity effect in electron beam induced deposition was studied, and the beam scan sequence which minimizes the effect was suggested.

Nanometer-sized Pt-dendrite structures were fabricated on an insulator Al2O3 substrate using an electron-beam-induced deposition (EBID) process in a transmission electron microscope (TEM). The as-fabricated structures were characterized using conventional and high-resolution transmission electron microscopies (CTEM and HRTEM) and X-ray energy dispersive spectroscopy (EDS). The as-fabricated nanodendrites consisted of many nano-grains and amorphous state structures. The nanometer-sized grains were determined to be Pt crystals with face-centered cubic (fcc) structure. The formation of the nanodendrite structures are discussed to relate to a mechanism involving charge-up produced on surface of the substrate, movement of charges to and accumulation at the convex surface of the substrate and the tips of the deposits.

Two methods were used to fabricate tungsten supertips by electron-beam-induced deposition using 200 keV electrons. The first method is stationary deposition of self-standing tips. The smallest lateral size is less than 10 nm with a rather low aspect ratio of tip. High aspect ratio (up to 30) can only be obtained at a big lateral size with a saturated root diameter of 60–65 nm. The other method is scan deposition of self-supporting tip, with a root width of 7–10 nm and a sharp apex in size of 3 nm. Using this method a higher aspect ratio (more than 72) can be achieved at a smaller lateral size, which is better to fabricate fine supertips for usage.

Nanometer-sized dendrite-like structures with a designed element, W, is fabricated on an insulator substrate, Al 2 O 3 , with an electron-beam-induced decomposition (EBID) in a transmission electron microscope (TEM). The fabricated structures are characterized with convention and high resolution TEM. The dendritic structure with tips in about 3 nm grows radially at convex surface of a substrate. The bcc structural W crystal grains in nanometers are composed in the dendrites. A mechanism is proposed to explain the growth and morphology of the deposit involving a charge-up on surface, a movement to and an accumulation of charges at convex surface or tips of substrate or the branched deposit.

Nanometer-sized W-dendritic form structure was fabricated with electron-beam-induced deposition (EBID) in a 200 kV transmission electron microscope. The as-prepared nanodendrites are composed of W-nanocrystals and amorphous. The as-prepared nanodendrites were then irradiated with 1 MeV electron beam in a high voltage transmission electron microscope. The effect of the irradiation is investigated. The irradiation transformed effectively almost all the amorphous part to crystalline state. Morphology of the nanodendrite also changes. The irradiation induced crystallization and morphology change are discussed.

Self-standing tungsten nanowires, nanodendrites, and nanofractal-like trees were fabricated on insulator (Al2O3) substrates with a process of electron-beam-induced decomposition in a transmission electron microscope. The conditions for fabricating different morphologies are described. The fabricated structures are characterized with high-resolution transmission electron microscopy and X-ray energy-dispersive spectroscopy. A high concentration of tungsten and a high crystallinity of the structure are confirmed. The growth process is discussed, involving charges produced on the surface of the substrate and the behavior of precursor molecules under electron-beam irradiation. The formation of these structures is considered to relate to nanoscaled unevenness of the charge distribution on the surface of the substrate, movement of charges to the convex surface of the substrate, and accumulation of charges at the tips of the grown structures.

Attempts were made to fabricate three-dimensional nanostructures on and out of a substrate by electron-beam-induced deposition in a 200-kV scanning transmission electron microscope. Structures with parallel wires over the substrate surface were difficult to fabricate due to the direct deposition of wires on both top and bottom surfaces of the substrate. Within the penetration depth of the incident electron beam, nanotweezers were fabricated by moving the electron beam beyond different substrate layers. Combining the deposition of self-supporting wires and self-standing tips, complicated three-dimensional doll-like, flag-like, and gate-like nanostructures that extend out of the substrate were successfully fabricated with one-step or multi-step scans of the electron beam. Effects of coarsening, nucleation, and distortion during electron-beam-induced deposition are discussed.

