Light Doping Research Articles

High Carrier Mobility and Promising Thermoelectric Module Performance of N-Type PbSe Crystals.

The scarcity of Te hampers the widespread use of Bi2Te3-based thermoelectric modules. Here, the thermoelectric module potential of PbSe is investigated by improving its carrier mobility. Initially, large PbSe crystals are grown with the temperature gradient method to mitigate grain boundary effects on carrier transport. Subsequently, light doping with <1mole‰ halogens (Cl/Br/I) increases room-temperature carrier mobility to ~1600cm2V-1s-1, achieved by reducing carrier concentration compared to traditional heavy doping. Crystal growth design and light doping enhance carrier mobility without affecting effective mass, resulting in a high power factor ~40µWcm-1K-2 in PbSe-Cl/Br/I crystals at 300K. Additionally, Cl/Br/I doping reduces thermal conductivity and bipolar diffusion, leading to significantly lower thermal conductivity at high temperature. Enhanced carrier mobility and suppressed bipolar effect boost ZT values across the entire temperature range in n-type PbSe-Cl/Br/I crystals. Specifically, ZT values of PbSe-Br crystal reach ~0.6 at 300K, ~1.2 at 773K, and the average ZT (ZTave) reaches ~1.0 at 300-773K. Ultimately, ~5.8% power generation efficiency in a PbSe single leg with a maximum temperature cooling difference of 40K with 7-pair modules is achieved. These results indicate the potential for cost-effective and high-performance thermoelectric cooling modules based on PbSe.

Highly efficient (V2O5)0.91Zn0.09 powdered catalyst for water organic pollutant elimination

(V2O5)1-x Znx powdered samples with different light doping levels (x = 0.03–0.09) were prepared by a solid-state thermal reaction and studied by X-ray diffraction (XRD), field emission scanning electron microscope (FE-SEM), energy dispersive analysis (EDAX), and optical diffuse reflectance spectroscopies. The prepared samples has been revealed that the increments in Zn-doping levels accompanied by vacuum heat treatment lead to the appearance of an additional V12O26 phase beside the pure V2O5 oxide, resulting not only in more donor vanadium atom liberation but also in multi-heterojunction component formation. Besides, Eg values decrease from 2.38 to 2.2 eV as Zn doping increases from x = 0 to x = 0.09. All previous observations improve the process of purifying water from pollutants by increasing the number of free carriers of V2O5 powder by adding Zn atoms and making vacuum heat treatments. The photocatalytic examination has been carried out using constants of 0.5 g and 0.01 g/L (10 ppm) of the catalyst quantity and MB-dye concentration, respectively, under Vis – irradiations. The acidic solution medium with a pH of 2 strongly motivated the degradation activity. The highest catalytic efficiency of 99.78% was attained by the (V2O5)0.91 Zn 0.09 compound within a time of 70 min and continued invariably for 5 hours in the dark. These catalytic results have proved the possibility of their reusability.

Accelerating Hydrogen Desorption of Nickel Molybdenum Cathode via Copper Modulation for Pure‐Water‐Fed Hydroxide Exchange Membrane Electrolyzer

AbstractThe more sluggish kinetics of hydrogen evolution catalysts in base as compare to that in acid to some degree restricts hydrogen production performance of hydroxide exchange membrane electrolyzers, especially when using earth‐abundant catalysts. Here a ternary nickel–copper–molybdenum hydrogen evolution catalyst is reported that exhibits ≈5 times higher turnover frequency than without copper doping. The X‐ray absorption near‐edge structure and valence band spectrum demonstrate that the light doping of copper into nickel–molybdenum alloy modulates the electronic structure and downshifts the d‐band center, resulting in accelerated hydrogen desorption, as consolidated by H2 temperature programmed desorption and theoretical calculation. An electrolyzer employing this cathode catalyst and a nickel–iron anode, gives a current density of 1.7 A cm−2 at 2.0 V with a pure‐water feed through the anode, which outperforms the 2025 target proposed by the United States Department of Energy, and even is operated continuously for over 1000 h with a decay rate of as low as 0.5 mV h−1. Post‐mortem analysis discloses that hydroxide exchange ionomer migration is one of the key factors affecting long‐term durability. This work demonstrates the feasibility of a low‐cost, water‐fed hydroxide exchange membrane electrolyzer achieving industrial‐level performance and lifetime.

