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A terahertz (THz) dielectric property characterization method based on a unified single oscillator model has been developed and applied to a variety of multi-component silicate oxide glasses. The experimental values of dielectric constant determined by THz time-domain spectroscopy (TDS) in the sub-THz region have been confirmed to agree well with the values calculated by the single oscillator model which incorporates the local field effects and the material’s ionicity. This has provided a unified formulation that enables systematic determination of the key physical parameters solely from the high-frequency (optical) and low-frequency (sub-THz) dielectric constants and characteristic resonance frequency in the (sub-)THz region. The low-frequency dielectric constant has been demonstrated to be fully determined by a single parameter of the microscopic total susceptibility. Also, the polarization ionicity, which is defined by the ionic fraction in the microscopic total susceptibility, has been found to be a good indicator to represent the ionic nature of the material. Through this analysis, an increasing trend of the effective ionic charge has been found in high-dielectric constant glasses such as oxyfluorosilicate glasses, and the physical mechanism of their dielectric constant enhancement has been discussed. The present method is expected to be applied to design and characterize dielectric properties of a wide range of multi-component glasses and other isotropic, insulating materials.

Mechanical systems on all length scales may be subjected to nanoscale thin film lubrication (TFL). Molecular dynamics (MD) simulations were conducted to investigate the lubrication mechanism and boundary slip of squalane confined in nanogap at 293 K with two different film thicknesses and a wide range of pressures. The molecular distribution, density and velocity profiles of squalane were analyzed. The results show that the lubricant atoms tend to form layers parallel to the wall, but the lubricant molecules orient randomly throughout the film in the directions both parallel and perpendicular to the wall. Most squalane molecules appear twisted and folded, and extend to several atomic layers so that there are no slips between lubricant layers. The distances between the lubricant layers are irregular rather than broadening far away from the walls. The boundary slip at the interface of bcc Fe (001) and squalane only occurs at high pressure because of the strong nonbond interactions between lubricant atoms and wall atoms. The tendency of boundary slip is more obvious for films with thinner film thickness. According to the simulations, the relationship between the slip length and the pressure is given.

Dielectric properties of oxyfluorosilicate (OFS) glasses have been characterized using Terahertz (THz)-time domain spectroscopy in the sub-THz region as well as optical reflection measurement. OFS glass containing 20 mol% of Nb2O5, which is termed ZNbKLSNd glass, has the highest refractive index of 3.70 in the sub-THz region. The THz and optical refractive indices of various silicate oxide glasses, including OFS glasses, have been confirmed to be correlated by a unified relationship utilizing a parameter defined by the ratio of ionic to electronic polarizability. Additionally, the frequency dependence of the THz dielectric constant has been interpreted by a single oscillator model for all silicate oxide glasses including OFS glasses. On the basis of the present unified dielectric model, the very high refractive index of ZNbKLSNd glass has been attributed to the lowering of oscillator resonance wavelength originated from the incorporation of Nb2O5 intermediate network former.

Poly (3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) is known for its potential to replace indium&ndash, tin oxide in various devices. Herein, when fabricating finger-type PEDOT:PSS electrodes using conventional photolithography, the cross-sectional profiles of the patterns are U-shaped instead of rectangular. The films initially suffer from non-uniformity and fragility as well as defects owing to undesirable patterns. Adding a small amount of hydrolyzed silane crosslinker to PEDOT:PSS suspensions increases the mechanical durability of PEDOT:PSS patterns while lifting off the photoresist. To further improve their microfabrication, we observe the effects of two additional oxygen (O2) plasma treatments on conventional photolithography processes for patterning PEDOT:PSS, expecting to observe how O2 plasma increases the uniformity of the patterns and changes the thickness and U-shaped cross-sectional profiles of the patterns. Appropriately exposing the patterned photoresist to O2 plasma before spin-coating PEDOT:PSS improves the wettability of its surface, including its sidewalls, and a similar treatment before lifting off the photoresist helps partially remove the spin-coated PEDOT:PSS that impedes the lift-off process. These two additional processes enable fabricating more uniform, defect-free PEDOT:PSS patterns. Both increasing the wettability of the photoresist patters before spin-coating PEDOT:PSS and reducing its conformal coverage are key to improving the photolithographic microfabrication of PEDOT:PSS.

