bluuebunny/crossref_metadata_2025 huggingface dataset:
Suppression of the blinking of single QDs by using an N-type semiconductor nanomaterial
Authors: Wang Zao  , Zhang Guo-Feng  , Li Bin  , Chen Rui-Yun  , Qin Cheng-Bing  , Xiao Lian-Tuan  , Jia Suo-Tang  ,   State Key Laboratory of Quantum Optics and Quantum Optics Devices, Institute of Laser Spectroscopy, Shanxi University, Taiyuan 030006, China
Published: December 2020

Single quantum dots (QDs) always exhibit strong blinking in fluorescence intensity when they are on some inert substrates. The blinking activity is attributed to the photoinduced charging of QDs by electron transfer (ET) to trap states in QDs and the surrounding matrix, which has been considered as an undesirable property in many applications. Here, we use N-doped indium tin oxide (ITO) semiconductor nanoparticles to suppress fluorescence blinking activity of single CdSe/ZnS core/shell QDs. The fluorescence characteristics of single QDs in ITO and on SiO2 cover glass are measured by a laser scanning confocal fluorescence microscopy, respectively. It is found that the on-and off-state probability densities of QDs on different substrates both can be fit by a truncated power law. Blinking rates for single QDs on glass and in ITO are also calculated. By contrast, single QDs doped in ITO show that their blinking rate and fluorescence lifetime both decrease. The on-state probability density of single QDs in ITO is approximately two orders of magnitude higher than that of QDs on SiO2 cover glass. It means that single QDs doped in ITO have a longer time to be on-state. Because the Fermi level in QDs is lower than in ITO, when they are in contact, electrons in ITO will transfer to QDs. As a result, the equilibration of their Fermi levels leads to the formation of negatively charged QDs. These electrons fill in the holes of QDs shell and enhance the on-state probability of QDs. Fluorescence decays of single QDs on glass and in ITO are measured by TAC/MCA, and they can be fit by biexponential function. The two lifetime values correspond to the single exciton lifetime and biexciton lifetime of QDs, respectively. It is worth noting that the distribution of the amplitude weighted average lifetime for single QDs in ITO is approximately 41% of that for single QDs on SiO2 cover glass and its full width at half maximum (FWHM) is changed to 50%. For the conduction band potential of QDs is higher than that of ITO, which contributes to photoinduced interfacial electron transfer from QDs to ITO and leads to the increase of nonradiative transition. These indicate that ITO can reduce single exciton and biexciton lifetime of QDs. The study demonstrates that ITO can effectively suppress the blinking activity of QDs.
Fabrications of different Sb content p-SnO2 thin films
Authors: Feng Qiu-Ju  , Liu Yang  , Pan De-Zhu  , Yang Yu-Qi  , Liu Jia-Yuan  , Mei Yi-Ying  , Liang Hong-Wei  ,   School of Physics and Electronic Technology, Liaoning Normal University, Dalian 116029, China;,   School of Physics and Optoelectronic Engineering, Dalian University of Technology, Dalian 116024, China
Published: December 2020

Tin oxide (SnO2) is a wide-band-gap semiconductor with a bandwidth of 3.6 eV at room temperature, which is widely used in many fields, such as gas sensors, transparent electrodes and optoelectronic devices due to its high optical transparency, low resistivity, and higher chemical and physical stability. However for the real applications of SnO2 based optoelectronic devices, it is necessary to obtain both n-type and p-type SnO2 materials. Unfortunately, SnO2 is intrinsically an n-type semiconductor material, therefore most efforts have been made to obtain p-type SnO2 materials. In this paper, SnO2 thin films with different Sb12 concentrations are grown on Al2O3 substrates by chemical vapor deposition method through using Sb2O3 and SnO as reaction source. The surface morphology, elemental concentration, and structural properties of SnO2 thin films with different Sb concentrations are investigated by field-emission scanning electron microscopy, energy-dispersive spectroscopy and X-ray diffraction, respectively. As the Sb content increases, the SnO2 thin films become more smooth and the grain size increases, indicating that the crystal quality of the thin film is improved. It is also found small amount of Sb doping of SnO2 thin film can be act as a surfactant. Moreover, the Hall measurement results indicate that the Sb doped SnO2 thin film has a p-type conductivity for an optimum Sb2O3/SnO mass ratio of 1:5. The optical absorption spectrum measurement indicates that the energy gap of sample is evidently blue-shifted with increasing Sb doping concentration. Furthermore, the Sb doped p-SnO2/n-SnO2 thin film homojunction is successfully fabricated to verify the p-type conductivity of Sb doped SnO2. The Sb doped p-SnO2/n-SnO2 homojunction device shows good rectifier characteristics, and its forward-turn-on voltage is 3.4 V.
Functional coupling analyses of electroencephalogram and electromyogram based on multiscale transfer entropy
Authors: Xie Ping  , Yang Fang-Mei  , Chen Xiao-Ling  , Du Yi-Hao  , Wu Xiao-Guang  ,   Key Laboratory of Measurement Technology and Instrumentation of Hebei Province, Institute of Electric Engineering, Yanshan University, Qinhuangdao 066004, China
Published: December 2020

