The Schottky barrier transistor in emerging electronic devices.

This paper explores how the Schottky barrier (SB) transistor is used in a variety of applications and material systems. A discussion of SB formation, current transport processes, and an overview of modeling are first considered. Three discussions follow, which detail the role of SB transistors in high performance, ubiquitous and cryogenic electronics. For high performance computing, the SB typically needs to be minimized to achieve optimal performance and we explore the methods adopted in carbon nanotube technology and two-dimensional electronics. On the contrary for ubiquitous electronics, the SB can be used advantageously in source-gated transistors and reconfigurable field-effect transistors (FETs) for sensors, neuromorphic hardware and security applications. Similarly, judicious use of an SB can be an asset for applications involving Josephson junction FETs.

Germanium Quantum-Well Josephson Field-Effect Transistors and Interferometers.

Hybrid superconductor-semiconductor structures attract increasing attention owing to a variety of potential applications in quantum computing devices. They can serve the realization of topological superconducting systems as well as gate-tunable superconducting quantum bits. Here, we combine a SiGe/Ge/SiGe quantum-well heterostructure hosting high-mobility two-dimensional holes and aluminum superconducting leads to realize prototypical hybrid devices, such as Josephson field-effect transistors (JoFETs) and superconducting quantum interference devices (SQUIDs). We observe gate-controlled supercurrent transport with Ge channels as long as one micrometer and estimate the induced superconducting gap from tunnel spectroscopy measurements. Transmission electron microscopy reveals the diffusion of Ge into the Al contacts, whereas no Al is detected in the Ge channel.

A gate-tunable graphene Josephson parametric amplifier.

With a large portfolio of elemental quantum components, superconducting quantum circuits have contributed to advances in microwave quantum optics1. Of these elements, quantum-limited parametric amplifiers2-4 are essential for low noise readout of quantum systems whose energy range is intrinsically low (tens of µeV)5,6. They are also used to generate non-classical states of light that can be a resource for quantum enhanced detection7. Superconducting parametric amplifiers, such as quantum bits, typically use a Josephson junction as a source of magnetically tunable and dissipation-free non-linearity. In recent years, efforts have been made to introduce semiconductor weak links as electrically tunable non-linear elements, with demonstrations of microwave resonators and quantum bits using semiconductor nanowires8,9, a two-dimensional electron gas10, carbon nanotubes11 and graphene12,13. However, given the challenge of balancing non-linearity, dissipation, participation and energy scale, parametric amplifiers have not yet been implemented with a semiconductor weak link. Here, we demonstrate a parametric amplifier leveraging a graphene Josephson junction and show that its working frequency is widely tunable with a gate voltage. We report gain exceeding 20 dB and noise performance close to the standard quantum limit. Our results expand the toolset for electrically tunable superconducting quantum circuits. They also offer opportunities for the development of quantum technologies such as quantum computing, quantum sensing and for fundamental science14.

Electric field-controlled rippling of graphene.

Metal-graphene interfaces generated by electrode deposition induce barriers or potential modulations influencing the electronic transport properties of graphene based devices. However, their impact on the local mechanical properties of graphene is much less studied. Here we show that graphene near a metallic interface can exhibit a set of ripples self-organized into domains whose topographic roughness is controlled by the tip bias of a scanning tunneling microscope. The reconstruction from topographic images of graphene bending energy maps sheds light on the local electro-mechanical response of graphene under STM imaging and unveils the role of the stress induced by the vicinity of the graphene-metal interface in the formation and the manipulation of these ripples. Since microscopic rippling is one of the important factors that limit charge carrier mobility in graphene, the control of rippling with a gate voltage may have important consequences in the conductance of graphene devices where transverse electric fields are created by contactless suspended gate electrodes. This opens up also the possibility to dynamically control the local morphology of graphene nanomembranes.

Cross correlation of incoherent multiple Andreev reflections.

We use a semiclassical theory to calculate the current correlations in a multiterminal structure composed of a normal metallic dot connected to all superconducting leads at arbitrary voltage and temperature. This theory holds when the proximity effect is suppressed in the dot. At low voltage, eV<

Related effects of cell adaptation to serum-free conditions on murine EPO production and glycosylation by CHO cells.

The necessity to perform serum-free cultures to produce recombinant glycoproteins generally requires an adaptation procedure of the cell line to new environmental conditions, which may therefore induce quantitative and qualitative effects on the product, particularly on its glycosylation. In previous studies, desialylation of EPO produced by CHO cells was shown to be dependent on the presence of serum in the medium. In this paper, to discriminate between the effects of the adaptation procedure to serum-free medium and the effects of the absence of serum on EPO production and glycosylation, adapted and non-adapted CHO cells were grown in serum-free and serum-containing media. The main kinetics of CHO cells were determined over batch processes as well as the glycosylation patterns of produced EPO by HPCE-LIF. A reversible decrease in EPO production was observed when cells were adapted to SFX-CHO(TM) medium, as the same cells partially recovered their production capacity when cultivated in serum-containing medium or in the enriched SFM(TM) serum-free medium. More interestingly, EPO desialylation that was not observed in both serum-free media was restored if the serum-independent cells were recultured in presence of serum. In the same way, while the serum-independent cells did not release a sialidase activity in both serum-free media, a significant activity was recovered when serum was added. In fact, the cell adaptation process to serum-free conditions did not specifically affect the sialidase release and the cellular mechanism of protein desialylation, which appeared to be mainly related to the presence of serum for both adapted and non-adapted cells.

Half-integer Shapiro steps at the 0-pi crossover of a ferromagnetic Josephson junction.

We investigate the current-phase relation of S/F/S junctions near the crossover between the 0 and the pi ground states. We use Nb/CuNi/Nb junctions where this crossover is driven both by thickness and temperature. For a certain thickness a nonzero minimum of critical current is observed at the crossover temperature. We analyze this residual supercurrent by applying a high frequency excitation and observe the formation of half-integer Shapiro steps. We attribute these fractional steps to a doubling of the Josephson frequency due to a sin((2phi) current-phase relation. This phase dependence is explained by the splitting of the energy levels in the ferromagnetic exchange field.