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We propose a two-step silicon carbide (SiC) solution growth method for dislocation reduction to produce the high-quality silicon carbide SiC crystals. The two-step growth consists of the growth on a Si face and a C face. Firstly, seed crystal with low threading dislocation density was prepared by the growth on a Si face utilizing the threading dislocation conversion. Secondly, the growth on the C face was conducted on the prepared seed crystal with low threading dislocation density to reduce the density of basal plane dislocations and keep smooth growth surface. We demonstrate that the two-step growth leads to the reduction of the density for all types of dislocations by two orders of magnitude compared to the initial density of the seed crystal.

In order to achieve a high-quality SiC crystal in solution growth, one of the most difficult issues is to grow a thick layer on Si face avoiding polytype transformation. In this case, two-dimensional nucleation, which leads to the polytype transformation, is frequently induced because a density of threading screw dislocations acting as a source of spiral step decreases and wide terraces form by step bunching as growth proceeds. Therefore, it is very difficult to stabilize the polytype of crystals grown with extremely low density of threading screw dislocations. In this study, we tried to overcome these problems by using specially designed seed crystal and optimizing growth temperature and temperature distribution. We successfully grew thick low-threading-dislocation density SiC crystal without polytype transformation under the condition of high growth temperature and homogeneous temperature distribution.

The relationship between surface morphology and spatial distribution of basal plane dislocations in 4H-SiC crystal grown by top-seeded solution growth on the C face was investigated by the differential interference microscopy as well as X-ray topography. Basal plane dislocations were generated at the boundaries of the domains with the different macrosteps advance directions. On the other hand, at the position where macrosteps advance to the same direction, BPDs were hardly observed. This results suggest that BPD density can be decreased by the suppression of the collision of macrosteps during the solution growth on the C face controlling the surface morphology.

Dendritic growth at the Li anode during charging is caused by a morphological inhomogeneity of Li electrodeposition. In this study, we investigate the dependence of the morphology of Li electrodeposited on a polycrystalline Cu current collector on the Cu grain orientation both experimentally and by numerical analysis. The experimental results show that the Li precipitates that form on Cu grains that have close to (111) orientations are the smallest and the most uniform in size. Such a morphology is expected to be effective for the suppression of dendrite growth. Numerical analysis indicates that the initial stage of electrodeposition plays an important role in determining morphological variation, and this is due to the crystal orientation dependence of the adatom concentration at equilibrium.

The conversion of threading screw dislocations (TSDs) to defects on the basal plane during SiC solution growth caused by macrostep advance is a key factor to improve crystal quality. We realized the TSD conversion in 4H-SiC C face solution growth by modification of the surface morphology including macrosteps by addition of 5 atom % Ti into pure Si solvent. Synchrotron X-ray topography revealed that the possibility of TSD conversion increased to about 10% with the addition of 5 atom % Ti. In addition, the TSD conversion ratio depends on the shape of the macrostep edge. The gentle slope hardly made TSD conversion. The elastic energy of dislocations in anisotropy crystals was postulated as an explanation for the influence of step shape on TSD conversion behavior.

Defects generated during 4H-SiC (0001) solution growth have been investigated by synchrotron X-ray topography and transmission electron microscopy (TEM). The defects unidentified before are recognized as V-shaped contrast features in the X-ray topographic images. The detailed analysis combining TEM results revealed that the newly generated defects are identified as a pair of dislocations on a basal plane with opposite Burgers vectors parallel to the [1120] direction. It is found that no defects in the substrate are directly associated with the formation of the V-shaped defects. Geometric analysis of the size and shape of the V-shaped defects indicates that they nucleate in pairs intermittently during the growth process. On the basis of the observed morphology of these defect configurations, a mechanism of two-dimensional nucleation during solution growth is postulated for the generation of the V-shaped defects.

