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Origin of milky optical features in type IaB diamonds: Dislocations, nano-inclusions, and polycrystalline diamond
摘要： The milky appearance shown by certain type IaB diamonds has been subjected to several recent studies, but the origin of this feature is not fully understood. Here several type IaB diamonds with a milky appearance have been studied by cathodoluminescence (CL), electron backscatter diffraction (EBSD), and transmission electron microscopy (TEM). CL of several hazy type IaB diamonds shows scattered or orientated micro-sized spots or short linear luminescence features. TEM observation revealed that those spots and linear features are caused by dislocation loops that are likely responsible for the hazy appearance of the host diamonds. It is also shown that type IaB diamonds with a cloudy appearance contain nano-sized inclusions with negative crystals of octahedral shape. Some of these negative crystals contain a precipitate that can be explained by a compressed disordered cubic δ-N2 phase observed by high-resolution TEM. In one of the milky IaB diamonds with platelet defects, polycrystalline areas composed of columnar diamond crystals elongated radially in [110], similar to ballas diamond, were revealed by EBSD. Taking into account these observations, it is suggested that the dislocation loops, nano-sized inclusions (negative crystals) and/or characteristic grain boundaries of the radiating fibrous crystals would be the origins for the milky appearance of the type IaB diamonds studied here. Those results add a complementary explanation that accounts for the milkiness of type IaB diamonds studied before.
关键词： Type IaB diamonds,Nanominerals and Mineral Nanoparticles,milky,voidites,dislocations,polycrystalline diamond
更新于2025-11-21 11:18:25
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Detailed surface analysis of V-defects in GaN films on patterned silicon(111) substrates by metal–organic chemical vapour deposition
摘要： The growth mechanism of V-defects in GaN films was investigated. It was observed that the crystal faces of both the sidewall of a V-defect and the sidewall of the GaN film boundary belong to the same plane family of {10￣11}, which suggests that the formation of the V-defect is a direct consequence of spontaneous growth like that of the boundary facet. However, the growth rate of the V-defect sidewall is much faster than that of the boundary facet when the V-defect is filling up, implying that lateral growth of {10￣11} planes is not the direct cause of the change in size of V-defects. Since V-defects originate from dislocations, an idea was proposed to correlate the growth of V-defects with the presence of dislocations. Specifically, the change in size of the V-defect is determined by the growth rate around dislocations and the growth rate around dislocations is determined by the growth conditions.
关键词： transmission electron microscopy,threading dislocations,gallium nitride
更新于2025-11-14 17:04:02
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Grain boundaries and tilt angle-dependent transport properties of 2D Mo2C superconductor
摘要： Grain boundaries (GBs) of graphene and molybdenum disulfide have been extensively demonstrated to have strong influence on their electronic, thermal, optical and mechanical properties. 2D transition metal carbides (TMCs), known as MXenes, are a rapidly growing new family of 2D materials with many fascinating properties and promising applications. However, the GB structure of 2D TMCs and the influence of GB on their properties still remain unknown. Here, we used aberration-corrected scanning transmission electron microscopy combined with electrical measurements to study the GB characteristic of highly crystalline 2D Mo2C superconductor, a newly emerging member of 2D TMC family. 2D Mo2C superconductor shows unique tilt angle-dependent GB structure and electronic transport properties. Different from the reported 2D materials, the GB of 2D Mo2C shows peculiar dislocation configuration or sawtooth pattern depending on the tilt angle. More importantly, we found two new periodic GBs with different periodic structure and crystallographic orientations. Electrical measurements on individual GBs show that GB structure strongly affects the transport properties. In the normal state, an increasingly stronger electron localization behavior is observed at the GB region with increasing tilt angle. In the superconducting state, the magnitude of the critical current across the GBs is dramatically reduced, associated with local suppression of superconductivity at GBs. These findings provide new understandings on the GB structure of 2D TMCs and the influence of GB on 2D superconductivity, which would be helpful for tailoring the properties of 2D TMCs through GB engineering.