Synchronization analyses of electroencephalogram (EEG) and electromyogram (EMG) could reveal the functional corticomuscular coupling (FCMC) between sensorimotor cortex and motor units firing in a target muscle. In order to quantitatively analyze the nonlinear functional coupling characteristics of EEG and EMG on a multiple time scale, a multiscale transfer entropy (MSTE) method based on the transfer entropy theory is proposed. Considering the multi-scale characteristics of EEG and EMG signals, the EEG and EMG signals are firstly decomposed into multiscale ones, respectively, to show the information on different time scales. Then the signals on different time scales are decomposed into different frequency bands to show the frequency domain characteristics. Finally, the EEG and EMG in different frequency bands on different scales are calculated by the MSTE method to obtain the FCMC characteristics on different time scales and in coupling frequency bands. In this study the MSTE is used to quantitatively analyze the nonlinear functional connection between EEG over the brain scalp and the surface EMG from the flexor digitorum surerficialis (FDS), which are recorded simultaneously during grip task with steady-state force output.#br#In the process of data processing, the coarse graining method is introduced firstly to decompose the EEG and EMG recorded in the task. Secondly, MSTEs between EEG and EMG on various scales are calculated to describe the nonlinear FCMC characteristics in different pathways (EEG→EMG and EMG→EEG). Furthermore, a significant indicator of MSTE is defined to quantitatively analyze the discrepancy between FCMC interaction strengths in the specific frequency band. The results show that the functional corticomuscular coupling is significant in both descending (EEG→EMG) and ascending (EMG→EEG) directions in the beta-band (15-35 Hz) in the static force output stage, especially that the interaction strength in descending direction is stronger in beta2-band (15-35 Hz) than that in the ascending direction. Meanwhile, the maximum FCMC strength value and the maximum or minimum discrepancy value between coupling directions on different scales almost occur on the high scales (15-30). Our study confirms that beta oscillations of EEG travel bidirectionally between the sensorimotor cortex and contralateral muscles in the sensorimotor loop system, and beta2 band is likely to reflect the motor control commands from the cortex to the muscle. Additionally, the discrepancy varies on different time scales and in different coupling frequency bands. The results show that the MSTE can quantitatively estimate the nonlinear interconnection and functional corticomuscular coupling between the sensorimotor cortex and the muscle.
A strip anvil apparatus with linear uniform pressure distribution
Authors: Tang Fei  , Chen Li-Ying  , Liu Xiu-Ru  , Wang Jun-Long  , Zhang Lin-Ji  , Hong Shi-Ming  ,   Key Laboratory of Advanced Technologies of Materials, Ministry of Education of China, School of Physical Science and Technology, Southwest Jiaotong University, Chengdu 610031, China;,   School of Science, Wuhan University of Technology, Wuhan 430070, China
Published: December 2020

Bridgman anvil is a useful and effective tool in high-pressure research. However, in this apparatus, the pressure distribution is essentially centrosymmetric. Thus, considerable pressure gradients exist in the gasket and in the sample chamber respectively, and the uniform pressure area is limited. To improve the pressure uniformity in flat face supported anvils, we design a strip face anvil instead of conventional round face anvil and adopt an assortive strip gasket. Principle analysis and a series of pressure calibration experiments are also presented in this paper.The construction of the strip anvil and relevant parts of the apparatus are shown in the diagrams and photos. The relationship between pressure and shearing stress in the strip gasket is investigated by using the model of M. Wakatsuki, which indicates that the pressure distribution should be uniform along the central line of the strip gasket.Pressure calibration experiments are conducted by using strip anvils made of tungsten carbide with a length of 20 mm and width of 5 mm and by using the assortive strip gasket of pyrophyllite. Pressures at different places of the central line are calibrated according to the known phase transitions of bismuth in the same loading process, and the samples are assembled with symmetrical, unsymmerical, and separated local collocations, respectively.Experimental results exhibit that the pressure reaches up to 10 GPa in the central line of the strip gasket, and the pressures are almost equal at least within the range of 12 mm on the central line. The bias errores of oil pressures measured at different places of the central line are all less than 2.0% at 2.55 GPa and 3.6% at 7.7 GPa, indicating only a small pressure gradient along the central line. The main reason for the measuring bias errors lies in the difficulty of the assembly technique. Specifically, the bismuth wire is difficult to adhere to the central line of the anvil during compression. Hence, further improvement of the process is expected in the future.In conclusion, the strip anvil is a unique high-pressure apparatus. The principle analysis and pressure calibration experiments confirm that the pressure is uniform in one-dimensional direction along the central line of the strip anvil. This feature is propitious to the accurate investigation of linear samples under high pressure.
Influence of the anharmonic vibration on the Young modulus and the phonon frequency of the graphene
Authors: Cheng Zheng-Fu  , Zheng Rui-Lun  ,   College of Electronic and Electrical Engineering, Chongqing University of Arts and Sciences, Chongqing 402160, China
Published: December 2020

