Stable functionalised gold nanoparticles are prepared by simultaneous reduction of tetrachloroaurate ions and attachment of bifunctional organic thiol molecules to the growing gold nuclei leading to a material whose chemical behaviour is characterised by the vacant functionality of the bifunctional thiol ligand.

Nature © Macmillan Publishers Ltd 19988 letters to nature 444 NATURE | VOL 396 | 3 DECEMBER 1998 | www.nature.com orbital occupied at each V 3+ site and the second electron occupying, respectively, the d xz and d yz orbitals in two sublattices as shown in Fig. 4. According to the Goodenough±Kanamori rules 14 , this orbital occupation naturally leads to the G-type antiferromagnetism 11 . A similar result was also obtained by band-structure calculation 15 . From Fig. 1, we see that the ferromagnetic component is both above and below T s oriented parallel to the a-axis of the crystal; the magnetic structure above T s must therefore be of C-type. Then, according to Bertaut's symmetry considerations 12 , the easy axis below T s should be close to the c direction in order for the weak moment to remain along a. From this, we conclude that the easy axis must indeed change on going through the phase transition. The Ctype magnetic ordering observed between T s and T N (ref. 11) should then correspond to an orbital structure, with the alternation of the sublattices also being along the c direction and, as discussed above, with the easy axis almost parallel to b. Such a drastic change of the magnetic properties at T s can lead to a change in the relative role of the DM interaction and the anisotropy. Careful neutron scattering experiments are needed to clarify the behaviour of YVO 3 across T s .Our results make it dif®cult to compare LaVO 3 and YVO 3 in detail: single crystals of LaVO 3 are needed, although the close proximity of T N and T t in LaVO 3 will be a complicating factor. M Figure 4 An electron micrograph of a raft of bimodal Au nanoparticles of the type shown in Fig.1b after storage for two months under ambient conditions. We note that the smaller particles have partially sintered, and formed a semi-continuous network around the larger particles.

Naked" colloidal gold solutions have been prepared in toluene using a two-phase system. The phase-transfer reagent used, a quaternary ammonium bromide salt (R 4 N + Br -), is specifically adsorbed on the clusters through the formation of surface ion pairs, probably with the Brion attached to the Au surface. The separation between clusters for two-dimensional structures is dependent on the chain length in R 4 N + . When more than one layer is present, the nanosized particles show unusual self-organization properties: the occupancy of 2-fold saddle sites is preferred to that of 3-fold hollow sites, leading to linear and circular arrangements. It is proposed that this is due to the balance between local electrostatic repulsion and dispersion forces between the particles.

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Colloidal alloy superlattices of two different nanoclusters are demonstrated here for the first time. Thiol‐functionalized Ag and Au nanoclusters were prepared separately in toluene before mixing and solvent evaporation. For certain Au/Ag proportions, the particles spontaneously self‐organized into ordered 2D arrays, which can be seen in the bright field STEM image in the Figure.