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This study aims to analytically measure the fully developed laminar flow and heat transfer the water-based nanofluids, Cu, CuO, and Al2O3, within a micropipe with constant heat flux, under the temperature jump and slip rate boundary conditions. Knudsen number, nanoparticle volumes, and ratios of liquid layer thickness to particle radius are assumed, 0, 0.02, 0.04; 0%, 4%, %8, and 0.1, 0.2, 0.4, respectively. The findings suggest that adding nanoparticles to flow area has significant effect on both the velocity field and the heat transfer. There is a significant decline in the velocity both at the core and on the walls in the velocity area, due to the increase in the solid volume and the ratios of liquid layer thickness to particle radius after adding nanoparticles to flow area, and the increase of Nusselt number is significantly proportional to that of the solid volume and the ratios of liquid layer thickness to particle radius. Among the nanoparticles, Cu, CuO, and Al2O3, used as nanofluids within the micropipe, Cu is found to be the one with the highest heat transfer enhancement, followed by Al2O3, and CuO, respectively.

Silicon carbide is a sound semiconductor material because of its good performance in high-voltage and high-frequency fields. However, micropipe — a special 3 dimensions defect commonly is introduced at the epitaxial growth stage — is easy to be passed to the machining stage, and deteriorates the final device performance. In the current work, we employ micromachining atomistic simulations with a single abrasive particle to evaluate whether these defects are eliminated by varying the penetration depth. The simulation results are analyzed from the aspects of structure and energy, atomistic flow field, stress distribution, and temperature; the behavior models of the finished groove are proposed. By these analyses, it is found that it seems to be impossible to completely eliminate the effect of the micropipe by adjusting the penetration depth during micromachining, based on our MD simulation cases; but 4H-SiC shows different dynamic behaviors under different penetration depths, which may be a strategy to detect or control the effect of micropipe.

Enhancement of heat transfer during the evaporation process investigated experimentally. Sub-cooled carbon dioxide flows inside nontraditional heat exchangers; micropipe heat exchanger with internal diameter of 0.6 mm and a porous tube one filled with gravel sand with porosity of 39.8 %. The experiments were carried out at different operating conditions. It is found that the heat transfer coefficient of the micropipe heat exchangers reached twice of the porous tube heat exchanger. Correlations utilized in the literature were used to validate experimental results. Good conformity was obtained.

Micropipe, a “killer” defect in SiC crystals, severely hampers the outstanding performance of SiC-based devices. In this paper, the etching behavior of micropipes in 4H-SiC and 6H-SiC wafers was studied using the molten KOH etching method. The spectra of 4H-SiC and 6H-SiC crystals containing micropipes were examined using Raman scattering. A new Raman peak accompanying micropipes located near −784 cm−1 was observed, which may have been induced by polymorphic transformation during the etching process in the area of micropipe etch pits. This feature may provide a new way to distinguish micropipes from other defects. In addition, the preferable etching conditions for distinguishing micropipes from threading screw dislocations (TSDs) was determined using laser confocal microscopy, scanning electron microscopy (SEM) and optical microscopy. Meanwhile, the micropipe etching pits were classified into two types based on their morphology and formation mechanism.

