Using two-phase (water-toluene) reduction of AuC14-by sodium borohydride in the presence of an alkanethiol, solutions of 1-3 nm gold particles bearing a surface coating of thiol have been prepared and characterised; this novel material can be handled as a simple chemical compound.

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.

A technique to measure the electrical conductivity of single molecules has been demonstrated. The method is based on trapping molecules between an STM tip and a substrate. The spontaneous attachment and detachment of a,o-alkanedithiol molecular wires was easily monitored in the time domain. Electrical contact between the target molecule and the gold probes was achieved by the use of thiol groups present at each end of the molecule. Characteristic jumps in the tunnelling current were observed when the tip was positioned at a constant height and the STM feedback loop was disabled. Histograms of the measured current jump values were used to calculate the molecular conductivity as a function of bias and chain length. In addition, it is demonstrated that these measurements can be carried out in a variety of environments, including aqueous electrolytes. The changes in conductivity with chain length obtained are in agreement with previous results obtained using a conducting AFM and the origin of some discrepancies in the literature is analysed.

Self-assembled multilayer thin films consisting of alternating layers of ∼6-nm Au nanoparticles and α,ω-dithiols have been prepared on glass substrates. They have been studied by UV/Vis spectroscopy, ellipsometry, scanning tunneling microscopy, and temperature-dependent conductivity measurements. The electronic and optical properties of the thin film material are nonmetallic, and the Au particles maintain their individual character without fusion to larger units. Electronic conduction within the films occurs via activated electron hopping.

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.