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A phase-change thin film-tuned photonic crystal device
摘要： This paper reports a tunable photonic device that incorporates a thin layer of phase-change material, Ge2Sb2Te5 (GST), in a photonic crystal (PC) structure. The PC structure is based on a one-dimensional grating waveguide with a metal cladding. The metal-cladded PC structure supports a guided-mode resonance (GMR) that selectively absorbs light at a particular wavelength. Inserting the GST material into the gating waveguide makes it possible to control the GMR mode. Here, the GST-PC device was numerically designed and optimized to obtain significant tuning of the GMR mode around 1550 nm. The tuning phenomena were experimentally demonstrated by the heat-induced phase change between crystalline and amorphous phases of the GST thin film. A spectral shift of the resonant wavelength from 1440 nm to 1610 nm was achieved via the crystallization process. The phase tuning of GST exhibits good repeatability as demonstrated by switching between amorphous and crystalline phases of GST for multiple cycles. The GST-PC device represents a new approach for tuning optical resonances with potential applications including but not limited to integrated photonic circuits, optical communications, and high-performance optical filters.
关键词： tunable filter,Photonic crystal,phase-change material
更新于2025-09-23 15:21:01
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<i>(Invited) The Scaling-Down and Performance Optimization of InAs Nanowire Field Effect Transistors</i>
摘要： Due to their fascinating properties, InAs nanowires have drawn great attention for the channel material in future transistors. Scaling-down has been an effective way to improve the performance of transistors continuously for decades. Here, we review our recent progresses on InAs nanowire field effect transistors (FETs) when they are scaled down. Our group investigates the electrical characteristics of InAs nanowire thinner than 10 nm. Both the size-effect and the contact properties of ultrathin nanowires are explored. Moreover, the effects of InAs crystal phase and orientation are studied for further optimizing the device performance. In addition, FETs with partial gate are studied to suppress the BTBT-induced off-current. Furthermore, to improve the electrostatics control of the gate, our group develops a method to fabricate vertical GAA FETs with all-metal electrodes based on self-catalyzed grown InAs nanowire arrays.
关键词： orientation,crystal phase,performance optimization,field effect transistors,partial gate,vertical GAA FETs,InAs nanowires,scaling-down
更新于2025-09-23 15:21:01
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Transmissive flexoelectro-optic liquid crystal optical phase modulator with 2 <b>??</b> modulation
摘要： In this paper, we demonstrate analog phase modulation in a transmissive configuration using the flexoelectro-optic effect in short-pitch chiral nematic liquid crystal (LC) devices. Two different modes are considered, both of which are shown to generate full 2π phase modulation at 1 kHz switching frequency. The first configuration that is considered consists of a half-wave plate that is placed between two flexoelectro-optic LC devices that are subjected to electric fields that are applied in phase. Second, we demonstrate that a similar phase modulation response can be observed by removing the half-wave plate and subjecting the two flexoelectro-optic LC devices to electric fields whereby the polarities are out of phase. Both configurations demonstrated herein are promising for the development of next-generation LC spatial light modulators, particularly when reflective geometries are challenging or impractical.
关键词： spatial light modulators,flexoelectro-optic effect,liquid crystal,phase modulation,transmissive configuration
更新于2025-09-23 15:21:01
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Polymer functionalized nanoparticles in liquid crystals: combining PDLCs with LC nanocomposites
摘要： Liquid crystal (LC)–polymer blends are important stimuli responsive materials already employed in a wide range of applications whereas nanoparticle (NP)–LC blends are an emerging class of nanocomposites. Polymer ligands offer the advantages of synthetic simplicity along with chemical and molecular weight tunability. Here we compare the phase behavior of 5CB blended with poly(ethylene oxide) (PEO) and with gold NPs functionalized with thiolated PEO (AuNP–PEO) as a function of PEO concentration by DSC, POM and 13C NMR spectroscopy. Both PEO and the AuNP–PEO form uniform dispersions in isotropic 5CB and phase separate below the I–N phase transition temperature. Above the PEO crystallization temperature, the PEO/5CB blends show the expected biphasic state of PEO rich-isotropic liquid co-existing with PEO-poor nematic droplets. At PEO concentrations above 10 wt%, nematic 5CB nucleates with PEO crystallization. Both PEO and AuNP–PEO induce homeotropic alignment of the 5CB matrix immediately below TNI. The AuNP–PEO/5CB blends form thermally reversible cellular networks similar to AuNPs functionalized with low molecular weight mesogenic ligands. A thermodynamic model to account for the observed phase behavior is presented.
