General theory for designing phonon transport in alloyed/doped materials

Alloying/doping is a widely used technique for improving the electrical,mechanical,and optical properties of materials.However,this technology induces significant distortions in the lattice structure,mass distribution,and potential field,greatly enhancing phonon scattering.Here,we introduce the concept of alloying/doping path and employ crystal symmetry,lattice deformation,and electron distribution to characterize it.Based on this new concept,the phonon thermal transport behavior in alloyed/doped materials can be well designed,and along different alloying/doping paths,the difference in thermal conductivity can be up to 45 times.On one hand,strategic alloying/doping that combines high crystal symmetry,large lattice contraction,and the same electron distribution suppresses phonon-phonon scattering phase space,induces phonon stiffening,and bolsters electronic structure symmetry,respectively.These synergistic effects significantly improve thermal conductivity.On the other hand,random alloying/doping has a low symmetry,leading to the typical“U”shape of alloying/doping level-dependent thermal conductivity.Our theory is corroborated in three-dimensional(3D)Si,2D MoS_(2),and quasi-1D TiS_(3),affirming its efficacy and broad applicability in controlling phonon transport.

Design and analysis of doped left-handed materials

We devise three sorts of doped left-handed materials （DLHMs） by introducing inductors and capacitors into the traditional left-handed material （LHM） as heterogeneous elements. Some new properties are presented through finitedifference time-domain （FDTD） simulations. On the one hand, the resonance in the traditional LHM is weakened and the original pass band is narrowed by introducing inductors. On the other hand, the original pass band of the LHM can be shifted and a new pass band can be generated by introducing capacitors. When capacitors and inductors are introduced simultaneously, the resonance of traditional LHM is somewhat weakened and the number of original pass bands as well as its bandwidth can be changed.

Developing Suitable Sensitive Compound Semiconductor Materials Doped by Transition Metals for Occupational Thermoluminescence Dosimetry

The essential objective of radiation dosimetry is to develop suitable sensitive materials for different measurements in radiation fields. Our exploration is to find potentially suitable high gamma radiation dosimeters in the range from 0.5E4 to 1.5E4 Gy. Gamma rays source (60Co, 136 Gy/min) has been used. Many compound semiconductor materials were prepared and investigated. Thermoluminescence (TL) glow curve was analyzed into its component by analytical segregation program using computerized glow curve deconvolution (CGCD). Three zero dose readings for non-irradiated powders of the materials have been taken as lower limit of detection. The results indicated that some of the tested materials have exhibited TL linearly with respect to dose. In addition, dose response of these materials was found to be useful for high radiation dosimetry. Glow curve structures exhibited several peaks corresponding to the various energies of the emptied traps. Variation in the standard deviation for reusability cycles has been ten readout. The fading at ambient temperature was studied up to 60 days which reached a relative stability (~1.5% for all), 10 days after irradiation. A typical glow curve of CoPa which irradiated with 1.5E4 Gy was analyzed. Characterizations of tested materials indicated that crystals of ZnLa:Li, ZnLa:Cd, and ZnLa:Cr have stable and increasing thermoluminescent responses with high gamma radiation dose range. Special glow peaks can be used as estimators for absorbed doses as well as re-estimation for time elapsed exposures.

Spectroscopic study of the Pr-doped BiBO glass and Ca_4GdO(BO_3)_3 single crystals

Detailed spectroscopic studies of Pr3＋ ions in BiBO glass and Ca4GdO（BO3）3 crystal were performed. Experimental absorption spectra were measured at room temperature and assigned. The first principles discrete variational multielectron method was used to model the polarized absorption spectra of the Ca2GdO（BO3）3：Pr3＋; without any fitting parameters, the overall appearance of the spectra was reproduced satisfactorily. The energy intervals between different molecular orbitals in the [PrO6] cluster were estimated. The conventional Judd-Ofelt theory was used to calculate the oscillator strengths of the 4f-4f transitions in the BiBO：Pr3＋ system; the set of the phenomenological intensity parameters was determined.

