Epitaxial growth of CsPbBr_(3)/PbS single-crystal film heterostructures for photodetection

Epitaxial high-crystallization film semiconductor heterostructures has been proved to be an effective method to prepare single-crystal films for different functional devices in modern microelectronics,electro-optics,and optoelectronics.With superior semiconducting properties,halide perovskite materials are rising as building blocks for heterostructures.Here,the conformal vapor phase epitaxy of CsPbBr3 on PbS single-crystal films is realized to form the CsPbBr3/PbS heterostructures via a two-step vapor deposition process.The structural characterization reveals that PbS substrates and the epilayer CsPbBr3 have clear relationships:CsPbBr3(110)//PbS(100),CsPbBr3[001]//PbS[001]and CsPbBr3[001]//PbS[010].The absorption and photoluminescence(PL)characteristics of CsPbBr3/PbS heterostructures show the broadband light absorption and efficient photogenerated carrier transfer.Photodetectors based on the heterostructures show superior photoresponsivity of 15 A/W,high detectivity of 2.65×10^(11) Jones,fast response speed of 96 ms and obvious rectification behavior.Our study offers a convenient method for establishing the high-quality CsPbBr3/PbS single-crystal film heterostructures and providing an effective way for their application in optoelectronic devices.

Vapor phase epitaxy of PbS single-crystal films on water-soluble substrates and application to photodetectors

Lead sulfide(PbS),a typical functional semiconductor material,has attracted serious attention due to its great potential in optoelectronics applications.However,controllable growth of PbS single-crystal film still remains a great challenge.Here,we report heteroepitaxial growth of large-scale highly crystalline PbS films on alkali salt(NaCl and KCl)substrates via chemical vapor deposition(CVD).Structural characterizations demonstrate that the as-grown PbS films exhibit an atomically sharp interface with the underlying substrates.The epitaxial relationships between the epilayers and substrates were determined to be PbS(100)//NaCl(100)or KCl(100),PbS[010]//NaCl[010]or KCl[010].Owing to the high solubility of alkali salt,the epitaxial PbS films can be rapidly released from the underlying substrates and transferred to other substrates of interest while maintaining good integrity and crystallinity,the process of which is particularly attractive in the fields of electronics and optoelectronics.Furthermore,photodetectors based on the transferred PbS films were fabricated,exhibiting a high photoresponsivity of 7.5 A/W,a detectivity of 1.44×10^(12)Jones,and a rapid response time of approximately 0.25 s.This work sheds light on the batch production,green transfer,and optoelectronic application of PbS films.

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.

Comparison of α particle detectors based on single-crystal diamond films grown in two types of gas atmospheres by microwave plasma-assisted chemical vapor deposition

Chemical vapor deposition(CVD)-grown diamond films have been developed as irradiation-resistant materials to replace or upgrade current detectors for use in extreme radiation environments. However, their sensitivity in practical applications has been inhibited by space charge stability issues caused by defects and impurities in pure diamond crystal materials. In this study, two high-quality CVD-grown single-crystal diamond(SCD) detectors with low content of nitrogen impurities were fabricated and characterized. The intrinsic properties of the SCD samples were characterized using Raman spectroscopy, stereomicroscopy, and X-ray diffraction with the rocking curve mode, cathode luminescence(CL), and infrared and ultraviolet-visible-near infrared spectroscopies. After packaging the detectors, the dark current and energy resolution under α particle irradiation were investigated. Dark currents of less than 5 pA at 100 V were obtained after annealing the electrodes, which is comparable with the optimal value previously reported. The detector that uses a diamond film with higher nitrogen content showed poor energy resolution, whereas the detector with more dislocations showed poor charge collection efficiency(CCE). This demonstrates that the nitrogen content in diamond has a significant effect on the energy resolution of detectors, while the dislocations in diamond largely contribute to the poor CCE of detectors.

