Designed for the structural analysis of advanced
materials and thin films, a new X-ray diffraction system combines flexible
instrument geometry with a comprehensive knowledge-based software platform.
Above: The SmartLabTM X-ray
X-ray scattering is a powerful tool in the determination
of the structure of materials. It is possible to calculate the positions of
scattering centers within a material by looking at the pattern of X-rays
scattered by the sample. Since X-rays are scattered by electrons, these
scattering centers are associated with regions of electron density. Atoms,
molecules, nanoparticles, pores, etc. can all give rise to characteristic X-ray
scattering patterns that can be modeled to determine structural features in
In the ceramic industry, X-ray scattering is used routinely
to examine the phase composition of bulk materials, thickness and perfection of
thin films, and residual stress and texture of composites. Applications exist
across a range of ceramic disciplines, from basic research and process
development to QC/QA analyses for materials production. Examples include the
study of ferroelectrics for optical devices, hydroxyl apatites in dentistry,
and high Tc superconductors for power transmission.
An X-ray diffractometer is an instrument that measures
the intensity of scattered X-rays as a function of position relative to the
sample. The instrument consists of a source of X-rays, a goniometer to move the
sample into different orientations, and a moveable detector to detect X-rays at
different positions. For the non-specialist, these measurements can be
complicated to make, especially when many different types of measurements are
required for the complete characterization of a sample. Traditional,
multi-purpose diffractometers require the reconfiguration of a number of
critical optical components in order to be optimized for a particular
measurement type. These reconfigurations can be time consuming and lead to
imprecise results when done incorrectly.
Figure 1. The system's patented Cross Beam Optics.
An Award-Winning Alternative
Recently, a new high-resolution diffractometer has been
developed with horizontal sample mounting theta-theta geometry.* Designed for
the structural analysis of advanced materials and thin films, the system
combines flexible instrument geometry with a comprehensive knowledge-based software
platform. The unit enables users with little or no expertise in diffraction
methods to quickly and easily make advanced structural measurements.
The new system offers a complete range of X-ray
diffraction measurements in one fully automated tool suitable for use by the
non-specialist. It combines a high-resolution, high-powered horizontal sample mount X-ray
diffractometer with an automated, knowledge-based control system. Offering
simplified automated operation, the system can address a full range of samples,
including bulk solids, liquids, powders and thin films. In addition, it can
analyze all crystalline forms, such as perfect, textured, polycrystalline,
disordered and amorphous materials, and provide a complete range of structural
X-ray measurements, including powder X-ray diffraction (PXRD), high-resolution
X-ray diffraction (HRXRD), grazing incidence X-ray diffraction (GIXRD), X-ray
reflectometry (XRR), and small angle X-ray scattering (SAXS).
PXRD methods use signature diffraction patterns from
powdered crystalline materials as fingerprints in the identification of
crystalline composites. In contrast, HRXRD and XRR measurements are used to
gauge the structure and perfection of thin films and multilayer interfaces.
SAXS analysis provides structural information on materials that may not be
crystalline or that may have very long periodicities that are difficult to
measure with traditional diffraction techniques.
The unit uses Cross Beam Optics (CBO) as the foundation
of a fully automated flexible optical system (see Figure 1). CBO allows the
system to operate in both parallel beam and focusing geometries without
reconfiguring the diffractometer system. Both geometries are permanently
mounted, simultaneously aligned and user selectable.
developed by Rigaku Group, Tokyo,
winner of the 2006 R&D 100 Award.
Figure 2. The software's main status screen shows the
system's current configuration and available optics.
The system offers completely automated control and
sensing of all downstream monochromators and slit optics. Non-expert users
benefit by the time saved and ease of use afforded by a dual geometry system,
as well as by the ability of the software** to monitor and recommend optics
configurations. The software is used to automate all processes, from the
setting and aligning of the optics to sample measurements.
