List mode acquisition for examining kinetic processes in thin film systems
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Date
2012-07-25
Journal Title
Journal ISSN
Volume Title
Publisher
Saha Institue of Nuclear Physics
Abstract
Many systems that are studied by reflectometry techniques exhibit interesting kinetic behaviour over a wide range of timescales. Instruments that possess a wide dynamic Q range, such as energy dispersive reflectometers, have the greatest ability to follow such pathways. The most common case is where the kinetics are reasonably slow compared to acquisition time — one takes repeated measurements over a long period, with each of those measurements representing the sample at a particular time. Another example is a stroboscopic experiment (such as oscillatory shear), where the sample has an external stimulus applied to it at regular intervals and the sample response is repeatable. Here one accumulates statistics in several reflectivity curves that correspond to different subperiods in the time frame between applied stimuli. However, most of the current approaches to acquiring kinetic information are suboptimal. In the first case one has to decide on how long an individual measurement will be, but what happens if the kinetics occur on a much faster or much slower time scale — sometimes you only get one shot! In the second case has to decide on how many subperiods are required, and the possibility of the sample changing over time is ignored.
At the Platypus reflectometer at ANSTO we have been pioneering the application of list mode acquisition to study kinetic processes. Here, the X/Y/Time-of-flight/Frame number of each neutron hitting the detector is recorded (the frame structure is created by the pulsed nature of our beam). By the use of processing techniques we can produce reflectivity proles corresponding to the desired time periods of interest. Quite simply, one can add all neutron events together if there is no kinetic evolution, or divide into arbitrary periods if the sample changes. This processing can occur during or after acquisition - nowadays every measurement should be considered to be kinetic in nature.
In this paper we demonstrate the utility of list mode acquisition with two different examples. The first concens the interdiffusion of electron transport and light emitting polymer layers in OLED devices. The second follows the attack of lipid membranes by phospholipases
Description
Physical copy held by ANSTO Library at DDC: 539.758/30
Keywords
Thin Films, Kinetics, Reflectivity, ANSTO, Measuring instruments, Energy
Citation
Nelson, A., Lesha, M., Lee, K. H., James, M., Burn, P. L., Gentle. I. R., McGillivray, D., Knobloch, J. (2012). List mode acquisition for examining kinetic processes in thin film systems. Paper presented to SXNS12, 12th International Conference on Surface X-Ray and Neutron Scattering, 25-28 July 2012, Kolkata, India, (pp. 41).