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The hybridization of fullerene and nanotube structures in newly isolated C90 with the D 5h symmetric group (D 5h (1)-C90) provides an ideal model as a mediating allotrope of nanocarbon from zero-dimensional (0D) fullerene to one-dimensional nanotube. Raman and infrared spectroscopy combined with classical molecular dynamics simulation were used to investigate the structural evolution of D 5h (1)-C90 at ambient and high pressure up to 35.1 GPa. Interestingly, the high-pressure transformations of D 5h (1)-C90 exhibit the features of both fullerene and nanotube. At around 2.5 GPa, the D 5h (1)-C90 molecule in the crystal undergoes an orientational transition to a restricted rotation. At 6.6 GPa, the tubular hexagonal part occurs and transforms into a dumbbell-like structure at higher pressure. The material starts to amorphize above 13.9 GPa, and the transition is reversible until the pressure exceeds 25 GPa. The amorphization is probably correlated with both the intermolecular bonding and the morphology change. Our results enrich our understanding of structural changes in nanocarbon from 0D to 1D.

Twisted bilayer graphene (TBG), which has drawn much attention in recent years, arises from van der Waals materials gathering each component together via van der Waals force. It is composed of two sheets of graphene rotated relatively to each other. Moiré potential, resulting from misorientation between layers, plays an essential role in determining the band structure of TBG, which directly relies on the twist angle. Once the twist angle approaches a certain critical value, flat bands will show up, indicating the suppression of kinetic energy, which significantly enhances the importance of Coulomb interaction between electrons. As a result, correlated states like correlated insulators emerge from TBG. Surprisingly, superconductivity in TBG is also reported in many experiments, which drags researchers into thinking about the underlying mechanism. Recently, the interest in the atomic reconstruction of TBG at small twist angles comes up and reinforces further understandings of properties of TBG. In addition, twisted multilayer graphene receives more and more attention, as they could likely outperform TBG although they are more difficult to handle experimentally. In this review, we mainly introduce theoretical and experimental progress on TBG. Besides the basic knowledge of TBG, we emphasize the essential role of atomic reconstruction in both experimental and theoretical investigations. The consideration of atomic reconstruction in small-twist situations can provide us with another aspect to have an insight into physical mechanism in TBG. In addition, we cover the recent hot topic, twisted multilayer graphene. While the bilayer situation can be relatively easy to resolve, multilayer situations can be really complicated, which could foster more unique and novel properties. Therefore, in the end of the review, we look forward to future development of twisted multilayer graphene.

We report a perpendicular magnetic tunnel junction (pMTJ) cell with a tunnel magnetoresistance (TMR) ratio of nearly 200% at room temperature based on CoFeB/Ta/CoFeB as the free layer (FL) and a synthetic antiferromagnetic (SAF) multilayer [Pt/Co]/Ru/[Pt/Co]/Ta/CoFeB as the reference layer (RL). The field-driven magnetization switching measurements show that the pMTJs exhibit an anomalous TMR hysteresis loop. The spin-polarized layer CoFeB of SAF-RL has a lower critical switching field than that of FL. The reason is related to the interlayer exchange coupling (IEC) through a moderately thick Ta spacer layer among SAF-RLs, which generates a moderate and negative bias magnetic field on CoFeB of RL. However, the IEC among RLs has a negligible influence on the current-driven magnetization switching of FL and its magnetization dynamics.

We investigate the magnetic damping parameter of Fe1 – x Cr x thin films using the time-resolved magneto-optical Kerr effect technique. It is demonstrated that the overall effective damping parameter is enhanced with the increasing Cr concentration. The effective damping at high field α 0 is found to be significantly enhanced when increasing the Cr concentration with the α 0 = 0.159 in the Fe45Cr55 enhanced by 562% compared with that of α 0 = 0.024 in the pure Fe film. This study provides a new approach of controlling the effective damping parameter with a desired magnitude via varying Cr composition.

Magnonic devices based on spin waves are considered as a new generation of energy-efficient and high-speed devices for storage and processing of information. Here we experimentally demonstrate that three distinct dominated magneto-dynamic modes are excited simultaneously and coexist in a transversely magnetized ferromagnetic wire by the ferromagnetic resonance (FMR) technique. Besides the uniform FMR mode, the spin-wave well mode, the backward volume magnetostatic spin-wave mode, and the perpendicular standing spin-wave mode are experimentally observed and further confirmed with more detailed spatial profiles by micromagnetic simulation. Furthermore, our experimental approach can also access and reveal damping coefficients of these spin-wave modes, which provides essential information for development of magnonic devices in the future.

