Germanium selenide monolayer is promising in photoelectric applications for its natural p-type semiconductor and complicated band structures. Basic experimental investigations of few-to-monolayer germanium selenide are still absent; major scientific challenge is to develop of techniques for controllably thinned monolayers. In this study laser thinned monolayer germanium selenide on SiO 2 /Si substrates is demonstrated. A broad photoluminescence spectrum with eight continues peaks is observed from visible to infrared wavebands centered at ≈589, 655, 737, 830, 1034, 1178, 1314, and 1456 nm, respectively. First-principle calculations based on density functional theory illuminate the band structures of few-to-monolayer germanium selenide. Photoluminescence investigation combined with first-principle calculations indicates that the indirect to direct bandgap transition happens at few layers of N = 3. Current-voltage and photoresponse characteristics of monolayer based devices show 3.3 times the photosensitivity and much faster falling edges compared with those of the pristine nanosheet based devices. The present results provide useful insight into deep understanding of thickness dependent performances of germanium selenide monocrystalline.

We developed a non-mechanical straining method to simultaneously modulate the bandgap and photoluminescence (PL) quantum efficiency of a synthesized molybdenum disulfide (MoS) monolayer on SiO, by vacuum annealing and subsequent quick cooling in ethanol. Influences of the thermal treatments at different temperatures from 100 °C to 600 °C on the PL and Raman spectra of the MoS monolayers are reported. A maximum PL peak intensity, twice that of the untreated counterparts under the same measurement conditions, was observed at the treating temperature of 200 °C. At the same time, approximately permanent tensile strains were induced, due to the quick cooling from high temperatures, which led to a red-shift of the direct optical bandgap. Modulation of the bandgap was achieved by changing the treating temperatures; nearly linear PL and Raman frequency shifts of ∼3.82 meV per 100 °C and ∼-0.28 cm/100 °C for A exciton photoluminescence and Raman E mode frequency were observed, respectively. The proposed thermal modulation promises a wide range of applications in functional 2D nanodevices and semiconductors. To our knowledge, our findings constitute the first demonstration of thermal engineering by combinational manipulation of annealing and quick cooling of the 2D transition-metal dichalcogenides.

Few-to-monolayer germanium selenide, a new IV–VI group layered material recently fabricated by mechanical exfoliation and subsequent laser thinning, is promising in very fast and broadband optoelectronic applications for its excellent stability, complicated band structures, inert surface properties, and being a natural p-type semiconductor. However, large-scale production of such few-layer GeSe devices with superior performance is still in early stages. In this study, field-effect transistors made of few-layer GeSe with direct band gaps are fabricated. Transistor performance with Schottky contact characteristics is measured at room temperature. A field-effect mobility of 4 cm2/(V s) and drain currents modulated both by holes and electrons are measured. Photoresponses as a function of illumination wavelength, power, and frequency are characterized. The few-layer GeSe transistor shows photoresponse to the illumination wavelengths from visible up to 1400 nm and a photoresponse rise (fall) time of 13 μs (19 μs), demonstrating very broadband and fast detection. The ambipolar behavior and the photoresponse characteristics demonstrate great potential of few-layer GeSe for applications in highly stable, very fast, and very broadband optoelectronic devices.

In this article, the scheme of quantum computing based on the Stark-chirped rapid adiabatic passage (SCRAP) technique [L. F. Wei, J. R. Johansson, L. X. Cen, S. Ashhab, and F. Nori, Phys. Rev. Lett. 100, 113601 (2008)] is extensively applied to implement quantum state manipulations in flux-biased Josephson phase qubits. The broken-parity symmetries of bound states in flux-biased Josephson junctions are utilized to conveniently generate the desirable Stark shifts. Then, assisted by various transition pulses, universal quantum logic gates as well as arbitrary quantum state preparations can be implemented. Compared with the usual π -pulse operations widely used in experiments, the adiabatic population passages proposed here are insensitive to the details of the applied pulses and thus the desirable population transfers can be satisfyingly implemented. The experimental feasibility of the proposal is also discussed.

Abstract. Single photon source is one of the key devices for optical quantum information processing. Differing from the usual stimulated Raman adiabatic passage to obtain single-photon radiation, here we propose an approach to produce optical Fock state on demand in the usual atom-cavity system by utilizing the technique of transitionless quantum driving. The present proposal effectively suppresses the unwanted but practically unavoidable nonadiabatic transitions in the previous adiabatic schemes. Therefore, the efficiency of Fock state production by the present technique could be significantly high, even in the presence of various atomic and cavity dissipations.