Enhanced thermal stability and nanoparticle-mediated surface patterning: Pt/TiO2(110)

This letter reports (i) the enhanced thermal stability (up to 1060 degrees C) against coarsening and/or desorption of self-assembled Pt nanoparticles synthesized by inverse micelle encapsulation and deposited on TiO2(110) and (ii) the possibility of taking advantage of the strong nanoparticle/support interactions present in this system to create patterned surfaces at the nanoscale. Following our approach, TiO2 nanostripes with tunable width, orientation, and uniform arrangement over large surface areas were produced

Formation, thermal stability, and surface composition of size-selected AuFe nanoparticles

The surface composition of isolated Au0.5Fe0.5 nanoparticles (NPs) synthesized by micelle encapsulation and supported on TiO2(110) has been investigated. The study reveals that phase-segregated structures are present after annealing at 300 degrees C. A subsequent thermal treatment at 700 degrees C resulted in the formation of a AuFe alloy. At this temperature, a state characteristic of Fe was identified at the NPs\u27 surface. Annealing at 900 degrees C resulted in the disappearance of the Fe surface state, which is attributed to Au segregation to the surface. The initial hexagonal NP arrangement on the TiO2(110) surface was preserved up to 900 degrees C. At 1000 degrees C, Au desorption was observed

Formation, thermal stability, and surface composition of size-selected AuFe nanoparticles

The surface composition of isolated Au0.5Fe0.5 nanoparticles (NPs) synthesized by micelleencapsulation and supported on TiO2 (110) has been investigated. The study reveals thatphase-segregated structures are present after annealing at 300 ° C. A subsequent thermal treatmentat 700 ° C resulted in the formation of a AuFe alloy. At this temperature, a state characteristic of Fewas identified at the NPs’ surface. Annealing at 900 ° C resulted in the disappearance of the Fesurface state, which is attributed to Au segregation to the surface. The initial hexagonal NParrangement on the TiO2 (110) surface was preserved up to 900 ° C. At 1000 ° C, Au desorption wasobserved

Enhanced thermal stability and nanoparticle-mediated surface patterning: Pt/TiO₂(110)

This letter reports (i) the enhanced thermal stability (up to 1060 °C) against coarsening and/or desorption of self-assembled Pt nanoparticles synthesized by inverse micelle encapsulation and deposited on TiO2(110) and (ii) the possibility of taking advantage of the strong nanoparticle/support interactions present in this system to create patterned surfaces at the nanoscale. Following our approach, TiO2 nanostripes with tunable width, orientation, and uniform arrangement over large surface areas were produced

Local investigation of the electronic properties of size-selected Au nanoparticles by scanning tunneling spectroscopy

The relationship between the structural/morphological and electronic properties of size-selected gold nanoparticles was investigated using scanning tunneling microscopy and spectroscopy. The nanoparticles were synthesized by inverse micelle encapsulation and were dip-coated on TiO2∕Ti(15 nm)∕Si(111). Annealing in vacuum to 500°C resulted in the removal of the polymer and the formation of an ultrathin TiC support. Significant changes in the electronic local density of states (LDOS) of the nanoparticles, in particular, the onset of nonmetallic behavior, were observed with decreasing particle size. The nanoparticle-support interactions were studied and evidence for substrate-induced modifications in the LDOS of interfacial gold atoms is found

Thermal Stability and Segregation Processes in Self-Assembled Size-Selected Au_xFe_1-x Nanoparticles deposited on TiO₂(110): Composition Effects

Department of Civil, Environmental, and Construction Engineering, University of Central Florida, Orlando, Florida 32816In-situ scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS) measurements have been performed to investigate the formation and thermal stability of mono- and bimetallic AuxFe1-x (x = 1, 0.8, 0.5, 0.2, 0) nanoparticles (NPs) supported on TiO2(110). Nearly hexagonal arrangements of size-selected Au, Fe, and Au−Fe NPs with well-defined interparticle distances have been achieved by diblock-copolymer encapsulation. Upon stepwise annealing from 300 to 1060 °C, a remarkable thermal stability of the Au−Fe NPs was observed, maintaining their original spatial arrangement on the TiO2 surface up to 900 °C. A majority phase of a gold−iron alloy (solid solution) was achieved for our Au0.5Fe0.5 NPs in the temperature range of 700 °C - 800 °C, and for Au0.2Fe0.8 NPs at 800 °C, while a phase mixture of bcc Fe and Au−Fe alloy was observed for the Au0.8Fe0.2 system at 800 °C-900 °C. For all samples the segregation of Au atoms toward the NP surface was detected upon high temperature annealing (800 °C) in vacuum. Nearly complete Au desorption was observed by XPS at 900 °C for Au0.2Fe0.8 NPs, at 1000 °C for Au0.5Fe0.5 NPs, and at 1060 °C for Au0.8Fe0.2 NPs. The enhanced thermal stability of Au in the Au0.8Fe0.2 NPs is believed to be related to the formation of core(Fe)/shell(Au) structures. Furthermore, contrary to the case of pure Fe or Fe-rich NPs where nearly complete Fe desorption or Fe diffusion into TiO2 was observed at 1000 °C, an Fe signal was detected at this temperature for the Au-rich samples (Au0.8Fe0.2 and Au0.5Fe0.5)

