Molecular beam epitaxial growth of multilayer 2D-boron nitride on Ni substrates from borazine and plasma-activated nitrogen.

2D boron nitride (2D-BN) was synthesized by gas-source molecular beam epitaxy on polycrystalline and monocrystalline Ni substrates using gaseous borazine and active nitrogen generated by a remote plasma source. The excess of nitrogen atoms allows to overcome the thickness self-limitation active on Ni when using borazine alone. The nucleation density and the shape of the 2D-BN domains are clearly related to the Ni substrate preparation and to the growth parameters.

Surface modification of carbon dots with tetraalkylammonium moieties for fine tuning their antibacterial activity.

The widespread of bacterial infections including biofilms drives the never-ending quest for new antimicrobial agents. Among the great variety of nanomaterials, carbon dots (CDs) are the most promising antibacterial material, but still require the adjustment of their surface properties for enhanced activity. In this contribution, we report a facile functionalization method of carbon dots (CDs) by tetraalkylammonium moieties using diazonium chemistry to improve their antibacterial activity against Gram-positive and Gram-negative bacteria.

Transport Properties of Methyl-Terminated Germanane Microcrystallites.

Germanane is a two-dimensional material consisting of stacks of atomically thin germanium sheets. It's easy and low-cost synthesis holds promise for the development of atomic-scale devices. However, to become an electronic-grade material, high-quality layered crystals with good chemical purity and stability are needed.

Van Hove Singularities and Trap States in Two-Dimensional CdSe Nanoplatelets.

Semiconductor nanoplatelets, which offer a compelling combination of the flatness of two-dimensional semiconductors and the inherent richness brought about by colloidal nanostructure synthesis, form an ideal and general testbed to investigate fundamental physical effects related to the dimensionality of semiconductors. With low temperature scanning tunnelling spectroscopy and tight binding calculations, we investigate the conduction band density of states of individual CdSe nanoplatelets. We find an occurrence of peaks instead of the typical steplike function associated with a quantum well, that rule out a free in-plane electron motion, in agreement with the theoretical density of states.

Trap-Free Heterostructure of PbS Nanoplatelets on InP(001) by Chemical Epitaxy.

Semiconductor nanocrystalline heterostructures can be produced by the immersion of semiconductor substrates into an aqueous precursor solution, but this approach usually leads to a high density of interfacial traps. In this work, we study the effect of a chemical passivation of the substrate prior to the nanocrystalline growth. PbS nanoplatelets grown on sulfur-treated InP (001) surfaces at temperatures as low as 95 °C exhibit abrupt crystalline interfaces that allow a direct and reproducible electron transfer to the InP substrate through the nanometer-thick nanoplatelets with scanning tunnelling spectroscopy.

Tunneling mechanism and contact mechanics of colloidal nanoparticle assemblies.

Nanoparticle assemblies with thiol-terminated alkyl chains are studied by conducting atomic force microscopy (c-AFM) regarding their use as strain gauges for touch-sensitive panels. Current-force spectroscopy is used as a characterization tool complementary to the macroscopic setup since it allows a bias to be applied to a limited number of junctions, overcoming the Coulomb blockade energy and focusing on the contact electromechanics and the transport mechanism across the ligand. First, transition voltage spectroscopy is applied with varying force to target the underlying tunneling mechanism by observing whether the transition between the ohmic and exponential current-voltage behavior is force-dependent.

Noise performance of frequency modulation Kelvin force microscopy.

Noise performance of a phase-locked loop (PLL) based frequency modulation Kelvin force microscope (FM-KFM) is assessed. Noise propagation is modeled step by step throughout the setup using both exact closed loop noise gains and an approximation known as "noise gain" from operational amplifier (OpAmp) design that offers the advantage of decoupling the noise performance study from considerations of stability and ideal loop response. The bandwidth can be chosen depending on how much noise is acceptable and it is shown that stability is not an issue up to a limit that will be discussed.

Toward the understanding of the interfacial dairy fouling deposition and growth mechanisms at a stainless steel surface: a multiscale approach.

The microstructures of two dairy fouling deposits obtained at a stainless steel surface after different processing times in a pilot plate heat exchanger were investigated at different scales. Electron-Probe Micro Analysis, Time-of-Flight Secondary Ion Mass Spectrometry, Atomic Force Microscopy, and X-Ray Photo-electron Spectroscopy techniques were used for this purpose. The two model fouling solutions were made by rehydrating whey protein in water containing calcium or not.

Chemical functionalization of electrodes for detection of gaseous nerve agents with carbon nanotube field-effect transistors.