Internalization of Foreign Ions into Meta-stable Lattices:a Case Study of Transition-metal-doped Brookite

The connections between the building units of meta-stable lattice were generally considered to be easily disturbed during the doping process, causing serious hindrances blocking the development of functional doped materials. In this work, the synthesis of doped brookite, a typical meta-stable phase of TiO2, has been explored novelly by in-situ adding of cations of VIIIB and IB,IIB elements in the 3rd period（Fe, Co, Ni, Cu, Zn） during the urea-lactate aided low-basicity hydrothermal process. The results showed that only Cu-doped brookite could be successfully synthesized with trace amount of copper intensively internalized into the brookite lattice, while the other dopants lead to the formation of anatase TiO2. Extensive characterizations indicated a two-step doping process, where copper ions were firstly dispersed in an amorphous layer on the lattice surface and then they were internalized into brookite lattice. Cu-doped brookite exhibited significantly enhanced photocatalytic activity in the phenol degradation under visible light compared to bare brookite. The enhancement of catalytic performance was assigned to the impurity band gap and the reduction of charge carriers＇ recombination introduced by the internalization of Cu ions. The investigation reported herein contributes to the understanding of complex ion-doping effects on the structures of meta-stable materials, and provides hints for obtaining other functional doped materials.

Rare Earth Doped Optical Fibers for Temperature Sensing Utilizing Ratio-Based Technology

A new and practical fluorescence temperature detecting system based on fluorescence intensity ratio was proposed . The background theory of fluorescence intensity-ratio method was presented simply. And the characters of rare earth doped samples were detailed. The erbium-doped fiber was chosen as the sensing element. The energy levels of 2H11/2 and 4S3/2 are responsible for the emission of radiation at approximately 530 and 555 nm. The erbium-doped (960 ppm) fiber of length 20 cm and core diameter 3.2μm was used as the sensing part. A silica photodiode transfers the fluorescence signal to electric signal, then the ratio of the average of the two different signals was calculated by the computer and the temperature was obtained. The ratio R of the intensity resulting from the transition between the two levels varies proportionly with temperature interval from 293 K to 373 K. The sensitivity of the sensor is approximately 0.05 K-1.

Synergetic effect of nitrogen‐doped carbon catalysts for high‐efficiency electrochemical CO_(2) reduction

The use of carbon‐based materials is an appealing strategy to solve the issue of excessive CO_(2) emis‐sions.In particular,metal‐free nitrogen‐doped carbon materials(mf‐NCs)have the advantages of convenient synthesis,cost‐effectiveness,and high conductivity and are ideal electrocatalysts for the CO_(2) reduction reaction(CO_(2)RR).However,the unclear identification of the active N sites and the low intrinsic activity of mf‐NCs hinder the further development of high‐performance CO_(2)RR electrocat‐alysts.Achieving precise control over the synthesis of mf‐NC catalysts with well‐defined active N‐species sites is still challenging.To this end,we adopted a facile synthesis method to construct a set of mf‐NCs as robust catalysts for CO_(2)RR.The resulting best‐performing catalyst obtained a Far‐adaic efficiency of CO of approximately 90%at−0.55 V(vs.reversible hydrogen electrode)and good stability.The electrocatalytic performance and in situ attenuated total reflectance surface‐enhanced infrared absorption spectroscopy measurements collectively revealed that graphitic and pyridinic N can synergistically adsorb CO_(2) and H_(2)O and thus promote CO_(2) activation and protonation.