A Yb2Si2O7/SiC bilayer anti-oxidation coating was fabricated on the surface of C/SiC composites by the chemical vapor deposition (CVD) and the combination of sol-gel and air spraying method to enhance the oxidation resistance of C/SiC composites. Results indicated that the bilayer coating can efficiently prevent the oxidation of C/SiC composites in ambient air at 1773 K for more than 100 h with slight weight loss rate of 8.12 × 10-5 g cm-2 h-1 and retained compression strength of 96.78%. Microstructure characterization revealed that the gradual densification of Yb2Si2O7 outer coating exposed to 1773 K reduced the oxygen diffusion pathes within the Yb2Si2O7/SiC bilayer coating, therefore, the weight loss rate of specimens decreased as oxidation proceeded. The oxidation activation energy of bilayer coating coated C/SiC specimen was 107.73 kJ/mol during long time oxidation within the temperature range from 1573 K to 1773 K. Based on the microstructure analysis and oxidation behavior of the specimens with different exposure time of oxidation, the oxygen diffusion rate in the bilayer coating was the controlling link during the long time oxidation course.

Open source 3D printers (OS3DPs) have become increasingly more widespread in recent years because of their ease of use and budget friendliness, with the majority being fused deposition modeling (FDM) printers. However, due to natural deficiencies of the FDM printing methodology, different printing parameters can cause various properties of printed parts. To obtain printed polylactic acid (PLA) parts with improved tensile properties, a tension model of the part and an orthogonal experiment scheme were constructed in this paper. The effects of three printing parameters (layer height, orientation angle (OA) of the part, and print speed) on tensile properties (elastic modulus, tensile strength, and elongation at break) were investigated. The results demonstrated that the printing parameters affected the tensile properties of PLA parts. Larger layer height and lower print speed contributed to the improvement of tensile strength. The OA of the part had the greatest effect on the parts’ elastic modulus and elongation at break among the three parameters. Both layer height and OA of the part affected part tensile strength significantly. In this research, layer height of 0.2 mm and print speed of 20 ~ 30 mm/s are found to be the optimal printing parameters. Adjusting the OA of the part can provide targeted tensile properties, and the parts with the OA of 45° resulted in the lowest tensile strength because the tensile force is only held by fibers parallel to the force orientation instead of all fibers.

We demonstrate indium-tin-oxide (ITO) finger-type pattern (FTP) as an effective transparent conducting electrode for terahertz (THz) application. The average transmittance of ITO-FTP is as high as 85% in the frequency range of 0.2–1.2 THz. A pair of fused silica substrates with ITO-FTP was employed for constructing an electrically tunable twisted nematic liquid crystal (LC) based THz phase shifter. The cross-orientation pair of ITO-FTPs served as wavelength-insensitive and transparent electrodes for the LC layer. A maximum phase shift exceeding π/2 at 1.2 THz was demonstrated for a device with a 600-μm-thick LC cell. The required driving voltage for quarter-wave operation and threshold voltage were 5.3 and 0.8 V RMS, respectively. Performance of the THz phase shifter is discussed by defining a figure of merit (FOM) for LC-based THz shifters and compared with previously reported devices.

Wood plastic composites (WPCs) have emerged as environmentally benign filaments for fused deposition modeling (FDM) printing. Using WPCs filaments to print light weight and strong cellular structures could create new application potentials for WPCs and provide sustainable feedstock for cellular materials. In this research, the compression performance of FDM printed circle, square, and voronoi WPCs cellular structures were investigated using finite element simulations and compression experiments. Simulated results did not agree with experimental results due to the presence of cavities in the prints. Cavities were formed in the cellular structures with arcs and curvature. The results showed that the circle cellular structure demonstrated great fluctuations between the simulations and experimental results. The cavity porosity was also found to increase with the increase of the print line width. Further, to improve the accuracy of simulations, the cavity porosity exists in the cellular structures was considered while revising the models. After modification, square cellular models compressed the least, followed by the circle and voronoi ones, which was consistent with the experimental results. Minimizing the print line width could reduce cavity porosity. Nonetheless, thinner print line width and smaller wood fiber size in filaments will likely increase manufacturing cost and difficulty.