Transition of zinc morphology and crystallographic orientations with increasing charge capacity is examined to identify the origin of non-uniform electrodeposition. Galvanostatic charge experiments for zinc are carried out for both polycrystalline and oriented zinc substrates to investigate the effects of electrodeposited zinc on electrodepositing zinc. The results show that the crystallographic orientations of the zinc substrates strongly affect the morphology of the electrodeposited zinc. Non-uniformity appears in the (0001)-oriented case prior to the polycrystalline, 10 1 ¯ 0 - and 2 1 ¯ 1 ¯ 0 -oriented cases. The (0001) plane initiates non-uniform zinc electrodeposition even in the polycrystalline case. It is attributed to the high density and low diffusivity of the ad-atom on the wide terrace structure. It is also indicated that porous structure appears from aggregated hexagonal hillocks with random orientations which initially are oriented hexagonal hillocks.

For the solution growth of 4H–SiC with Si 1− x Cr x solvents, the change in surface step structure by 4 at% Al addition to the solvent was investigated. Without Al addition, step bunching resulted in the formation of giant macrosteps with height greater than several micrometers, and trench-like surface defects formed with solvent inclusion. The edge of the giant macrosteps composing trench-like defects was faceted into low-index facet planes, ( 1 1 ¯ 0 m ) ( m =1–4). The formation of the trench-like surface defects is considered to originate from the self-pinning of macrosteps owing to the step-faceting phenomenon, which facilitates further development of macrosteps. On the other hand, the addition of Al to the solvents significantly improved the surface roughening, and suppressed the formation of the trench-like surface defects. In this case, smaller bunched steps with heights from several nanometers to about 10 nm formed on the terraces of the macrosteps, while regularly arranged trains of unit-cell-size steps formed on the terrace of macrosteps in growth without Al addition. The decrease in step stiffness might be a possible cause for the formation of the smaller bunched steps on the terrace in growth with Al addition.

We realized the growth of 3C-SiC crystal on sapphire by solution growth method. The carbon deposition on a sapphire substrate before growth is the key point for this technology. This carbon layer plays a role to protect the dissolution of sapphire by Si solvent. Single crystal of 3C-SiC was grown on the whole surface of the sapphire substrate. Surprisingly, the 3C-SiC layer did not directly grown on the sapphire substrate. The single crystal 3C-SiC layer formed by the reaction between the deposited carbon and the Si wafer that is a solvent material below the melting point of silicon during heating process before the growth. The 3C-SiC grew on the 3C-SiC layer. In this process, the deposited carbon play another important role.

The solution growth of SiC on an off-axis seed is effective on the reduction of threading dislocations. We proposed a novel method to grow a SiC crystal on an off-axis seed by top-seeded solution growth (TSSG). In our previous study, a unidirectional solution flow above a seed crystal is effective to suppress surface roughness in the growth on the off-axis seed. However, it is difficult to apply the unidirectional flow in an axisymmetric TSSG set-up. In this study, the unidirectional flow could be achieved by shifting the rotational axis away from the center of the seed crystal. As a result, the smooth surface was obtained in the wider area where the solution flow direction was opposite to the step-flow direction.

Surface morphology of the SiC crystal grown on the C face of the 4H-SiC seed crystal by TSSG method using pure Si, Si-1at%Ti-C, Si-5at%Ti-C and Si-20at%Ti-C solvents was investigated. The surface morphology of the crystal grown from pure Si solvent was smooth. By the addition of Ti to the solvent, the surface morphology became rougher. The RMS value is not proportional to the concentration of Ti. The formation of macrosteps with several micrometers was observed when the addition of Ti increased to 5at% indicating the possibility of the threading screw dislocation conversion on the C face of the 4H-SiC crystal.

Solution growth of SiC has attracted significant attention due to its potential for the production of high-quality SiC wafers. We have recently investigated the dislocation propagation behavior during SiC solution growth with the aim of reducing the dislocation density. Threading dislocations were found to be converted to defects on the basal planes during solution growth. Utilizing this dislocation conversion phenomenon, we have proposed a dislocation reduction process during solution growth and achieved high-quality 4H-SiC crystal growth. Here we confirm the potential of SiC solution growth for the production of high-quality SiC wafers.

