Properties of n-Ge epilayer on Si substrate with in-situ doping technology

The properties of n-Ge epilayer deposited on Si substrate with in-situ doping technology in a cold-wall ultrahigh vacuum chemical vapor deposition（UHVCVD） system are investigated.The growth temperature of 500℃ is optimal for the n-Ge growth in our equipment with a phosphorus concentration of 1018cm-3.In the n-Ge epilayer,the depth profile of phosphorus concentration is box-shaped and the tensile strain of 0.12% confirmed by x-ray diffraction measurement is introduced which results in the red shift of the photoluminescence.The enhancements of photoluminescence intensity with the increase of the doping concentration are observed,which is consistent with the modeling of the spontaneous emission spectrum for direct transition of Ge.The results are of significance for guiding the growth of n-Ge epilayer with in-situ doping technology.

In-situ doping-induced lattice strain of NiCoP/S nanocrystals for robust wide pH hydrogen evolution electrocatalysis and supercapacitor

Developing high-efficiency multifunctional nanomaterials is promising for wide p H hydrogen evolution reaction(HER) and energy storage but still challenging. Herein, a novel in-situ doping-induced lattice strain strategy of NiCoP/S nanocrystals(NCs) was proposed through using seed crystal conversion approach with NiCo_(2)S_(4) spinel as precursor. The small amount of S atoms in NiCoP/S NCs perturbed the local electronic structure, leading to the atomic position shift of the nearest neighbor in the protocell and the nanoscale lattice strain, which optimized the H* adsorption free energy and activated H_(2)O molecules, resulting the dramatically elevated HER performance within a wide p H range. Especially, the NiCoP/S NCs displayed better HER electrocatalytic activity than comical 20% Pt/C at high current density in 1 M KOH and natural seawater: it only needed 266 m V vs. reversible hydrogen electrode(RHE) and660 m V vs. RHE to arrive the current density of 350 m A cm^(-2) in 1 M KOH and natural seawater, indicating the application prospect for industrial high current. Besides, NiCoP/S NCs also displayed excellent supercapacitor performance: it showed high specific capacity of 2229.9 F g^(-1) at 1 A g^(-1) and energy density of87.49 Wh kg^(-1), when assembled into an all-solid-state flexible device, exceeding performance of most transition metal phosphides. This work provides new insights into the regulation in electronic structure and lattice strain for electrocatalytic and energy storage applications.

One-step electrochemical in-situ Li doping and LiF coating enable ultra-stable cathode for sodium ion batteries

Despite of the higher energy density and inexpensive characteristics,commercialization of layered oxide cathodes for sodium ion batteries(SIBs)is limited due to the lack of structural stability at the high voltage.Herein,the one-step electrochemical in-situ Li doping and LiF coating are successfully achieved to obtain an advanced Na0.79Lix[Li_(0.13)Ni_(0.20)Mn_(0.67)]O_(2)@LiF(NaLi-LNM@LiF)cathode with superlattice structure.The results demonstrate that the Li^(+)doped into the alkali metal layer by electrochemical cycling act as"pillars"in the form of Li-Li dimers to stabilize the layered structure.The supplementation of Li to the superlattice structure inhibits the dissolution of transition metal ions and lattice mismatch.Furthermore,the in-situ LiF coating restrains side reactions,reduces surface cracks,and greatly improves the cycling stability.The electrochemical in-situ modification strategy significantly enhances the electrochemical performance of the half-cell.The NaLi-LNM@LiF exhibits high reversible specific capacity(170.6 m A h g^(-1)at 0.05 C),outstanding capacity retention(92.65%after 200 cycles at 0.5 C)and excellent rate performance(80 mA h g^(-1)at 7 C)in a wide voltage range of 1.5-4.5 V.This novel method of in-situ modification by electrochemical process will provide a guidance for the rational design of cathode materials for SIBs.