In the frame of the Harrison bonded-orbital method, the variations of the force constant, the Young modulus, the torsional modulus and the phonon frequency with temperature are given through the relevant theory or method of the solid state physics with considering the non-harmonic effect and the short-range interaction of atoms. Results show that the force constant, the Young modulus, the torsional modulus, the phonon frequency and the Poissons coefficient all vary with temperature. The results show that the first three quantities increase with temperature but not very much; the phonon frequency increases with temperature rapidly; the Poissons coefficient decreases fast with the increase of temperature. There are transverse vibrations along the direction perpendicular to the bond-length direction and the longitudinal vibrations along the bond-length direction, in which the longitudinal vibrations are dominant. The nonharmonic effect of the longitudinal vibration is much larger than that of the transverse vibration. The first and the second non-harmonic coefficient of the transverse vibration are both much less than those of the longitudinal vibration, where 0/0 8.477 and 2/2 156. The above five physical quantities are constant at different temperatures if the first and second nonhamonic effects are omitted, which does not conform to the experimental results. After the first and second nonhamonic effects are considered, they all increase with temperature and results are in good agreement with experimental data. The anharmonic effect increases with temperature.
Analysis of the dynamics of water confined in hydrated calcium silica(C-S-H) based on the quasi-elastic neutron scattering spectra
Authors: Deng Pei-Na  , Yi Zhou  , Zhang Li-Li  , Li Hua  ,   Department of Physics, Jinan University, Guangzhou 510632, China
Published: December 2020

Cement is a widely used construction material in the world. Calcium-silicate-hydrate (C-S-H) is the main component of aged cement (concrete). The quality and durability of concrete are strongly affected by the dynamics of water confined in it. Dynamics of the confined water can be studied experimentally by the quasi-elastic neutron scattering (QENS). In this paper, the jump-diffusion and rotation-diffusion model (JRM) is used to fit the QENS spectra of C-S-H paste samples at different measured temperatures for the whole scattering vector Q-range from 0.3 to 1.7 -1. Five important parameters are extracted to describe the dynamics of water confined in C-S-H samples: the index of immobile water C, the rotational diffusion constant Dr, the mean square displacement (MSD) u2 , the self-diffusion coefficient Dt, and the average residence time between jumps 0. Here, all the C-S-H samples, each with a 30% weight ratio of water to cement, are measured at temperatures ranging from 230 to 280 K. The fitted parameters can quantitatively describe the dynamics of water confined on different scales of C-S-H gel pores. The results show that the QENS spectra are fitted very well not only for small Q (Q 1 -1) but also for large Q (Q 1 -1). The obtained rotational diffusion constant is Q dependent. Thus the contribution of the water molecule rotation to a QENS spectrum increases with the value of Q increasing. The mean square displacement (MSD) u2 decreases with the increase of Q, which can be used to distinguish the confined water, ultra-confined water, and bound water contained in C-S-H samples. When Q is small, the fitted Dt and 0 vary with the measured temperature. Dt has a maximum value at 230 K and 0 has a peak at 240 K. These indicate that the dynamics of the confined water shows different behaviors at 230 K and 240 K. There are crossover or critical phenomena for water confined in C-S-H sample at low temperature.
Theoretical research on the generation of a submicron localized hollow beam and its applications in the trapping and cooling of a single atom
Authors: Ren Rui-Min  , Yin Ya-Ling  , Wang Zhi-Zhang  , Guo Chao-Xiu  , Yin Jian-Ping  ,   Department of Physics, State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai 200062, China
Published: December 2020

In order to generate a submicron localized hollow laser beam and realize the more efficient laser cooling and trapping of a single atom, a simple and promising scheme with using the system of a single mode fiber a circle binary phase plate and a microlens is proposed in this paper. From Rayleigh-Sommerfeld diffraction theory, the intensity distribution of the generated localized hollow laser beam near the focal plane and its propagating properties in free space are calculated. Also, the dependences of the dark-spot size of the localized hollow beam on the mode radius of single mode fiber and the focal length of the mocrolens are studied. The calculated results show that the intensity distribution of the localized hollow beam presents approximately symmstrical distribution near the focal plane. In the center of the focal plane, the light intensity is 0 and increases gradually around it. So a closed spherical light field (i.e., localized hollow laser beam) with a radius of 0.4 m is generated. The calculated results also show that the dark-spot size of the localized hollow laser beam decreases with the increasing of the microlens focal length and the decreasing of the single mode fiber mode radius. So proper parameters of this optical system can be chosen to generate localized hollow laser beams with different sizes for various applications. When the localized hollow laser beam is blue detuned, atoms will be trapped in the minimum light filed. If a repumping laser beam is applied, the trapped atoms will be also cooled by the intensity-gradient Sisyphus cooling. In this paper, we build a device for trapping and cooling a single atom by using the generated blue detuned submicron localized hollow laser beam. We study the dynamical process of intensity-gradient cooling of a single 87Rb atom trapped in the localized hollow beam by Monte-Carlo method. Our study shows that a single 87Rb atom with a temperature of 120 K (the corresponding momentum is 30ħk) from a magneto-optical trap (MOT) can be directly cooled to a final tempreture of ～ 5.8 K (the corresponding momentum is ～ 6.6ħk). So an ultracold single atom is generated and trapped in our submicro localized hollow beam. This device for obtaining ultralcold single atom can be widely uesd in the regions of the optical physics, the atom and molecule optics, such as the detecting of the fundamental physical parameters, realizing the quantum computer, studying the cold collision of singe atoms, and realizing the single atom laser.
A method of evaluating the quality of dual-path entangled quantum microwave signal generated based on von Neumann entropy
Authors: Li Xiang  , Wu De-Wei  , Wang Xi  , Miao Qiang  , Chen Kun  , Yang Chun-Yan  ,   School of Information and Navigation, Air Force Engineering University, Xi'an 710077, China
Published: December 2020