Pair density wave and superconductivity in a kinetically frustrated doped Emery model on a square lattice

The quest to understand the nature of superconductivity in the cuprates has spotlighted the pair density wave (PDW)–a superconducting state characterized by a spatially modulated order parameter. Despite significant advances in understanding PDW properties, conclusively demonstrating its presence in systems pertinent to cuprate superconductors remains elusive. In this study, we present a systematic density-matrix renormalization group study to investigate the Emery model (or the three-band Hubbard model) on two-leg square cylinders with negative electron hopping term tpp between adjacent oxygen sites. Kinetic frustration - introduced by changing the sign of oxygen-oxygen hopping - leads to a much reduced Cu-Cu antiferromagnetic exchange along with an enlarged charge transfer energy that changes the local properties of the model. At light doping levels, our findings reveal a ground state remarkably consistent with a PDW, exhibiting mutually commensurate superconducting (SC), charge, and spin density wave correlations. Intriguingly, the dominant SC pairing is observed between neighboring oxygen sites, diverging from the expected Cu sites in the positive tpp case. When the system incorporates moderate near-neighbor interactions, particularly an attractive Vpp between adjacent oxygen sites, the SC correlations become quasi-long-ranged, accompanied by a pronounced divergence in the PDW susceptibility. When the attractive Vpp increases further, the system gives way to an unconventional d-wave superconductivity.

Enhanced Thermoelectric Performance of Lightly Pb-Doped Sb2Te3 Polycrystalline Alloys for Power Generation in Midtemperature Range

Sb2Te3 alloys are promising thermoelectric materials because of their outstanding electrical transport properties in the midtemperature range of 500–700 K, while codoping with multiple elements has been successful to improve their thermoelectric performance. In this study, enhanced thermoelectric properties with a maximum thermoelectric figure of merit of 0.97 are reported for singly and lightly Pb-doped Sb2Te3 polycrystalline alloys (Sb2– x Pb x Te3). Very light Pb doping in the range 0.005 ≤ x ≤ 0.0125 in the Sb2– x Pb x Te3 alloys yielded significantly improved carrier transport properties and increased electrical conductivity while the Seebeck coefficient is decreased moderately, since the density-of-state effective mass is improved much. As a result, power factor for the Pb-doped Sb2Te3 is largely increased up to 3.7 mW/mK2 at 300 K. The lattice thermal conductivity decreased considerably owing to the additional point defect phonon scattering by the Pb despite slight doping. Consequently, a maximum thermoelectric figure of merit of 0.97 was obtained for Sb1.9875Pb0.0125Te3 ( x = 0.0125 ) at 600 K, which is the highest reported value for singly doped Sb2Te3-based alloys. A maximum energy conversion efficiency was calculated to be 9.0% for a temperature difference of 350 K, which is higher than that for other singly or codoped Sb2Te3 alloys.

Pair density wave in the doped three-band Hubbard model on two-leg square cylinders

A pair density wave (PDW) is a superconducting (SC) state with a spatially modulated order parameter. Although much is known about the properties of the PDW state, its realization in microscopic models with divergent susceptibility has been challenging. Here we report a density-matrix renormalization group study of a three-band Hubbard model (also known as the Emery model) for cuprates on long two-leg square cylinders. Upon light doping, we find that the ground state of the system is consistent with that of a PDW state with mutually commensurate and power-law SC, charge (CDW), and spin (SDW) density wave correlations. The SC correlations are dominant between neighboring Cu sites with $d$-wave pairing symmetry. Interestingly, we find that the near-neighbor interactions, especially the near-neighbor attractive ${V}_{pd}$ interaction between neighboring Cu and oxygen sites, can notably enhance the SC correlations while simultaneously suppressing the CDW correlations. For a modestly strong attractive ${V}_{pd}$, the SC correlations become quasi-long-ranged with a divergent PDW susceptibility.

