We investigated the electronic and thermoelectric properties of half-Heusler alloys NiTZ
(T = Sc and Ti; Z = P, As, Sn, and Sb) having an 18 valence electron count. Calculations
were performed by ...means of density functional theory and the Boltzmann transport equation
with constant relaxation time approximation, validated by NiTiSn. The chosen half-Heuslers
were found to be indirect bandgap semiconductors, and the lattice thermal conductivity was
comparable with the state-of-the-art thermoelectric materials. The estimated power factor
for NiScP, NiScAs, and NiScSb revealed that their thermoelectric performance can be
enhanced by an appropriate doping rate. The value of ZT found for NiScP,
NiScAs, and NiScSb is 0.46, 0.35, and 0.29, respectively, at 1200 K.
Material-by-design has been a long-standing aspiration that has recently become a reality. Such designer materials have been repeatedly demonstrated using the top-down approach of mechanical ...exfoliation and stacking, leading to a variety of artificial 2D heterostructures with new properties that are otherwise unattainable. Consequently, tremendous research frontiers in physics, chemistry, engineering, and life science have been created. While thousands of layered crystals exist in nature, only a few dozen of them with manageable chemical-stability have been made into heterostructures using this method. Moreover, experimental investigations of materials that have received limited exploration in the 2D realm, such as cuprates, halides, and perovskites, along with their heterostructures, have been fundamentally hindered by their rapid chemical degradation. Another critical challenge imposed by exfoliating and stacking 2D layers in ambient environment is the absorption of itinerant gas molecules that further contaminate sensitive 2D interfaces in the heterostructures. Such contamination and compromised material properties significantly hinder surface-sensitive local probes—scanning probe microscopy (SPM)—that often require nanometer to atomic scale surface cleanliness. In this article, we aim to provide a technical review of recent development toward 2D materials and heterostructure fabrication in more controlled environments that are suitable for SPM characterizations. These include the development of more efficient mechanical exfoliation and dry-transfer techniques, as well as the incorporation of 2D material exfoliation and transfer in inert gas, low vacuum, and, eventually, ultra-high vacuum environments. Finally, we provide an outlook on the remaining challenges and opportunities in ultra-clean 2D material fabrication techniques.
Synthetic quantum systems provide a pathway for exploring the physics of complex quantum matter in a programmable fashion. This approach becomes particularly advantageous when it comes to systems ...that are thermodynamically unfavorable. By sculpting the potential landscape of Cu(111) surfaces with carbon monoxide quantum corrals in a cryogenic scanning tunneling microscope, we created analogue simulators of planar organic molecules, including antiaromatic and non-Kekulé species that are generally reactive or unstable. Spectroscopic imaging of such synthetic molecules reveals close replications of molecular orbitals obtained from ab initio calculations of the organic molecules. We further illustrate the quantitative nature of such analogue simulators by faithful extraction of bond orders and global aromaticity indices, which are otherwise technically daunting using real molecules. Our approach therefore sets the stage for new research frontiers pertaining to the quantum physics and chemistry of designer nanostructures.
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IJS, KILJ, NUK, PNG, UL, UM
Thermoelectric phenomena provide an alternative for power generation and refrigeration, which could be the best solution to the energy crisis by utilizing waste heat energy in the near future. In ...this study, we have investigated the structural, elastic, electronic, and thermoelectric properties of 18-valence electron count rhodium-based half-Heusler alloys focusing on RhTiP, RhTiAs, RhTiSb, and RhTiBi. The non-existence of imaginary frequencies in the phonon dispersion curve for these systems verifies that they are structurally stable. RhTiP is ductile, while others are brittle. The alloys are semiconducting with indirect band gaps ranging from 0.94 to 1.01 eV. While considering thermoelectricity, we discovered that p-type doping is more favorable in improving the thermoelectric properties. The calculated power factor values with p-type doping are comparable to some of the reported half-Heusler materials. The optimum figure of merit
ZT
is ∼1 for RhTiBi, and in between ∼(0.38-0.67) for RhTiP, RhTiAs, and RhTiSb. The low thermal conductivities and sufficiently large value of power factor of these alloys suggest that they are promising thermoelectric materials for use in thermoelectric applications.
Thermoelectric phenomena provides an alternative for power generation and refrigeration. Half-Heusler are excellent candidates for use in thermoelectric devices.
We have investigated the electronic and thermoelectric properties of half-Heusler alloys NiTZ (T = Sc, and Ti; Z = P, As, Sn, and Sb) having 18 valence electron. Calculations are performed by means ...of density functional theory and Boltzmann transport equation with constant relaxation time approximation, validated by NiTiSn. The chosen half-Heuslers are found to be an indirect band gap semiconductor, and the lattice thermal conductivity is comparable with the state-of-the-art thermoelectric materials. The estimated power factor for NiScP, NiScAs, and NiScSb reveals that their thermoelectric performance can be enhanced by appropriate doping rate. The value of ZT found for NiScP, NiScAs, and NiScSb are 0.46, 0.35, and 0.29, respectively at 1200 K.
On the basis of density functional theory and semi-classical Boltzmann theory, we have investigated the structural, elastic, electronic, optical and thermoelectric properties of 18--valence electron ...count rhodium based half-Heusler alloys focusing on RhTiP, RhTiAs, RhTiSb, and RhTiBi. The absence of imaginary frequencies in the phonon dispersion curve for these system verifies that they are structurally stable. RhTiP is ductile in nature, while others are brittle. The alloys are found to be semiconducting with indirect band gaps ranging from 0.94 to 1.01 eV. Our calculations suggest these materials to have high absorption coefficient and optical conductivity in the ultraviolet as well as visible region. While considering thermoelectricity, we found that \(p\)--type doping is more favorable in improving the thermoelectric properties. The calculated values of power factor with \(p\)-type doping are comparable to some of the reported half-Heusler materials. The optimum figure of merit \zt\ is \(\sim1\) for RhTiBi suggesting it as a promising candidate for thermoelectric applications while RhTiP, RhTiAs, and RhTiSb with optimum \zt \ values between 0.38 to 0.67 are possible candidates for use in thermoelectric devices.
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