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Nanoscale ; 11(40): 18550-18558, 2019 Oct 28.
Artigo em Inglês | MEDLINE | ID: mdl-31363719


Introduction of in situ HCl etching to an epitaxial growth process has been shown to suppress radial growth and improve the morphology and optical properties of nanowires. In this paper, we investigate the dynamics of photo-generated charge carriers in a series of indium phosphide nanowires grown with varied HCl fluxes. Time resolved photo-induced luminescence, transient absorption and time resolved terahertz spectroscopy were employed to investigate charge trapping and recombination processes in the nanowires. Since the excitation photons generate charges predominantly in less than a half length of the nanowires, we can selectively assess the charge carrier dynamics at their top and bottom. We found that the photoluminescence decay is dominated by the decay of the mobile hole population due to trapping, which is affected by the HCl etching. The hole trapping rate is in general faster at the top of the nanowires than at the bottom. In contrast, electrons remain highly mobile until they recombine non-radiatively with the trapped holes. The slowest hole trapping as well as the least efficient non-radiative recombination was recorded for etching using the HCl molar fraction of χHCl = 5.4 × 10-5.

Phys Chem Chem Phys ; 19(8): 6006-6012, 2017 Feb 22.
Artigo em Inglês | MEDLINE | ID: mdl-28182179


Photoinitiated charge carrier dynamics in ZnO nanoparticles sensitized by CdSe quantum dots is studied using transient absorption spectroscopy and time-resolved terahertz spectroscopy. The evolution of the transient spectra shows that electron injection occurs in a two-step process, where the formation of a charge transfer state (occurring in several picoseconds) is followed by its dissociation within tens of picoseconds. The photoconductivity of electrons injected into the ZnO nanoparticles is lower than that of charges photogenerated directly in ZnO. We conclude that the motion of injected electrons in ZnO nanoparticles is strongly influenced by their interaction with positive charges left in the sensitizing quantum dots.

J Phys Chem Lett ; 3(17): 2442-6, 2012 Sep 06.
Artigo em Inglês | MEDLINE | ID: mdl-26292130


Time-resolved terahertz spectroscopy was employed for the investigation of charge-transport dynamics in benzothiadiazolo-dithiophene polyfluorene ([2,7-(9,9-dioctyl-fluorene)-alt-5,5-(4',7'-di-2-thienyl-2',1',3'-benzothiadiazole)]) (APFO-3) polymers with various chain lengths and in its monomer form, all blended with an electron acceptor ([6,6]-phenyl-C61-butyric acid methyl ester, PCBM). Upon photoexcitation, charged polaron pairs are created, negative charges are transferred to fullerenes, while positive polarons remain on polymers/monomers. Vastly different hole mobility in polymer and monomer blends allows us to distinguish the hole and electron contributions to the carrier mobility.

Phys Chem Chem Phys ; 13(7): 2850-6, 2011 Feb 21.
Artigo em Inglês | MEDLINE | ID: mdl-21305068


Time-resolved terahertz spectroscopy and combination of quantum chemistry modeling and molecular dynamics simulations were used for the determination of charge carrier mobility in poly[methyl(phenyl)silylene]. Using time-resolved THz spectroscopy we established the on-chain charge carrier drift mobility in PMPSi as 0.02 cm(2) V(-1) s(-1). This value is low due to the formation of polarons: the hole is self-trapped in a potential formed by local chain distortion and the transient THz conductivity spectra show signatures of its oscillations within this potential well. This view is supported by the agreement between experimental and calculated values of the on-chain charge carrier mobility.

J Phys Chem B ; 114(15): 5196-205, 2010 Apr 22.
Artigo em Inglês | MEDLINE | ID: mdl-20353252


We combined various experimental (scanning tunneling microscopy and Raman spectroscopy) and theoretical (density functional theory and molecular dynamics) approaches to study the relationships between the base-pairing patterns and the charge transfer properties in DNA 32-mer duplexes that may be relevant for identification and repair of defects in base pairing of the genetic DNA and for DNA use in nanotechnologies. Studied were two fully Watson-Crick (W-C)-paired duplexes, one mismatched (containing three non-W-C pairs), and three with base pairs chemically removed. The results show that the charge transport varies strongly between these duplexes. The conductivity of the mismatched duplex is considerably lower than that of the W-C-paired one despite the fact that their structural integrities and thermal stabilities are comparable. Structurally and thermally much less stable abasic duplexes have still lower conductivity but not markedly different from the mismatched duplex. All duplexes are likely to conduct by the hole mechanism, and water orbitals increase the charge transport probability.

Oligodesoxirribonucleotídeos/química , Pareamento Incorreto de Bases , Pareamento de Bases , Transporte de Íons , Simulação de Dinâmica Molecular , Nanotecnologia , Análise Espectral Raman , Termodinâmica , Água/química
Appl Opt ; 43(9): 1965-70, 2004 Mar 20.
Artigo em Inglês | MEDLINE | ID: mdl-15065728


One-dimensional photonic crystals composed of silicon and air layers with and without twinning defect (i.e., a periodicity break where one half of the photonic structure is a mirror image of the other one) are studied by means of terahertz time-domain transmission and reflection spectroscopy. The structure with defect is decomposed into building blocks: two twins and a defect. A phase-sensitive characterization in transmission and reflection allows us to fully determine the transfer matrices of any block and consequently to predict the properties of composed structures regardless of the microstructure of the constituting blocks. It is shown and experimentally demonstrated that the defect level position is controlled by the reflectance phase of the twins. Possible approach of the reflectance phase determination by use of Kramers-Kronig analysis is also discussed.