Surface doping manipulation of the insulating ground states in Ta_(2)Pd_(3)Te_(5) and Ta_(2)Ni_(3)Te_(5)

Manipulating emergent quantum phenomena is a key issue for understanding the underlying physics and contributing to possible applications.Here we study the evolution of insulating ground states of Ta_(2)Pu_(3)Te_(5) and Ta_(2)Ni_(3)Te_(5) under in-situ surface potassium deposition via angle-resolved photoemission spectroscopy.Our results confirm the excitonic insulator character of Ta_(2)d_(3)Te_(5).Upon surface doping,the size of its global gap decreases obviously.After a deposition time of more than 7 min,the potassium atoms induce a metal-insulator phase transition and make the system recover to a normal state.In contrast,our results show that the isostructural compound Ta_(2)Ni_(3)Te_(5) is a conventional insulator.The size of its global gap decreases upon surface doping,but persists positive throughout the doping process.Our results not only confirm the excitonic origin of the band gap in Ta_(2)Pd_(3)Te_(5),but also offer an effective method for designing functional quantum devices in the future.

A novel Ce_(0.485)Zr_(0.485)Y_(0.03)O_(2) composite oxide with surface doping of Y and its application in Pd-only three-way catalyst

The ceria-zirconia compound oxide-supported noble metal Pd(Pd@CZ)is widely used in three-way catalyst.Moreover,the surface structure of CZ plays an important role in catalytic activity of Pd.However,how to regulate the surface structure of CZ and clarify the structure–activity relationship is still a challenge.In this paper,a strategy is proposed to develop high activity Pd@CZ nanocatalysts by tuning Y doping sites in CZ.The precipitate-deposition method is developed to prepare the novel Ce_(0.485)Zr_(0.485)Y_(0.03)O_(2) composite with surface doping of Y(CZ-Y-S).In addition,the Pd@CZ-Y-S(Pd supported on CZ-Y-S)exhibits superior catalytic activity for HC,CO,and NO oxide,wherein,for CO and C_(3)H_(6) oxidation,the low-temperature activity of Pd@CZ-Y-S is still 20%higher than that of Pd@CZ-Y-B(Y bulk doping)and commercial Pd@CZ after 1000℃/4 h aging.The effect mechanism is further studied by density functional theory(DFT)calculation.Compared with Pd@CZ-Y-B,Pd@CZ-Y-S shows the lower CO oxide reaction energy barriers due to the weaker adsorption strength of O2.The Y surface doping strategy could provide valuable insights for the development of highly efficient Pd@CZ catalyst with extensive applications.

Surface Doping vs.Bulk Doping of Cathode Materials for Lithium-Ion Batteries:A Review

To address the capacity degradation,voltage fading,structural instability and adverse interface reactions in cathode materi-als of lithium-ion batteries(LIBs),numerous modification strategies have been developed,mainly including coating and doping.In particular,the important strategy of doping(surface doping and bulk doping)has been considered an effective strategy to modulate the crystal lattice structure of cathode materials.However,special insights into the mechanisms and effectiveness of the doping strategy,especially comparisons between surface doping and bulk doping in cathode materials,are still lacking.In this review,recent significant progress in surface doping and bulk doping strategies is demonstrated in detail by focusing on their inherent differences as well as effects on the structural stability,lithium-ion(Li-ion)diffusion and electrochemical properties of cathode materials from the following mechanistic insights:preventing the exposure of reactive Ni on the surface,stabilizing the Li slabs,mitigating the migration of transition metal(TM)ions,alleviating unde-sired structural transformations and adverse interface issues,enlarging the Li interslab spacing,forming three-dimensional(3D)Li-ion diffusion channels,and providing more active sites for the charge-transfer process.Moreover,insights into the correlation between the mechanisms of hybrid surface engineering strategies(doping and coating)and their influences on the electrochemical performance of cathode materials are provided by emphasizing the stabilization of the Li slabs,the enhancement of the surface chemical stability,and the alleviation of TM ion migration.Furthermore,the existing challenges and future perspectives in this promising field are indicated.