We achieved the convex growth interface shape in top-seeded solution growth of SiC applying non-axisymmetric solution convection induced by non-axisymmetric temperature distribution. The detailed solution flow, temperature distribution and carbon concentration distribution were calculated by 3-dimensional numerical analysis. In the present case, the solution flow below the crystal was unidirectional and the supersaturation was increased along the solution flow direction. By the rotation of the crystal in the unidirectional flow and the temperature distribution, we successfully obtained the crystal with the convex growth interface shape.

Chiral symmetry breaking during the chiral crystallization from a sodium chlorate (NaClO3) aqueous solution is an intriguing phenomenon because it provides insights into the prebiotic process of biohomochirality. However, a mechanism of the emergence and amplification of chirality remains controversial, especially for crystallization from highly supersaturated solution, and one of the hypotheses proposed before is a transition toward the homochiral state during the early stages of crystallization. In this contribution, we directly examined the early stage of crystallization by in situ polarized-light microscopy. The observation revealed that achiral crystals, which appear prior to the formation of chiral crystals, transform to the chiral crystal through two kinds of polymorphic transformations: (1) martensitic transformation (MT) and (2) solution-mediated phase transition (SMPT). The SMPT is remarkably facilitated by contact with a chiral crystal. Notably, the resulting enantiomorph through contact-facili...

Surface morphology and threading dislocation conversion behavior during solution growth of 4H-SiC using pure Si and Al-Si solvents was investigated. The growth surfaces on the C face were smoother than the Si face. By the addition of Al to the solvent, the growth surface became smooth on the C face and rough on the Si face. Threading screw dislocation conversion took place only in the grown crystals on the Si face and threading edge dislocation conversion occurs both on the Si face and the C face using the pure Si solvent. On the other hand, in the grown crystal on the C face using the Al-Si solvent, the threading dislocation conversion was hardly observed. These results indicate that the threading dislocation conversion behavior is influenced by the surface morphology.

Chiral symmetry breaking in NaClO3 crystallization from an aqueous solution with perturbations has been of great interest. To understand the mechanism, several models focusing on the early stage of the crystallization have been proposed. However, they are ambiguous because the early stage has been barely explored directly. Here, we investigate the early stages of the crystallization process driven by droplet evaporation using a combination of direct in situ microscopic observations and cryogenic single-crystal XRD experiments. We demonstrate that an achiral crystal having P21/a symmetry, which is newly discovered for a solution growth, first appears in the droplet and then transforms into the chiral crystals. Additionally, determination of the lattice constants by XRD experiments (a = 8.42 A, b = 5.26 A, c = 6.70 A, β = 109.71°) revealed that the achiral phase should be identical to Phase III (a = 8.78 A, b = 5.17 A, c = 6.83 A, β = 110°), which is a high-temperature phase from a melt growth of NaClO3. We...

The control of step bunching by solution flow in 4H-SiC solution growth is proposed. We achieved the solution flow control with the specially designed top-seeded solution growth method as follows: by deviating a seed crystal from the center of a crucible and rotating the crucible in one direction, the solution flow direction was controlled to be parallel or antiparallel to the step-flow direction. After the growth, the widely spaced, accumulated macrosteps were observed and the surface of the grown crystal became rough under the parallel flow. On the other hand, the development of the macrosteps was suppressed under the antiparallel flow. As the growth proceeds, the surface roughness of the growth surface increases under the parallel flow, while the surface roughness decreases under the antiparallel flow. This fact suggests the solution flow control can be an effective method to suppress the step bunching during the solution growth of SiC single crystals.

