A simple and controlled single electron transistor based on doping modulation in silicon nanowires

A simple and highly reproducible single electron transistor (SET) has been fabricated using gated silicon nanowires. The structure is a metal-oxide-semiconductor field-effect transistor made on silicon-on-insulator thin films. The channel of the transistor is the Coulomb island at low temperature. Two silicon nitride spacers deposited on each side of the gate create a modulation of doping along the nanowire that creates tunnel barriers. Such barriers are fixed and controlled, like in metallic SETs. The period of the Coulomb oscillations is set by the gate capacitance of the transistor and therefore controlled by lithography. The source and drain capacitances have also been characterized. This design could be used to build more complex SET devices.Comment: to be published in Applied Physics Letter

Size scaling of the addition spectra in silicon quantum dots

We investigate small artificial quantum dots obtained by geometrically controlled resistive confinement in low mobility silicon-on-insulator nanowires. Addition spectra were recorded at low temperature for various dot areas fixed by lithography. We compare the standard deviation of the addition spectra with theory in the high electron concentration regime. We find that the standard deviation scales as the inverse area of the dot and its absolute value is comparable to the energy spacing of the one particle spectrum.Comment: 4 pages, 5 figure

Background charges and quantum effects in quantum dots transport spectroscopy

We extend a simple model of a charge trap coupled to a single-electron box to energy ranges and parameters such that it gives new insights and predictions readily observable in many experimental systems. We show that a single background charge is enough to give lines of differential conductance in the stability diagram of the quantum dot, even within undistorted Coulomb diamonds. It also suppresses the current near degeneracy of the impurity charge, and yields negative differential lines far from this degeneracy. We compare this picture to two other accepted explanations for lines in diamonds, based respectively on the excitation spectrum of a quantum dot and on fluctuations of the density-of-states in the contacts. In order to discriminate between these models we emphasize the specific features related to environmental charge traps. Finally we show that our model accounts very well for all the anomalous features observed in silicon nanowire quantum dots.Comment: 7 pages, 6 figure

Hyaluronan: Biosynthesis and signaling

Background Hyaluronan is a critical component of extracellular matrix with several different roles. Besides the contribution to the tissue hydration, mechanical properties and correct architecture, hyaluronan plays important biological functions interacting with different molecules and receptors. Scope of review The review addresses the control of hyaluronan synthesis highlighting the critical role of hyaluronan synthase 2 in this context as well as discussing the recent findings related to covalent modifications which influence the enzyme activity. Moreover, the interactions with specific receptors and hyaluronan are described focusing on the importance of polymer size in the modulation of hyaluronan signaling. Major conclusions Due to its biological effects on cells recently described, it is evident how hyaluronan is to be considered not only a passive component of extracellular matrix but also an actor involved in several scenarios of cell behavior. General significance The effects of metabolism on the control of hyaluronan synthesis both in healthy and pathologic conditions are critical and still not completely understood. The hyaluronan capacity to bind several receptors triggering specific pathways may represent a valid target for new approach in several therapeutic strategies. This article is part of a Special Issue entitled Matrix-mediated cell behaviour and properties

Oxidized low density lipoprotein (LDL) affects hyaluronan synthesis in human aortic smooth muscle cells

Thickening of the vessel in response to high low density lipoprotein(s) (LDL) levels is a hallmark of atherosclerosis, characterized by increased hyaluronan (HA) deposition in the neointima. Human native LDL trapped within the arterial wall undergoes modifications such as oxidation (oxLDL). The aim of our study is to elucidate the link between internalization of oxLDL and HA production in vitro, using human aortic smooth muscle cells. LDL were used at an effective protein concentration of 20-50 \u3bcg/ml, which allowed 80% cell viability. HA content in the medium of untreated cells was 28.9 \ub1 3.7 nmol HA-disaccharide/cell and increased after oxLDL treatment to 53.9 \ub1 5.6. OxLDL treatments doubled the transcripts of HA synthase HAS2 and HAS3. Accumulated HA stimulated migration of aortic smooth muscle cells and monocyte adhesiveness to extracellular matrix. The effects induced by oxLDL were inhibited by blocking LOX-1 scavenger receptor with a specific antibody (10 \u3bcg/ml). The cholesterol moiety of LDL has an important role in HA accumulation because cholesterol-free oxLDL failed to induce HA synthesis. Nevertheless, cholesterol-free oxLDL and unmodified cholesterol (20 \u3bcg/ml) induce only HAS3 transcription, whereas 22,oxysterol affects both HAS2 and HAS3. Moreover, HA deposition was associated with higher expression of endoplasmic reticulum stress markers (CHOP and GRP78). Our data suggest that HA synthesis can be induced in response to specific oxidized sterol-related species delivered through oxLDL

Coulomb Blockade in low mobility nanometer size Si:MOSFETs

We investigate coherent transport in Si:MOSFETs with nominal gate lengths 50 to 100nm and various widths at very low temperature. Independent of the geometry, localized states appear when G=e^{2}/h and transport is dominated by resonant tunnelling through a single quantum dot formed by an impurity potential. We find that the typical size of the relevant impurity quantum dot is comparable to the channel length and that the periodicity of the observed Coulomb blockade oscillations is roughly inversely proportional to the channel length. The spectrum of resonances and the nonlinear I-V curves allow to measure the charging energy and the mean level energy spacing for electrons in the localized state. Furthermore, we find that in the dielectric regime, the variance var(lng) of the logarithmic conductance lng is proportional to its average value consistent with one-electron scaling models.Comment: 4 pages, 4 figure

Individual charge traps in silicon nanowires: Measurements of location, spin and occupation number by Coulomb blockade spectroscopy

We study anomalies in the Coulomb blockade spectrum of a quantum dot formed in a silicon nanowire. These anomalies are attributed to electrostatic interaction with charge traps in the device. A simple model reproduces these anomalies accurately and we show how the capacitance matrices of the traps can be obtained from the shape of the anomalies. From these capacitance matrices we deduce that the traps are located near or inside the wire. Based on the occurrence of the anomalies in wires with different doping levels we infer that most of the traps are arsenic dopant states. In some cases the anomalies are accompanied by a random telegraph signal which allows time resolved monitoring of the occupation of the trap. The spin of the trap states is determined via the Zeeman shift.Comment: 9 pages, 8 figures, v2: section on RTS measurements added, many improvement

Advances, Challenges and Opportunities in 3D CMOS Sequential Integration

3D sequential integration enables the full use of the third dimension thanks to its high alignment performance. In this paper, we address the major challenges of 3D sequential integration: in particular, the control of molecular bonding allows us to obtain pristine quality top active layer. With the help of Solid Phase Epitaxy, we can match the performance of top FET, processed at low temperature (600°C), with the bottom FET devices. Finally, the development of a stable salicide enables to retain bottom performance after top FET processing. Overcoming these major technological issues offers a wide range of applications

ELECTRON TRANSPORT IN HYDROGENATED AMORPHOUS SILICON SCHOTTKY BARRIERS AND DEEP LOCALIZED STATES KINETICS

We present a method for analysing transport in Schottky diodes on hydrogenated amorphous silicon (aSiH). Experimental results show a correlation between the reduction of carrier collection velocity, the reduction of barrier height for reduced space-charge regions. In the same way, the kinetics of "midgap" localized states is slowered as bulk states located near the Pt-aSiH contact contribute to capacitance

ELECTRON-TRANSPORT IN HYDROGENATED AMORPHOUS-SILICON SCHOTTKY BARRIERS AND DEEP LOCALIZED STATES KINETICS

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