Insight into the capacity degradation and structural evolution of single-crystal Ni-rich cathodes

Single-crystal Ni-rich cathodes are a promising candidate for high-energy lithium-ion batteries due to their higher structural and cycling stability than polycrystalline materials.However,the phase evolution and capacity degradation of these single-crystal cathodes during continuous lithation/delithation cycling remains unclear.Understanding the mapping relationship between the macroscopic electrochemical properties and the material physicochemical properties is crucial.Here,we investigate the correlation between the physical-chemical characteristics,phase transition,and capacity decay using capacity differential curve feature identification and in-situ X-ray spectroscopic imaging.We systematically clarify the dominant mechanism of phase evolution in aging cycling.Appropriately high cut-off voltages can mitigate the slow kinetic and electrochemical properties of single-crystal cathodes.We also find that second-order differential capacity discharge characteristic curves can be used to identify the crystal structure disorder of Ni-rich cathodes.These findings constitute a step forward in elucidating the correlation between the electrochemical extrinsic properties and the physicochemical intrinsic properties and provide new perspectives for failure analysis of layered electrode materials.

Preparation and Tribological Investigation of Rare Earth Nanofilm on Single-Crystal Silicon Substrate

The self-assembled silicon substrate. The resultant contact angle meter and atomic method was introduced to successfully obtain film was characterized by means of X-ray rare earth（RE） nanofilm on a single-crystal photoelectron spectroscopy （XPS）, ellipsometer, force microscopy （AFM）. The scratch experiment was performed for interfacial adhesion measurement of the RE film. The friction and wear behavior of RE nanofilm was examined on a DF-PM reciprocating friction and wear tester. The results indicate the RE nanofilm is of low coefficient of friction （COF） and high wear resistance. These desirable characteristics of RE nanofilm together with its nanometer thickness, strong bonding to the substrate and low surface energy make it a promising choice as a solid lubricant film in micro electromechanical system （MEMS） devices.

Surface-to-bulk engineering with high-valence W^(6+) enabling stabilized single-crystal LiNi_(0.9)Co_(0.05)Mn_(0.05)O_(2) cathode

Single-crystal Nickel-rich layered oxides has been recognized as one of the promising cathodes for nextgeneration lithium batteries on account of their high capacity,while its practical application was hindered by structural instability and slow Li^(+) transfer kinetics.Herein,a surface-to-bulk engineered single-crystal LiNi_(0.9)Co_(0.05)Mn_(0.05)O_(2)(Ni90) cathode,which features W-doped bulk and Li_(2)WO_(4) surface layer,was successfully achieved by a one-step high-valence W^(6+) modification.The as-obtained W-modified Ni90 delivers excellent cycling stability(89.8% capacity retention after 300 cycles at 0.5 C)and rate capability.The enhanced electrochemical performance was ascribed to the doped-W induced stabilized lattice oxygen,reduced Li^(+)/Ni^(2+) mixing and inhibited H2-H3 phase transition in the bulk,and Li_(2)WO_(4) layer generated stabilized cathode/electrolyte interface.In addition,the thinner LiF-rich cathode electrolyte interphase(CEI) on surface and smaller grain size for W-modified Ni90 benefit to its Li^(+) diffusion dynamics.The effect of high-valence W^(6+)on single-crystal Ni-rich cathode was firstly revealed in detail,which deepens the understanding of electrochemical behavior of Ni-rich cathode with high-valence cations modification,and provides clues for design of high-performance layered cathodes.

Understanding the failure mechanism towards developing high-voltage single-crystal Ni-rich Co-free cathodes

Benefited from its high process feasibility and controllable costs,binary-metal layered structured LiNi_(0.8)Mn_(0.2)O_(2)(NM)can effectively alleviate the cobalt supply crisis under the surge of global electric vehicles(EVs)sales,which is considered as the most promising nextgeneration cathode material for lithium-ion batteries(LIBs).However,the lack of deep understanding on the failure mechanism of NM has seriously hindered its application,especially under the harsh condition of high-voltage without sacrifices of reversible capacity.Herein,singlecrystal LiNi_(0.8)Mn_(0.2)O_(2) is selected and compared with traditional LiNi_(0.8)Co_(0.1)Mn_(0.1)O_(2)(NCM),mainly focusing on the failure mechanism of Cofree cathode and illuminating the significant effect of Co element on the Li/Ni antisite defect and dynamic characteristic.Specifically,the presence of high Li/Ni antisite defect in NM cathode easily results in the extremely dramatic H2/H3 phase transition,which exacerbates the distortion of the lattice,mechanical strain changes and exhibits poor electrochemical performance,especially under the high cutoff voltage.Furthermore,the reaction kinetic of NM is impaired due to the absence of Co element,especially at the single-crystal architecture.Whereas,the negative influence of Li/Ni antisite defect is controllable at low current densities,owing to the attenuated polarization.Notably,Co-free NM can exhibit better safety performance than that of NCM cathode.These findings are beneficial for understanding the fundamental reaction mechanism of single-crystal Ni-rich Co-free cathode materials,providing new insights and great encouragements to design and develop the next generation of LIBs with low-cost and high-safety performances.

