4 research outputs found
Distinguishing between Mechanical and Electrostatic Interaction in Single Pass Multi Frequency Electrostatic Force Microscopy Measurements on a Molecular Material
Single-pass
electrostatic force microscopy is postulated as one
of the most advanced techniques in terms of spatial resolution and
fastness in data acquisition for the study of electrostatic phenomena
at the nanoscale. However, crosstalk anomalies, in which mechanical
interactions combine with tip–sample electrostatic forces,
are still a major issue to overcome, specifically in soft and biological
samples. In this paper we propose a novel method based on bimodal-atomic
force microscopy to distinguish mechanical crosstalk from electrostatic
images. The method is based in the comparison of bimodal AFM images
with electrostatic ones, where pure mechanical interaction can be
discerned from a mixture of mechanical and electrostatic interactions.
The proposed method is optimized and demonstrated using a supramolecular
charge transfer material. Finally, the method is used as a tool to
depict different crosstalk levels in tetrathiafulvalene-based (TTF)
assemblies, discerning between electrical and mechanical interactions.
This kind of observation is important for obtaining accurate descriptions
of charge distribution in samples made from organic and molecular
layers and materials
Supramolecularly Oriented Immobilization of Proteins Using Cucurbit[8]uril
A supramolecular strategy is used for oriented positioning
of proteins
on surfaces. A viologen-based guest molecule is attached to the surface,
while a naphthol guest moiety is chemoselectively ligated to a yellow
fluorescent protein. Cucurbit[8]uril (CB[8]) is used to link the proteins
onto surfaces through specific charge-transfer interactions between
naphthol and viologen inside the CB cavity. The assembly process is
characterized using fluorescence and atomic force microscopy, surface
plasmon resonance, IR-reflective absorption, and X-ray photoelectron
spectroscopy measurements. Two different immobilization routes are
followed to form patterns of the protein ternary complexes on the
surfaces. Each immobilization route consists of three steps: (i) attaching
the viologen to the glass using microcontact chemistry, (ii) blocking,
and (iii) either incubation or microcontact printing of CB[8] and
naphthol guests. In both cases uniform and stable fluorescent patterns
are fabricated with a high signal-to-noise ratio. Control experiments
confirm that CB[8] serves as a selective linking unit to form stable
and homogeneous ternary surface-bound complexes as envisioned. The
attachment of the yellow fluorescent protein complexes is shown to
be reversible and reusable for assembly as studied using fluorescence
microscopy
Monolayer Contact Doping from a Silicon Oxide Source Substrate
Monolayer
contact doping (MLCD) is a modification of the monolayer
doping (MLD) technique that involves monolayer formation of a dopant-containing
adsorbate on a source substrate. This source substrate is subsequently
brought into contact with the target substrate, upon which the dopant
is driven into the target substrate by thermal annealing. Here, we
report a modified MLCD process, in which we replace the commonly used
Si source substrate by a thermally oxidized substrate with a 100 nm
thick silicon oxide layer, functionalized with a monolayer of a dopant-containing
silane. The thermal oxide potentially provides a better capping effect
and effectively prevents the dopants from diffusing back into the
source substrate. The use of easily accessible and processable silane
monolayers provides access to a general and modifiable process for
the introduction of dopants on the source substrate. As a proof of
concept, a boron-rich carboranyl-alkoxysilane was used here to construct
the monolayer that delivers the dopant, to boost the doping level
in the target substrate. X-ray photoelectron spectroscopy (XPS) showed
a successful grafting of the dopant adsorbate onto the SiO<sub>2</sub> surface. The achieved doping levels after thermal annealing were
similar to the doping levels acessible by MLD as demonstrated by secondary
ion mass spectrometry measurements. The method shows good prospects,
e.g. for use in the doping of Si nanostructures
Konkurrenz und Solidaritaet im laendlichen Raum
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