Reduction of threading screw dislocation without polytype transformation from 4H-SiC was performed by the combination of step-flow growth and spiral growth. On a vicinal 4H-SiC seed crystal, threading screw dislocations are converted to Frank-type stacking faults by step-flow during solution growth. As the growth proceeds, the defects are excluded to the crystal. Thus utilizing the conversion, high quality SiC crystal growth without threading screw dislocations is expected to achieve. However, at the same time, polytype transformation is caused by the occurrence of 2D nucleation. By using the special shape of seed crystal, we successfully grew high quality 4H-SiC crystal without threading screw dislocation and polytype transformation.

In this paper, we review our researches on the high-quality 3C-SiC bulk crystal growth. The polytype control and the suppression of defects are essential in the growth 3C-SiC on hexagonal SiC seed crystals. The growth polytype of SiC is usually controlled by the inheritance of the seed crystal. In contrast, we established kinetic polytype control in which the preferential growth of 3C-SiC can be achieved by the difference in the growth rates depending on supersaturation for the polytypes. In the growth of 3C-SiC, double positioning boundaries (DPBs) are often formed by the existence of twinned domain. The elimination of DPBs can be achieved utilizing the anisotropy of the step advance velocity.

We investigated the dislocation behaviors during the solution growth on Si-face and C-face off-axis 4H-SiC seed crystals by using synchrotron X-ray topography. On Si-face, almost all threading screw dislocations (TSDs) and threading edge dislocations (TEDs) are converted into Frank-type defects and basal plane dislocations (BPDs), respectively. On the other hand, on C-face, TSDs were hardly converted. Some of TEDs were converted to BPDs and BPD-TED reconversion was often occurred. Therefore, to reduce density of threading dislocations in the grown crystal, it is better to use Si-face off-axis seed crystal.

We realized the polytype-selective growth of 3C–SiC and 6H–SiC on a 6H–SiC (0 0 0 1) seed crystal by controlling the supersaturation. Both 6H–SiC and 3C–SiC grew on the 6H–SiC seed crystal at low supersaturation, but 3C–SiC increased with increasing supersaturation. At high supersaturation, 3C–SiC grew so rapidly that it completely covered the 6H–SiC seed crystal. The growth rates of 3C–SiC and 6H–SiC have different dependences on supersaturation. In the present case, the growth rate of 3C–SiC in 2D nucleation mode is compared with that of 6H–SiC in spiral growth mode. The present kinetic polytype-control technique is based on polytypes having different growth rates and it differs considerably from the conventional technique that is based on “inheritance” of stacking sequence, which is well known as “step-controlled epitaxy”.

Polytype transformations on the 4H-SiC(0001) Si face during top-seeded solution growth have been investigated by transmission electron microscopy and micro-Raman spectroscopy. 4H-, 15R-, and 6H-SiC...

Solution growth is considered to be a powerful method for high quality SiC crystals. This work reports that the conversion process from a threading screw dislocation into a few Frank partial dislocations in basal planes was investigated by synchrotron X-ray topography. This process was effectively assisted by step-flow growth on off-oriented (0001) seed crystals. The Frank partials were not extended into the crystal grown toward the [0001] direction perpendicular to the basal plane. Thus, the conclusion of this study suggests the use of off-oriented seed crystal is important to improve crystal quality.

The crystal structure and microstructure of ReSi1.75 were investigated by synchrotron X-ray diffraction combined with scanning transmission electron microscopy. ReSi1.75 contains an ordered arrangement of vacancies in Si sites in the underlying tetragonal C11b lattice of the MoSi2-type and the crystal structure is monoclinic with the space group Cm. Atomic positions of Si atoms near vacancies are considerably displaced from the corresponding positions in the parent C11b structure, and they exhibit anomalously large local thermal vibration accompanied by large values of atomic displacement parameter. There are four differently-oriented domains with two of them being related to each other by the 90° rotation about the c-axis of the underlying C11b lattice and the other two being their respective twins. The habit planes for domain boundaries observed experimentally are consistent with those predicted with ferroelastic theory.