Controllably grown single-crystal films as flexoelectric nanogenerators for continuous direct current output

Until now,conventional nanogenerators could only produce electric pulses with relatively low-power densities.Herein,we invent a novel controllable growth technique for two-dimensional(2-D)cuprous oxide(p-Cu2O)single-crystal films,and on this basis,a new concept of 2-D single-crystal film flexoelectric nanogenerators(FENGs)are rationally designed and constructed for the first time,which has the characteristics of long-range order lattice,few grain boundaries and defects.More importantly,the accumulated built-in polarization potential in the bent 2-D p-Cu2O single-crystal film FENGs is in the same orientation as the output electricity,resulting in the first nanogenerator that can output continuous and stable electric signals with high voltage(Voc of 2.8 V),current(Jsc of 11.5μA·cm^(-2))and power density(14.4μW·cm^(-2)),exhibiting great practical application potential for power generation and motion capture.This research breaks new ground and establishes a precedent for high-performance and continuous-output nanogenerators,as well as smart wearable sensors.

Oxidation behavior of 4774DD1 Ni-based single-crystal superalloy at 980℃ in air

The oxidation behavior of a novel Ni-based single-crystal 4774DD1 superalloy for industrial gas turbine applications was investigated by the isothermal oxidation at 980℃ and discontinuous oxidation weight gain methods.The phase constitution and morphology of surface oxides and the characteristics of the crosssection oxide film were analyzed by XRD,SEM and EDS.Results show that the oxidation kinetics of the 4774DD1 superalloy follows the cubic law,indicating its weak oxidation resistance at this temperature.As the oxidation time increases,the composition of the oxide film evolves as following:One layer consisting of a bottom Al_(2)O_(3)sublayer and an upper(Al_(2)O_(3)+NiO)mixture sublayer after oxidized for 25 h.Then,two layers composed of an outermost small NiO discontinuous grain layer and an internal layer for 75 h.This internal layer is consisted of the bottom Al_(2)O_(3)sublayer,an intermediate narrow CrTaO_(4)sublayer,and an upper(Al_(2)O_(3)+NiO)mixture sublayer.Also two layers comprising an outermost relative continuous NiO layer with large grain size and an internal layer as the oxidation time increases to 125 h.This internal layer is composed of the upper(Al_(2)O_(3)+NiO)mixture sublayer,an intermediate continuous(CrTaO_(4)+NiWO_(4))mixture sublayer,and a bottom Al_(2)O_(3)sublayer.Finally,three layers consisting of an outermost(NiAl2O_(4)+NiCr2O_(4))mixture layer,an intermediate(CrTaO_(4)+NiWO_(4))mixture layer,and a bottom Al_(2)O_(3)layer for 200 h.

Fe_(16)N_2 single-crystal films with high saturation magnetization

Though the structure of α"-Fe16N2 was well known, the great interest in Fe16N2 arose from its giant saturation magnetic flux density which was found to be 2.58T at room temperature. The research work on preparing Fe16N2 in high abundance is active on both bulk materials and thin film form. However, up to now, only Sugita and his coworkers have successfully prepared Fe16N2 single-crystal films on semiconductor substrates because of its metastable property. They manifested that the Ms was up to 2.9 T at

The spin Hall effect in single-crystalline gold thin films

The spin Hall effect has been investigated in 10-nm-thick epitaxial Au(001) single crystal films via H-pattern devices,whose minimum characteristic dimension is about 40 nm. By improving the film quality and optimizing the in-plane geometry parameters of the devices, we explicitly extract the spin Hall effect contribution from the ballistic and bypass contribution which were previously reported to be dominating the non-local voltage. Furthermore, we calculate a lower limit of the spin Hall angle of 0.08 at room temperature. Our results indicate that the giant spin Hall effect in Au thin films is dominated not by the interior defects scattering, but by the surface scattering. Besides, our results also provide an additional experimental method to determine the magnitude of spin Hall angle unambiguously.

