Zhengchun Peng

Black Phosphorus Quantum Dots with Tunable Memory Properties and Multilevel Resistive Switching Characteristics.

Solution‐processed black phosphorus quantum‐dot‐based resistive random access memory is demonstrated with tunable characteristics, multilevel data storage, and ultrahigh ON/OFF ratio. Effects of the black phosphorous quantum dots layer thickness and the compliance current setting on resistive switching behavior are systematically studied. Our devices can yield a series of SET voltages and current levels, hence having the potential for practical applications in the flexible electronics industry.

Recent advances in black phosphorus-based photonics, electronics, sensors and energy devices

In the past several years, two-dimensional black phosphorus (BP) has captured the research communitys interest because of its unique electronic, photonic, and mechanical properties. Remarkable efforts have been made regarding the synthesis, fundamental understanding, and applications of BP in the fields of nanoelectronics, nanophotonics, and optoelectronics. In this review, we summarize the recent developments in the study of BP, which covers the state-of-the-art synthesis methods for preparing single-layer or few-layer BP, the recent advances in characterizing its electronic, optical and mechanical properties, and the reported functional devices utilizing such properties. Finally we discuss the existing challenges in developing BP-based nanoelectronics and optoelectronics, and describe the prospects for future BP-related research.

Ac Dielectrophoresis of Tin Oxide Nanobelts Suspended in Ethanol: Manipulation and Visualization

This article presents results of detailed and direct real-time observations of the wide variety of SnO(2) nanobelt motions induced by ac dielectrophoresis (DEP) in an innovative microfluidic setup. High ac electric fields were generated on a gold microelectrode (approximately 20 microm electrode gap) array, patterned on a glass substrate and covered by a approximately 10 microm tall polydimethylsiloxane (PDMS) microchannel. Ethanol suspended SnO(2) nanobelts were introduced into the microchannel, and the DEP experiments were performed. Negative DEP (repulsion) of the nanobelts was observed in the low-frequency range (<100 kHz) of the applied electric field, which caused rigid body motion as well as deformation of the nanobelts. The negative DEP effect observed in ethanol is unusual and contrary to what is predicted by the Clausius-Mossotti factor (using bulk SnO(2) conductivity and permittivity values) of the dipole approximation theory. In the high-frequency range (approximately 1-10 MHz), positive DEP (attraction) of the nanobelts was observed. Pearl chain formation involving short nanobelts and particles was also observed in the two DEP regimes.

Visualization Recording and Storage of Pressure Distribution through a Smart Matrix Based on the Piezotronic Effect

Pressure sensors that can both directly visualize and record applied pressure/stress are essential for e-skin and medical/health monitoring. Here, using a WO3 -film electrochromic device (ECD) array (10 × 10 pixels) and a ZnO-nanowire-matrix pressure sensor (ZPS), a pressure visualization and recording (PVR) system with a spatial resolution of 500 µm is developed. The distribution of external pressures can be recorded through the piezotronic effect from the ZPS and directly expressed by color changes in the ECD. Applying a local pressure can generate piezoelectric polarization charges at the two ends of the ZnO nanowires, which leads to the tuning of the current to be transported through the system and thus the color of the WO3 film. The coloration and bleaching process in the ECD component show good cyclic stability, and over 85% of the color contrast is maintained after 300 cycles. In this PVR system, the applied pressure can be recorded without the assistance of a computer because of the color memory effect of the WO3 material. Such systems are promising for applications in human-electronic interfaces, military applications, and smart robots.

A Highly Stretchable Transparent Self‐Powered Triboelectric Tactile Sensor with Metallized Nanofibers for Wearable Electronics

Recently, the quest for new highly stretchable transparent tactile sensors with large-scale integration and rapid response time continues to be a great impetus to research efforts to expand the promising applications in human-machine interactions, artificial electronic skins, and smart wearable equipment. Here, a self-powered, highly stretchable, and transparent triboelectric tactile sensor with patterned Ag-nanofiber electrodes for detecting and spatially mapping trajectory profiles is reported. The Ag-nanofiber electrodes demonstrate high transparency (>70%), low sheet resistance (1.68-11.1 Ω □-1 ), excellent stretchability, and stability (>100% strain). Based on the electrode patterning and device design, an 8 × 8 triboelectric sensor matrix is fabricated, which works well under high strain owing to the effect of the electrostatic induction. Using cross-locating technology, the device can execute more rapid tactile mapping, with a response time of 70 ms. In addition, the object being detected can be made from any commonly used materials or can even be human hands, indicating that this device has widespread potential in tactile sensing and touchpad technology applications.

