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Photocatalytic
cell with schematic of elementary processes
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Understanding
the microscopic details of carrier transport in nanocrystalline
colloidal thin films is required for complete understanding of a
variety of photochemical and photoelectrochemical cells utilizing
interpenetrating networks. Measuring the photoconductivity in
these materials, however, is a challenging problem because of the
inherent difficulty of attaching wires to nanometer-sized
objects. Furthermore, picosecond carrier dynamics play an
important role in efficient charge separation and transport, but the
low temporal resolution of traditional methods used to determine their
photoconductivity precludes their use in studying sub-ps to ps
dynamics.
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Ultrafast
laser spectrometer
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| Time-resolved
THz spectroscopy (TRTS)
is a non-contact electrical probe capable of measuring the
photoconductivity on a sub-ps to nanosecond timescale. In
essence, materials with high conductivity strongly absorb terahertz
(THz) radiation, while those with low conductivity do not. Using
THz spectroscopy, not only are the average time-dependent conductivity
properties measured, but we also determine the complete
frequency-dependent, complex-valued conductivity (i.e., real and
imaginary components). All on a sub-ps timescale, and all without
attaching any electrical leads to the sample! |
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410
nm
pump/THz probe of electron injection in
functionalized
TiO2 NP films of the following:
N719 (red), 2
(blue), and [MnII(H2O)3(2)]2+ (green)
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| In
summary: In addition to providing a bright source with sensitive
detection methods in the far-infrared region of the spectrum, THz
spectroscopy is the only way to carry out time-resolved far-IR
studies. This capability has been utilized for quantifying the
primary steps in charge transfer required for catalytic processes such
as water oxidation (a.k.a. water-splitting). |
 
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| Charlie
Schmuttenmaer, Christiaan
Richter and Becky Milot |
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