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We propose a two-step hydrogen-ion implantation approach for realizing crystalline-defect-free Si1-xGex channels for potential use in gate-all-around field-effect-transistors beyond the 3 nm transistor-design rule. A dislocation sink was created in a projected range of ion implantation 100 and 200 nm above the strain-relaxed Si0.7Ge0.3 layer and Si substrate interface using two-step H+ -ion implantation. Doses of 5 × 1015 and 2 × 1015 atoms/cm2 were used at 100 and 200 nm, respectively, above the interface, and post-annealing was performed at 800 °C for 30 min. The two-step implantation annihilated the misfit and threading dislocations near the relaxed Si0.7Ge0.3/Si interface. The annihilation efficiency strongly depended on the location and second ion dose of the implantation: the maximum annihilation efficiency was obtained at 100 and 200 nm above the interface with multiple H+-ion doses of 5 × and 2 × 1015 atoms/cm2.

In this paper, a numerical analysis of the cold thread-rolling process using flat dies is presented as a function of the die geometry design. Five die geometries with different threading and finishing ratios were modelled to induce different screw deformation rates. An analytical method was proposed by the authors to design die geometries as a function of screw roll rotation. Screw geometry accuracy, induced stress, and die wear were selected to compare the tested geometries. The results showed that three screw rotations in the threading step were sufficient to guarantee good geometry accuracy. Moreover, the results highlighted that die wear is the most affected parameter among all the tested geometries. Finally, a new solution was proposed by the authors to obtain uniform wear and reduce the die length.

Mono- or few-layer sheets of covalent organic frameworks (COFs) represent an attractive platform of two-dimensional materials that hold promise for tailor-made functionality and pores, through judicious design of the COF building blocks. But although a wide variety of layered COFs have been synthesized, cleaving their interlayer stacking to obtain COF sheets of uniform thickness has remained challenging. Here, we have partitioned the interlayer space in COFs by incorporating pseudorotaxane units into their backbones. Macrocyclic hosts based on crown ethers were embedded into either a ditopic or a tetratopic acylhydrazide building block. Reaction with a tritopic aldehyde linker led to the formation of acylhydrazone-based layered COFs in which one basal plane is composed of either one layer, in the case of the ditopic macrocyclic component, or two adjacent layers covalently held together by its tetratopic counterpart. When a viologen threading unit is introduced, the formation of a host-guest complex facilitates the self-exfoliation of the COFs into crystalline monolayers or bilayers, respectively.

Thread profiles can be considered as mechanical components which contributed to improving the evolution of machines and devices throughout all the history of man. The great importance of using threaded components, in industries and everyday life, is related to the versatility that allows the assembly and disassembly of components exceptionally quickly. Basically, since its invention, the threading tool has been developed, and its geometry has been optimised. Besides, new materials for tooling and coatings have been developed, allowing a significant evolution in the threading process. Thus, this article provides a review, demonstrating the evolution and the main studies in threading processes in the last 20 years, showing the main results obtained and the influence of threading in manufacturing processes. The traditional threading operations such as machining and forming tapping were contextualised, showing the main research with the advances generated in these processes. Furthermore, special internal threading processes were also revised, demonstrating the current developments and their gaps for new studies. Finally, based on this review are proposed lines of research, considering the shortcomings of the contemporary and revised works, that can increase the number of technical information for all threading processes, optimising the current way of making threads.

During internal threading, small alterations in cutting parameters, tool geometry, or process characteristics produce considerable effects on torque and temperature behavior. Understanding these effects is critical to the design and development of new taps. In this work, the torque behavior for a tap operation is evaluated as a function of the number of threads, tool manufacturer, and angle of the taper region of the tool. The chip–tool interface temperature was analyzed, considering the influence of cutting speed and number of threads. Experimental tests were carried out using M10x1.5 taps and cutting speeds of 10 m/min and 25 m/min. Taps with two different geometries were considered in this analysis. The results show a difference in the distribution of the torque along the threads of the conical part between the tools. The presence of adhered material increased the torque during the reverse stage. The torque during the reverse stage for a tap with a damaged tooth was approximately 50% of the torque during the cutting stage. The temperature showed an increase with the number of threads stabilizing between the fourth and fifth threads and increasing again in the sixth filled due to adhesion of workpiece material.

