Intercalation of hafnium oxide between epitaxially-grown monolayer graphene and Ir(111)substrate

Intercalation of insulating materials between epitaxial graphene and the metal substrates is highly demanded to restore the intrinsic properties of graphene,and thus essential for the graphene-based devices.Here we demonstrate a successful solution for the intercalation of hafnium oxide into the interface between full-layer graphene and Ir(111)substrate.We first intercalate hafnium atoms beneath the epitaxial graphene.The intercalation of the hafnium atoms leads to the variation of the graphene moire superstructure periodicity,which is characterized by low-energy electron diffraction(LEED)and lowtemperature scanning tunneling microscopy(LT-STM).Subsequently,we introduce oxygen into the interface,resulting in oxidization of the intercalated hafnium.STM and Raman's characterizations reveal that the intercalated hafnium oxide layer could effectively decouple the graphene from the metallic substrate,while the graphene maintains its high quality.Our work suggests a high-k dielectric layer has been successfully intercalated between high-quality epitaxial graphene and metal substrate,providing a platform for applications of large-scale,high-quality graphene for electronic devices.

Recent Progress on Flexible Room-Temperature Gas Sensors Based on Metal Oxide Semiconductor

With the rapid development of the Internet of Things,there is a great demand for portable gas sensors.Metal oxide semiconductors(MOS)are one of the most traditional and well-studied gas sensing materials and have been widely used to prepare various commercial gas sensors.However,it is limited by high operating temperature.The current research works are directed towards fabricating high-performance flexible room-temperature(FRT)gas sensors,which are effective in simplifying the structure of MOS-based sensors,reducing power consumption,and expanding the application of portable devices.This article presents the recent research progress of MOS-based FRT gas sensors in terms of sensing mechanism,performance,flexibility characteristics,and applications.This review comprehensively summarizes and discusses five types of MOS-based FRT gas sensors,including pristine MOS,noble metal nanoparticles modified MOS,organic polymers modified MOS,carbon-based materials(carbon nanotubes and graphene derivatives)modified MOS,and two-dimensional transition metal dichalcogenides materials modified MOS.The effect of light-illuminated to improve gas sensing performance is further discussed.Furthermore,the applications and future perspectives of FRT gas sensors are also discussed.

Machine learning the nuclear mass

Background:The masses of-2500 nuclei have been measured experimentally;however,>7000 isotopes are predicted to exist in the nuclear landscape from H(Z=1)to Og(Z=118)based on various theoretical calculations.Exploring the mass of the remaining isotopes is a popular topic in nuclear physics.Machine learning has served as a powerful tool for learning complex representations of big data in many fields.Purpose:We use Light Gradient Boosting Machine(LightGBM),which is a highly efficient machine learning algorithm,to predict the masses of unknown nuclei and to explore the nuclear landscape on the neutron-rich side from learning the measured nuclear masses.Methods:Several characteristic quantities(e.g.,mass number and proton number)are fed into the LightGBM algorithm to mimic the patterns of the residual δ(Z,A)between the experimental binding energy and the theoret-ical one given by the liquid-drop model(LDM),Duflo–Zucker(DZ,also dubbed DZ28)mass model,finite-range droplet model(FRDM,also dubbed FRDM2012),as well as the Weizsacker–Skyrme(WS4)model to refine these mass models.Results:By using the experimental data of 80%of known nuclei as the training dataset,the root mean square devia-tions(RMSDs)between the predicted and the experimental binding energy of the remaining 20%are approximately 0.234±0.022,0.213±0.018,0.170±0.011,and 0.222±0.016 MeV for the LightGBM-refined LDM,DZ model,WS4 model,and FRDM,respectively.These values are approximately 90%,65%,40%,and 60%smaller than those of the corresponding origin mass models.The RMSD for 66 newly measured nuclei that appeared in AME2020 was also significantly improved.The one-neutron and two-neutron separation energies predicted by these refined models are consistent with several theoretical predictions based on various physical models.In addition,the two-neutron separation energies of several newly measured nuclei(e.g.,some isotopes of Ca,Ti,Pm,and Sm)pre-dicted with LightGBM-refined mass models are also in good agreement with the latest experimental data.Conclusions:LightGBM can be used to refine theoretical nuclear mass models and predict the binding energy of unknown nuclei.Moreover,the correlation between the input characteristic quantities and the output can be inter-preted by SHapley additive exPlanations(a popular explainable artificial intelligence tool),which may provide new insights for developing theoretical nuclear mass models.