In current work, h-BN powders were introduced into carbon fiber needle felt via powder addition in order to prepare chemical vapor infiltration (CVI) based C/C-BN composites. The microstructures and mechanical properties of as-prepared carbon/carbon (C/C) with 9 vol% of h-BN (C/C-BN9) were investigated in comparison to the pure C/C composites with same fiber architecture. The results indicated that the pyrolytic carbon (PyC) with higher degree of texture caused by h-BN in C/C-BN9 composites enhanced the interfacial bonding of PyC/fiber. Moreover, compared to C/C composites, the addition of h-BN resulted in smaller-sized PyC, leading to less and narrower microcracks in matrix. After introduction of h-BN into matrix, the flexural strength remained almost the same, while decreased impact toughness and more brittle fracture behavior were achieved in C/C-BN9 composites. However, the h-BN powders as addition could result in significantly enhanced compressive strength with higher isotropic stress-strain response in both vertical and parallel directions.

For the first time, ultrafast laser annealed BEOL gate-all-around (GAA) transistor and FeFET memory were demonstrated with monolithic 3D near-memory-computing (NMC) circuit. The GAA MOSFETs employing ultrafast picosecond visible laser dopant activation exhibit record-high Ion (nFETs=407 uA/um, pFETs=345 uA/um). The BEOL FeFETs memory exhibits large memory window ΔV th = 1.2V, more than 106 cycle endurance. Moreover, the 3D stackability of the GAA MOSFETs and FeFET memory bit cell enable reduces the area of the NMC circuitry and improve the readout throughput.

In this paper, we tune the terahertz (THz) optical and electrical properties of indium tin oxide (ITO) nano-thick film by rapid thermal annealing (RTA). Besides, thickness-dependent THz transmittance properties of as-deposited ITO thin film is investigated. The ITO film can be functioned as a THz reflective conductive electrodes by RTA at 600°C. THz power transmittance improved from 6 to 49 % at 0.2 THz by RTA at 800°C. Furthermore, we extracted complex refractive indices of as sputtered and annealed ITO films, and fitted the results with the Drude model. Additionally, the structural and morphological properties of ITO samples are presented.

In this work, we observed enhanced terahertz emission from the interface between indium tin oxide (ITO) and semi-insulating gallium arsenide (SI-GaAs) substrate. Further, we investigated the dependence of THz emission on pump power and angle of incident excitation beam. We found more than 3 times of THz emission power enhancement for incident angle below 70°. Besides, we found enhancement of THz radiation at low pump intensity and saturation with increasing peak excitation intensity beyond 20 TW/m2. The experimental results are well explained by plasmonic effects at the metal-semiconductor interface.

In this work, we analyzed silicon (Si) ion implanted semi-insulting gallium arsenide substrates (SI-GaAs) by using a terahertz time-domain spectroscopy (THz-TDS) system. The main goal is to determine the ion doping profile via a nondestructive approach by using THz-TDS spectroscopy. This approach will bring a new appliance to replace secondary ion mass spectroscopy (SIMS). For that, we have carried out the ion implantation experiment with an implantation energy of 200 keV at different doses. Then, we analyzed the THz-TDS experimental data of implanted SI-GaAs substrates by the Drude model to achieve depth-dependent dielectric and electrical properties at THz frequencies.

As a natural macromolecule-based biomaterial, fish gelatin is used in medical materials for its low pathogen infection risk. However, because of poor mechanical properties, its application has been limited. In this study, microcrystalline cellulose-reinforced fish gelatin (FG/MCC) composite films were prepared with a biological cross-linking agent (genipin) under ultrasonic treatment. SEM micrographs showed that the smooth microstructure of FG film became increasingly disordered with the addition of MCC. The infrared spectrum analysis (FTIR) demonstrated the existence of hydrogen bond interaction between MCC and FG. Compared with the pure FG film, the tensile strength (TS) and modulus of elasticity (MOE) of composite films with MCC were improved, and the elongation at break (EAB) and swelling ratios (SR) were decreased. Ultrasonic treatment could further improve TS, MOE, and SR. When the composite film was prepared with 15% MCC and treated with ultrasound, the TS and MOE increased by 115% and 227%, respectively, while the EAB decreased by 35% and the SR decreased by 4% in comparison with pure FG films. Thermo-gravimetric analysis (TGA) showed that the FG/MCC composite films were stable below 100 &deg, C. The above results indicate that the FG/MCC films have optimistic application prospects in the biomedical field.

We studied terahertz pulse generation by a photoconductive dipole antenna excited by noise-like pulses both theoretically and experimentally.

