5 research outputs found
Crystal Morphologies of Organolead Trihalide in Mesoscopic/Planar Perovskite Solar Cells
The crystal morphology of organolead
trihalide perovskite (OTP)
light absorbers can have profound influence on the perovskite solar
cells (PSCs) performance. Here we have used a combination of conventional
transmission electron microscopy (TEM) and high-resolution TEM (HRTEM),
in cross-section and plan-view, to characterize the morphologies of
a solution-processed OTP (CH<sub>3</sub>NH<sub>3</sub>PbI<sub>3</sub> or MAPbI<sub>3</sub>) within mesoporous TiO<sub>2</sub> scaffolds
and within capping and planar layers. Studies of TEM specimens prepared
with and without the use of focused ion beam (FIB) show that FIBing
is a viable method for preparing TEM specimens. HRTEM studies, in
conjunction with quantitative X-ray diffraction, show that MAPbI<sub>3</sub> perovskite within mesoporous TiO<sub>2</sub> scaffold has
equiaxed grains of size 10–20 nm and relatively low crystallinity.
In contrast, the grain size of MAPbI<sub>3</sub> perovskite in the
capping and the planar layers can be larger than 100 nm in our PSCs,
and the grains can be elongated and textured, with relatively high
crystallinity. The observed differences in the performance of planar
and mesoscopic-planar hybrid PSCs can be attributed in part to the
striking differences in their perovskite-grain morphologies
Combination of Functional Nanoengineering and Nanosecond Laser Texturing for Design of Superhydrophobic Aluminum Alloy with Exceptional Mechanical and Chemical Properties
Industrial application of metallic
materials is hindered by several
shortcomings, such as proneness to corrosion, erosion under abrasive
loads, damage due to poor cold resistance, or weak resistance to thermal
shock stresses, <i>etc</i>. In this study, using the aluminum-magnesium
alloy as an example of widely spread metallic materials, we show that
a combination of functional nanoengineering and nanosecond laser texturing
with the appropriate treatment regimes can be successfully used to
transform a metal into a superhydrophobic material with exceptional
mechanical and chemical properties. It is demonstrated that laser
chemical processing of the surface may be simultaneously used to impart
multimodal roughness and to modify the composition and physicochemical
properties of a thick surface layer of the substrate itself. Such
integration of topographical and physicochemical modification leads
to specific surface nanostructures such as nanocavities filled with
hydrophobic agent and hard oxynitride nanoinclusions. The combination
of superhydrophobic state, nano- and micro features of the hierarchical
surface, and the appropriate composition of the surface textured layer
allowed us to provide the surface with the outstanding level of resistance
of superhydrophobic coatings to external chemical and mechanical impacts.
In particular, experimental data presented in this study indicate
high resistance of the fabricated coatings to pitting corrosion, superheated
water vapor, sand abrasive wear, and rapid temperature cycling from
liquid nitrogen to room temperatures, without notable degradation
of superhydrophobic performance
Effective Antibacterial Nanotextured Surfaces Based on Extreme Wettability and Bacteriophage Seeding
A method
based on nanosecond laser treatment was used to design
superhydrophobic and superhydrophilic aluminum alloy substrates showing
enhanced cytotoxic activity with respect to <i>Escherichia coli</i> K12 C600 strain. It was shown that the survival of cells adhered
to the superhydrophobic substrates was significantly affected by the
presence of organic contaminants, which are ubiquitous in hospital
practice and the food industry. The peculiarities of the texture also
played a notable role in antibactericidal activity. It was found that
the superhydrophilic surfaces had much higher toxicity than the superhydrophobic
ones, which was explained by the mechanisms of adhesion of cells to
the surface. Scanning electron microscopy and tomographic reconstruction
of the adhered cells were used to study the variation of cell morphology
after attachment to surfaces with different wettability. It was shown
that the cytotoxicity of superhydrophobic surfaces could be significantly
enhanced by using the combined antimicrobial action of bacteriophages
and the superhydrophobicity of the objects
Size-Dependent Structure Relations between Nanotubes and Encapsulated Nanocrystals
The structural organization
of compounds in a confined space of nanometer-scale cavities is of
fundamental importance for understanding the basic principles for
atomic structure design at the nanolevel. Here, we explore size-dependent
structure relations between one-dimensional PbTe nanocrystals and
carbon nanotube containers in the diameter range of 2.0–1.25
nm using high-resolution transmission electron microscopy and ab initio
calculations. Upon decrease of the confining volume, one-dimensional
crystals reveal gradual thinning, with the structure being cut from
the bulk in either a <110> or a <100> growth direction
until a certain limit of ∼1.3 nm. This corresponds to the situation
when a stoichiometric (uncharged) crystal does not fit into the cavity
dimensions. As a result of the in-tube charge compensation, one-dimensional
superstructures with nanometer-scale atomic density modulations are
formed by a periodic addition of peripheral extra atoms to the main
motif. Structural changes in the crystallographic configuration of
the composites entail the redistribution of charge density on single-walled
carbon nanotube walls and the possible appearance of the electron
density wave. The variation of the potential attains 0.4 eV, corresponding
to charge density fluctuations of 0.14 e/atom
BaTiO<sub>3</sub> Thin Films from Atomic Layer Deposition: A Superlattice Approach
A superlattice
approach for the atomic layer deposition of polycrystalline
BaTiO<sub>3</sub> thin films is presented as an example for an effective
route to produce high-quality complex oxide films with excellent thickness
and compositional control. This method effectively mitigates any undesirable
reactions between the different precursors and allows an individual
optimization of the reaction conditions for the Ba–O and the
Ti–O subcycles. By growth of nanometer thick alternating BaÂ(OH)<sub>2</sub> and TiO<sub>2</sub> layers, the advantages of binary oxide
atomic layer deposition are transferred into the synthesis of ternary
compounds, permitting extremely high control of the cation ratio and
superior uniformity. Whereas the BaÂ(OH)<sub>2</sub> layers are partially
crystalline after the deposition, the TiO<sub>2</sub> layers remain
mostly amorphous. The layers react to polycrystalline, polymorph BaTiO<sub>3</sub> above 500 °C, releasing H<sub>2</sub>O. This solid-state
reaction is accompanied by an abrupt decrease in film thickness. Transmission
electron microscopy and Raman spectroscopy reveal the presence of
hexagonal BaTiO<sub>3</sub> in addition to the perovskite phase in
the annealed films. The microstructure with relatively small grains
of ∼70 Å and different phases is a direct consequence
of the abrupt formation reaction. The electrical properties transition
from the initially highly insulating dielectric semiamorphous superlattice
into a polycrystalline BaTiO<sub>3</sub> thin film with a dielectric
constant of 117 and a dielectric loss of 0.001 at 1 MHz after annealing
at 600 °C in air, which, together with the suppression of ferroelectricity
at room temperature, are very appealing properties for voltage tunable
devices