Self-assembled nanofold network formation on layered crystal surfaces during metal intercalation

We study the formation of planar network nanostructures, which develop during metal deposition on initially smooth surfaces of layered compounds. Using in situ low-energy electron microscopy for dynamic observation and high-resolution transmission electron microscopy for structure analysis, we have observed the rapid formation of hexagonal networks of linear "nanofolds" with prismatic cavities on top of layered VSe2 crystals. Their formation results from relaxation of compressive strains which build up during Cu intercalation into a thin surface layer.     

High-speed microcontact printing

We have demonstrated microcontact printing (muCP) of self-assembled monolayers in the millisecond regime. The contact formation and separation of the stamp and substrate was studied with high-speed video recordings. Using high ink concentrations and contact times as short as 1 ms, we printed monolayers of hexadecanethiol on Au, which served as a selective etch resist. High-speed muCP yields defect-free monolayers that are independent of the dimensions of the printed patterns, have high contrast between printed and unprinted areas, and enable perfect reproducibility of prints.     

Photoacoustic spectroscopy for process analysis

Photoacoustic spectroscopy (PAS) is based on the absorption of electromagnetic radiation by analyte molecules. The absorbed energy is measured by detecting pressure fluctuations in the form of sound waves or shock pulses. In contrast to conventional absorption spectroscopy (such as UV/Vis spectroscopy), PAS allows the determination of absorption coefficients over several orders of magnitude, even in opaque and strongly scattering samples. Small absorption coefficients, such as those encountered during trace gas monitoring, can be detected with cells with relatively short pathlengths. Furthermore, PA techniques allow absorption spectra of solid samples (including powders, chips or large objects) to be determined, and they permit depth profiling of layered systems. These features mean that PAS can be used for on-line monitoring in technical processes without the need for sample preparation and to perform depth-resolved characterization of industrial products. This article gives an overview on PA excitation and detection schemes employed in analytical chemistry, and reviews applications of PAS in process analytical technology and characterization of industrial products.     

Exchange processes in interlayer diffusion – kinks, corners and the growth mode

Interlayer diffusion, i.e. mass transport between different terraces, is known to be an essential process for obtaining layer-by-layer growth, avoiding formation of three-dimensional (3D) islands when growing thin films. We present experimental results for the growth of cobalt on Pt (111), which demonstrate the importance of kinks and corners for interlayer diffusion. We show that Co grows two-dimensionally as long as strain caused by the Pt-Co interface keeps the step edges rough, with a high kink density, and then transforms to 3D growth with straight steps. The results for growth with adsorbed carbon monoxide show that CO acts as a surfactant, causing two-dimensional growth unless heterogeneous nucleation occurs. Again, this process is related to roughening of the steps, being a new mechanism for the action of a surfactant. A scanning tunneling microscopy study at the atomic scale confirms the fact that step descent happens only at kinks and (concave) corners, and in conjunction with simulations allows us to identify some of the relevant atomic-exchange processes. We finally argue that the dependence of the growth mode on the step morphology, together with straightening of the steps by step–step interaction, can lead to an instability of the growth mode. Received: 27 March 2000 / Accepted: 4 September 2000 / Published online: 7 March 2001     

Shears bands in the Pb region

The properties of the M1 bands in the Pb region are reviewed. They can be explained by ‘magnetic rotation’ which is a new concept in nuclear excitations. Spin and excitation energy along the bands are increased by the shears effect, a step-by-step alignment of large proton-particle and large neutron-hole spins into the direction of the total angular momentum. First evidence is presented for band termination connected with the closing of the shears.     

ÜBER PHOSPHAZO-VERBINDUNGEN AUS NITRILEN V.1 DIE REAKTIONEN VON ACETONITRIL,PHENYLACETONITRIL UND MALONSÄUREDINITRIL MIT [C13P˭N‒PC13]C1

Abstract

Acetonitrile reacts with P₂NC1₇ to give a mixture of the ring compounds CC1?CC1?N?PC1₂?N?PC1₂ (1) and CC?CC1?N?PC1₂?N?PC1₂ (2), phenyl acetonitrile to give C(C₆H₅)?CC1?N?PC1₂?N?PC1₂ (3). Malonic acid dinitrile and P₂NC1₇ in dichloroethane yield a mixture of the ring compound C(CN)?CC1?N?PC1₂?N?PC1₂ (4) and the chain compound PC1₃?N?PC1₂?N?CC1?CH?CN (5), while the latter compound is exclusively formed when the reaction is carried out in PC1₃. Preparation, nmr and mass spectra of the new compound are described and discussed.

Acetonitrile reacts with P₂NC1₇ zu einem Gemisch der ringförmigen Verbindungen CC1?CC1?N?PC1₂?N?PC1₂ (1) und CC?CC1?N?PC1₂?N?PC1₂ (2), Phenylacetonitril zu C(C₆H₅)?CC1?N?PC1₂?N?PC1₂ (3). Aus Malonsäuredinitril und P₂NC1₇ entsteht in Dichloräthan ein Gemisch des Heterocyclus C(CN)?CC1?N?PC1₂?N?PC1₂ (4) und der kettenförmigen Verbindung PC1₃?N?PC1₂?N-CC1?CH?CN (5), wöhrend in PC1₃ als Reaktionsmedium ausschlieβlich die Verbindung 5 gebildet wird. Darstellung, NMR- und Massenspektren der neuen Verbindungen sind beschrieben und diskutiert.     

Single-Photon Ionization of Organic Molecules Beyond 10 kDa

The volatilization and soft ionization of complex neutral macromolecules at low energies has remained an outstanding challenge for several decades [1]. Most volatilization techniques in mass spectrometry produce ions already in the source and most of them lead to particle velocities in excess of several hundred meters per second. For many macromolecules, post-ionization is inefficient since electronic or optical excitations can be followed by competing non-ionizing internal conversion, electron recapture, or fragmentation processes. Here, we explore the laser-assisted volatilization of neutral perfluoroalkyl-functionalized tetraphenylporphyrins as well as their single-photon ionization using vacuum ultraviolet (VUV) light at 157 nm. A systematic investigation of the ionization curves allows us to determine the molecular velocity distribution and ionization cross sections. We demonstrate the detection of single photon ionized intact organic molecules in excess of 10 kDa from a slow molecular beam.      

Nanoscale Chemical Imaging Using Tip‐Enhanced Raman Spectroscopy: A Critical Review

Methods for chemical analysis at the nanometer scale are crucial for understanding and characterizing nanostructures of modern materials and biological systems. Tip‐enhanced Raman spectroscopy (TERS) combines the chemical information provided by Raman spectroscopy with the signal enhancement known from surface‐enhanced Raman scattering (SERS) and the high spatial resolution of atomic force microscopy (AFM) or scanning tunneling microscopy (STM). A metallic or metallized tip is illuminated by a focused laser beam and the resulting strongly enhanced electromagnetic field at the tip apex acts as a highly confined light source for Raman spectroscopic measurements. This Review focuses on the prerequisites for the efficient coupling of light to the tip as well as the shortcomings and pitfalls that have to be considered for TERS imaging, a fascinating but still challenging way to look at the nanoworld. Finally, examples from recent publications have been selected to demonstrate the potential of this technique for chemical imaging with a spatial resolution of approximately 10 nm and sensitivity down to the single‐molecule level for applications ranging from materials sciences to life sciences.