Amorphous silicon was crystallized using a blue ultrafast Ti:Sapphire laser system. Polysilicon with average grain size of 280 nm was achieved with fluence 30 of mJ/cm2 and overlapping of 93.75% at room temperature.

We present a simple, reliable, and fast method to automatically generate noise-like or mode-locked pulses in a fiber laser. To generate the targeted pulses, we employed two-photon-induced current from a photocell as the feedback signal to control a set of rotatable wave plates in the laser. The effectiveness of using the two-photon absorption signal to discriminate noise-like pulses from mode-locked pulses is theoretically analyzed and experimentally confirmed. We demonstrate our method by using a dispersion-mapped ytterbium-doped fiber ring laser with nonlinear polarization evolution that can generate either noise-like or mode-locked pulses. The average time to attain the prescribed pulses is within a few minutes.

A short multi-wavelength fiber Bragg grating (MW-FBG) fabrication method is proposed and demonstrated. The MW-FBG fabrication method includes making expanded core in the photosensitive single mode fiber (P-SMF) by the discharge-based thermal diffusion technique and writing FBGs on the pre-processed P-SMF through ultraviolet exposure technique. The effect of the arc discharge is to make the dopant in the core of the P-SMF diffuse to the cladding, which can reduce the refractive index of the core at the discharged region. As a result, a single exposure through one phase mask can produce a FBG with multiple resonant wavelengths. The strain and temperature responses of a two-wavelength FBG are experimentally investigated. Results show that the multiple wavelengths of the FBG have almost the same responses to the strain or temperature. The strain sensitivities of the two wavelengths of the FBG are 0.9025 pm/ μ e and 0.9101 pm/ μ e , respectively, and the temperature sensitivities are 10.55 pm/°C and 10.33 pm/°C, respectively. Such MW-FBGs have potential applications in the case of small size and high spatial resolution measurement.

Two-dimensional black phosphorus (BP) recently emerged as an outstanding material for optoelectronics and nanophotonics applications. In contrast to graphene, BP has a sufficiently large electronic bandgap and its high carrier mobility allows for efficient free-carrier absorption in the infrared and terahertz regimes. Here, we present a reflective structure to enhance the response of nanostructured monolayer BP at terahertz frequencies and investigate localized surface plasmon resonances in BP nanostrip arrays. Anisotropic absorption is observed in the proposed BP metamaterials due to the puckered crystal structure of the monolayer BP, and further investigations show that the plasmonic resonances are strongly depending on the geometric parameters of the nanostrips and the coupling between the adjacent nanostrips. We expect that the monolayer BP is an outstanding candidate of highly anisotropic plasmonic material for ultrascaled optoelectronic integration.

Biomineralization technology is a feasible and promising route to fabricate phosphate cathode materials with hierarchical nanostructure for high-performance lithium-ion batteries (LIBs). In this work, to improve the electrochemical performance of LiMn0.8Fe0.2PO4 (LMFP), hierarchical LMFP/carbon nanospheres are wrapped in situ with N-doped graphene nanoribbons (GNRs) via biomineralization by using yeast cells as the nucleating agent, self-assembly template, and carbon source. Such LMFP nanospheres are assembled by more fine nanocrystals with an average size of 18.3 nm. Moreover, the preferential crystal orientation along the [010] direction and certain antisite lattice defects can be identified in LMFP nanocrystals, which promote rapid diffusion of Li ions and generate more active sites for the electrochemical reaction. Moreover, such N-doped GNR networks, wrapped between LMFP/carbon nanospheres, are beneficial to the fast mobility of electrons and good penetration of the electrolyte. As expected, the as-p...