An innovative sensor for the detection of nerve agents in the gas phase based on a carbon nanotube field-effect transistor was developed. A high sensitivity to organophosphorus gases was obtained by modifying gold electrodes with specific tailor-made self-assembled monolayers.

Note: Quantitative (artifact-free) surface potential measurements using Kelvin force microscopy.

The measurement of local surface potentials by Kelvin force microscopy (KFM) can be sensitive to external perturbations which lead to artifacts such as strong dependences of experimental results (typically in a ∼1 V range) with KFM internal parameters (cantilever excitation frequency and/or the projection phase of the KFM feedback-loop). We analyze and demonstrate a correction of such effects on a KFM implementation in ambient air. Artifact-free KFM measurements, i.

High on-off conductance switching ratio in optically-driven self-assembled conjugated molecular systems.

A new azobenzene-thiophene molecular switch is designed, synthesized, and used to form self-assembled monolayers (SAM) on gold. An "on/off" conductance ratio up to 7 x 10(3) (with an average value of 1.5 x 10(3)) is reported.

Dynamic behavior of amplitude detection Kelvin force microscopy in ultrahigh vacuum.

The acquisition rate of all scanning probe imaging techniques with feedback control is limited by the dynamic response of the control loops. Performance criteria are the control loop bandwidth and the output signal noise power spectral density. Depending on the acceptable noise level, it may be necessary to reduce the sampling frequency below the bandwidth of the control loop.

Kelvin force microscopy at the second cantilever resonance: an out-of-vacuum crosstalk compensation setup.

We investigate the gap-voltage control loop in a Kelvin force microscopy setup with simultaneous non-contact topography imaging. The Kelvin controller electrostatically excites the second resonance of the cantilever at about 6.3 times the first resonance frequency and adjusts the DC component of the gap voltage to cancel the oscillation amplitude at this frequency, while the non-contact topography imaging is based on a frequency control loop that maintains a constant frequency of the mechanically excited first resonance of the cantilever by adjusting the tip-sample separation.

Probing the carrier capture rate of a single quantum level.

The performance of many semiconductor quantum-based structures is governed by the dynamics of charge carriers between a localized state and a band of electronic states. Using scanning tunneling spectroscopy, we studied the transport of inelastic tunneling electrons through a prototypical localized state: an isolated dangling-bond state on a Si(111) surface. From the saturation of the current at an energy resonant with this state, the hole capture rate by the dangling bond was determined.

Electron transport via local polarons at interface atoms.

Electronic transport is profoundly modified in the presence of strong electron-vibration coupling. We show that in certain situations, the electron flow takes place only when vibrations are excited. By controlling the segregation of boron in semiconducting Si(111)-square root 3 x square root 3 R 30 degrees surfaces, we create a type of adatom with a dangling-bond state that is electronically decoupled from any other electronic state.

Langmuir-Blodgett monolayers of InP quantum dots with short chain ligands.

We demonstrate the organization of nearly monodisperse colloidal InP quantum dots at the air/water interface in Langmuir monolayers. The organization of the particles is monitored in situ by surface pressure-surface area measurements and ex situ by AFM measurements on films transferred to mica by Langmuir-Blodgett deposition. The influence of different ligands on the quality of the monolayer formed has been studied.

Direct evidence for shallow acceptor states with nonspherical symmetry in GaAs.

We investigate the energy and symmetry of Zn and Be dopant-induced acceptor states in GaAs using cross-sectional scanning tunnelling microscopy (STM) and spectroscopy at low temperatures. The ground and first excited states are found to have a nonspherical symmetry. In particular, the first excited acceptor state has a T(d) symmetry.

Semiconducting surface reconstructions of p-type Si(100) substrates at 5 K.

We report scanning tunneling microscopy (STM) studies of the technologically important Si(100) surface that reveal at 5 K the coexistence of stable surface domains consisting of the p(2 x 1) reconstruction along with the c(4 x 2) and p(2 x 2) reconstructions. Using highly resolved tunneling spectroscopic measurements and tight binding calculations, we prove that the p(2 x 1) reconstruction is asymmetric and determine the mechanism that enables the contrast variation observed in the formation of the bias-dependent STM images for this reconstruction.

Probing nanoscale dipole-dipole interactions by electric force microscopy.

We address the issue of dipole-dipole interaction measurements at the nanometer scale. Electric dipoles with tunable effective momentum in the range 10(3)-10(4) D are generated by charge injection in single silicon nanoparticles on a conductive substrate and probed by a spectroscopic electric force microscopy analysis. Weak dipole-dipole force gradients are measured and identified from their quadratic momentum dependence.