Processing efficiency optimization is often conducted in production environments. For turning, however, the introduction of noncircular cross-section workpieces generates new complexity. This paper presents the kinematic analysis and efficiency optimization of turning a noncircular cross-section workpiece on the basis of ISO 10208:1991 male rope thread machining, characterized by a smooth contour. This thread can be machined, for example, with standard thread turning or using X-axis motions characteristic of noncircular objects, i.e., rope threading. In that case, selecting the proper method and machining parameter values for efficiency can be more challenging than in circular cross-section workpiece turning. The latter method avoids many tool passes but requires highly dynamic movements of the machine in the X-axis. In addition to these two methods, a hybrid method is presented that is characterized by reduced dynamics in the X-axis and more passes than the rope threading method. A description of the methods using mathematical parameters is developed to optimize the process efficiency. Numerical calculations to select a method and its associated cutting parameters are carried out for exemplary cutting edges, theoretical roughness values, tool life models, and other variables. The obtained results and the optimization algorithm of the process are presented.

Multithreading is the core of mainstream heterogeneous programming methods such as CUDA and OpenCL. However, multithreaded parallel programming requires programmers to handle low-level runtime details, making the programming process complex and error prone. This paper presents no-threading (NoT), a high-level no-threading programming method. It introduces the association structure, a new language construct, to provide a declarative runtime-free expression of different data parallelisms and avoid the use of multithreading. The NoT method designs C-like syntax for the association structure and implements a compiler and runtime system using OpenCL as an intermediate language. We demonstrate the effectiveness of our techniques with multiple benchmarks. The size of the NoT code is comparable to that of the serial code and is far less than that of the benchmark OpenCL code. The compiler generates efficient OpenCL code, yielding a performance competitive with or equivalent to that of the manually optimized benchmark OpenCL code on both a GPU platform and an MIC platform.

Tapping process is an important machining process to produce internal threads with accuracy, quickness, and low costs. The constant study of the tapping process is necessary due to the value added to the product when the tapping step occurs. The threading operation is the last manufacturing process used in a component having one or more threaded regions. Thus, because several manufacturing processes were used before the threading process, the value added to the product is significant, and the loss of this component represents severe financial damages to the industrial sector. This work analysed the tapping process with two types of taps considering the torque and thrust force as the main response. Workpieces of SAE 1020 steel with dimensions of 122 × 22 × 20 mm were used due to its broad application in industry and mainly because this steel presents excellent machinability. The torque and thrust forces were monitored using a piezoelectric dynamometer with an acquisition rate of 600 Hz. Taps M8 with the pitch of 1.25 mm with and without chip breaker were applied in experimental tests. The initial hole was the same for all experiments with the value of 6.8 mm. The results demonstrated that torque and thrust force had a different behaviour increasing or decreasing with the change of cutting speed, type of coating, and the use or not of chip breaker. Thus, it can be concluded that taps with higher helix angle, without chip breaker, and coated were the best option for tapping in threaded blind holes.

In order to evaluate various buffer layers for metamorphic devices, threading dislocation densities have been calculated for uniform composition In x Ga1−xAs device layers deposited on GaAs (001) substrates with an intermediate graded buffer layer using the LMD model, where LMD is the average length of misfit dislocations. On this basis, we compare the relative effectiveness of buffer layers with linear, exponential, and S-graded compositional profiles. In the case of a 2 μm thick buffer layer linear grading results in higher threading dislocation densities in the device layer compared to either exponential or S-grading. When exponential grading is used, lower threading dislocation densities are obtained with a smaller length constant. In the S-graded case, lower threading dislocation densities result when a smaller standard deviation parameter is used. As the buffer layer thickness is decreased from 2 μm to 0.1 μm all of the above effects are diminished, and the absolute threading dislocation densities increase.

In order to improve the threading stability and the head thickness precision in tandem hot rolling process, an adaptive threading strategy was proposed. The proposed strategy was realized by the rolling characteristics analysis, and factors which affect the rolling force and the final thickness were determined and analyzed based on the influence coefficients calculation process. An objective function consisting of the influenced factors was founded, and the disturbance quantity was obtained by minimizing the function with the Nelder-Mead simplex method, and the proposed adaptive threading strategy was realized based on the calculation results. The adaptive threading strategy has been applied to one 7-stand hot tandem mill successfully, actual statistics data show that the predicted rolling force prediction in the range of ±5.0% is improved to 97.8%, the head thickness precision in the range of ±35 μm is improved to 98.5%, and the threading stability and the head thickness precision are enhanced to a high level.