The changes in microstructure and defect structure of two different semiconducting transition-metal silicides, ReSi1.75 and Ru2Si3 with ternary alloying of substitutional elements with a valence electron number different from that of the constituent metal have been investigated in order to see if the crystal and defect structures of these silicides and thereby their physical properties can be controlled through defect engineering according to the valence electron counting rule. The Si vacancy concentration and its arrangement can be successfully controlled in ReSi1.75 while the relative magnitude of the metal and silicon subcell dimensions in the chimney-ladder structures can be successfully controlled in Ru2Si3.

Two-dimensional (2D) form of DNA-functionalized gold nanoparticles (DNA–AuNPs) has been studied. To confine the DNA–AuNPs in 2D space, we utilized the strong affinity between DNA molecules and supported lipid bilayers (SLBs). DNA–AuNPs adsorbed onto cationic SLB consisting of Dimethyl dioctadecyl ammonium bromide (DDAB) on mica substrate with high affinity. Owing to the high mobility of lipid molecules, 2D diffusion and transportation of DNA–AuNPs on the SLB was achieved. Using AFM imaging we confirmed a selective adsorption of DNA–AuNPs onto cationic lipid bilayer patches on mica surface, and then we confirmed a drastic formation change of DNA–AuNPs on the SLB with annealing. We observed that the DNA–AuNPs assembled into a densely-packed single-layered 2D superstructure through DNA hybridization.

One of the most important issues of SiC solution growth is to increase the growth rate. In our previous study, we reported that increasing the rotational speed of the seed crystal is effective for improving the growth rate in top-seeded solution growth. In the present study, we investigated the origin of the growth rate improvement through a continuous fluid dynamics simulation with a full-scale three-dimensional model of the experimental setup for actual growth experiment. The numerical results indicated that the stagnant layer above the growth interface decreased in thickness and the carbon concentration gradient then became steep with an increase in the rotational speed of the seed crystal. The experimental growth rate was proportional to the calculated carbon concentration gradient, which indicates that the carbon diffusion through the stagnant layer is the rate-determining process.

The effect of divalent cations on lipid-bilayer-assisted DNA-functionalized nanoparticle (DNA-NP) assembly has been studied. We previously reported the lateral diffusion of DNA-NPs on planar lipid bilayer patches, owing to the mobility of lipid molecules in a supported lipid bilayer (SLB), and the resultant two-dimensional (2D) assembly of DNA-NPs. We here report the structural change of the assembled 2D DNA-NP lattices by magnesium ion concentration control on a successfully formed uniform SLB. In the magnesium-free buffer solution, DNA-NPs on SLB loosely assembled into quasi-hexagonal ordered lattices. In buffer solution containing 1 mM magnesium acetate, the interparticle distance of DNA-NPs decreased and the lattice structure became disordered. In buffer solution containing 5 mM magnesium acetate, the structure of DNA-NP arrays changed markedly and square lattices appeared. It is suggested that magnesium ions affected DNA molecules, which linked nanoparticles, and enabled the control of the structure of DNA-NP 2D arrays.

The crystal structure of thermoelectric rhenium silicide with an ordered arrangement of vacancies is investigated by utilizing spherical aberration (Cs) corrected scanning transmission electron microscopy (STEM) combined with synchrotron X-ray diffraction and conventional transmission electron microscopy. By STEM Cs corrected imaging, we can clearly observe Si vacancies in rhenium silicide, which is impossible without Cs correction. In addition, significantly reduced contrast levels are noted in STEM images for particular Si sites near vacancies. From the STEM image simulation, the reduced contrast levels are concluded to be due to anomalously large local thermal vibration of these Si atoms. The crystal structure of rhenium silicide can be successfully refined by the synchrotron X-ray diffraction starting with the deduced structure model from the STEM images and the occurrence of large local thermal vibration can be qualitatively confirmed. Furthermore, we confirm the validity of the refined crystal structure of rhenium silicide by comparing experimental images with simulated image generating with the refined crystal structure parameters.

