Aryl-viologen pentapeptide self-assembled conductive nanofibers.

A pentapeptide sequence was functionalized with an asymmetric arylated methyl-viologen (AVI3D2) and through controllable β-sheet self-assembly, conductive nanofibers were formed. Using a combination of spectroscopic techniques and conductive atomic force microscopy, we investigated the molecular conformation of the resultant AVI3D2 fibers and how their conductivity is affected by β-sheet self-assembly. These conductive nanofibers have potential for future exploration as molecular wires in optoelectronic applications.ERC (‘ASPiRe’, 240629) Marie Curie (FP7 ‘SASSYPOL’ ITN, 607602

Electrical detection of 31P spin quantum states

In recent years, a variety of solid-state qubits has been realized, including quantum dots, superconducting tunnel junctions and point defects. Due to its potential compatibility with existing microelectronics, the proposal by Kane based on phosphorus donors in Si has also been pursued intensively. A key issue of this concept is the readout of the P quantum state. While electrical measurements of magnetic resonance have been performed on single spins, the statistical nature of these experiments based on random telegraph noise measurements has impeded the readout of single spin states. In this letter, we demonstrate the measurement of the spin state of P donor electrons in silicon and the observation of Rabi flops by purely electric means, accomplished by coherent manipulation of spin-dependent charge carrier recombination between the P donor and paramagnetic localized states at the Si/SiO2 interface via pulsed electrically detected magnetic resonance. The electron spin information is shown to be coupled through the hyperfine interaction with the P nucleus, which demonstrates the feasibility of a recombination-based readout of nuclear spins

Defect correlated with positive charge trapping in functional HfO2 layers on (100)Si revealed by electron spin resonance: Evidence for oxygen vacancy?

We report on the results of low-temperature K- and Q-band electron spin resonance (ESR) measurements on three types of device-grade HfO2 films deposited on p-(100)Si by chemical vapor deposition (CVD) using different precursors. The study has been carried out in combination with ex situ contactless charge injection, complemented with various post-growth irradiation treatments, with the intent to assess the presence and atomic nature of occurring charge trapping centers. In HfO2 layers grown by atomic layer (AL) and metal-organic (MO) CVD, this reveals the reproducible appearance of a paramagnetic center, termed H5, in firm correlation with alternate positive/negative charge injection, i.e., distinct signal intensity increase/decrease, respectively. Simulation of the observed powder pattern for both K- and Q-band consistently points to a defect of orthorhombic symmetry characterized by g1=1.880±0.006, g2=1.900±0.006, g3=1.981±0.0015. Analysis based on the inferred spectroscopic ESR characteristics in comparison with previous theoretical work leads to the suggestion that the observed center may concern an O-vacancy defect, closest perhaps to the 4-fold 1+charged O-vacancy (VO4 + ). The revealed defect may account, at least partly, for the previously reported distinct propensity of positive charge trapping in Si/hafnia structures grown by ALCVD and MOCVD.status: publishe

Interaction between silicene and non-metallic surfaces

© Springer International Publishing Switzerland 2016. Silicene has so far been successfully grown on metallic substrates, like Ag(111), ZrB2(0001) and Ir(111) surfaces. However, characterization of its electronic structure is hampered by the metallic substrate. In addition, potential applications of silicene in nanoelectronic devices will require its growth/integration with semiconducting or insulating substrates. In this chapter, we review recent theoretical works about the interaction of silicene with several non-metallic templates, distinguishing between the weak van der Waals like interaction of silicene with e.g. AlN or layered metal (di)chalcogenides, and the stronger covalent bonding between silicene and e.g. ZnS surfaces. Recent experimental results on the possible growth of silicene on MoS2are also highlighted and compared to the theoretical predictions.status: publishe

Structural, electronic and transport properties of silicene and germanene

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Comparative analysis of thermally induced degradation of condensation-grown (100)Ge0.75Si0.25/SiO2 interfaces by electron spin resonance