Fabrication of ion doped WO_3 photocatalysts through bulk and surface doping

Na＋doped WO3 nanowire photocatalysts were prepared by using post-treatment（surface doping） and in situ（bulk doping） doping methods. Photocatalytic degradation of Methyl Blue was tested under visible light irradiation, the results showed that 1 wt.% Na＋bulk-doped WO3 performed better, with higher photoactivity than surface-doped WO3. Photoelectrochemical characterization revealed the differences in the photocatalytic process for surface doping and bulk doping. Uniform bulk doping could generate more electron–hole pairs, while minimizing the chance of electron–hole recombination. Some bulk properties such as the bandgap, Fermi level and band position could also be adjusted by bulk doping, but not by surface doping.

Highly efficient modulation of the electronic properties of organic semiconductors by surface doping with 2D molecular crystals

Doping is a critically important strategy to modulate the properties of organic semiconductors(OSCs) to improve their optoelectrical performances. Conventional bulk doping involves the incorporation of foreign molecular species(i.e., dopants) into the lattice of the host OSCs, and thus disrupts the packing of the host OSCs and induces structural defects, which tends to reduce the mobility and(or) the on/off ratio in organic field-effect transistors(OFETs). In this article, we report a highly efficient and highly controllable surface doping strategy utilizing 2D molecular crystals(2DMCs) as dopants to boost the mobility and to modulate the threshold voltage of OFETs. The amount of dopants, i.e., the thickness of the 2DMCs, is controlled at monolayer precision, enabling fine tuning of the electrical properties of the OSCs at unprecedented accuracy. As a result, a prominent increase of the average mobility from 1.31 to 4.71 cm2 V-1 s-1 and a substantial reduction of the threshold voltage from -18.5 to -1.8 V are observed. Meanwhile, high on/off ratios of up to 108 are retained.

Surface electron doping induced double gap opening in T_(d)-WTe_(2)

By using scanning tunneling microscopy,we investigated the electronic evolution of T_(d)-WTe_(2) via in-situ surface alkali K atoms deposition.The T_(d)-WTe_(2) surface is electron doped upon K deposition,and as the K coverage increases,two gaps are sequentially opened near Fermi energy,which probably indicates that two phase transitions concomitantly occur during electron doping.The two gaps both show a dome-like dependence on the K coverage.While the bigger gap shows no prominent dependence on the magnetic field,the smaller one can be well suppressed and thus possibly corresponds to the superconducting transition.This work indicates that T_(d)-WTe_(2) exhibits rich quantum states closely related to the carrier concentration.

Surface charge transfer doping of graphene using a strong molecular dopant CN6-CP

Surface charge transfer doping of graphene plays an important role in graphene-based electronics due to its simplicity,high doping efficiency,and easy-controllability.Here,we demonstrate the effective surface charge transfer hole doping of graphene by using a strong p-type molecular dopant hexacyanotrimethylene-cyclopropane (CN6-CP).The CN6-CP exhibits a very high intrinsic work function of 6.37 e V,which facilitates remarkable electron transfer from graphene to CN6-CP as revealed by in situ photoelectron spectroscopy investigations.Consequently,hole accumulation appears in the graphene layer at the direct contact with CN6-CP.As evidenced by Hall effect measurements,the areal hole density of graphene significantly increased from 8.3×10^(12)cm^(-2) to 2.21×10^(13)cm^(-2) upon 6 nm CN6-CP evaporation.The CN6-CP acceptor with strong p-doping effect has great implications for both graphene-based and organic electronics.

Surface yttrium-doping induced by element segregation to suppress oxygen release in Li-rich layered oxide cathodes

Doping electrochemically inert elements in Li-rich layered oxide cathodes usually stabilizes the structure to improve electrochemical performance at the expense of available capacity.Here,we use an element segregation principle to realize a uniform surface doping without capacity sacrifice.On the basis of Hume-Rothery rule,element yttrium is chosen as a candidate dopant to spontaneously segregate at particle surface due to mismatched ionic size.Combined with X-ray photoelectron spectroscopy and electron energy loss spectroscopy mapping,yttrium is demonstrated uniformly distributed on particle surface.More importantly,a significant alleviation of oxygen release after surface doping is detected by operando differential electrochemical mass spectrometry.As a result,the modified sample exhibits improved reversibility of oxygen redox with 82.1%coulombic efficiency and excellent cycle performances with 84.15%capacity retention after 140 cycles.Postmortem analysis by transmission electron microscopy,Raman spectroscopy and X-ray diffraction reveal that the modified sample maintains the layered structure without a significant structure transformation after long cycles.This work provides an effective strategy with a series of elements to meet the industrial application.