We propose a new CaN4 high pressure structure with the P21/m space group. The P21/m-CaN4 structure is constituted by the infinite armchair N-chain. The dynamical stability and mechanical stability are verified by the calculations of phonon dispersion curves and elastic constants. The enthalpy difference calculation shows that the P21/m phase is more stable than the reported P41212 phase. The advantaged properties of P21/m-CaN4, such as high nitrogen content (58.3%) and low polymerization pressure (18.3 GPa), allow it to be a potential high energy material. Band structure calculation shows that the P21/m-CaN4 structure is a metallic phase. The nonpolar covalent single N–N bond is a sigma bond. The charge transfer between the Ca and N atoms results in an ionic bond interaction.

Topological crystalline insulators (TCIs) have attracted worldwide interest since their theoretical predication and have created exciting opportunities for studying topological quantum physics and for exploring spintronic applications. In this work, we successfully synthesize PbTe nanowires via the chemical vapor deposition method and demonstrate the existence of topological surface states by their 2D weak anti-localization effect and Shubnikov–de Haas oscillations. More importantly, the surface state contributes ~61% of the total conduction, suggesting dominant surface transport in PbTe nanowires at low temperatures. Our work provides an experimental groundwork for researching TCIs and is a step forward for the applications of PbTe nanowires in spintronic devices.

The velocity non-uniformity of the particle movement in the living cells is investigated. Introducing the concept of molecular fluctuation in the living cells, the phenomenon of the velocity non-uniformity is explained. A quantitative relation between molecular fluctuation and velocity non-uniformity of the particle movement is derived.

An optimized device structure for reducing the RESET current of phase-change random access memory (PCRAM) with blade-type like (BTL) phase change layer is proposed. The electrical thermal analysis of the BTL cell and the blade heater contactor structure by three-dimensional finite element modeling are compared with each other during RESET operation. The simulation results show that the programming region of the phase change layer in the BTL cell is much smaller, and thermal electrical distributions of the BTL cell are more concentrated on the TiN/GST interface. The results indicate that the BTL cell has the superiorities of increasing the heating efficiency, decreasing the power consumption and reducing the RESET current from 0.67 mA to 0.32 mA. Therefore, the BTL cell will be appropriate for high performance PCRAM device with lower power consumption and lower RESET current.

The stimulated Brillouin scattering (SBS) threshold enhancement factor in a pure white noise linewidth broadening Yb-doped fiber amplifier (YDFA) with a short large mode area fiber is theoretically and experimentally studied. We demonstrate a 1064.08 nm, 11.6 GHz linewidth, 1.5 kW output power YDFA with an SBS threshold enhancement of ~57 (26 W SBS threshold with single frequency seed). The output beam is near-diffraction limited with a beam quality factor of M2 = 1.15 and a slope efficiency of up to 87%. No SBS or stimulated Raman scattering effects are observed in the whole power range. Further power scaling is limited by the available pump power in our system.

A novel technique to suppress stimulated Raman scattering in a high power narrow-band fiber amplifier is reported. By seeding with a combination of a broadband amplified spontaneous emission seed and a narrowband master oscillator seed, the Raman Stokes components can be reduced about 16 dB at a total output power of 1 kW. Raman suppression results are depicted in a different wavelengths seeding case and the same wavelength seeding case, respectively, with different seed power ratios.

The fractal property of the cytoskeleton in the living cells is investigated. Based on the experimental data of intracellular particle movement, the self-similarity of the cytoskeleton in the living cells is observed and the fractal dimensions of different parts of the cytoskeleton determined by means of line-segment method vary from 1.35 to 2. The Quasi-Brownian movements of intracellular particles are clearly shown.

