A dipping method was developed to fabricate three-dimensional colloidal crystal films. The thickness of the films fabricated by this method can be precisely controlled from one layer to several tens of layers by controlling the particle concentration and the film formation speed. Experimental results showed that the spheres form a face-centered cubic structure and that single crystals in the film can extend to centimeter dimensions.

Thin films were grown on amine-primed Si and glass substrates by sequential adsorption reactions of polyallylamine hydrochloride (PAH) and anionic colloids derived from HTiNbO5 and HCa2Nb3O10. The acid−base chemistry of polycation/polyanion adsorption was studied in detail for PAH/HTiNbO5. The pK a of PAH, defined as the pH at which it is half protonated, is 8.7. Titanoniobate colloids, prepared by reaction of HTiNbO5 with tetra(n-butylammonium) hydroxide, TBA+OH-, are unilamellar at pH ≥ 8.5 and restack below pH 7.0. Efficient tiling of a PAH-terminated surface by a layer of unilamellar titanoniobate sheets occurs only at intermediate pH values (8.5−9.0). At lower pH, the colloid restacks on the surface, and at higher pH, only partial coverage by single sheets is observed by atomic force microscopy (AFM). At pH 8.5, high-quality multilayer films can be grown by sequentially adsorbing PAH with either the titanoniobate or niobate colloid. TGA/DTA studies of bulk PAH/titanoniobate intercalation compounds show that they decompose oxidatively to form HTiNbO5 at 310−350 °C and that this decomposition is followed by interlayer condensation to make Ti2Nb2O9. A similar process occurs in the PAH/titanioniobate multilayer films at 350 °C.

The magnetic properties of the spin-crossover compounds, [Fe(qsal)2]NCSe-MeOH (1) and [Fe(qsal)2]NCSe-CH2Cl2 (2), have been measured. We have discovered that both compounds 1 and 2 exhibit a wide thermal hysteresis loop of 140 K (T(1/2) upward arrow = 352 K and T(1/2) downward arrow = 212 K) and 180 K (T(1/2) upward arrow = 392 K and T(1/2) downward arrow = 212 K), respectively, in the first cycle. Thermogravimetric analysis shows that solvent molecules escape from compounds 1 and 2 around 340 and 395 K, respectively. This means that the hysteresis loops observed for the first cycle are only apparent ones. Following the first loop, they show a two-step spin-crossover in warming mode. The so-called "step 1" and "step 2" are centered around T(1/2(S1)) upward arrow = 215 K and T(1/2(S2)) upward arrow = 282 K, respectively. On the other hand, a one-step spin-crossover occurs at T(1/2) downward arrow = 212 K in cooling mode. The hysteresis widths can be estimated to be 3 K (step 1) and 70 K (step 2), assuming that the widths in steps 1 and 2 are defined as the differences between T(1/2(S1)) upward arrow and T(1/2) downward arrow, and T(1/2(S2)) upward arrow and T(1/2) downward arrow, respectively. The hysteresis width of 70 K in step 2 is one of the widest values reported so far for spin-crossover complexes. It is thought that the cooperativity operating in the complexes arises mainly from the intermolecular pi interactions between quinoline and phenyl rings. Using a previously reported model, we are able to simulate the hysteresis loop with a two-step spin-crossover in warming mode and a one-step transition in cooling mode.