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One central task of developing nonvolatile phase change memory (PCM) is to improve its scalability for high‐density data integration. In this work, by first‐principles molecular dynamics, to date the thinnest PCM material possible (0.8 nm), namely, a monolayer Sb2Te3, is proposed. Importantly, its SET (crystallization) process is a fast one‐step transition from amorphous to hexagonal phase without the usual intermediate cubic phase. An increased spatial localization of electrons due to geometrical confinement is found to be beneficial for keeping the data nonvolatile in the amorphous phase at the 2D limit. The substrate and superstrate can be utilized to control the phase change behavior: e.g., with passivated SiO2 (001) surfaces or hexagonal Boron Nitride, the monolayer Sb2Te3 can reach SET recrystallization in 0.54 ns or even as fast as 0.12 ns, but with unpassivated SiO2 (001), this would not be possible. Besides, working with small volume PCM materials is also a natural way to lower power consumption. Therefore, the proposed PCM working process at the 2D limit will be an important potential strategy of scaling the current PCM materials for ultrahigh‐density data storage., By first‐principles molecular dynamics, this work proposes a phase change memory (PCM) process at the 2D limit that is achieved in a monolayer Sb2Te3 for the first time. This will be a potential strategy for improving the performance of PCM technology to realize high integrated density, fast speed, low power consumption, or even artificial intelligence applications.

Direct optical ferroelectric switching (FE switch) has the advantage of being ultrafast over the traditional FE switch, which relies on domain nucleation and growth. However, how to realize nonvolatility in such an optical FE switch poses a serious challenge. Time-dependent density-functional theory molecular dynamics study reveals that subpicosecond nonvolatile FE switches can be realized in GeTe and ${\mathrm{PbTiO}}_{3}$. While optical tuning of the transition barrier and initiation of a directional atomic motion are crucial, the dephasing of the excited state holds the key for the realization of nonvolatility.

Phase-change memory (PCM) material is the promising material system for nonvolatile-memory technology. Performance optimization of PCM device urgently requires the deeper clarification of its material “Gene”. In this study, through first-principles calculations, p-orbital-aligned atom chains are identified to play important roles in governing optoelectronic reflectivity in amorphous Ge2Sb2Te5. These atom chains make the electronic state of the amorphous Ge2Sb2Te5 hold strong electron-polarized components, thereby governing the optical property. The present study offers a new understanding of “Gene” for PCM materials which benefit the material design and the performance improvement of PCM devices.

External electric fields can be used to manipulate the electronic properties of two-dimensional (2D) materials. 2D InSe semiconductors possess high electron mobility and wide band gap tunability. Therefore, they have been proposed for use in ultrathin electronic devices. Here, using first-principles calculations, we study the charge polarization, structure, electronic structure, and gas adsorption of an InSe monolayer under vertical electric fields. We find that both the structural evolution and charge polarization rely on the directions of the electric fields. The hole effective mass at the valance band maximum can be decreased by fields that offer a possible route to increase mobility. In contrast, the fields have little impact on the effective mass of electrons at the conduction band minimum. Therefore, high electron mobility in InSe is retained under the fields. Besides, electric fields could alter the absorption intensity for gas molecules. Therefore, gas sensors could be an expected application. More importantly, this work systematically points out some key steps for setting up electric-field calculations in the popular VASP code, such as the cancellation of the symmetrisation of the charge density, avoiding electrons spilling out into the vacuum under high fields.

