HPHT growth and x-ray characterization of high-quality type IIa diamond

Abstract

The trend in synchrotron radiation (x-rays) is towards higher brilliance. This may lead to a very high power density, of the order of hundreds of watts per square millimetre at the x-ray optical elements. These elements are, typically, windows, polarizers, filters and monochromators. The preferred material for Bragg diffracting optical elements at present is silicon, which can be grown to a very high crystal perfection and workable size as well as rather easily processed to the required surface quality. This allows x-ray optical elements to be built with a sufficient degree of lattice perfection and crystal processing that they may preserve transversal coherence in the x-ray beam. This is important for the new techniques which include phase-sensitive imaging experiments like holo-tomography, x-ray photon correlation spectroscopy, coherent diffraction imaging and nanofocusing. Diamond has a lower absorption coefficient than silicon, a better thermal conductivity and lower thermal expansion coefficient which would make it the preferred material if the crystal perfection (bulk and surface) could be improved. Synthetic HPHT-grown (high pressure, high temperature) type Ib material can readily be produced in the necessary sizes of 4-8 mm square and with a nitrogen content of typically a few hundred parts per million. This material has applications in the less demanding roles such as phase plates: however, in a coherence-preserving beamline, where all elements must be of the same high quality, its quality is far from sufficient. Advances in HPHT synthesis methods have allowed the growth of type IIa diamond crystals of the same size as type Ib, but with substantially lower nitrogen content. Characterization of this high purity type IIa material has been carried out with the result that the crystalline (bulk) perfection of some of the HPHT-grown materials is approaching the quality required for the more demanding applications such as imaging applications and imaging applications with coherence preservation. The targets for further development of the type IIa diamond are size, crystal perfection, as measured by the techniques of white beam and monochromatic x-ray diffraction imaging (historically called x-ray topography), and also surface quality. Diamond plates extracted from the cubic growth sector furthest from the seed of the new low strain material produces no measurable broadening of the x-ray rocking curve width. One measures essentially the crystal reflectivity as defined by the intrinsic reflectivity curve (Darwin curve) width of a perfect crystal. In these cases the more sensitive technique of plane wave topography has been used to establish a local upper limit of the strain at the level of an 'effective misorientation' of 10(-7) rad.

High-reflectivity high-resolution X-ray crystal optics with diamonds

“…Progress in fabrication, characterization and X-ray optics applications of synthetic diamonds was substantial in the past decade [5][6][7][8][9][10][11][12][13] . Still the diamond crystals available commercially as a rule suffer from defects: dislocations, stacking faults, inclusions, impurities and so on.…”

Performance of a beam-multiplexing diamond crystal monochromator at the Linac Coherent Light Source

“…3 originates from the x-ray induced luminescence of impurities in the diamond crystal, from which growth sectors with different impurity concentrations can be identified. 24 The diamond luminescence can be used to identify the location of the beam on the crystal and help the initial alignment. The first diamond crystal has a thickness of ∼100 μm and the second of ∼300 μm.…”

“…Recent improvements in High Pressure High-Temperature (HPHT) synthesis processes have shown promising results in improved crystal quality. [24][25][26][27][28][29] A set of diamond crystals of the (111) orientation, mounted on an all-diamond mounting frame assembly, was prepared by the Technological Institute for Superhard and Novel Carbon Materials (TISNCM, Troisk, Russia). They were characterized and optimized at the Advanced Photon Source (APS, Argonne, IL) by high resolution topography and then installed in the XPP LODCM for splitting the FEL beam.…”

X-Ray Topographic Study of a Homoepitaxial Diamond Layer on an Ultraviolet-Irradiated Precision Polished Substrate

“…Techniques for growing high-crystalline-quality single-crystal diamond under high-pressure and high--temperature conditions (also known as HPHT diamond) have been developed by several researchers [8,9]. The defect density of commercially available diamond is approximately 10 3 10 5 cm −2 [10].…”