Thin-film diffractometer

Thin-film diffractometer. A glancing angle geometry is used with the sample surface at an angle of 5-10° to the X-ray beam. The basic idea is that the penetration depth of the X-rays is reduced so they are analyzing the surface. Longer wavelength X-rays can be used, which also reduces penetration (switch to a Cr Ka... 

Sintered alloy films of reasonable thickness, e.g., opaque, mirrorlike films, can provide an adequate number of diffraction peaks for the determination of a lattice constant of adequate accuracy for present purposes. Thus, the apparent lattice constants calculated from the centroids of individual diffraction peaks, observed with a counter-diffractometer, may be extrapolated to 0 = 90°, using the Nelson-Riley function to give a value of a0. There has been some discussion about differences in lattice constants for thin films compared with bulk metals values of ao for pure silver films ( 1000 A nominal thickness) were found (74) to be consistently small compared with bulk silver but only by 0.05%. For alloy films a similar deviation would correspond to a variation of 1% in the composition of the alloy. Larger deviations have been reported for very thin films, e.g., —0.2% in copper films of 100 A nominal thickness (75).]... 

Diffractometer (Model PW 1710), using CuKa radiation. A thin film ( lnun) of 1.5 by 1.5 cm square sample was used for X-ray studies. Both water and gas phase permeability measurements were done with a machined 1 cm diameter thin sample ( limn). The molecular wei t distribution was obtauned using a gel permeation chromatograph (Waters) with a styragel column and using tetrahydrofuran as the solvent. Attenuated total reflectance (ATR) and KBr pellet techniques were used for FTIR. Solid state NMR was done on precipitated powdered samples. A Rayonet RPR-100 reactor at 35 C was used for UV irradiation of the samples. 

Salje EKH (1995) A novel 7-circle diffractometer for the rapid analysis of extended defects in thin films, single crystals and ceramics. Phase Trans 55 37-56... 

X-ray diffraction (XRD) for phase analysis, crystallographic information, residual stress, texture analysis, and reflectometry on powders, bulk, or thin films. Philips X Pert PRO, and a second Philips dual diffractometer system with automated PC control, independent theta/20, sample spinner, and 21 sample changer can be used for crystallography and Rietveld analysis of samples flat, irregular, thin films, or in glass capillaries. 

First, a polyciystalline sample usually has a size that ranges in millimeters and the beam irradiating this sample is partially absoibed. This means that a crystal located in a given area of the sample sees an incident intensity 1 that is different from the initial beam s intensity lo. Furthermore, the diffracted beams are also partially absoibed. As a result, the actual intensity that is measured is attenuated by an absorption factor which we will denote by A. The form of this factor depends on the geometric characteristics of the diffractometer used for the experiment. This point will be detailed later on, in particular when describing the diffractometers designed for the study of thin films. 

We have described in detail the features of the different types of diffractometers used for diffraction on polycrystalline samples. The analyzed samples take various forms, can be powdery or bulky, and can be analyzed in transmission or in reflection. Virtually all existing diffractometers can be described based one or the other of these typical configurations. We should point out, however, that samples in the form of thin films are a different matter and diffractometers designed for the study of these samples have to be adapted. We will detail in the following sections the characteristics of these diffraction systems. 

As we saw previously, the system designed at the beginning of the century by Seemann and Bohlin to study powdery samples is one of the three traditional diffraction systems for polycrystalline samples. We saw in section 12.12 that this diffractometer enables the user to study the sample either in transmission or in reflection. When the sample is analyzed in reflection, it is possible to arrange the elements of the system in a way, so as to have a low incidence angle between the beam and the sample. In this case, the system will make it possible to characterize thin films [HAA 85, VAL 90, FIS 96, LIG 94]. This configuration is shown in Figure 2.63. 

The study by X-ray diffraction of epitaxial films is a field of its owm Because they are comprised of a set of crystals all of which have practically the same crystallographic orientation, epitaxial thin films ate close to being single crystals. However, they are polycrystalline samples, so they deserve their own section in this book. Note, however, that the development of instruments designed for the study of these films owe a lot to the diffractometers intended for single crystals, and particularly those that focus on the study of defects in single crystals. 

Generally speaking, diffractometers designed for the study of epitaxial thin films need to present two essential featiues. First, the incident beam on the sample and the beams detected after diffraction by the sample have to be as parallel and as monochromatic as possible. Second, it has to be possible to orient the sample very precisely with respect to the incident beam, meaning that the diffractometer has to be equipped with a multi-axis sample holder able to move with an angular precision in the range of a thousandth of a degree. 

Figure 2.66. Schematic drawing of a diffractometer designed for the study of epitaxial thin films...

Rubrene was purchased from Aldrich (elemental purity > 98%) and additionally purified by gradient sublimation Freshly cleaved mica (001) was used as substrate. Rubrene thin films were deposited by hot wall epitaxy in a vacuum chamber with a base pressure below 10 Pa at different deposition rates and substrate temperatures (Ts). Pole figures were measured with a Philips X pert x-ray diffractometer using CrKa radiation and a secondary side graphite monochromator. Specular scans were performed on a Bruker D8-Discover diffractometer using CuKa radiation. POWDER CELL and STEREOPOLE were used for the evaluation of the specular scans and simulation of pole figures. 

Takagi, Y., Kikuchi, T., Mizutani, T., Imafuku, M., Sasaki, S., and Mori, T., Upgrade of triple-axis/four-circle diffractometer at PF-BL3A, Rev. Sci. Instrum. 66,1802,1995. Huang, T.C., Toney, M.F., Brennan, S., and Rek, Z., Analysis of cobalt-doped iron oxide thin films by synchrotron radiation. Thin Solid Films 154, 439, 1987. Scherrer, R, Estimation of Size and Internal Structure of Colloidal Particles by Means of Rontgen Rays, Gdttinger Nachrichten 2, 98, 1918. King, H.P and Alexander, L.E. X-ray diffraction procedures, WUey, New York, 1954. 

X-Ray Diffraction. X-ray diffractometer scans of various atactic PPBA samples are shown in Figure 7. Sample A was obtained by precipitation from CHCI3 solution directly after polymerization. Samples B and C were obtained by casting thin films from CHCI3 solution onto clean flat substrates (lead and glass). 

Conformation and structure of A-block in solid state Infrared spectra of solid films of the samples cast from solution were measured with a Shimazu Modjl-30 A IR spectrophotometer in a region of 4000 to 400 cm. X-ray diagrams were obtained by using Ni-filtered Cu Ka radiation, setting a flat surface of the film parallel to a reflecting surface with an automatic diffractometer. For the electron microscopy measurement, thin films cast from solution were stained with osmium tetroxide and examined by transmission microscopy. 

---