In-situ doping strategy for improving the photocatalytic hydrogen evolution performance of covalent triazine frameworks

A highly conjugated network of covalent triazine frameworks(CTFs)on the one hand promotes light-harvesting,but on the other hand,also results in high carrier recombination which eventually limits their photocatalytic hydrogen evolution reaction(HER)rates.Thus,strategies to favorably tune the electronic configuration of CTFs for efficient photocatalytic HERs need to be developed,but still remain challenging.Herein,a simple in-situ defect strategy involving element doping is developed for the first time to introduce a heteroatom including S and Se into CTF-1 via the condensation of aldehydes with the mixture of the terephthalimidamide and the S-or Se-substituted terephthalimidamide under mild conditions.The doping content(X)is varied,resulting in a series of S-and Se-doped CTFs,named CTFS-1-X and CTFSe-1-X,respectively.Interestingly,for the S-doped CTFs,CTFS-1-10 shows the most excellent HER rate(4,992.3μmol g^(-1)h^(-1))from water splitting,while for the Se-doped ones,CTFSe-1-10 exhibits a photocatalytic HER rate of 5,792.8μmol g^(-1)h^(-1),both of which far surpass undoped CTFs(693.3μmol g^(-1)h^(-1)).In-depth studies indicate that the introduction of S or Se atoms into CTFs could extend the light absorption and promote photo-generated electron-hole pairs migration.Meanwhile,S-or Se-doping could create heterogeneous electronic configuration in CTFs,which can help to suppress carrier recombination.

In-situ interfacial passivation and self-adaptability synergistically stabilizing all-solid-state lithium metal batteries

The function of solid electrolytes and the composition of solid electrolyte interphase(SEI)are highly significant for inhibiting the growth of Li dendrites.Herein,we report an in-situ interfacial passivation combined with self-adaptability strategy to reinforce Li_(0.33)La_(0.557)TiO_(3)(LLTO)-based solid-state batteries.Specifically,a functional SEI enriched with LiF/Li_(3)PO_(4) is formed by in-situ electrochemical conversion,which is greatly beneficial to improving interface compatibility and enhancing ion transport.While the polarized dielectric BaTiO_(3)-polyamic acid(BTO-PAA,BP)film greatly improves the Li-ion transport kinetics and homogenizes the Li deposition.As expected,the resulting electrolyte offers considerable ionic conductivity at room temperature(4.3 x 10~(-4)S cm^(-1))and appreciable electrochemical decomposition voltage(5.23 V)after electrochemical passivation.For Li-LiFePO_(4) batteries,it shows a high specific capacity of 153 mA h g^(-1)at 0.2C after 100 cycles and a long-term durability of 115 mA h g^(-1)at 1.0 C after 800 cycles.Additionally,a stable Li plating/stripping can be achieved for more than 900 h at 0.5 mA cm^(-2).The stabilization mechanisms are elucidated by ex-situ XRD,ex-situ XPS,and ex-situ FTIR techniques,and the corresponding results reveal that the interfacial passivation combined with polarization effect is an effective strategy for improving the electrochemical performance.The present study provides a deeper insight into the dynamic adjustment of electrode-electrolyte interfacial for solid-state lithium batteries.

Interplay of laser power and pore characteristics in selective laser melting of ZK60 magnesium alloys:A study based on in-situ monitoring and image analysis

This study offers significant insights into the multi-physics phenomena of the SLM process and the subsequent porosity characteristics of ZK60 Magnesium(Mg)alloys.High-speed in-situ monitoring was employed to visualise process signals in real-time,elucidating the dynamics of melt pools and vapour plumes under varying laser power conditions specifically between 40 W and 60 W.Detailed morphological analysis was performed using Scanning-Electron Microscopy(SEM),demonstrating a critical correlation between laser power and pore formation.Lower laser power led to increased pore coverage,whereas a denser structure was observed at higher laser power.This laser power influence on porosity was further confirmed via Optical Microscopy(OM)conducted on both top and cross-sectional surfaces of the samples.An increase in laser power resulted in a decrease in pore coverage and pore size,potentially leading to a denser printed part of Mg alloy.X-ray Computed Tomography(XCT)augmented these findings by providing a 3D volumetric representation of the sample internal structure,revealing an inverse relationship between laser power and overall pore volume.Lower laser power appeared to favour the formation of interconnected pores,while a reduction in interconnected pores and an increase in isolated pores were observed at higher power.The interplay between melt pool size,vapour plume effects,and laser power was found to significantly influence the resulting porosity,indicating a need for effective management of these factors to optimise the SLM process of Mg alloys.