关键词： dislocations,MXene,2D materials,grain boundaries,superconductivity
更新于2025-09-23 15:22:29
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V-Defect and Dislocation Analysis in InGaN Multiple Quantum Wells on Patterned Sapphire Substrate
摘要： InGaN/GaN multiquantum well (MQW) structures have been grown on cone-shaped patterned sapphire substrates (CPSS) by metalorganic chemical vapor deposition (MOCVD). From the transmission electron microscopy (TEM) results, we found that most of the threading dislocations (TDs) in the trench region of the CPSS were bent by lateral growth mode. Also the staircase-like TDs were observed near the slant region of the cone pattern, they converged at the slope of the cone patterned region by staircase-upward propagation, which seems to effectively prevent TDs from vertical propagation in the trench region. The associated dislocation runs up into the overgrown GaN layer and MQW, and some (a+c) dislocations were shown to decompose inside the multi-quantum well, giving rise to a misfit segment in the c-plane and a V-shape defect. From cross-sectional TEM, we found that all V defects are not always connected with TDs at their bottom, some V defects are generated from the stacking mismatch boundaries induced by stacking faults which are formed within the MQW due to the strain relaxation.
关键词： V defects,Transmission electron microscopy (TEM),InGaN multi-quantum well (MQW),Threading dislocations (TDs)
更新于2025-09-23 15:22:29
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A theoretical investigation of the glide dislocations in the sphalerite ZnS
摘要： The 90(cid:1) and 30(cid:1) partial glide dislocations in ZnS are investigated theoretically in the framework of the fully discrete Peierls model and first-principles calculation. It is found that there are four types of equilibrium cores for each kind of partial glide dislocation, which are named as the O-Zn-core, the B-Zn-core, the O-S-core, and the B-S-core, according to their geometrical feature and atomic ingredient at the core. For the 90(cid:1) partial dislocation, the O-Zn-core (double-period core) and the B-S-core (single-period core) are stable. The Peierls barrier heights of the O-Zn-core and the B-S-core are about 0:03 eV/? and 0:01 eV/?, respectively. For the 30(cid:1) partial dislocation, the O-Zn-core (double-period core) and the B-Zn-core (single-period core) are stable and their Peierls barrier heights are approximately the same as that of the O-Zn-core of the 90(cid:1) partial dislocation. The Peierls stress related to the barrier height is about 800 MPa for the 90(cid:1) partial dislocation with the B-S-core. The existence of unstable equilibrium cores enables us to introduce the concept of the partial kink. Based on the concept of the partial kink, a minimum energy path is proposed for the formation and migration of kinks. It is noticed that the step length in kink migration is doubled due to the core reconstruction.
关键词： glide dislocations,sphalerite ZnS,Peierls model,partial kink,first-principles calculation
更新于2025-09-23 15:21:21
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Reference Module in Materials Science and Materials Engineering || Organometallic Vapor Phase Epitaxial Growth of Group III Nitrides ☆
摘要： The III-nitrides of aluminum nitride (AlN), gallium nitride (GaN), and indium nitride (InN) and their solid solutions form most commonly in the low-temperature wurtzite crystal structure shown in Fig. 1(a). Overall, this structure possesses a hexagonal unit cell with lattice constants c (o00014 axes) and a (o11204 axes). The atomic arrangement within this structure consists of two interpenetrating, closest packed metal and nitrogen lattices in which each atom of one type is bonded to four atoms of the other to form AB4 tetrahedra. The space group is P63mc.
关键词： GaN,OMVPE,Organometallic Vapor Phase Epitaxy,Group III Nitrides,Polarization,Dislocations,InN,Buffer Layers,AlN,Substrates
更新于2025-09-23 15:21:01
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Guidelines for establishing an etching procedure for dislocation density measurements on multicrystalline silicon samples
摘要： With multicrystalline silicon becoming the main material used for photovoltaic applications and dislocations being one of the main material limitations to better solar cell efficiency, etch pit density measurements are gaining more importance. Traditionally, etch pit density measurements are based on selective etching of silicon samples. The majority of the etchants have been developed for monocrystalline samples with known orientation, while those developed for multicrystalline samples have been investigated and might need some optimization. In this study, we use and compare the PVScan tool, which provides a quick way to assess dislocation density on selectively etched samples, and microscope image analysis. We show how the etching methods used for dislocation density measurements can affect the results, and we suggest how to optimize the Sopori etching procedure for multicrystalline silicon samples with high dislocation densities. We also show how the Sopori etchant can be used to substitute Secco while maintaining a high precision of dislocation density measurements, but without the toxic hexavalent chromium compounds.