The internal threading with tap or forming tap, is a widely applied factoring process throughout industry. However, the knowledge held by the toolmakers is not transferred to the scientific literature, which justifies the small number of studies regarding this matter. This data limitation reduces the tool and cutting condition selection guide to geometrical characteristics. This current work has two main goals; the first one is to study the process behavior regarding the secondary and uncontrollable characteristics, such as thread length, tool coating, feed rate, and hole’s diameter. It also investigated the load distribution in the cutting edge for a tap operation. The second goal of this work is the investigation of the behavior of a new type of floating system in terms of torque and axial force. One of the outcomes of this work was that the torque distribution along the fillet was not uniform, with the torque of the third fillet higher than the others. The floating system tested reduces the axial force and torque by reducing synchronicity errors even in extremely conditions.

The aim of this work is to develop an experimental device useful to evaluate the friction coefficient in triangular thread joints (M12) manufactured with rolling and machining processes, and therefore, to relate precisely the clamping force to the tightening torque. Experimental static tests of clamp force during 10 tightening–loosening cycles were applied to specific threaded specimens obtained with the rolling and machining process. To analyze the mechanical and tribological behaviors of the manufactured threads, the torque coefficient (K) (nut factor), the average friction coefficient (μ m ), and the clamped force (F) have been evaluated during 10 cycles of tightening–loosening. The results of this study showed that the range of the variability of the torque coefficient and friction coefficient is between 0.151 and 0.54 and from 0.19 to 0.69 for the rolled thread, respectively. However, these coefficients are between 0.187 and 0.55 and from 0.25 to 0.72 for the machined thread, respectively. The clamping force preserves a linear relationship with the tightening torque and decreases as the number of tightening increases. The use of the rolling process to manufacture the thread joint can preserve a higher mechanical resistance and ameliorate the tribological behavior of the thread compared to the machining process.

In order to mitigate the formation of threading dislocations in an In0.1Ga0.9Sb heteroepitaxial buffer layer grown on a (001) GaSb substrate, an AlSb blocking layer was grown within the buffer layer. Transmission electron microscopy measurements revealed that the film with the AlSb blocking layer had a significantly lower threading dislocation density than a buffer layer of equivalent thickness in the absence of the blocking layer. Because the AlSb blocking layer is of greater mechanical stiffness than the In0.1Ga0.9Sb buffer layer, attractive image forces that act to draw dislocations to the film surface are countered by repulsive image forces traceable to the In0.1Ga0.9Sb/AlSb interface. These experimental results are consistent with calculations based on anisotropic elasticity theory for repulsive image forces acting on a dislocation beneath the blocking layer.

In addition to pure threading screw dislocations (TSDs), the presence of threading mixed dislocations (TMDs) (with a component) has been reported both in 4H-SiC axial slices (wafers cut parallel to the growth axis) and in commercial offcut wafers (cut almost perpendicular to the growth axis). In this paper, we first demonstrate a method to quickly distinguish TMDs from TSDs in axial slices via synchrotron white-beam x-ray topography. Since such axial slices are usually not available for commercial purposes, a systematic method is then developed and demonstrated here to unambiguously determine the Burgers vectors of TMDs in 4H-SiC commercial offcut wafers. In this second study, both synchrotron monochromatic-beam x-ray topography and ray-tracing simulation are used. The x-ray topographs were recorded using grazing-incidence geometry. The principle of this method is that the contrast of dislocations on different reflections varies with the relative orientation of Burgers vectors with respect to the diffraction vectors. Measurements confirm that, in a commercial offcut wafer, the majority of the threading dislocations with screw component are mixed-type dislocations.

Mechanical components with easy assembly, especially those that use the threading process, are es- sential for industrial products. Fixtures using threaded components are employed from the aircraft to medical industry. The mechanical fixings by tapping, for exam- ple, in the biomedical field have the function of facili- tating the initial insertion of orthopedic and dental com- ponents and of ensuring excellent grip. The aim of this work was to study the external thread by the forming process in Ti-6Al-4V titanium alloy using a forming head with three rollers. Ti-6Al-4v titanium alloy was used due to its excellent mechanical properties and wide application as an aircraft and mechanical component material. A statistical methodology (DoE) was per- formed to identify and evaluate the effect of the factors (initial diameter, forming speed, and measuring position) on the responses; hardness, fill rate, and thread profile. The results showed that the characteristics of the threads depend on the factors of the threading processes. The forming and machining speeds were the main parame- ters affecting the process. The hardness in the thread's crest was lower than at the base and the middle regions. Finally, the threads reached a desired profile with an excellent fill rate not only for formed threads but also for machined threads.