Background Oxford Nanopore Technology (ONT) long-read sequencing has become a popular platform for microbial researchers due to the accessibility and affordability of its devices. However, easy and automated construction of high-quality bacterial genomes using nanopore reads remains challenging. Here we aimed to create a reproducible end-to-end bacterial genome assembly pipeline using ONT in combination with Illumina sequencing. Results We evaluated the performance of several popular tools used during genome reconstruction, including base-calling, filtering, assembly, and polishing. We also assessed overall genome accuracy using ONT both natively and with Illumina. All steps were validated using the high-quality complete reference genome for the Escherichia coli sequence type (ST)131 strain EC958. Software chosen at each stage were incorporated into our final pipeline, MicroPIPE. Further validation of MicroPIPE was carried out using 11 additional ST131 E. coli isolates, which demonstrated that complete circularised chromosomes and plasmids could be achieved without manual intervention. Twelve publicly available Gram-negative and Gram-positive bacterial genomes (with available raw ONT data and matched complete genomes) were also assembled using MicroPIPE. We found that revised basecalling and updated assembly of the majority of these genomes resulted in improved accuracy compared to the current publicly available complete genomes. Conclusions MicroPIPE is built in modules using Singularity container images and the bioinformatics workflow manager Nextflow, allowing changes and adjustments to be made in response to future tool development. Overall, MicroPIPE provides an easy-access, end-to-end solution for attaining high-quality bacterial genomes. MicroPIPE is available at https://github.com/BeatsonLab-MicrobialGenomics/micropipe.

Oxford Nanopore Technology (ONT) long-read sequencing has become a popular platform for microbial researchers; however, easy and automated construction of high-quality bacterial genomes remains challenging. Here we present MicroPIPE: a reproducible end-to-end bacterial genome assembly pipeline for ONT and Illumina sequencing. To construct MicroPIPE, we evaluated the performance of several tools for genome reconstruction and assessed overall genome accuracy using ONT both natively and with Illumina. Further validation of MicroPIPE was carried out using 11 sequence type (ST)131 Escherichia coli and eight publicly available Gram-negative and Gram-positive bacterial isolates. MicroPIPE uses Singularity containers and the workflow manager Nextflow and is available at https://github.com/BeatsonLab-MicrobialGenomics/micropipe.

This paper presents an investigation on micropipe evolution from hexagonal voids in physical vapor transport-grown 4H-SiC single crystals using the cathodoluminescence (CL) imaging technique. Complementary techniques optical microscopy, scanning electron microscopy, and energy-dispersive spectroscopy (EDS) are also used to understand the formation mechanism of hexagonal voids along with the origin of pipes from these voids. The ability of CL to image variations along the depth of the sample provides new insights on how micropipes are attached to hexagonal voids that lie deep within the bulk single crystals. CL imaging confirms that multiple micropipes can originate from a single hexagonal void. EDS mapping shows that the inside of the micropipe walls exhibits higher levels of carbon. Investigation of the seed region by optical imaging shows that improper fixing of the seed to the crucible lid is the root cause for the formation of hexagonal voids that subsequently lead to micropipe formation.

We have developed a process that is able to detect, count, and map micropipes on SiC substrates. This process uses a polarized light microscope to scan the wafer. The pictures taken are analyzed with a program that produces a micropipe map as well as numerical defect distribution data in a text file. The results of the process were validated with x-ray topography measurement. The repeatability of this process is also studied and reported.

This paper performs a theoretical analysis of suspended microchannel resonators (SMRs) containing one single or two parallel channels, modeled here as cantilevered micropipes conveying fluid and nanoparticle, and investigates the effects of flow velocity and nanoparticle’s instantaneous position on natural frequency, stability, and damping. For two-channel micropipes (TCMPs), the governing equation is derived using the Newtonian approach by essentially accounting for the flow-induced tensile force due to the fact that the flow reverses direction near the free end of the micropipe. Results of eigenvalue analysis show that the presence of a moving nanoparticle can make originally stable micropipe systems become unstable. The stability of both single-channel micropipes (SCMPs) and TCMPs is strongly dependent on the instantaneous position of the moving nanoparticle. For a TCMP system, of particular interest is that in the absence of external damping, flutter instability may concurrently occurs in several modes even for infinitesimal flow velocity. The same TCMP system but with consideration of external damping, however, can retain stability at low flow velocity. These results highlight the importance of considering fluid–structure interactions in the design of SMRs containing internal flow and nanoparticle.

