Lithographical gap-size engineered nanoarrays for surface-enhanced Raman probing of biomarkers.

Engineered gold nanostructured arrays with feature separation in the sub-10-nm range were fabricated and used for highly sensitive surface enhanced Raman scattering (SERS) detection of biomarkers. Nanostructuring is achieved by combining electron beam lithography with the so-called shadow evaporation technique which involves a two-step Au vapor deposition through a suspended Ge mask while the substrate is tilted in opposite directions. This results in a regular triangular surface pattern with extremely small gap distances that allow positive enhancement of the local electric fields by enabling improvements in the electromagnetic coupling between adjacent nanoparticles. The resulting SERS active surfaces are suitable for the realization of reference procedures for quantifying marker molecules like urea or creatinine at physiologically relevant concentrations.

High pressure Raman spectroscopic study on the relaxor ferroelectric PbSc(0.5)Nb(0.5)O(3).

The pressure evolution of the local structure and dynamics of polar nanoregions in PbSc(0.5)Nb(0.5)O(3) relaxor ferroelectric is analysed by Raman spectroscopy. The pressure dependence of phonon modes up to 10 GPa reveals three characteristic pressures related to changes in the local structure: near 2 GPa, at which ferroic ordering in the Pb system occurs; near 4 GPa, at which significant structural transformations, involving decoupling of Pb and B-cations in polar nanoclusters and suppression of the B-cation off-centring take place; and near 6 GPa, at which the system reaches a saturation state. The structural transformations observed in PbSc(0.5)Nb(0.5)O(3) are compared to those in PbSc(0.5)Ta(0.5)O(3) and other Pb-based perovskite-type relaxor ferroelectrics.

Pressure-induced phase transition in PbSc0.5Ta0.5O3 as a model Pb-based perovksite-type relaxor ferroelectric.

We report pressure-induced structural changes in PbSc(0.5)Ta(0.5)O3 studied by single-crystal x-ray diffraction and Raman scattering. The appearance of a soft mode, a change in the volume compressibility, broadening of the diffraction peaks, and suppression of the x-ray diffuse scattering show that a phase transition occurs near pc approximately 1.9 GPa. The critical pressure is associated with a decoupling of the displacements of the B site and Pb cations in the existing polar nanoregions, leading to the suppression of B-cation off-center shifts and enhancement of the ferroic distortion in the Pb-O system.

Reference measurement procedure for Delta9-tetrahydrocannabinol in serum.

An isotope dilution gas chromatography/mass spectrometry (ID-GC/MS) reference measurement procedure for Delta9-tetrahydrocannabinol (THC) in serum was developed and validated. The method complies with the concept of a ratio primary reference measurement procedure. The uncertainty was determined for two concentrations of THC in serum (1 ng/mL and 2.4 ng/mL). The calculation procedure is based on the Guide to the Expression of Uncertainty in Measurement (GUM). The relative expanded uncertainty was found to be less than 2% for both concentration levels, corresponding to a 95% confidence interval. For the reference method, it was shown that the measurement of THC within the concentration range covered by the current threshold values is very accurate. The method has the potential to provide traceability for the methods used in practical forensics.

Ferroic nanoclusters in relaxors: the effect of oxygen vacancies.

Single crystals of PbSc(0.5)Ta(0.5)O(3) with suppressed and enhanced oxygen deficiencies and different degrees of long-range B-site ordering were studied by Raman spectroscopy in order to clarify the significance of the different factors for the formation and growth of ferroic clusters in relaxors. It is shown that the presence of oxygen vacancies impacts more strongly on the incipient ferroic clustering than the degree of long-range B-site ordering. The oxygen deficiency hinders the formation of ferroelectric crystalline-type nanoregions, regardless of the presence/absence of long-range B(')/B('')-ordered regions. The low degree of defects in the O system enhances the long-range ferroelectric ordering, even in entirely B-site-disordered materials.

Low-temperature scanning system for near- and far-field optical investigations.

A combined system for far- and near-field optical spectroscopy consisting of a compact scanning near-field optical microscope and a dedicated spectrometer was realized. The set-up allows the optical investigation of samples at temperatures from 10 to 300 K. The sample positioning range is as large as 5 x 5 x 5 mm3 and the spatial resolution is in the range of 1.5 micro m in the far-field optical microscopy mode at low temperatures. In the scanning near-field optical microscope mode the resolution is defined by the microfabricated cantilever probe, which is placed in the focus of a double-mirror objective. The tip-to-sample distance in the scanning near-field optical microscope is controlled by a beam deflection system in dynamic scanning force microscopy mode. After a description of the apparatus, scanning force topography images of self-assembled InAs quantum dots on a GaAs substrate with a density of less than one dot per square micrometre are shown, followed by the first spectroscopic investigations of such a sample. The presented results demonstrate the potential of the system.