Enhanced electrochemical performance of CoNiS_(x)@Ti_(3)C_(2)T_(x)electrode material through in-situ doping of cobalt element

The composite electrode of CoNiS_(x)and Ti_(3)C_(2)T_(x)MXene was successfully prepared using a onestep hydrothermal method under the in-situ doping of the cobalt element.The effects of in-situ doping of the cobalt element on the micromorphology and electrochemical performance of the electrodes were investigated.After insitu doping of the cobalt element,NiS with a needle-like structure was converted into a CoNiS_(x)with petal-like structure.The petal-like CoNiS_(x)with a rough surface was very dense and evenly wrapped on the surface and interlamination of Ti_(3)C_(2)T_(x),which helped increase the specific surface area and pore volume of the electrode.Under the identical test conditions,CoNiS_(x)@Ti_(3)C_(2)T_(x)had a higher specific capacitance and capacitance retention than NiS@Ti_(3)C_(2)T_(x).This result indicated that the in-situ doping of the cobalt element promoted the electrochemical performance of the electrode.The energy density of the CoNiS_(x)@Ti_(3)C_(2)T_(x)/nickel foam(NF)//activated carbon(AC)/NF asymmetric supercapacitor device was 59.20 Wh·kg^(–1)at a power density of 826.73 W·kg^(–1),which was much higher than that of NiS@Ti_(3)C_(2)T_(x)/NF//AC/NF.Three CoNiS_(x)@Ti_(3)C_(2)T_(x)/NF//AC/NF in series were able to illuminate the light emitting diode lamp for about 10 min,which was higher than the 5 min of three NiS@Ti_(3)C_(2)T_(x)/NF//AC/NF in series under the same condition.The CoNiS_(x)@Ti_(3)C_(2)T_(x)/NF//AC/NF with high energy density had better application potential in energy storage than the NiS@Ti_(3)C_(2)T_(x)/NF//AC/NF.

Enhancing the stability of Ni Fe-layered double hydroxide nanosheet array for alkaline seawater oxidation by Ce doping

Electrocatalytic hydrogen production from seawater holds enormous promise for clean energy generation.Nevertheless,the direct electrolysis of seawater encounters significant challenges due to poor anodic stability caused by detrimental chlorine chemistry.Herein,we present our recent discovery that the incorporation of Ce into Ni Fe layered double hydroxide nanosheet array on Ni foam(Ce-Ni Fe LDH/NF)emerges as a robust electrocatalyst for seawater oxidation.During the seawater oxidation process,CeO_(2)is generated,effectively repelling Cl^(-)and inhibiting the formation of Cl O-,resulting in a notable enhancement in the oxidation activity and stability of alkaline seawater.The prepared Ce-Ni Fe LDH/NF requires only overpotential of 390 m V to achieve the current density of 1 A cm^(-2),while maintaining long-term stability for 500 h,outperforming the performance of Ni Fe LDH/NF(430 m V,150 h)by a significant margin.This study highlights the effectiveness of a Ce-doping strategy in augmenting the activity and stability of materials based on Ni Fe LDH in seawater electrolysis for oxygen evolution.

Co-doped BaFe_(2)As_(2) Josephson junction fabricated with a focused helium ion beam

Josephson junction plays a key role not only in studying the basic physics of unconventional iron-based superconductors but also in realizing practical application of thin-film based devices,therefore the preparation of high-quality iron pnictide Josephson junctions is of great importance.In this work,we have successfully fabricated Josephson junctions from Co-doped BaFe_(2)As_(2)thin films using a direct junction fabrication technique which utilizes high energy focused helium ion beam(FHIB).The electrical transport properties were investigated for junctions fabricated with various He^(+)irradiation doses.The junctions show sharp superconducting transition around 24 K with a narrow transition width of 2.5 K,and a dose correlated foot-structure resistance which corresponds to the effective tuning of junction properties by He^(+)irradiation.Significant J_c suppression by more than two orders of magnitude can be achieved by increasing the He^(+)irradiation dose,which is advantageous for the realization of low noise ion pnictide thin film devices.Clear Shapiro steps are observed under 10 GHz microwave irradiation.The above results demonstrate the successful fabrication of high quality and controllable Co-doped BaFe_(2)As_(2)Josephson junction with high reproducibility using the FHIB technique,laying the foundation for future investigating the mechanism of iron-based superconductors,and also the further implementation in various superconducting electronic devices.