Micropipe conveying fluid as a core element can be found in many microfluidic devices. In such scale, size effect phenomenon in micropipe may play a significant role in the mechanical behavior of system. In addition, due to the improper production process, the micropipe may be fabricated with a geometric imperfection. Hence, this study objects to investigation of the size-dependent and -independent stability behavior of geometrically perfect and imperfect extensible micropipe conveying fluid under different boundary conditions. In the framework of modified couple stress theory, the nonlinear equations of system are established based on Euler-Bernoulli beam theory. Statics-based analytical solutions are developed to study the nonlinear stability characteristics of system. The statics-based results are verified by aid of a dynamics-based numerical solution. It is indicated that for a perfect case the system becomes unstable at a critical velocity via a pitchfork bifurcation. But, for an imperfect case the system may lose its stability at a primary critical velocity by a perturbed pitchfork bifurcation also it becomes unstable at a secondary critical velocity by a transcritical bifurcation. It is found that the primary and secondary critical velocities of the imperfect case are, respectively, smaller and greater than the critical velocity of the perfect case. A parametric study is conducted to highlight the influence of different dimensionless parameter as well as boundary conditions on the nonlinear stability behavior of system. Finally, it should be pointed out that the analytical solution and the presented results not only for the size-dependent pipe conveying fluid in micro scale but also for the size-independent pipe conveying fluid from macro to micro scale can be utilized.

Hillocks on N-face GaN (000 1 ¯ ) films are effectively eliminated by group-III-source flow-rate modulation epitaxy (FME), wherein the flow-rate of group-III sources are sequentially modulated under a constant supply of NH 3 . A hillock-free smooth surface obtained by group-III-source FME is attributed to the enhancement of step-flow growth. We found that a hillock originates from a micropipe and grows by spiral growth around the micropipe. The spiral growth rate rapidly decreases with decreasing the degree of surface supersaturation σ , while the step-flow growth rate decreases linearly. For group-III-source FME, wherein σ is lower than conventional continuous growth, the spiral growth rate could be lower than the step-flow growth one so that the formation of hillocks is suppressed.

The method to attach seed to crucible lid as well as seed quality is very important for obtaining high quality crystals. Therefore, modified seeding method was developed for improving adhesive layer between seed and graphite crucible lid. SiC single crystal grown with modified seeding method definitely exhibited lower micropipe density (MPD) and lower full width at half maximum (FWHM) values comparing with values from conventional seeding method. Etch pit density of SiC crystal was successfully decreased with using the modified seeding method.

The distribution of extended defects in silicon carbide (SiC) crystals grown on profiled seeds by the sublimation (physical vapor transport) method has been studied by optical microscopy in combination with chemical etching. It is established that free lateral growth on protruding relief elements (mesas) is accompanied by a sharp decrease in the density of threading dislocations and micropipes. The decreased density of dislocations is retained after growing a thick layer that involves the overgrowth of grooves that separated individual mesas.

An abnormal star-like defect was found on the failed SiC gate turn-off thyristor (GTO) devices after metal removal and KOH etching at 450 &deg, C in this work. It is of extraordinary larger size of 210&ndash, 580 &micro, m, even much larger than the etch pit of a micropipe in 4H-SiC. In addition, the abnormal star-like defect, exhibiting the consistent orientation with the six-fold symmetry of silicon carbide, was found to consist of several penetrating dislocations with the help of a LEXT OLS4000 3D laser confocal microscope. These abnormal star-like etch pits can severely reduce the forward blocking characteristic of GTOs, while exerting insignificant influence on the forward current-voltage characteristics between anode and gate electrode of the 4H-SiC GTO devices. Interestingly, the relationship between forward voltage drop and dislocation density is affected by the abnormal star-like defect. A regular increase of forward voltage drop at 100 A/cm2 was observed with the increasing dislocation density, while this correlation disappears in the presence of an abnormal star-like defect.