Epitaxial Growth, Magnetic Properties, And Lattice Dynamics Of Fe Nanoclusters On Gaas(001)

Epitaxial bcc-Fe(001) ultrathin films have been grown at ∼50°C on reconstructed GaAs (001) - (4×6) surfaces and investigated in situ in ultrahigh vacuum (UHV) by reflection high-energy electron diffraction, scanning tunneling microscopy (STM), x-ray photoelectron spectroscopy (XPS), and Fe57 conversion electron Mössbauer spectroscopy (CEMS). For tFe =1 ML (monolayer) Fe coverage, isolated Fe nanoclusters are arranged in rows along the [110] direction. With increasing tFe the Fe clusters first connect along the [-110], but not along the [110] direction at 2.5 ML, then consist of percolated Fe clusters without a preferential orientation at 3 ML, and finally form a nearly smooth film at 4 ML coverage. Segregation of Ga atoms within the film and on the Fe surface appears to occur at tFe =4 ML, as evidenced by XPS. For coverages below the magnetic percolation, temperature-dependent in situ CEMS measurements in zero external field provided superparamagnetic blocking temperatures TB of 62±5, 80±10, and 165±5 K for tFe =1.9, 2.2, and 2.5 ML, respectively. At T\u3c TB, freezing of superparamagnetic clusters is inferred from the observed quasilinear T dependence of the mean hyperfine magnetic field Bhf. By combining the STM and CEMS results, we have determined a large magnetic anisotropy constant of ∼5× 105 and ∼8× 105 J m3 at tFe =1.9-2.2 and 2.5 ML, respectively. For tFe ≤2.5 ML, our uncoated free Fe clusters exhibit intrinsic magnetic ordering below TB, contrary to literature reports on metal-coated Fe clusters on GaAs. Our present results demonstrate that the nature of the percolation transition for free Fe nanoclusters on GaAs(001) in UHV is from superparamagnetism to ferromagnetism. From the Mössbauer spectral area, a very low Debye temperature ΘD of 196±4 K is deduced for these uncoated Fe nanoclusters in UHV, indicating a strong phonon softening in the clusters. © 2007 The American Physical Society

Thermal Stability And Segregation Processes In Self-Assembled Size-Selected Au XFe 1-X Nanoparticles Deposited On Tio 2(110): Composition Effects

In-situ scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS) measurements have been performed to investigate the formation and thermal stability of mono- and bimetallic Au xFe 1-x (x 1, 0.8, 0.5, 0.2, 0) nanoparticles (NPs) supported on TiO 2(110). Nearly hexagonal arrangements of sizeselected Au, Fe, and Au-Fe NPs with well-defined interparticle distances have been achieved by diblockcopolymer encapsulation. Upon stepwise annealing from 300 to 1060 °C, a remarkable thermal stability of the Au-Fe NPs was observed, maintaining their original spatial arrangement on the TiO 2 surface up to 900 °C. A majority phase of a gold-iron alloy (solid solution) was achieved for our Au 0.5Fe 0.5 NPs in the temperature range of 700 °C - 800 °C, and for Au 0.2Fe 0.8 NPs at 800 °C, while a phase mixture of bcc Fe and Au-Fe alloy was observed for the Au 0.8Fe 0.2 system at 800 °C-900 °C. For all samples the segregation of Au atoms toward the NP surface was detected upon high temperature annealing (800 °C) in vacuum. Nearly complete Au desorption was observed by XPS at 900 °C for Au 0.2Fe 0.8 NPs, at 1000 °C for Au 0.5Fe 0.5 NPs, and at 1060 °C for Au 0.8Fe 0.2 NPs. The enhanced thermal stability of Au in the Au 0.8Fe 0.2 NPs is believed to be related to the formation of core(Fe)/shell(Au) structures. Furthermore, contrary to the case of pure Fe or Fe-rich NPs where nearly complete Fe desorption or Fe diffusion into TiO 2 was observed at 1000 °C, an Fe signal was detected at this temperature for the Au-rich samples (Au 0.8Fe 0.2 and Au 0.5Fe 0.5). © 2009 American Chemical Society