Ag nanorods receive intensive attention due to the excellent plasmonic properties. However, the difficulty in synthesis of monodisperse Ag nanorods with broad aspect ratios has limited their in‐depth applications. Here, a seed‐mediated method is reported for the synthesis of Ag nanorods with lengths from 65 to 5000 nm, corresponding to aspect ratios from 2 to 156. The plasmonic resonance is tuned from visible to mid‐infrared wavelength. The synthesis protocol relies on robust Au seeds synthesized in
- Award ID(s):
- 1808108
- NSF-PAR ID:
- 10168596
- Date Published:
- Journal Name:
- Chemistry of Materials
- ISSN:
- 0897-4756
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract N ,N ‐dimethylformamide (DMF), which induces the one‐dimensional (1D) growth of Ag atoms. To maintain symmetry breaking initiated by the Au seeds, the reduction rate of Ag+is decreased by adding hexadecyltrimethylammonium chloride (CTAC) to form AgCl particles. The optimized conditions to prevent the homogeneous nucleation of Ag nanoparticles and residue of AgCl particles in products are identified, under which the conversion efficiency of Ag ions to Ag nanorods is evaluated about 48%. More importantly, the anisotropic Ag nanorods are self‐assembled into monolayers at interfaces with the long axis of Ag nanorods perpendicular or parallel to the interfaces, respectively. The as‐fabricated monolayers exhibit uniform and reproducible surface‐enhanced Raman scattering (SERS) activities. The optimal SERS performance is achieved from Ag nanorod monolayer with vertical orientation and the longest rod length. -
Tunneling field effect transistors (TFETs) have gained much interest in the previous decade for use in low power CMOS electronics due to their sub-thermal switching [1]. To date, all TFETs are fabricated as vertical nanowires or fins with long, difficult processes resulting in long learning cycle and incompatibility with modern CMOS processing. Because most TFETs are heterojunction TFETs (HJ-TFETs), the geometry of the device is inherently vertically because dictated by the orientation of the tunneling HJ, achieved by typical epitaxy. Template assisted selective epitaxy was demonstrated for vertical nanowires [2] and horizontally arranged nanorods [3] for III-V on Si integration. In this work, we report results on the area selective and template assisted epitaxial growth of InP, utilizing SiO2 based confined structures on InP substrates, which enables horizontal HJs, that can find application in the next generation of TFET devices. The geometries of the confined structures used are so that only a small area of the InP substrate, dubbed seed, is visible to the growth atmosphere. Growth is initiated selectively only at the seed and then proceeds in the hollow channel towards the source hole. As a result, growth resembles epitaxial lateral overgrowth from a single nucleation point [4], reaping the benefits of defect confinement and, contrary to spontaneous nanowire growth, allows orientation in an arbitrary, template defined direction. Indium phosphide 2-inch (110) wafers are used as the starting substrate. The process flow (Fig.1) consists of two plasma enhanced chemical vapor deposition (PECVD) steps of SiO2, appropriately patterned with electron beam lithography (EBL), around a PECVD amorphous silicon sacrificial layer. The sacrificial layer is ultimately wet etched with XeF2 to form the final, channel like template. Not shown in the schematic in Fig.1 is an additional, ALD deposited, 3 nm thick, alumina layer which prevents plasma damage to the starting substrate and is removed via a final tetramethylammonium hydroxide (TMAH) based wet etch. As-processed wafers were then diced and loaded in a Thomas Swan Horizontal reactor. Successful growth conditions found were 600°C with 4E6 mol/min of group III precursor, a V/III ratio of 400 and 8 lpm of hydrogen as carrier gas. Trimethylindium (TMIn) and tertiarybutylphosphine (TBP) were used as In and P precursors respectively. Top view SEM (Fig.2) confirms growth in the template thanks to sufficient Z-contrast despite the top oxide layer, not removed before imaging. TEM imaging shows a cross section of the confined structure taken at the seed hole (Fig.3). The initial growth interface suggests growth was initiated at the seed hole and atomic order of the InP conforms to the SiO2 template both at the seed and at the growth front. A sharp vertical facet is an encouraging result for the future development of vertical HJ based III-V semiconductor devices.more » « less
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Abstract The geometrical structure of the Au‐Fe2O3interfacial perimeter, which is generally considered as the active sites for low‐temperature oxidation of CO, was examined. It was found that the activity of the Au/Fe2O3catalysts not only depends on the number of the gold atoms at the interfacial perimeter but also strongly depends on the geometrical structure of these gold atoms, which is determined by the size of the gold particle. Aberration‐corrected scanning transmission electron microscopy images unambiguously suggested that the gold particles, transformed from a two‐dimensional flat shape to a well‐faceted truncated octahedron when the size slightly enlarged from 2.2 to 3.5 nm. Such a size‐induced shape evolution altered the chemical bonding environments of the gold atoms at the interfacial perimeters and consequently their catalytic activity. For Au particles with a mean size of 2.2 nm, the interfacial perimeter gold atoms possessed a higher degree of unsaturated coordination environment while for Au particles with a mean size of 3.5 nm the perimeter gold atoms mainly followed the atomic arrangements of Au {111} and {100} facets. Kinetic study, with respect to the reaction rate and the turnover frequency on the interfacial perimeter gold atom, found that the low‐coordinated perimeter gold atoms were intrinsically more active for CO oxidation.18O isotopic titration and Infrared spectroscopy experiments verified that CO oxidation at room temperature occurred at the Au‐Fe2O3interfacial perimeter, involving the participation of the lattice oxygen of Fe2O3for activating O2and the gold atoms for CO adsorption and activation.
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1021/acs.chemmater.0c01494
