15 research outputs found
Hot carrier extraction from 2D semiconductor photoelectrodes
Hot carrier-based energy conversion systems could double the efficiency of
conventional solar energy technology or drive photochemical reactions that
would not be possible using fully thermalized, ``cool'' carriers, but current
strategies require expensive multi-junction architectures. Using an
unprecedented combination of photoelectrochemical and in situ transient
absorption spectroscopy measurements, we demonstrate ultrafast (<50 fs) hot
exciton and free carrier extraction under applied bias in a proof-of-concept
photoelectrochemical solar cell made from earth-abundant and potentially
inexpensive monolayer (ML) MoS2. Our approach facilitates ultrathin 7\AA charge
transport distances over 1 cm^2 areas by intimately coupling ML-MoS2 to an
electron-selective solid contact and a hole-selective electrolyte contact. Our
theoretical investigations of the spatial distribution of exciton states
suggest greater electronic coupling between hot exciton states located on
peripheral S atoms and neighboring contacts likely facilitates ultrafast charge
transfer. Our work delineates future 2D semiconductor design strategies for
practical implementation in ultrathin photovoltaic and solar fuels
applications.Comment: 6 pages, 3 figures main text; 6 pages, 8 figures, 1 table, 57 refs.
appendice
Breaking Barriers in Ultrafast Spectroscopy and Imaging Using 100 kHz Amplified Yb-Laser Systems
Ultrafast spectroscopy and imaging have become tools utilized by a broad
range of scientists involved in materials, energy, biological, and chemical
sciences. Commercialization of ultrafast spectrometers including transient
absorption spectrometers, vibrational sum frequency generation spectrometers,
and even multidimensional spectrometers have put these advanced spectroscopy
measurements into the hands of practitioners originally outside the field of
ultrafast spectroscopy. There is a technology shift occurring in ultrafast
spectroscopy, made possible by new Yb-based lasers, that is opening exciting
new experiments in the chemical and physical sciences. Amplified Yb-based
lasers operate at many times the repetition rate of the previous generation of
Ti:Sapphire amplifier technology, enabling improvements to long-standing
techniques, new experiments, and the transformation of spectroscopies to
microscopies. The impact of this technology will be felt across a great swath
of the scientific communities. This review focuses on amplified Yb-based laser
systems used in conjunction with 100 kHz spectrometers operating with
shot-to-shot pulse shaping and detection. The shift to 100 kHz lasers is a
transformative step in nonlinear spectroscopy and imaging, much like the
dramatic expansion that occurred with the commercialization of Ti:Sapphire
laser systems in the 1990s
Bosonization and Fermion Liquids in Dimensions Greater Than One
(Revised, with postscript figures appended, corrections and added comments.)
We develop and describe new approaches to the problem of interacting Fermions
in spatial dimensions greater than one. These approaches are based on
generalizations of powerful tools previously applied to problems in one spatial
dimension. We begin with a review of one-dimensional interacting Fermions. We
then introduce a simplified model in two spatial dimensions to study the role
that spin and perfect nesting play in destabilizing Fermion liquids. The
complicated functional renormalization group equations of the full problem are
made tractable in our model by replacing the continuum of points that make up
the closed Fermi line with four Fermi points. Despite this drastic
approximation, the model exhibits physically reasonable behavior both at
half-filling (where instabilities occur) and away from half-filling (where a
Luttinger liquid arises). Next we implement the Bosonization of higher
dimensional Fermi surfaces introduced by Luther and advocated most recently by
Haldane. Bosonization incorporates the phase space and small-angle scattering
.... (7 figures, appended as a postscript file at the end of the TeX file).Comment: 48 text pages, plain TeX, BUP-JBM-
Factors Associated with Revision Surgery after Internal Fixation of Hip Fractures
Background: Femoral neck fractures are associated with high rates of revision surgery after management with internal fixation. Using data from the Fixation using Alternative Implants for the Treatment of Hip fractures (FAITH) trial evaluating methods of internal fixation in patients with femoral neck fractures, we investigated associations between baseline and surgical factors and the need for revision surgery to promote healing, relieve pain, treat infection or improve function over 24 months postsurgery. Additionally, we investigated factors associated with (1) hardware removal and (2) implant exchange from cancellous screws (CS) or sliding hip screw (SHS) to total hip arthroplasty, hemiarthroplasty, or another internal fixation device. Methods: We identified 15 potential factors a priori that may be associated with revision surgery, 7 with hardware removal, and 14 with implant exchange. We used multivariable Cox proportional hazards analyses in our investigation. Results: Factors associated with increased risk of revision surgery included: female sex, [hazard ratio (HR) 1.79, 95% confidence interval (CI) 1.25-2.50; P = 0.001], higher body mass index (fo