Fabrication of large-scale graphene/2D-germanium heterostructure by intercalation

We report a large-scale, high-quality heterostructure composed of vertically-stacked graphene and two-dimensional(2D) germanium.The heterostructure is constructed by the intercalation-assisted technique.We first synthesize large-scale,single-crystalline graphene on Ir(111) surface and then intercalate germanium at the interface of graphene and Ir(111).The intercalated germanium forms a well-defined 2D layer with a 2 × 2 superstructure with respect to Ir(111).Theoretical calculations demonstrate that the 2D germanium has a double-layer structure.Raman characterizations show that the 2D germanium effectively weakens the interaction between graphene and Ir substrate, making graphene more like the intrinsic one.Further experiments of low-energy electron diffraction, scanning tunneling microscopy, and x-ray photoelectron spectroscopy(XPS) confirm the formation of large-scale and high-quality graphene/2D-germanium vertical heterostructure.The integration of graphene with a traditional 2D semiconductor provides a platform to explore new physical phenomena in the future.

Correction to:Machine learning the nuclear mass

Following publication of the original article,Formula(2)is missing and Fig.11,Fig.9 are identical.The original article has been corrected and the Publisher apologized to the authors and the readers for the inconve-nience caused by this error.

A Degree Condition for Graphs Having All(a,b)-parity Factors

Let a and b be positive integers such that a≤b and a≡b(mod 2).We say that G has all(a,b)-parity factors if G has an h-factor for every function h:V(G)→{a,a+2,…,b-2,b} with b|V(G)| even and h(v)≡b(mod 2) for all v∈V(G).In this paper,we prove that every graph G with n≥2(b+1)(a+b) vertices has all(a,b)-parity factors if δ(G)≥(b^(2)-b)/a,and for any two nonadjacent vertices u,v ∈V(G),max{d_(G)(u),d_(G)(v)}≥bn/a+b.Moreover,we show that this result is best possible in some sense.

Sexual size monomorphism may evolve in lizards with a body size maximizing reproductive performance for both sexes

We used Takydromus septentrionalis,a sexually size-monomorphic lacertid lizard,as a model system to test the hypothesis that sexual size monomorphism may evolve in lizards where reproductive performance is maximized at a similar body size for both sexes.We allowed lizards housed in laboratory enclosures to lay as many clutches(for females)as they could or to mate as many times(for males)as they could in a breeding season.Size-assortative mating was weak but evident in T.septentrionalis,as revealed by the fact that male and female snout–vent lengths(SVLs)in mating pairs were significantly and positively correlated.Mating frequency(indicative of male reproductive performance)varied from 1 to 8 per breeding season,generally increasing as SVL increased in adult males smaller than 67.4 mm SVL.Clutch frequency varied from 1 to 7 per breeding season,with female reproductive performance(determined by clutch frequency,annual fecundity,and annual reproductive output)maximized in females with a SVL of 68.0 mm.Accordingly to our hypothesis,the reproductive performance was maximized in the intermediate sized rather than the largest individuals in both sexes,and the body size maximizing reproductive performance was similar for both sexes.Future work could usefully investigate other lineages of lizards with sexually monomorphic species in a phylogenetic context to corroborate the hypothesis of this study.

Solving Schrodinger equations using a physically constrained neural network

Deep neural networks(DNNs)and auto differentiation have been widely used in computational physics to solve variational problems.When a DNN is used to represent the wave function and solve quantum many-body problems using variational optimization,various physical constraints have to be injected into the neural network by construction to increase the data and learning efficiency.We build the unitary constraint to the variational wave function using a monotonic neural network to represent the cumulative distribution function(CDF)F(x)=ʃ^(x)_(-∞)Ψ*Ψdx',.Using this constrained neural network to represent the variational wave function,we solve Schrodinger equations using auto-differentiation and stochastic gradient descent(SGD)by minimizing the violation of the trial wave function(x)to the Schrodinger equation.For several classical problems in quantum mechanics,we obtain their ground state wave function and energy with very low errors.The method developed in the present paper may pave a new way for solving nuclear many-body problems in the future.

Integration Technology of Micro-LED for Next-Generation Display

Inorganic micro light-emitting diodes(micro-LEDs)based on II-V compound semiconductors have been widely studied for self-emissive displays.From chips to applications,integration technology plays an indispensable role in micro-LED displays.

Polarization-induced photocurrent switching effect in heterojunction photodiodes

The unipolar photocurrent in conventional photodiodes(PDs)based on photovoltaic effect limits the output modes and potential versatility of these devices in photodetection.Bipolar photodiodes with photocurrent switching are emerging as a promising solution for obtaining photoelectric devices with unique and attractive functions,such as optical logic operation.Here,we design an all-solid-state chip-scale ultraviolet(UV)PD based on a hybrid GaN heterojunction with engineered bipolar polarized electric field.By introducing the polarization-induced photocurrent switching effect,the photocurrent direction can be switched in response to the wavelength of incident light at 0 V bias.In particular,the photocurrent direction exhibits negative when the irradiation wavelength is less than 315 nm,but positive when the wavelength is longer than 315 nm.The device shows a responsivity of up to−6.7 mA/W at 300 nm and 5.3 mA/W at 340 nm,respectively.In particular,three special logic gates in response to different dual UV light inputs are demonstrated via a single bipolar PD,which may be beneficial for future multifunctional UV photonic integrated devices and systems.

