Quarterly progress report for Q1 FY06 for Complex Transient Events in Materials Studied Using Ultrafast Electron Probes and Terascale Simulation (FWP SCW0289)

Campbell, G.

Lawrence Livermore National Laboratory

关键词: Signal-To-Noise Ratio;    Electrons;    Cathodes;    Monitoring;    Replicas;   

DOI  :  10.2172/896008
RP-ID  :  UCRL-TR-217892
RP-ID  :  W-7405-ENG-48
RP-ID  :  896008

美国|英语

来源: UNT Digital Library

【 摘 要 】

This quarter (Q1 FY06) marked the first time that the LLNL dynamic transmission electron microscope (DTEM) configuration had advanced to the point whereby it was possible to conduct in-situ experiments on specimens. DTEM improvements continue to progress at a rapid pace. We summarize important achievements in the following list: (1) Instrument performance and design improvements - (a) Reproducibly achieving >1 x 10{sup 7} e{sup -} per pulse. Adjustments in the cathode laser system design led to an improved quantum efficiency and electron yield per pulse. The current number of electrons in the pulse is sufficient for acquiring high quality, single-shot electron diffraction patterns. (b) Implementation of computer interface and Labview{reg_sign} programs for cathode and specimen drive alignment and cathode and pump laser trigger and delay settings. These controls provide a user friendly interface and ease in the experimental setup and implementation. (c) Cathode test chamber (offline test apparatus to asses photocathode design and laser induced photoemission) construction has been completed. (2) Notable instrument features brought into service - (a) Drive laser system was enhanced to improve beam shape and uniformity and to include continuous laser energy monitoring. The drive laser spot size on the specimen was also reduced from 70 {mu}m x 110 {mu}m to 50 {mu}m x 75 {mu}m. (b) New phosphor coated face plate manufactured by TVIPS was installed. The sensitivity and signal noise ratio improved by factor 2 (sensitivity {approx}110 CCD counts/e{sup -} and signal to noise ratio {approx}5). (3) Experimental Progress - (a) First time-resolved experiment: observation of the {alpha} (hcp) to {beta} (bcc) phase transition in pure Ti films via single shot electron diffraction. Results of this experiment were published in the MRS Fall 2005 proceedings and are under review for article in the FEMMS proceedings, which will to be published in Journal of Material Science. See Experimental Results section for more on this experiment. (b) First single-shot image captured on the LLNL DTEM (image of diffraction grating replica with dispersed latex spheres): It is believed that this image holds the world's record for the highest combined spatial and temporal resolution in single shot image. The image was generated using a 1.5 ns-long electron pulse and has better than 20 nm spatial resolution.