Threading dislocations in aluminum nitride boules grown by physical vapor transport method were systematically studied via synchrotron x-ray topography (white beam and monochromatic) in conjunction with ray tracing simulations. Two major types of threading dislocations were observed in the c-axis-grown boules: threading screw dislocations (TSDs) and threading edge dislocations (TEDs) with Burgers vectors along the [0001] and \(\langle 11\bar{2}0 \rangle \) directions, respectively. TSDs were typically observed in the middle of the boule while TEDs were commonly observed to aggregate into arrays along the \( \langle 1\bar{1}00 \rangle \) and \( \langle 11\bar{2}0 \rangle \) directions in various parts of the boule on basal plane oriented wafers. By comparison with ray tracing simulations, the absolute Burgers vectors of both TSDs and TEDs in the arrays could be unambiguously determined. TEDs comprise over 90 % of all threading dislocations observed. The relationships between TED arrays and low angle grain boundaries and their possible formation mechanisms are discussed.

Metamorphic GaInAs/AlInAs buffers with a total mismatch of 2 % with respect to GaAs have been grown by metal organic chemical vapor deposition on GaAs substrates with miscuts of 2°, 7° and 15° toward (111)A. The buffer grown on 2° miscut substrate exhibits a dislocation pile-up formation which increases the threading dislocation density greatly. However, using 7° and 15° off substrates eliminates the dislocation pile-up and decreases the dislocation density by an order of magnitude compared with that on the 2° substrate miscut, and the best crystalline quality of buffer is obtained on the 15° substrate miscut. Experimental results show that the buffers grown on the 7° and 15° miscut substrate exhibit shallower trenches on the surface and a weaker strain field in the InGaAs cap layers, and these help to suppress the occurrence of dislocation pile-up, leading to a lower threading dislocation density.

Effect of the V/III ratio during buffer layer growth on the yellow and blue luminescence in undoped GaN epilayer has been studied by means of photoluminescence spectroscopy and high resolution X-ray diffraction. It is found that the densities of screw and edge threading dislocations increase with the V/III ratio of the buffer layer, and the intensities of the yellow luminescence (YL) and blue luminescence (BL) emissions also increase dramatically. However, the density ratio of the edge threading dislocation to the screw threading dislocation remains invariant, as well as the intensity ratio of YL emission to BL emission. It can be concluded from these phenomena that the edge threading dislocation and screw threading dislocation can enhance the YL and BL emissions, respectively.

This work presents the fabrication of micro threads of pitch less than 100 μm for micro components. The micro sized threading tool having a tool nose radius less than 40 μm is manufactured by micro wire electric dis- charge machining (μWEDM) process. This μWEDM pro- cess overcomes the difficulties in conventional machining process for production of threading tools and helps in achieving a corner radius as small as 15 μm with specialized wire tool path strategies. This method also helps in fabrica- tion of special micro tools from commercially available or worn-out tungsten carbide tool inserts.

This study describes the elimination of threading dislocations (TDs) in GaN nanostructures. Cross-sectional transmission electron microscopy (XTEM) analysis reveals that the nominal [0001] line direction of a TD changes when it enters a GaN nanostructure and the dislocation then terminates at a sidewall facet. It is suggested that the driving force for this process is the reduction of dislocation line energy, and for a pure-edge dislocation, this TD elimination process can be accomplished simply by dislocation climb. This mechanism is active whenever a threading defect is in close proximity to a surface. Preliminary XTEM analysis of defects in AlGaN and InGaN core–shell growth onto GaN nanostructures is also shown. Although more work is required to improve the quality of core–shell InGaN epitaxial growth, nanostructures appear to offer a route to defect-free, nonpolar GaN-based devices.