关键词： Polymer blends,Nanoparticles,Liquid crystal,Phase behavior,Thermodynamic model
更新于2025-09-23 15:21:01
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Liquid Crystal-Based Enclosed Coplanar Waveguide Phase Shifter for 54a??66 GHz Applications
摘要： A 0–10 V bias voltage-driven liquid crystal (LC) based 0–180? continuously variable phase shifter was designed, fabricated, and measured with insertion loss less than ?4 dB across the spectrum from 54 GHz to 66 GHz. The phase shifter was structured in an enclosed coplanar waveguide (ECPW) with LC as tunable dielectrics encapsulated by a unified ground plate in the design, which significantly reduced the instability due to floating effects and losses due to stray modes. By competing for spatial volume distribution of the millimeter-wave signal occupying lossy tunable dielectrics versus low-loss but non-tunable dielectrics, the ECPW’s geometry and materials are optimized to minimize the total of dielectric volumetric loss and metallic surface loss for a fixed phase-tuning range. The optimized LC-based ECPW was impedance matched with 1.85 mm connectors by the time domain reflectometry (TDR) method. Device fabrication featured the use of rolled annealed copper foil of lowest surface roughness with nickel-free gold-plating of optimal thickness. Measured from 54 GHz to 66 GHz, the phase shifter prototype presented a tangible improvement in phase shift effectiveness and signal-to-noise ratio, while exhibiting lower insertion and return losses, more ease of control, and high linearity as well as lower-cost fabrication as compared with up-to-date documentations targeting 60 GHz applications.
关键词： tunable circuits and devices,true time delay,millimeter-wave,60 GHz,liquid crystal,phase shifter,enclosed coplanar waveguide
更新于2025-09-19 17:13:59
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Anisotropies of the g-factor tensor and diamagnetic coefficient in crystal-phase quantum dots in InP nanowires
摘要： Crystal-phase low-dimensional structures offer great potential for the implementation of photonic devices of interest for quantum information processing. In this context, unveiling the fundamental parameters of the crystal phase structure is of much relevance for several applications. Here, we report on the anisotropy of the g-factor tensor and diamagnetic coefficient in wurtzite/zincblende (WZ/ZB) crystal-phase quantum dots (QDs) realized in single InP nanowires. The WZ and ZB alternating axial sections in the NWs are identified by high-angle annular dark-field scanning transmission electron microscopy. The electron (hole) g-factor tensor and the exciton diamagnetic coefficients in WZ/ZB crystal-phase QDs are determined through micro-photoluminescence measurements at low temperature (4.2 K) with different magnetic field configurations, and rationalized by invoking the spin-correlated orbital current model. Our work provides key parameters for band gap engineering and spin states control in crystal-phase low-dimensional structures in nanowires.
关键词： g-factor tensor,crystal-phase quantum dot,InP NWs,diamagnetic coefficient
更新于2025-09-19 17:13:59
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Determination of Phase Transition and Electro-optical Behaviors of Quantum Dot Doped Polymer Dispersed Liquid Crystal
摘要： This paper describes our research into phase transition, electro-optical and dielectric behaviors of polymer dispersed liquid crystal (PDLC) and cadmium selenide sulphide/zinc sulphide quantum dot (QD) doped PDLC (PDLC/QD). The PDLC was prepared with nematic liquid crystal (E63) and UV-curable photopolymer (NOA65) by using a polymerization induced phase separation technique. Dielectric properties of composites were investigated with a dielectric/impedance analyzer at 1 kHz–10 MHz frequency range. Electro-optical measurements of investigated samples were carried out using an electro-optical switching method. Phase transition temperature of PDLC and PDLC/QD composites was also determined, using a differential scanning calorimeter. The results showed that the introduction of QD signi?cantly changes the physical properties of PDLC, and these changes could become a focus of interest for future applications.
