Xueshen Wang

Investigation of single quantum Hall device of resistance standard in NIM

We report in CPEM 2014 our latest results of the study of single quantum Hall device for the resistance standard in National Institute of Metrology, China (NIM). Experimental results indicate quantized Hall devices with satisfied longitudinal resistance, low contact resistance, and good breakdown current are obtained. Comparison of the quantum Hall resistance to a precise transfer resistance standard is made using direct current comparator (DCC). A measurement resolution on the level of 10-7 is obtained which is limited by the DCC resolution.

Material preparation and fabrication of graphene-based quantum hall resistance devices

We report in CPEM 2012 the preparation of the micromechanical cleavage (MC) and the chemical vapor deposition (CVD) graphene films and the fabrication of the quantum Hall resistance (QHR) devices on these films. Graphene films are on the SiO2/Si substrates. Spectroscopic Raman analysis indicates monolayer graphene films are obtained. Hall bar structures are formed on graphene films by e-beam lithography, metallization, and oxygen plasma etching.

Study of dry etching process using SF 6 and CF 4 /O 2 for Nb/Nb x Si 1−x /Nb Josephson-junction fabrication

Both SF₆ and CF₄ are plasma chemistries that are often used during dry etching in fabricating the niobium Josephson junctions. This paper presents the preliminary experimental results of using these two etches on etching Nb/Nb_xSi_1-x/Nb Josephson junctions in NIM.

Improvement of chemical vapor deposition graphene for quantum Hall resistance standards

Quantum Hall (QH) standard devices based on chemical vapor deposition (CVD) graphene have not shown properties as excellent as the one based on epitaxial graphene on SiC. This is because of the impurity, defects and inhomogeneity. In this paper, we demonstrate the progress on improving the quality of CVD graphene by the surface acidic processing and the low oxygen growth procedure.

Investigation of niobium nanoSQUIDs based on nanobridge junctions

NanoSQUIDs with Dayem nanobridge weak-link junctions were fabricated on single layer niobium film by focus ion beam(FIB) milling. The dimension of the nanobridge is less than 60 nm and the loop scale is from 400×400 nm to 2.5×20 μm. The working temperature range for this device was researched. The voltage-flux transfer properties were measured at different working temperatures.

Development of single quantum Hall devices for the resistance standard in NIM

In this paper we report the progress on single quantum Hall devices for the resistance standards in NIM. We use the NIM-made device and the LEP-made device distributed to NIM by BIPM to calibrate a Tinsley 100 Ω transfer resistor using a cryogenic current comparator (CCC) at the filling factor k=2. The deviations of resistance values from the nominal value were -4.4808×10^-6±3.5×10^-9 by NIM-1 and -4.4987×10^-6±3.5×10^-9 by BIPM-2 separately. We assume the relative difference 1.8×10^-8 is due to the drift of the 100 Ω transfer resistor. More stable resistor will be used in future experiments.

Reactive ion etching processes for Nb/Nb x Si 1−x /Nb Josephson junction arrays

Reactive ion etching (RIE) is a common tool in micro- and nano-scale device fabrication. This paper presents experimental results of using the RIE tool to etch different films in Nb/NbxSi1-x/Nb Josephson junction array fabrication process in NIM.

GaAs/AlGaAs quantum hall resistance devices with AuGeNi and in contacts

We present in CPEM 2012 the latest quantum Hall (QH) experimental results of GaAs-AlGaAs Hall devices fabricated by NIM. AuGeNi and In are utilized as the contacts material. Precision measurement indicates quantized Hall devices with low contact resistance and good breakdown current are obtained.