Xiaoyue Zhang

Highly uniform bipolar resistive switching characteristics in TiO2/BaTiO3/TiO2 multilayer

Nanoscale multilayer structure TiO2/BaTiO3/TiO2 has been fabricated on Pt/Ti/SiO2/Si substrate by chemical solution deposition method. Highly uniform bipolar resistive switching (BRS) characteristics have been observed in Pt/TiO2/BaTiO3/TiO2/Pt cells. Analysis of the current-voltage relationship demonstrates that the space-charge-limited current conduction controlled by the localized oxygen vacancies should be important to the resistive switching behavior. X-ray photoelectron spectroscopy results indicated that oxygen vacancies in TiO2 play a crucial role in the resistive switching phenomenon and the introduced TiO2/BaTiO3 interfaces result in the high uniformity of bipolar resistive switching characteristics.

Mechanical characteristics of human red blood cell membrane change due to C60 nanoparticle infiltration

The mechanical characteristics of human red blood cell (RBC) membrane change due to C(60) nanoparticle (NP) infiltration have been investigated in the present work. Using experimental approaches, including optical tweezer (OT) stretching and atomic force microscopy (AFM) indentation, we found that RBCs in the presence of C(60) NPs are softer than normal RBCs. The strain-stress relations of both normal and C(60) infiltrated RBC membranes are extracted from the data of AFM indentation, from which we proved that C(60) NP infiltration can affect the mechanical properties of RBC membrane and tend to weaken the tensile resistance of lipids bilayers. In order to explain this experimental phenomenon, a mechanical model has been developed. Based on this model, the strain-stress relations of both normal and C(60) infiltrated lipid bilayers are calculated with consideration of intermolecular interactions. The theoretical results are in great agreement with the experimental results. The influence of C(60) NP concentration on the mechanical properties of RBC membrane is successfully predicted. Higher concentrations of C(60) NPs in the lipid bilayers will lead to increased damage to the cell membrane, implying that the dosage of C(60) NPs should be controlled in medical applications.

Structure-dependent electrical conductivity of protein: its differences between alpha-domain and beta-domain structures

Electron transports in the α-domain and β-domain of proteins have been comprehensively investigated. The structure-dependent electron transport of proteins has been experimentally measured and theoretically simulated, and both the theoretical and experimental results demonstrate significant differences in electrical conductivity between the α-domain and β-domain. By controlling the feedback system of the scanning tunneling microscope (STM), the conductance of a single α-domain protein hemoglobin (Hgb) and a β-domain protein superoxide dismutase enzyme (SOD) were measured, respectively. The current signal of Hgb is obviously stronger, indicating that the α-domain is more conductive. To confirm our finding, molecular orbitals of both the β-domain in SOD and α-domain in Hgb have been analyzed based on first-principles calculations. As expected, tunneling transport and hopping in the α-domain are both more efficient, indicating that it is easier for electrons to transport through the α-domain, which are in great agreement with our experimental data. In order to explain our results, molecular structures of α- and β-domains have been carefully analyzed and show that the explanation should lie in the differences in packing mode between the α-domain and β-domain. This research should be very important to application prospects in molecular electronics.

Switchable diode effect in ferroelectric thin film: High dependence on poling process and temperature

Pb(Zr0.53Ti0.47)O3 (PZT) thin film was fabricated on Pt/Ti/SiO2/Si substrate by chemical solution deposition method. Our results show a very great switchable ferroelectric diode effect (SFDE) in Pt-PZT-Au structure, which is more obvious and controllable than that in other ferroelectric thin films. The electrical conduction exhibits high rectifying behavior after pre-poling and the polarity of ferroelectric diode can be switched by changing the orientation of polarization in ferroelectric thin film. Our results also indicate that the SFDE in PZT film is highly dependent on remanent polarization and temperature. With the increase of remanent polarization, the forward current of bistable rectifying behavior observably reduces. Therefore, our measurement indicated that the biggest rectification ratio can reach about 220, which is found in 250K after +10V poling. By analyzing the conduction data, it is found that the dominant conduction mechanism of the SFDE in this sample is due to the space-charge-limited b...

Charge carrier transition in an ambipolar single-molecule junction: Its mechanical-modulation and reversibility

Precise control from the bottom-up for realizing tunable functionality is of utmost importance to facilitate the development of molecular electronic devices. Until now, however, manipulating charge carriers over single-molecule scale remains intractable. The origin of the problem is that the nature of charge carriers is often hindered by the complexity of the investigated molecular systems. Here, via ab initio simulations, we show a force-modulated and switched ambipolar single-molecule junction with Au/cyclopropane-1,2-dithiol/Au structure. The cyclopropane ring in the molecule can be opened and closed reversibly and repeatedly by the mechanical force. This structural transition from its closed state to open state enables the ambipolarity in charge carriers—from p-type to n-type. Analysis of electronic structure reveals unambiguously the force-dependent correlation between C–S bond order and the nature of charge carriers. Based on this, we design a binary interconnected junction exhibiting resistance, rectification and negative differential resistance functionalities under mechanical modulation, i.e., loading/unloading or pull/push. This interesting phenomenon provides both illuminating insight and feasible controllability into charge carriers in molecules, and a very general idea and useful approach for single-molecule junctions in practical single-molecule devices.Single-molecule switch for modular electronicsApplying force to a junction linking gold atoms leads to reversible switching of its electric properties, facilitating development of single-molecule devices. Building electronics from the molecular level up could lead to drastically smaller electronic circuits. Precisely controlling their functionality at the single-molecule scale is challenging. Yue Zheng and colleagues from China’s Sun Yat-sen University demonstrated by computer simulation that a cyclopropane-1,2-dithiol ring linking two gold atoms can be opened and closed reversibly and repeatedly using mechanical force, switching its electric properties from one that internally donates electrons to one that accepts them. Using the molecule as modular building block, they design a multifunctional junction that, with the application of mechanical force, exhibited resistance (increasing voltage leads to increased current), rectification (converts alternating current to direct) and negative differential resistance (increasing voltage leads to decreased current).