The features of self-supporting tungsten nanowire fabricated by electron-beam-induced deposition using 200 keV electrons were investigated. The width of wire first decreases with the increase of the scan speed, then saturates at about 7–10 nm when the scan speed is higher than 10 nm/s. The wire has belt-shipped morphology elongated along the incident beam. The wire parallel to the substrate surface was fabricated at the beam scan speed of 4.0 nm/s, while those with upward and downward features were obtained by changing the scan speed. Nanobelt, nanorod, and nanotip with high aspect ration and small lateral size were fabricated with this method. Considering the forward scattering of electrons and the beam Gaussian profile, a model was developed for the growth of wire using high-energy electrons.

The effects of focus change on the electron-beam-induced deposition (EBID) of tungsten nanowire in a scanning transmission electron microscope (STEM), were systematically investigated. By focusing the electron beam on the surface of carbon film, smooth tungsten nanowires were fabricated. The lateral size of the nanowire first decreased with the increase of beam scan speed, then became constant at about 7 nm when the scan speed was higher than 10 nm s−1. During the deposition of nanowire on carbon film, both overfocus and underfocus changes resulted in a conical profile with a central core line, whose deposition strongly depends on the electron dose. Broken wires can be fabricated by controlling the focus. For the deposition of self-supporting wire out of carbon film, the influence of focus change depended on the morphology of the deposited wire. Overfocus change can be used to keep the upward feature of the wire, while underfocus change is useful for the downward feature.

Electron beam-induced deposition was carried out using a scanning transmission electron microscope with a field emission gun to fabricate nanometre-sized structures. A small amount of a metal-organic gas was introduced near the substrate in the microscope chamber, and focused electron beams were irradiated. Two- and three-dimensional structures were fabricated by scanning the beam position. The minimum line width of the freestanding structures was 8 nm at a constant gas flux used. This line width of 8 nm is considered to be achieved by employing a high accelerating voltage, which leads to a small probe size, and the optimum scanning speed.

A layer-doubling method developed in LEED calculation is applied to the ADF-STEM image simulation. This approach makes it possible to simulate image intensities of systems having a repeated slab structure, such as embedded precipitates or defects, with a much higher efficiency because it does not require the diagonalization of repeated slabs. As a simple example of this method, channeling effects are calculated for a system with embedded crystalline displaced slabs for various different slab thicknesses.

We demonstrated the droplet epitaxial growth of InAs quantum dots on a GaAs(111)A substrate, which emitted at telecommunication wavelengths. A high-quality metamorphic In0.52Al0.48As layer was formed by inserting three monolayers of InAs between GaAs(111)A and InAlAs. InAs quantum dots were grown on the InAlAs surface by droplet epitaxy. They exhibited a laterally symmetrical shape owing to the C3v symmetry of the {111} surface. The photoluminescence signals of capped quantum dots indicated broadband spectra covering wavelengths from 1.3 to 1.55 µm. Thus, our dots are potentially useful for constructing entangled photon sources compatible with current telecommunication networks.

The stability of a double-slab configuration of two-phase particles confined in a third phase is studied as a function of shape in two and three dimensions. The condition of stability against splitting one phase in the particle into two separate identical slabs is shown to be the sum of the wetting factor and the change in the interface area relative to the shape of the two-phase particle. It is found that the double-slab configuration can be stable for a wide range of wetting factors and shapes.

As the first step toward understanding the electrical properties of SiO2/GaN systems, the interface was characterized using high-resolution scanning transmission electron microscopy (STEM) and energy dispersive X-ray spectroscopy (EDS). An epitaxial crystalline intermediate layer with a thickness of ~1.5 nm was observed at the SiO2/GaN interface. STEM-EDS analyses revealed that this intermediate layer contained gallium and oxygen and mostly comprised the e-Ga2O3 phase. The e-Ga2O3/GaN interface was atomically smooth and free from misfit dislocations despite lattice mismatch of ~8.0%, suggesting that the initial oxidation of GaN surfaces is crucial to achieve good interfacial properties.