We have developed a 3.3 kV ultra-high power density SiC power module, which was realized by fulfilment with only SiC-MOSFETs. As a countermeasure for bipolar degradation issues related to body diodes in the MOSFET structure, a high throughput screening process has been introduced. In the screening process, over 10000 chips of 3.3 kV SiC-MOSFET were evaluated. The large amount of data firstly reveals the probability distribution of the degradation phenomena and enables us to study the relationship with defect densities of the state-of-the-art SiC wafers. Furthermore, origins of the degradation were investigated by teardown analysis. The degradation is caused by the expansion or generation of bar-shaped stacking faults. It was identified that their origins are pre-existing bar-shaped stacking faults in a SiC epi-layer, a basal plane dislocation in a SiC substrate, or a closed micropipe.

A new type of morphological defects related to substrate micropipe is observed in 4H-SiC thick homoepitaxial layers. The structure and formation mechanism are investigated by optical microscopy, laser microscopy, scanning electron microscopy, micro-Raman spectroscopy, micro-photoluminescence spectroscopy and molten KOH etching. The observed new defect has truncated hexagonal prism morphology with a closed-core hexagonal pit, and it is 4H-SiC without polytype transition. It is found that the micropipe in the substrate can not only extend to the epilayer, but also cause a morphological defect to disturb the step-flow growth on the epilayer surface. A model has been proposed to interpret the formation mechanism of the morphological defect. It show that the morphology of the observed defect is mainly determined by the wider terrace in 4° off-angle substrate, the interaction between step-flow growth and spiral growth, and the thickness of the epilayer.

Advances in the growth processes of 4H-SiC epitaxial layers have led to the continued expansion of epilayer thickness, allowing for the detection of more penetrative radioactive particles. We report the fabrication and characterization of high-resolution Schottky barrier radiation detectors on 250 μm thick n-type 4H-SiC epitaxial layers, the highest reported thickness to date. Several 8 × 8 mm2 detectors were fabricated from a diced 100 mm diameter 4H-SiC epitaxial wafer grown on a conductive 4H-SiC substrate with a mean micropipe density of 0.11 cm−2. From the Mott–Schottky plots, the effective doping concentration was found to be in the range (0.95–1.85) × 1014 cm−3, implying that full depletion could be achieved at ∼5.7 kV (0.5 MV/cm at the interface). The current-voltage characteristics demonstrated consistently low leakage current densities of 1–3 nA/cm2 at a reverse bias of −800 V. This resulted in the pulse-height spectra generated using a 241Am alpha source (5486 keV) manifesting an energy resolution of less than 0.5% full width at half maximum (FWHM) for all the detectors at −200 V. The charge collection efficiencies (CCEs) were measured to be 98–99% with no discernable correlation to the energy resolution. A drift-diffusion model fit to the variation of CCE as a function of bias voltage, revealed a minority carrier diffusion length of ∼10 μm. Deep level transient spectroscopy measurements on the best resolution detector revealed that the excellent performance was the result of having ultralow concentrations of the order of 1011 cm−3 lifetime limiting defects—Z1/2 and EH6/7.

A survey dealing with the technology of the formation of three-dimensional structures in silicon carbide substrates is presented. As for technology, this problem can be solved by variational ion-stimulated plasma-chemical etching, and most successfully by the source of inductively coupled plasma (ICP). Silicon carbide consists of silicon and carbon that form volatile fluorides in the reaction with fluorine. The etching reaction takes place in the interaction of silicon and carbon with reactive intermediates and fluorine ions. That is why the fluorine-containing gas, sulfur hexafluoride SF6 in most cases (often with an admixture of oxygen and sometimes argon), is used for the plasma-chemical etching of silicon carbide. The materials that do not react with fluorine are applied for masking during the plasma-chemical etching of silicon carbide. The films of metals such as Cu, Al, and Ni are mainly used and silicon oxide is less used. The formation of through-holes in these substrates followed by the metallization of the holes is a particularly important technological concept related to the plasma-chemical etching of the SiC substrates with the deposited GaN epitaxial layers. Examples of the use of ICP sources for the formation of micro- and nanosize three-dimensional structures in silicon carbide are given. Among them, the formation of the through-holes in the substrates of silicon carbide with epitaxial layers of gallium nitride is discussed.

