Electron spin resonance investigation of ultra-small double walled carbon nanotubes embedded in zeolite nanochannels.

We report on the low temperature electron spin resonance (ESR) properties of ultra-small (0.45 nm) double walled carbon nanotubes (DWCNTs) embedded in zeolite nanochannels. An isotropic ESR signal is observed at g(c) = 2.

Quantum cutting in Li (770 nm) and Yb (1000 nm) co-dopant emission bands by energy transfer from the ZnO nano-crystalline host.

Li-Yb co-doped nano-crystalline ZnO has been synthesized by a method of thermal growth from the salt mixtures. X-ray diffraction, transmission electron microscopy, atomic absorption spectroscopy and optical spectroscopy confirm the doping and indicate that the dopants may form Li-Li and Yb(3+)-Li based nanoclusters. When pumped into the conduction and exciton absorption bands of ZnO between 250 to 425 nm, broad emission bands of about 100 nm half-height-width are excited around 770 and 1000 nm, due to Li and Yb dopants, respectively.

Normal mode analysis of Trp RNA binding attenuation protein: structure and collective motions.

The Trp RNA-binding protein (TRAP) has a toroidal topology and a perfect 11-fold symmetry, which makes it an excellent candidate for a vibrational study of elastic properties. Normal mode analysis in combination with correlation matrix calculations was used to detect collective low-frequency motions in TRAP. The results reveal the presence of highly correlated modes at the lower end of the spectrum, which directly reflect the annular and toroidal topology.

Dark and bright localized surface plasmons in nanocrosses.

A metallic nanocross geometry sustaining broad dipole and sharp higher order localized surface plasmon resonances is investigated. Spectral tunability is achieved by changing the cross arm length and the angle between the arms. The degree of rotational symmetry of the nanocross is varied by adding extra arms, changing the arm angle and shifting the arm intersection point.

The leapfrog principle for boron fullerenes: a theoretical study of structure and stability of B112.

Two leapfrog isomers of a B(112) boron fullerene are constructed from small C(28) fullerenes (T(d) and D(2) symmetries) by the leapfrog transformation combined with omnicapping of the new hexagons. Their electronic structure is analyzed using the density functional theory at the B3LYP/SVP and BHLYP/SVP levels. Both isomers are characterized as minima on the potential energy hypersurface with a HOMO-LUMO gap at B3LYP/SVP of 1.

Carbon monoxide adsorption on silver doped gold clusters.

Well controlled gas phase experiments of the size and dopant dependent reactivity of gold clusters can shed light on the surprising discovery that nanometer sized gold particles are catalytically active. Most studies that investigate the reactivity of gold clusters in the gas phase focused on charged, small sized clusters. Here, reactivity measurements in a low-pressure reaction cell were performed to investigate carbon monoxide adsorption on neutral bare and silver doped gold clusters (Au(n)Ag(m); n = 10-45; m = 0, 1, 2) at 140 K.

Plasmon line shaping using nanocrosses for high sensitivity localized surface plasmon resonance sensing.

The detection of small changes in the wavelength position of localized surface plasmon resonances in metal nanostructures has been used successfully in applications such as label-free detection of biomarkers. Practical implementations, however, often suffer from the large spectral width of the plasmon resonances induced by large radiative damping in the metal nanocavities. By means of a tailored design and using a reproducible nanofabrication process, high quality planar gold plasmonic nanocavities are fabricated with strongly reduced radiative damping.

Preparation and luminescence of bulk oxyfluoride glasses doped with Ag nanoclusters.

Bulk oxyfluoride glasses doped with Ag nanoclusters have been prepared using the melt quenching technique. When pumped in the absorption band of Ag nanoclusters between 300 to 500 nm, these glasses emit a very broad luminescence band covering all the visible range with a weak tail extending into the near infrared. The maximum of the luminescence band and its color shifts to the blue with a shortening of the excitation wavelength and an increasing ratio of oxide to fluoride components, resulting in white color luminescence at a particular ratio of oxide to fluoride; with a quantum yield above 20%.

Cathodo- and photoluminescence in Yb(3+)-Er(3+) co-doped PbF(2) nanoparticles.