Magnetization reversal process in Fe/Si(001) single-crystalline film investigated by planar Hall effect

A planar Hall effect（PHE） is introduced to investigate the magnetization reversal process in single-crystalline iron film grown on a Si（001） substrate.Owing to the domain structure of iron film and the characteristics of PHE,the magnetization switches sharply in an angular range of the external field for two steps of 90° domain wall displacement and one step of 180°domain wall displacement near the easy axis,respectively.However,the magnetization reversal process near the hard axis is completed by only one step of 90° domain wall displacement and then rotates coherently.The magnetization reversal process mechanism near the hard axis seems to be a combination of coherent rotation and domain wall displacement.Furthermore,the domain wall pinning energy and uniaxial magnetic anisotropy energy can also be derived from the PHE measurement.

Electronic structure of single-crystalline graphene grown on Cu/Ni(111) alloy film

Graphene with a Dirac cone-like electronic structure has been extensively studied because of its novel transport properties and potential application for future electronic devices.For epitaxially grown graphene,the process conditions and the microstructures are strongly dependent on various substrate materials with different lattice constants and interface energies.Utilizing angle-resolved photoemission spectroscopy,here we report an investigation of the electronic structure of single-crystalline graphene grown on Cu/Ni(111)alloy film by chemical vapor deposition.With a relatively low growth temperature,graphene on Cu/Ni(111)exhibits a Dirac cone-like dispersion comparable to that of graphene grown on Cu(111).The linear dispersions forming Dirac cone are as wide as 2 e V,with the Fermi velocity of approximately 1.1×10^6 m/s.Dirac cone opens a gap of approximately 152 meV at the binding energy of approximately 304 meV.Our findings would promote the study of engineering of graphene on different substrate materials.

Magnetic Damping Properties of Single-Crystalline Co_(55)Mn_(18)Ga_(27) and Co_(50)Mn_(18)Ga_(32) Films

We investigate the structural,static magnetic and damping properties in two Mn-deficient magnetic Weyl semimetal Co-Mn-Ga(CMG) alloy films,i.e.,Co_(55)Mn_(18)Ga_(27)(CMG1) and Co_(50)Mn_(18)Ga_(32)(CMG2),which were epitaxially grown on MgO(001) substrates.CMG1 has a mixing phase of B2and L21,larger saturation magnetization(M_(s) ~760 emu/cm^(3)),stronger in-plane magnetic anisotropy.CMG2 has an almost pure B2phase,smaller M_(s)(~330 emu/cm^(3)),negligible in-plane magnetic anisotropy.Time-resolved magneto-optical Kerr effect results unambiguously demonstrate an obvious perpendicular standing spin wave(PSSW) mode in addition to the Kittel mode for both of the CMG films.The intrinsic damping constant is about 0.0055 and 0.015 for CMG1 and CMG2,respectively,which are both significantly larger than that of the stoichiometric CMG(i.e.,Co_(2)MnGa)film reported previously.In combination with the first-principles calculations,the intrinsic damping properties of the Mn-deficient CMG films can be well explained by considering the increase of density of states at the Fermi level,reduction of M_(s),and excitation of the PSSW mode.These findings provide a new clue to tuning the magnetic damping of the magnetic Weyl semimetal film through slight off-stoichiometry.

Heteroepitaxial Growth of Single-Crystalline Diamond Film

Using high temperature heteroepitaxial growth method the single-crystalline diamond film growth conditions have been studied by Raman spectrum and transmission electron diffraction.High temperature,low alcohol concentration,slow gas flow velocity,long epitaxial time and substrate located near the gas exit side on the susceptor are the favourable conditions for growing single-crystalline diamond film.