An electron spin resonance study has been carried out on the influence of isochronal annealing on theGeSi/SiO2interfaces of the condensation grown (1 0 0)Si/SiO2/Ge0.75Si0.25/SiO2structure. The thermalinterface stability has been monitored in terms of the evolution of occurring paramagnetic interfacedefects, in particular, here involving the Ge dangling bond GePb1point defect, previously identified asa detrimental interface trap. This reveals thermal post-growth interface degradation, initiating fromannealing at the temperature ∼440◦C onward, identified as substantial generation of GePb1interfacetraps in addition to those naturally introduced into the system during sample manufacturing. In termsof GePb1density, the interface thus appears only robust for thermal treatment in vacuum up to 440◦C.For Tanreaching ∼520◦C, a drastic degradation occurs as exposed by an about two-fold increase in GePb1density, which state is maintained up to Tan∼ 900◦C. Annealing in H2(∼1 atm) has a similar effect, exceptthat the interface degrades more gradually. Above 900◦C, the structure’s integrity gradually collapsesbecause of disintegration (Ge escape) of the SiGe layer. As to device implementation, the data indicatethat temperatures of processing steps in O-deficient ambient should be kept below ∼440◦C.status: publishe

ESR study of p-type natural 2H-polytype MoS2 crystals: The As acceptor activity

Low-temperature (T = 1.7-77 K) multi frequency electron spin resonance (ESR) study on p-type 2H-polytype geological MoS2 crystals reveals p-type doping predominantly originating from As atoms substituting for S sites in densities of (2.4 +/- 0.2) x 10(17) cm(-3). Observation of a "half field" (g similar to 3.88) signal firmly correlating with the central Zeeman As accepter signal indicates the presence of spin S > 1/2 As agglomerates, which together with the distinct multicomponent makeup of the Zeeman signal points to manifest non-uniform As doping; only similar to 13% of the total As response originates from individual decoupled As dopants. From ESR monitoring the latter vs. T, an activation energy E-a = (0.7 +/- 0.2) meV is obtained. This unveils As as a noticeable shallow acceptor dopant, appropriate for realization of effective p-type doping in targeted 2D MoS2-based switching devices.status: publishe

Nitrogen acceptor in 2H-polytyp synthetic MoS2 assessed by multifrequency electron spin resonance

© 2018 Published by the AVS. Electron spin resonance (ESR) study on 2H-polytype synthetic MoS2 revealed the N acceptor dopants as being characterized by a spectrum of axial symmetry [g∥ = 2.032(2); g⊥ = 2.270(2)], typical for a hole-type center in MoS2. The N impurities substitute for S sites, with a density of ∼2.3 × 1017 cm−3, which accounts for the overall p-type doping. With respect to measurements for the applied magnetic field directed along the c-axis, the signal consists of a 14N primary hyperfine triplet of splitting constant A∥ = 14.7 ± 0.2 G superimposed on a correlated Gaussian single central line of peak-to-peak width ΔBpp = 15.3 ± 0.5 G, the latter making up only ∼26% of the total signal intensity. The current work extends on these results through extensive monitoring of the temperature (T) dependence of salient ESR parameters and studying the impact of thermal treatment. ESR signal saturation studies indicate a N acceptor spin-lattice relaxation time T1 (4.2 K) ≈ 3 × 10−4 s, notably different from the much smaller As acceptor’s T1 in geological MoS2. Concerning the thermal stability of the dopant, the N acceptor is found to be drastically passivated when exposed to H2 at ∼500 °C. Yet, subsequent reactivation attempts in vacuum at temperatures up to 740 °C appear unsuccessful, urging great caution with conventional forming gas treatments at T ≳ 500 °C. Combination of careful K- and Q-band ESR monitoring of the T-dependent signal intensity resulted in the consolidation of the N dopant as a shallow acceptor of activation energy Ea = 45 ± 7 meV. The consolidated results establish N as a promising candidate for stable covalently bonded p-type doping of MoS2 layers intended for application in novel nanoelectronic devices.status: publishe

First-Principles Study of the Contact Resistance at 2D Metal/2D Semiconductor Heterojunctions

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