关键词： Photovoltaic,Etch pit density,Silicon,Secco,Selective etching,EPD,Dislocations,Sopori
更新于2025-09-23 15:21:01
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[IEEE 2019 IEEE 46th Photovoltaic Specialists Conference (PVSC) - Chicago, IL, USA (2019.6.16-2019.6.21)] 2019 IEEE 46th Photovoltaic Specialists Conference (PVSC) - Modeling of Injection-dependent Non-radiative Recombination via Point and Extended Defects in mc-Si
摘要： Non-radiative (NR) carrier recombination limits the efficiency of photovoltaic energy conversion. Minority carrier lifetimes in Si exhibit a variety of dependences on optical injection levels, depending on the types of defects present. To date, models of non-radiative recombination in silicon were proposed for point defects (e.g., Fe interstitials) and extended defects (e.g., dislocations). Direct measurement of local carrier concentration near recombination centers is technically difficult, therefore, computational modeling may be helpful to understand various carrier recombination pathways in materials such as mc-Si. In this paper, modeling is used to compare intensity-dependent NR recombination lifetimes in Si. The usefulness of the model goes beyond mc-Si photovoltaics.
关键词： interstitials,numerical modeling,non-radiative recombination,silicon,Dislocations
更新于2025-09-23 15:19:57
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Microstructural Characterization of Defects and Chemical Etching for HgCdSe/ZnTe/Si (211) Heterostructures
摘要： In this work, transmission electron microscopy has been used to investigate HgCdSe/ZnTe/Si (211) heterostructures grown by molecular beam epitaxy and to study the effects of chemical etchants for measurements of defect density in the HgCdSe epilayers. Both ZnTe/Si and HgCdSe/ZnTe interfaces were decorated with {111}-type stacking faults inclined at angles of ~19° or ~90° with respect to the interface plane. Similar stacking faults were also present in the upper regions of the HgCdSe films. High-resolution imaging and Fourier image analysis revealed dislocations, mostly with a Burgers vector, at both ZnTe/Si and HgCdSe/ZnTe interfaces. Etching solutions based on different combinations of nitric acid, hydrochloric acid and lactic acid were tried in attempts to identify an etchant that provided one-to-one correspondence between etch pits and defects in the HgCdSe layer. Focused-ion-beam milling and transmission electron microscopy were used to prepare site-specific cross-section samples from across the etch pits. However, many defects in regions surrounding the etch pits were unaffected by the various different etchants.
关键词： dislocations,etch pits,HgCdSe (211),alternative substrates,ZnTe
更新于2025-09-23 15:19:57
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Non-radiative recombination at dislocations in InAs quantum dots grown on silicon
摘要： We study the impact of misfit dislocations on the luminescence from InAs quantum dots (QDs) grown on Si substrates. Electron channeling contrast imaging is used together with cathodoluminescence mapping to locate misfit dislocations and characterize the resulting nonradiative recombination of carriers via near-infrared light emission profiles. With a 5 kV electron beam probe, the dark line defect width due to a typical misfit dislocation in a shallow QD active layer is found to be approximately 1 lm, with a 40%–50% peak emission intensity loss at room temperature. Importantly, we find that at cryogenic temperatures, the dislocations affect the QD ground state and the first excited state emission significantly less than the second excited state emission. At the same time, the dark line defect width, which partially relates to carrier diffusion in the system, is relatively constant across the temperature range of 10 K–300 K. Our results suggest that carrier dynamics in the QD wetting layer control emission intensity loss at dislocations, and that these defects reduce luminescence only at those temperatures where the probability of carriers thermalizing from the dots into the wetting layer becomes significant. We discuss the implications of these findings toward growing dislocation-tolerant, reliable quantum dot lasers on silicon.
关键词： silicon substrates,nonradiative recombination,quantum dot lasers,InAs quantum dots,cathodoluminescence,misfit dislocations
更新于2025-09-16 10:30:52