Multi-core processors are becoming prevalent rapidly in personal computing and embedded systems. Nevertheless, the programming environment for multi-core processor-based systems is still quite immature and lacks efficient tools. In this work, we present a new VERTAF/Multi-Core framework and show how software code can be automatically generated from SysML models of multi-core embedded systems. We illustrate how model-driven design based on SysML can be seamlessly integrated with Intel’s threading building blocks (TBB) and the quantum framework (QF) middleware. We use a digital video recording system to illustrate the benefits of the framework. Our experiments show how SysML/QF/TBB help in making multi-core embedded system programming model-driven, easy, and efficient.

Machines at a molecular level are in perpetual Brownian motion even at an ambient temperature. One of the representative issues of researches on molecular machines is a development of technology, which can control Brownian motion. This review presents our efforts to achieve the first rationally designed molecular brake systems of threading/dethreading motions, a shuttling motion, and a rocking motion that work reversibly and quantitatively in response to external stimuli without producing any chemical wastes. These molecular brake systems were constructed from a dumbbell shaped secondary ammonium axle and a ring component having photo and thermally reactive moiety.

The electrical discharge machining (EDM) is a machining process based on pulsed electrical discharge effects, which appear between the electrode tool and the workpiece. One may say that the electrical discharge machining is one of the most frequently used nonconventional processes, allowing the obtaining of surfaces which cannot be otherwise achieved through classical machining methods. The electrical discharge machining is also used in order to manufacture hard and extra-hard materials; this process is used to obtain pieces with complex shapes, which would otherwise be difficult or even impossible to obtain, by the use of classical machining methods. The profiled surfaces can be classified according to the final service role. In this respect one may mention threaded, spherical, conical or polygonal surfaces as profiled surfaces. The threaded surfaces could be obtained by classical methods and nonconventional machining methods, among which cutting machining and plastic deformation as classical machining methods are worth mentioning.

Spacer fabrics have been used in many areas varying from medical applications to protection applications. Especially the three dimensional characteristic of spacer fabrics presents different opportunities for special applications. The compression resistant characteristic of spacer fabrics is one of their main properties. In this research the compression behaviour of spacer fabrics designed for concrete applications has been investigated. The effects of some parameters such as spacer yarn material, pattern and threading on the compression behaviour of spacer fabrics have been studied. According to the test results it was found that the material, pattern and the threading of spacer yarns are important parameters for the compression characteristics of spacer fabrics. It was also observed that the location angle of spacer yarn and the amount of the spacer yarns influence the compression behaviour of spacer fabrics.

Conventional threading operations involve two distinct machining processes: drilling and threading. Therefore, it is time consuming for the tools must be changed and the workpiece has to be moved to another machine. This paper presents an analysis of the combined process (drilling followed by threading) using a single tool for both operations: the tap-milling tool. Before presenting the methodology used to evaluate this hybrid tool, the ODS (operating deflection shapes) basics is shortly described. ODS and finite element modeling (FEM) were used during this research to optimize the process aiming to achieve higher stable machining conditions and increasing the tool life. Both methods allowed the determination of the natural frequencies and displacements of the machining center and optimize the workpiece fixture system. The results showed that there is an excellent correlation between the dynamic stability of the machining center-tool holder and the tool life, avoiding a tool premature catastrophic failure. Nevertheless, evidence showed that the tool is very sensitive to work conditions. Undoubtedly, the use of ODS and FEM eliminate empiric decisions concerning the optimization of machining conditions and increase drastically the tool life. After the ODS and FEM studies, it was possible to optimize the process and work material fixture system and machine more than 30,000 threaded holes without reaching the tool life limit and catastrophic fail.

We report the results of theoretical and experimental investigations to determine how the design and geometrical parameters of the cutting part of taps affect the dynamic characteristics and accuracy of thread cutting. Our investigations identified the main mechanisms that change the force characteristics during thread cutting. This makes it possible to determine measures to increase the accuracy and stability of thread cutting with taps.

In order to verify an edge breakout predicting model in orthogonal cutting, which was proposed by the author’s previous work, orthogonal machining experiments must be conducted. A CNC lathe was utilized to carry out simulated orthogonal cuttings. The workpiece, made of aluminum alloy Al 6061-T6, is a cylindrical bar with square threads and axial/radial grooves. Threading and grooving inserts with a flat cutting edge were chosen as the cutting tools. The experimental data were used to verify the previously developed edge breakout model. The tests showed excellent agreement with the model predictions.

