Quantitative analysis of ferroelectric domain imaging with piezoresponse force microscopy

The contrast mechanism for ferroelectric domain imaging via piezoresponse force microscopy (PFM) is investigated. A novel analysis of PFM measurements is presented which takes into account the background caused by the experimental setup. This allows, for the first time, a quantitative, frequency independent analysis of the domain contrast which is in good agreement with the expected values for the piezoelectric deformation of the sample and satisfies the generally required features of PFM imaging

UN FORUM SERIES – three is the magic number

This post was contributed by Margaret Jungk, Chair of UN Working Group on Business and Human Rights, Mauricio Lazala, Deputy Director of Business and Human Rights Resource Centre, and Mark Hodge, Executive Director of Global Business Initiative on Human Rights. The upcoming 2015 UN Forum on Business and Human Rights offers an opportunity to pay increased attention to the simultaneous application of all three pillars of the UN Guiding Principles on Business and Human Rights (UNGPs), and the dynamics between their implementation. How can State action (regulatory or other) best encourage better corporate conduct? Are companies considering potential adverse impacts on access to remedy as part of human rights due diligence? Do corporate accountability efforts ever divert attention from State duties

UN FORUM SERIES – implementing the guiding principles: the challenge of measurement

This post was contributed by Margaret Jungk, Chair of the United Nations Working Group on Business and Human Rights. They called it ‘the plane that became a convertible’. In 1988, on a routine flight from Hilo to Honolulu, Aloha Airlines flight 243 depressurized mid-flight, ripping the top off the plane. A flight attendant, the only one who wasn’t strapped in, was sucked out of the plane with it

Detection mechanism for ferroelectric domain boundaries with lateral force microscopy

The contrast mechanism for the visualization of ferroelectric domain boundaries with lateral force microscopy is generally assumed to be caused by mechanical deformation of the sample due to the converse piezoelectric effect. We show, however, that electrostatic interactions between the charged tip and the electric fields arising from the surface polarization charges dominate the contrast mechanism. This explanation is sustained by quantitative analysis of the measured forces as well as by comparative measurements on different materials

A stochastical model for periodic domain structuring in ferroelectric crystals

A stochastical description is applied in order to understand how ferroelectric structures can be formed. The predictions are compared with experimental data of the so-called electrical fixing: Domains are patterned in photorefractive lithium niobate crystals by the combination of light-induced space-charge fields with externally applied electrical fields. In terms of our stochastical model the probability for domain nucleation is modulated according to the sum of external and internal fields. The model describes the shape of the domain pattern as well as the effective degree of modulation

On the Biosynthesis of Irregular Terpenes: Mechanistic Studies Employing the Thiamine Thiazole as an Isoprenoid Analogue.

The irregular terpene, 2,6,9,13-tetramethyl-6-vinyl-tetradeca-2,8,12-trien-7-one (18), and the terpenoid, 1-phenyl-2,6-dimethyl-2-vinyl-hept-5-en-1-one (19) were synthesized by the Continuous Flow Reformatsky method using geranoyl chloride and benzoyl chloride, respectively. Geranyl bromide was used to generate the required organo-zinc adduct. Citral and geranyl bromide produced 3,6,9,13-tetramethyl-9-vinyl-tetradeca-3,7,12-trien-6-ol (17) by this method. Attempts to isomerize 17 to 2,6,9,13-tetramethyl-6-vinyl-tetradeca-2,8,12-trien-7-ol failed. It is postulated that 17 is more stable due to steric compression around the quaternary carbon. Comparison of 18 and the terpene isolated from yeast enzyme preparations by Bell(\u27135) showed them to be identical. Attempts to synthesize 2-hydroxygeranyl thiamine by the addition of thiamine to citral failed. Cinnamaldehyde also failed to react with thiamine to yield 2-hydroxycinnamyl thiamine. Thiamine and 3-methylbenzothiazolium hemisulfate both react with benzaldehyde to produce 2-benzoyl-3-(2-methyl-4-aminopyrimidin-5-yl) methyl-3a-methylperhydrofuro {2,3-d} thiazole (5) and 3-methylbenzothiazolinyl phenyl ketone (8), respectively. Since 8 is formed via a carbene, a similar proposal is made to account for the behavior of thiamine. Tritiated citronellal, prepared by the selective hydrogenation of the (alpha),(beta)-olefin of tritiated citral, was reacted with thiamine to produce labelled 2-(1-hydroxy-3,7-dimethyl-1-oct-6-enyl) thiamine chloride hydrochloride ((\u273)H-1). When (\u273)H-1 was incubated with geraniol or farnesol 7% of the label was incorporated into 2,6,9,13-tetramethyl-6-vinyl-2,12-tetradecadien-7-one (18a) and 2,6,9,13,17-pentamethyl-9-vinyl-octadeca-2,11,16-trien-8-one (26), respectively. Labelling studies suggest that squalene synthetase is less specific for chain length of the terpene substrate at Site II, than at Site I. Also the thiamine thiazole mimics an isoprenoid moiety of farnesol and the cofactor is not involved in squalene synthesis as proposed by Woodward. The terpenoid, 2-(1-hydroxy-3,7-dimethyloct-6-enyl)-4-methyl-5-(2-hydroxyethyl) thiazole (2) was found to be inactive in yeast enzyme preparations.(\u27). The formation of 2-alkyl derivatives of thiamine via the Hantzsch Thiazole Synthesis was investigated. Using model systems, S-phenacyl thiobenzanilide and S-(p-chlorophenacyl) thiononanilide were synthesized but failed to yield the desired thiazolium salts. Steric hindrance of the substituents was responsible for this failure. Thus, based on the isolation of 18 from the cell-free yeast enzyme preparation, it is suggested that while thiamine is not involved in tail-tail dimerization, the vitamin may play a role in the formation of artemisia ketone and bakuchiol

Crosstalk Correction in Atomic Force Microscopy

Commercial atomic force microscopes usually use a four-segmented photodiode to detect the motion of the cantilever via laser beam deflection. This read-out technique enables to measure bending and torsion of the cantilever separately. A slight angle between the orientation of the photodiode and the plane of the readout beam, however, causes false signals in both readout channels, so-called crosstalk, that may lead to misinterpretation of the acquired data. We demonstrate this fault with images recorded in contact mode on ferroelectric crystals and present an electronic circuit to compensate for it, thereby enabling crosstalk-free imaging

Contrast Mechanisms for the Detection of Ferroelectric Domains with Scanning Force Microscopy

We present a full analysis of the contrast mechanisms for the detection of ferroelectric domains on all faces of bulk single crystals using scanning force microscopy exemplified on hexagonally poled lithium niobate. The domain contrast can be attributed to three different mechanisms: i) the thickness change of the sample due to an out-of-plane piezoelectric response (standard piezoresponse force microscopy), ii) the lateral displacement of the sample surface due to an in-plane piezoresponse, and iii) the electrostatic tip-sample interaction at the domain boundaries caused by surface charges on the crystallographic y- and z-faces. A careful analysis of the movement of the cantilever with respect to its orientation relative to the crystallographic axes of the sample allows a clear attribution of the observed domain contrast to the driving forces respectively.Comment: 8 pages, 8 figure