Guangdong Zhou

Investigation of the behaviour of electronic resistive switching memory based on MoSe2-doped ultralong Se microwires

MoSe2-doped ultralong Se microwires of length/diameter ratio in the order of ∼240 are synthesized by hydrothermal method. An electronic resistive switching memory (ERSM) device using a single MoSe2-doped ultralong Se microwire is attained. The ERSM exhibits stable resistance ratio of ∼102 for 5000 s, highly stable performance during 500 stressing cycles, and excellent immunity to the frequency of the driving voltage. By investigating the dynamic processes of trap filling, de-trapping, and free-charge migration, trap-controlled space-charge-limited current mechanism is found to dominate the observed ERSM behaviour.

Hydrogen-peroxide-modified egg albumen for transparent and flexible resistive switching memory

Egg albumen is modified by hydrogen peroxide with concentrations of 5%, 10%, 15% and 30% at room temperature. Compared with devices without modification, a memory cell of Ag/10% H2O2-egg albumen/indium tin oxide exhibits obviously enhanced resistive switching memory behavior with a resistance ratio of 104, self-healing switching endurance for 900 cycles and a prolonged retention time for a 104 s @ 200 mV reading voltage after being bent 103 times. The breakage of massive protein chains occurs followed by the recombination of new protein chain networks due to the oxidation of amidogen and the synthesis of disulfide during the hydrogen peroxide modifying egg albumen. Ions such as Fe3+, Na+, K+, which are surrounded by protein chains, are exposed to the outside of protein chains to generate a series of traps during the egg albumen degeneration process. According to the fitting results of the double logarithm I-V curves and the current-sensing atomic force microscopy (CS-AFM) images of the ON and OFF states, the charge transfer from one trap center to its neighboring trap center is responsible for the resistive switching memory phenomena. The results of our work indicate that hydrogen- peroxide-modified egg albumen could open up a new avenue of biomaterial application in nanoelectronic systems.

Band gap energies for white nanosheets/yellow nanoislands/purple nanorods of CeO2

White nanosheets, yellow nanoislands and purple nanorods of CeO2 have been synthesized by a hydrothermal method. Indirect and direct photon energies of CeO2 of the white nanosheets (1.8, 2.1 eV), yellow nanoislands (2.2, 2.4 eV) and purple nanorods (2.0, 2.2 eV) are demonstrated, respectively. The difference in the electron spin–orbit coupling states between Ce 3d and O 2p may play an important role in their band gap energies.

Two-bit memory and quantized storage phenomenon in conventional MOS structures with double-stacked Pt-NCs in an HfAlO matrix

A two-bit memory and quantized storage phenomenon are observed at room temperature for a device based on the traditional MOS structure with double-stacked Pt-nanocrystals (Pt-NCs). A 2.68 and 1.72 V flat band voltage shift (memory window) has been obtained when applying a ±7 V programming/erasing voltage to the structures with double-stacked Pt-NCs. The memory windows of 2.40 and 1.44 V can be retained after stress for 10(5) seconds, which correspond to 89.55% and 83.72% stored charges reserved. The quantized charge storage phenomenon characterized by current-voltage (J-V) hysteresis curves was detected at room temperature. The shrinkage of the memory window results from the decreasing tunneling probability, which strongly depends on the number of stacks. The traps, de-traps and quantum confinement effects of Pt-NCs may contribute to the improvement of dielectric characteristics and the two-bit memory behavior. The multi-bit memory and quantized storage behavior observed in the Pt-NCs stacks structure at room temperature might provide a feasible method for realizing the multi-bit storage in non-volatile flash memory devices.

The interface degradation of planar organic–inorganic perovskite solar cell traced by light beam induced current (LBIC)

The light beam induced current (LBIC) method was adopted to nondestructively map the photoresponse of real planar organic–inorganic hybrid perovskite solar cells (PSCs). It is found that the photoresponse of the devices is not uniform even though the morphology of the perovskite films from scanning electron microscope (SEM) or atomic force microscope (AFM) images shows uniform character. This nonuniformity of the photoresponse of the devices is further exacerbated after degradation, which can be well traced by the LBIC method. The indistinguishable morphology change during the device degradation indicates that the degradation of the device is not mainly determined by the morphology of the perovskite layer, but by the interface between the perovskite and the electrode. By using the LBIC method, the worse performing area of the device is identified and then removed accordingly. The current density of the device can be enhanced from 19.44 mA cm−2 to 21.72 mA cm−2 after this clearance of the worse performing area.

Mechanism for bipolar resistive switching memory behaviors of a self-assembled three-dimensional MoS2 microsphere composed active layer

A self-assembled three-dimensional (3-D) MoS2 microsphere-based memristor with a favorable ON/OFF resistance ratio of ∼104, endurance, and retention time is demonstrated at room temperature. The formation and rupture of a localized Ag metallic filament, establishment and destruction of a boundary-based hopping path, and charge trapping and detrapping from the space charge region co-contribute to the bipolar resistive switching memory behaviours observed in the device of Ag/MoS2/ITO. This work may give insight into the mechanism of the resistive switching memory behaviours of a device with a 3-D micro-scale.

A novel retractable spring-like-electrode triboelectric nanogenerator with highly-effective energy harvesting and conversion for sensing road conditions

Integrated multi-layer structural triboelectric nanogenerators (TENGs) have been verified as an effective approach to solving the insufficient energy supply to single-layer devices. Unfortunately, the contact/separation asynchronism between triboelectric materials during the working stage severely hinders promotion of further output performance from TENGs. In this work, based on spring steel as both skeleton and electrode, we demonstrated a novel retractable spring-like-electrode TENG (SL-TENG) for harvesting vibratory energy. Benefiting from the specific elasticity of spring steel and the unique spring structure of the device, the contact/separation synchronism of a SL-TENG is integrally enhanced and further strengthened as vibration frequency increases, which can be used to tandem stack springs to efficiently collect and convert vibration energy in a small volume. A three-layer SL-TENG in a volume of approximate 5 cm3 can reach a maximum negative current of 9.4 μA and positive current of 8 μA at a frequency of 7 Hz, which is 4.09 and 2.29 times that at a frequency of 2 Hz, respectively. Including appropriate frequency, separation distance, and enlarged friction area, it was found that a devices internal resistance is decreased gradually with an increased number of layers. This may be one important reason for the boost in output performance of multi-layer SL-TENGs. In addition, the three-layer SL-TENG was applied to alternately illuminate tens of commercial LEDs, and the results attest that a SL-TENG is promising in the application of a self-powered sensor for monitoring road potholes.