Tunable In-Plane Anisotropy in Amorphous Sm Co Films Grown on(011)-Oriented Single-Crystal Substrates

Amorphous Sm-Co films with uniaxial in-plane anisotropy have great potential for application in information-storage media and spintronic materials.The most effective method to produce uniaxial inplane anisotropy is to apply an in-plane magnetic field during deposition.However,this method inevitably requires more complex equipment.Here,we report a new way to produce uniaxial in-plane anisotropy by growing amorphous Sm-Co films onto(011)-cut single-crystal substrates in the absence of an external magnetic field.The tunable anisotropy constant,kA,is demonstrated with variation in the lattice parameter of the substrates.A kA value as high as about 3.3×10^4J·m^-3 was obtained in the amorphous Sm-Co film grown on a LaAlO3(011)substrate.Detailed analysis indicated that the preferential seeding and growth of ferromagnetic(FM)domains caused by the anisotropic strain of the substrates,along with the formed Sm-Co,Co-Co directional pair ordering,exert a substantial effect.This work provides a new way to obtain in-plane anisotropy in amorphous Sm-Co films.

Laser patterning of large-scale perovskite single-crystal-based arrays for single-mode laser displays

Lead halide perovskites have attracted considerable attention as potential candidates for high-performance nano/microlasers,owing to their outstanding optical properties.However,the further development of perovskite microlaser arrays(especially based on polycrystalline thin films)produced by the conventional processing techniques is hindered by the chemical instability and surface roughness of the perovskite structures.Herein,we demonstrate a laser patterning of large-scale,highly crystalline perovskite single-crystal films to fabricate reproducible perovskite single-crystal-based microlaser arrays.Perovskite thin films were directly ablated by femtosecond-laser in multiple low-power cycles at a minimum machining line width of approximately 300 nm to realize high-precision,chemically clean,and repeatable fabrication of microdisk arrays.The surface impurities generated during the process can be washed away to avoid external optical loss due to the robustness of the single-crystal film.Moreover,the high-quality,large-sized perovskite single-crystal films can significantly improve the quality of microcavities,thereby realizing a perovskite microdisk laser with narrow linewidth(0.09 nm)and low threshold(5.1µJ/cm2).Benefiting from the novel laser patterning method and the large-sized perovskite single-crystal films,a high power and high color purity laser display with single-mode microlasers as pixels was successfully fabricated.Thus,this study may offer a potential platform for mass-scale and reproducible fabrication of microlaser arrays,and further facilitate the development of highly integrated applications based on perovskite materials.

Effect of crystal orientation on tensile mechanical properties of single-crystal tungsten nanowire

Based on the high-purity single-crystal tungsten nanowire firstly prepared by the metal-catalyzed vapor-phase reaction method, molecular dynamics method was used to calculate tensile stress-strain curves and simulate microscopic deformation structures of the single-crystal tungsten nanowires with different crystal orientations of 〈100〉, 〈110〉and 〈111〉, in order to reveal the effect of crystal orientation on their tensile mechanical properties and failure mechanisms. Research results show that all of the stress-strain curves are classified into four stages： elastic stage, damage stage, yielding stage and failure stage, where 〈100〉orientation has a special hardening stage after yielding and two descending stages. The crystal orientation has little effect on elastic modulus but great effect on tensile strength, yielding strength and ductility, depending on different atomic surface energies and principal sliding planes. The calculated values of elastic modulus are in good agreement with the tested values of elastic modulus.

Dynamic recrystallization of single-crystal nickel-based superalloy

The dynamic recrystallization behavior of single-crystal（SC） superalloy SR.R99 at low strain rate was investigated by high-temperature creep testing.The results show that dynamic recrystallization may take place after the uncoated samples have been creep-tested in air at high temperature and low stress for a long time.Both the threshold temperature and strain for the dynamic recrystallization of SC superalloy SRR99 at low strain rate are lower than those for the static recrystallization.Dynamically recrystallized grains with the depth less than 15 μm are only located in the surface γ＇-free layers,and the recrystallized grains are well-developed grains without columnar y＇precipitates within them.The dynamic recrystallization behavior of SC superalloy SRR99 at low strain rate is mainly related to high-temperature oxidation.Suitable protective coating can effectively prevent the dynamic recrystallization of SC superalloy components in service.In addition,the dynamic recrystallization behavior of SC superalloy SRR99 at high strain rate was also studied by high-temperature compression testing.At high strain rate,a higher temperature and larger strain are needed for the occurrence of dynamic recrystallization than at low strain rate,and the recrystallized grains have cellular structures with an amount of columnar γ＇ precipitates within them.