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Growth mechanisms of F4-TCNQ on inorganic substrates and nanostructures
摘要： The organic semiconductor tetrafluorotetracyanoquinodimethane (F4-TCNQ) is a promising candidate for the doping of organic semiconductors, two-dimensional materials and inorganic compounds, such as ZnO, and also to enhance the charge carrier injection at contacts in organic electronics. In order to evaluate its applicability as a functionalization material or as an electrically active part in devices, we present a systematic study on the growth mode of F4-TCNQ beyond the first few monolayers on different inorganic substrates that cover a broad variety regarding their physical, chemical and morphological surface properties. The materials used are silicon, silicon carbide, graphene on silicon, sapphire, nanocrystalline diamond, as well as gallium nitride (GaN) layers and nanowire arrays. While the surface termination influences the shape and morphology of the islands of F4-TCNQ which form on all substrates investigated, no significant dependence of the growth mode on the substrate doping type and concentration is observed. GaN nanowires are found to act as nucleation sites for F4-TCNQ islands and to be covered by few monolayers of F4-TCNQ forming a closed coaxial shell. In conclusion, F4-TCNQ is identified to nucleate via Stranski-Krastanov growth consisting of monolayers and islands of different size and shape. The findings in this work provide basic growth information for the implementation of F4-TCNQ as functionalization material for nanowire-based applications.
关键词： GaN nanowires,surface functionalization,growth mode,organic semiconductors,organic electronics,surface doping,F4-TCNQ
更新于2025-09-23 15:21:01
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Dual growth mode of boron nitride nanotubes in high temperature pressure laser ablation
摘要： The morphological analysis of the end of boron nitride nanotubes (BNNTs) using high-resolution transmission electron microscopy (HR-TEM) can provide valuable insight into the growth mechanism in high temperature pressure (HTP) laser ablation where the best quality of BNNT materials can be obtained so far. Two growth modes of BNNT coexisting during the synthesis process have been proposed based on HR-TEM observation and length analysis. One is the root growth mode, in which boron nitride (BN) species formed via the surface interaction between surrounding N2 molecules and boron nanodroplets incorporate into the tubular structure. Another mode called open-end growth mode means the prolongation of tube growth from the exposed BN edge surrounding the surface of boron nanodroplets which is constructed by the heterogeneous nucleation of absorbed BN radicals from the gas plume. The statistical data, the proportions of end structures and the length of BNNTs, could be fitted to two growth modes, and the open-end growth mode is found to be especially effective in producing longer nanotubes with a higher growth rate. The scientific understanding of the growth mechanism is believed to provide the control for optimized production of BNNTs.
关键词： growth mechanism,high temperature pressure laser ablation,open-end growth mode,root growth mode,boron nitride nanotubes,HR-TEM
更新于2025-09-12 10:27:22
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Effects of 6H-SiC Substrate Polarity on the Morphology and Microstructure of AlN Films by HVPE with Varied V/III Ratio
摘要： AlN films grown by high temperature hydride vapor phase epitaxy (HVPE) on Si-face and C-face 6H-SiC substrates were investigated. The influences of the substrate polarity with varied V/III ratio on growth mode, structural characteristics and crystalline quality of hetero-epitaxial AlN films have been studied. With the increasing of V/III ratio, AlN grown on Si-face 6H-SiC substrates changed the growth mode from step-flow to 3D island growth, and correspondingly, its surface morphology got rougher. On the contrast, AlN on C-face substrates were consistently in 3D growth mode and maintained a relatively rough surface, with a high density of nanotubes generated, each of which consisting of hexagonal sides defined by {01 0} facets and locating at the bottom of a V-shaped pit on the surface. Based on XRD, Raman and TEM analyses, it was found that the best AlN layer quality was obtained on the Si-face 6H-SiC at V/III ratio of 10.
关键词： Crystalline quality,Morphology,Dislocations,Substrate polarity,Nanotubes,Growth mode
更新于2025-09-11 14:15:04
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Au Nanocluster Growth on Graphene Supported on Ni(111)
摘要： Low energy alkali ion scattering is used to investigate the deposition of Au onto a single layer of graphene grown onto Ni(111) by chemical vapor deposition. The yield of 3.0 keV Na+ singly scattered from Au as a function of coverage indicates that it grows in a Volmer-Weber mode forming nanoclusters that increase in size with the amount of deposition. The neutralization probability of the scattered Na+ is high for the smallest clusters and decreases as they increase in size. This is presumably caused by the cluster edge atoms being positively charged combined with the fact that the ratio of edge to center atoms decreases with size, which is similar to the behavior of Au nanoclusters on oxide substrates. In addition, oxygen is intercalated under the graphene film to decouple it from the substrate, but no changes in the growth mode or neutralization probability are observed.
关键词： Au nanoclusters,Ni(111),graphene,Volmer-Weber growth mode,charge transfer,low energy alkali ion scattering
更新于2025-09-11 14:15:04
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Growth, Morphology and Stability of Au in Contact with the Bi2Se3(0001) Surface
摘要： We report a combined microscopy and spectroscopy study of Au deposited on the Bi2Se3(0001) single crystal surface. At room temperature Au forms islands, according to the Volmer–Weber growth mode. Upon annealing to 100° C the Au deposits are not stable and assemble into larger and thicker islands. The topological surface state of Bi2Se3 is weakly affected by the presence of Au. Contrary to other metals, such as Ag or Cr, a strong chemical instability at the Au/Bi2Se3 interface is ruled out. Core level analysis highlights Bi diffusion toward the surface of Au islands, in agreement with previous findings, while chemical interaction between Au and atomic Se is limited at the interfacial region. For the investigated range of Au coverages, the Au/Bi2Se3 heterostructure is inert towards CO and CO2 exposure at low pressure (10-8 mbar) regime.
关键词： metal to topological insulator contact,chemical properties,photoemission spectroscopy,growth mode,electronic properties,microscopy
更新于2025-09-09 09:28:46