Epitaxial growth of III‐nitrides on 2D materials enables the realization of flexible optoelectronic devices for next‐generation wearable applications. Unfortunately, it is difficult to obtain high‐quality III‐nitride epilayers on 2D materials such as hexagonal BN (h‐BN) due to different atom hybridizations. Here, the epitaxy of single‐crystalline GaN films on the chemically activated h‐BN/Al2O3 substrates is reported, paying attention to interface atomic configuration. It is found that chemical‐activated h‐BN provides B—O—N and N—O bonds, where the latter ones act as effective artificial dangling bonds for following GaN nucleation, leading to Ga‐polar GaN films with a flat surface. The h‐BN is also found to be effective in modifying the compressive strain in GaN film and thus improves indium incorporation during the growth of InGaN quantum wells, resulting in the achievement of pure green light‐emitting diodes. This work provides an effective way for III‐nitrides epitaxy on h‐BN and a possible route to overcome the epitaxial bottleneck of high indium content III‐nitride light‐emitting devices., Epitaxy of single‐crystalline GaN films is performed on hexagonal BN (h‐BN)/sapphire substrates. This success is achieved through chemical activation on h‐BN, which generates N—O bonds, and thus provides nucleation sites for Ga‐polar GaN. Subsequently, pure green InGaN‐based light‐emitting diodes are fabricated with a considerable increase of indium incorporation, manifesting a great potential in long wavelength light‐emitting diodes.

Organic single-crystalline semiconductors with long-range periodic order have attracted much attention for potential applications in electronic and optoelectronic devices due to their high carrier mobility, highly thermal stability, and low impurity content. Molecular doping has been proposed as a valuable strategy for improving the performance of organic semiconductors and semiconductor-based devices. However, a fundamental understanding of the inherent doping mechanism is still a key challenge impeding its practical application. In this study, solid evidence for the "perfect" substitutional doping mechanism of the stacking mode between the guest and host molecules in organic single-crystalline semiconductors using polarized photoluminescence spectrum measurements and first-principles calculations is provided. The molecular host-guest doping is further exploited for efficient color-tunable and even white organic single-crystal-based light-emitting devices by controlling the doping concentration. The clarification of the molecular doping mechanism in organic single-crystalline semiconductor host-guest system paves the way for their practical application in high-performance electronic and optoelectronic devices.

Femtosecond lasers (fs) can cause a disparity between electronic and lattice temperatures in the very short period after irradiation. In this relatively cool lattice regime, the material properties can differ drastically from those under thermal equilibrium. In particular, first-principles calculations reveal two general mechanical effects on semiconductors. Firstly, the excitation can induce a negative pressure on the lattice, causing a >10% expansion, even for superhard diamond. Secondly, it induces inhomogeneous local forces on the atoms, for both perfect and distorted lattices. In the case of phase-change-memory for Ge2Sb2Te5 and GeTe alloys, such random forces cause a simultaneous phase transition from crystalline to amorphous, which enables faster data writing. These excitation effects are further supported by the time-dependent density functional theory. This work could be an important step in advancing fs laser techniques for the atomic-level control of structures, rather than relying on traditional melting or ablation approaches which often apply to much larger and non-atomic scales.

Orthogonal experiments at concrete materials proved: notable errors will occur when using chemical catalyzing to predict the concrete strength. Errors are unavoidable since such methods have neglected much factors. Ground on test data, effects on concrete intensity were analyzed with changes of sand ratio, bigger aggregate, and environment humidity, cement components. Error origins of concrete intensity were found, and the fact of avoidless errors from chemical catalyzing was notarized. Materials testing combining with fieldwork, new technique was proposed for monitoring quality of fresh concrete in building site. So hidden trouble would be known betimes before elementary solidification in concrete. Practices indicated that this technique is simple and speedy, it can avoid the loss of doing over again in concrete structures and can effectively improve quality of concrete engineering.

Found on data of accelerated life test, the relationship between outward disease of structural concrete and holistic deterioration of building was analysed. The results indicated that: outward diseases of structural concrete, such as abrasion, scour erosion, and peeling, carbonization etc, are not hypostatic breakage for holistic building, so could not be regarded as the key points of deterioration identification at building. Deterioration appraisement should be focused on detections of engineering indices relating to structural inbeing quality and analyses of multifarious remainder relating to bearing capacity. Only in this way, deterioration degree of structural concrete and efficacious repair indices could be factually incarnated. Ground on testing multifarious bearing capacities, deterioration identification of concrete buildings was founded, and remedy principles corresponding to inbeing deterioration indices were put forward.