We have set up an experimental system consisting of an ion gun and a Rutherford backscattering spectrometry(RBS) analysis chamber. Using this system, in situ 2 MeV 4He+ RBS analysis of films is carried out by combination with sputter etching of low energy Ar+ ions. As an example of the sputtering/RBS method, the analysis of three samples, i.e., Si/(GexSi1-x/Si)/Si(100), WSix/SiO2/Si and CoSix/Si, is presented in this paper. After an appropriate fraction of the thick layer is removed by sputtering, the back edge of the Ge peak is separated from Si RBS spectrum on the interface and the O peak of the buried SiO2 layer can be identified. The change of the doped Ti and W concentrations related to Co on the top surface is observed. The advantages of this analytical method and its possible applications in film are discussed.

From the full stopping scenario, a relativistic hydrodynamic model describing the evolution of the baryon-rich quark-gluon matter fire-cylinder has been established. Based on it, the rapidity distribution of dileptons with intermediate invariant masses has been studied. It is found that the quark phase gives the dominant contribution to the dilepton spectrum due to the influence of the phase boundary on the evolution of the system, especially the dilepton yield is strongly suppressed with the increasing rapidity.

Two statistical properties, the nearest neighbor energy level spacing distribution P(s) and the spectral rigidity Delta(3)(L), are reported for energy level of a quantum well in a tilted magnetic field. Time-reversal (T) symmetry is broken in the system. The system is invariant under the anti-unitary combination of symmetric operations which include T, leading to what is called false T-violation. With the increasing magnetic field, P(s) and Delta(3)(L) change from Brody type-like distribution to the Gaussian orthogonal ensemble (GOE) distribution. This result is a dear manifestation of quantum chaos in the system and is in agreement with the prediction of which the false T-violation suffices to give the energy spectra the properties of the GOE, instead of the Gaussian unitary ensemble (GUE). The result indicates that the system translates from mixed-type state to quantum chaotic state. However, the spectral rigidity Delta(3) (L) turns into GUE with the magnetic field increasing. The different demonstration of P(s) and the Delta(3)(L) is due to the counting of only finite semi-classical orbits.

Debye screening mass st the next-to-leading order is studied by the resummation method based on perturbation theory at finite temperature. We find that the critical temperature for the J/psi dissociation is 0.211 GeV. The contributions from the next-to-leading order are important, and critical temperature and chemical potential are shifted lower values.

The phase change material of Ge-doped Sb2Te3 is shown to have higher crystallization temperature and better thermal stability compared with pure Sb2Te3. Ge0.11Sb2Te3 alloys are considered to be a potential candidate for phase change random access memories, as proved by a higher crystallization temperature, a better data retention ability, and a faster switching speed in comparison with those of Ge2Sb2Te5. In addition, Ge0.11Sb2Te3 presents extremely rapid reverse switching speed (10 ns), and up to 105 programming cycles are obtained with stable set and reset resistances.

A novel slow-down set waveform is proposed to improve the set performance and a 1 kb phase change random access memory chip fabricated with a 130 nm CMOS technology is implemented to investigate the set performance by different set programming strategies based on this new set pulse. The amplitude difference (I1 — I2) of the set pulse is proved to be a crucial parameter for set programming. We observe and analyze the cell characteristics with different I1 — I2 by means of thermal simulations and high-resolution transmission electron microscopy, which reveal that an incomplete set programming will occur when the proposed slow-down pulse is set with an improperly high I1 — I2. This will lead to an amorphous residue in the active region. We also discuss the programming method to avoid the set performance degradations.

The eigenvalues and eigenfunctions of the stadium-shaped quantum dot subjected to a constant magnetic field in the perpendicular direction are computed by a simple and efficient method. With the magnetic field increasing, the nearest-neighour-energy-level-spacing distribution of the stadium-shaped quantum dot is found to transform gradually from the Wigner distribution to the Poisson distribution. The transition of the nearest-neighour-energy-level-spacing distribution indicates that system changes from quantum chaotic to regular. The variation of the spatial charge distribution indicates that the system varies from bulk Landau state to the edge state that mainly affects the transport properties of the stadium-shaped quantum dot. The change of the two dimensional charge distribution near the anticrossing point is also discussed.