Structural and optical properties of InGaN/GaN multiple triangular quantum well (QW) structures with different threading dislocation (TD) densities of 1.5×108 (sample A) and 4.5×108 cm-2 (sample B) have been studied. High resolution transmission electron microscopy and x-ray diffraction analysis showed more fluctuation of local In composition in the sample B, which was attributed to the stress field created by the dislocations as it provides a driving force for the migration of In atoms towards dislocations. Severe degradation of photoluminescence intensity of the sample B was also observed at < 50 K. The optical and structural properties of the InGaN/GaN triangular QW structures are overall substantially affected by the TD density.

In situ transmission electron microscopy (TEM) was performed to study dislocation motion during temperature cycles in aluminum films passivated with a SiO2 layer. The films were cycled from room temperature to 450 °C. Wedge-haped cross-sectional TEM samples were used to retain the constraint of the Si substrate. Besides interactions between dislocations and interfaces, the movement of threading dislocations within the constrained aluminum film was observed. This observation provides an experimental corroboration of the occurrence of threading dislocation motion, which is the basis for rationalizing the high-ield strength of thin films in available models of thin-film plasticity.

Thickness deviation of hot strip rolling needs to be strictly controlled in the computer system. An adaptive threading technique was researched, in which the measured data from threaded stands were used to predict thickness and material hardness errors, to modify the setup for the remaining unthreaded stands. After the adaptive threading model was used online on the hot strip mill of the Panzhihua Iron and Steel Group Co Ltd, the thickness deviation was decreased obviously. The hit rate of thickness control of different steel grades increases.

A pseudorotaxane monomer consisting of cucurbit[6]uril (CB[6]) and N′-3-vinylbenzyldiaminobutane dihydrochloride (3VBCB) was prepared in aqueous solution. This monomer was then polymerized using potassium persulfate as the initiator to give side-chain polypseudorotaxanes (P3VBCB). The CB[6] “beads” were localized on butyl units in side chains of P3VBCB. The hydrodynamic radius distribution of P3VBCB increased as the concentration of P3VBCB or NaCl increased. Interestingly, it was possible to control the threading and dethreading of CB[6] onto the side chains of P3VBCB by adding Ba2+ and SO4 2−. P3VBCB also showed pH-responsive behavior. Significantly, applying P3VBCB caused the T m of λ-DNA to decrease from 59.5 °C to 38 °C by damaging the double-helix structure of λ-DNA.

The combined application of section and projection topography carried out using synchrotron white beam radiation can be a powerful tool for the determination of the three-dimensional configurations of defects in single crystals. In this paper, we present examples of the application of this combination of techniques to the analysis of defect configurations in PVT-grown 4H-SiC wafers cut perpendicular and parallel to the growth axis. Detailed correlation between section and projection topography of threading screw dislocations (TSDs) is presented with particular emphasis being laid on the determination of the signs of the dislocations. Further, information can also be determined regarding the position of the dislocations within the crystal depth. In addition, similar correlation is presented for threading edge dislocations (TEDs) and basal plane dislocations (BPDs). The section topography images of dislocations can comprise direct, intermediary and dynamical contrast and all three types are observed. The application to the study of stacking faults will be also discussed in detail.

Within the framework of a grand partition function formalism, we examine the occupancy of the dangling bond dislocation defect sites and the VGa-ON dislocation defect sites within uncompensated n-type gallium nitride. The sensitivity of these results to variations in the unoccupied dislocation defect energy level is examined. We find that the VGa-ON dislocation defect sites’ greater capacity to store charge plays a large role in influencing the results, i.e., greater free electron and bulk donor concentrations are required in order to fully saturate the threading dislocation lines with charge.

We suggest a model of mismatched interface and calculate its energy in order to describe formation of threading edge dislocations by the mechanism of rotational relaxation of interface stresses. The model takes into account strongly layered perovskite structure of high-temperature superconductors. We have shown that rotational relaxation occurs due to finite size of clusters and to non-equilibrium effect of the film growth. We have predicted the subgrain size and the expected rotation of domains depending on the lattice mismatch. The computed values are consistent with the observed YBCO film nanostructure.

The thread load distribution has been examined, as is known, in literature both theoretically and experimentally. in the present paper the load distribution is validated by strain-gage measurements. Starting from the theoretical load distribution the stresses on the outer surface of the female member of a threaded connection are calculated. The theoretical and experimental stress values obtained are reasonably close.