Comparison of GaN/AlGaN/AlN/GaN HEMTs Grown on Sapphire with Fe-Modulation-Doped and Unintentionally Doped GaN Buffer:Material Growth and Device Fabrication

AlGaN/GaN high electron mobility transistors （HEMTs） grown on Fe-modulation-doped （MD） and unintentionally doped （UID） GaN buffer layers are investigated and compared. Highly resistive GaN buffers （10^9Ω·cm） are induced by individual mechanisms for the electron traps＇ formation： the Fe MD buffer （sample A） and the UID buffer with high density of edge-type dislocations （7.24×10^9cm^-2, sample B）. The 300K Hall test indicates that the mobility of sample A with Fe doping （2503cm^2V^-1s^-1） is much higher than sample B （1926cm^2V^-1s^-1） due to the decreased scattering effect on the two-dimensional electron gas. HEMT devices are fabricated on the two samples and pulsed I–V measurements are conducted. Device A shows better gate pinch-off characteristics and a higher threshold voltage （-2.63V） compared with device B （-3.71V）. Lower gate leakage current ｜IGS｜ of device A （3.32×10^-7A） is present compared with that of device B （8.29×10^-7A）. When the off-state quiescent points Q_2 （V GQ2=-8V, V DQ2=0V） are on, V th hardly shifts for device A while device B shows ＋0.21V positive threshold voltage shift, resulting from the existence of electron traps associated with the dislocations in the UID-GaN buffer layer under the gate. Under pulsed I–V and transconductance G m–V GS measurement, the device with the Fe MD-doped buffer shows more potential in improving reliability upon off-state stress.

Photoelectric Property of Polyaniline Doped with Organic Sulphonic Acid

Photoelectric property of polyaniline doped with dodecyl-benzene sulphonic acid (DBSA) is studied. The result shows that the concentration of carrier increases obviously, when polyaniline doped with DBSA is irradiated with light. Mixture of sensitive material is advantageous to the absorption of polyaniline in visible light spectrum, and the conductivity is also improved. The results of dielectric measurements on polyaniline doped with DBSA in an Al-PAn-DBSA-Al configuration as function of frequency and temperature are reported. The space-charge polarization phenomenon is observed. Carrier lifetime is microsecond magnitude and mobility is (0.001～0.1) cm 2/V·s, which are obtained by calculation or experiment. The active energy is obtained from the relation between conductivity and temperature. The conducting mechanism of PAn-DBSA is analyzed.

Preparation and upconversion luminescence of YVO_4:Er^(3+),Yb^(3+)

YVO4：Er^3＋,Yb^3＋ with varying Yb^3＋ concentrations were prepared by a precipitation method.The results of X-ray diffraction （XRD） show that all the samples have a tetragonal zircon structure; the calculated average crystallite sizes are in the range of 14-22 nm.The lattice constants and cell volume of the samples decrease slightly with the increase in Yb^3＋ concentration.The upconversion luminescence spectra of all the samples were studied under 980 nm laser excitation.The strong green emission is observed,which is attributed to the 2^H11/2→4I15/2 and 4^S3/2→4^I15/2 transitions of Er^3＋,and the red emission peaks in 650-675 nm can be ignored.The emission intensity for the sample depends on the Yb^3＋concentration.These results reveal that the upconversion processes of YVO4：Er^3＋,Yb^3＋ are related to the structure and the doping Yb^3＋ concentration of the sample.

Transition metal-nitrogen sites for electrochemical carbon dioxide reduction reaction

Electrochemical CO2 reduction reaction(CO2RR)powered by renewable electricity has emerged as the most promising technique for CO2 conversion,making it possible to realize a carbon‐neutral cycle.Highly efficient,robust,and cost‐effective catalysts are highly demanded for the near‐future practical applications of CO2RR.Previous studies on atomically dispersed metal‐nitrogen(M‐Nx)sites constituted of earth abundant elements with maximum atom‐utilization efficiency have demonstrated their performance towards CO2RR.This review summarizes recent advances on a variety of M‐Nx sites‐containing transition metal‐centered macrocyclic complexes,metal organic frameworks,and M‐Nx‐doped carbon materials for efficient CO2RR,including both experimental and theoretical studies.The roles of metal centers,coordinated ligands,and conductive supports on the intrinsic activity and selectivity,together with the importance of reaction conditions for improved performance are discussed.The mechanisms of CO2RR over these M‐Nx‐containing materials are presented to provide useful guidance for the rational design of efficient catalysts towards CO2RR.