The entangled state of continuous variables of microwave frequency is an important resource in the field of quantum. In order to apply it to quantum communication protocol and quantum radar, the entanglement between two spatially separated subsystems, namely dual-path entangled quantum microwave is needed. However, for the circuit that generates the entangled quantum microwave, there is no suitable method to indicate whether the quality of the entangled microwave signal is good or not. Aiming at this problem, we put forward a method of evaluating the quality of dual-path entangled quantum microwave signals generated based on von Neumann entropy. The origin of the entangled quantum microwave is that vacuum state signals are transformed into squeezed state signals in driven pump, so in this paper we use a two-mode squeezed vacuum state to describe the formation of dual-path entangled quantum microwave signal, thus providing the function relation between the photon number and the squeezed parameter. In a communication system, the signal-noise ratio is usually used to express the reliability of system. Entropy is a measure of disorder degree in information. If both of them can be made the analogy, the entropy is used to evaluate the proportion of entangled state signals, the quality of original signals will be evaluated and the relationship among the entropy and squeezed parameter and the photon number will be analyzed. The simulation results show that the photon number in the entangled quantum microwave signal is determined by the squeezed parameter, and there is an index change with the square rule between them. Entropy decreases with the increase of squeezed parameter: its minimum value is 0, and its maximum value can be found from 0.9 to 1. The slope of curve is steep near the maximum, which reflects that the influence of squeezed parameter on the degree of entanglement is obvious, and that the range of optimal value choices in squeezed parameter is very narrow. The optimal value of squeezed parameter is dependent on photon number; it increases with the increase of the photon number. Entropy tends to decrease smoothly with the increase of squeezed parameter and it approximately has a negative exponent relation. The photon number in an actual signal is limited, so the limit value of entropy is estimated to be about 65%. The research shows that the quality of the entangled microwave signal can be improved by choosing appropriate squeezed parameter in different circuits that generate dual-path entangled quantum microwave signals for meeting the actual needs. Therefore, the research can provide the method of choosing the parameters of dual-path entangled quantum microwave circuit and improve the availability of system.
Stochastic multi-resonance induced by partial time delay in a Watts-Strogatz small-world neuronal network
Authors: Sun Xiao-Juan  , Li Guo-Fang  ,   Department of Mathematics, School of Science, Beijing University of Posts and Telecommunications, Beijing 100876, China
Published: December 2020

In a neuronal system, propagation speed of neuronal information is mainly determined by the length, the diameter, and the kind of the axons between the neurons. Thus, some communications between neurons are not instantaneous, and others are instantaneous or with some negligible delay. In the past years, effects of time delay on neuronal dynamics, such as synchronization, stochastic resonance, firing regularity, etc., have been investigated. For stochastic resonance, it has been reported recently that stochastic multi-resonance in a neuronal system can be induced by time delay. However, in these studies, time delay has been introduced to every connection of the neuronal system. As mentioned in the beginning, in a real neuronal system, communication between some neurons can be instantaneous or with some negligible delays. Thus, considering the effect of partial time delay (time delay is called as partial time delay if only part of connections are delayed) on neuronal dynamics could be more meaningful.In this paper, we focus on discussing effect of partial time delay on response amplitude of a Watts-Strogatz neuronal network which is locally modeled by Rulkov map. With the numerically obtained results, we can see that partial time delay can induce a stochastic multi-resonance which is indicated by the multi-peak characteristics in the variation of response amplitude with partial time delay. Namely, partial time delay could also induce stochastic multi-resonance in a neuronal system. Moreover, we also find that optimal response amplitude can be reached in much wider range of the partial time delay value when delayed connections are less (i.e., the partial time delay probability is small). This is different from the case in which all connections are delayed, where response amplitude become optimal only when time delay is nearly the multiples of external signal's period. But the range of the partial time delay value becomes narrower and narrower with the increasing of the partial time delay probability and when the partial time delay probability is large enough, response amplitude becomes optimal only when time delay is nearly the multiples of external signal period. It is similar to the case where all connections are delayed. Furthermore, effects of random rewiring probability and total link number in the neuronal network on partial time delay induced stochastic multi-resonance are also studied. It is found that partial time delay induced stochastic multi-resonance is robust to random rewiring probability but not robust to total link number. Stochastic resonance is a very important nonlinear phenomenon in neuroscience, thus, our obtained results could have some implications in this field.
Bacteria sterilization application by using plasma activated physiological saline
Authors: Wang Xue-Yang  , Qi Zhi-Hua  , Song Ying  , Liu Dong-Ping  ,   School of Physics and Materials Engineering, Dalian Minzu University, Dalian 116600, China
Published: December 2020

