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Research to realize full electrical spin manipulation and spin–photon coupling on silicon using micromagnets has been prevalent. To realize spin–photon coupling, micromagnets should be placed parallel to the double quantum dot connection direction. However, the parallelly placed micromagnet will also generate detrimental magnetic field gradients, which results in substantial dephasing of the qubit [Yoneda et al., Nat. Nanotechnol. 13, 102–106 (2018); Struck et al., npj Quantum Inf. 6(1), 40 (2020); Takeda et al., Nat. Nanotechnol. 16, 965–969 (2021)]. Here, we develop a scheme of an iterative polygonal micromagnet, which maximizes the qubit Rabi oscillation quality factor [Takeda et al., Sci. Adv. 2, e1600694 (2016)] Q, while allowing strong spin–photon coupling. To find the optimal structure of the micromagnet in the iterative process, the appropriate objective function R (proportional to 1/Q) is selected as the evaluation standard of micromagnet performance. The simulation results by the RADIA package show that the Q value of the polygonal micromagnet is 15% better than that of the rectangular micromagnet at most and up to approximately 30% in subsequent simulation using the OOMMF tool.

Transition metal dichalcogenides (TMDs) with only a few atoms thickness provide an excellent solution to scale down current semiconductor devices. Many studies have demonstrated that molybdenum disulfide (MoS2), a member of TMDs, is promising as a channel material to fabricate field-effect transistors (FETs). However, the carrier mobility in MoS2 FET is always far lower than the theoretical prediction. Although this poor performance can be attributed to the defects, it still lacks a quantitative analysis clarifying the correlation between carrier mobility and defect density. In this work, by using scanning tunneling microscopy, we directly counted the defects in MoS2 FETs with different carrier mobility. We found that vacancies and impurities equally contribute to carrier mobility and the total defect density induces a power-law decreasing tendency to the carrier mobility of MoS2 FET. Our current results directly prove that the reduction of point defects can exponentially improve the carrier mobility of FETs made by TMDs.

Photoresponse is affected by the microscopic structure and orientation of the perovskite crystals, but it is difficult to quantify the individual grain size and always acts as homogeneous. Using scanning probe microscopy, the local electrical properties of individual grains in all-inorganic perovskites are mapped. Surface potential variations on lateral distance scales within or larger than one grain size are presented. Among perovskite grains, three discrete photoconductivity levels are identified, corresponding to the facet-dependent density of trap states, which was further demonstrated by the light intensity dependence of the local current–voltage curve of each grain.

In this work, high-quality SnO2 and Hf0.38Sn0.62O2 thin films were grown on c-plane sapphire substrates by pulsed laser deposition for a comparative study. The optical and electrical tests show that Hf doping leads to significantly increased bandgap and resistivity of the HfSnO2 alloy as compared to SnO2. Then, SnO2- and Hf0.38Sn0.62O2-based UV detectors were fabricated and compared. The Hf0.38Sn0.62O2 film-based detector exhibits an excellent performance. Its dark current is as low as 0.2 pA under 20 V, and the rise/decay response time is as short as 69 ms/50 ms. The cut-off wavelength and the rejection ratio are 290 nm and 4100, respectively. Our work demonstrates that the Hf0.38Sn0.62O2 ternary alloy compound semiconductor has great potential for applications in solar-blind ultraviolet detections.

Metamaterial absorbers have proven their ability to sense in the terahertz domain. However, the sensitivity is always limited by the poor spatial overlap between the analyte and the localized enhanced electromagnetic field. Here, we try to tackle this challenge by utilizing an absorber with a bilayer cross-shaped plate-hole structure to ingeniously excite hot-spots covering the analyte. As a result, the sensitivity is significantly improved, theoretically about 7 and 18 times higher than that of the conventional cross-shaped absorber and its complementary cross-shaped absorber, respectively. We then experimentally demonstrate its ability to quantitatively detect biotin with a sensitivity of 153 GHz/μM, higher than that of previously reported biotin sensors. Additionally, the polarization-independent nanostructure decreases the design and fabrication complexity and maintains high reflection at a wide range of incident angles over ±50°. These findings open up opportunities for metamaterial absorbers to realize ultrasensitive biosensing in the fingerprint region of the terahertz regime.

In contrast to conventional bulk optical components, metasurface-based flat optical devices have shown excellent superiorities on manipulating polarization, phase, and amplitude of incident light. Specifically, flat metalenses play an essential role for applications in imaging and optoelectronic integration. Several metalenses operating at visible or near-infrared wavelengths have been recently demonstrated. However, flat optics for the long-wavelength infrared (LWIR) has received relatively less attention. Here, we demonstrate a polarization-insensitive, all-dielectric metalens operating at LWIR. The metalens has a numerical aperture of 0.6 at the wavelength λ = 10.6 μm. It can focus incident light down to a spot as small as ∼1.08λ and exhibits high-resolution imaging performance. In addition, because the metalens is fabricated by single step photolithography and CMOS-compatible processes, it is easy to realize high-throughput manufacture, which provides an efficient way for the development of compact optical devices for LWIR technology.

A systematic investigation of the nanoscale conduction behavior of vanadium dioxide (VO2) films deposited on aluminum oxide (Al2O3) substrates, using conductive atomic force microscopy, is presented. Aside from the macroscale resistance-temperature characteristics, which show a steep insulator-metal transition at the transition point Tm ∼ 68 °C, our experiments demonstrate a coexistence of nanoscale high-conduction and low-conduction phases over a broad temperature window (50 K range) across the Tm. In addition, the area (volume) fraction of the high-conduction phase increases with increasing temperature across the transition point. The current-voltage data obtained on a nanoscale indicate that the high-conduction phase is not a good metal. When the temperature increased across the Tm, the probed charge transport behavior of the high-conduction phase is found to change from a mechanism dominated by space-charge limited current to a mechanism dominated by Schottky emission.

