Complex χ(2) spectra of buried silica/isotopically diluted water (HOD-D2O) interfaces were measured using multiplex heterodyne-detected vibrational sum frequency generation spectroscopy to elucidate the hydrogen bond structure and up/down orientation of water at the silica/water interface at different pHs. The data show that vibrational coupling (inter- and/or intramolecular coupling) plays a significant role in determining the χ(2) spectral feature of silica/H2O interfaces and indicate that the doublet feature in the H2O spectra does not represent two distinct water structures (i.e., the ice- and liquid-like structures) at the silica/water interface. The observed pH dependence of the imaginary χ(2) spectra is explained by (1) H-up oriented water donating a hydrogen bond to the oxygen atom of silanolate, which is accompanied by H-up water oriented by the electric field created by the negative charge of silanolate, (2) H-up oriented water which donates a hydrogen bond to the neutral silanol oxygen, and (3) H-down oriented water which accepts hydrogen bonds from the neutral silanol and donates hydrogen bonds to bulk water molecules. The broad continuum of the OH stretch band of HOD-D2O and a long tail in the low frequency region represent a wide distribution of strong hydrogen bonds at the silica/water interface, particularly at the low pH.

Despite recent significant advances in interface-selective nonlinear spectroscopy, the topmost water structure at a charged silica surface is still not clearly understood. This is because, for charged interfaces, not only interfacial molecules at the topmost layer but also a large number of molecules in the electric double layer are probed even with second-order nonlinear spectroscopy. In the present study, we studied water structure at the negatively charged silica/aqueous interface at pH 12 using heterodyne-detected vibrational sum frequency generation spectroscopy, and demonstrated that the spectral component of the topmost water can be extracted by examining the ionic strength dependence of the Imχ spectrum. The obtained Imχ spectrum indicates that the dominant water species in the topmost layer is hydrogen-bonded to the negatively charged silanolate at the silica surface with one OH group. There also exists minor water species that weakly interacts with the oxygen atom of a siloxane bridge or the remaining silanol at the silica surface, using one OH group. The ionic strength dependence of the Imχ spectrum indicates that this water structure of the topmost layer is unchanged in a wide ionic strength range from 0.01 to 2 M.

Small Bi nanoparticles prepared upon reduction of Bi‐III compounds catalyze the growth of thick CdSe nanowires (see image). The control of Bi particle and CdSe nanowire growth rate allows adjustment of the dimensions of the nanowires, which is important for the preparation of various types of nanowires in solution.

The diameter dependence of the optical band gap of single CdSe nanowires (NWs) is investigated by a combination of atomic force microscopy, scanning fluorescence microscopy, and transmission electron microscopy. We find a good congruence of the experimental data to calculations within the effective mass approximation taking into account quantization, exciton Coulomb interaction, and dielectric mismatch. The experimental data are furthermore compared to different theoretical approaches. We discuss the influence of alternating wurtzite and zinc blende segments along the NWs on their optical properties.

Confocal optical microscopy was employed to study the effect of surface-enhanced Raman scattering on individual single-walled carbon nanotubes covered with isolated gold particles. The gold particles with diameters between 10 and 120 nm were deposited in low densities on the tubes' sidewalls by an electrochemical method. In the spectra, Raman peaks associated with the nanotubes were found to be superimposed on a broad luminescence background originating from the metal particles. With increasing particle size, both the luminescence intensity as well as the Raman enhancement increased at longer wavelengths. This finding is consistent with a size-dependent broadening of the gold plasmon frequency and a corresponding extension of the energetic range for local field enhancement on the particle surface. In addition, wavelength-dependent experiments revealed a maximum Raman intensity when both nanotube and metal particle were in optical resonance.

The formation of monodisperse, tunable sized, alloyed nanoparticles of Ni, Co, or Fe with Pt and pure Pt nanoparticles attached to carbon nanotubes has been investigated. Following homogeneous nucleation, nanoparticles attach directly to non-functionalized singlewall and multiwall carbon nanotubes during nanoparticle synthesis as a function of ligand nature and the nanoparticle work function. These ligands do not only provide a way to tune the chemical composition, size and shape of the nanoparticles but also control a strong reversible interaction with carbon nanotubes and permit controlling the nanoparticle coverage. Raman spectroscopy reveals that the sp2 hybridization of the carbon lattice is not modified by the attachment. In order to better understand the interaction between the directly attached nanoparticles and the non-functionalized carbon nanotubes we employed first-principles calculations on model systems of small Pt clusters and both zig-zag and armchair singlewall carbon nanotubes. The detailed comprehension of such systems is of major importance since they find applications in catalysis and energy storage.Composites of metallic nanoparticles (NPs) and carbon nanotubes (CNTs) exhibit high catalytic activity for various chemical reactions [1][2][3][4][5][6] and have also been explored for hydrogen storage applications [7]. Recent reports include platinum [6,8,9] [19,20] and catalytic properties [21][22][23]. Beyond that, 1D alignment of NPs enables to modify the saturation magnetization and coercitivity through magnetostatic coupling [24][25][26]. A convenient way for 1D alignment is the attachment of NPs to CNTs, which is usually achieved by electrochemical deposition [27,28], the reduction of metallic salts in the presence of functionalized CNTs [15,29], or chemical vapor deposition [10], among others [30]. On the other hand, concerning the NP synthesis, the organometallic synthesis route provides nanocrystalline alloyed materials with precise size control and tunable composition in several systems [20,31,32]. Here, we report on the synthesis of alloyed N i x P t 1−x [20], Co x P t 1−x and F e x P t 1−x [32] NPs as well as pure P t [33] NPs and their attachment to non-functionalized singlewall (SWCNTs), multiwall carbon nanotubes (MWCNTs) and glassy carbon by their simple integration in the organometallic synthesis. The experimental procedure involves only a single synthetic step, whereby the crucial parameter for attachment was found in the correct balance of the ligands oleylamine (OA) and oleic acid (Oac).

Down to the wire: High‐resolution photoluminescence (PL) and Raman images of CdSe nanowires were obtained using tip‐enhanced near‐field optical microscopy. They show that the optical properties of the CdSe nanowires vary significantly within a few nanometers leading to strong spatial fluctuations in both PL intensities and energies (see picture).

Single-wall carbon nanotubes decorated by gold nanoparticles with sizes of a few tens of nanometers were investigated by confocal Raman microscopy. It was found that individual nanoparticles impart a sizable Raman enhancement exceeding one order of magnitude, without appreciably interfering with polarization dependent Raman measurements. By contrast, cavity effects within small nanoparticle agglomerates resulted in a 20-fold stronger enhancement and significant distortions of the polarization characteristic.