We have prepared and studied the PbF(2):(Yb(3+),Er(3+)) co-doped nanoparticles, with chemical formula (Yb-Er)(x)Pb(1-x)F(2+x), where x = 0.29, Yb(3+)/Er(3+) = 6, and estimated the energy efficiency for their cathodoluminescence, mostly of Yb(3+), and up-conversion photoluminescence of Er(3+) to reach more than 0.5% and 20%, respectively, which may be the highest to date for rare-earth doped nanoparticles.

Helical structure of xylose-DNA.

Synthetic biology and systems chemistry demonstrate a growing interest in modified nucleotides to achieve an enzymatically stable artificial nucleic acid. A potential candidate system is xylose-DNA, in which the 2'-deoxy-beta-D-ribo-furanose is substituted by 2'-deoxy-beta-D-xylo-furanose. We present here the helical structure and conformational analysis of xylose-DNA on the basis of 35 ns MD simulations of a 29-base-pair DNA duplex.

Symmetry-induced giant vortex state in a superconducting Pb film with a fivefold Penrose array of magnetic pinning centers.

A direct visualization of the flux distribution in a Pb film covering a fivefold Penrose array of Co dots is obtained by mapping the local field distribution with a scanning Hall probe microscope. We demonstrate that stable vortex configurations can be found for fields H approximately 0.8H_{1}, H_{1}, and 1.

Tryptophan conformations associated with partial unfolding in ribonuclease T1.

The origin of the biexponential fluorescence decay of Trp in ribonuclease T1 under mildly destabilizing conditions, such as increased pH or temperature, or the presence of detergent, is still not understood. We have performed two extended replica-exchange molecular dynamics simulations to obtain a detailed representation of the native state at two protonation states corresponding to a high and low pH. At high pH, the appearance of partially unfolded states is evident.

Optical nanoheater based on the Yb3+-Er3+ co-doped nanoparticles.

Yb(3+)-Er(3+) co-doped fluoride nanoparticles have been prepared. When pumped by 975 nm laser diode into absorption band of Yb(3+), the laser-induced temperature rise up to 800 degrees C has been detected in the nanoparticles by measuring the ratio of the intensities of the thermalised up-conversion luminescence bands (2)H(11/2)-->(4)I(15/2) and (4)S(3/2)-->(4)I(15/2) of Er(3+). These results show that a controlled optical heating of the nanoparticles and their surrounding nano-volumes can be realised, while the location and temperature rise of the nanoparticles and heated nano-volumes can be detected distantly by means of luminescence.

Type-1.5 superconductivity.

We demonstrate the existence of a novel superconducting state in high quality two-component MgB2 single crystalline superconductors where a unique combination of both type-1 (lambda{1}/xi{1}<1/sqrt[2]) and type-2 (lambda{2}/xi{2}>1/sqrt[2]) superconductor conditions is realized for the two components of the order parameter. This condition leads to a vortex-vortex interaction attractive at long distances and repulsive at short distances, which stabilizes unconventional stripe- and gossamerlike vortex patterns that we have visualized in this type-1.5 superconductor using Bitter decoration and also reproduced in numerical simulations.

Two-dimensional chirality at liquid-solid interfaces.

This tutorial review highlights the formation of chiral molecular patterns at the liquid-solid interface, revealed at the submolecular level with scanning tunnelling microscopy. It is shown that chiral patterns can be formed by both chiral and achiral molecules. The assembly of mixtures of mirror-image-like molecules gets special attention.

Electron spin resonance observation of an interfacial Ge P(b 1)-type defect in SiO(2)/(100)Si(1-x)Ge(x)/SiO(2)/Si heterostructures.

Using electron spin resonance (ESR), we report on the observation of a first Ge dangling bond (DB)-type interface defect in the SiO(2)/(100)Ge(x)Si(1-x)/SiO(2)/(100)Si heterostructure manufactured by the condensation technique. The center, exhibiting monoclinic-I (C(2v)) symmetry with principal g values g(1) = 2.0338 ± 0.

Growth mechanism and chemical bonding in scandium-doped copper clusters: experimental and theoretical study in concert.

