231 research outputs found
The structures and thermoelectric properties of the infinitely adaptive series (Bi2)m(Bi2Te3)n
The structures and thermoelectric properties of the (Bi2)m(Bi2Te3)n
homologous series, derived from stacking hexagonal Bi2 and Bi2Te3 blocks, are
reported. The end-members of this series are metallic Bi and semiconducting
Bi2Te3; nine members of the series have been studied. The structures form an
infinitely adaptive series and a unified structural description based on a
modulated structure approach is presented. The as-synthesized samples have
thermopowers (S) that vary from n-type for Bi2Te3 to p-type for phases rich in
Bi2 blocks but with some Bi2Te3 blocks present, to n-type again for Bi metal.
The thermoelectric power factor (S2/rho) is highest for Bi metal (43 muW/K2 cm
at 130 K), followed by Bi2Te3 (20 muW/K2 cm at 270 K), while Bi2Te (m:n = 5:2)
and Bi7Te3 (m:n = 15:6) have 9 muW/K2 cm (at 240 K) and 11 muW/K2 (at 270 K),
respectively. The results of doping studies with Sb and Se into Bi2Te are
reported.Comment: accepted for publication in PR
Effect of finite temperature and uniaxial anisotropy on the Casimir effect with three-dimensional topological insulators
In this work we study the Casimir effect with three-dimensional topological
insulators including the effects of temperature and uniaxial anisotropy.
Although precise experimental values for the optical properties of these
materials are yet to be established, qualitative analysis is still possible. We
find qualitatively that the reported repulsive behavior and the equilibrium
point are robust features of the system, and are favored by low temperatures
and the enhancement of the optical response parallel to the optical axis. The
dependence of the equilibrium point with temperature and with the topological
magnetoelectric polarizability characteristic of three-dimensional topological
insulators is also discussed.Comment: 17 pages, 7 figures. Published versio
Strongly Correlated Cerium Systems: Non-Kondo Mechanism for Moment Collapse
We present an ab initio based method which gives clear insight into the
interplay between the hybridization, the coulomb exchange, and the
crystal-field interactions, as the degree of 4f localization is varied across a
series of strongly correlated cerium systems. The results for the ordered
magnetic moments, magnetic structure, and ordering temperatures are in
excellent agreement with experiment, including the occurence of a moment
collapse of non-Kondo origin. In contrast, standard ab initio density
functional calculations fail to predict, even qualitatively, the trend of the
unusual magentic properties.Comment: A shorter version of this has been submitted to PR
Near-Zero Moment Ferromagnetism in the Semiconductor SmN
The magnetic behaviour of SmN has been investigated in stoichiometric
polycrystalline films. All samples show ferromagnetic order with Curie
temperature (T_c) of 27 +/- 3 K, evidenced by the occurrence of hysteresis
below T_c. The ferromagnetic state is characterised by a very small moment and
a large coercive field, exceeding even the maximum applied field of 6 T below
about 15 K. The residual magnetisation at 2 K, measured after cooling in the
maximum field, is 0.035 mu_B per Sm. Such a remarkably small moment results
from a near cancellation of the spin and orbital contributions for Sm3+ in SmN.
Coupling to an applied field is therefore weak, explaining the huge coercive
field . The susceptibility in the paramagnetic phase shows
temperature-independent Van Vleck and Curie-Weiss contributions. The Van Vleck
contribution is in quantitative agreement with the field-induced admixture of
the J=7/2 excited state and the 5/2 ground state. The Curie-Weiss contribution
returns a Curie temperature that agrees with the onset of ferromagnetic
hysteresis, and a conventional paramagnetic moment with an effective moment of
0.4 mu_B per Sm ion, in agreement with expectations for the crystal-field
modified effective moment on the Sm3+ ions.Comment: 5 pages, 3 figure
Low-temperature properties of the heavy-fermion system U Cd
We present electrical-resistivity, magnetic-susceptibility, specific-heat, and thermal-expansion data for UCd11. The low-temperature specific heat indicates that the electronic subsystem has a highly enhanced specific heat which is partially removed by a phase transition at 5.0 K. © 1984 The American Physical Society
Growth of Large-Area and Highly Crystalline MoS2 Thin Layers on Insulating Substrates
The two-dimensional layer of molybdenum disulfide (MoS2) has recently
attracted much interest due to its direct-gap property and potential
applications in optoelectronics and energy harvesting. However, the synthetic
approach to obtain high quality and large-area MoS2 atomic thin layers is still
rare. Here we report that the high temperature annealing of a thermally
decomposed ammonium thiomolybdate layer in the presence of sulfur can produce
large-area MoS2 thin layers with superior electrical performance on insulating
substrates. Spectroscopic and microscopic results reveal that the synthesized
MoS2 sheets are highly crystalline. The electron mobility of the bottom-gate
transistor devices made of the synthesized MoS2 layer is comparable with those
of the micromechanically exfoliated thin sheets from MoS2 crystals. This
synthetic approach is simple, scalable and applicable to other transition metal
dichalcogenides. Meanwhile, the obtained MoS2 films are transferable to
arbitrary substrates, providing great opportunities to make layered composites
by stacking various atomically thin layers.Comment: manuscript submitted on 11-Dec-2011, revision submitted on
16-Feb-201
Atomic Layer Deposition of 2D Metal Dichalcogenides for Electronics, Catalysis, Energy Storage, and Beyond
2D transition metal dichalcogenides (TMDCs) are among the most exciting materials of today. Their layered crystal structures result in unique and useful electronic, optical, catalytic, and quantum properties. To realize the technological potential of TMDCs, methods depositing uniform films of controlled thickness at low temperatures in a highly controllable, scalable, and repeatable manner are needed. Atomic layer deposition (ALD) is a chemical gas-phase thin film deposition method capable of meeting these challenges. In this review, the applications evaluated for ALD TMDCs are systematically examined, including electronics and optoelectonics, electrocatalysis and photocatalysis, energy storage, lubrication, plasmonics, solar cells, and photonics. This review focuses on understanding the interplay between ALD precursors and deposition conditions, the resulting film characteristics such as thickness, crystallinity, and morphology, and ultimately device performance. Through rational choice of precursors and conditions, ALD is observed to exhibit potential to meet the varying requirements of widely different applications. Beyond the current state of ALD TMDCs, the future prospects, opportunities, and challenges in different applications are discussed. The authors hope that the review aids in bringing together experts in the fields of ALD, TMDCs, and various applications to eventually realize industrial applications of ALD TMDCs.Peer reviewe
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