Stretchable ferroelectric nanoribbon and the mechanical stability of its domain structures

The high stability to maintain stored information under mechanical deformation is an essential requirement for the practical applications of stretchable electronics. In addition to storage stability, large deformation and easy fabrication are also desirable features for stretchable devices. In this work, we use wavy P(VDF-TrFE) nanoribbons to achieve a mechanical deformation of more than 20%, and the fabricating procedure eliminates the need for complicated etching steps and lithographic masks. The stored information, which is written on the ribbons in the form of ferroelectric domains, is able to remain unchanged after large mechanical deformation. After 10 000 stretching/releasing cycles, the polarization orientation remains the same with very little change of the intensity. These P(VDF-TrFE) nanoribbons with large deformation and high stability demonstrate great potential for the enhanced storage performance of future stretchable electronics.The high stability to maintain stored information under mechanical deformation is an essential requirement for the practical applications of stretchable electronics. In addition to storage stability, large deformation and easy fabrication are also desirable features for stretchable devices. In this work, we use wavy P(VDF-TrFE) nanoribbons to achieve a mechanical deformation of more than 20%, and the fabricating procedure eliminates the need for complicated etching steps and lithographic masks. The stored information, which is written on the ribbons in the form of ferroelectric domains, is able to remain unchanged after large mechanical deformation. After 10 000 stretching/releasing cycles, the polarization orientation remains the same with very little change of the intensity. These P(VDF-TrFE) nanoribbons with large deformation and high stability demonstrate great potential for the enhanced storage performance of future stretchable electronics.

High Current Density and Low Hysteresis Effect of Planar Perovskite Solar Cells via PCBM-doping and Interfacial Improvement

We propose a doping method by using [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) to fill the grain boundary interstices of the methylammonium lead iodide (CH3NH3PbI3) perovskite for the elimination of pinholes. A sandwiched PCBM layer is also used between the perovskite and TiO2 layers to improve the interfacial contact. By using these two methods, the fabricated perovskite solar cells show a low hysteresis effect and high current density, which result from the improved compactness at the grain boundaries of the perovskite surface and the interface between the TiO2/perovskite layers. The theoretical and experimental results indicate that PCBM can effectively suppress carrier recombination, regardless of the interfacial layer or dopant. We also found that the dark current reduced during the analysis of dark state current-voltage ( I- V) characteristics. The slopes of the I- V curves for the fluorine-doped tin oxide/PCBM-doped perovskite/Au device reduce monotonically with the increase in the PCBM concentration from 0.01 to 0.1 wt %, which suggest the decreasing defects in the perovskite layer. By tuning the PCBM doping and controlling the preparation process, we have successfully fabricated a planar TiO2/PCBM-based PCBM-doped perovskite photovoltaic device that reaches a high current density of 22.6 mA/cm2 and an outstanding photoelectric conversion efficiency up to 18.3%. The controllability of the PCBM doping concentration and interfacial preparation shed light on further optimization of the photoelectric conversion efficiency of perovskite solar cells.

The mechanics-modulated tunneling spectrum and low-pass effect of viscoelastic molecular monolayer

Understanding the force-induced conductance fluctuation in molecules is essential for building molecular devices with high stability. While stiffness of molecule is usually considered to be desirable for stable conductance, we demonstrate mechanical dragging in viscoelastic molecules integrates both noise resistance and mechanical controllability to molecular conductance. Via conductive atomic force microscope measurement and theoretical modeling, it’s found that viscoelastic Azurin monolayer has spectrum-like pattern of conductance corresponding to the duration and strength of applied mechanical pulse under low-frequency excitation. Conductance fluctuation is prevented under high-frequency excitation by dragging dissipation, which qualifies molecular junction with electric robustness against mechanical noise.

Reliable resistive switching and its tunability in La-doped PbTiO3\TiO2 composite bilayer

Nanoscale La-doped PbTiO3(PLT)\TiO2 (PLTT) composite structures have been fabricated. It shows that the structure presents reliable resistive switching (RS) behavior, and importantly, has great tunability on RS characteristics such as forming/set/reset voltages and resistance ratio by adjusting the PLT layer thickness. Particularly, the set voltage can be tuned at a large range from several volts to dozens of volts. Meanwhile, the set current keeps almost the same, indicating the RS is current dominating. The space-charge-limited current (SCLC) feature indicates that the localized traps are decisive for the RS. Our result sheds light on the prospects of composite structures for designing tunable RS devices.