Hierarchical highly ordered SnO_(2) nanobowl branched ZnO nanowires for ultrasensitive and selective hydrogen sulfide gas sensing

Highly sensitive and selective hydrogen sulfide(H_(2)S)sensors based on hierarchical highly ordered SnO_(2) nanobowl branched ZnO nanowires(NWs)were synthesized via a sequential process combining hard template processing,atomic-layer deposition,and hydrothermal processing.The hierarchical sensing materials were prepared in situ on microelectromechanical systems,which are expected to achieve high-performance gas sensors with superior sensitivity,long-term stability and repeatability,as well as low power consumption.Specifically,the hierarchical nanobowl SnO_(2)@ZnO NW sensor displayed a high sensitivity of 6.24,a fast response and recovery speed(i.e.,14 s and 39 s,respectively),and an excellent selectivity when detecting 1 ppm H_(2)S at 250°C,whose rate of resistance change(i.e.,5.24)is 2.6 times higher than that of the pristine SnO_(2) nanobowl sensor.The improved sensing performance could be attributed to the increased specific surface area,the formation of heterojunctions and homojunctions,as well as the additional reaction between ZnO and H_(2)S,which were confirmed by electrochemical characterization and band alignment analysis.Moreover,the well-structured hierarchical sensors maintained stable performance after a month,suggesting excellent stability and repeatability.In summary,such well-designed hierarchical highly ordered nanobowl SnO_(2)@ZnO NW gas sensors demonstrate favorable potential for enhanced sensitive and selective H_(2)S detection with long-term stability and repeatability.

Effect of thermal acclimation on thermal preference, resistance and locomotor performance of hatchling soft-shelled turtle

The significant influence of thermal acclimation on physiological and behavioral performance has been documented in many ectothermic animals, but such studies are still limited in turtle species. We acclimated hatchling soft-shelled turtles Pelodiscus sinensis under three thermal conditions （10, 20 and 30~C） for 4 weeks, and then measured selected body temperature （Tsel）, critical thermal minimum （CTMin） and maximum （CTM^x）, and locomotor performance at different body temperatures. Thermal acclimation significantly affected thermal preference and resistance of P sinensis hatchlings. Hatchling turtles accli- mated to 10~C selected relatively lower body temperatures and were less resistant to high temperatures than those acclimated to 20~C and 30~C. The turtles＇ resistance to low temperatures increased with a decreasing acclimation temperature. The thermal re- sistance range （i.e. the difference between CTM^x and CTMin, TRR） was widest in turtles acclimated to 20~C, and narrowest in those acclimated to 10~C. The locomotor performance of turtles was affected by both body temperature and acclimation tem- perature. Hatchling turtles acclimated to relatively higher temperatures swam faster than did those acclimated to lower temperatures. Accordingly, hatchling turtles acclimated to a particular temperature may not enhance the performance at that temperature. Instead, hatchlings acclimated to relatively warm temperatures have a better performance, supporting the ＂hotter is better＂ hypothesis.

High responsivity and flexible deep-UV phototransistor based on Ta-doped β-Ga_(2)O_(3)

Deep-ultraviolet(DUV)phototransistors have shown great potential applications in UV imaging,artificial intelligence,and wearable optoelectronics.Among a large number of wide bandgap semiconductors,the quasi-two-dimensionalβ-Ga_(2)O_(3) is considered as an ideal candidate for DUV photodetector applications.Herein,we report a high responsivity(R)and fully flexible Ta-dopedβ-Ga_(2)O_(3) DUV phototransistor which exhibits outstanding optoelectrical properties with a high R of 1.32×10^(6) A/W,a large detectivity of 5.68×10^(14) Jones,a great photo-to-dark current ratio of 1.10×10^(10)%,a high external quantum efficiency of 6.60×10^(8)%,and an ultra-fast response time of~3.50 ms.Besides,the flexible Ta-dopedβ-Ga_(2)O_(3) device also displays high reliability and mechanical flexibility that can sustain well after over 1×10^(4) bending cycles.Moreover,high-contrast imaging of UV light was obtained on the flexible DUV detector arrays,which can be efficiently trained and recognized by an artificial neural network.Our findings offer a perspective to develop wearable optoelectronics and UV imaging based on high-performance flexibleβ-Ga_(2)O_(3) DUV phototransistors,providing an inspiration for the future work in artificial intelligence and bionic robot fields.