Flexible Light Emission Diode Arrays Made of Transferred Si Microwires-ZnO Nanofilm with Piezo-Phototronic Effect Enhanced Lighting

Due to the fragility and the poor optoelectronic performances of Si, it is challenging and exciting to fabricate the Si-based flexible light-emitting diode (LED) array devices. Here, a flexible LED array device made of Si microwires-ZnO nanofilm, with the advantages of flexibility, stability, lightweight, and energy savings, is fabricated and can be used as a strain sensor to demonstrate the two-dimensional pressure distribution. Based on piezo-phototronic effect, the intensity of the flexible LED array can be increased more than 3 times (under 60 MPa compressive strains). Additionally, the device is stable and energy saving. The flexible device can still work well after 1000 bending cycles or 6 months placed in the atmosphere, and the power supplied to the flexible LED array is only 8% of the power of the surface-contact LED. The promising Si-based flexible device has wide range application and may revolutionize the technologies of flexible screens, touchpad technology, and smart skin.

Wafer-scale process for fabricating arrays of nanopore devices

Nanopore-based single-molecule analysis is a subject of strong scientific and technological interest. Recently, solid state nanopores have been demonstrated to possess advantages over biological (e.g., protein) pores due to the relative ease of tuning the pore dimensions, pore geometry, and surface chemistry. Previously demonstrated methods have been confined to the production of single nanopore devices for fundamental studies. Most of these techniques (e.g., electron microscope beams and focused ion beams) are limited in scalability, automation, and reproducibility. We demostrate a wafer-scale method for reproducibly fabricating large arrays of solid state nanopores. The method couples high-resolution electron-beam lithography and atomic layer deposition (ALD). Arrays of nanopores (825 per wafer) are successfully fabricated across 4-in. wafers with tunable pore sizes. The nanopores are fabricated in 16- to 50-nm thin silicon nitride. ALD of aluminum oxide is used to tune the nanopore size. By careful optimization of the processing steps, a device survival rate of up to 96% is achieved on a wafer with 50-nm thin silicon nitride films. Our results facilitate an important step in the development of large-scale nanopore arrays for practical applications such as biosensing.

Direct and rapid detection of RNAs on a novel RNA microchip.

Direct, rapid, and accurate detection of pathogen RNAs is essential for controlling the spread of infectious diseases, such as H1N1 influenza or other infectious agents that can cause epidemics.[1-3] Nucleic acid-based detection systems, such as real-time PCR and DNA microchips (or microarrays), offer high detection specificity and sensitivity and are able to detect single-nucleotide differences in pathogens, genes, and diseases.[4-14] Though these technologies are powerful, RNAs from viable pathogens are not directly detected, and must be indirectly analyzed by cDNA amplification and detection. It is also difficult to use these technologies to detect the partially degraded pathogenic RNAs that can provide information on pathogen viability. Since it is difficult to amplify and label RNAs, it is extremely challenging to directly detect RNAs, let alone fragments. In addition, a few of the current methods for RNA direct detection, such as the Northern blot, RNase protection assay, microRNA profiling, and direct RNA sequencing,[15] are labor intensive, costly or instrument-intensive. They are not well suited to rapid and high-throughput RNA detection, especially not for point-of-care diagnosis and other applications.

Interdigitated Array Electrodes with Magnetic Function as a Particle-Based Biosensor

A particle-based electrochemical biosensor was developed by integrating soft magnetic material, NiFe, with interdigitated array (IDA) electrodes. The NiFe strips were embedded beneath the IDA electrodes and acted as magnetic traps to collect the enzyme labeled paramagnetic particles from a microchannel flow of particle suspension. The IDA electrodes, which overlap on top of the NiFe strips, are designed to detect in close proximity the enzyme product that is produced from the particle surface. The sensors were fabricated in such a way that the particles were positioned among IDA electrodes without blocking the active electrode surface. The theoretical prediction of the sensor response is presented. It is expected that both sensitivity and limit of detection of the biosensor would be improved significantly.

Ultra-Low Power Microbridge Gas Sensor

A miniature, ultra-low power, sensitive, microbridge gas sensor has been developed. The heat loss from the bridge is a function the thermal conductivity of the gas ambient. Miniature thermal conductivity sensors have been developed for gas chromatography systems [1] and microhotplates have been built with MEMS technology which operates with mW’s of power [2]. In this work a lower power microbridge was built with polysilicon silicon micromachining. Sixteen microbridges were fabricated on each die, of length 50-100 um, thickness 1 um, and width 1 um, as shown in Fig. 1. A voltage was applied to the sensor and the resistance calculated based upon the current flow. The response has been tested with air, carbon dioxide, helium, and nitrogen. A comparison of the resistance change for each gas is given in Fig. 2 for a 50um long bridge. The resistance and temperature change for carbon dioxide was the greatest, while that for helium was the least. The sensor responds to ambient gas very rapidly. Fig. 3 shows transient response in helium, giving a time constant of 12 μs. Another aspect of the sensor is that has very low power consumption. With helium present, at 4 Volts, for the time period shown in Figure 3, the power consumption is that of 54.1 μJ. The sensor response to different concentrations of helium is shown in Fig 4. At 5V operation it was found to have a resistance change of 2.05 milliohms per ppm helium. The higher voltages yielded higher resistance changes for all of the gases tested. In conclusion, the microbridge has a very fast response and is sensitive to the thermal conductivity of the gas mixture and operates at low power. Acknowledgements: Many thanks to NASA for financial support and KWJ Engineering for technical assistance during the course of the work.