Modeling of NC-AFM Imaging of Alkanethiols on the Au (111) Surface

We investigate the mechanisms of contrast formation in NC-AFM imaging of self-assembled monolayers of alkanethiols on the Au (111) surface. Comparing the potential models with implicit and explicit electrostatics, we demonstrate that, similar to the imaging of polar solid surfaces, the electrostatic interaction plays the central role in contrast formation. Careful comparison of several tip models showed that the model of a clean SiO₂ tip gives the closest agreement with the experimental data.     

Microelectrochemical lithography: A method for direct writing of surface oxides

An experimental set-up is presented that allows direct writing on a metal by local anodisation in a confined electrolyte volume. A scanning droplet cell with reference electrode and counter electrode is attached to an automated xyz stage and allows an efficient addressing of a small surface area. An automatic mode investigation of a material under systematic variation of formation parameters such as formation voltage, scan rate and potentiostatic or potentiodynamic formation mode is demonstrated. The influence of these parameters on the oxide film thickness and film properties are discussed. An example for the method of direct electrochemical oxide spot writing is given. The set-up can also be used in a manual mode to address a surface area of interest such as a pit, single grain, grain boundary or intermetallic inclusion.     

Photoluminescence properties of pyrolytic boron nitride

We report on spectroscopic study of pyrolytic hBN (pBN) by means of time- and energy-resolved photoluminescence methods. A high purity pBN samples (though low crystallinity) allow complementary information about excited states involved into the luminescence process. We affirm our recent conclusions about the impurity-related nature of most of fluorescence bands in microcrystalline hBN. In addition, a broad band centred at 3.7 eV previously not considered because of its superposition with an intense structured impurity emission is attributed to the radiative recombination of deep DAPs.     

Mass Spectrometric Measurements of the Gas Phase Composition over Mould Powder Samples in Vacuum Conditions at 50‐1550°C

Heating and melting of mould powders in a steel caster may lead to harmful gaseous emissions into the atmosphere. In the present work the volatility of commercial mould powders used in continuous casting processes was studied by the mass spectrometric Knudsen effusion method. Partial pressures of the vapour phase components were measured under vacuum conditions in the temperature range 50‐1550°C at a heating rate of 100°C/hour. In the temperature interval 50‐600°C gas phase is formed by H₂O and CO₂. At higher temperatures the principle vapour species are Na, NaF, Na₂F₂, KF, SiF₄, SiF₂, SiO, CaF₂, and CO. Gaseous AIF₃, MgF₂ and AIOF were identified less reliably. A preliminary decarburised sample exhibited a noticeably different vaporisation pattern. HF was not detected. Under plant conditions SiF₄ was pointed out as the most probable air polluting vapour component.     

Electromechanical Imaging and Spectroscopy of Ferroelectric and Piezoelectric Materials: State of the Art and Prospects for the Future

Piezoresponse force microscopy (PFM) has emerged as a powerful and versatile tool for probing nanoscale phenomena in ferroelectric materials on the nanometer and micrometer scales. In this review, we summarize the fundamentals and recent advances in PFM, and describe the nanoscale electromechanical properties of several important ferroelectric ceramic materials widely used in memory and microelectromechanical systems applications. Probing static and dynamic polarization behavior of individual grains in PZT films and ceramics is discussed. Switching spectroscopy PFM is introduced as a useful tool for studying defects and interfaces in ceramic materials. The results on local switching and domain pinning behavior, as well as nanoscale fatigue and imprint mapping are presented. Probing domain structures and polarization dynamics in polycrystalline relaxors (PMN-PT, PLZT, doped BaTiO₃) are briefly outlined. Finally, applications of PFM to dimensionally confined ferroelectrics are demonstrated. The potential of PFM for studying local electromechanical phenomena in polycrystalline ferroelectrics where defects and other inhomogeneities are essential for the interpretation of their macroscopic properties is illustrated.     

A combinatorial passivation study of Ta-Ti alloys

A combinatorial study of the kinetics of anodic oxide formation was performed on a co-deposited Ta-Ti composition spread sample (from 2 to 76 at.% Ti). The samples were characterized by High Resolution Scanning Electron Microscopy (HRSEM) and Grazing Angle X-Ray Diffraction (GIXRD). High-throughput-screening was performed with an automated scanning-droplet-cell to anodise incrementally by cyclic voltammetry and perform electrochemical impedance spectroscopy. A comprehensive set of oxide parameters, including film formation factor, dielectric constant, specific oxide resistance, flat band potential and donor density was obtained. The observed changes could be directly correlated to the microstructure of the parent metal.     

Single Component Self‐Assembled Monolayers of Aromatic Azo‐Biphenyl: Influence of the Packing Tightness on the SAM Structure and Light‐Induced Molecular Movements

Aiming at modulating the packing density within functional self‐assembled monolayers (SAMs), two azo‐biphenyl derivatives AZO1 and AZO2 comprising a terminal sulfur anchor group have been designed and synthesized. While AZO1 allows for a coplanar arrangement of both biphenyl subunits, additional steric repulsion due to two methyl side groups attached to the footing biphenyl of AZO2 results in an increased intermolecular distance within the SAM, providing additional free volume. SAMs of both derivatives on gold and platinum substrates have been formed and thoroughly investigated by photoelectron (XPS) and near‐edge absorption fine structure (NEXAFS) spectroscopy as well as cyclic voltammetry and scanning tunneling microscopy. These measurements confirmed the formation of tightly packed SAMs for AZO1 , while AZO2 formed SAMs consisting of less organized and more loosely packed molecules. Optical investigations of both azo derivatives in solution as well as their SAMs displayed efficient photoisomerization in solution and in SAMs. Comparable maximal cis/trans ratios of ca. 0.9 have been observed in all cases upon irradiation at λ = 370 and 360 nm for AZO1 and AZO2 , respectively. The thermally induced cis → trans back reaction on AZO1 was found to be slower by a factor of 3 in SAMs as compared to solution, while AZO2 displayed comparable rates of the back reaction in both environments. This behavior can be explained by the different nature of molecular isomerization in the two SAM systems: whereas the isomerization in AZO1 SAMs takes place in a highly coordinated, collective way and involves many adjacent molecules, AZO2 species behave rather individually even packed in SAMs, such that their isomerization process is similar in SAMs and in solutions.