Surface charge transfer doping for two-dimensional semiconductor-based electronic and optoelectronic devices

Doping of semiconductors,i.e.,accurately modulating the charge carrier type and concentration in a controllable manner,is a key technology foundation for modern electronics and optoelectronics.However,the conventional doping technologies widely utilized in silicon industry,such as ion implantation and thermal diffusion,always fail when applied to two-dimensional(2D)materials with atomically-thin nature.Surface charge transfer doping(SCTD)is emerging as an effective and non-destructive doping technique to provide reliable doping capability for 2D materials,in particular 2D semiconductors.Herein,we summarize the recent advances and developments on the SCTD of 2D semiconductors and its application in electronic and optoelectronic devices.The underlying mechanism of STCD processes on 2D semiconductors is briefly introduced.Its impact on tuning the fundamental properties of various 2D systems is highlighted.We particularly emphasize on the SCTD-enabled high-performance 2D functional devices.Finally,the challenges and opportunities for the future development of SCTD are discussed.

Tuning anionic redox activity to boost high-performance sodium-storage in low-cost Na_(0.67)Fe_(0.5)Mn_(0.5)O_(2) cathode

Na-based layered iron-manganese oxide Na_(0.67)Fe_(0.5)Mn_(0.5)O_(2) containing only low-cost elements is a promising cathode for Na-ion batteries used in large-scale energy storage systems.However,the poor cycle stability restricts its practical application.The capacity decay of Na_(0.67)Fe_(0.6)Mn_(0.5)O_(2) mainly originates from the irreversible anionic redox reaction charge compensation due to the high-level hybridization between oxygen and iron.Herein,we rationally design a surface Ti doping strategy to tune the anionic redox reaction activity of Na_(0.67)Fe_(0.5)Mn_(0.5)O_(2) and improve its Na-storage properties.The doped Ti ions not only enlarge the Na migration spacing layer but also improve the structure stability thanks to the strong Ti-O bond.More importantly,the d0-shell electronic structure of Ti^(4+) can suppress the charge transfer from the oxidized anions to cations,thus reducing the anionic redox reaction activity and enhancing the reversibility of charge compensation.The modified Na_(0.67)Fe_(0.5)Mn_(0.5)O_(2) cathode shows a reversible capacity of 198 mA h g^(-1) and an increased capacity retention from 15% to 73% after about1 month of cycling.Meanwhile,a superior Na-ion diffusion kinetics and rate capability are also observed.This work advances the commercialization process of Na-based layered iron-manganese oxide cathodes;on the other hand,the proposed modification strategy paves the way for the design of high-performance electrode materials relying on anionic redox reactions.

Garnet-type Solid-state Electrolyte Li7La3Zr2O12:Crystal Structure,Element Doping and Interface Strategies for Solid-state Lithium Batteries

The eetimous devedqpmaut et soid-ae elestrolyte(SSEs)has slimuliteal immese progres in the development of lllia stle batrierdA8S8s Particularly,grmestyped S8Es in fomula of Li7La3Zr2O12(LLZO)are under intesive invesigtion如eaplit their advantage im high lithium ious condaxtiriy(>1 mSicm)wide cletrochemical window(>5V),and good chenical electrochemical stability for lithium,which are critical factors to ensure a stabl,and high performance ASSBs.This review will focus on the challages related to LLZOs-based electrolyte,and update the recent developments in structurl design of LLZOs,which are disussed in three major sections;(i)crystal structure and the lithium-ion transport mechanismn of LLZ0;(ii)single-site and multi-ite doping of Li sites,La sites and Zr sites to enhance Li ions conductivity(LIC)and sability of LLZO;(iii)interface strategies between electrodes and LLZ0 to decrease inertaee re-pcife reistence(ASR).