In-situ coating and surface partial protonation co-promoting performance of single-crystal nickel-rich cathode in all-solid-state batteries

The poor electrochemical performance of all-solid-state batteries(ASSBs),which is assemblied by Ni-rich cathode and poly(ethylene oxide)(PEO)-based electrolytes,can be attributed to unstable cathodic interface and poor crystal structure stability of Ni-rich cathode.Several coating strategies are previously employed to enhance the stability of the cathodic interface and crystal structure for Ni-rich cathode.However,these methods can hardly achieve simplicity and high efficiency simultaneously.In this work,polyacrylic acid(PAA)replaced traditional PVDF as a binder for cathode,which can achieve a uniform PAA-Li(LixPAA(0<x≤1))coating layer on the surface of single-crystal LiNi_(0.83)Co_(0.12)Mn_(0.05)O_(2)(SC-NCM83)due to H^(+)/Li^(+)exchange reaction during the initial charging-discharging process.The formation of PAA-Li coating layer on cathode can promote interfacial Li^(+)transport and enhance the stability of the cathodic interface.Furthermore,the partially-protonated surface of SC-NCM83 casued by H^(+)/Li^(+)exchange reaction can restrict Ni ions transport to enhance the crystal structure stability.The proposed SC-NCM83-PAA exhibits superior cycling performance with a retention of 92%compared with that(57.3%)of SC-NCM83-polyvinylidene difluoride(PVDF)after 200 cycles.This work provides a practical strategy to construct high-performance cathodes for ASSBs.

Enhanced conductivity and weakened magnetism in Pb-doped Sr_(2)IrO_(4)

Group IV element Pb has been selected as the dopant to dope at the Sr site of Sr_(2)IrO_(4). It is exciting to find that the single-phase crystal structure could be maintained with a high Pb doping level of up to x=0.3 in Sr_(2-x)Pb_(x)IrO_(4). The mapping data obtained from energy-dispersive x-ray spectroscopy analyses give solid evidence that the Pb ions are uniformly distributed in the Sr_(2)IrO_(4) matrix. The incorporation of Pb leads to a moderate depression of the canted antiferromagnetic ordering state. The electrical conductivity could be greatly enhanced when the Pb doping content is higher than x=0.2.The present results give a fresh material base to explore new physics in doped Sr_(2)IrO_(4) systems.

Hole-Doped Nonvolatile and Electrically Controllable Magnetism in van der Waals Ferroelectric Heterostructures

Electrical control of magnetism in van der Waals semiconductors is a promising step towards development of two-dimensional spintronic devices with ultralow power consumption for processing and storing information.Here, we propose a design for two-dimensional van der Waals heterostructures(vdWHs) that can host ferroelectricity and ferromagnetism simultaneously under hole doping. By contacting an In Se monolayer and forming an InSe/In_(2)Se_(3) vd WH, the switchable built-in electric field from the reversible out-of-plane polarization enables robust control of the band alignment. Furthermore, switching between the two ferroelectric states(P_↑ and P_↓)of hole-doped In_(2)Se_(3) with an external electric field can interchange the ON and OFF states of the nonvolatile magnetism. More interestingly, doping concentration and strain can effectively tune the magnetic moment and polarization energy. Therefore, this provides a platform for realizing multiferroics in ferroelectric heterostructures,showing great potential for use in nonvolatile memories and ferroelectric field-effect transistors.

Assessing the conservation impact of Chinese indigenous chicken populations between ex-situ and in-situ using genome-wide SNPs

Conservation programs require rigorous evaluation to ensure the preservation of genetic diversity and viability of conservation populations. In this study, we conducted a comparative analysis of two indigenous Chinese chicken breeds, Gushi and Xichuan black-bone, using whole-genome SNPs to understand their genetic diversity, track changes over time and population structure. The breeds were divided into five conservation populations(GS1, 2010, ex-situ;GS2, 2019, ex-situ;GS3, 2019, in-situ;XB1, 2010, in-situ;and XB2, 2019, in-situ) based on conservation methods and generations. The genetic diversity indices of three conservation populations of Gushi chicken showed consistent trends, with the GS3 population under in-situ strategy having the highest diversity and GS2 under ex-situ strategy having the lowest. The degree of inbreeding of GS2 was higher than that of GS1 and GS3. Conserved populations of Xichuan black-bone chicken showed no obvious changes in genetic diversity between XB1 and XB2. In terms of population structure, the GS3 population were stratified relative to GS1 and GS2. According to the conservation priority, GS3 had the highest contribution to the total gene and allelic diversity in GS breed, whereas the contribution of XB1 and XB2 were similar. We also observed that the genetic diversity of GS2 was lower than GS3, which were from the same generation but under different conservation programs(in-situ and ex-situ). While XB1 and XB2 had similar levels of genetic diversity. Overall, our findings suggested that the conservation programs performed in ex-situ could slow down the occurrence of inbreeding events, but could not entirely prevent the loss of genetic diversity when the conserved population size was small, while in-situ conservation populations with large population size could maintain a relative high level of genetic diversity.