The morphology of a macrodefect in a single-crystal silicon carbide wafer has been investigated by the computer simulation of an experimental X-ray phase-contrast image. A micropipe, i.e., a long cavity with a small (elliptical in the general case) cross section, in a single crystal has been considered as a macrodefect. A far-field image of micropipe has been measured with the aid of synchrotron radiation without a monochromator. The parameters of micropipe elliptical cross section are determined based on one projection in two directions: parallel and perpendicular to the X-ray beam propagation direction, when scanning along the pipe axis. The results demonstrate the efficiency of the phase contrast method supplemented with computer simulation for studying such macrodefects when the defect position in the sample volume is unknown beforehand.

The aim of this paper is to develop a nonlinear theoretical model for cantilevered micropipes/microbeams conveying fluid and to explore the possible size-dependent nonlinear responses based on the modified couple stress theory. Compared to previous work, this newly developed nonlinear model can be utilized for predicting the post-instability nonlinear dynamics of fluid-conveying micro-cantilever more than its linear dynamics. By considering the geometric nonlinearities, the gravity, and the effect of loose supports at the downstream end, the nonlinear equation of motion is derived using the Hamilton's principle. The governing partial differential equation is further discretized with the aid of Galerkin's approach. Numerical results show that the fluid-conveying micro-cantilever is capable of displaying rich dynamical behaviors. For a ‘horizontal’ or ‘hanging’ micropipe conveying fluid, it is found that flutter instability occurs at a critical flow velocity, beyond which the micropipe would undergo a limit cycle motion; for a ‘standing’ micropipe with relatively long length, however, both buckling and flutter instabilities could occur. More interesting dynamical behavior has been obtained for a modified micropipe system with loose supports at its tip end. In the presence of nonlinear constraining force resulted from loose supports, construction of bifurcation diagrams with the flow velocity as variable parameter and some corresponding phase-plane portraits have shown that chaotic vibrations do indeed arise, following a sequence oof period-doubling bifurcations. It is also demonstrated that the presence of small length scale can enhance the stability of the micropipe. However, size dependence of the post-flutter responses for the system is not pronounced.

Understanding the growth and propagation of defects in SiC remains of interest in an effort to continue to improve device performance. A post-growth boule heat-treatment revealed to form micropipe pairs from apparent single screw dislocations is reviewed. In the treated samples almost no 1c threading screw dislocations were found. Instead, micropipe pairs were observed in similar densities to 1c threading screw dislocations in non-heat treated samples. It is hypothesized that the elevated temperatures allowed for enhanced dislocation mobility, enabling the transition.

In this paper, the effects of hydrogen concentration on growth rate, micropipe density and nitrogen concentration of 4H-SiC crystals were discussed. It was shown that the growth rate is a linear function of the hydrogen concentration, which can be explained not only by C/Si ratio but also the temperature gradient. It was also found that the micropipe density was increased rapidly when the hydrogen concentration exceed a critical value, because the defects such as Si droplets, carbon inclusions and polytype formation were generated at that time. The results of secondary ion mass spectroscopy (SIMS) showed that with increasing the hydrogen concentration, the nitrogen concentration falls down but reaches a constant value which meets the requirements for high purity semi-insulating (HPSI) SiC single crystal growth. Finally, the HPSI 4H-SiC crystals were obtained using 15% hydrogen concentration, the resistivities of wafers cut from these crystals were more than 109Ω•cm, micropipe densities were less than 5cm-2, the full width at the half-maximum (FWHM) were between 30-40 arcsec, making these wafers suitable for microwave devices fabrication.