Blast furnace dust is a typical secondary resource produced in manufacturing iron. This substance contains many recyclable components, such as iron, lead, zinc, and carbon, which have not been properly utilized. Zinc is a dispersed component in blast furnace dust, but its volatility depends on its carrier minerals, such as hematite, coke, and silicate in descending order of zinc volatility. Volatilization is the necessary procedure of removing toxicity and recycling zinc from blast furnace dust. However, two critical limits exist: the amount of carbon in the residue and the amount of franklinite in the blast furnace dust. Zinc can be enclosed by the carbon grains according to kinetic analysis and energy dispersive spectrometer (EDS) tests. Therefore, the coke dosage should be controlled carefully to avoid carbon residue and increase the volatilization rate of zinc. Meanwhile, both franklinite and zincite are general zinc-bearing phases in the adopted dust, but neither can volatilize before being reduced to metallic form. Calculations show that the available reduction temperature of zincite is higher than that of franklinite. Nearly all the zinc in hematite and carbon is in the form of zincite and can be easily reduced in the heating process. However, the zinc in silicate mainly exists in the form of franklinite and is difficult to be reduced and volatilized, which explains the lower volatilization rate of zinc in silicate than in coke and hematite. In the last part of this investigation, the mineral phase and morphology of the volatiles obtained after fume reduction volatilization are tested for the first time to evaluate their potential application value. Only high-purity crystal zincite is found, which means that the volatiles can be used directly as high-grade zinc smelting materials without purification.

The dielectric constant, energy band parameters and ionicity are key physical parameters for fully understanding the dielectric properties of glasses, but their mutual interrelationship and its applicability to a wide variety of multi-component glasses have not yet been confirmed. We have applied the optical and THz spectroscopic characterization to a set of multi-component silicate oxide glasses incorporating vastly different additive components. The key physical parameters evaluated in the optical region have been interpreted consistently by the single oscillator based dielectric model. The bandgap energy (Eg) and ionicity parameter (Wemple and DiDomenico's β parameter) estimated in the optical region have shown reasonable correspondence, respectively, with the homopolar energy (Eh) and the polarization ionicity (IP) which are evaluated from the THz dielectric constant measurement. The comprehensive interrelation thus confirmed has provided simple rules between the physical parameters without limitation of glass compositions. For example, a tradeoff relation between the oscillator strength and characteristic resonance wavelength and a simple correlation between the dielectric constant and bandgap energy have been determined for the present set of multi-component glasses. The energy band parameters have been used for deriving the joint density of state diagrams, and characteristic physical/chemical nature has been identified to each glass.

Molecular dynamics simulations are used to study the boundary lubrication behaviors of squalane lubricant between two iron wall structures during shearing at different pressures and temperatures. Boundary lubrication models with a smooth iron wall and a nanostructured iron wall, respectively, are constructed, and the density distribution of the lubricating film and the velocity distribution in the shearing process are analyzed. The mechanical response of the solid wall is output, and the friction coefficient is calculated. A tribological test is performed with a UMT-2 tribometer under sliding conditions to evaluate the reliability of the simulation method. The results show that the surface nanostructure has a significant effect on the film thickness and delamination of the lubricating film but little effect on the velocity distribution of the lubricating film. The nano strip groove helps to reduce the friction coefficient of the boundary lubrication system.

Through a numerical study, we proposed and demonstrated that the one-dimensional periodic plasmonic-grooves (1D-PPG) can give rise to a super chiral field inside grooves under normal illumination with off-groove linear polarization. The handedness of the optical chirality of chiral field can be reversed by modifying the incident polarization angle from + 45° relative to groove's period direction to its mirror-symmetrical angle -45°. This makes possible a novel sensing scheme that utilize this polarization-dependent local chiral field for circular dichroism detecting; meanwhile, the dielectric environment-sensitive plasmonic resonance of 1D-PPG can be employed for refractive index sensing. This dual-sensing strategy offers great potential for low-cost chirality sensing for chiral molecules.

Graphene oxide (GO) was prepared by modified Hummer’s method, and reduced by solvothermal method using ethanol as the solvent and modified diethylene triamine (amine curing agent 593) as reducing agent and modifier. The effect of reduction time and temperature on the structure and conductive property of reduced graphene oxide (593-rGO) was investigated by SEM, FT-IR and XRD. The results show that the graphene modified by 593 is obviously improved in dispersibility and sedimentation stability in dichloromethane, as well as in conductivity. The optimal reduction processing is that the mass ratio of GO to 593 is 2:1, the reduction time and temperature is 6 h and 160°C, respectively.

We designed and fabricated bi-polar type photoconductive antenna (PCA) for efficient generation of broadband terahertz (THz) radiation. The falling time of overlayingly generated photocurrent from bi-polar PCA can achieve 200 fs via superimposing two primarily opposite polarity photocurrent pulses having falling time of 100 ps with time delay of 200 fs. The simulation results disclosed a possibility to shift the central frequency from 0.1 to 1.3 THz and enhance the THz power by twice in the range 1.5-3.3 THz by using low cost substrate with long carrier life time such as semi-insulating gallium arsenide (SI-GaAs).