The thermoelectric properties of Magneli phase titanium oxides TinO2n−1 (n=2,3,…) have been investigated, paying special attention to how the thermoelectric performance can be altered by changing the microstructure. Dense polycrystalline specimens with nominal composition of TiO2−x (x=0.05, 0.10, 0.15, and 0.20) prepared by conventional hot-pressing are all identified to be one of the Magneli phases, in which crystallographic shear planes are regularly introduced according to the oxygen deficiency. Electrical conduction is n-type for all specimens and the carrier concentration increases with the increase in the oxygen deficiency. The values of lattice thermal conductivity, on the other hand, decrease with the increase in the oxygen deficiency, which can be attributed to phonon scattering at the crystallographic shear plane. The largest value of thermoelectric figure of merit Z, 1.6×10−4 K−1 was obtained at 773 K for the hot-pressed specimen of TiO1.90.

The concentration and arrangement of Si vacancy in aluminum or phosphorus containing ReSi1.75 based silicides have been investigated. Both aluminum and phosphorus are substituted with silicon. In addition to the (001)C11b twins usually observed in binary ReSi1.75, planar defects are heterogeneously formed in both of the silicon substituted ternary alloys with small amount. By using the high resolution electron micrograph (HREM) technique, the planar defects are assigned as crystallographic shear (CS) planes lying on (109) C11b and (107) C11b in aluminum and phosphorus containing ReSi1.75, respectively. The CS vector in both ternary alloys is [100]C11b. Since the concentration of vacancies in the ReSi1.75 structure is changed by the introduction of these crystallographic shear, ternary alloys with silicon substituted by aluminum and phosphorus contain more or less amount of vacancies than the binary alloy, respectively. This implies us that concentration of Si vacancies changes so as to retain the average number of valence electron. We can control the concentration of Si vacancy in the ReSi1.75 based alloys.

We report a marked reduction in the dislocation density of a 4H-SiC crystal using a high-efficiency dislocation conversion phenomenon. During the solution growth, threading dislocations were efficiently converted to basal plane defects by the step flow of macrosteps. Utilizing this dislocation conversion phenomenon, we achieved the marked reduction of threading dislocation density. Consequently, the threading screw dislocation density was only 30 cm−2, which was two orders of magnitude lower than that of the seed crystal. The 4H-SiC polytype of the seed crystal was replicated in the grown crystal, which was attributed to the spiral growth owing to a few remaining threading screw dislocations upstream of the step flow.

Evolution of threading screw dislocation (TSD) conversion during the solution growth of 4H-SiC on a vicinal crystal of 4H-SiC(0001) was investigated by synchrotron X-ray topography. Selecting appropriate X-ray wavelength and g vector, we can change the penetration of X-ray, and the dislocation behaviors with the different depth were successfully observed. Evidently TSDs parallel to the c-axis having c-component Burgers vector were changed into defects on the (0001) basal planes with the same Burgers vector as the TSDs, propagating to the [112¯0] step-flow direction by advancing macrosteps during the solution growth. The TSD conversions stochastically took place during the growth. The conversion rate was almost uniform and finally almost all TSDs were converted to the basal plane defects. The conversion rate was low at the very early stage of the growth, which implies that the macrosteps were not formed at the initial stage of the solution growth.

The high-efficiency conversion of threading screw dislocations (TSDs) in 4H-SiC by solution growth provides an efficient method of obtaining ultra high-quality SiC crystals. The behavior of TSDs on on-axis and off-axis 4H-SiC0001 seed crystals was investigated by synchrotron X-ray topography. Almost all TSDs in the off-axis Si-face seed crystal were converted to Frank-type stacking faults on the basal planes. The conversion ratio of TSDs was highly influenced by the surface polarity of the seed crystal. The stacking faults laterally propagate toward the outside of the crystal.