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<jats:p>Steering ultrafast electron dynamics with well-controlled laser fields is very important for generation of intense supercontinuum radiation. It can be achieved through coherent control of the symmetry of the interaction between strong-field laser fields and a metal nanotip. We employ a scheme of two-color laser pulses combined with a weak static field to realize the control of a single quantum path to generate high harmonic generation from a single solid-state nanoemitter. Moreover, a smooth and ultrabroad supercontinuum in the extreme ultraviolet region is obtained, which can produce a single attosecond pulse. Our findings are beneficial for efficient generation of isolated sub-100 as XUV pulses from solid-state sources.</jats:p>

<jats:p>We demonstrate a broadband optical parametric oscillation, using a sheet cavity, via cavity phase-matching. A 21.2 THz broad comb-like spectrum is achieved, with a uniform line spacing of 133.0 GHz, despite a relatively large dispersion of 275.4 fs<jats:sup>2</jats:sup>/mm around 1064 nm. With 22.6% high slope efficiency, and 14.9 kW peak power handling, this sheet optical parametric oscillator can be further developed for <jats:italic>χ</jats:italic> <jats:sup>(2)</jats:sup> comb.</jats:p>

<jats:p>Algorithms for wavefront sensing and error correction from intensity attract great concern in many fields. Here we propose Bayesian optimization to retrieve phase and demonstrate its performance in simulation and experiment. For small aberration, this method demonstrates a convergence process with high accuracy of phase sensing, which is also verified experimentally. For large aberration, Bayesian optimization is shown to be insensitive to the initial phase while maintaining high accuracy. The approach’s merits of high accuracy and robustness make it promising in being applied in optical systems with static aberration such as AMO experiments, optical testing shops, and electron or optical microscopes.</jats:p>

<jats:p>Reactions between dislocations are investigated in two-dimensional colloidal crystals. It is found that, because of the conservation of total Burgers vectors, the kinetics of the reaction is dependent on the the symmetry of the crystal lattice. Merging is possible only when the total Burgers vector of the reacting dislocations is in line with existing crystal lines. In non-merging reactions, the number of dislocations cannot be reduced but the interacting dislocations can exchange their Burgers vectors and migrate to different gliding lines. The changing of gliding lines promises additional annihilation in multi-dislocation reactions. The bonding of non-merging dislocations determines the configuration and the orientation of the grain boundaries. The findings in this study may shed new light on understanding of dislocations and have potential applications in fabrication of crystalline materials.</jats:p>

<jats:p>Polymeric nitrogen is a promising candidate for a high-energy-density material. Synthesis of energetic compounds with high chemical stability under ambient conditions is still a challenging problem. Here we report a theoretical study on yttrium nitrides by first principles calculations combined with an effective crystal structure search method. It is found that many yttrium nitrides with high nitrogen content can be formed under relatively moderate pressures. The results indicate that the nitrogen-rich YN<jats:sub>5</jats:sub> and YN<jats:sub>8</jats:sub> compounds are recoverable as metastable high-energy materials under ambient conditions, and can release enormous energies (2.51 kJ·g<jats:sup>−1</jats:sup> and 3.18 kJ·g<jats:sup>−1</jats:sup>) while decomposing to molecular nitrogen and YN. Our findings enrich the family of transition metal nitrides, and open avenues for design and synthesis of novel high-energy-density materials.</jats:p>

<jats:p>Interfacial structures and interactions of two-dimensional (2D) materials on solid substrates are of fundamental importance for fabrications and applications of 2D materials. However, selection of a suitable solid substrate to grow a 2D material, determination and control of 2D material-substrate interface remain a big challenge due to the large diversity of possible configurations. Here, we propose a computational framework to select an appropriate substrate for epitaxial growth of 2D material and to predict possible 2D material-substrate interface structures and orientations using density functional theory calculations performed for all non-equivalent atomic structures satisfying the symmetry constraints. The approach is validated by the correct prediction of three experimentally reported 2D material-substrate interface systems with only the given information of two parent materials. Several possible interface configurations are also proposed based on this approach. We therefore construct a database that contains these interface systems and has been continuously expanding. This database serves as preliminary guidance for epitaxial growth and stabilization of new materials in experiments.</jats:p>