Development of the wideband and tunable quasi-optic terahertz (THz) components is in high demand. In this work, we demonstrate a tunable achromatic quarter-wave plate (AQWP) for the THz frequency range. The phase retardation of this device can be set at 90° ± 9° from 0.20 to 0.50 THz. The operation range from 0.20 to 0.50 THz can be tuned to from 0.30 to 0.70 THz by introducing three nematic liquid crystals phase retarders, of which the birefringence can be magnetically tuned. The frequency-dependent phase retardation is in good agreement with theoretical predictions.

For this study, we demonstrated three different types of twisted nematic (TN) liquid crystal (LC) terahertz (THz) phase shifters using pristine poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT: PSS) thin films as transparent conducting electrodes (TCEs). The transmittance of spin-coated pristine PEDOT: PSS thin film was as high as 92% in the frequency range of 0.2&ndash, 1.2 THz. This is among the highest reported. Several TN-LC cells were constructed in a comparative study, which confirmed the reliability of pristine PEDOT: PSS as a TCE layer for THz phase shifter applications. The highest phase shift, required root-mean-square (RMS) driving voltage, and threshold voltage achieved by devices tested were 95.2&deg, at 1 THz, 7.2 VRMS, and 0.5 VRMS, respectively. The thickness of the LC layer for the phase shifter was 250 &micro, m, approximately half as thick as previous designs. In addition, the pristine PEDOT: PSS-based TN-LC phase shifter exhibited a figure-of-merit (FOM) value of approximately 6.65 degree&middot, dB&minus, 1&middot, V&minus, 1. This compared favorably with previously reported homogeneously aligned phase shifters with an FOM of 2.19 degree&middot, 1. Our results indicated that a twisted nematic LC cell with pristine PEDOT: PSS thin films as electrodes is a good combination for a THz phase shifter and wave plates as well as other LC-based THz devices.

We have investigated tunable terahertz (THz) phase shifters that are based on a sandwiched liquid crystal (LC) cell with indium&ndash, tin&ndash, oxide (ITO) nanowhiskers (NWhs) as transparent electrodes. More than 360&deg, of phase shift at 1.0 THz was achieved at a driving voltage as low as ~2.6 V (rms). This is approximately 40 times smaller than that reported in previous works using an electrically tuned LC device. Significance of the NWhs in reducing the required voltage is demonstrated. Overall transmittance of the device is as high as 30%, which is accountable by absorption losses of ITO NWhs, quartz substrate and LC. Experimental results are in good agreement with a theoretical formulism while taking into account super-thick LC cells (~1 mm) and pretilt angles. We also propose and demonstrate a novel THz technique for measuring pretilt angles of liquid crystals.

Phase shift exceeding 2π at 1.0 THz with high transmittance was achieved in liquid-crystal THz phase shifters of three different designs. Indium-tin-oxide nanowhiskers and graphene were employed as transparent electrodes. The driving voltage required for a 2π wave plate is as low as 5 Vrms.

Molecular dynamics (MD) simulations using the polymer consistent force field (PCFF) were adopted to investigate the pressure and thickness dependent density of squalane film in a nanogap at 373 K, with three different initial film thicknesses, and for a wide range of pressures. The equivalent densities predicted by MD simulations were compared with the empirical data. Results show that the squalane atoms tend to form layers parallel to the confining substrates but the orientations of squalane molecules are irregular throughout the film. In addition, distinct excluded volumes are not found at the interfaces of the film and substrates. Furthermore, with the same initial film thickness h0, the film thickness h and compressibility decrease with increasing pressure, but the compressibility is similar for films with different initial film thicknesses. The equivalent densities predicted by MD simulations with the maximum initial film thickness (9.44 nm) are accurate to the values of Tait equation. The MD simulation with adequate initial film thickness can accurately and conveniently predict the bulk densities of lubricants.