Effective unit weight, inner friction angle and cohesion are the main engineering indices of rock-soil mass anti-slide. Deviant leakage brings about obvious decrease of effective unit weight, inner friction angle and cohesion under combined action of thrust, buoyancy, and lubrication. So as to slip in unstable rock-soil mass. Deviant leakage schleps out weensy particles, induces seepage failure, so geotechnical engineering would collapse. Therefore the reasonable anti-leakage in unstable mountain is one of the key technologies that urgently to be solved in geotechnical engineering. Combined with the typical landslide geology, several groundwork anti-leakage were studied for earth-rock dam, correlative processes and technologies were discussed, and construction parameters were designed. The abnormal situations that may occur in construction were analysed, and preparative schemes were put forward. The results had been validated in practical engineering.

Resources of memory are frequently used times without number for reducing cost of control system. Rewriting in memory would cause occasional hardware conflict when especial data are inputted or are calculated, thereby system faults even accidents are elicited. Origin of occasional malfunction was analysed in automatic control system, necessity of program storage separate from data storage was discussed, and the notion was put forward that resource allocation of memory should be compatible with the system function. So dead halt owing to codes cover each other could be avoided, and reliability of measurement or control system could be effectively improved.

Ge-Sb-Te alloys have been widely used in optical/electrical memory storage. Because of the extremely fast crystalline-amorphous transition, they are also expected to play a vital role in next generation nonvolatile microelectronic memory devices. However, the distribution and structural properties of vacancies have been one of the key issues in determining the speed of melting (or amorphization), phase-stability and heat-dissipation of rock-salt GeSbTe, which is crucial for its technological breakthrough in memory devices. Using spherical aberration-aberration corrected scanning transmission electron microscopy and atomic scale energy-dispersive X-ray mapping, we observe a new rock-salt structure with high-degree vacancy ordering (or layered-like ordering) at an elevated temperature, which is a result of phase transition from the rock-salt phase with randomly distributed vacancies. First-principles calculations reveal that the phase transition is an energetically favored process. Moreover, molecular dynamics studies suggest that the melting of the cubic rock-salt phases is initiated at the vacancies, which propagate to nearby regions. The observation of multi-rock-salt phases suggests another route for multi-level data storage using GeSbTe.

The repairing of incomplete measured data caused by the inaccessibility or invisibility of some portions of the product surface for measure tools plays an important role in Reverse Engineering. The fundamental principles of Reverse Engineering and Anatomical CAD are introduced. The main functional advantages of 3-matic package integrated with Anatomical CAD are presented. There is a big difference in the working flows between Anatomical CAD and traditional CAD packages in the process of RE data repairing. In this paper, we propose a new method of data repairing based on Anatomical CAD. The point cloud of the stamping part obtained by a Potable CMM is repaired successfully by 3-matic, which reduces preparation times by working with a triangular mesh directly, and saves the turn-around time and works more effectively.

Organic single crystals have a great potential in the field of organic optoelectronics because of their advantages of high carrier mobility and high thermal stability. However, the application of the organic single crystals in light-emitting devices (OLEDs) has been limited by single-layered structure with unbalanced carrier injection and transport. Here, fabrication of a multilayered-structure crystal-based OLED constitutes a major step toward balanced carrier injection and transport by introducing an anodic buffer layer and electron transport layer into the device structure. Three primary color single-crystal-based OLEDs based on the multilayered structure and molecular doping exhibit a maximum luminance and current efficiency of 820 cd cm−2 and 0.9 cd A−1, respectively, which are the highest performance to date for organic single-crystal-based OLEDs. This work paves the way toward high-performance organic optoelectronic devices based on the organic single crystals.