High pressure coupled with synchrotron x-ray diffraction has been witnessed as one powerful technique for discovering novel physics and chemistry with a wide spectrum of applications. CHESS has been playing a significant role in developing high pressure synchrotron facilities and helping national and international users to perform unique and excellent researches.
B2 station has been combined with B1 station and merged to form one versatile station. This upgraded station has all experimental capabilities that the old B1 and B2 stations have. The expanded hutch space further enables development of new in-situ techniques using a series of solid and portable instruments. The improved research capabilities include three-dimensional rotating stage for side x-ray diffraction, laser-excited Raman spectroscopy, Mar345 detector control system, high temperature tuning system etc.
The current B2 station is equipped for both angle and energy dispersive x-ray diffraction studies with diamond anvil cells. The source for B2 station is a bending magnet. The beam is stopped down to about 3 mm before entering the station. The beam is further reduced by a set of apertures to the final beam size of 5 to 1000 microns. The final size depends on the requirements of the experiments.
A monochromatic box is installed at a separated room to optimize the incident white beam into monochromatic x-ray beam for high pressure angle dispersive x-ray diffraction study. Two large area Mar345 detectors are available at B2 station for collecting the x-ray diffraction images. Upon automatic moving one pair of monochromatic crystals, the white beam can be still introduced into the station. A solid state detector is installed at a fixed angle (depend on the request) to collect energy dispersive x-ray diffraction. Using Mar345 detecotr, some Laue Experiments with and without DAC can also be done.
The on-site and off-site High Pressure Facilities exist to provide experimental support for high pressure experiments with diamond anvil cells. In these cells, pressures from around 0.1 GPa (1 kbar) to well over 300 GPa (3 Mbar) can be generated. The facility has stages for mounting diamond anvil cells permanently installed in the B2 hutch. There is a micro-optical system for in situ pressure, temperature, and Raman spectroscopy measurements in the hutch. In addition, several off-site instruments enable loading of gases and samples into DAC cells for performing high pressure studies at hydrostatic and quasi-hydrostatic conditions. A schematic of the diffraction stage and optical system in the B2 hutch is shown below. Currently a miniature solid state laser (532 nm) is used for ruby pressure and Raman spectroscopy measurements at high PT. High temperature experiments using internal resistive heating method are possible (See Rev. Sci. Instrum. 74(3), Part 1, p1255, 2003).
As shown in the photo below, we have a micro-drill press and microscope for precise drilling of the diamond anvil cell gasket. A pre-indented gasket is clamped in a precision holder, which is attached to a kinematic mount. The drill position related to the indentation made by diamond anvil on the gasket can be precisely centered in a special microscope, which can look straight into the diamond anvil indentation and adjusted with precise translation stage. A polarized, photographable, stereo microscope for diamond cell preparing work and sample loading is available in our on-site high pressure laboratory. Extra micro-optical system for pressure, temperature, and Raman spectroscopy measurements is also available on the outside of B2 hutch for the convenience in case of multiple user groups attended.
Microscope for sample preparation
The photo below shows the 4-axis control system is capable of movement of large area Mar345 detector. Slightly tilt and rotation of Mar345 detector enables an accurate calibration of the sample-to-detector distance and a series of parameters. Most importantly, a new in-situ technique was developed enabling conduction of both small and wide angle x-ray diffraction measurements under pressure and high temperature without multiple calibrations. A simple and easy optimization of x-ray energy and sample-to-detector distance allow the two types of measurements capable at one single pressure run.
4-axis control system of Mar345 detector: 1) Mar345 Detector; 2) Horizontal (x); (3) Back-forward (y); (4) Vertical (z); (5) Rotation (x-y); (6) Moving tracks
|B2 Station Summary|
|Source:||electrons, CESR bendmagnet HB6W, 1.5 mrads|
|Source size:||FWHM (horizontal) = 3.78 mm, FWHM (vertical) = 1.00 mm|
|Distance to source:||source to optical table center 15.1m|
|Be windows:||0.035 inch Be and 0.89mm to experiment|
|Cave slit sizes:||0.1 - 4 mm (horizontal), 0 to 18 mm (vertical)|
|Monochromators:||Double-bounce down with 17mm offset|
|Energy Width||(0.5mm cave slit)|
|Si (111)||4.7-35||4.5eV @ 12KeV||6-16|
|Monochromatic Mirrors - Gold, rhodium, quartz|
|Focusing capillaries - Contact Don Bilderback|
|Detectors available - Solid state detectors, ion chambers, MAR345|