The plasma activated water has great application prospects in the fields of environmental protection, biomedicine, food safety, et al., due to its unique chemical activity. In this work, the plasma activated physiological saline is successfully generated by using hollow fiber-based cold microplasma jet array running in physiological saline solution. This design can lead to an obvious increase in the contact area between microplasmas and treated physiological saline solution, thus improving the chemical reaction efficiency of short-lived species. The influences of working gases such as He, N2, O2 and air on the sterilization efficiency of E. Coli by using this plasma activated physiological saline are investigated as a function of discharge time. As the discharge time increases from 10 to 180 s, the sterilization efficiency of the plasma activated physiological saline significantly increases. It is found that the bactericidal efficiency of the air discharge activated physiological saline is highest. For a discharge time of 120 s, the sterilization efficiency of E. Coli in this plasma activated physiological saline can reach as high as 99.999%. The pH value of this air discharge activated physiological saline is achieved by using acidity meter and as the discharge time increases from 10 to 60 s, the pH value decreases from 7.3 to 3.1 and the physiological solution becomes acidic. This may be due to the NOX produced in the plasma reacting with water and producing nitric and nitrate acids. The reactive oxygen species generated in the plasma activated physiological saline are supposed to be O3 and H2O2. The concentrations of O3 and H2O2 are identified by using UV-visible absorption spectra and chemical deposition methods. The strong absorption peak of O3 in UV-visible absorption spectrum is at a wavelength of 253.7 nm. The concentration of O3 is calculated by using Beer-Lambert Law. As the discharge time increases, the concentration of O3 in the plasma activated physiological saline obviously increases. For a discharge time of 60 s, the concentration of O3 is 43.1210-3 mol/L and nearly saturated. The concentration of H2O2 is obtained by the total amount of reactive oxygen species, which is calculated by using the chemical deposition method, deducting the O3 content. As the discharge time increases from 10 to 180 s, the concentration of H2O2 increases from 1.510-3 to 4.710-3 mol/L. The analyses of experimental data from various methods indicate that air discharge activated physiological saline containing a variety of long-lived reactive oxygen species, such as H2O2 and O3, is very effective in killing E. Coli cells in the acidic saline solution. The air discharge activated physiological saline can provide a means to store the advanced oxidation species induced by the discharge for sterilization applications.
Kinetic study of nanorods self-assembly process based on logistic function model
Authors: Yan Zhao  , Zhao Wen-Jing  , Wang Rong-Yao  ,   School of Physics, Beijing Institute of Technology, Beiing 100081, China
Published: December 2020

Understanding the complicated kinetic process involved in nanoparticle self-assembly is of considerable importance for designing and fabricating functional nanostructures with desired properties. In this work, using the stopped-flow absorption technique, we investigate kinetic behaviors involved in gold nanorod assembly mediated by cysteine molecules. Further combining with SEM microstructural analyses of the assembly structure of gold nanorods, we establish the correlations between the kinetic parameter and the assembled structure. The dynamical surface plasmonic absorptions of gold nanorods are monitored during the formation of GNRs chains with different assembly rates. And the acquired kinetic data are analyzed in the frame of the second-order theoretical model, which has been widely used in the literature for linear assembly of gold nanorods. We find that the second-order theoretical model for describing the kinetic behaviors is merely limited to the case of slow assembly process of gold nanorods, but shows large deviation when the assembly process is relatively fast. We, therefore, propose in this work a new kinetic model on the basis of the logistic function, to make kinetic analyses for the different assembly rates of gold nanorods. Compared with the second-order theoretical model, this new logistic function model possesses an extended validity in describing the kinetic behaviors of both the slow and relatively fast nanorods assembly. Particularly, due to introduction of a new parameter, i.e., the exponential parameter p, the logistic function model enables a more accurate description of the kinetic behavior at a very earlier assembly stage (e.g., on a millisecond scale), in addition to quantifying the assembly rate T0. More importantly, the value of p derived from the new logistic function model allows us to establish the kinetics-structure relationship. The slow assembly process that produces mainly the one-dimensional linear chains of nanorods, is featured by the value of kinetic parameter p close to 1. By contrast, for the relatively fast assembly process that results in the formations of irregular zigzag chains even two-dimensional assembled structures of nanorods, the value of kinetic parameter approaches to 2. Furthermore, in the present study, the kinetic parameter p based on the logistic model might be related to the fractal dimension (Df) of the aggregated structures of the gold nanorods self-assembly processes. These results suggest that the logistic function model could provide the kinetic features for directly quantifying the fractal structures of the nanorods assembly. We believe that the new kinetic analysis method presented in this work could be helpful for an in-depth understanding of the kinetics-structure-property relationship in self-assembled plasmonic nanostructures.
Effects of annealing temperature and Ga content on properties of solution-processed InGaZnO thin film
Authors: Zhang Shi-Yu  , Yu Zhi-Nong  , Cheng Jin  , Wu De-Long  , Li Xu-Yang  , Xue Wei  ,   Thin Film and Display Laboratory, School of Optoelectronics, Beijing Institute of Technology, Beijing 100081, China
Published: December 2020

