Surface Plasmon Resonance (SPR) Phenomenon of the Oxidizing and Reducing Polypyrrole

Surface Plasmon Resonance (SPR) phenomenon of the oxidizing and reducing polypyrrole (PPy) have been observed using a modified Au/PPy Kretschmann configuration. The observation was carried out through simulation Winspall 3.02 software and compared with some experimental data refractive index (n), absorbance index (), and thickness (τ) reported in other literatures with spectroscopy ellipsometry. This simulation assumed that the SPR system use BK-7 halfcylinder prism (n= 1,515) and the laser beam was generated by HeNe (λ= 632,8 nm). The result showed that the optimum layer thickness of polypyrrole with neutral electrolyte solution in the reduction state is of about 20 nm. The polypyrrole with an acid solution in the oxidation state showed that the reflectivity curve is sharper and the width of the curve is smaller than the neutral electrolyte solution in the reduction state with the SPR angle of about 46,810 and the reflectivity value of about 0,217. Polypyrrole in a state of oxidation and reduction, related to the absorption, film thickness, and dielectric constant of materials, affected to the SPR angle shift and dip curve

A quick convergent-beam laboratory X-ray reflectometer using a simultaneous multiple-angle dispersive geometry

An X-ray reflectometer using a laboratory X-ray source for quick measurements of the specular X-ray reflectivity curve is presented. It uses a bent–twisted crystal to monochromatize and focus the diverging X-rays (Cu Kα1) from a laboratory point source onto the sample. The reflected X-rays are recorded with a two-dimensional detector. Reflectivity curves can be measured without rotating the sample, detector or X-ray source during measurements. The instrument can separate the specularly reflected X-rays from the diffuse scattering background, so low reflectivities can be measured accurately. For a gold thin film on silicon, the reflectivity down to the order of 10−6 was obtained with a measurement time of 100 s and that down to 10−5 with a measurement time of 10 s. Reflectivity curves of a silicon wafer and a liquid ethylene glycol surface are shown as well. Time-resolved measurements of a TiO2 surface during UV irradiation are also reported.

A computationally efficient method to solve the Takagi–Taupin equations for a large deformed crystal

A treatise is presented on solving the Takagi–Taupin equations in the case of a strain field with an additional, spatially slowly varying component (owing to, for example, heat expansion or angular compression). It is shown that such a component typically has a negligible effect on the shape of the reflectivity curve when considering the reflectivity of a microscopic surface area of the crystal. However, it makes the centroid of that curve shift in terms of the wavelength (or the incidence angle) as a function of the position of the mentioned area, which alters the shape of the overall reflectivity curve integrated over the crystal's macroscopic surface. The validity of the method is demonstrated by comparing computed reflectivity curves with experimental ones for bent silicon wafers. A good agreement is observed.

A quick laboratory X-ray reflectometer for time-resolved observations

The measurement of the X-ray reflectivity curve is a widely used method to obtain structural information about thin films, surfaces and interfaces. With conventional instruments, the reflectivity curve is measured sequentially for a range of incident angles, which takes a long time. A recently developed method using white synchrotron radiation can measure the whole curve at once [1, 2]. In this contribution, the adaption of this method to a laboratory characteristic X-ray source is presented. This will make it possible to do time-resolved or high-throughput measurements using standard laboratory sources. The basic idea of our method is to focus the divergent X-ray beam emitted from a point source with either a doubly-curved Si crystal monochromator or a bent-twisted Si crystal monochromator [1]. Instead of using the whole beam, however, only the fan-shaped beam from a diagonal line on the monochromator is focused onto the sample. This is realized by placing an inclined slit before the monochoromator. The beam reflected from the sample forms a line on a two-dimensional pixel array detector. For each horizontal position on the detector, the incident angle onto the sample, and therefore the momentum transfer, is different. The reflectivity curve for a range of momentum transfers can therefore be measured with a single detector exposure without moving the sample, monochromator or detector. Reflectivity curves from a silicon wafer sample measured by our method are compared with the conventional angle scan method in the figure. The reflectivity down to 10 to the -7th power can be obtained, because the background can be subtracted from the measured intensity. We will show an example of time-resolved (10 s) measurements of specular X-ray reflectivity curves. We will also discuss the momentum transfer range that can be measured simultaneously and factors limiting the resolution of the method.

