Overlapping-gate architecture for silicon Hall bar MOSFET devices in the low electron density regime

We report the fabrication and study of Hall bar MOSFET devices in which an overlapping-gate architecture allows four-terminal measurements of low-density 2D electron systems, while maintaining a high density at the ohmic contacts. Comparison with devices made using a standard single gate show that measurements can be performed at much lower densities and higher channel resistances, despite a reduced peak mobility. We also observe a voltage threshold shift which we attribute to negative oxide charge, injected during electron-beam lithography processing.Comment: 4 pages, 4 figures, submitted for Applied Physics Letter

Injecting-related trust, cooperation, intimacy, and power as key factors influencing risk perception among drug injecting partnerships

Sharing of injection drug use paraphernalia is a dyadic process linked to the transmission of HIV and hepatitis C virus (HCV). Despite this, limited research exists identifying specific dyadic interpersonal factors driving injecting partners' engagement in needle/syringe and ancillary injecting equipment sharing among young adults. Using semi-structured in-depth interview data collected between 2014 and 2015 from twenty-seven people who inject drugs (PWID), we applied an inductive approach to identify key injection drug-related interpersonal factors and developed a conceptual model integrating the findings based on interdependence theory. Interactions between injecting partners resulted in varying levels of injecting-related trust, cooperation, intimacy, and power. These factors interacted to collectively influence the type and level of risk perceived and enacted by injecting partners. The relationship between these injecting-related interpersonal factors, on the one hand, and risk perception on the other was dynamic and fluctuated between actions that protect the self (person-centered) and those that protect the partnership (partnership-centered). These findings indicate that the interpersonal context exerts substantial influence that shapes risk perception in all types of injecting partnerships. Partnership-focused prevention strategies should consider the dynamics of trust, cooperation, intimacy, and power, in characterizing dyadic risk perceptions and in understanding risky injecting practices among PWID

Overlapping-gate architecture for silicon Hall bar MOSFET devices in the low electron density and high magnetic field regime

A common issue in low temperature measurements of enhancement-mode metal-oxide-semiconductor (MOS) field-effect transistors (FETs) in the low electron density regime is the high contact resistance dominating the device impedance. In that case a voltage bias applied across the source and drain contact of a Hall bar MOSFET will mostly fall across the contacts (and not across the channel) and therefore magneto-transport measurements become challenging. However, from a physical point of view, the study of MOSFET nanostructures in the low electron density regime is very interesting (impurity limited mobility [1], carrier interactions [2,3] and spin-dependent transport [4]) and it is therefore important to come up with solutions [5,6] that work around the problem of a high contact resistance in such devices (c.f. Fig. 1 (a)).Comment: 3 page

Hierarchy of modes in an interacting one-dimensional system.

Studying interacting fermions in one dimension at high energy, we find a hierarchy in the spectral weights of the excitations theoretically, and we observe evidence for second-level excitations experimentally. Diagonalizing a model of fermions (without spin), we show that levels of the hierarchy are separated by powers of R^{2}/L^{2}, where R is a length scale related to interactions and L is the system length. The first-level (strongest) excitations form a mode with parabolic dispersion, like that of a renormalized single particle. The second-level excitations produce a singular power-law line shape to the first-level mode and multiple power laws at the spectral edge. We measure momentum-resolved tunneling of electrons (fermions with spin) from or to a wire formed within a GaAs heterostructure, which shows parabolic dispersion of the first-level mode and well-resolved spin-charge separation at low energy with appreciable interaction strength. We find structure resembling the second-level excitations, which dies away quite rapidly at high momentum.We acknowledge financial support from the UK EPSRC through Grant No. EP/J01690X/1 and EP/J016888/1.This is the accepted manuscript. The final version is available at http://journals.aps.org/prl/abstract/10.1103/PhysRevLett.114.196401

Investigation of the terahertz vibrational modes of ZIF-8 and ZIF-90 with terahertz time-domain spectroscopy.

We present experimental and computational evidence that gate-opening modes for zeolitic imidazole frameworks can be observed at terahertz frequencies. Our work highlights the critical importance to correctly optimise the crystal structure prior to computational lattice dynamics analysis. The results support the hypothesis that the low energy vibrational modes do indeed play a significant role in host-guest interactions for ZIFs, such as gas loading.C.O.T. thanks Becas Chile and the Cambridge Trust for funding; D.F.-J. thanks the Royal Society (U.K.) for funding through a University Research Fellowship. T.M.K. would like to acknowledge the Royal Society as well as the Royal Society of Chemistry for support.This is the accepted manuscript. The final version is available at via http://dx.doi.org/10.1039/C5CC06455