关键词： quantum dot,electro-optical and dielectric behaviors,Polymer dispersed liquid crystal,phase transition
更新于2025-09-16 10:30:52
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Crystal phase control synthesis of metallic 1T-WS2 nanosheets incorporating single walled carbon nanotubes to construct superior microwave absorber
摘要： Two-dimensional transition metal dichalcogenides (TMDs) have attracted tremendous attentions due to their unique properties, and the development of phase control technique brings out new opportunities in emerging application fields. In this work, tungsten disulfide (WS2) nanosheets containing 1T phase predominately were incorporated with single walled carbon nanotubes (SWCNTs) through a facial hydrothermal method. Two-dimensional flexible and ultrathin WS2 nanosheets were in-situ grown on one-dimensional SWCNTs bundles, further forming typical urchin-like microsphere with diameters distributing in the range of 2~3 μm uniformly. Accordingly, dielectric loss could be significantly enhanced due to the strong interface coupling effect between WS2 nanosheets and SWCNTs bundles, which induced considerable electrical conductivity and abundant capacitor-like structures. Consequently, the minimum reflection loss (RL) could reach up to -66 dB at 8.3 GHz with a matching thickness of 2.2 mm. Furthermore, RL values lower than -10 dB could be attained in the range of 3.0~18.0 GHz with integrated thicknesses from 5.0 to 1.0 mm. Prospectively, our present work may provide new opportunity to design TMDs based composites by means of crystal phase control technique as lightweight and high-performance microwave absorbers.
关键词： urchin-like microsphere,high-efficient microwave absorber,crystal phase control,1T-WS2/SWCNTs hybrid composites
更新于2025-09-12 10:27:22
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Phase shift formulas in electro-optical crystals with an arbitrary incident direction
摘要： The calculation of the phase shift in electro-optical crystals is related to an extensive range of optical devices. A set of analytical phase shift formulas at arbitrary incidence angle and azimuth angle for a plane-parallel electro-optical crystal plate is derived. This enables us to analyze the phase shift induced by an electro-optical crystal with an arbitrary incident direction. As an example, the derived formulas are used to investigate the influence of incidence angle and azimuth angle on the phase shift in a lithium niobate crystal plate. For the field-free lithium niobate crystal, the phase shift depends only on the incidence angle. In contrast, when an external electric field is applied to the crystal, the phase shift is not only strongly influenced by the incidence angle, but also periodically changes with the azimuth angle. In order to validate the correctness of the derived formulas, the experiments are also conducted. The theoretical results are proved to be in good agreement with the experimental results.
关键词： Electro-optical crystal,Phase shift,Biaxial crystal,Birefringent,Uniaxial crystal
更新于2025-09-11 14:15:04
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Use of Aggregation-Induced Emission for Selective Detection of Phase Transformation during Evaporative Crystallization of Hexaphenylsilole
摘要： Crystallization of organic molecules is quite complicated because the crystallization process is governed by the weak intermolecular interactions. By exploiting the aggregation-induced emission (AIE), we attempted to realize the selective detection of phase transformation during the evaporative crystallization of hexaphenylsilole (HPS), which shows different fluorescence colors in the amorphous and crystalline phases. No fluorescence emission was observed in the HPS solution immediately after dropping on the glass substrate due to the non-radiative deactivation induced by intramolecular rotational or vibrational motion, suggesting that HPS exists as a monomer in solution. As time elapsed after dropping, green emission first appeared, which changed to blue after solvent evaporation, because of phase transformation from the amorphous state to the crystalline state. This phenomenon supports not only the two-step nucleation model involving an intermediate such as a liquid-like cluster prior to nucleation, but also the real time-detection of Ostwald’s rule of stages during evaporative crystallization.
关键词： molecular interaction,amorphous-crystal phase transformation,AIE,Ostwald’s rule of stages,evaporative crystallization
更新于2025-09-10 09:29:36