Catálogo de publicaciones - revistas

<jats:p>This work aimed to tune the comprehensive properties of Fe-P-C-based amorphous system through investigating the role of microalloying process on the crystallization behavior, glass forming ability (GFA), soft magnetic features, and mechanical properties. Considering minor addition of elements into the system, it was found that the simultaneous microalloying of Ni and Co leads to the highest GFA, which was due to the optimization of compositional heterogeneity and creation of near-eutectic composition. Moreover, the FeCoNiCuPC amorphous alloy exhibited the best anelastic/viscoplastic behavior under the nanoindentation test, which was owing to the intensified structural fluctuations in the system. However, the improved plasticity by the extra Cu addition comes at the expense of magnetic properties, so that the saturation magnetization of this alloying system is significantly decreased compared to the FeCoPC amorphous alloy with the highest soft magnetic properties. In total, the results indicated that a combination of added elemental constitutes, <jats:italic>i.e</jats:italic>., Fe<jats:sub>69</jats:sub>Co<jats:sub>5</jats:sub>Ni<jats:sub>5</jats:sub>Cu<jats:sub>1</jats:sub>P<jats:sub>13</jats:sub>C<jats:sub>7</jats:sub> composition, provides an optimized state for the comprehensive properties in the alloying system.</jats:p>

<jats:p>We observe characteristic atomic behaviors in the Bose–Einstein-condensation-Bardeen–Cooper–Schrieffer (BECBCS) crossover, by accurately tuning the magnetic field across the Feshbach resonance of lithium atoms. The magnetic field is calibrated by measuring the Zeeman shift of the optical transition. A non-monotonic anisotropic expansion is observed across the Feshbach resonance. The density distribution is explored in different interacting regimes, where a condensate of diatomic molecules forms in the BEC limit with the indication of a bimodal distribution. We also measure the three-body recombination atom loss in the BEC-BCS crossover, and find that the magnetic field of the maximum atom loss is in the BEC limit and gets closer to the Feshbach resonance when decreasing the atom temperature, which agrees with previous experiments and theoretical prediction. This work builds up a controllable platform for the study on the strongly interacting Fermi gas.</jats:p>

<jats:p>We report on observing photon recoil effects in the absorption of a single monochromatic light at 689 nm through an ultracold <jats:sup>88</jats:sup>Sr gas, where the recoil frequency is comparable to natural linewidth of the narrow-line transition 5s<jats:sup>2 1</jats:sup>S<jats:sub>0</jats:sub>–5s5p <jats:sup>3</jats:sup>P<jats:sub>1</jats:sub> in strontium. In the regime of high-saturation, the absorption profile becomes asymmetric due to the photon-recoil shift, which is of the same order as the natural linewidth. The lineshape is described by an extension of the optical Bloch equations including the momentum transfers to atoms during emission and absorption of photons. Our work reveals the photon recoil effects in a simplest single-beam absorption setting, which is of significant relevance to other applications such as saturation spectroscopy, Ramsey interferometry, and absorption imaging.</jats:p>

<jats:title>Abstract</jats:title> <jats:p>Three-dimensional (3D) vertical architecture transistors represent an important technological pursuit, which have distinct advantages in device integration density, operation speed, and power consumption. However, the fabrication processes of such 3D devices are complex, especially in the interconnection of electrodes. In this paper, we present a novel method which combines suspended electrodes and focused ion beam (FIB) technology to greatly simplify the electrodes interconnection in 3D devices. Based on this method, we fabricate 3D vertical core-double shell structure transistors with ZnO channel and Al<jats:sub>2</jats:sub>O<jats:sub>3</jats:sub> gate-oxide both grown by atomic layer deposition. Suspended top electrodes of vertical architecture could be directly connected to planar electrodes by FIB deposited Pt nanowires, which avoid cumbersome steps in the traditional 3D structure fabrication technology. Both single pillar and arrays devices show well behaved transfer characteristics with an <jats:italic>I</jats:italic> <jats:sub>on</jats:sub>/<jats:italic>I</jats:italic> <jats:sub>off</jats:sub> current ratio greater than 10<jats:sup>6</jats:sup> and a low threshold voltage around 0 V. The ON-current of the 2 × 2 pillars vertical channel transistor was 1.2 μA at the gate voltage of 3 V and drain voltage of 2 V, which can be also improved by increasing the number of pillars. Our method for fabricating vertical architecture transistors can be promising for device applications with high integration density and low power consumption.</jats:p>

<jats:p>Luminescent properties of Tm<jats:sup>3+</jats:sup>-doped GdYTaO<jats:sub>4</jats:sub> are studied for exploring their potential applications in temperature and pressure sensing. Two main emission peaks from <jats:sup>3</jats:sup>H<jats:sub>4</jats:sub> → <jats:sup>3</jats:sup>H<jats:sub>6</jats:sub> transition of Tm<jats:sup>3+</jats:sup> are investigated. Intensity ratio between the two peaks evolves exponentially with temperature and has a highest sensitivity of 0.014 K<jats:sup>−1</jats:sup> at 32 K. The energy difference between the two peaks increases linearly with pressure increasing at a rate of 0.38 meV/GPa. Intensity ratio between the two peaks and their emission lifetimes are also analyzed for discussing the pressure-induced variation of the sample structure. Moreover, Raman spectra recorded under high pressures indicate an isostructural phase transition of GdYTaO<jats:sub>4</jats:sub> occurring at 4.46 GPa.</jats:p>