Using the first principle method, we investigate the influence of Sr/Ti ratio on the atomic structure and dislocation behavior of Srn+1TinO3n+1(Ruddlesden—Popper phase) and SrnTin+1O3n+2 (Magneli phase). A linear lattice expansion versus the Sr/Ti ratio exhibits in the Ruddlesden—Popper and Magneli phases. The Ruddlesden—Popper phase has lower formation energy and superior structural stability than the Magneli phase. The two phases show different dislocation behaviors and it is found that a possibly preferred slip system 〈110〉 {110} emerges in the two phases, and the dislocations are more likely to dissociate into partial dislocations in Magneli phases.

Nitrogen doping is applied to improve the thermal stability of SnTe. The crystallization temperature Tc of SnTe is below room temperature, which can be elevated to 216°C by 7.65at.% nitrogen doping. Nitrogen doping results in the formation of SnNx in the nitrogen doped SnTe (N-SnTe) materials, which hinders the movement of atoms and suppresses the crystallization, leading to a better thermal stability. The crystallization activation energy (Ea) and data retention for ten years of 7.65at.% N-SnTe are 1.89eV and 81°C, respectively. Moreover, the voltage pulses have successfully triggered the SET and RESET operations of the N-SnTe based device at the voltage of 0.9 V and 2.6 V. The good thermal stability and reversible phase-change ability have proved the potential of N-SnTe for phase-change memory application.

We investigate the emission properties of CuI film scintillators and the effect of distributed Bragg reflectors. The free-exciton emission and the donor-acceptor pair emission from the CuI thin film with the peak wavelengths of 410 nm and 420 nm are observed. However, for the two emission bands, the distributed Bragg reflector reflection results in different enhancements, which is interpreted by the varying transmittance with wavelength. Angle-dependence of emission profile is decided by the transmittance and DBR reflection, which may be useful in scintillation detection applications.

We try to find the analytical solutions to the time-independent Gross-Pitaevskii equation, a nonlinear Schrodinger equation used in the simulation of Bose—Einstein condensates trapped in a harmonic potential. Both the homotopy analysis method and the Galerkin spectral method are applied. We investigate the one-dimensional case and obtain the approximate analytical solutions successfully. Comparison between the analytical solutions and the numerical solutions has been made. The results indicate that they agree very well with each other when the atomic interaction is not too strong.

The results of adhesion improvement and SET-RESET operation voltage reduction for the GeN buffer layer are presented. It is found that the adhesive strength between the Ge2Sb2Te5(GST) layer and the layer below could be increased at least 20 times, which is beneficial for solving the phase change material peeling issue in the fabrication process of phase change memory (PCM). Meanwhile, the RESET voltage of the PCM cell with a 3-nm-thick GeN buffer layer can be reduced from 3.5 V to 2.2 V. The GeN buffer layer will play an important role in high density and low power consumption PCM applications.

An integrated phase change memory cell with dual trench epitaxial diode is successfully integrated in the traditional 0.13 μm CMOS technology. By using dual trench isolated structure in the memory cell, it is feasible to employ a Si-diode as a selector for integration in a crossbar structure for high-density phase change memory even at 45 nm technology node and beyond. A cross-point memory selector with a large on/off current ratio is demonstrated, the diode provides nine orders of magnitude isolation between forward and reverse biases in the SET state. A low SET programming current of 0.7 mA is achieved and RESET/SET resistance difference of 10000× is obtained.

Using proper beam energy chirp and the undulator detuning effect, we propose a modified optical replica synthesizer scheme to characterize the temporal structure of a relativistic electron bunch, which predicts a 100-fs temporal resolution in numerical simulation. The proof of principle experiment demonstrates a peak current of 9 A and a slice energy spread of about 0.5 keV for the uncompressed electron beam of the Shanghai Deep UV Free Electron Laser Facility., 4 pages, 5 figures, 1 table

We report on a three-colour InAs/InP(100) quantum dot laser under continuous wave mode at an operation temperature of 20°C. Three lasing peaks are observed simultaneously, the high-energy peak undergoes continuous blueshift, while the splitting energy gap between the low-energy peaks is somewhat fixed as the injection current increases. The maximum output power from one facet without coating is more than 34 mW with a slope efficiency of 102 mW/A just above the threshold current. Three peaks of differential efficiency of output power are observed, just corresponding to each peak in lasing spectra, respectively. At the same time, the far-field distribution shows only a single transverse mode over the full range of injection current.

National Natural Science Foundation of China [51075344]; Natural Science Foundation of Fujian Province [2010J01015]