Size matters! The electronic structure and size-dependent stability of neutral and cationic scandium-doped copper clusters have been investigated by mass spectrometric studies (for the cations) and also quantum chemical computations. The proposed reaction paths ultimately lead to the most stable Frank-Kasper-shaped Cu(16)Sc(+) cluster (shown here), which could be the germ of a new crystallization process.Electronic structure and size-dependent stability of scandium-doped copper cluster cations, Cu(n)Sc(+), were investigated by using a dual-target dual-laser vaporization production scheme followed by mass spectrometric studies and also quantum chemical computations in the density functional theory framework.

Propagation of magnetic avalanches in Mn12Ac at high field sweep rates.

Time-resolved measurements of the magnetization reversal in single crystals of Mn12Ac in pulsed magnetic fields, at magnetic field sweep rates from 1.5 kT/s up to 7 kT/s, suggest a new process that cannot be scaled onto a deflagrationlike propagation driven by heat diffusion. The sweep rate dependence of the propagation velocity, increasing from a few 100 m/s up to the speed of sound in Mn12Ac, indicates the existence of two new regimes at the highest sweep rates, with a transition around 4 kT/s that can be understood as a magnetic deflagration-to-detonation transition.

Controlled nanostructuring of a gold film covered with alkanethiol SAM by low energy cluster implantation.

We report on the deposition of gas-phase gold clusters on an organic self-assembled monolayer (SAM) of dodecanethiol molecules on a Au(111) surface. This study was performed by means of ambient-conditions scanning tunnelling microscopy. As a result of cluster implantation through the SAM followed by molecular reorganization, clusters are found to be located under the monolayer where they do not diffuse.

Two-dimensional supramolecular self-assembly: nanoporous networks on surfaces.

This tutorial review addresses the formation and properties of surface-confined molecular networks as revealed with scanning probe microscopy tools, especially scanning tunneling microscopy. It could be of interest to all interested in surface nano-engineering, and supramolecular chemistry on surfaces. More specifically, this review highlights recent developments in the design of regular nanoporous networks, with a pore diameter ranging from 1 nm to more than 10 nm.

Two-dimensional crystal engineering at the liquid-solid interface.

Three-dimensional crystal engineering is a well-known concept. The invention of the scanningtunneling microscope opened the door to explore this engineering concept in two dimensions with submolecularresolution. The tools of supramolecular chemistry are also at play on surfaces but the large varietyof interactions-molecule-molecule, molecule-substrate, molecule-solvent, solvent-substrate-area challenge for the design of appropriate molecules which self-assemble at the liquid-solidinterface into the targeted pattern.

How do rotameric conformations influence the time-resolved fluorescence of tryptophan in proteins? A perspective based on molecular modeling and quantum chemistry.

We discuss the dynamics of tryptophan rotamers in the context of the non-exponential fluorescence decay in proteins. The central question is: how does the ground-state conformational heterogeneity influence the time evolution of tryptophan fluorescence? This problem is examined here from the theoretical perspective. Three methods at different levels of theory, and with different scopes and computational requirements are reviewed.

Preparation and up-conversion luminescence of 8 nm rare-earth doped fluoride nanoparticles.

Free-standing, 8 nm diameter, rare-earth doped nanoparticles Re(10)Pb(25)F(65) have been prepared, where Re stands for either single rare-earth ion, such as Er(3+), Yb(3+), Eu(3+), Dy(3+), Ho(3+), Tm(3+) or combinations of those ions. The nanoparticles have been extracted by chemical etching from the oxyfluoride nano-glass-ceramics template and analyzed by transmission electron microscope with energy dispersion spectroscopy. The nanoparticles show durable up-conversion photoluminescence, which is neither concentration nor impurity quenched after 6 months ageing in ambient atmosphere.

Classification and control of the origin of photoluminescence from Si nanocrystals.

Silicon dominates the electronics industry, but its poor optical properties mean that III-V compound semiconductors are preferred for photonics applications. Photoluminescence at visible wavelengths was observed from porous Si at room temperature in 1990, but the origin of these photons (do they arise from highly localized defect states or quantum confinement effects?) has been the subject of intense debate ever since. Attention has subsequently shifted from porous Si to Si nanocrystals, but the same fundamental question about the origin of the photoluminescence has remained.