Superlattices of Self-Assembled Tetrahedral Ag Nanocrystals

808 Ó WILEY-VCH Verlag GmbH, D-69469 Weinheim, 1998 0935-9648/98/1007-0808 $ 17.50+.50/0 Adv. Mater. 1998, 10, No. 10 1.504 Š). Patterns were indexed using TREOR or METRIC-LS programs. SEM/EDX was carried out on a JEOL JSM820 microscope, equipped with a Kevex Quantum Detector Delta 4, and a Hitachi SEM S-570. Infrared spectra were recorded on a Nicolet 205 spectrometer using KBr pressed discs. Elemental compositions were determined by the departmental service using combustion in oxygen with tin powder as a combustion aid. The EELS spectra from the commercial VC powder (Alpha chemicals) were recorded using a GATAN 666 PEELS spectrometer on a VG Microscopes HB5 scanning transmission electron microscope operated at 100 keV, whereas those from the V8C7 produced by the SSM reaction were recorded using a similar spectrometer system on a Phillips CM20 transmission electron microscope with a field emission gun operated at 200 keV. Reactions of Al4C3 and Transition Metal Halides (TiCl3, ZrCl4, VCl3, WCl4, MoCl3, and MoCl5): Transition metal halide, MXn, and aluminum carbide, n/12 Al4C3 (0.1 mmol), were ground together and heated inside an evacuated ampoule. The ampoule was placed with 2/3 of its length inside a tube furnace at 500 C. The reaction was left for 2±3 h at 500 C and then the temperature was raised by 100 C every 12 h to 1000 C and left to anneal for 2±5 days. The coformed AlCl3 separated from the black-gray carbide product by sublimation to the cool end of the ampoule. The black or gray solids obtained were treated with THF (2 ́ 5 mL) and methanol (1 ́ 10 mL) and dried in vacuo. The resulting gray to black powders were analyzed using powder XRD (Table 1), SEM/EDX, FTIR, elemental microanalysis and, in the case of vanadium, PEELS. (Microanalysis: V8C7: Obs. C 13.75, H 0.21, N 0.19 %; Calcd. C = 17.07 %; Mo2C: Obs. C 6.66, H 0.0, N 0.0 %; Calcd. C = 5.88 %; WC: Obs. C 6.64, H 0.14, N 0.0 %; Calcd. C = 6.12 %.) Reactions of CaC2 with TiCl3, ZrCl4, VCl3, WCl4, MoCl3, and MoCl5: Metal halide, MXn, and calcium carbide, n/2 CaC2 (0.2 mmol), were ground together and heated in an evacuated Pyrex glass ampoule. This induced a rapid reaction that produced a red glow at ca. 200±350 C with the product spread along the inside walls of the ampoule. The temperature was ramped to 500 C (20 C/min), left for an hour, and allowed to cool to room temperature. The solids obtained were triturated with methanol (5 ́ 6 mL), dried in vacuo and analyzed by powder XRD (Table 1), SEM/EDX, and FTIR.