3 research outputs found
Surface Mobility and Nucleation of a Molecular Switch: Tetraaniline on Hematite
Understanding
the dynamics of organic thin film formation is crucial
to quality control in organic electronics and smart coatings. We have
studied the nucleation and growth of the reduced and the oxidized
states of phenyl-capped aniline tetramer (PCAT) deposited on hematite(1000)
surfaces by physical vapor deposition. The fully reduced PCAT molecules
form 2D islands on the surface, whereas the fully oxidized molecules
form 3D islands. Through scaled island size distribution, it was found
that the critical island sizes, <i>i</i>, for the reduced
and oxidized molecules are <i>i</i> = 4 and 5, respectively.
From the dependence of the island density on substrate temperature,
the activation energies for the diffusion of the molecules away from
the critical cluster were calculated to be 1.30 and 0.55 eV, respectively.
At low temperatures, the reduced and the oxidized PCAT molecules form
compact islands on the surface. At higher temperatures, the reduced
islands become dendritic, whereas the oxidized islands become slightly
dendritic. The attempt frequencies for surface diffusion of the reduced
and the oxidized islands were estimated to be about 5 × 10<sup>25</sup> and 8 × 10<sup>11</sup> s<sup>–1</sup>, respectively.
The former value is in line with the high degree of surface wetting
by the reduced PCAT, whereas the latter value shows the higher degree
of intermolecular interaction in the fully oxidized PCAT and the low
degree of its interaction with the iron oxide surface. Interconversion
between oxidized and reduced islands through exposure to a reducing
environment, and its impact on island morphology was examined. We
also found that the presence of Fe<sup>2+</sup> defects on the hematite
surface did not impact the nucleation and growth of the molecular
islands, likely due to a discrepancy in time scale. This study elucidates
the interactions between an oligoaniline-based molecular switch (PCAT)
and hematite surfaces as a function of molecular oxidation state,
with applications in molecular electronics, chemical sensors, and
smart coatings
Ultrasmooth Gold Surfaces Prepared by Chemical Mechanical Polishing for Applications in Nanoscience
For
over 20 years, template stripping has been the best method
for preparing ultrasmooth metal surfaces for studies of nanostructures.
However, the organic adhesives used in the template stripping method
are incompatible with many solvents, limiting the conditions that
may subsequently be used to prepare samples; in addition, the film
areas that can be reliably prepared are typically limited to ∼1
cm<sup>2</sup>. In this article, we present chemical–mechanical
polishing (CMP) as an adhesive-free, scalable method of preparing
ultrasmooth gold surfaces. In this process, a gold film is first deposited
by e-beam evaporation onto a 76-mm-diameter silicon wafer. The CMP
process removes ∼4 nm of gold from the tops of the grains comprising
the gold film to produce an ultrasmooth gold surface supported on
the silicon wafer. We measured root-mean-square (RMS) roughness values
using atomic force microscopy of 12 randomly sampled 1 μm ×
1 μm areas on the surface of the wafer and repeated the process
on 5 different CMP wafers. The average RMS roughness was 3.8 ±
0.5 Ã…, which is comparable to measured values for template-stripped
gold (3.7 ± 0.5 Å). We also compared the use of CMP and
template-stripped gold as bottom electrical contacts in molecular
electronic junctions formed from <i>n</i>-alkanethiolate
self-assembled monolayers as a sensitive test bed to detect differences
in the topography of the gold surfaces. We demonstrate that these
substrates produce statistically indistinguishable values for the
tunneling decay coefficient β, which is highly sensitive to
the gold surface topography
Continuous Hydrothermal Decarboxylation of Fatty Acids and Their Derivatives into Liquid Hydrocarbons Using Mo/Al<sub>2</sub>O<sub>3</sub> Catalyst
In
this study, we report a single-step continuous production of
straight-chain liquid hydrocarbons from oleic acid and other fatty
acid derivatives of interest including castor oil, frying oil, and
palm oil using Mo, MgO, and Ni on Al<sub>2</sub>O<sub>3</sub> as catalysts
in subcritical water. Straight-chain hydrocarbons were obtained via
decarboxylation and hydrogenation reactions with no added hydrogen.
Mo/Al<sub>2</sub>O<sub>3</sub> catalyst was found to exhibit a higher
degree of decarboxylation (92%) and liquid yield (71%) compared to
the other two examined catalysts (MgO/Al<sub>2</sub>O<sub>3</sub>,
Ni/Al<sub>2</sub>O<sub>3</sub>) at the maximized conditions of 375
°C, 4 h of space time, and a volume ratio of 5:1 of water to
oleic acid. The obtained liquid product has a similar density (0.85
kg/m<sup>3</sup> at 15.6 °C) and high heating value (44.7 MJ/kg)
as commercial fuels including kerosene (0.78–0.82 kg/m<sup>3</sup> and 46.2 MJ/kg), jet fuel (0.78–0.84 kg/m<sup>3</sup> and 43.5 MJ/kg), and diesel fuel (0.80–0.96 kg/m<sup>3</sup> and 44.8 MJ/kg). The reaction conditions including temperature,
volume ratio of water-to-feed, and space time were maximized for the
Mo/Al<sub>2</sub>O<sub>3</sub> catalyst. Characterization of the spent
catalysts showed that a significant amount of amorphous carbon deposited
on the catalyst could be removed by simple carbon burning in air with
the catalyst recycled and reused