Structural evolution of hexa-peri-hexabenzocoronene adlayers in heteroepitaxy on n-pentacontane template monolayers

The growth and structure of self-assembled adlayers of hexakis(n-dodecyl)-peri-hexabenzocoronene (HBC-C12) adsorbed on highly ordered pyrolitic graphite (HOPG) decorated by an n-pentacontane (n-C50H102) monolayer have been investigated by scanning tunneling microscopy (STM). Whereas on HOPG the HBC-C12 molecules readily self-assemble into a unique stable 2D structure, on the [n-C50H102 monolayer/graphite] system we observe morphological phase transitions with formation of time dependent alpha, beta, and gamma phases (alpha-->beta-->gamma). The initial alpha-phase is similar to that obtained on bare graphite, while intermediate beta- and final gamma-structures present molecular dimers and rows, respectively. The observed two-dimensional polymorphism is due to weak interaction between HBC-C12 molecules and n-C50H102-modified graphite substrate. Our results constitute an important step toward the control of the growth and structure of highly ordered monolayers of functional conjugated molecules by modifying the graphite surface with an n-alkane monolayer of appropriate chain length.     

Exploring the self-assembly of dumbbell-shaped polyoxometalate hybrids,from molecular building units to nanostructured soft materials

The formation of hierarchical nanostructures using preformed dumbbell-like species made of covalent organic–inorganic polyoxometalate (POM)-based hybrids is herein described. In this system, the presence of charged subunits (POM, metal linkers, and counter ions) in the complex molecular architecture can drive their aggregation, which results from a competition between the solvation energy of the discrete species and intermolecular electrostatic interactions. We show that the nature of the POM and the charge of the metal linker are key parameters for the hierarchical nanoorganization. The experimental findings were corroborated with a computational investigation combining DFT and molecular dynamics simulation methods, which outlines the importance of solvation of the counter ion and POM/counter ion association in the aggregation process. The dumbbell-like species can also form gels, in the presence of a poorer solvent, displaying similar nanoorganization of the aggregates. We show that starting from the designed molecular building units whose internal charges can be controlled by redox trigger we can achieve their implementation into soft nanostructured materials through the control of their supramolecular organization.

The formation of hierarchical nanostructures using supramolecular dumbbell-like species made of organic–inorganic polyoxometalate-based hybrids is investigated by combination of SAXS and computational methods.     

Magnetospectroscopy of double HgTe/CdHgTe QWs with inverted band structure in high magnetic fields up to 30 T

Magnetoabsorption in far and mid IR ranges in double HgTe/CdHgTe quantum wells with inverted band structure has been studied in high magnetic fields up to 30 T. Numerous intraband and interband transitions have been revealed in the spectra and interpreted within axial 8 × 8 k·p model. Splitting of dominant magnetoabsorption lines resulting from optical transitions from hole-like zero-mode Landau level has been discovered and discussed in terms of a built-in electric field and collective phenomena.     

Optical diagnosis of peritoneal metastases by infrared microscopic imaging

Fourier transform infrared (FTIR) spectroscopy is nowadays widely accepted as a technique with high potential for diagnosis of cancerous tissues. This study presents an example of the investigation of peritoneal metastases by FTIR microimaging. Peritoneal malignancies are generally secondary localizations of primary visceral cancers such as ovarian, stomach or colon cancers. By analysing simultaneously both formalin-fixed paraffin-embedded and frozen specimens, we examined malignant and non-malignant (i.e. fibrotic and cicatricial) peritoneal lesions. Paraffin-embedded tissues were analysed without any previous dewaxing. Multivariate statistical approaches, based on the classification of infrared data by hierarchical cluster analysis, allowed the discrimination of these various samples. Microimaging also permits the revelation of the heterogeneity of the tissue: it was possible to localize precisely the cancerous areas, and to distinguish, on the basis of their spectral signatures, the peritumoral neighbouring connective tissue close to the carcinomatous areas from the connective tissue distant from the cancerous areas. These spectral differences could be useful as complementary information to study molecular changes associated with the malignancy.     

Generation and characterization of electron bunches with ramped current profiles in a dual-frequency superconducting linear accelerator

We report on the successful experimental generation of electron bunches with ramped current profiles. The technique relies on impressing nonlinear correlations in the longitudinal phase space using a superconducing radio frequency linear accelerator operating at two frequencies and a current-enhancing dispersive section. The produced ~700-MeV bunches have peak currents of the order of a kilo-Ampère. Data taken for various accelerator settings demonstrate the versatility of the method and, in particular, its ability to produce current profiles that have a quasilinear dependency on the longitudinal (temporal) coordinate. The measured bunch parameters are shown, via numerical simulations, to produce gigavolt-per-meter peak accelerating electric fields with transformer ratios larger than 2 in dielectric-lined waveguides.     

An in-depth analysis of reflections in MMI couplers using optical low-coherence reflectometry: design optimization and performance evaluation

This paper describes a comprehensive report on the high potential of optical low-coherence reflectometry (OLCR) measurements to assist the design optimization and performance evaluation of symmetric MMI couplers. Using three sets of deep-ridge InGaAsP–InP couplers on InP and by performing OLCR measurements simultaneously in reflection and transmission modes, the nature and origin of all reflections in MMI have first been identified with respect to a deliberately chosen design parameter, namely, the coupler length. In addition, and in total agreement with the self-imaging principle and also the BPM simulations, the back reflections in combiner mode are shown to be prominent even in fully optimized devices. Finally, a simple design artifact has been proposed and demonstrated experimentally for the first time to suppress back reflections. Received: 16 May 2001 / Published online: 2 November 2001     

Origin of Structure Inversion Asymmetry in Double HgTe Quantum Wells

JETP Letters - The density dependences of the splitting values of the dominant magneto-absorption lines in undoped p-type double HgTe/CdHgTe quantum wells are studied. An analysis of the splitting...     

Vibrational spectroscopies for the analysis of cutaneous permeation: experimental limiting factors identified in the case of caffeine penetration

Caffeine is utilised as a reference for permeation studies in dermatology and cosmetology. The present work aimed to monitor the permeation of a caffeine solution through the skin. For this purpose, Raman and infrared studies were performed. Raman microspectroscopy permitted a dynamic follow-up of the caffeine diffusion. In complementary, infrared microimaging provided information of the caffeine localization in the skin by applying multivariate statistical processing on skin tissue sections. Herein, we prove the possibility of tracking low concentrations of caffeine through the skin and we highlight some experimental limitations of vibrational spectroscopies.     

Semi-preparative purification and characterization of peptides from complex haemoglobin hydrolysate by HPLC-mass spectrometry

Summary An important goal of previous high-performance liquid chromatography (HPLC) studies was the development of a simple procedure for the purification of peptides from very complex haemoglobin enzymatic hydrolysates. This report demonstrates that the separation system described can be used for large sample loadings at laboratory preparative scale (more than 50 mg) without loss of resolution. The efficiency of peptide purification was shown by fast atom bombardment-mass spectrometry (FAB-MS) and tandem mass spectrometry (tandem M S). The procedure described will be of interest in the biotechnology area for the extensive preparation of peptides for fine applications from complex enzymatic hydrolysates.