The software is pre-programmed at the factory with
various optical alignment, sample alignment, and data analysis applications
packages called modular guidance packages (GPAKS). The software's main status
screen is shown in Figure 2. GPAKS contain the techniques and know-how to make
advanced measurements, such as film thickness, texture and pore/particle size
analyses. GPAKS suggest the best optical configuration for each application,
check the hardware settings and run automatic alignment sequences.
The unit contains a horizontal sample mount and a
theta/theta goniometer with high-resolution scanning in both the plane of the
sample surface and perpendicular to the sample surface. This geometry provides
users with a simple, uniform, stress-free mount for all sample types. The
high-resolution scanning in both parallel and orthogonal directions eliminates
the requirement for users to change and realign the instrument configuration
when making in-plane and out-of-plane measurements. Also available is a 9 kW
rotating anode X-ray source. This high-power source is optimal for many
applications, including the measurement of ultra-thin films.
software, developed by Rigaku Group.
Figure 3. X-ray reflectivity of BaSrTiO3
films drops sharply with the increase in film thickness due to growing surface
Consider the study of a typical ferroelectric ceramic
material like BaSrTiO3
. Thin films of single crystal
have potential applications in piezoelectric
actuators, electro-optical devices and non-volatile memories. A crucial aspect
of all of these applications is the structural quality of the films in
nanometer scale. In this example, X-ray reflectivity, X-ray rocking curve
measurements and traditional wide angle XRD were used to analyze the
composition and surface roughness of laser deposited BaSrTiO3
thin films of 10, 50 and 150 nm thick on Nb doped SrTiO3
As shown in Figure 3, the X-ray reflectivity of these
films drops sharply with an increase in film thickness due to growing surface
roughness. Theoretical modeling of the reflectivity curves, assuming uniform
composition throughout the entire thickness, estimates the surface roughness of
the 10, 50 and 150 nm films to be about 0.4, 1.0 and 4.4 nm, respectively.
Moreover, the 150 nm film shows a smaller critical angle for total external
reflection when compared to the 10 and 50 nm films, suggesting that the average
density of this film is lower than that of the thinner films. Since BaTiO3
has a higher density
, this means that the
150 nm film has a higher Sr/Ba ratio
than the other two films.
Figure 4. X-ray theta/2theta scans in the
vicinity of SrTiO3 (002) reflection.
This dependence of average composition on thickness is
also evident in the diffraction patterns of these films. From the position of
the film peaks, the average out-of-plane lattice constants of the 10, 50 and
150 nm films are about 0.3984 nm, 0.3984 nm and 0.3946 nm, respectively.
Because cubic SrTiO3
has a smaller lattice constant
(0.391 nm) than the tetragonal BaTiO3
c=0.404 nm), this indicates that the 150 nm film contains more Sr than Ba, a
conclusion that is consistent with the results of X-ray reflectivity (see
Figure 5. High-resolution X-ray rocking curves of three
Figure 5 shows high-resolution rocking curves of the same
three samples. The rocking curves of the 10 and 50 nm samples are narrow and
indicate no strain relaxation. The 150 nm film shows a broadened rocking curve,
which is a typical feature of relaxed films with dislocations.
As evidenced in the preceding example, the new system can
combine three very different measurements to provide detailed information on a
series of ferroelectric samples. Automatic alignment, CBO and advanced software
combine to create a flexible, intelligence-based X-ray diffraction instrument.
The system's software is used to gather information about
the samples, suggest measurement configurations, set up the diffractometer, and
execute measurements with the help of an interactive graphical user interface.
The components of the overall system design combine to make X-ray diffraction
measurements easy and accessible.
information regarding X-ray diffraction instrumentation, contact Rigaku
Americas Corp. at 9009 New Trails Dr., The Woodlands, TX 77381; (281) 362-2300;
fax (281) 364-3628; e-mail info@Rigaku.com; or visit www.Rigaku.com.