Defects such as dislocations and interfaces play a crucial role in the performance of heterostructure devices. The full potential of GaAs on Si heterostructures can only be realized by controlling the defect density. The nature of misfit dislocations at the heterointerface has been studied and a mechanism for the formation of 60° and 90° misfit dislocations has been proposed. Threading dislocations in the epilayer are the most prominent defects and their density has to be controlled to fully utilize the properties of semiconductor heterostructures. Various processes to reduce defect densities in the epilayers have been discussed and in particular, the use of strained layer superlattices to reduce the threading dislocation density has been presented in this paper. Several superlattice structures have been used to reduce the density of threading dislocations in the GaAs epilayer. In this study, we have optimized the use of strained layer superlattices with respect to the position, period and number to reduce and control the dislocation density. The use of strained layer superlattices in conjunction with rapid thermal annealing was found to be the most effective method in reducing threading dislocation density. Transmission electron microscopy has been used to study the dislocation density reduction and the interaction of threading dislocations with the strained layers.

In our study, closed-core threading screw dislocations and micropipes were studied using synchrotron x-ray topography of various geometries. The Burgers vector magnitude of TSDs can be quantitatively determined from their dimensions in back-reflection x-ray topography, based on ray-tracing simulation and this has been verified by the images of elementary TSDs. Dislocation senses of closed-core threading screw dislocations and micropipes can be revealed by grazing-incidence x-ray topography. The threading screw dislocations can be converted into Frank partial dislocations on the basal planes and this has been confirmed by transmission synchrotron x-ray topography.

We have synthesized polyester systems containing pendant iptycene units and compared their mechanical/structural properties to a homologous reference polymer wherein benzene replaces iptycene units. Iptycenes have unique structural properties called internal molecular free volume (IMFV). The incorporation of iptycene into polyester backbones results in a polymer chain contour resembling “molecular barbed wire.” The contribution of iptycene to the mechanical properties of polyesters is significant and robust across concentration and processing conditions. The triptycene polyester films displayed a nearly 3-fold increase in Young's modulus, an approximately 3-fold increase in strength, and a more than 20-fold increase in strain to failure. We proposed that the presence of triptycene introduces two mechanisms for the enhancement of tensile mechanical properties: molecular threading and molecular interlocking.

The interpretation of ECCI images in the forescattered geometry presents a more complex diffraction configuration than that encountered in the backscattered geometry. Determining the Kikuchi line that is the primary source of image intensity often requires more than simple inspection of the electron-channeling pattern. This problem can be addressed, however, by comparing recorded ECCI images of threading screw dislocations in 4H-SiC with simulated images. An ECCI image of this dislocation is found to give the orientation of the dominant Kikuchi line, greatly simplifying the determination of the diffraction simulation. In addition, computed images of threading screw dislocations in 4H-SiC were found to exhibit channeling contrast essentially identical to that obtained experimentally by ECCI and allowing determination of the dislocation Burgers vector.

Electron-hole recombination enhanced glide of Shockley partial dislocations bounding expanding stacking faults and their interactions with threading dislocations in 4H silicon carbide epitaxial layers have been studied using synchrotron white beam X-ray topography and in situ electroluminescence. The mobile silicon-core Shockley partial dislocations bounding the stacking faults are able to cut through threading edge dislocations leaving no trailing dislocation segments in their wake. However, when the Shockley partial dislocations interact with threading screw dislocations, trailing 30° partial dislocation dipoles are initially deposited in their wake due to the pinning effect of the threading screw dislocations. These dipoles spontaneously snap into their screw orientation, regardless the normally immobile carbon-core Shockley partial dislocation components in the dipoles. The subsequent cross slip and annihilation of screw oriented Shockley partial dipole leave a prismatic stacking fault in (2-1-10) plane with the displacement vector 1/3[01-10]. The formation of such prismatic stacking fault is energetically favorable, reducing the strain energy by one to two orders of magnitude.

