ABSTRACT
Single-crystalline thin films of complex oxides show a rich variety of functional properties such as ferroelectricity, piezoelectricity, ferro and antiferromagnetism and so on that have the potential for completely new electronic applications. Direct synthesis of such oxides on silicon remains challenging because of the fundamental crystal chemistry and mechanical incompatibility of dissimilar interfaces. Here we report integration of thin (down to one unit cell) single crystalline, complex oxide films onto silicon substrates, by epitaxial transfer at room temperature. In a field-effect transistor using a transferred lead zirconate titanate layer as the gate insulator, we demonstrate direct reversible control of the semiconductor channel charge with polarization state. These results represent the realization of long pursued but yet to be demonstrated single-crystal functional oxides on-demand on silicon.
ABSTRACT
Two-dimensional electron systems offer enormous opportunities for science discoveries and technological innovations. Here we report a dense electron system on the surface of single-crystal vanadium dioxide nanobeam via electrolyte gating. The overall conductance of the nanobeam increases by nearly 100 times at a gate voltage of 3 V. A series of experiments were carried out which rule out electrochemical reaction, impurity doping, and oxygen vacancy diffusion as the dominant mechanism for the conductance modulation. A surface insulator-to-metal transition is electrostatically triggered, thereby collapsing the bandgap and unleashing an extremely high density of free electrons from the original valence band within a depth self-limited by the energetics of the system. The dense surface electron system can be reversibly tuned by the gating electric field, which provides direct evidence of the electron correlation driving mechanism of the phase transition in VO(2). It also offers a new material platform for implementing Mott transistor and novel sensors and investigating low-dimensional correlated electron behavior.
ABSTRACT
Metformin is a widely used antidiabetic agent that is generally considered safe. However, metformin-associated lactic acidosis (MALA), though not common, occurs from time to time and results in significantly high mortality. A series of 23 MALA cases in a local major hospital in Hong Kong is reported in this article to demonstrate the epidemiological data, risk factors, clinical features as well as the clinical outcomes for better understanding of this disease entity. It is the first MALA case series in which plasma metformin levels were assessed. However, the results show that plasma metformin levels in MALA bear no diagnostic and prognostic values. Risk factors of mortality were identified as shock and high plasma lactate levels. The majority of patients were found to have significantly raised creatinine versus a normal baseline value before the acute illness. Concomitant illnesses taking place alongside MALA were common. With a high utility rate of renal replacement therapy (82.6%) in the study group, the mortality rate was 30.4%.
