High-Frequency Stroboscopic X-ray Topography Under Surface Acoustic Wave Excitation
- PDF / 1,376,975 Bytes
- 6 Pages / 417.6 x 639 pts Page_size
- 0 Downloads / 149 Views
Fig. 1. Time structure of synchrotron radiation
47 Mat. Res. Soc. Symp. Proc. Vol. 591 0 2000 Materials Research Society
According to the aforementioned features of synchrotron radiation, the timeresolved measurements are performed in two very different ways. The first one is used to study dynamic processes with characteristic timing, t >> vr' . In this mode one can neglect the time structure of x-ray bursts and consider the synchrotron source as a continuous one. Nevertheless, due to the huge average x-ray intensity, the data acquisition intervals can be greatly reduced, which makes it possible to perform x-ray diffraction measurements in real time. Nowadays, diffraction patterns can be taken and processed with a rate of 40 ms per frame. For much faster (t < vr-) and periodic processes the stroboscopic technique is used, which allows us to study crystal dynamics in a /•s- and ns-scale. In this mode of measurement an external periodic influence of the sample (electric, optical, acoustic etc.) should be synchronized (phase-locked) with the arrival of the x-ray packets from the storage ring to the sample [1-3]. It can be shown that this synchronization requires the frequency of periodic triggering of the sample to be a multiple of v• . In this mode we are not restricted by the data collection time. It should also be stressed that in highfrequency stroboscopic measurements all the x-ray bursts are utilized, i.e. the x-ray intensity is not lost "on the road". In order to study slower periodic processes in the ms range, a mechanical chopper can be installed on the beam line. The repetition rate is determined by the rotation speed of the chopper and cannot exceed a few kHz limit. The synchronization is done with the x-ray packets being transmitted through the chopper's window during its open time. Unfortunately, in such systems the open time to dead time ratio is very small, so less than one percent of the synchrotron intensity is really used. It is very important to emphasize that the time-resolved mode of measurement can be applied to every known x-ray technique, be it based on diffraction, scattering or imaging. In this paper the experimental results collected by the aid of high-frequency stroboscopic x-ray diffraction imaging are presented. The abilities of the new method are demonstrated by means of x-ray topographs taken in situ from crystals, in which short wavelength (6 - 12 jim) surface acoustic waves (SAW) were generated. EXPERIMENT Stroboscopic x-ray topography measurements were performed on the ID19 beam line of the European Synchrotron Radiation Facility (ESRF, Grenoble). The storage ring operated in al 6-bunch mode with a bunch repetition frequency of yr = 5.68 MHz. The radiation provided by a double-crystal monochromator with a wavelength of •,=0.069 nim, was used in order to take diffraction patterns from the (060) atomic planes of LiNbO 3based SAW devices. The scattering geometry is shown in Fig. 2. SAW devices were produced on the polished surfaces of the Y-cut LiNbO 3 wafers, 3 inch in diameter and
Data Loading...