<jats:p>Despite the recent discovery of superconductivity in Nd<jats:sub>1–<jats:italic>x</jats:italic> </jats:sub>Sr<jats:sub> <jats:italic>x</jats:italic> </jats:sub>NiO<jats:sub>2</jats:sub> thin films, the absence of superconductivity and antiferromagnetism in their bulk materials remains a puzzle. Here we report the <jats:sup>1</jats:sup>H NMR measurements on powdered Nd<jats:sub>0.85</jats:sub>Sr<jats:sub>0.15</jats:sub>NiO<jats:sub>2</jats:sub> samples by taking advantage of the enriched proton concentration after hydrogen annealing. We find a large full width at half maximum of the spectrum, which keeps increasing with decreasing the temperature <jats:italic>T</jats:italic> and exhibits an upturn behavior at low temperatures. The spin-lattice relaxation rate <jats:inline-formula> <jats:tex-math> <?CDATA ${}^{1}{T}_{1}^{-1}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msup> <mml:mrow /> <mml:mn>1</mml:mn> </mml:msup> <mml:msubsup> <mml:mi>T</mml:mi> <mml:mn>1</mml:mn> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msubsup> </mml:mrow> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpl_38_6_067401_ieqn1.gif" xlink:type="simple" /> </jats:inline-formula> is strongly enhanced when lowering the temperature, developing a broad peak at about 40 K, then decreases following a spin-wave-like behavior <jats:inline-formula> <jats:tex-math> <?CDATA ${}^{1}{T}_{1}^{-1}\propto {T}^{2}$?> </jats:tex-math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msup> <mml:mrow /> <mml:mn>1</mml:mn> </mml:msup> <mml:msubsup> <mml:mi>T</mml:mi> <mml:mn>1</mml:mn> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>1</mml:mn> </mml:mrow> </mml:msubsup> <mml:mo>∝</mml:mo> <mml:msup> <mml:mi>T</mml:mi> <mml:mn>2</mml:mn> </mml:msup> </mml:mrow> </mml:math> <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="cpl_38_6_067401_ieqn2.gif" xlink:type="simple" /> </jats:inline-formula> at lower temperatures. These results evidence a short-range glassy antiferromagnetic ordering of magnetic moments below 40 K and dominant antiferromagnetic fluctuations extending to much higher temperatures. Our findings reveal the strong electron correlations in bulk Nd<jats:sub>0.85</jats:sub>Sr<jats:sub>0.15</jats:sub>NiO<jats:sub>2</jats:sub>, and shed light on the mechanism of superconductivity observed in films of nickelates.</jats:p>

<jats:p>GaAs/Ge heterostructures have been employed in various semiconductor devices such as solar cells, high-performance CMOS transistors, and III–V/IV heterogeneous optoelectronic devices. The performance of these devices is directly dependent on the material quality of the GaAs/Ge heterostructure, while the material quality of the epitaxial GaAs layer on the Ge is limited by issues such as the antiphase domain (APD), and stacking-fault pyramids (SFP). We investigate the epitaxial growth of high-quality GaAs on a Ge (001) mesa array, via molecular beam epitaxy. Following a systematic study of the Ge terrace via an <jats:italic>in situ</jats:italic> scanning tunneling microscope, an atomically step-free terrace on the Ge mesa measuring up to 5 × 5 μm<jats:sup>2</jats:sup> is obtained, under optimized growth conditions. The step-free terrace has a single-phase <jats:italic>c</jats:italic> (4 × 2) surface reconstruction. The deposition of a high-quality GaAs layer with no APD and SFP is then achieved on this step-free Ge terrace. High-resolution transmission electron microscopy and electron channel contrast image characterizations reveal the defect-free growth of the GaAs layer on the step-free Ge mesa. Furthermore, InAs quantum dots on this GaAs/Ge mesa reveal photoluminescent intensity comparable to that achieved on a GaAs substrate, which further confirms the high quality of the GaAs layer on Ge.</jats:p>

<jats:p>The contact characteristic between p-InP and metal plays an important role in InP-related optoelectronic and microelectronic device applications. We investigate the low-resistance Au/Pt/Ni and Au/Ni ohmic contacts to p-InP based on the solid phase regrowth principle. The lowest specific contact resistivity of Au(100 nm)/Pt(115 nm)/Ni (50 nm) can reach 2.64 × 10<jats:sup>−6</jats:sup> Ω ⋅ cm<jats:sup>2</jats:sup> after annealing at 380 °C for 1 min, while the contact characteristics of Au/Ni deteriorated after annealing from 340 °C to 480 °C for 1 min. The results of scanning electron microscopy, atomic force microscopy and x-ray photoelectron spectroscopy show that the Pt layer is an important factor in improving the contact characteristics. The Pt layer prevents the diffusion of In and Au, inhibits the formation of Au<jats:sub>3</jats:sub>In metal compounds, and prevents the deterioration of the ohmic contact. The metal structures and optimized annealing process is expected to be helpful for obtaining high-performance InP-related devices.</jats:p>

<jats:p>The continuing demand for new optoelectronic devices drives researchers to seek new materials suitable for photodetector applications. Recently, ternary compound semiconductors have entered researchers’ field of vision, among which chalcohalides have attracted special interest because of their rich properties and unique crystal structure consisting of atom chains and inter-chain van der Waals gaps. We have synthesized high-quality BiSeI single crystals with [110]-plane orientation and fabricated a photodetector. The optoelectronic measurements show a pronounced photocurrent signal with outstanding technical parameters, namely high responsivity (3.2 A/W), specific detectivity (7 × 10<jats:sup>10</jats:sup> Jones) and external quantum efficiency (622%) for <jats:italic>λ</jats:italic> = 635 nm, <jats:italic>V</jats:italic> <jats:sub>ds</jats:sub> = 0.1 V and <jats:italic>P</jats:italic> <jats:sub>opt</jats:sub> = 0.23 mW/cm<jats:sup>2</jats:sup>. The high performance of BiSeI photodetector and its layer structure make it a promising candidate for low-dimensional optoelectronic applications.</jats:p>