Interaction between basal plane dislocations and single or well-spaced threading dislocations is discussed based on synchrotron white beam X-ray topographic studies carried out on physical vapor transport grown hexagonal silicon carbide single crystals. The basal plane dislocations are able to cut through single or well-spaced threading edge dislocations even if the formation of kinks/jogs is energetically unfavorable while threading screw dislocations were mostly observed to act as effective pinning points. However, basal plane dislocations can sometimes cut through a threading screw dislocation, forming a superjog and which subsequently migrates on the prismatic plane via a cross-slip process. Threading edge dislocation walls act as obstacles for the glide of basal plane dislocations and the mechanism by which this occurs is discussed. The character of low angle grain boundaries and their dislocation content are discussed.

Dislocation glide kinetics dictate in relaxed graded buffers a fundamental opposition between the defectivity and throughput. For state-of-the-art Si-based applications, the trade-off between defect level and wafer cost (inversely related to throughput) has made the insertion of SiGe graded buffers into production difficult. We aim to mitigate the trade-off by reporting two advances that enable simultaneous improvements in both defectivity and throughput. The first is use of a high growth temperature to allow very fast dislocation glide velocities and growth rates as high as 1.0 μm/min. The second is the use of “pre-threaded” Si substrates, substrates with an elevated density of threading dislocations. By having dislocation nucleation controlled by uniformly distributed substrate threading dislocations, instead of unpredictable heterogeneous sources, impediments to dislocation glide, such as dislocation bundles and pile-ups, are reduced. By incorporating both advances into SiGe graded buffer epitaxy, dislocation pile-up densities are reduced by nearly three orders of magnitude, threading dislocation densities are reduced by a factor of 7.4×, and wafer throughput is increased at least 33%.

We present a framework for obtaining high quality relaxed graded SiGe buffers on Si for III-V integration. By avoiding dislocation nucleation in Si1−xGex layers of x>0.96, we have achieved a relaxed Si0.04Ge0.96 platform on Si(001) offcut 2° that has a threading dislocation density of 7.4×105 cm−2. This 2° offcut orientation was determined to be the minimum necessary for APB-free growth of GaAs. Furthermore, we found that we could compositionally grade the Ge content in the high-Ge portion of the buffer at up to 17 %Ge μm−1 with no penalty to the dislocation density. The reduction in both threading dislocation density and buffer thickness exhibited by our method is an especially significant development for relatively thick minority-carrier devices which use III-V materials such as multi-junction solar cells.

In this article, we propose a new model to explain how heteroepitaxial layers grown on a twist-bonded thin layer may have a significantly reduced number of threading dislocations even if the strain in the epitaxial layers is relaxed. We first point out the deficiency in the existing compliant substrate theory by showing that all the synthesized “compliant substrates” fail to behave as “ideal” free-standing templates assumed by the current theory. Our new model is constructed on the base of stress field interactions between the heteroepitaxial layer and the embedded twist boundary. In the new model, the reduction in threading dislocation density originates from the extension of the dislocation half loops due to the effect of misfit dislocation pinning by the twist boundary. When the average size of the dislocation half loops increases substantially from micrometers to millimeters or even to the size of the wafer, the density of threading dislocations drops significantly. This model does not require any “macroscopic” motion between the bonded thin layer and the handle wafer as the current theory does, which makes it more agreeable with the experimental results

To engineer high-quality InxGal-xP graded buffers on GaP substrates (InxGa1-xP/GaP), we have explored the evolution of microstructure and dislocation dynamics in these materials. We show that the primarily limiting factor in obtaining high-quality InxGa1-xP/GaP is a new defect microstructure that we call branch defects. Branch defects pin dislocations and result in dislocation pileups that cause an escalation in threading dislocation density with continued grading. The morphology of branch defects is dominated by growth temperature, which can be used to suppress the strength or density of branch defects. In the absence of branch defects, we observe nearly ideal dislocation dynamics that are controlled by the kinetics of dislocation glide. This new understanding results in two primary design rules for achieving high-quality materials: 1) control branch defects, and 2) maximize dislocation glide kinetics. Combining these design rules into optimization strategies, we develop and demonstrate processes based on single and multiple growth temperatures. With optimization, threading dislocation densities below 5 × 106 cm−2 are achieved out to x = 0.39 and a nearly steady-state relaxation process is recovered.

Stepwise equilibrated graded GexSii-x (x≤0.2) buffers with threading dislocation densities between 102 and 103 cm−2 on the whole area of 4 inch silicon wafers were grown and studied by transmission electron microscopy, defect etching, atomic force microscopy and photoluminescence spectroscopy.