An in situ study on the coalescence of monolayer-protected Au-Ag nanoparticle deposits upon heating.

The structural evolution of thiolate-protected nanoparticles of gold, silver, and their alloys with various Au/Ag ratios (3:1, 1:1, and 1:3) upon heating was investigated by means of in situ synchrotron radiation X-ray diffraction. The relationships between the coalescence and composition of nanoparticles, as well as the surfactant reactions, were clarified. Experimental results show that there existed a critical temperature ranging from 120°C to 164°C, above which the tiny broad X-ray diffraction peaks became sharp and strong due to particle coalescence. The coalescence temperatures for alloy nanoparticle deposits were clearly lower than those for pure metals, which can be ascribed to the rivalry between the thermodynamic effect due to alloying and the interactions between surface-assembled layers and the surface atoms of the nanoparticles. The strong affinity of thiolates to Ag and thus complex interactions give rise to a greater energy barrier for the coalescence of nanoparticles into the bulk and subsequent high coalescence temperature. The influences of particle coalescence on the optical and electrical properties of the nanoparticle deposits were also explored.

Observations on PVP-protected noble metallic nanoparticle deposits upon heating via in situ synchrotron radiation X-ray diffraction.

Through monitoring the evolution of the X-ray diffraction peaks, the phase transformation of PVP-protected Ag and Au nanoparticle deposits (NPDs) on electronic substrates of Cu and Ni upon heating in air was investigated via in situ synchrotron radiation X-ray diffraction. With an increasing temperature, the broad diffraction peak of nano-sized Ag and Au particles with the original average diameters of 4.2 nm and 9.6 nm, respectively, became sharp because of particle coarsening and coalescence. Complex phase transitions among Au, Cu, AuCu(3) and CuO(x) were observed, mainly due to the negative enthalpy of mixing between Au and Cu. The interactions between NPDs and the substrates affected the shift of diffraction peaks to lower angles, caused by thermal expansion and also the temperature for the oxide formation. Compared to Au, Ag NPDs did not form intermetallic compounds with Cu and the formation of copper oxides can also be retarded mainly due to the phase separation feature of the Ag-Cu system.

Constructions of silver nanowires and copper oxide microrings by a surface-formation technique.

We demonstrate a simple method to synthesize silver wires by thermal reduction of aqueous AgNO(3) droplet with catalytic anatase TiO(2) nanoparticles which were spin-coated on Si wafer. Structural characterization of the silver wires shows that the nanowires grow primarily along the [011] direction. SEM image of the silver wires clearly shows the catalytic TiO(2) nano-cluster attached to the end of the each silver wire. Since the process was surfactant-free, the silver nanowires prepared by our method retain the excellent electrical conductivity. The intrinsic resistivity calculated from the current-voltage curve for a wire with 12880.41 nm(2) cross-section area was 18.72 microohm cm, which is about 11.6 times higher than that of bulk silver (1.61 microohm cm). Our simple method can be also applied to generate CuO with ring-shaped microstructure by using ITO conducting glass as matrix. We have found that the size and reproducibility are well-controllable. A single phase of CuO ring-shaped microstructure with outer diameters ranging from approximately 13 to 17 microm and inner diameters ranging from approximately 1.4 to 3.3 microm was obtained. The composition of CuO microring was confirmed by thin-film XRD and XPS analyses.

One-step synthesis of uniform silver nanoparticles capped by saturated decanoate: direct spray printing ink to form metallic silver films.

The one-step synthesis and spectroscopic characterizations of size-controlled silver nanoparticles are described. The transmission electron microscopy (TEM), nuclear magnetic resonance (NMR), Fourier transform infrared spectroscopy (FT-IR), thermal gravimetric-mass analysis (TGA-MS) and X-ray photoelectron spectroscopy (XPS) techniques were used to characterize the decanoate-protected silver nanoparticles. TEM analysis showed that spherical nanoclusters of 7.52 +/- 0.57 nm were produced. Furthermore, the particle sizes are uniform with a narrow size distribution. For all samples, Ag 3d(5/2) and 3d(3/2) components appeared at 368.5 and 374.5 eV, respectively, in the XPS spectrum; these values compare very well with the typical values of carboxylate-protected Ag nanoparticles. A thermal analysis mass spectrometer was used to analyze the desorption behavior of decanoate-protected nanoparticles. From the desorption maximum temperatures of 181 and 263 degrees C, activation energies of 27.2 and 32.2 kcal mol(-1) for the desorption processes in the Ag MPCs were obtained, assuming a first-order reaction and using a pre-exponential factor of 1 x 10(13) s(-1). A specific resistivity of 6.097 microOmega cm for the silver metal film (0.7 microm) on a Si wafer can be produced simply by thermal annealing of an Ag monolayer-protected clusters film under an atmosphere of 90% N(2)-10% H(2) at 300 degrees C for 1 h.