Significantly enhanced of tungsten diselenide functionalization optoelectronic performance phototransistor via surface

Two-dimensional （2D） layered transition metal dichalcogenides （TMDs） have attracted enormous research interests and efforts towards the development of versatile electronic and optical devices, owing to their extraordinary and unique fundamental properties and remarkable prospects in nanoelectronic applications. Among the TMDs, tungsten diselenide （WSe2） exhibits tunable ambipolar transport characteristics and superior optical properties such as high quantum efficiency. Herein, we demonstrate significant enhancement in the device performance of WSe2 phototransistor by in situ surface functionalization with cesium carbonate （Cs2CO3）. WSe2 was found to be strongly doped with electrons after Cs2CO3 modification. The electron mobility of WSe2 increased by almost one order of magnitude after surface functionalization with 1.6-nm-thick Cs2CO3 decoration. Furthermore, the photocurrent of the WSe2-based phototransistor increased by nearly three orders of magnitude with the deposition of 1.6-nm-thick Cs2CO3. Characterizations by in situ photoelectron spectroscopy techniques confirmed the significant surface charge transfer occurring at the Cs2COB/WSe2 interface. Our findings coupled with the tunable nature of the surface transfer doping method establish WSe2 as a promising candidate for future 2D materials- based optoelectronic devices.

Thickness-dependent enhanced optoelectronic performance of surface charge transfer-doped ReS2 photodetectors

Surface charge transfer doping has been widely utilized to tune the electronic and optical properties of semiconductor photodetectors based on low-dimensional materials.Although many studies have been conducted on the performance(response time,responsivity,etc.)of doped photodetectors and their mechanisms,they merely examined a specific thickness and did not systematically explore the dependence of doping effects on the number of layers.This work performs a series of investigations on ReS_(2)photodetectors with different numbers of layers and demonstrates that the p-dopant tetrafluorotetracyanoquinodimethane(F_(4)-TCNQ)converts the deep trap states into recombination centers for few-layer ReS_(2)and induces a vertical p-n junction for thicker ReS_(2).A response time of 200 ms is observed in the decorated 2-layer ReS_(2)photodetector,more than two orders of magnitude faster than the response of the pristine photodetector,due to the disappearance of deep trap states.A current rectification ratio of 30 in the F_(4)-TCNQ-decorated sandwiched ReS_(2)device demonstrates the formation of a vertical p-n junction in a thicker ReS_(2)device.The responsivity is as high as 2,000 A/W owing to the strong carrier separation of the p-n junction.Different thicknesses of ReS_(2)enable switching of the prominent operating mechanism between transforming deep trap states into recombination centers and forming a vertical p-n junction.The thicknessdependent doping effect of a two-dimensional material serves as a new mechanism and provides a scheme toward improving the performance of other semiconductor devices,especially optical and electronic devices based on low-dimensional materials.

Improved dual-channel 4H-SiC MESFETs with high doped n-type surface layers and step-gate structure

An improved dual-channel 4H-SiC MESFET with high doped n-type surface layer and step-gate structure is proposed, and the static and dynamic electrical performances are analyzed.A high doped n-type surface layer is applied to obtain a low source parasitic series resistance, while the step-gate structure is utilized to reduce the gate capacitance by the elimination of the depletion layer extension near the gate edge, thereby improving the RF characteristics and still maintaining a high breakdown voltage and a large drain current in comparison with the published SiC MESFETs with a dual-channel layer.Detailed numerical simulations demonstrate that the gate-to-drain capacitance, the gate-to-source capacitance, and the source parasitic series resistance of the proposed structure are about 4%, 7%, and 18% smaller than those of the dual-channel structure, which is responsible for 1.4 and 6 GHz improvements in the cut-off frequency and the maximum oscillation frequency.

