Tuning the electrical transport of type II Weyl semimetal WTe2 nanodevices by Mo doping.

We fabricated nanodevices from MoxW1-xTe2 (x = 0, 0.07, 0.35), and conducted a systematic comparative study of their electrical transport. Magnetoresistance measurements show that Mo doping can significantly suppress mobility and magnetoresistance. The results for the analysis of the two band model show that doping with Mo does not break the carrier balance. Through analysis of Shubnikov-de Haas oscillations, we found that Mo doping also has a strong suppressive effect on the quantum oscillation of the sample, and the higher the ratio of Mo, the fewer pockets were observed in our experiments. Furthermore, the effective mass of electron and hole increases gradually with increasing Mo ratio, while the corresponding quantum mobility decreases rapidly.

Ca2+ detection utilising AlGaN/GaN transistors with ion-selective polymer membranes.

We demonstrate highly selective and sensitive potentiometric ion sensors for calcium ion detection, operated without the use of a reference electrode. The sensors consist of AlGaN/GaN heterostructure-based transistor devices with chemical functionalisation of the gate area using poly (vinylchloride)-based (PVC) membranes having high selectivity towards calcium ions, Ca2+. The sensors exhibited stable and rapid responses when introduced to various concentrations of Ca2+. In both 0.01 M KCl and 0.01 M NaCl ionic strength buffer solutions, the sensors exhibited near Nernstian responses with detection limits of less than 10-7 M, and a linear response range between 10-7-10-2 M. Also, detection limits of less than 10-6 M were achieved for the sensors in both 0.01 M MgCl2 and 0.01 M LiCl buffer solutions. AlGaN/GaN-based devices for Ca2+ detection demonstrate excellent selectivity and response range for a wide variety of applications. This work represents an important step towards multi-ion sensing using arrays of ion-selective field effect transistor (ISFET) devices.

Mercury(II) selective sensors based on AlGaN/GaN transistors.

This work presents the first polymer approach to detect metal ions using AlGaN/GaN transistor-based sensor. The sensor utilised an AlGaN/GaN high electron mobility transistor-type structure by functionalising the gate area with a polyvinyl chloride (PVC) based ion selective membrane. Sensors based on this technology are portable, robust and typically highly sensitive to the target analyte; in this case Hg2+. This sensor showed a rapid and stable response when it was introduced to solutions of varying Hg2+ concentrations. At pH 2.8 in a 10-2 M KNO3 ion buffer, a detection limit below 10-8 M and a linear response range between 10-8 M-10-4 M were achieved. This detection limit is an order of magnitude lower than the reported detection limit of 10-7 M for thioglycolic acid monolayer functionalised AlGaN/GaN HEMT devices. Detection limits of approximately 10-7 M and 10-6 M in 10-2 M Cd(NO3)2 and 10-2 M Pb(NO3)2 ion buffers were also achieved, respectively. Furthermore, we show that the apparent gate response was near-Nernstian under various conditions. X-ray photoelectron spectroscopy (XPS) experiments confirmed that the sensing membrane is reversible after being exposed to Hg2+ solution and rinsed with deionised water. The success of this study precedes the development of this technology in selectively sensing multiple ions in water with use of the appropriate polymer based membranes on arrays of devices.