不同极性6H-SiC表面石墨烯的制备及其电子结构的研究

在超高真空设备中,采用高温退火的方法在6H-SiC两个极性面(0001)和(000 1 - )面(即Si面和C面)外延石墨烯(EG). 利用低能电子衍射(LEED)和同步辐射光电子能谱(SRPES)对样品的生长过程进行了原位研究,而后利用激光拉曼光谱(Raman)和近边X射线吸收精细结构(XANES)等实验技术对制备的样品进行了表征. 结果表明我们在两种极性面均制备出了质量较好的石墨烯样品. 而有关两种石墨烯的对比性研究发现:Si面EG呈同一取向而C面EG呈各向异性;Si面EG与衬底存在类似 关键词： 石墨烯 6H-SiC 同步辐射 电子结构     

Advancing and receding wetting behavior of a droplet on a narrow rectangular plane

The contact angle (CA) measurements are generally performed on a large planar surface of a specific substrate with the width larger than the droplet size. In this study, the contact angle hysteresis on a narrow rectangular plane with a width smaller than the droplet size is experimentally studied through the inflation–deflation process by the needle–syringe method. The inflation process by stepwise addition of the liquid to the droplet leads to the contact line advancing outwardly along the major axis with advancing angle (θ_a). Although the droplet width is constrained by the edge of the plane, the CA along the minor axis (θ_w) increases and its value is greater than θ_a (θ_w > θ_a). Deflation process by stepwise withdrawal of liquid from the droplet results in the contact line retracting inwardly along the major axis as the CA reduces to receding angle (θ_r). In the meantime, the CA along the minor axis decreases as well. Both advancing and receding angles acquired from the narrow rectangular plane are confirmed with those obtained form the typical large surface of acrylic glass. On the basis of free energy minimization and liquid-induced defects model, Surface Evolver simulations are performed to reproduce the behavior of droplet on the narrow rectangular plane during the inflation–deflation process. The results of experiment and simulation agree with each other very well.     

Fabrication and characterisation of high performance polypyrrole modified microarray sensor for ascorbic acid determination

In this study, gold microelectrode array (Au/MEA) with electrode of 12 μm diameter was fabricated by photolithography technique. Subsequently, polypyrrole (Ppy) modified gold microarrays sensor (Ppy/Au/MEA) was prepared by cyclic voltammetry technique. The deposition potential range and number of cycles were optimised in order to get optimum thickness of Ppy film. Scanning Electron Microscope and Atomic Force Microscope investigations reveal that Ppy coating formed at 3 cycles is porous with thickness of 1.5 μm which exhibiting high catalytic current for ascorbic acid (AA) in square wave technique (SWV). In contrast to earlier sensors designs, these Ppy/Au/MEA sensors exhibits lower detection limit (LOD) of 10 nm towards AA at physiological conditions. It also exhibits enhanced sensitivity (2.5 mA cm⁻² mM⁻¹) and long range of linear detection limit from 10 nm to 2.8 mM. In the same way, polypyrrole modified macro Au (Ppy/Au/MA) biosensor was also fabricated and its electro catalytic property towards AA was compared with that of Ppy/Au/MEA. The Ppy/Au/MA exhibits sensitivity of only 0.27 mA cm⁻² mM⁻¹, LOD of 5 μM and linear range of 10 μM to 2.2 mM. Hence, our investigations indicate that the Ppy/Au/MEA could serve as highly sensitive sensor for AA than any of the earlier designs. So, the Ppy/Au/MEA electrode was utilised for determination AA in a wide variety of real samples.