Enhanced thermoelectric performance of PEDOT: PSS films via ionic liquid post-treatment

Thermoelectric(TE)energy harvesting can effectively convert waste heat into electricity,which is a crucial technology to solve energy concerns.As a promising candidate for energy conversion,poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate)(PEDOT:PSS)has gained significant attention owing to its easy doping,high transparency,and solution processability.However,the TE performance of PEDOT:PSS still needs to be further enhanced.Herein,different approaches have been applied for tuning the TE properties:(i)direct dipping PEDOT:PSS thin films in ionic liquid;(ii)post-treatment of the films with concentrated sulfuric acid(H₂SO₄),and then dipping in ionic liquid.Besides,the same bis(trifluoromethanesulfonyl)amide(TFSI)anion and different cation salts,including 1-ethyl-3-methylimidazolium(EMIM+)and lithium(Li+),are selected to study the influence of varying cation types on the TE properties of PEDOT:PSS.The Seebeck coefficient and electrical conductivity of the PEDOT:PSS film treated with H2SO4EMIM:TFSI increase simultaneously,and the resulting maximum power factor is 46.7μW·m^-1·K^-2,which may be attributed to the ionic liquid facilitating the rearrangement of the molecular chain of PEDOT.The work provides a reference for the development of organic films with high TE properties.     

High power-added-efficiency AlGaN/GaN HEMTs fabricated by atomic level controlled etching

An atomic-level controlled etching(ACE)technology is invstigated for the fabrication of recessed gate AlGaN/GaN high-electron-mobility transistors(HEMTs)with high power added efficiency.We compare the recessed gate HEMTs with conventional etching(CE)based chlorine,Cl₂-only ACE and BCl³/Cl₂ACE,respectively.The mixed radicals of BCl₃/Cl₂were used as the active reactants in the step of chemical modification.For ensuring precise and controllable etching depth and low etching damage,the kinetic energy of argon ions was accurately controlled.These argon ions were used precisely to remove the chemical modified surface atomic layer.Compared to the HEMTs with CE,the characteristics of devices fabricated by ACE are significantly improved,which benefits from significant reduction of etching damage.For BCl₃/Cl₂ACE recessed HEMTs,the load pull test at 17 GHz shows a high power added efficiency(PAE)of 59.8%with an output power density of 1.6 W/mm at Vd=10 V,and a peak PAE of 44.8%with an output power density of 3.2 W/mm at Vd=20 V in a continuous-wave mode.     

Facile synthesis of monodispersed α-Fe2O3 microspheres through template-free hydrothermal route

Monodisperse α-Fe₂O₃ microspheres have been selectively synthesized through a facile hydrothermal method without the assistance of any surfactant, employing FeCl₃·6H₂O and NH₄NaHPO₄ as initial materials. The products were characterized by X-ray diffraction, scanning electron microscopy, and transmission electron microscopy. α-Fe₂O₃ microspheres with average size about 250 nm were constructed by single crystalline nanoparticles with average diameter about 15 nm. The investigation on the evolution formation revealed that growth temperature was critical to control the assembly of the fresh formed nanocrystallites, and the microsphere formation was proved to be the Ostwald ripening process by tracking the structures of the products at different growth temperature. α-Fe₂O₃ microspheres showed a weak ferromagnetic behavior with a remanent magnetization of 0.208 emu g⁻¹ and a coercivity of 1,034.27 Oe at room temperature.     

Preparation and characterization of spinel Li4Ti5O12 nanoparticles anode materials for lithium ion battery

Spinel Li₄Ti₅O₁₂ nanoparticles were prepared via a high-temperature solid-state reaction by adding the prepared cellulose to an aqueous dispersion of lithium salts and titanium dioxide. The precursors of Li₄Ti₅O₁₂ were characterized by thermogravimetry and differential scanning calorimetry. The obtained Li₄Ti₅O₁₂ nanoparticles were characterized using X-ray diffraction, transmission electron microscopy (TEM) and electrochemical measurements. The TEM revealed that the Li₄Ti₅O₁₂ prepared with cellulose is composed of nanoparticles with an average particle diameter of 20–30 nm. Galvanostatic battery testing showed that nano-sized Li₄Ti₅O₁₂ exhibit better electrochemical properties than submicro-sized Li₄Ti₅O₁₂ do especially at high current rates, which can deliver a reversible discharge capacity of 131 mAh g⁻¹ at the rate of 10 C, whereas that of the submicro-sized sample decreases to 25 mAh g⁻¹ at the same rate (10 C). Its reversible capacity is maintained at ~172.2 mAh g⁻¹ with the voltage range 1.0–3.0 V (vs. Li) at the current rate of 0.5 C for over 80 cycles.     