De Novo Studies of Working Mechanisms for Self-Driven Narrowband Perovskite Photodetectors.

Self-driven narrowband perovskite photodetectors have recently attracted significant attention due to their simple preparation, high performance, and amenability for system integration. However, the origin of narrowband photoresponse and the related regulation mechanisms still remains elusive. To address these issues, we herein perform a systematic investigation by formulating an analytic model in conjunction with finite element simulation. The optical and electrical simulations have resulted in design principles for perovskite narrowband photodetectors in terms of the dependence of external quantum efficiency (EQE) on perovskite layer thickness, doping concentration, and band gap as well as trap state concentration. Careful investigations on the profiles of electric field, current, and optical absorption reveal the dependence of narrowband EQE on the direction of incident light and perovskite doping types: only p-type perovskite can yield the narrowband photoresponse for illumination from the hole transport layer (HTL) side. The simulation results demonstrated in this study shed new light on the mechanism of perovskite-based narrowband photodetectors and provide valuable guidance for their design.

Effect of Light and Heavy Rare Earth Doping on the Physical Structure of Bi2O2CO3 and Their Performance in Photocatalytic Degradation of Dimethyl Phthalate

In order to solve the problem of environmental health hazards caused by phthalate esters, a series of pure Bi2O2CO3 and light (La, Ce, Pr, Nd, Sm and Eu) and heavy (Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu) rare earth-doped Bi2O2CO3 samples were prepared by hydrothermal method. The crystalline phase composition and physical structure of the samples calcined at 300 °C were studied, and we found that the rare earth ion doping promoted the transformation of Bi2O2CO3 to β-Bi2O3 crystalline phase, thus obtaining a mixed crystal phase photocatalyst constituted by rare earth-ion-doped Bi2O2CO3/β-Bi2O3. The Bi2O3/Bi2O2CO3 heterostructure had a lower band gap and more efficient charge transfer. The fabricated samples were applied to the photocatalytic degradation of dimethyl phthalate (DMP) under a 300 W tungsten lamp, and it was found that the rare earth ion doping enhanced the photocatalytic degradation activity of DMP, in which the heavy rare earth of Er-doped sample reached 78% degradation for DMP at 150 min of light illumination. In addition, the doping of rare earths resulted in a larger specific surface area and a stronger absorption of visible light. At the same time, the formation of Bi2O2CO3/β-Bi2O3 heterogeneous junction enhanced the separation efficiency of photogenerated electrons and holes.

Light doping of tungsten into copper-platinum nanoalloys for boosting their electrocatalytic performance in methanol oxidation

Coupling the bi-functional mechanism with compressive lattice strain might be an effective way to boost the electrocatalysis of platinum (Pt)-based nanoparticles for methanol oxidation reaction (MOR). This strategy weakens the chemisorption of poisoning CO-like intermediates generated during MOR on the active Pt sites by lowering their d-band center. In this context, we herein report the synthesis of ternary copper-tungsten-platinum (CuWPt) nanoalloys with light doping of W element by simply co-reducing their precursors at elevated temperature. In this ternary alloy system, the presence of only small amount of W element not only weakens the chemisorption of CO-like intermediates by lowering the Pt d-band center through compressive lattice strain, but also cleans the active Pt sites by "hydrogen spillover effect", endowing the as-prepared CuWPt nanoalloys at an appropriate Cu/W/Pt ratio with good activity for MOR. In specific, the ternary CuWPt alloy nanoparticles at a Cu/W/Pt molar ratio of 21/4/75 show a specific activity of 2.5 mA·cm⁻² and a mass activity of 2.11 A·mg⁻¹ with a better durability, outperforming those ternary CuWPt alloy nanoparticles at other Cu/W/Pt ratios, binary CuPt alloys and commercial Pt/C catalyst as well as a large number of reported Pt-based electrocatalysts. In addition, a single direct methanol fuel cell (DMFC) assembled using ternary CuWPt nanoalloys as anodic catalysts shows a power density of 24.3 mW·cm⁻² and an open-circle voltage of 0.6 V, also much higher than those of the single DMFC assembled from commercial Pt/C catalysts.