Heterogeneous nucleation is a frequently encountered phenomenon in the crystallization of inorganic nanoparticle/polymer systems, and has a great influence on the morphology and properties (such as optical, mechanical and degradable properties) of the nanocomposites. In this study, a solution casting method was adopted to fabricate CdSe–ZnS quantum dots (QDs)/poly(lactic acid) (PLA) nanocomposites films of various QDs concentrations by using chloroform as the solvent. Fourier transform infrared (FT-IR) spectroscopy, polarized optical microscopy (POM), differential scanning calorimetry (DSC), and X-ray diffractometry (XRD) were used to characterize the crystallization behavior of the nanocomposites films that had been thermally treated differently from the as-cast state. The FT-IR and POM results showed that the nucleation density and the crystallization ability of PLA are greatly enhanced with addition of the QDs in the processes of isothermal crystallization at 403 K. The results of DSC revealed that the glass transition temperature of PLA has no obvious change with the addition of QDs. For the QDs/PLA samples which were isothermally annealed at 403 K for 30 min, the degree of (melt) crystallinity increased with increase of QD concentrations in the PLA matrix. All the results obtained from FT-IR spectroscopy, POM, DSC, and XRD were consistent, suggesting that the CdSe–ZnS QDs can serve as an efficient heterogeneous nucleating agent for the acceleration and enhancement of the melt crystallization of PLA at the optimized condition.

The enhanced broadband THz radiation excited by pre-chirping the femtosecond pumping laser pulse is explored from a photoconductive antenna made by the low-temperature molecular-beam-epitaxy (LT-MBE) grown Gallium Arsenide (GaAs). Nearly 3-dB enlargement on peak amplitude of THz radiation accompanied with broadened bandwidth is achieved with positively chirped pulse excitation. The laser with short pulsewidth assists the broadening of THz bandwidth, whereas the peak intensity of THz relies strictly on lengthened carrier lifetime. The enhancement of high-frequency radiation components at low pumping intensity also indicates the nature of power dependence in such a coherently controlled process. When photocurrent saturation occurs in the LT-MBE-grown GaAs under high-power pumping condition, the clipping effect on peak amplitude of current pulse lengthens the duration of current surge effect. Both the peak intensity and the frequency spectrum of the generated THz pulse concurrently declines. The physical mechanism related to pre-chirped pulse excitation dependent carrier dynamics is proposed to elucidate the spectral response as well as the power dependence in such a coherently controlled THz radiation process.

The design, analysis, and demonstration of flip-chip bonding packaged uni-traveling-carrier photodiodes (UTC-PDs) with THz (dc to 315 GHz) 3-dB bandwidth and high-power performance are reported. The high-frequency roll-off (up to 0.4 THz) of the flip-chip bonding structure and device heating under high power operation are both minimized through properly downscaling the area of the bonding pad and minimizing the solder distance to the active area of the miniaturized UTC-PD. In order to suppress the serious space-charge screening effect in miniaturized UTC-PDs under high-current density (~180 kA/cm 2 ) operation, an n-type charge layer is inserted into the collector. The detailed dynamic measurement results of these packaged PD modules indicate that non-equilibrium electron transport plays an important role in determining the maximum speed and THz output power. In addition, a femtosecond (fs) optical pulse train generator with a ~300 fs pulse-width output and repetition rate up to ~0.3 THz is also developed to further boost the photo-generated THz-power. Compared with using an optical signal with a sinusoidal envelope for PD excitation, the short-pulse approach can offer a 3-dB enhancement in output power under the same output photocurrent and operating frequency (around 0.3 THz). By utilizing such an fs light source and our PD module, a continuous wave output power as high as 1 mW at an operating frequency of ~0.3 THz is successfully demonstrated.

Interest in asymmetric transmission (AT) at terahertz frequencies has increased dramatically in recent years. We present an all-silicon metamaterial to achieve the AT effect for linearly polarized electromagnetic waves in the terahertz regime. The metamaterial is constructed by rectangular silicon pillars and a thick silicon substrate. The magnetic Mie resonance excited by the incident polarized terahertz wave contributes to the AT effect, which is verified by the field distributions. In addition, the rotation angle and dimensions of the silicon pillars are shown to have a great influence on the AT efficiency. The proposed metamaterial with straightforward design has promising applications in polarization control scenarios.

Practicability of CsSnI3 has been limited by the lack of stability in humid environment. Here we calculated phase stability, the impact of H2O embedded in CsSnI3 and surface adsorption by the first-principles calculations. Total energy results show that γ-CsSnI3 and Y-CsSnI3 are more stable. However, the γ-CsSnI3 is hydrophilic-like and Y-CsSnI3 is hydrophobic-like. Further studies show that H2O tend to adsorb at the hollow sites on the (001) surface. The strong coupling between O and Cs atoms and hydrogen bonding render the deformation of (001) surface. These results are partially explained the phase instability of perovskites in air.