In-situ AFM and quasi-in-situ studies for localized corrosion in Mg-9Al-1Fe-(Gd) alloys under 3.5 wt.% NaCl environment

Revealing the localized corrosion process of Mg alloy is considered as one of the most significant ways for improving its corrosion resistance.The reliable monitor should be high distinguishability and real-time in liquid environment.Herein,Mg-9Al-1Fe and Mg-9Al-1Fe-1Gd alloys were designed to highlight the impact of intermetallic on the corrosion behaviour.In-situ AFM with a special electrolyte circulation system and quasi-in-situ SEM observation were used to monitor the corrosion process of the designed alloys.SEM-EDS and TEM-SAED were applied to identify the intermetallic in the designed alloys,and their volta potentials were measured by SKPFM.According to the real-time and real-space in-situ AFM monitor,the corrosion process consisted of dissolution of anodicα-Mg phase,accumulation of corrosion products around cathodic phase and shedding of some fine cathodic phase.Then,the localized corrosion process of Mg alloy was revealed combined with the results of the monitor of corrosion process and Volta potential difference.

Mott Gap Filling by Doping Electrons through Depositing One Sub-Monolayer Thin Film of Rb on Ca_(2)CuO_(2)Cl_(2)

Understanding the doping evolution from a Mott insulator to a superconductor probably holds the key to resolve the mystery of unconventional superconductivity in copper oxides. To elucidate the evolution of the electronic state starting from the Mott insulator, we dose the surface of the parent phase Ca_(2)CuO_(2)Cl_(2) by depositing Rb atoms, which are supposed to donate electrons to the CuO_(2) planes underneath. We successfully achieved the Rb sub-monolayer thin films in forming the square lattice. The scanning tunneling microscopy or spectroscopy measurements on the surface show that the Fermi energy is pinned within the Mott gap but close to the edge of the charge transfer band. In addition, an in-gap state appears at the bottom of the upper Hubbard band(UHB), and the Mott gap will be significantly diminished. Combined with the Cl defect and the Rb adatom/cluster results, the electron doping is likely to increase the spectra weight of the UHB for the double occupancy. Our results provide information to understand the electron doping to the parent compound of cuprates.

An in-situ study of static recrystallization in Mg using high temperature EBSD

It has been a common method to improve the mechanical properties of metals by manipulating their microstructures via static recrystallization,i.e.,through heat treatment.Therefore,the knowledge of recrystallization and grain growth is critical to the success of the technique.In the present work,by using in-situ high temperature EBSD,the mechanisms that control recrystallization and grain growth of an extruded pure Mg were studied.The experimental results revealed that the grains of priority for dynamic recrystallization exhibit fading competitiveness under static recrystallization.It is also found that grain boundary movement or grain growth is likely to show an inverse energy gradient effect,i.e.,low energy grains tend to swallow or grow into high energy grains,and grain boundaries of close to 30°exhibit superior growth advantage to others.Another finding is that{10-12}tensile twin boundaries are sites of hardly observed for recrystallization,and are finally swallowed by adjacent recrystallized grains.The above findings may give comprehensive insights of static recrystallization and grain growth of Mg,and may guide the design of advanced materials processing in microstructural engineering.