SiC powders having different purities were prepared by carbothermal reduction under different conditions from traditional process and SiC single crystals were grown by the PVT method from the powders. After crystal growth, boule was cut to wafers and they were polished for chemical and defect analyses. Total impurities including Al, B and Ti which were derived from powders decreased remarkably during crystal growth. The formation of defects including micropipe and dislocations such as TED, TSD and BPD was strongly influenced by impurity content. The effect of impurity seemed to be negligible at below 1ppm level for MPD. On the other hand, dislocations continuously decreased even more when higher purity SiC powder below 1ppm level was used.

Recent advances in the development of thick 4H-SiC epitaxial layers for the fabrication of surface barrier radiation detectors have been paving the way for their use in highly penetrating radiation detection. Challenges still exist to achieve full depletion all the way to the epilayer width, while maintaining a low leakage current at high reverse bias conditions. We report the fabrication of high-resolution and low leakage current Schottky barrier alpha particle detectors with a large active area of 11 mm2 on 50 μm thick n-type 4H-SiC epitaxial layers, which can be fully depleted. The detectors were cut out of large substrates of 100 mm diameter with a micropipe density

High quality nanocrystalline silicon carbide (nc-SiC) thin films sputtered deposited on Pt/Ti/SiO 2 /Si substrate were investigated for its crystallinity dependent dielectric properties ( e r -f, e r -E ) and J–E characteristics. The gain in intensity of highly oriented (105) X-ray reflection evident the improvement in crystallinity of nc-SiC thin films with increase in deposition temperature. An observable enhancement in dielectric properties and reduction in leakage current density ( J ) with increase in crystallinity was ascribed to enhanced dipole density and reduced micropipe density respectively. A minimum J ∼10 −9 A/cm 2 at 0 kV/cm was observed with increase in the crystallinity of SiC thin films. The conduction mechanism in all nc-SiC thin films endures a transition from low field dominating ohmic conduction to interface limited Schottky emission prevailing at high field ( E >60 kV/cm).

This paper presents the results of the infrared spectroscopic study of silicon carbide epitaxial layers grown by the substitution of atoms on the surface of single-crystal silicon. It has been found that, in the infrared spectra, there is a band at 798 cm–1, which corresponds to a transverse optical (TO) phonon in the lattice of silicon carbide. The parameters of disordered silicon carbide on the surface of pores between the epitaxial layer of silicon carbide and the silicon substrate have been determined. It has been revealed that, in the infrared spectra of silicon carbide, there is a band in the wavenumber range of 960 cm–1. A hypothesis has been proposed, according to which this band corresponds to the energy of the previously theoretically predicted elastic dipole consisting of an elastically interacting carbon atom located in an interstitial position and a silicon vacancy.

Specific features of silicon carbide layer formation with the structure (polytype) different from the SiC-substrate structure (polytype) are considered. Simple theoretical foundations of the nonstoichiometric character, impurities, C- and Si-faces effect on the heteropolytype epitaxy (HPE) of silicon carbide are proposed. By means of Harrison’s bond orbital model it is shown that the adsorption possibility for the C-face is much greater than for the Si-face. Within the scopes of the earlier proposed models (D-model and vacancy model) it is demonstrated that the presence of impurities changes characteristic lifetimes of the HPE process and the transition layer widths: impurities which enforce the interpolytype transition decrease corresponding life-time constants and the transition layer widths. For interpretation of the polytype stripes existence within the transition layer, the model of specific spinodal decomposition taking into account vacancy concentrations variations in both SiC sublattices is used.

— The distribution of extended defects in silicon carbide (SiC) crystals grown on profiled seeds by the sublimation (physical vapor transport) method has been studied by optical microscopy in combination with chemical etching and AFM. It is established that free lateral growth on protruding relief elements (mesas) is accompanied by a sharp decrease in the density of threading dislocations and micropipes. The decreased density of dislocations is retained after growing a thick layer that involves the overgrowth of grooves that separated individual mesas.