Oxide thin film transistor with an oxide channel layer is investigated to cater to the requirements of transparent electronics for the high mobility, good uniformity, and large band gap. Owing to its special conduction mechanism, high carrier mobility can be realized even in the amorphous phase. Oxide-based thin films have been prepared by using a number of methods, such as pulsed laser deposition, chemical vapor deposition, radio-frequency sputtering and solution-derived process. Solution processing is commonly used in TFT applications because of its simplicity and potential application in printed device fabrication. In the solution process, the conductivity of multicomponent oxide films can be controlled by incorporating charge-controlling cations. In this paper, bottom-gat topcontact thin film transistors are fabricated by using solution processed InGaZnO channel layers. The effects of annealing temperature and Ga content on the properties of thin film transistor are examined. Optical transmittance of InGaZnO thin film is greater than 80% in the visible region. Electrical characteristics of InGaZnO thin film transistor are improved by increasing annealing temperature. The threshold voltage of solution-processed InGaZnO transistor decreases from 6.74 to -0.62 V with annealing temperature increasing from 250 to 400 ℃, owing to the increase in electron concentration in the active layer. A lower annealing temperature suppresses the generation of carriers outside of the control of Ga cations. X-ray photoelectron spectrum measurement shows that the electron concentration increases because oxygen vacancies generate electrons. The incorporation of Ga into a InZnO compound system results in reducing the carrier concentration of the film and an off-current of thin film transistor. As the Ga ratio is increased at an identical In and Zn content, the carrier concentration of the film decreases and the threshold voltage of thin film transistor shifts towards the positive direction. As the content of Ga is increased in the oxide active layer of transistor, the subthreshold amplitude decreases, and the on/off ratio is improved. This is a consequence of the Ga ions forming strong chemical bonds with oxygen as compared with the Zn and In ions, acting as a carrier suppressor. The performances of thin film transistor with an atomic ratio of In: Ga: Zn=5:1.3:2 are optimized as follows: saturation mobility of 0.43 cm2/(Vs), threshold voltage of -1.22 V, on/off current ratio of 4.7104, subthreshold amplitude of 0.78 V/decade.
Research progress on oxide-based thin film transisitors
Authors: Lan Lin-Feng  , Zhang Peng  , Peng Jun-Biao  ,   State Key Laboratory of Luminescence Materials and Devices, South China University of Technology, Guangzhou 510640, China
Published: December 2020

Oxide semiconductor is regarded as one of most suitable active materials of thin-film transistors (TFTs) for driving organic light-emitting diodes because of its advantages of high mobility, low-temperature processing, good electrical uniformity, visible-light transparency, and low cost. Currently oxide TFTs have been successfully applied to the backplanes of the flat-panel displays. This review gives a comprehensive understanding of the development process of oxide TFTs. In the present article, we review the major trend in the field of oxide TFTs. First, the questions of how to achieve high-mobility and high-stability oxide semiconductors are introduced, and the carrier transport mechanism is also addressed. Next, the device structures and the fabrication processes of the oxide TFTs are introduced. The electrical instability of the oxide TFTs is also discussed, which is critical for their applications in backplanes of the flat-panel displays. Especially, the mechanism of the threshold voltage instability of the oxide TFTs under negative bias illuminant stress is discussed in detail. Finally, the applications of oxide TFTs in flat-panel displays, such as active matrix organic light-emitting diodes and flexible displays, are addressed.
Reconstruction of polarization parameters in channel modulated polarization imaging system
Authors: Qiang Fan  , Zhu Jing-Ping  , Zhang Yun-Yao  , Zhang Ning  , Li Hao  , Zong Kang  , Cao Ying-Yu  ,   Shanxi Key Laboratory of Information Photonic Technique, Key Laboratory for Physical Electronics and Devices of the Ministry of Education, School of Electronic and Information Engineering, Xi’an Jiaotong University, Xi’an 710049, China;,   Xichang Satellite Launch Center, Xichang 615000, China;,   Beijing Area Key Laboratory of Opt-Mechatronic Equipment Technology, Beijing 102617, China
Published: December 2020