Synthesis and Electrochemical Characterization of Azomethine Containing N-Ethylcarbazole Group

Conjugated aromatic azomethines containing a carbazole group were synthesized. Their structures have been confirmed by IR, MS and UV spectrometries. When iodine was used as the dope to the conjugated compounds, the electrical conductivities （EC） of the doped conjugated compounds were increased by several orders of magnitude. The thermal stability of these two compounds investigated by TGA shows a good result, which guarantees the correct result of EC when the compounds are heated. As can be seen from the CV characterization of the electrochemical properties of these two compounds, the azomethine diamine and p-aminophenyl-9-ethylcarbazolyl azomethine possess electrochemical activity, which arises from the heteroatom of molecules.

Synthesis and Electrical Properties of La_ 0.8Sr_(0.2)-x Ca_xCo_(0.9)Fe_ 0.1O_3-δ

Effects of small amount of Ca doping in La site in LaCoO 3-based oxide on th e synthesis and electrical conductivity were investigated by using X-ray diffra ction (XRD), differential scanning calorimetry and thermogravimetry (DSC/TG), or dinary four-probe dc measurement methods. La 0.8Sr 0.2-xCa x Co 0.9Fe 0.1O 3-δ (LSCCF, 0≤x≤0.1) prepared by solid r eact ion synthesis is all of a single phase and the calcined process may be divided i nt o three stages: (1) decomposition of reactants; (2) formation of LaCoO 3-based oxides; and (3) formation of LSCCF solid solution. The maximum of electrical co nductivity of the LSCCF composites is above 100 S·cm -1 and the co nduction me chanism is attributed to the adiabatic-hopping of p-type small polarons.

Oxygenated boron-doped carbon via polymer dehalogenation as an electrocatalyst for high-efficiency O_(2)reduction to H_(2)O_(2)

The direct electrochemical synthesis of H_(2)O_(2)from O_(2)is currently the most promising alternative to energyintensive industrial anthraquinone oxidation/reduction methods. However, its widespread use is hampered by the lack of efficient low-cost electrocatalysts. In the current study,oxygenated boron-doped carbon(O-BC) materials were realized via a green synthetic strategy involving polymer dehalogenation and employed as electrode materials for the electrochemical synthesis of H_(2)O_(2)via a 2 e-oxygen reduction.The catalytic activity of the O-BC materials was optimized through systematic variation of the boron source(H_(2)BO_(2))dosage and annealing temperature. Electrochemical measurements revealed that the optimal sample(O-BC-2-650)exhibited a selectivity of 98% for the 2 e-oxygen reduction to H2 O_(2)and an average H_(2)O_(2)production rate of412.8 mmol g_(cat)^(-1) h^(-1)in an H-type alkaline electrolyzer. Density functional theory simulations indicated that the functionalization of active B sites with one oxygen atom provides the lowest Gibbs free energy change(ΔG) of 0.03 e V for the hydrogenation of*O_(2), while functionalization with zero or two O atoms results in much larger ΔG values(0.08 and 0.10 e V,respectively). Thus, this work details a new type of green, lowcost, and metal-free electrocatalyst for H_(2)O_(2)production.

