Plastic optoelectronic materials and thin film devices are very attractive in future optical sensor and solar energy applications due to their lightweight, flexible shape, high photon absorption coefficients, low cost, and environmental benefits. In this study, optoelectronic properties of D, D/fA blend, DfA, and a series of DBfA type of conjugated block copolymers has been investigated, where D is a donor type PPV conjugated block, B is a non-conjugated and flexible aliphatic hydrocarbon bridge chain containing different number of aliphatic methylene units, and fA is a fluorinated acceptor type PPV conjugated block. The optical absorptions of the D/fA blend, DfA, and DBfAs are typical overlaps of individual absorptions of D and fA blocks, while the solution steady state photoluminescence (PL) emission of D were quenched to different levels in blends and block copolymers, with DBfAs containing one methylene unit bridge (DB1fA) quenched most. This could be attributed to an intra-molecular photo induced electron transfer or charge separation in DBfA systems. Theoretical first principles study of the equilibrium atomic configuration of DfA reveals the existence of twisting angles between the D and fA blocks in DfA stable states which may account for a less PL quenching of DfA as compared to DB1fA. These results are important for designing and developing high efficiency polymer based optoelectronic systems.
Efficient engineering of metamaterials involves modeling of electric field profiles around these structures. Realistic modeling of the electric field in metamaterials requires accurate knowledge of optical constants of the compo- nents for which traditionally the bulk values are taken. Further progress in the developing of metamaterials is characterized by a reduction of the pattern size, dimensions of single layers in multilayered structures etc. It has been understood that optical functions in low-dimensional and nano-sized materials substantially differ from their bulk values increasingly affecting by quantum processes. In this work we develop a complex method for analytical modeling of electric field profiles in metamaterials including quantum processes in nano-sized multi-layered structures. In particular based on first principles density functional theory we obtained simple analytical functions allowing predictions the optical functions variations with the size reduction of single metamaterial components over a wide spectral region. It is shown that optical functions of nano-sized films substantially (by 50 percent and more) differ from those in bulk. The new calculated optical functions of the components are used for electric field profile modeling of nano-sized multilayered structures by nonlocal Green function technique including effects of spatial dispersion. Silicon, silicon dioxide, and water layers are used as an example. The method effectively incorporates real atomic structure reconstruction on surfaces and inner interfaces thus providing with a more realistic picture for modeling. By comparison with experiment it is demonstrated that our method predicts image potential of the nanostructures in better agreement with experiment than if using traditional classic electrodynamics approach neglecting the quantum effects. The results are discussed in comparison with literature.
The pulsed laser deposited nanocrystalline ZnO films doped by Ga up to six weight percent are studied by X-ray
difraction and generalized spectro-ellipsometry. We report substantial atomic structure modification of heavy
Ga-doped ZnO resulted and a concentration dependent increase of inter-planar distance. Measured dielectric
function spectra show strong blue-shift of the samples studied. Equilibrium atomic configurations and electron
energy structure of ZnO containing defects (voids and Ga impurities) are studied by the density functional theory
(DFT) and generalized gradient approximation (GGA). Atomic geometries are obtained from the total energy
minimization method. Optical functions are calculated within the random phase approximation including the
quasi-particles corrections and plasma excitation effects. We report energetically favorable paths of the voids
growth and aggregation in ZnO. Comparative analysis of experimental and theoretical results indicate that
measured blue-shift in ZnO:Ga substantially exceeds the Burstein-Moss shift as used in many previous work to
interpret concentration dependence of optical functions in heavy doped ZnO. We demonstrate that additional
mechanisms, such as structural and alloying effect, should be involved for quantitative interpretation of optics
of the nano-crystalline heavy-doped ZnO films.
Chemical engineering of metamaterials to reduce optical losses is studied by first principle density functional
theory. Contribution of the surface states to optical losses is studied by calculations of the imaginary part of the
dielectric function for several organic molecules (water, methanol, and ethanol) adsorbed on the (111) surface of
Ag nano-slabs. Substantial modifications of optical functions of metallic nano-slabs in near infrared and visible
spectral regions, caused by surface states and molecular adsorption, are predicted, discussed, and compared to
experimental data.
Optical absorption spectra of poly(thienylenevinylene) (PTV) conjugated polymers are measured at room temperature
in spectral range 400 to 800 nm. A dominant peak located at 575 nm and a prominent shoulder at
614 nm are observed. Equilibrium atomic geometries of PTV conjugated polymers are studied by first principles
density functional theory (DFT). Electron energy structure is obtained through self-consistent solution of eigen
energy problem using ab initio ultrasoft pseudopotentials and generalized gradient approximation method. This
is a non traditional approach for complex organic systems which is shown to be very promising especially for
optical simulations. Linear optical absorption is calculated within Random Phase Approximation (RPA) picture.
By comparative analysis of experimental and theoretical data it is demonstrated that dominant contribution to
the optical excitations of PTV in visible spectral range are related to the delocalized electrons within the polymer
chains. Obtained optical data together with equilibrium geometry analysis indicate that interchain interactions
substantially effect electronic structure and optical absorption of PTV conjugated polymers.
Sum Frequency Generation (SFG) spectra of nanocrystalline porous silicon (por-Si) exposed to different chemical treatments are studied. We report the first SFG studies of por-Si in direct contact with a liquid. SFG is excited by a regeneratively amplified Ti:sapphire system (787 nm, 120 fs, 1 kHz). The sum frequency is generated by combining this light with infrared that is generated with an optical parametric amplifier (OPA) that delivers 100-200 μJ pulses at 1370-1770 nm. Por-Si is made from a 10-20 Ω cm p-type Si(001) wafer. Comparisons are made to planar Si(001) as well as GaAs(001). First principle electronic structure theory based on density functional theory (DFT) is used to study the adsorption and optical response functions from the system of ethanol molecule adsorbed on Si(001) and Si(111) surfaces. Equilibrium atomic geometries are obtained through molecular dynamics and total energy minimization methods. Electron energy structure and optical properties are calculated using generalized gradient approximation method with ab initio pseudopotentials. Predicted differential optical absorption spectra for chemisorbed Si(001) and Si(111) surfaces are analyzed in comparison with SFG data measured on differently treated porous silicon. Substantial modifications of the surface atomic and electron energy structures of silicon surfaces due to chemisorption are shown to provide the dominant contributions to the SFG response.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.