Contributions of source population and incubation temperature to phenotypic variation of hatchling Chinese skinks

Phenotypic plasticity and local adaptation are viewed as the main factors that result in between-population variation in phenotypic traits,but contributions of these factors to phenotypic variation vary between traits and between species and have only been explored in a few species of reptiles.Here,we incubated eggs of the Chinese skink(Plestiodon chinensis)from 7 geographically separated populations in Southeast China at 3 constant temperatures(24,28,and 32℃)to evaluate the combined effects of dutch origin,source population,and incubation temperature on hatchling traits.The relative importance of these factors varied between traits.Nearly all examined hatchling traits,including body mass,snout-vent length(SVL),tail length,head size,limb length,tympanum diameter,and locomotor speed,varied among populations and were affected by incubation temperature.Measures for hatchling size(body mass and SVL)varied considerably among clutches.Source population explained much of the variation in hatchling body mass,whereas incubation temperature explained much of the variation in other examined traits.Our results indicate that between-population variation in hatchling traits of P.chinensis likely reflects the difference in natural incubation conditions and genetic divergence.

Highly sensitive and stable β-Ga_(2)O_(3) DUV phototransistor with local back-gate structure and its neuromorphic application

Deep ultraviolet(DUV)phototransistors are key integral of optoelectronics bearing a wide spectrum of applications in flame sensor,military detector,oil spill detection,biological sensor,and artificial intelligence fields.In order to further improve the responsivity of UV photodetectors based onβ-Ga_(2)O_(3),in present work,high-performanceβ-Ga_(2)O_(3) phototransistors with local back-gate structure were experimentally demonstrated.The phototransistor shows excellent DUV photoelectrical performance with a high responsivity of 1.01×107 A/W,a high external quantum efficiency of 5.02×109%,a sensitive detectivity of 2.98×1015 Jones,and a fast rise time of 0.2 s under 250 nm illumination.Besides,first-principles calculations reveal the decent stability ofβGa_(2)O_(3) nanosheet against oxidation and humidity without significant performance degradations.Additionally,the hexagonal boron nitride(h-BN)/β-Ga_(2)O_(3) phototransistor can behave as a photonic synapse with ultralow power consumption of~9.6 fJ per spike,which shows its potential for neuromorphic computing tasks such as facial recognition.Thisβ-Ga_(2)O_(3) phototransistor will provide a perspective for the next generation optoelectrical systems.

Novel two-dimensional transition metal chalcogenides created by epitaxial growth

Two-dimensional(2D) materials have been a very important field in condensed matter physics, materials science, chemistry, and electronics. In a variety of 2D materials, transition metal chalcogenides are of particular interest due to their unique structures and rich properties. In this review, we introduce a series of 2D transition metal chalcogenides prepared by epitaxial growth. We show that not only 2D transition metal dichalcogenides can be grown, but also the transition metal chalcogenides that do not have bulk counterparts, and even patterned transition metal chalcogenides can be fabricated. We discuss the formation mechanisms of the novel structures, their interesting properties, and potential applications of these 2D transition metal chalcogenides. Finally, we give a summary and some perspectives on future studies.

A Note on the Strong Edge-coloring of Outerplanar Graphs with Maximum Degree 3

A strong k-edge-coloring of a graph G is an assignment of k colors to the edges of G in such a way that any two edges meeting at a common vertex, or being adjacent to the same edge of G, axe assigned different colors. The strong chromatic index of G is the smallest integer k for which G has a strong k-edge-coloring. In this paper, we have shown that the strong chromatic index is no larger than 6 for outerplanax graphs with maximum degree 3.

MgO intercalation and crystallization between epitaxial graphene and Ru(0001)

Graphene on insulator is the foundation of its practical applications in electronic information technology.However,fabrication of graphene on insulating substrates suffers from small size and limited quality by direct growth of graphene on dielectric substrates,and the method of transferring graphene onto insulating substrates is not so compatible with the large-scale production in industry.Here,we report the fabrication of high-quality,large-area,single-crystal graphene on crystalline magnesium oxide(MgO),which has a dielectric constant of 7–10.Magnesium and oxygen are intercalated at the interface of epitaxial graphene/Ru(0001)and form crystalline structure after high-temperature annealing.The graphene/MgO/Ru(0001)sample was characterized by low energy electron diffraction(LEED),scanning tunneling microscopy(STM),X-ray photoelectron spectroscopy(XPS),and scanning transmission electron microscopy(STEM).LEED pattern shows that the magnesium oxide displays crystalline structure,and STM studies show clearly that the top layer is graphene.STEM characterization of as-intercalated sample demonstrates that the MgO intercalation layer,with a thickness of up to 2.3 nm,has a crystal structure of rock salt MgO,and the out-of-plane crystal orientation is[001].Our work provides a new route for fabrication of graphene on high dielectric constant insulators,which may have potential applications in future electronics.