Christine M. Brizard

In situ X-ray diffraction of the early stages of the crystallization of Fe80B20

A new technique has been used for the early stages of crystallization of amorphous materials, like metallic alloys. In situ X-ray diffraction has been performed during the early stages of crystallization of Fe80B20. The samples are resistively heated to 600°C in a customized vacuum chamber. A programmable charge-coupled device detector records simultaneously the evolution of the three phases: α-Fe, Fe3B and Fe2B in the minute scale. This is the first in situ X-ray diffraction study of this system in these temperature and time scales. Interesting behaviours have been seen: appearance and disappearance of phases, α-Fe supersaturation solution in boron (found for the first time in this compound), and migration of B out of the α-Fe matrix. The two-dimensional diffraction pictures show topography irregularities indicating crystallite inhomogeneties.

Synchrotron radiation applications of charge coupled device detectors (invited)

Scientific charge coupled devices (CCDs) offer many opportunities for high brightness synchrotron radiation applications where good spatial resolution and fast data acquisition are important. We describe the use of virtual‐phase CCD pixel arrays as two‐dimensional area detectors illustrating the techniques with results from recent x‐ray scattering, imaging, and absorption spectroscopy studies at NSLS, CHESS, SRC, and LURE DCI. The virtual phase architecture allows direct frontside illumination of the CCD detector chips giving advantages in the speed and sensitivity of the detector. Combining developments in x‐ray optics (dispersive geometry), position sensitive area detectors (CCDs), and fast data acquisition, we have been able to perform time‐resolved measurements at the microsecond level. Current developments include faster data transfer rates so that the single bunch timing structure of third generation synchrotron sources can be exploited.

Programmable CCD imaging system for synchrotron radiation studies

Abstract A real-time imaging system for the detection of photons from the infrared to X-ray region of the electromagnetic spectrum has been developed. The active detection element in the system is a charge-coupled device (CCD). The system, based on the Computer Automated Measurement And Control (CAMAC) modular IEEE 583 standard in which all modules are programmable, allows one to use the detector in many modes, as described below. Further, the programmability also enables one to easily change the waveform shapes and timings vs the readout requirements of CCDs from different vendors. Three different CCDs with radically different readout timings and waveforms have been tested. The CCD that is characterized and described in this paper is the TC 215 manufactured by Texas Instruments (TI). Uniformity, charge transfer efficiency (CTE), linearity and sensitivity measurements have been carried out using visible light. Preliminary data obtained from a time-resolved experiment performed at the NSLS X6 beamline is shown and potential time-resolved experiments that are feasible are described.

Real time x-ray studies of rapidly annealed epitaxial layers

Time‐resolved x‐ray scattering studies of epitaxial overlayers are presented. The results illustrate the usefulness of high‐brightness synchrotron probes for studying the cooperative kinetics of interfaces during rapid thermal processing.

Soft x-ray spectro-microscope

An X-ray photoelectron microscope capable of providing both spatial and chemical information on the nature of a sample has been developed. Photons from the Aladdin Synchrotron are monochromatized by an extended-range Grasshopper monochromator covering the range from 40 to 1500 eV with an energy resolution between 10 and 200 meV. The monochromatized radiation generates photoelectrons in the sample, which is energy-analyzed with a resolving power E/delta E greater than 50,000 and imaged by a multichannel plate array. The visible image is transferred to a computer by a virtual-phase charge-coupled device camera with a dynamic range of 4096:1. Preliminary coarse measurements indicate a spatial resolution of the instrument better than 1 micron, although a limit of 600 A is possible. The instrument provides chemical shift-resolved images of low-lying core levels in a variety of samples.

X-ray detector for time-resolved studies

The development of ultrahigh-brightness x-ray sources makes time-resolved x-ray studies more and more feasible. Improvements in x-ray optics components are also critical for obtaining the appropriate beam for a particular type of experiment. Moreover, fast parallel detectors will be essential in order to exploit the combination of high intensity x-ray sources and novel optics for time-resolved experiments. A CCD detector with a time resolution of microseconds has been developed at the Advanced Photon Source (APS). This detector is fully programmable using CAMAC electronics and a MicroVax computer. The techniques of time- resolved x-ray studies, which include scattering, microradiography, microtomography, stroboscopy, etc., can be applied to a range of phenomena (including rapid thermal annealing, surface ordering, crystallization, and the kinetics of phase transition) in order to understand these time-dependent microscopic processes. Some of these applications are illustrated by recent results performed at synchrotrons. New powerful x-ray sources now under construction offer the opportunity to apply innovative approaches in time-resolved work.