Based on the reconstruction of the polarization parameters in a channel modulating polarization imaging system, the polarization features of the target could be extracted effectively. Considering that the reconstruction of polarization parameters can provide important reference for target recognition, material analysis, remote sensing and bio-medical treatment, the research on accurate reconstruction of polarization parameters is now urgently required. In order to improve the accuracy of polarization parameter reconstruction, we first study the influence of sample frequency of interference fringes on the imaging process. For the same carrier frequency, conjugate spectra are separated and also the spectra are not aliasing for two adjacent spectral lines. It is concluded that to prevent the image spectrum from aliasing, the sample frequency should be at least 4 times the maximum fringe frequency of the polarization interference image. Then we study Stokes parameter reconstruction method when the spectral line positions of interference image are changed by assembling error. Since different Stokes parameters are amplitude modulated at different frequencies, we apply segment filters to split the frequency domain into different regions, and seek for the largest spectrum in corresponding regions. The largest spectrum in different regions can be used to determine the spectral line position of polarization carrier frequency, and the two-dimensional images of the target are rebuilt in sequence by the frequency shifting, spectral filtering, and Fourier inversion transforming. According to the above method, we could obtain an exact polarization rebuilding image when the line position of polarization carrier frequency is modified. Finally, we use the computer simulation and experiment to verify the feasibility and effectiveness of such a rebuilding method. The results demonstrate that the reconstruction of polarization parameters in channel modulating polarization imaging by this rebuilding method is better than by the traditional theoretical rebuilding method. In detail, the mean square error between the reconstruction and original input image could be suppressed to 0.001 while the peak-signal-to-noise ratio is improved and the structural similarity index measurement could be more than 0.9 by utilizing the new rebuilding method. It turns out that the reconstruction method with great superiority can provide a promising reference for further research of channel modulating polarization imaging system.
Molecular dynamics simulations of the adsorption of bisphenol A on graphene oxide
Authors: Lin Wen-Qiang  , Xu Bin  , Chen Liang  , Zhou Feng  , Chen Jun-Lang  ,   School of Sciences, Zhejiang A & F University, Lin’an 311300, China;,   School of Information and Industry, Zhejiang A & F University, Lin’an 311300, China;,   Zhejiang Province Environmental Radiation Monitoring Center, Hangzhou 310012, China
Published: December 2020

The elimination of bisphenol A (BPA) from water solution is of great importance, since BPA can cause the functional abnormalities of human endocrine system. One feasible removal method is the adsorption by graphene oxide (GO). However, the interactions between BPA and GO at an atomic level are still unclear. In this study, molecular dynamics simulations are performed to investigate the adsorption of BPA on the GO surface. The results show that all BPA molecules are attached to both sides of GO. The adsorption conformations of BPA in the closest layer to GO surface mainly exhibit two patterns. One is that the benzene rings of BPA are parallel to the basal plane of GO to form - structures, and the other is the two hydroxyl groups of BPAs interacting with the oxygen-contained groups on GO to form hydrogen bonds. Exploration of the detailed interactions between BPA and GO indicates that the hydrophobic - stacking interaction is the dominant force in the adsorption of BPA on GO, while hydrogen bonding enhances the binding of BPA on GO surface. Eventually, potential of mean forces (PMF) of BPA and water molecules on GO are calculated by umbrella sampling. The binding energy of BPA on GO reaches 30 kJ/mol, six times as large as that of water on GO, which is only about 5 kJ/mol. Our simulations further confirm that GO owns strong adsorption capacity and GO can be used as sorbent to eliminate BPA in water solution.
Warping transform of the refractive normal mode in a shallow water waveguide
Authors: Qi Yu-Bo  , Zhou Shi-Hong  , Zhang Ren-He  ,   State Key Laboratory of Acoustics, Institute of Acoustics, Chinese Academy of Sciences, Beijing 100190, China
Published: December 2020

In a shallow water waveguide, the low-frequency acoustic field can be viewed as a sum of normal modes. Warping transform provides an effective tool to filter the normal modes from the received signal of a single hydrophone, which can be used for source ranging and geoacoustic inversion. However, it should be noted that the conventional warping operator h(t) = t2+tr2 is only valid for a signal consisting of reflection dominated modes, where r represents the source range. In a waveguide with a strong thermocline or a surface channel where refracted modes dominate the received sound field, the dispersive characteristics of the waveguide become different and the performance of the warping operator h(t) = t2+tr2 will be significantly degraded. In this paper, the dispersive characteristics and warping transform of the refractive normal modes in a waveguide with a linearly decreased sound speed profile are discussed. The formulae for the horizontal wavenumber, the phase in frequency domain and the instantaneous phase in time domain of the refractive mode are deduced. Based on these formulae, the time warping and frequency warping operators verified by the simulated data are presented. Through time-axis stretching or compression, the time warping operator h(t) =tr-t2, where tr= r/c(h) and c(h) represents the bottom sound speed, can transform the refracted modes into single-tone components of frequencies determined by source range, sound speed gradient of water, bottom sound speed and mode number. The frequency warping operator h(f) = Df3, where D is a constant, can transform the refracted modes into separable impulsive sequences through frequency-axis stretching or compression and the time delay of the impulsive sequences changes linearly with the source range. As the warped modes are separated in time domain or frequency domain, these two operators can be used for filtering the refracted normal modes from the received signal. The theories in this paper are also applicable for refractive modes in the waveguide with a linearly increased sound speed profile or a linear variation of the square of the index of refraction (n2-linear sound speed profile).
Electrical resistivity of nanostructured aluminum at low temperature
Authors: Sun Li-Jun  , Dai Fei  , Luo Jiang-Shan  , Yi Yong  , Yang Meng-Sheng  , Zhang Ji-Cheng  , Li Jun  , Lei Hai-Le  ,   School of Material Science and Engineering, Southwest University of Science and Technology, Mianyang 621010, China;,   Research Center of Laser Fusion, China Academy of Engineering Physics, Mianyang 621900, China
Published: December 2020