Doped Mott insulators in the triangular-lattice Hubbard model

We investigate the evolution of the Mott insulators in the triangular lattice Hubbard Model, as a function of hole doping $\delta$ in both the strong and intermediate coupling limits. Using the advanced density matrix renormalization group (DMRG) method, at light hole doping $\delta\lesssim 10\%$, we find a significant difference between strong and intermediate couplings. Notably, at intermediate coupling an unusual metallic state emerges, with short ranged spin correlations but long ranged spin-chirality order. Moreover, no clear Fermi surface or wave-vector is observed, this chiral metal also exhibits staggered loop current, which breaks the translational symmetry. These features disappear on increasing interaction strength or on further doping. At strong coupling, the 120 degree magnetic order of the insulating magnet persists for light doping, and produces hole pockets with a well defined Fermi surface. On further doping, $\delta \approx 10\%\sim 20\%$ SDW order and coherent hole Fermi pockets are found at both strong and intermediate couplings. At even higher doping $\delta \gtrsim 20\%$, the SDW order is suppressed and the spin-singlet Cooper pair correlations are simultaneously enhanced. We also briefly comment on the strong particle-hole asymmetry of the model.

Carbon‐Doped Porous Polymeric Carbon Nitride with Enhanced Visible Light Photocatalytic and Photoelectrochemical Performance

The photocatalytic activity of polymeric carbon nitride (CN) is strongly tied to its surface area, morphology, optical, and electronic properties. Herein, a straightforward approach to adjusting the electronic properties and morphology of CN materials by fine tuning their carbon content while preserving their high surface area is proposed. To do so, supramolecular assemblies based on CN monomers together with an additional carbon‐rich monomer that does not participate in the preorganization are calcinated. The use of a supramolecular assembly as the precursor endows the CN material with a high specific surface area and an ordered morphology, whereas the addition of a carbon‐rich monomer provides light carbon doping. As a result, the new CN exhibits excellent activity as a photoanode material in photoelectrochemical cells and as a photocatalyst for the hydrogen evolution reaction. Detailed studies reveal that the modified CN samples show enhanced charge carrier transfer and separation efficiency, improved light absorption response, a tunable energy band structure, a higher electrochemical surface area, and better electronic conductivity compared with a reference CN.

Thermal interface doping strategies based on Bayesian optimization

Enhancing interfacial thermal conductance (ITC) plays a crucial role in microelectronics cooling because the continued reduction of the device size and increased power intensity demand more efficient heat dissipation. Although light atom doping and interface roughness were reported to enhance ITC in certain cases, they could also reduce ITC depending on the specific interface configurations. By leveraging Bayesian optimization, we provide the practical guidelines to achieve enhancement of ITC with high confidence via a proper selection of dopant mass and/or concentration, regardless of actual interfacial configurations. We demonstrate that the data-driven approach could be a helpful tool for interface design with desired ITCs.

Contribution of Dislocations in SiC Seed Crystals on the Melt-Back Process in SiC Solution Growth.

The melt-back process has a significant effect on the quality of solution-grown SiC crystals. However, the phenomena surrounding the SiC dissolution into the molten alloy during the melt-back process have not been clarified. In this study, the behavior of 4H-SiC dissolution into molten alloy was investigated by using high-temperature in situ observation and subsequent KOH etching, and the effects of different doping conditions and crystal polarity were studied. Local dissolutions with hexagonal pyramid-shape originating from threading screw dislocation (TSD) were observed on the C face of n-type SiC with light nitrogen doping. Our analysis of their behavior revealed that the process was governed by the spiral dissolution. In addition to the dissolution at TSD, local dissolutions at threading-edge dislocations were observed on the Si face of the same crystal. The shape of the local dissolution at the dislocation was significantly affected by the doping conditions and the polarity of the SiC crystal. This local dissolution may occur during the melt-back process, suggesting that it is important to promote the dissolution while maintaining a smooth interface through the selection of the seed crystal and by keeping the degree of interface undersaturation small.