In-situ Gelation of Sodium Alginate-chitosan for Oral Delivery of Probiotics

We developed a new preparation to protect probiotic cells from adverse environmental conditions and improve their livability,which is called Lactobacillus casei-Sodium alginate-Chitosan (LSC).The LSC was prepared by mixing probiotics with sodium alginate-chitosan sol.The preparation contained complex calcium ions,which were released in the acidic environment of gastric juice,thus crosslinking to form in-situ gel.Different proportions of sodium alginate-chitosan were prepared to add to simulate gastrointestinal fluid to get the best ratio.The optimal ratio of LSC preparation was compared with traditional gel microspheres to observe the survival effect of probiotics in gastrointestinal fluid environment.Compared with sodium alginate sol,the porosity of sodium alginate-chitosan sol is lower,which is beneficial to the protection of probiotics.When the ratio of chitosan to sodium alginate is 1.5:1.5 (w/v),the protective effect is the best.The protective ability of LSC is 64 times that of traditional microspheres,and it has the potential of synergistic anti-tumor.A probiotic preparation with simple preparation process and better protection effect compared with traditional microspheres was prepared,which has joint anti-tumor potential.

Enhancing multifunctional photocatalysis with acetate-assisted cesium doping and unlocking the potential of Z-scheme solar water splitting

Graphitic carbon nitride(g-C_(3)N_(4))has been extensively doped with alkali metals to enlarge photocatalytic output,in which cesium(Cs)doping is predicted to be the most efficient.Nevertheless,the sluggish diffusion and doping kinetics of precursors with high melting points,along with imprecise regulation,have raised the debate on whether Cs doping could make sense.For this matter,we attempt to confirm the positive effects of Cs doping on multifunctional photocatalysis by first using cesium acetate with the character of easy manipulation.The optimized Csdoped g-C_(3)N_(4)(CCN)shows a 41.6-fold increase in visible-light-driven hydrogen evolution reaction(HER)compared to pure g-C_(3)N_(4) and impressive degradation capability,especially with 77%refractory tetracycline and almost 100%rhodamine B degradedwithin an hour.The penetration ofCs+is demonstrated to be a mode of interlayer doping,and Cs–N bonds(especially with sp^(2) pyridine N in C═N–C),along with robust chemical interaction and electron exchange,are fabricated.This atomic configuration triggers the broadened spectral response,the improved charge migration,and the activated photocatalytic capacity.Furthermore,we evaluate the CCN/cadmium sulfide hybrid as a Z-scheme configuration,promoting the visible HER yield to 9.02 mmol g^(−1) h^(−1),which is the highest ever reported among all CCN systems.This work adds to the rapidly expanding field of manipulation strategies and supports further development of mediating served for photocatalysis.

A continuous and long-term in-situ stress measuring method based on fiber optic. Part I: Theory of inverse differential strain analysis

A method for in-situ stress measurement via fiber optics was proposed. The method utilizes the relationship between rock mass elastic parameters and in-situ stress. The approach offers the advantage of long-term stress measurements with high spatial resolution and frequency, significantly enhancing the ability to measure in-situ stress. The sensing casing, spirally wrapped with fiber optic, is cemented into the formation to establish a formation sensing nerve. Injecting fluid into the casing generates strain disturbance, establishing the relationship between rock mass properties and treatment pressure.Moreover, an optimization algorithm is established to invert the elastic parameters of formation via fiber optic strains. In the first part of this paper series, we established the theoretical basis for the inverse differential strain analysis method for in-situ stress measurement, which was subsequently verified using an analytical model. This paper is the fundamental basis for the inverse differential strain analysis method.

Investigation on p-type doping of PBn unipolar barrier InAsSb photodetectors

The lattice-matched XBn structures of InAsSb,grown on GaSb substrates,exhibit high crystal quali⁃ty,and can achieve extremely low dark currents at high operating temperatures(HOT).Its superior performance is attributed to the unipolar barrier,which blocks the majority carriers while allowing unhindered hole transport.To further explore the energy band and carrier transport mechanisms of the XBn unipolar barrier structure,this pa⁃per systematically investigates the influence of doping on the dark current,photocurrent,and tunneling character⁃istics of InAsSb photodetectors in the PBn structure.Three high-quality InAsSb samples with unintentionally doped absorption layers(AL)were prepared,with varying p-type doping concentrations in the GaSb contact layer(CL)and the AlAsSb barrier layer(BL).As the p-type doping concentration in the CL increased,the device’s turn-on bias voltage also increased,and p-type doping in the BL led to tunneling occurring at lower bias voltages.For the sample with UID BL,which exhibited an extremely low dark current of 5×10^(-6) A/cm^(2).The photocurrent characteristics were well-fitted using the back-to-back diode model,revealing the presence of two opposing space charge regions on either side of the BL.