A1/Ti/4H-SiC Schottky barrier diodes with inhomogeneous barrier heights

This paper investigates the current-voltage （I-V） characteristics of Al/Ti/4H-SiC Schottky barrier diodes （SBDs） in the temperature range of 77 K-500 K, which shows that Al/Ti/4H SiC SBDs have good rectifying behaviour. An abnormal behaviour, in which the zero bias barrier height decreases while the ideality factor increases with decreasing temperature （T）, has been successfully interpreted by using thermionic emission theory with Gaussian distribution of the barrier heights due to the inhomogeneous barrier height at the A1/Ti/4H-SiC interface. The effective Richardson constant A＊ = 154 A/cm2 . K2 is determined by means of a modified Richardson plot In（I0/T2） - （qσ）2/2（κT）2 versus q/kT, which is very close to the theoretical value 146 A/cm2 · K2.     

TBT/CuPc复合薄膜的制备及能量/电荷转移研究

在4,7-二(4-三-苯胺基)-2,1,3-苯并噻二唑[4,7-bis(4-triphenylamino)-2,1,3-benzothiadiazole,TBT]和酞菁铜(copper phthalocyanine,CuPc)的混合硝基甲烷溶液中,采用质子化-共电沉积( PCD)的方法制备得到了TBT∶CuPc共混复合...     

Vectorial structure of far field of cylindrically polarized beams diffracted at a circular aperture

Based on the vector angular spectrum representation and the method of stationary phase, the analytical vectorial structure of the cylindrically polarized Laguerre-Gaussian beam diffracted at a circular aperture is derived in the far field, which provides an approach to further comprehend the vectorial properties of the apertured cylindrically polarized beams. The radially polarized, azimuthally polarized, and unapertured cases can be viewed as the special cases of our general result. The analyses show that the far-field energy flux distributions of the entire beam, the TE term, and the TM term depend on the beam order, the ratio of the waist width to the wavelength, the truncation parameter, and the angle between the electric field vector and the radial direction.     

Fabrication of silicon microwire arrays for?photovoltaic?applications

A?novel method of combining photolithography, wet chemical etching and oxidation process was proposed to fabricate large area of silicon microwire (SiMW) arrays. The dimensions of the SiMWs can be easily controlled by photomask and etching conditions. Solar cells based on the heterojunction between SiMW and double-walled carbon nanotubes (DWNTs) were constructed. The initial test on the DWNT/SiMW shows efficiency (??) of?0.59%. By adding a few drops of HBr/B₂ electrolyte, the efficiency was improved to 1.96% with J _sc=19.2?mA/cm² and V _oc=0.35?V, FF=29.2%, showing the potential of SiMWs in photovoltaic applications.     

Guided wave propagation in single and double layer hollow cylinders embedded in infinite media

Millions of miles of pipes are being used for the transportation, distribution, and local use of petroleum products, gas, water, and chemicals. Most of the pipes are buried in soil, leading to the significance of the study on the subject of guided wave propagation in pipes with soil influence. Previous investigations of ultrasonic guided wave propagation in an elastic hollow cylinder and in an elastic hollow cylinder coated with a viscoelastic material have led to the development of inspection techniques for bare and coated pipes. However, the lack of investigation on guided wave propagation in hollow cylinders embedded in infinite media like soil has hindered the development of pipe inspection methods. Therefore the influence of infinite media on wave propagation is explored in this paper. Dispersion curves and wave structures of both axisymmetric and nonaxisymmetric wave modes are developed. Due to the importance of the convergence of numerical calculations, the requirements of thickness and element number of the finite soil layer between hollow cylinder and infinite element layer are discussed, and an optimal combination is obtained in this paper. Wave structures are used for the mode identification in the non-monotonic region caused by the viscoelastic properties of coating and infinite media.     

Enhanced β Crystalline Phase in Poly(vinylidene fluoride) via the Incorporation of Graphene Oxide Sheets assisted by Supercritical CO2 Treatment

Graphene oxide (GO) sheets were pre-modified with a typical piezoelectric polymer, poly(vinylidene fluoride) (PVDF), using a simple supercritical carbon dioxide (SC CO₂) method, and then the PVDF-decorated GO was added into a PVDF matrix by solution blending. Transmission electron microscopy (TEM) revealed that the decorating degree of PVDF on the surface of the GO increased significantly with increasing of SC CO₂ pressure and PVDF concentration. The mechanism of the polymer adsorption on the GO sheets through favorable interaction between the GO and PVDF chains was identified via Fourier transform infrared spectroscopy (FTIR). Further, the crystallization behavior of PVDF/GO composites was investigated by differential scanning calorimetry (DSC), FTIR and polarized optical microscopy (POM). Interestingly, the composite with PVDF-decorated GO as the filler showed higher β-phase content compared to the composite with pristine GO as the filler. The study showed that the supercritical fluid-induced epitaxial crystallization process has significant potential for fabricating functional GO-based nanocomposties containing piezoelectric or conducting materials.