24 research outputs found
Spin Coated Plasmonic Nanoparticle Interfaces for Photocurrent Enhancement in Thin Film Si Solar Cells
Nanoparticle (NP) arrays of noble metals strongly absorb light in the visible
to infrared wavelengths through resonant interactions between the incident
electromagnetic field and the metal's free electron plasma. Such plasmonic
interfaces enhance light absorption and photocurrent in solar cells. We report
a cost effective and scalable room temperature/pressure spin-coating route to
fabricate broadband plasmonic interfaces consisting of silver NPs. The NP
interface yields photocurrent enhancement (PE) in thin film silicon devices by
up to 200% which is significantly greater than previously reported values. For
coatings produced from Ag nanoink containing particles with average diameter of
40 nm, an optimal NP surface coverage of 7% was observed. Scanning electron
microscopy of interface morphologies revealed that for low surface coverage,
particles are well-separated, resulting in broadband PE. At higher surface
coverage, formation of particle strings and clusters caused red-shifting of the
PE peak and a narrower spectral response.Comment: 25 pages, 7 figure
Plasmonic Nanogels with Robustly Tunable Optical Properties
Low viscosity fluids with tunable optical properties can be processed to manufacture thin film and interfaces for molecular detection, light trapping in photovoltaics and reconfigurable optofluidic devices. In this work, self-assembly in wormlike micelle solutions is used to uniformly distribute various metallic nanoparticles to produce stable suspensions with localized, multiple wavelength or broad-band optical properties. Their spectral response can be robustly modified by varying the species, concentration, size and/or shape of the nanoparticles. Structure, rheology and optical properties of these plasmonic nanogels as well as their potential applications to efficient photovoltaics design are discussed
A novel mixed matrix membrane of phenolphthalein hydrazide and polysulfone for the detection of copper ions in environmental water samples.
The novel membrane test strip of phenolphthalein hydrazide (PH)-polysulfone has been designed and demonstrated for Cu2+ ions detection. Before finding performance of membrane the studies with PH alone has been performed. Aqueous solutions of PH are colorless, but upon interaction with Cu2+ ions become pink (when 8.2 ≤ pH ≥ 12). The colorimetric change is initiated by the coordination of Cu2+ with PH as a polydentate ligand, opening the spirolactam ring that subsequently hydrolyses releasing phenolphthalein (P). Further membrane was preloaded with PH that could be used as a simple, low cost, and portable sensor for Cu2+ ions in environmental water samples. Given the detection limits of this sensor, a maximum response would warn the tester that Cu2+ concentrations were above safe drinking regulation values. Approximate concentrations can be determined via a color comparison chart. Different metal ions were tested in order to determine the chemodosimeters specificity, of the 12 tested ions only Hg2+ induced a similar molecular transformation (i.e., PH to P). The chemodosimeter allows the quantification of Cu2+ ions in the linear dynamic range of 0–22 μM. The Sandell sensitivity, limit of detection, limit of quantification, and relative standard deviation were found to be 0.276 μg/mL/cm2, 0.279 μM, 1.674 μM, and 0.682% respectively
Investigation of pulsed laser induced dewetting in nanoscopic metal films
Hydrodynamic pattern formation (PF) and dewetting resulting from pulsed laser
induced melting of nanoscopic metal films have been used to create spatially
ordered metal nanoparticle arrays with monomodal size distribution on
SiO_{\text{2}}/Si substrates. PF was investigated for film thickness h\leq7 nm
< laser absorption depth \sim11 nm and different sets of laser parameters,
including energy density E and the irradiation time, as measured by the number
of pulses n. PF was only observed to occur for E\geq E_{m}, where E_{m} denotes
the h-dependent threshold energy required to melt the film. Even at such small
length scales, theoretical predictions for E_{m} obtained from a
continuum-level lumped parameter heat transfer model for the film temperature,
coupled with the 1-D transient heat equation for the substrate phase, were
consistent with experimental observations provided that the thickness
dependence of the reflectivity of the metal-substrate bilayer was incorporated
into the analysis. The spacing between the nanoparticles and the particle
diameter were found to increase as h^{2} and h^{5/3} respectively, which is
consistent with the predictions of the thin film hydrodynamic (TFH) dewetting
theory. These results suggest that fast thermal processing can lead to novel
pattern formation, including quenching of a wide range of length scales and
morphologies.Comment: 36 pages, 11 figures, 1 tabl
Self-similar shear-thickening behavior in CTAB/NaSal surfactant solutions
The effect of salt concentration Cs on the critical shear rate required for
the onset of shear thickening and apparent relaxation time of the
shear-thickened phase, has been investigated systematically for dilute
CTAB/NaSal solutions. Experimental data suggest a self-similar behavior of the
critical shear rate and relaxation time as functions of Cs. Specifically, the
former ~ Cs^(-6) whereas the latter ~ Cs^(6) such that an effective Weissenberg
number for the onset of the shear thickened phase is only weakly dependent on
Cs. A procedure has been developed to collapse the apparent shear viscosity
versus shear rate data obtained for various values of Cs into a single master
curve. The effect of Cs on the elastic modulus and mesh size of the
shear-induced gel phase for different surfactant concentrations is discussed.
Experiments performed using different flow cells (Couette and cone-and-plate)
show that the critical shear rate, relaxation time and the maximum viscosity
attained are geometry-independent. The elastic modulus of the gel phase
inferred indirectly by employing simplified hydrodynamic instability analysis
of a sheared gel-fluid interface is in qualitative agreement with that
predicted for an entangled phase of living polymers. A qualitative mechanism
that combines the effect of Cs on average micelle length and Debye parameter
with shear-induced configurational changes of rod-like micelles is proposed to
rationalize the self-similarity of SIS formation.Comment: 27 pages, 17 figure
Uniaxial Extension of Surfactant Micelles: Counterion Mediated Chain Stiffening and a Mechanism of Rupture by Flow-Induced Energy Redistribution
We study the configurational dynamics
in uniaxial elongational
flow of rodlike and <i>U</i>-shaped cationic surfactant
micelles of cetyltrimethylammonium chloride (CTAC) in the presence
of sodium salicylate (NaSal) counterions in water using molecular
dynamics simulations. Above the critical strain rate, approximately
equal to the inverse of the micelle relaxation time, hydrodynamic
forces overcome the conformational entropy of the micelle and a configurational
transition from a folded to a stretched state occurs. As the accumulated
strain exceeds a critical value of O(100), the micelle ruptures through
a midplane thinning mechanism facilitated by the advection of the
counterions toward the micelle end-caps. The change in the total pair-potential
energy as a function of micelle elongation is well described by a
Hookean spring model that allowed to estimate the stretching modulus
of the micelle. Micelle stiffness depends greatly on the degree of
screening of electrostatic repulsion among the CTA<sup>+</sup> head
groups by the Sal<sup>–</sup> counterions condensed on the
surface. A moderate increase in the counterion concentration makes
the molecular assembly tighter and more immune to deformation by hydrodynamic
stresses, resulting in an order magnitude enhancement in the stretching
modulus