ZrSe3 with a quasi-one-dimensional (quasi-1D) crystal structure belongs to the transition metal trichalcogenides (TMTCs) family. Owing to its unique optical, electrical, and optoelectrical properties, ZrSe3 is promising for applications in field effect transistors, photodetectors, and thermoelectrics. Compared with extensive studies of the above-mentioned physical properties, the thermal properties of ZrSe3 have not been experimentally investigated. Here, we report the crystal growth and thermal and optical properties of ZrSe3. Millimeter-sized single crystalline ZrSe3 flakes were prepared using a chemical vapor transport method. These flakes could be exfoliated into microribbons by liquid-phase exfoliation. The transmission electron microscope studies suggested that the obtained microribbons were single crystals along the chain axis. ZrSe3 exhibited a specific heat of 0.311 J g−1 K−1 at 300 K, close to the calculated value of the Dulong–Petit limit. The fitting of low-temperature specific heat led to a Debye temperature of 110 K and an average sound velocity of 2122 m s−1. The thermal conductivity of a polycrystalline ZrSe3 sample exhibited a maximum value of 10.4 ± 1.9 W m−1 K−1 at 40 K. The thermal conductivity decreased above 40 K and reached a room-temperature value of 5.4 ± 1.3 W m−1 K−1. The Debye model fitting of the solid thermal conductivity agreed well with the experimental data below 200 K but showed a deviation at high temperatures, indicating that optical phonons could substantially contribute to thermal transport at high temperatures. The calculated phonon mean free path decreased with temperatures between 2 and 21 K. The mean free path at 2 K approached 3 μm, which was similar to the grain size of the polycrystalline sample. This work provides useful insights into the preparation and thermal properties of quasi-1D ZrSe3.
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Thermal conductivity of hexagonal BC 2 P – a first-principles study
In this work, we report a high thermal conductivity ( k ) of 162 W m −1 K −1 and 52 W m −1 K −1 at room temperature, along the directions perpendicular and parallel to the c -axis, respectively, of bulk hexagonal BC 2 P (h-BC 2 P), using first-principles calculations. We systematically investigate elastic constants, phonon group velocities, phonon linewidths and mode thermal conductivity contributions of transverse acoustic (TA), longitudinal acoustic (LA) and optical phonons. Interestingly, optical phonons are found to make a large contribution of 30.1% to the overall k along a direction perpendicular to the c -axis at 300 K. BC 2 P is also found to exhibit high thermal conductivity at nanometer length scales. At 300 K, a high k value of ∼47 W m −1 K −1 is computed for h-BC 2 P at a nanometer length scale of 50 nm, providing avenues for achieving efficient nanoscale heat transfer.
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- Award ID(s):
- 1847129
- NSF-PAR ID:
- 10211478
- Date Published:
- Journal Name:
- RSC Advances
- Volume:
- 10
- Issue:
- 70
- ISSN:
- 2046-2069
- Page Range / eLocation ID:
- 42628 to 42632
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Raman spectroscopy has been widely used to measure thermophysical properties of 2D materials. The local intense photon heating induces strong thermal nonequilibrium between optical and acoustic phonons. Both first principle calculations and recent indirect Raman measurements prove this phenomenon. To date, no direct measurement of the thermal nonequilibrium between optical and acoustic phonons has been reported. Here, this physical phenomenon is directly characterized for the first time through a novel approach combining both electrothermal and optothermal techniques. While the optical phonon temperature is determined from Raman wavenumber, the acoustic phonon temperature is precisely determined using high‐precision thermal conductivity and laser power absorption that are measured with negligible nonequilibrium among energy carriers. For graphene paper, the energy coupling factor between in‐plane optical and overall acoustic phonons is found at (1.59–3.10) × 1015W m−3K−1, agreeing well with the quantum mechanical modeling result of 4.1 × 1015W m−3K−1. Under ≈1 µm diameter laser heating, the optical phonon temperature rise is over 80% higher than that of the acoustic phonons. This observation points out the importance of subtracting optical–acoustic phonon thermal nonequilibrium in Raman‐based thermal characterization.
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Abstract This work explores the 2D interfacial energy transport between monolayer WSe2and SiO2while considering the thermal nonequilibrium between optical and acoustic phonons caused by photoexcitation. Recent modeling and experimental work have shown substantial temperature differences between optical and acoustic phonons (Δ
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Abstract Under photon excitation, 2D materials experience cascading energy transfer from electrons to optical phonons (OPs) and acoustic phonons (APs). Despite few modeling works, it remains a long‐history open problem to distinguish the OP and AP temperatures, not to mention characterizing their energy coupling factor (
G ). Here, the temperatures of longitudinal/transverse optical (LO/TO) phonons, flexural optical (ZO) phonons, and APs are distinguished by constructing steady and nanosecond (ns) interphonon branch energy transport states and simultaneously probing them using nanosecond energy transport state‐resolved Raman spectroscopy. ΔT OP −APis measured to take more than 30% of the Raman‐probed temperature rise. A breakthrough is made on measuring the intrinsic in‐plane thermal conductivity of suspended nm MoS2and MoSe2by completely excluding the interphonon cascading energy transfer effect, rewriting the Raman‐based thermal conductivity measurement of 2D materials.G OP↔APfor MoS2, MoSe2, and graphene paper (GP) are characterized. For MoS2and MoSe2,G OP↔APis in the order of 1015and 1014W m−3K−1andG ZO↔APis much smaller thanG LO/TO↔AP. Under ns laser excitation,G OP↔APis significantly increased, probably due to the reduced phonon scattering time by the significantly increased hot carrier population. For GP,G LO/TO↔APis 0.549 × 1016W m−3K−1, agreeing well with the value of 0.41 × 1016W m−3K−1by first‐principles modeling. -
null (Ed.)Breakdown of Fourier law of heat conduction at nanometer length scales significantly diminishes thermal conductivity, leading to challenges in thermal management of nanoelectronic applications. In this work we demonstrate using first-principles computations that biaxial strain can enhance k at a nanoscale in boron phosphide (BP), yielding nanoscale k values that exceed even the bulk k value of silicon. At a length scale of L = 200 nm, k of 4% biaxially strained BP is enhanced by 25% to a value of 150.4 W m −1 K −1 , relative to 120 W m −1 K −1 computed for unstrained BP at 300 K. The enhancement in k at a nanoscale is found to be due to the suppression of anharmonic scattering in the higher frequency range where phonon meanfreepaths are in nanometers, mediated by an increase in the phonon band gap in strained BP. Such a suppression in scattering enhances the meanfreepaths in the nanometer regime, thus enhancing nanoscale k . First-principles computations based on deriving harmonic and anharmonic force interactions from density-functional theory are used to provide detailed understanding of the effect in terms of individual scattering channels.more » « less
- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1039/d0ra08444a