Ag+/Bi3+ doping induced band structure and optoelectronic properties changes in CsPbBr3 crystals

Controllable doping is extensively used in designing the electronic and optical properties of perovskite. Bi-doped CsPbBr3 crystal shows a significant redshift at the absorption edge. However, the increase of defect states caused by Bi3+ ions will degrade the optical and electrical properties of the crystal. In this work, we report a series of Ag+/Bi3+ co-doped CsPbBr3 crystals prepared via a Bridgman method. The introduction of Ag+ ions could prevent the change for Fermi level and reduce the concentration of defect states caused by Bi3+ doping. Ag+/Bi3+ co-doped CsPbBr3 crystals show high carrier mobility that compare with undoped CsPbBr3 crystals. The light doping of Ag+/Bi3+ could remarkably improve the detection performances of CsPbBr3 to UV and laser. The maximum photocurrent for Ag+/Bi3+ co-doped CsPbBr3 crystal is even 50 times higher compared with undoped CsPbBr3 crystal under 365 nm UV lamps. Our findings provide a new strategy for controlling doping to improve the photoelectric properties of perovskite.

Graphdiyne doped with transition metal as ferromagnetic semiconductor

Long-range ferromagnetic ordering in semiconductors has become an attractive research hotspot due to its promising potential in spintronics and information technology. Especially the appearance of carbon-based semiconductors represented by graphdiyne (GDY) makes it easy to realize ferromagnetic semiconductors. Herein, a convenient and effective route has been developed to prepare GDY-based magnetic semiconductors using the modification with transition metal elements including Fe, Co, and Ni, respectively. Among them, lightly doped GDY with Co (Co-GDY) exhibits the most outstanding ferromagnetism with a typical Curie's temperature above room temperature. Meanwhile, the coercive field Hc = 78 Oe at T = 300 K of Co-GDY is the smallest, demonstrating characteristics of easy magnetization. Subsequent spin-polarized DFT calculation results reveal that the robust ferromagnetism of Co-GDY arises from the most significant local magnetic moment. Significantly, a noticeable band gap can still be maintained due to the very light doping level. These results reveal an optimization strategy for selecting doping elements, promoting carbon-based semiconductors application in spin-related fields.

Self-Doping for Synergistically Tuning the Electronic and Thermal Transport Coefficients in n-Type Half-Heuslers.

Ternary intermetallic half-Heusler (HH) compounds (XYZ) with 18 valence electron count, namely, ZrCoSb, ZrNiSn, and ZrPdSn, have revealed promising thermoelectric properties. Exemplarily, it has been experimentally observed that a slight change in the content of Y site atoms (by ∼3-12.5% i.e., m = 0.03 and 0.125 in ZrY1+mZ) leads to a drastic decrease in lattice thermal conductivity κL by more than 65-80% in many of these compounds. The present work aims at exploring the possibility of maximizing the electronic transport scenario after achieving the low κL limit in these compounds. By taking into account the full anharmonicity of the lattice dynamics, Boltzmann transport calculations are performed under the framework of density functional theory. Our results show that these excess atoms present in the vacant lattice site induce scattering either by acting as a rattling mode or by hybridizing with the acoustic modes of the host depending upon their mass and bonding chemistry, respectively. Furthermore, the introduction of these scattering centers may lead either to the formation of a defect midgap state in the electronic band structure (detrimental for electronic transport) or to light doping of the host compound. The latter is found to be particularly conducive for attaining synergy in both thermal and electronic transport.

