TY - JOUR
T1 - Structural evolution, epitaxy, and sublimation of silver nanoclusters on TiO2 (110)
AU - Sivaramakrishnan, S.
AU - Tedjasaputra, A. P.
AU - Sato, K.
AU - Zuo, J. M.
N1 - Funding Information:
This work was supported by the NSF Grant No. DMR 0449790. The electron microscopy, sample preparation, and AFM were carried out in the Center for Microanalysis of Materials, University of Illinois, which is partially supported by the U.S. Department of Energy under Grant No. DEFG02-91-ER45439. The authors would like to thank Dr. Weijie Huang for helpful discussions and Kevin Colravey for advice on sample preparation. FIG. 1. All RHEED patterns were obtained close to TiO 2 [001]. (a) RHEED pattern of furnace oxidized TiO 2 (110), and (b) RHEED pattern and (c) TEM micrograph of Ag NCs on furnace oxidized TiO 2 (110) at 25 ° C showing multiple NC orientations, (d) RHEED pattern of Ag NCs on furnace oxidized TiO 2 (110) at 460 ° C showing the appearance of weak Ag diffraction spots, (e) RHEED pattern of Ag NCs on furnace oxidized TiO 2 (110) at 585 ° C showing multiple epitaxies just prior to sublimation, (f) TEM micrograph at 585 ° C showing the presence of many singly twinned NCs prior to sublimation, and (g) schematic of RHEED pattern at 585 ° C ; spots corresponding to Ag (111) have been shaded horizontally while the spots corresponding to Ag (112) have been shaded vertically. When spots from two different stacking sequences overlap, it is shown as a filled dark circle. The electron beam is parallel to Ag [−110] for both kinds of NCs. FIG. 2. RHEED intensity vs temperature for silver NCs deposited at 25 ° C on furnace oxidized TiO 2 (110). The dashed line to the left shows the onset of sublimation and the dashed line to the right shows the completion of sublimation. FIG. 3. Silver NCs on reduced TiO 2 (110): RHEED pattern taken along [−110] TiO 2 at (a) 100 ° C showing the onset of epitaxy and weak Ag diffraction spots, (b) 350 ° C showing the completion of epitaxial rearrangement of NCs and a single epitaxial orientation (Ag diffraction spots have been indexed with electron beam being parallel to Ag [11−2]), and (c) 560 ° C showing TiO 2 spots becoming stronger and Ag spots becoming weaker signifying sublimation of some Ag NCs. FIG. 4. RHEED intensity vs temperature for silver NCs deposited at 25 ° C on reduced TiO 2 (110). The dashed line to the left shows the completion of epitaxial rearrangement and the dashed line to the right shows the completion of sublimation. FIG. 5. Silver NCs on reduced TiO 2 (110) at 350 ° C : (a) RHEED pattern taken along [−110] TiO 2 at 350 ° C showing formation of single epitaxy (Ag diffraction spots have been indexed with electron beam parallel to Ag [11−2]) and (b) RHEED pattern taken along [−110] TiO 2 at 620 ° C showing the presence of weaker Ag diffraction spots signifying sublimation of some Ag NCs. (c) TEM micrograph of NCs deposited at 350 ° C showing large size range of NCs. FIG. 6. RHEED intensity vs temperature for silver NCs deposited at 350 ° C on reduced TiO 2 (110). The dashed line shows the completion of sublimation.
PY - 2010
Y1 - 2010
N2 - The structural evolution, epitaxy, and sublimation temperature of silver nanoclusters (NCs) on TiO2 (110) surfaces prepared in two different ways are reported here based on a combination of in situ reflection high energy electron diffraction characterization and ex situ electron imaging. It is shown that silver NCs deposited at room temperature on oxidized TiO2 (110) surfaces are unable to form a single epitaxy prior to sublimation. When heated close to sublimation, two particle orientations dominate: (111) Ag∥(110) TiO2, [-110] Ag∥[001] TiO2 and (112) Ag∥(110) TiO2, [-110] Ag∥[001] TiO2. Single twinned silver NCs are found to be stable even at temperatures close to sublimation. On the other hand, silver NCs prepared similarly on reduced TiO2 (110) surfaces behave very differently when heated to higher temperatures. On the reduced surface, the NCs are able to evolve into a single epitaxy-(111) Ag∥(110) TiO2, [-110] Ag∥[001] TiO2. The sublimation temperature for silver NCs on the reduced surface is found to be less than those on the oxidized surface by about 35°. The epitaxy formed by annealing is the same as the one formed by depositing silver onto reduced TiO2 (110) at 350 °C (>0.5 Tm of Ag).
AB - The structural evolution, epitaxy, and sublimation temperature of silver nanoclusters (NCs) on TiO2 (110) surfaces prepared in two different ways are reported here based on a combination of in situ reflection high energy electron diffraction characterization and ex situ electron imaging. It is shown that silver NCs deposited at room temperature on oxidized TiO2 (110) surfaces are unable to form a single epitaxy prior to sublimation. When heated close to sublimation, two particle orientations dominate: (111) Ag∥(110) TiO2, [-110] Ag∥[001] TiO2 and (112) Ag∥(110) TiO2, [-110] Ag∥[001] TiO2. Single twinned silver NCs are found to be stable even at temperatures close to sublimation. On the other hand, silver NCs prepared similarly on reduced TiO2 (110) surfaces behave very differently when heated to higher temperatures. On the reduced surface, the NCs are able to evolve into a single epitaxy-(111) Ag∥(110) TiO2, [-110] Ag∥[001] TiO2. The sublimation temperature for silver NCs on the reduced surface is found to be less than those on the oxidized surface by about 35°. The epitaxy formed by annealing is the same as the one formed by depositing silver onto reduced TiO2 (110) at 350 °C (>0.5 Tm of Ag).
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U2 - 10.1063/1.3296065
DO - 10.1063/1.3296065
M3 - Article
AN - SCOPUS:77949662762
SN - 0021-8979
VL - 107
JO - Journal of Applied Physics
JF - Journal of Applied Physics
IS - 5
M1 - 053505
ER -