Codeposition of C60 and the three-dimensional molecular hydrocarbon 1,3,5,7-tetraphenyladamantane (TPA) on Au(111) leads to the spontaneous formation of molecular nanostructures in which each fullerene is locked into a specific orientation by three surrounding TPA. Scanning tunneling spectroscopy shows that the electronic coupling of C60 with the surface is significantly reduced in these nanostructures, enhancing the free-molecule properties. As evidenced by density functional theory simulations, the nanostructures are stabilized by 18 local electrostatic forces between C60 and TPA, resulting in a lifting of the C60 cage from the surface.

We measure a large valley-orbit splitting for shallow isolated phosphorus donors in a silicon gated nanowire. This splitting is close to the bulk value and well above previous reports in silicon nanostructures. It was determined using a double dopant transport spectroscopy which eliminates artifacts induced by the environment. Quantitative simulations taking into account the position of the donors with respect to the Si/SiO2 interface and electric field in the wire show that the values found are consistent with the device geometry.

We have used first-principles methods to investigate how metal atoms dispersed in the interlayer space of graphitic materials affect their hydrogen-binding properties. We have considered ideal stage-one metal-intercalated graphites of various compositions as representative model systems. Our calculations suggest that alkaline earth metals can significantly enhance the hydrogen storage properties: for example, Be and Mg atoms would act as binding sites of three or four hydrogen molecules, with binding energies per H2 in the 0.2-0.7 eV range, as required for applications. We also find that alkali and transition metals are not as effective in enhancing the storage capacity.

Using a density functional approach, we have explored the cycloaddition of acrylonitrile on the Si(100) surface. The buckling of the surface dimers characteristic for the (2x1) reconstructed surface is shown to favor structures with a dipolar moment such as the resonant form of acrylonitrile with cumulative double bonds. The bond of acrylonitrile via a single C atom is a possible intermediate leading to the nitrile structure of the adsorbed molecule.

The adsorption phenomenon of refrigerant R-1233zd­(E) molecules on a hematite Fe2O3(011̅2) surface is studied at the quantum level thanks to density functional theory + U (DFT + U) calculations employing a van der Waals functional combined with a spin-polarized system. The results show different adsorption sites on the solid surface depending on orientations of the molecule, characterizing strong interactions between the refrigerant molecule and both iron and oxygen atoms. A range of binding energy values of −0.92 to −0.22 eV is observed. These ab initio results are used to parametrize a force field at the refrigerant–hematite interface for larger scale molecular dynamics simulations. Effects of these ab initio considerations on density and velocity profiles are studied, in the case of a confined fluid between two surfaces as in a lubricated contact. The high binding energy values induce a locking effect of the R-1233zd­(E) molecules close to the hematite surface, showing a resistance to compression (P z = 500 MPa) and shearing (v s = 20 m/s).

We report on the acid ethylenedithiotetrathiafulvaleneamidoglycine (EDT-TTF-CO-NH-CH(2)-CO(2)H; 1; EDT-TTF=ethylenedithiotetrathiafulvalene) and the 1:1 adduct [(EDT-TTF)(·+)-CO-NH-CH(2)-(CO(2))(-)][(EDT-TTF)-CO-NH-CH(2)-(CO(2)H)]·CH(3)OH (2), a new type of hydrogen-bonded, 1:1 acid/zwitterion hybrid embrace of redox peptidics into a two-dimensional architecture, an example of a system deliberately fashioned so that oxidation of π-conjugated cores toward the radical-cation form would interfere with the activity of the appended ionizable residues in the presence of a templating base during crystal growth. First-principles calculations demonstrate that, notwithstanding preconceived ideas, a metallic state is more stable than the hole-localized alternatives for a neat 1:1 neutral acid/zwitterion hybrid. The inhomogeneous Coulomb field associated with proton-shared, interstacks O-H···O hydrogen bonds between the ionizable residues distributed on both sides of the two-dimensional π-conjugated framework leads, however, to a weak hole localization responsible for the activated but high conductivity of 1 S cm(-1). This situation is reminiscent of the role of the environment on electron transfer in tetraheme cytochrome c, in which the protonation state of a heme propionate becomes paramount, or ion-gated transport phenomena in biology. These observations open rather intriguing opportunities for the construction of electronic systems at the interface of chemistry and biology.

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By varying the gate and substrate voltage in a short silicon-on-insulator trigate field effect transistor we control the ionization state of three arsenic donors. We obtain a good quantitative agreement between 3D electrostatic simulation and experiment for the control voltage at which the ionization takes place. It allows us observing the three doubly occupied states As − at strong electric field in the presence of nearby source-drain electrodes.1 arXiv:1403.1079v1 [cond-mat.mes-hall] Mar 2014Although doping has always been the cornerstone of semiconductor technology, devices have started to enter a new era where a single dopant can be used for new (quantum) functionalities: charge and spin qubits, single-electron pumps, turnstiles and transistors 1,2 .Thin silicon-on-insulator (SOI) devices are particularly attractive for the implementation of donor-based functionalities, because they offer very good control of the transverse electric field in the channel. This electrostatic property is at the core of the Metal-OxideSemiconductor Field-Effect Transistors (MOSFETs) but is also crucial to address dopants individually and to control their electronic wavefunctions and couplings. These abilities are prerequisite for dopant-based applications.In this work we study both experimentally and with simulations how 3 arsenic donors are charged in a nanoscopic MOSFET when the substrate, gate and drain voltages are varied with respect to the grounded source. The ionization state of each donor is separately read out by detecting its corresponding resonance in the source-drain current. The ionization state of each donor -As + , As 0 and As − -is individually controlled at low temperature by the electric field. The scalability of a compact system of a few tunable shallow donors beyond the previously studied cases of 1 3-7 and 2 donors 4,8 is then shown.In our small MOSFETs -in the 10 nm range size-dopants are not isolated in the channel but see a complex electrostatic environment which includes other donors in the channel and in the source-drain (S-D) as well as offset charges in the gate stack. This environment should be considered cautiously. First other donors in the channel may result in the many-body problem of a Coulomb glass. For lightly doped semiconductors, long range fluctuation effects dominate over the immediate environment charges 9,10 . Fortunately in our short MOSFETs the interaction between donors is screened by the S-D. We can therefore treat the charging of a specific donor taking the ionization state of the others as constant over a large range of gate voltages, and therefore assign each line in the stability diagram to a specific dopant atom (see Fig.1).The ionization of donors at the graded edges -or extensions-of the source and drain is also explicitly considered in our simulation in a mean-field approach which neglects Kondo Once the potential landscape has been computed as a function of V b and V g , we have added a few bulk-like impurities in the channel at positions r i , and have tracke...