Radiation defects in NaCl matrix with reduced lattice symmetry caused by light cation doping and elastic uniaxial deformation

The processes of radiation defect creation and radiative relaxation of electronic excitations under applied local or/and uniaxial elastic deformation have been studied in NaCl crystals by means of optical absorption, luminescence and thermoactivation spectroscopy methods. In NaCl:Li at 80 K, X-ray-induced absorption bands peaked around 3.35 and 4.6 eV have been detected and ascribed to interstitial halide atoms located nearby Li impurity cations, HA(Li) centres. Subsequent thermal annealing of HA(Li) centres leads to the formation of polyhalide centres responsible for the absorption band at 5.35 eV. In an X-irradiated and stressed NaCl:Li crystal (degree of uniaxial elastic deformation of ε = 0.9%), the peak of thermally stimulated luminescence at ~115 K is composed of the ~2.7-eV emission appearing, in our opinion, due to the recombination of the electron, thermally released from an F′ centre, with a hole-type HA(Li) centre. The applied uniaxial elastic stress facilitates the self-trapping of anion excitons in regular regions of a NaCl lattice and impedes the energy transfer by mobile excitons to impurities/defects and, in turn, attenuates the Br-related luminescence peaked at 3.95 eV with respect to the π-emission of self-trapped excitons (~3.35 eV). The 3.95 eV emission has been detected in a natural NaCl crystal containing homologous Br impurity ions.

Design and optimization of CuSCN/CH[formula omitted]NH[formula omitted]PbI[formula omitted]/TiO[formula omitted] perovskite solar cell for efficient performance

A perovskite solar cell with FTO/CuSCN/Perovskite/TiO 2/Metal was proposed and analyzed theoretically using SCAPS-1D software. The electron transport layer (ETL), Absorber layer and hole transport layer (HTL) were optimized by varying their thickness, doping concentration and defect density. The absorber thickness and doping seem to heavily influence the performance of the device. ETL optimization also provided a significant boost in the efficiency of the device. This thickness of 900 nm and a light doping of 1014 cm −3 in absorber layer along with 1017 cm −3 donor density of ETL provided the highest efficiency of 28.9%. After proper optimization the perovskite solar cell has a power conversion efficiency of 28.9% with 82.08% fill factor. The open circuit voltage is 1.1 V and the short circuit current is 31.192 mA/cm 2.

Precursor of pair-density wave in doping Kitaev spin liquid on the honeycomb lattice

We study the effects of doping the Kitaev model on the honeycomb lattice where the spins interact via the bond-directional interaction JK, which is known to have a quantum spin liquid as its exact ground state. The effect of hole doping is studied within the t-JK model on a three-leg cylinder using density-matrix renormalization group. Upon light doping, we find that the ground state of the system has a dominant quasi-long-range charge-density-wave correlations but short-range single-particle correlations. In the pairing channel, the even-parity superconducting correlation is dominant with d-wave-like symmetry, which oscillates in sign as a function of separation with a period equal to that of the spin-density wave and two times the charge-density wave. Although these correlations fall rapidly (possibly exponentially) at long distances, this is never-the-less the example where a pair-density wave is the leading instability in the pairing channel on the honeycomb lattice.

Anomalous Andreev reflection on a torus-shaped Fermi surface

Andreev reflection (AR) refers to the electron-hole conversion at the normal metal-superconductor interface. In a three-dimensional metal with spherical Fermi surface, retro (specular) AR can occur with the sign reversal of all three (a single) components of particle velocity. Here, we predict a novel type of AR with the inversion of two velocity components, dubbed "anomalous-trajectory Andreev reflection" (AAR), which can be realized in a class of materials with torus-shaped Fermi surface, such as doped nodal line semimetals. For its toroidal circle perpendicular to the interface, the Fermi torus doubles the AR channels and generates multiple AR processes. In particular, the AAR and retro AR are found to dominate electron transport in the light and heavy doping regimes, respectively. We show that the AAR visibly manifests as a ridge structure in the spatially resolved nonlocal conductance, in contrast to the peak structure for the retro AR. Our work opens a new avenue for the AR spectroscopy and offers a clear transport signature of torus-shaped Fermi surface.