Near ultraviolet (λ ≈ 400 nm) femtosecond laser annealing (400 nm-FLA) in a scanning mode was employed to crystallize amorphous silicon (a-Si) films at room temperature. The average grain size of polycrystalline silicon annealed was studied as a function of the incident laser fluence and beam overlap or the number of laser shots irradiated. In general, the grain size can be enlarged by either increasing the beam overlap at a fixed laser fluence or increasing the laser fluence for a fixed number of laser shots. An apparent threshold for the onset of rapid enlargement of grain size was observed for processing at ∼90% overlap and fluences above 25 mJ/cm2. A maximum grain size of ∼280 nm was attained at a laser fluence of 30 mJ/cm2 and overlap of 93.75%, beyond which the grain size attained was smaller, and eventually, ablation was observed at an overlap of 97.5% and higher. These trends and observed surface morphology of annealed samples suggest that the crystallization mechanism is like sequential lateral solidification, similar to 800 nm-FLA and excimer laser annealing. Raman spectroscopic studies show that the degree of crystallization achieved with 400 nm-FLA is even higher than that of 800 nm-FLA. Cross-sectional scanning electron microscopic images indicate that the 100 nm-thick a-Si film is not fully crystallized. This can be explained by the much shorter penetration depth of 400 nm light than that of 800 nm light in a-Si.

Biomineralization is a green and skillful approach to prepare Li-rich layered oxides with hierarchical micro/nano structure as high-performance cathode for lithium-ion batteries. In this work, to e...

Terahertz time-domain spectroscopy was used to investigate the optical properties of oxyfluorosilicate glasses doped with neodymium (Nd3+) ions. The refractive indices and absorption coefficients of such glass samples were found to be ~3.7 and below 10 cm−1at 0.5 THz. Exhibiting high-refractive index and low loss, the Nd3+:Oxyfluorosilicate glasses are attractive for THs device applications.

We propose and demonstrate a liquid crystal (LC) based terahertz phase shifter with a thick ( $550 \ \mu \mathrm{m}$ in total) bi-Iayer LC cell structure incorporating a thin transparent polymeric intermediate layer. The present phase shifter exhibited remarkable performance improvement. The phase shift increased from 94° to 111° threshold and drive voltages decreased from 2.2 $\mathbf{V_{RMS}}$ to $\mathbf{1 V_{RMS}}$ and from $\mathbf{10 V_{RMS}}$ to $\mathbf{8.4 V_{RMM}}$ , respectively, in comparison with those for single-layer cell structure.

We demonstrate a liquid crystal based THz spatial light modulator (SLM). Indium tin oxide or gold finger type patterns were used for transparent (>70 % at 0.08 to 1.2 THz) conductor and self-cross polarizer. The phase shift and amplitude modulation achieved are greater than 90° and 30 % in broadband in THz frequency. This SLM could become a promising candidate for high speed THz imaging application via compress sensing algorithm

We report an automatic fiber laser system which can selectively generate mode-locked pulse (MLPs)or noise-like pulses (NLPs)using 3-dB optical bandwidth as the feedback signal.

Notothenioid fish and invertebrate samples from Antarctica were collected in the austral summer of 2009, and analyzed for persistent organic pollutants (POPs), including polycyclic aromatic hydrocarbons (PAHs), organochlorine pesticides (OCPs), and polybrominated diphenylethers (PBDEs), as well as δ13C and δ15N stable isotopes for trophic level determination. In this study, the POP levels in the Antarctic biota samples were found to be ranked in the following order: OCPs > PAHs >> PBDEs. The POP levels in notothenioid fish and krill correlate to trophic levels; however, the POP concentrations in intertidal benthic invertebrates are higher than in notothenioid fish implying that specific biogeochemical factors may affect bioaccumulation in the Antarctica ecosystem. Biomagnification of POPs may have a smaller role than bioconcentration in Antarctica environment. In addition to the source, transport, exposure, and absorption for each group of POPs in the short food chain in Antarctica, the biological variation among species, interaction habitats, diet and metabolism are also factors for future studies on contaminant bioaccumulation.