Towards a detailed resolution smearing kernel for time-of-flight neutron reflectometers

In this article a `detailed' form of the resolution kernel used to analyse data from reactor-based time-of-flight (TOF) neutron reflectometers is derived. In contrast to monochromatic neutron reflectometers, where the resolution kernel is close to Gaussian, TOF neutron reflectometers can have trapezoidal resolution kernels. This is a consequence of the disc chopper systems used to pulse the beam having a wavelength uncertainty that is rectangular in shape. The effect of using the detailed and approximate kernels is compared, with the main effects occurring where the width of the kernel is approximately the same as the width of the features in the reflectivity curve,i.e.around the critical edge and at highQz. The difference between the two kernels is greatest when the wavelength and angular components are of different sizes.

Quick X-ray reflectivity of spherical samples

Recently, a new experimental setup for quick X-ray reflectivity (q-XRR) measurements was proposed, which is based on simultaneous recording of an X-ray reflectivity curve over all angles of interest. This new setup for q-XRR allows measurements to be done within seconds, thus permitting studies of the time evolution of chemical, thermal, and mechanical changes at the surfaces and interfaces of different materials. Since the q-XRR measurement setup utilizes an extended X-ray source and detector, it is important to develop models and to account for the following two effects: (i) diffuse scattering associated with different points of the source and (ii) sample curvature. Models accounting for both effects are presented, and their influences on interpretation of the q-XRR measurement results are discussed.

A simultaneous multiple angle-wavelength dispersive X-ray reflectometer using a bent-twisted polychromator crystal

An X-ray reflectometer has been developed, which can simultaneously measure the whole specular X-ray reflectivity curve with no need for rotation of the sample, detector or monochromator crystal during the measurement. A bent-twisted crystal polychromator is used to realise a convergent X-ray beam which has continuously varying energyE(wavelength λ) and glancing angle α to the sample surface as a function of horizontal direction. This convergent beam is reflected in the vertical direction by the sample placed horizontally at the focus and then diverges horizontally and vertically. The normalized intensity distribution of the reflected beam measured downstream of the specimen with a two-dimensional pixel array detector (PILATUS 100K) represents the reflectivity curve. Specular X-ray reflectivity curves were measured from a commercially available silicon (100) wafer, a thin gold film coated on a silicon single-crystal substrate and the surface of liquid ethylene glycol with data collection times of 0.01 to 1000 s using synchrotron radiation from a bending-magnet source of a 6.5 GeV electron storage ring. A typical value of the simultaneously covered range of the momentum transfer was 0.01–0.45 Å−1for the silicon wafer sample. The potential of this reflectometer for time-resolved X-ray studies of irreversible structural changes is discussed.

Influence of Thickness and Substrate on the Transient Reflectivity of Copper Films

Cu films were deposited on Si and K9 glass substrates by magnetron sputtering technique. The influences of varying thicknesses and substrates on the transient reflectivity of Cu films were studied by using femtosecond laser pump-probe technology. The results show that the transient reflectivity curve of Cu films in different thicknesses have the same trend except that when they reach the peak value and recover to the balance. When the laser power is 40 mW, the influence of Si and K9 substrates on the transient reflectivity curve of 20 nm Cu films is relatively small. But when the laser power is160 mW, the influence of Si and K9 substrates on the transient reflectivity curve of 20 nm Cu films have obvious difference, the former needs much less time to reach the thermal equilibrium than of the later. At the same time, the influence of different substrates on the transient reflectivity curve of 200 nm Cu is also small.