In situ UHVEM study of {113}-defect formation in Si nanowires

Results are presented of a study of {113}-defect formation in vertical Si nanowire n-type tunnel field effect transistors with nanowire diameters ranging from 40 to 500 nm. The nanowires are etched into an epitaxial moderately As doped n-type layer grown on a heavily As doped n(+) Si substrate. p(+) contacts on the nanowire are created by epitaxial growth of a heavily B doped layer. Using focused ion beam cutting, samples for irradiation are prepared with different thicknesses so that the nanowires are fully or partially embedded in the sample thickness. {113}-defects are created in situ by 2 MeV e-irradiation in an ultra-high voltage electron microscope between room temperature and 375 degrees C. The observations are discussed in the frame of intrinsic point defect properties, taking into account the role of dopants and capping layers. The important impact of the specimen thickness is elucidated

Low-temperature synthesis of crystalline GeSn with high Sn concentration by electron excitation effect

The low-temperature synthesis of high-Sn-concentration GeSn is challenging in realizing flexible thin-film transistors and solar cells. Because of athermal processes, irradiation with energetic particles is anticipated to significantly reduce the processing temperature for device fabrication. Here, we demonstrated that polycrystalline Ge with ~30 at. % Sn can be realized at room temperature by the electron-beam-induced recrystallization of amorphous GeSn. We found that inelastic electronic stopping, the so-called electron excitation effect, plays an important role in the recrystallization of amorphous GeSn

Widely Extended [OIII] 88 um Line Emission around the 30 Doradus Region Revealed with AKARI FIS-FTS

We present the distribution map of the far-infrared [OIII] 88um line emission around the 30 Doradus (30 Dor) region in the Large Magellanic Cloud obtained with the Fourier Transform Spectrometer of the Far-Infrared Surveyor onboard AKARI. The map reveals that the [OIII] emission is widely distributed by more than 10' around the super star cluster R136, implying that the 30 Dor region is affluent with interstellar radiation field hard enough to ionize O^{2+}. The observed [OIII] line intensities are as high as (1-2) x 10^{-6} W m^{-2} sr^{-1} on the peripheral regions 4'-5' away from the center of 30 Dor, which requires gas densities of 60-100 cm^{-3}. However the observed size of the distribution of the [OIII] emission is too large to be explained by massive stars in the 30 Dor region enshrouded by clouds with the constant gas density of 10^2 cm^{-3}. Therefore the surrounding structure is likely to be highly clumpy. We also find a global correlation between the [OIII] and the far-infrared continuum emission, suggesting that the gas and dust are well mixed in the highly-ionized region where the dust survives in clumpy dense clouds shielded from the energetic photons.Comment: 17 pages, 9 figures, accepted for publication in Publications of the Astronomical Society of Japan (PASJ

コウブンギ ノ ヒカク 二 モトヅイタ プログラム サブン ノ ヒョウジ ホウシキ

Void formation and structure change by heavy ion irradiation were investigated in GaSb and InSb thin films. The voids were formed after irradiation in both materials. The average diameter of the voids was about 15nm in GaSb and 20nm in InSb irradiated with 60 keV Snþ ions to a fluence of 0:25 x 1018 ions/m2 at room temperature. The void size in InSb is larger than that in GaSb. The large void size is quantitatively explained by the amount of induced vacancies obtained by the SRIM code simulation. The Debye-Scherrer rings were observed in the SAED patterns on both materials. The structure changes into a polycrystal by ion irradiation. Additionally, the 200 superlattice reflections in the [001] net pattern were almost absent, and the streak pattern along the h110i direction was observed in InSb. It is considered that the anti phase domains of different lengths are formed by ion irradiation. Ion irradiation transforms the structure of InSb from chemical ordering to chemical disordering via the formation of anti phase boundaries

Fluctuation of long-range order in Co-Pt alloy nanoparticles revealed by time-resolved electron microscopy

The development of long-range order in disordered Co-Pt alloy nanoparticles has been atomically resolved in situ with an ultra-high voltage electron microscope equipped with a direct electron detection camera. Electron-irradiation-enhanced ordering occurred at 573 K with 1 MeV electrons at a dose rate of 8.9 × 10²⁴e/m²s. High-speed (400 frames/s) imaging revealed fluctuations of the c-axis orientation of the L1₀-type ordered structure. Specifically, the c-axis orientation changes occurred at 2.5-ms intervals. Thus, the atomic ordering rate at 573 K is deduced to be 3 × 10⁻¹⁷m²/s, which is 10¹³ times higher than that estimated for interdiffusion in a bulk Co-Pt alloy. The observed kinetic ordering temperature of 573 K is significantly lower than that reported previously (>800 K). The low-temperature ordering may be the result of enhanced atom migration via excess vacancies, 10⁶ times higher than that at thermal equilibrium, introduced by the high-energy electron irradiation.Kazuhisa Sato and Hidehiro Yasuda, "Fluctuation of long-range order in Co-Pt alloy nanoparticles revealed by time-resolved electron microscopy", Appl. Phys. Lett. 110, 153101 (2017) https://doi.org/10.1063/1.4980077

