Miao Lu

Conductance histogram evolution of an EC-MCBJ fabricated Au atomic point contact

This work presents a study of Au conductance quantization based on a combined electrochemical deposition and mechanically controllable break junction (MCBJ) method. We describe the microfabrication process and discuss improved features of our microchip structure compared to the previous one. The improved structure prolongs the available life of the microchip and also increases the success rate of the MCBJ experiment. Stepwise changes in the current were observed at the last stage of atomic point contact breakdown and conductance histograms were constructed. The evolution of 1G0 peak height in conductance histograms was used to investigate the probability of formation of an atomic point contact. It has been shown that the success rate in forming an atomic point contact can be improved by decreasing the stretching speed and the degree that the two electrodes are brought into contact. The repeated breakdown and formation over thousands of cycles led to a distinctive increase of 1G0 peak height in the conductance histograms, and this increased probability of forming a single atomic point contact is discussed.

Real-time spectroscopic monitoring of photocatalytic activity promoted by graphene in a microfluidic reactor

Photocatalytic microreactors have been utilized as rapid, versatile platforms for the characterization of photocatalysts. In this work, a photocatalytic microreactor integrated with absorption spectroscopy was proposed for the real-time monitoring of photocatalytic activity using different catalysts. The validity of this method was investigated by the rapid screening on the photocatalytic performance of a titanium oxide (TiO2)-decorated graphene oxide (GO) sheet for the degradation of methylene blue under monochromatic visible irradiation. The sampling interval time could be minimized to 10 s for achieving real-time detection. The best photocatalytic activity was observed for an optimized TiO2/GO weight mixing ratio of 7:11, with a reaction rate constant up to 0.067 min−1. The addition of GO into TiO2 enhances photocatalytic activity and adsorption of MB molecules. The synthetic reaction rate constant was up to approximately 0.11 min−1, which was also the highest among the catalysts. The microreactor exhibited good sensitivity and reproducibility without weakening the performance of the photocatalysts. Consequently, the photocatalytic microreactor is promising as a simple, portable, and rapid screening tool for new photocatalysts.

Low-temperature thermal reduction of suspended graphene oxide film for electrical sensing of DNA-hybridization

A reduced graphene oxide (RGO) based capacitive real time bio-sensor was presented. Suspended graphene oxide (GO) film was assembled electrophoretically between the source and drain electrodes of a transistor and then reduced by annealing in hydrogen/nitrogen forming gas to optimize the surface functional groups and conductivity. The resonance frequency of the transmission coefficient (S21) of the transistor was observed to shift with deoxyribonucleic acid (DNA)-hybridization, with a detecting limit of ~5nM. The advantages of the bio-sensing approach include low-noise frequency output, solution based real time detection and capable of on-chip integration.

Design and Fabrication of an MEA Microchip for Cell Culture Study

In this communication, we reported the design and fabrication of a gold microelectrode array (MEA) microchip for cell culture study in detail. The microchip contains a microfluidic channel with width of 20 μm, and solution is supplied via a syringe. Microelectrode array is fabricated by photolithography, reactive ion etching (RIE) and some other microfabrication techniques. Moreover, the microchip is compatible with Raman scattering investigation, providing a platform for simultaneous measurement of electrical and spectral response for a single cell under stimulation.

Defect-enhanced performance of a 3D graphene anode in a lithium-ion battery

Morphological defects were generated in an undoped 3D graphene structure via the involvement of a ZnO and Mg(OH)2 intermediate nanostructure layer placed between two layers of vapor-deposited graphene. Once the intermediate layer was etched, the 3D graphene lost support and shrank; during this process many morphological defects were formed. The electrochemical performance of the derived defective graphene utilized as the anode of a lithium (Li)-ion battery was significantly improved from ∼382 mAh g-1 to ∼2204 mAh g-1 at 0.5 A g-1 compared to normal 3D graphene. The derived defective graphene exhibited an initial capacity of 1009 mAh g-1 and retention of 83% at 4 A g-1 for 500 cycles, and ∼330 mAh g-1 at a high rate of 20 A g-1. Complicated defects such as wrinkles, pores, and particles formed during the etching of the intermediate layer, were considered to contribute to the improvement of the electrochemical performance.

Promising electroplating solution for facile fabrication of Cu quantum point contacts

In this article, we report on the fabrication and transport measurements of Cu quantum point contacts prepared by a novel, electrochemically assisted mechanically controllable break junction (EC-MCBJ) method. By employing photolithography and wet-etching processes, suspended electrode pairs were patterned and fabricated successfully on Si microchips. Rather than adopting an acid Cu electroplating solution, a novel alkaline electroplating solution was developed and utilized to establish Cu nanocontacts between electrode pairs. Typically, the widths of the as-fabricated Cu nanocontacts were found to be smaller than 18 nm. A large number of Cu quantum point contacts were then produced and characterized by a home-built MCBJ setup. In addition to the conventional histogram, where peaks tend to decrease in amplitude with increasing conductance, an anomalous type of conductance histogram, exhibiting different peak amplitudes, was observed. Through statistical analysis of the maximum allowable bending of the Si microchips, and theoretical calculations, we demonstrated that our alkaline Cu electroplating solution affords Cu nanocontacts that are compatible with subsequent MCBJ operations, which is essential for the fabrication of Cu quantum point contacts. As sophisticated e-beam lithography is not required, the EC-MCBJ method is fast, simple, and cost-effective. Moreover, it is likely to be suitable for the fabrication and characterization of quantum point contacts of various metals from their respective electroplating solutions.