Highly nitrogen and sulfur dual-doped carbon microspheres for supercapacitors

Heteroatom doping, especially dual-doped carbon materials have attracted much attention for the past few years, and have been regarded as one of the most efficient strategies to enhance the capacitance behavior of porous carbon materials. In this work, a facile two-step synthetic route was developed to fab- ricate nitrogen and sulfur co-doped carbon microsphere （NSCM） by using thiourea as dopant. The NJS doping content is controlled via varying the carbonization temperature. It has been proved that a suitable quantity of N and S groups could not only provide pseudo-capacitance but also promote the electron transfer for carbon materials, which ensures the further utilization of the exposed surfaces for charge storage. The optimized NSCM prepared at a carbonization temperature of 800 ℃ （NSCM-800） achieves a capacitance of 277.1 F g^-1 at a current density of 0.3 A g^-1 in 6.0 mol L^-1 KOH electrolyte, which is 71% higher than that of undoped carbon microsphere. Besides, NSCM-800 shows an excellent cycling stability, 98.2% of the initial capacitance is retained after 5,000 cvcles at a current densitv of 3.0 A g^-1.

Characterization and Electrochemical Properties of Nanostructured Zr-Doped Anatase TiO_2 Tubes Synthesized by Sol–Gel Template Route

A series of nanostructured Zr-doped anatase TiO_2 tubes with the Zr/Ti molar ratio of 0.01, 0.02, 0.03, and0.09 were prepared by a sol–gel technology on a carbon fiber template. The electrochemical performance of Zr-doped anatase TiO_2 as anodes for rechargeable lithium batteries was investigated and compared with undoped titania. Tests represented that after 35-fold charge/discharge cycling at C/10 the reversible capacity of Zr-doped titania（Zr/Ti = 0.03） reaches 135 m A h g^（-1）, while the capacity of undoped titania（Zr/Ti = 0） yielded only 50 m A h g^（-1）. Based on the results of the physicochemical investigation, three reasons of improving electrochemical performance of Zr-doped titania were suggested. According to the scanning electron microscopy and transmission electron microscopy, Zr^（4＋） doping induces a decrease in nanoparticle size, which facilitates the Li＋diffusion. The Raman investigations show the more open structure of Zr-doped TiO_2 as compared to undoped titania due to changing of the unit cell parameters, that significantly affects on the reversibility of the insertion/extraction process. The electrochemical impedance spectroscopy results indicate that substitution of Zr^（4＋） for Ti^（4＋） into anatase TiO_2 has favorable effects on the conductivity.

Black-phosphorus-based materials for application in solar cells

In the context of green development,the use of solar cells with renewable and environment-friendly characteristics has been rapidly growing.There has been a continuous search for materials that can enhance their performance.Black phosphorus,a new type of semiconductor material,has garnered significant attention due to its distinctive properties,particularly its direct band gap with tunable layers and high optoelectronic efficiency.This review summarizes the properties of black-phosphorus-based materials and focuses on their use as doping materials in various components of solar cells,such as the electron transport layer,hole transport layer,active layer,etc.The current challenges faced by black phosphorus materials and outlook on their future development have also been discussed.

High performance nonvolatile organic field-effect transistor memory devices based on pyrene diimide derivative

Developing high-quality electret layer is important for the fabrication of highperformance nonvolatile organic field effect transistor memory devices(OFETNVMs).In this work,three representative aromatic diimide frameworks are employed for comparative studies as n-type doping materials for the electret layers in OFET-NVMs,which are naphthalene diimide(NDI),perylene diimide(PDI),and pyrene diimide(PyDI).When blended with polystyrene(PS)to prepare the electret layers,all the memory devices containing aromatic diimide dopants exhibited significantly improved performances compared with the undoped counterparts,indicating that low-lying LUMO energy levels of these dopants are beneficial for charge injection.All the devices with n-type dopants exhibited long retention times(more than 104 s)and good switching reliability in more than 400 continuous write-read-erase-read cycles.Among them,the PyDI-based memory device exhibited superior performance compared with other aromatic diimides,which achieved a memory window of 34.0 V,a trapping charge density of 1.98×1012 cm−2 along with an on/off ratio higher than 104.This work indicates that PyDI framework could be a new platform for the future design of n-type dopant for high-performance nonvolatile organic field-effect transistor memory devices.