Order-Disorder Transitions Confined at the Interface of Pd@Co Core-Shell Nanoparticles: Implications for Magnetic Recording

Sato K., Yasuda H.. Order-Disorder Transitions Confined at the Interface of Pd@Co Core-Shell Nanoparticles: Implications for Magnetic Recording. ACS Applied Nano Materials 3, 1592 (2020); https://doi.org/10.1021/acsanm.9b02371.We observed an order-disorder transition confined to the interface of Pd@Co core-shell nanoparticles with a Pd core and Co shell. A local ordered region with the L1₀- and L1₂-type ordered structure 2-3 nm in size was formed in a ∼12 nm-sized particle. The local atomic order was only achieved in the narrow temperature range of 573-723 K, where the diffusion length is limited to a short-range comparable to the nearest-neighbor distance of the Co-Pd solid solution. Once the atom migration was activated (T ≥ 773 K), alloying of Co and Pd proceeded rapidly, and the ordered phase disappeared along with the core-shell structure. Namely, the stability of the ordered phase was diffusion controlled. Chemically sensitive atomic-resolution electron microscopy enabled detection of the local atomic order formed in a nanoparticle. Such local atomic order has the potential to enable tuning of the magnetic anisotropy of bimetallic nanomagnets, which may open a new route to realize ultrahigh-density magnetic storage media

Relation between Fractal Inhomogeneity and In/Nb-Arrangement in Pb(In1/2Nb1/2)O3

Relaxor ferroelectrics show substantial responses to electric fields. The key difference from normal ferroelectrics is a temperature-dependent inhomogeneous structure and its dynamics. The lead-based complex perovskite Pb(In1/2Nb1/2)O3 is an intriguing system in which the inhomogeneous structure can be controlled by thermal treatment. Herein, we report investigations of the phase transitions in single crystals of Pb(In1/2Nb1/2)O3 via changing the degree of randomness in which In and Nb occupy the B site of the ABO3 perovskite structure. We studied the dynamic properties of the structure using inelastic light scattering and the static properties using diffuse X-ray scattering. These properties depend on the degree of randomness with which the B site is occupied. When the distribution of occupied In/Nb sites is regular, the antiferroelectric phase is stabilised by a change in the collective transverse-acoustic wave, which suppresses long-range ferroelectric order and the growth of the inhomogeneous structure. However, when the B site is occupied randomly, a fractal structure grows as the temperature decreases below T*~475 K, and nanosized ferroelectric domains are produced by the percolation of self-similar and static polar nanoregions

Athermal Crystal Defect Dynamics in Si Revealed by Cryo-High-Voltage Electron Microscopy

Sato K., Yasuda H.. Athermal Crystal Defect Dynamics in Si Revealed by Cryo-High-Voltage Electron Microscopy. ACS Omega 5, 1457 (2020); https://doi.org/10.1021/acsomega.9b03028.Low-temperature crystal defect dynamics in Si has been studied by a newly developed cryo-high-voltage electron microscopy. The planar {113} defects of self-interstitial atoms were introduced at 94 K by 1 MeV electron irradiation with damage higher than 0.42 displacements per atom (dpa), unlike past findings. The defects once grew and then shrunk during the observation. We show that the nucleation and the dissociation dynamics of the {113} defects can be attributed to an athermal process, which is deduced from anomalously fast diffusion of self-interstitial atoms at a low temperature

Probing Crystal Dislocations in a Micrometer-Thick GaN Film by Modern High-Voltage Electron Microscopy

We report on extreme penetration power of relativistic electrons in a micrometer-thick gallium nitride epitaxial film and its application to probing threading dislocations, which were introduced during crystal growth. Maximum usable thickness of the specimen was quantitatively evaluated using high-voltage transmission electron microscopy (TEM) operating at 1 MV. The width of dislocation images was used as a measure for the evaluation of usable thickness. Superior maximum usable thickness was obtained in scanning transmission electron microscopy (STEM) than in TEM mode; the results were 6.9 μm for STEM and 4.4 μm for TEM. In STEM, dislocations can be imaged with an almost constant width of 15–20 nm in a wide thickness range 1–4 μm. The latest high-voltage STEM is thus useful for observing dislocations in micrometer-thick inorganic materials.Kazuhisa Sato and Hidehiro Yasuda, Probing Crystal Dislocations in a Micrometer-Thick GaN Film by Modern High-Voltage Electron Microscopy, ACS Omega 2018, 3(10), 13524–13529. © 2022 American Chemical Societ