28,403 research outputs found
High-performance Si microwire photovoltaics
Crystalline Si wires, grown by the vapor–liquid–solid (VLS)
process, have emerged as promising candidate materials for lowcost, thin-film photovoltaics. Here, we demonstrate VLS-grown Si microwires that have suitable electrical properties for high-performance photovoltaic applications, including long minority-carrier diffusion lengths (L_n » 30 µm) and low surface recombination velocities (S « 70 cm·s^(-1)). Single-wire radial p–n junction solar cells were fabricated with amorphous silicon and silicon nitride
surface coatings, achieving up to 9.0% apparent photovoltaic efficiency, and exhibiting up to ~600 mV open-circuit voltage with over 80% fill factor. Projective single-wire measurements and optoelectronic simulations suggest that large-area Si wire-array solar cells have the potential to exceed 17% energy-conversion efficiency, offering a promising route toward cost-effective crystalline Si photovoltaics
Detection of ultrafast oscillations in Superconducting Point-Contacts by means of Supercurrent Measurements
We present a microscopic calculation of the nondissipative current through a
superconducting quantum point contact coupled to a mechanical oscillator. Using
the non-equilibrium Keldysh Green function approach, we determine the
current-phase relation. The latter shows that at certain phases, the current is
sharply suppressed. These dips in the current-phase relation provide
information about the oscillating frequency and coupling strength of the
mechanical oscillator. We also present an effective two-level model from which
we obtain analytical expressions describing the position and width of the dips.
Our findings are of relevance for nanomechanical resonators based on
superconducting materials.Comment: 8 pages, 5 figures. Published in Phys. Rev.
Stability analysis of Lower Dimensional Gravastars in noncommutative geometry
The Ba\~{n}ados, Teitelboim and Zanelli \cite{BTZ1992}, black hole solution
is revamped from the Einstein field equations in (2 + 1)-dimensional anti-de
Sitter spacetime, in a context of noncommutative geometry \cite{Rahaman(2013)}.
In this article, we explore the exact gravastar solutions in three-dimension
anti-de Sitter space given in the same geometry. As a first step we derive BTZ
solution assuming the source of energy density as point-like structures in
favor of smeared objects, where the particle mass M, is diffused throughout a
region of linear size and is described by a Gaussian function
of finite width rather than a Dirac delta function. We matched our interior
solution to an exterior BTZ spacetime at a junction interface situated outside
the event horizon. Furthermore, stability analysis is carried out for the
dynamic case for the specific case when under radial
perturbations about static equilibrium solutions. To give theoretical support
we also trying to explore their physical properties and characteristics.Comment: 3 figure
Deterministic reordering of 40Ca+ ions in a linear segmented Paul trap
In the endeavour to scale up the number of qubits in an ion-based quantum
computer several groups have started to develop miniaturized ion traps for
extended spatial control and manipulation of the ions. Shuttling and separation
of ion strings have been the foremost issues in linear-trap arrangements and
some prototypes of junctions have been demonstrated for the extension of ion
motion to two dimensions (2D). While junctions require complex trap structures,
small extensions to the 1D motion can be accomplished in simple linear trap
arrangements. Here, control of the extended field in a planar, linear chip trap
is used to shuttle ions in 2D. With this approach, the order of ions in a
string is deterministically reversed. Optimized potentials are theoretically
derived and simulations show that the reordering can be carried out
adiabatically. The control over individual ion positions in a linear trap
presents a new tool for ion-trap quantum computing. The method is also expected
to work with mixed crystals of different ion species and as such could have
applications for sympathetic cooling of an ion string.Comment: 18 pages, 9 figures. Added section on possibility of adiabatic turn.
Added appendix on point charge model. Other minor alterations/clarifications.
Version now published (http://www.iop.org/EJ/abstract/1367-2630/11/10/103008
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