<jats:p>Defect levels in semiconductor band gaps play a crucial role in functionalized semiconductors for practical applications in optoelectronics; however, first-principle defect calculations based on exchange–correlation functionals, such as local density approximation, grand gradient approximation (GGA), and hybrid functionals, either underestimate band gaps or misplace defect levels. In this study, we revisited iodine defects in CH<jats:sub>3</jats:sub>NH<jats:sub>3</jats:sub>PbI<jats:sub>3</jats:sub> by combining the accuracy of total energy calculations of GGA and single-electron level calculation of the GW method. The combined approach predicted neutral I<jats:sub>i</jats:sub> to be unstable and the transition level of I<jats:sub>i</jats:sub>(+1/–1) to be close to the valence band maximum. Therefore, I<jats:sub>i</jats:sub> may not be as detrimental as previously reported. Moreover, V<jats:sub>I</jats:sub> may be unstable in the –1 charged state but could still be detrimental owing to the deep transition level of V<jats:sub>I</jats:sub>(+1/0). These results could facilitate the further understanding of the intrinsic point defect and defect passivation observed in CH<jats:sub>3</jats:sub>NH<jats:sub>3</jats:sub>PbI<jats:sub>3</jats:sub>.</jats:p>

<jats:p>Using first-principles calculations based on density functional theory, we have systematically studied the influence of in-plane lattice constant and thickness of slabs on the concentration and distribution of two-dimensional hole gas (2DHG) in AlN/GaN superlattices. We show that the increase of in-plane lattice constant would increase the concentration of 2DHG at interfaces and decrease the valence band offset, which may lead to a leak of current. Increasing the thickness of AlN and/or decreasing the thickness of GaN would remarkably strengthen the internal field in GaN layer, resulting in better confinement of 2DHG at AlN/GaN interfaces. Therefore, a moderate larger in-plane lattice constant and thicker AlN layer could improve the concentration and confinement of 2DHG at AlN/GaN interfaces. Our study could serve as a guide to control the properties of 2DHG at III-nitride interfaces and help to optimize the performance of p-type nitride-based devices.</jats:p>

<jats:p>We report <jats:sup>121</jats:sup>Sb nuclear quadrupole resonance (NQR) measurements on kagome superconductor CsV<jats:sub>3</jats:sub>Sb<jats:sub>5</jats:sub> with <jats:italic>T</jats:italic> <jats:sub>c</jats:sub> = 2.5 K. <jats:sup>121</jats:sup>Sb NQR spectra split after a charge density wave (CDW) transition at 94 K, which demonstrates a commensurate CDW state. The coexistence of the high temperature phase and the CDW phase between 91 K and 94 K manifests that it is a first order phase transition. The CDW order exhibits tri-hexagonal deformation with a lateral shift between the adjacent kagome layers, which is consistent with 2 × 2 × 2 superlattice modulation. The superconducting state coexists with CDW order and shows a conventional s-wave behavior in the bulk state.</jats:p>

<jats:p>Recently, transition-metal-based kagome metals have aroused much research interest as a novel platform to explore exotic topological quantum phenomena. Here we report on the synthesis, structure, and physical properties of a bilayer kagome lattice compound V<jats:sub>3</jats:sub>Sb<jats:sub>2</jats:sub>. The polycrystalline V<jats:sub>3</jats:sub>Sb<jats:sub>2</jats:sub> samples were synthesized by conventional solid-state-reaction method in a sealed quartz tube at temperatures below 850 °C. Measurements of magnetic susceptibility and resistivity revealed consistently a density-wave-like transition at <jats:italic>T</jats:italic> <jats:sub>dw</jats:sub> ≈ 160 K with a large thermal hysteresis, even though some sample-dependent behaviors were observed presumably due to the different preparation conditions. Upon cooling through <jats:italic>T</jats:italic> <jats:sub>dw</jats:sub>, no strong anomaly in lattice parameters and no indication of symmetry lowering were detected in powder x-ray diffraction measurements. This transition can be suppressed completely by applying hydrostatic pressures of about 1.8 GPa, around which no sign of superconductivity was observed down to 1.5 K. Specific-heat measurements revealed a relatively large Sommerfeld coefficient <jats:italic>γ</jats:italic> = 18.5 mJ⋅mol<jats:sup>–1</jats:sup>⋅K<jats:sup>–2</jats:sup>, confirming the metallic ground state with moderate electronic correlations. Density functional theory calculations indicate that V<jats:sub>3</jats:sub>Sb<jats:sub>2</jats:sub> shows a non-trivial topological crystalline property. Thus, our study makes V<jats:sub>3</jats:sub>Sb<jats:sub>2</jats:sub> a new candidate of metallic kagome compound to study the interplay between density-wave-order, nontrivial band topology, and possible superconductivity.</jats:p>

<jats:p>The dwell time and spin polarization (SP) of electrons tunneling through a parallel double <jats:italic>δ</jats:italic>-magnetic-barrier nanostructure in the presence of a bias voltage is studied theoretically in this work. This nanostructure can be constructed by patterning two asymmetric ferromagnetic stripes on the top and bottom of InAs/Al<jats:sub> <jats:italic>x</jats:italic> </jats:sub>In<jats:sub>1 – <jats:italic>x</jats:italic> </jats:sub>As heterostructure, respectively. An evident SP effect remains after a bias voltage is applied to the nanostructure. Moreover, both magnitude and sign of spin-polarized dwell time can be manipulated by properly changing the bias voltage, which may result in an electrically-tunable temporal spin splitter for spintronics device applications.</jats:p>