The nanostructured materials have been revealed to have exclusive physical and chemical properties due to their quantum-size effects, small-size effects and a large fraction of grain boundaries. Especially, the grain boundaries play an important role in the electrical resistivity of nanostructured metal. We use the four-point probe method to measure the values of electrical resistivity () of the nanostructured aluminum samples and the coarse-grained bulk aluminum samples at temperature (T) ranging from 8 K to 300 K to explore the relationship between the electrical resistivity and temperature. The aluminum nanoparticles produced by the flow-levitation method through electromagnetic induction heating are compacted into nanostructured samples in vacuum by the hot pressing and sintering technology. The microstructures of all nanostructured aluminum samples are analyzed by X-ray diffraction (XRD), transmission electron microscope (TEM), scanning electron microscope with the energy-dispersive spectrometer (SEM-EDS). The densities of all nanostructured aluminum samples are measured by using the Archimedes method (the medium is absolute alcohol). The experimental results show that the shape of aluminum nanoparticles is found to keep spherical from the SEM images and the relative density of all nanostructured aluminum samples is about 93% of the coarse-grained bulk aluminum. The XRD spectra state that the face-centered cubic (fcc) phase dominates the samples and no diffraction peak related to impurities appears in the XRD spectrum for each of all nanostructured aluminum samples. Amorphous alumina layers (about 2 nm thick) are found to surround the aluminum nanoparticles and hence connect the grains in the nanostructured aluminum as shown in the high-resolution TEM images. Owing to the scattering of grain boundaries on electrons and the phonon-electron scattering at grain boundaries, the electrical resistivity is far larger in the nanostructured aluminum than in the coarse-grained bulk aluminum and the relationship between the electrical resistivity and temperature for nanostructured aluminum shows a different feature from that for the coarse-grained bulk aluminum. Although the temperature dependent electrical resistivity ((T)) is a function of T4 at low temperatures for the coarse-grained bulk aluminum, it varies with the temperature not only according to the relation T4, but also according to the relation T3 for the nanostructured aluminum. The residual resistivity (0) of the nanostructured aluminum sample is about 5.510-4m, 5-6 orders magnitude larger than that of the coarse-grained bulk aluminum (2.0110-10m) due to the scattering of both the grain boundaries and amorphous alumina on electrons therein.
Simulation studies on the diffusion of water solitons in carbon nanotube
Authors: Li Yang  , Song Yong-Shun  , Li Ming  , Zhou Xin  ,   School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100049, China
Published: December 2020

Fluid transport is a very common phenomenon. Recently flow process in nanochannels has drawn much attention, since it differs quite much from that in macroscopic pipes. In particular, the motion of confined water molecules in nonpolar nanochannels has become a hotspot in nanotechnology, and also an important issue in biology and chemistry. Besides the experimental studies, computer simulations (e.g., molecular dynamics simulation) have also been proven to be a powerful tool to investigate such issues. Early simulations focused on the concurrent motion of all water molecules inside nanochannels such as carbon nanotubes (CNTs), where water molecules are evenly spaced in a single file and occasionally but collectively transport through CNTs. Recently, a new model of water transport in CNTs was presented, which indicates that water-density defects in the one-dimensional (1D) chain of water molecules can move as solitons. This is explained as a natural consequence of competition between water-water interactions and water-CNT interactions. While this new model is very appealing, the identification of soliton is not a trivial work (especially at not very low temperatures), since the density defects of water molecules might not be easily recognized from their thermal fluctuation. In this paper, a new method is developed to precisely identify the soliton by quenching the simulation conformations to their nearest neighboring local minima. Based on the new soliton identification method, we study the motion of water in single-walled armchair CNTs by all-atom molecular dynamics simulations. We investigate the motion of solitons in detail, which is observed as a standard 1D diffusion on a picosecond time scale. The simulations also show that the diffusion coefficient of solitons increases with temperature rising, and decreases with the number density of solitons increasing. These results are consistent with the postulation that there exists a weak repulsion between solitons.