Tune the photoresponse of monolayer MoS_(2) by decorating CsPbBr_(3) perovskite nanoparticles

Tuning the photoresponse of monolayer MoS_(2) could extend its potential application in many fields,however,it is still a challenge.In this study,CsPbBr_(3) nanoparticles were prepared and spin-coated on the surface of monolayer MoS_(2) to fabricate hybrid CsPbBr_(3)/MoS_(2) photodetectors.By combing the photoelectrical property of the CsPbBr_(3),the synergistic effect has been systematically studied from its carrier mobility,photoresponse and detectivity.It was found that nanofilm-coating of CsPbBr_(3)would impede the photoelectric performance due to the electron-hole recombination facilitated by the defects at the interface of C PbBr_(3) and MoS_(2) films.While the nanoparticles decorating was observed to significantly improve the conductivity of the monolayer Mo S_(2),which also increased the on/off ratio of the MoS_(2) transistor from 8.2×10~3 to 4.4×10^(4),and enhanced the carrier mobility from 0.090 cm^(2)V^(-1)s^(-1)to 0.202 cm^(2)V^(-1)s^(-1),ascribing to a mixed electron recombination-injection process.Furthermore,the CsPbBr_(3) nanofilm would decrease the responsivity to 136 and 178 A/W under the light wavelength of 400 and 500 nm,respectively,while decorating CsPbBr_(3) nanoparticles improve the photoresponse to 948 and 883 A/W with the detectivity at the level of 10^(11)Jones.This work may provide an easy and cost-efficient way to tune the photoresponse of MoS_(2) photodetectors.

Acetate-assistant efficient cation-exchange of halide perovskite nanocrystals to boost the photocatalytic CO_(2) reduction

The judicious implantation of active metal cations into the surface of semiconductor nanocrystal(NC)through cation-exchange is one of the facile and viable strategies to enhance the activity of catalysts for photocatalytic CO_(2)reduction,by shortening the transfer pathway of photogenerated carriers and increasing the active sites simultaneously.However,cation-exchange is hard to achieve for halide perovskite NCs owing to the stable octahedron of[PbX6]4−with strong interaction between halogen and lead.Herein,we report a facile method to overcome this obstacle by replacing partial Br−with acetate(Ac−)to generate CsPbBr_(3) NC(coded as CsPbBr_(3−x)Ac_(x)).A small amount of Ac−instead of Br−does not change the crystal structure of halide perovskite.Owing to the weaker interaction between acetate and lead in comparison with bromide,the corresponding octahedron structure containing acetate in CsPbBr_(3−x)Ac_(x) can be easily opened to realize efficient cation-exchange with Ni^(2+) ions.The resulting high loading amount of Ni^(2+) as active site endows CsPbBr_(3−x)Ac_(x) with an improved performance for photocatalytic CO_(2)reduction under visible light irradiation,exhibiting a significantly increased CO yield of 44.09μmol·g^(−1)·h^(−1),which is over 8 and 3 times higher than those of traditional pristine CsPbBr_(3) and nickel doped CsPbBr_(3) NC,respectively.This work provides a critical solution for the efficient metal doping of low-cost halide perovskite NCs to enhance their photocatalytic activity,promoting their practical applications in the field of photocatalysis.

Hydrothermal fabrication of selectively doped organic assisted advanced ZnO nanomaterial for solar driven photocatalysis

Hydrothermal fabrication of selectively doped（Ag＋＋ Pd3＋） advanced ZnO nanomaterial has been carried out under mild pressure temperature conditions（autogeneous; 150°C）.Gluconic acid has been used as a surface modifier to effectively control the particle size and morphology of these ZnO nanoparticles. The experimental parameters were tuned to achieve optimum conditions for the synthesis of selectively doped ZnO nanomaterials with an experimental duration of 4 hr. These selectively doped ZnO nanoparticles were characterized using powder X-ray diffraction（XRD）, Fourier transform infrared spectroscopy（FT-IR）, UV–Vis spectroscopy and scanning electron microscopy（SEM）. The solar driven photocatalytic studies have been carried out for organic dyes, i.e., Procion MX-5B dye,Cibacron Brilliant Yellow dye, Indigo Carmine dye, separately and all three mixed, by using gluconic acid modified selectively doped advanced ZnO nanomaterial. The influence of catalyst, its concentration and initial dye concentration resulted in the photocatalytic efficiency of 89% under daylight.