Digital coding metasurfaces have attracted attention due to their advantages compared to metamaterials. Many devices have been proposed by encoding the phase responses on metasurfaces such as orbit angular momentum generation, prefect absorbers, and holography. For complete manipulation for propagation of electromagnetic waves, it would be beneficial to control both phase and amplitude responses. Here, we propose a metasurface with independent control of phase and amplitude profiles, which is composed of four unit cells, and the amplitude responses of all unit cells range from 0.3 to 0.7. The four units have phase responses of 0, π/2, π, and 3π/2 separately to mimic the “00,” “01,” “10,” and “11” digital elements. The direction of the reflected beam from the metasurface can be manipulated by different sequences of digital elements, and meanwhile, the intensity of the reflected beam can be modulated through changing different amplitude responses in the same direction. We show that the distributions of both phase and amplitude responses of the metasurface will contribute to scattering reduction. We have used indium tin oxide to design the patterns of four units. The experiments and simulations confirm the physical phenomena mentioned above. The separate control of phase and amplitude responses suggests potential applications in high quality holography and mathematical operations of metasurfaces.

The electrical conductivity, charge transport behavior, and ferroelectricity of epitaxial BaNbxTi1-xO3 films (BNTO, 0.0 ≤ x ≤ 0.5) prepared by pulsed laser deposition are investigated. It is found that Nb-doping can tune the conventional insulating BaTiO3 films from an insulating to highly conductive semiconducting or metallic state, resulting in a variation of the electrical conductivity of the BNTO films over 105. For x ≤ 0.25, the charge transport is dominated by the small polaron hopping mechanism, while the charge transport for x = 0.5 transits from the bipolaron to the small-polaron, and then the thermal phonon scattering mechanisms with increasing temperature. Interestingly, the piezo-force microscopy imaging reveals the presence of ferroelectricity in the properly Nb-doped conductive BNTO films (x ≤ 0.25) deposited in the presence of a small amount of oxygen (3 × 10−3 Pa). Our work provides additional technical roadmaps to manipulate the conductivity and charge transport behaviors in ferroelectric...

MnM′X (M′ = Co, Ni; X = Ge, Si, etc.) alloys usually present a large volumetric change during the Martensitic (MA) transformation. This offers a great opportunity for exploring new negative thermal expansion (NTE) materials if the temperature interval of NTE can be extended. Here, we report colossal NTE in fine-powdered Mn0.98CoGe prepared by repeated thermal cycling (TC) through the MA transition or ball milling. Both treatments can expand the MA transformation, and thus broaden the NTE temperature window (ΔT). For the powders that have gone through TC for ten times, ΔT reaches 90 K (309 K–399 K), and the linear expansion coefficient (αL) is about −141 ppm/K, which rank among the largest values of colossal NTE materials. The difference between two kinds of treatments and the possible mechanisms of the extended MA transformation window are discussed based on the introduced strain.

The non-saturation phenomenon of contact angle change of a nonconductive droplet in an immiscible dielectric liquid with iso-density is demonstrated using the dielectric force due to the difference of the two dielectric constants. The concentric electrode design permits the dielectric force exerted at various contact angles. The droplet fully develops from 22° to 176° (nearly spherical) in contact angle as the voltages tuned from 0 to 215 Vrms. The contact angle change was found to behave almost linearly with respect to voltage by experiments. The dielectric force in the liquid/liquid interface was further simulated at the aspects of energy distribution, force distribution, and electric fields, found in a good agreement with experimental results.

Large scale, uniform single-layer graphene was transferred onto well-aligned ZnO nanowire arrays to produce high density nanoscale protrusions within graphene for efficient field emission. Polymethyl methacrylate (PMMA) was used as a supporting layer to provide a quasi-flat surface for graphene transfer. Highly efficient (maximum current density of ∼500 μA/cm2) and stable field emission with low turn-on fields (5.4 V/μm) was observed due to highly localized electric field, which is much better than those without using PMMA. F-N plot showed an unique up-bending feature of single-layer graphene. Our approach provides an efficient way to produce high quality single-layer graphene field emitters.

We have measured the optical and mechanical loss of commercial silicon nitride membranes. We find that 50 nm-thick, 1 mm^2 membranes have mechanical Q > 10^6 at 293 K, and Q > 10^7 at 300 mK, well above what has been observed in devices with comparable dimensions. The near-IR optical loss at 293 K is less than 2E-4. This combination of properties make these membranes attractive candidates for studying quantum effects in optomechanical systems., 4 pages, 4 figures

The fabrication process and performance characteristics of a vertical-structured GaN-based light-emitting diode (VM-LED) employing nickel electroplating and patterned laser liftoff techniques are presented. As compared to regular LED, the forward voltage drop of the VM-LED at 20–80 mA is about 10%–21% lower, while the light output power (Lop) is more than twice in magnitude. Especially, the Lop exhibits no saturation or degradation at an injection current up to 520 mA which is about 4.3 times higher than that of the regular one. Substantial improvements in the VM-LEDs performances are mainly attributed to the use of metallic substrate which results in less current crowding, larger effective area, and higher thermal conductivity.