Self-assembled nanofibers of organic dye thiacyanine (TC) with lengths of up to \( {\sim} 250\,\upmu {\text{m}} \) function as efficient active waveguides that propagate fluorescence (FL) over their entire lengths along the fiber axis. A spectroscopic investigation of the active waveguiding properties revealed that the FL strongly couples with molecular excitons and propagates in the form of exciton-polaritons. Such long-range propagation of exciton-polaritons at room temperature is rarely observed in inorganic materials. The high stability of the exciton-polaritons in the organic dye nanofibers is attributed to the large longitudinal transverse exciton splitting energy and exciton binding energy with respect to thermal energy. Unlike light propagating in conventional waveguides, exciton-polaritons can pass through bends in nanofibers with micron-scale radii of curvature. Utilizing this property, we fabricated miniaturized photonic circuit components using nanofiber building blocks. The fabricated components, including Mach–Zehnder interferometers and microring resonators, exhibit considerably high performance for their micron-scale dimensions. In addition to such photonic device applications, the organic dye nanofibers are ideal systems for studying the physics underlying strong light–matter interactions. In particular, the highly stable nature of the exciton-polaritons at relatively high temperature offers the possibility of a representative novel quantum phenomenon in their Bose–Einstein condensation (BEC). A theoretical analysis of this exciton-polariton BEC in the nanofiber system is presented in this chapter.

A new scheme of calculation of high-angle annular dark-field STEM image, capable of including both elastically diffracted and thermal diffuse scatter- ing waves, has been presented by a combination of Pennycook's and Nakamura's methods. The new scheme has been demonstrated for image simulations of Si(011) as functions of thickness, defocus values and detec- tor angles. In the present method, the TDS electron intensities are treated in the same way as in Pennycook's method, having a clear physical picture of its origin and reflecting the atom configuration in the systems. For the case of Si(011), it has been confirmed that at the detector angle of 60 to 160 mrad, which is usually applied, the image becomes highly incoherent, and even the image formed only from SOLZ beams becomes incoherent at the detector angle. At a low detector angle, however, the image has coherent features indicating the necessity of a simulation for individual systems.

We report the fabrication of submicron GaAs/AlAs double-barrier resonant tunneling diodes (RTDs) using wet etching with In droplets as a mask. Uniform mesas about 400 nm in size were formed and showed a clear resonance feature in current–voltage (I–V) characteristics, indicating that the mesa worked as a RTD. This simple technique can be applied to the fabrication of various submicron diodes.

We demonstrate the formation of InAs quantum dots (QDs) on InAlAs/InP(111)A by means of droplet epitaxy. The C3v symmetry of the (111)A substrate enabled us to realize highly symmetric QDs that are free from lateral elongations. The QDs exhibit a disk-like truncated shape with an atomically flat top surface. Photoluminescence signals show broad-band spectra at telecommunication wavelengths of 1.3 and 1.5 μm. Strong luminescence signals are retained up to room temperature. Thus, our QDs are potentially useful for realizing an entangled photon-pair source that is compatible with current telecommunication fiber networks. © 2014 AIP Publishing LLC.

Electron-beam-induced deposition was performed to fabricate nanostructures using a subnanometer-sized probe of high-energy electrons emitted by a 200 kV transmission electron microscope equipped with a field emission gun. We fabricated nanometer-sized dots with a diameter of less than 5 nm, controlling their position and size by the introduction of a organometallic precursor gas near the substrate surface. The relation between the size of the deposit and the deposition time was studied, and, in addition, the effect of the substrate thickness was examined.

Optical sectioning using scanning confocal electron microscopy (SCEM) is a new three-dimensional (3D) imaging technique which promises improved depth resolution, particularly for laterally extended objects. Using a stage-scanning system to move the specimen in three dimensions, two-dimensional (2D) images sliced from any plane in XYZ space can be obtained in shorter acquisition times than those required for conventional electron tomography. In this paper, a double aberration-corrected SCEM used in annular dark-field mode was used to observe the 3D structure of SiO(2) hollow spheres fabricated by a carbon template method. The double-shell structure of the sample was clearly reflected in both XY- and XZ-sliced images. However, elongation along the optical axis was still evident in the XZ-sliced images even when double aberration correctors were used. Application of a deconvolution technique to the experimental XZ-sliced images reduced the elongated shell thicknesses of the SiO(2) sphere by 40-50% and the selectivity of information at a certain sample depth was also enhanced. Subsequently, 3D reconstruction by stacking the deconvoluted slice images restored the spherical surface of a SiO(2) sphere.