Thermal transport in layered, two-dimensional (2D) black phosphorus (BP) is of great interest, not only due to its importance in the designs of BP devices, [1] but also because it provides a unique platform to study the physics of heat transport in highly anisotropic materials. [2] BP belongs to the orthorhombic Cmca point group, [3] with its puckered honeycomb basal planes weakly bonded together by interlayer van der Waals'forces. Due to the nature of its crystal structure, second order tensors (e.g., the thermal conductivity tensor Λ) of BP have three independent components along the principal axes of zigzag (ZZ), armchair (AC) and through-plane (TP), see Figure 1a, and the thermal conductivity tensor is strongly anisotropic along these axes. [4] (In this paper, we use ΛZZ, ΛAC and ΛTP to denote the three independent components of the thermal conductivity tensor.) Here, we accurately measured and report the anisotropic thermal conductivity tensor (ΛZZ, ΛAC and ΛTP) of bulk BP in a temperature range of 80 ≤ T ≤ 300 K. Our temperature dependence measurements provide a crucial benchmark for future studies of anisotropic heat transport in BP and phosphorene.To date, there are only few experimental works on anisotropic thermal conductivity of BP, even at 300 K. Luo et al. [5] and Lee et al. [6] measured BP flakes with a thickness of 9 -30 nm and 60 -310 nm using the opto-thermal Raman method and the micro-bridge technique, respectively, and reported ΛZZ = 11 -45 W m -1 K -1 and ΛAC = 5 -22 W m -1 K -1 at room temperature. These values of ΛZZ and ΛAC are substantially lower than predictions by first-principles calculations [4, 7, 8] for bulk BP and phosphorene. While these low values of thermal conductivity were attributed to additional boundary scattering of phonons in the thin flakes, [5, 6] we note that scattering of phonons along the basal planes by the interfaces is rather weak [9] and thus this explanation might not be satisfactory. The low values could also originate from degradation of the BP flakes by oxidation, [10] as the BP flakes in both studies were exposed to the air for a substantial amount of time during sample preparation and measurements. With the degradation, the reported thermal conductivity is probably not intrinsic. Jang et al. [11] encapsulated their BP flakes of thickness of 138 -552 nm with a 3- Zhu et al.'s samples were not seriously oxidized, their pump-probe measurements in the through-plane direction might be lower than the intrinsic ΛTP because the mean-free-paths () of a substantial portion of heat-carrying phonons are much longer than the characteristic length scales of their measurements (<500 nm), i.e., the thickness of the samples or the thermal penetration depth d. [12][13][14] In fact, we obtained a ΛTP value ~25 % higher than Jang et al. 's and Zhu et al.'s measurements, [4, 11] when we used a much lower modulation frequency in our measurements to achieve a larger thermal penetration depth.With the relatively few published works on the thermal properties of BP, kn...
We report optical, electrical and magnetotransport properties of oxygen deficient SrTiO(3) (SrTiO(3-x)) thin films fabricated by pulsed laser deposition technique. The oxygen vacancies (O(vac)) in the thin film are expected to be uniform. By comparing its electrical properties to those of bulk SrTiO(3-x), it was found that O(vac) in bulk SrTiO(3-x) is far from uniform over the whole material. The metal-insulator transition (MIT) observed in the SrTiO(3-x) film was found to be induced by the carrier freeze-out effect. The low temperature frozen state can be reexcited by Joule heating, electric and intriguingly magnetic field.
Three-dimensional (3D) bioprinting systems serve as advanced manufacturing platform for the precise deposition of cells and biomaterials at pre-defined positions. Among the various bioprinting techniques, the drop-on-demand jetting approach facilitates deposition of pico/nanoliter droplets of cells and materials for study of cell-cell and cell-matrix interactions. Despite advances in the bioprinting systems, there is a poor understanding of how the viability of primary human cells within sub-nanoliter droplets is affected during the printing process. In this work, a thermal inkjet system is utilized to dispense sub-nanoliter cell-laden droplets, and two key factors – droplet impact velocity and droplet volume – are identified to have significant effect on the viability and proliferation of printed cells. An increase in the cell concentration results in slower impact velocity, which leads to higher viability of the printed cells and improves the printing outcome by mitigating droplet splashing. Furthermore, a minimum droplet volume of 20 nL per spot helps to mitigate evaporation-induced cell damage and maintain high viability of the printed cells within a printing duration of 2 min. Hence, controlling the droplet impact velocity and droplet volume in sub-nanoliter bioprinting is critical for viability and proliferation of printed human primary cells.
Vertically self-ordered hexagonal boron nitride (ordered h-BN) is a highly ordered turbostratic BN (t-BN) material similar to hexagonal BN, with its planar structure perpendicularly oriented to the substrate. The ordered h-BN thin films were grown using a High Power Impulse Magnetron Sputtering (HiPIMS) system with a lanthanum hexaboride (LaB6) target reactively sputtered in nitrogen gas. The best vertical alignment was obtained at room temperature, with a grounded bias and a HiPIMS peak power density of 60 W cm(-2). Even though the film contains up to 7.5 at% lanthanum, it retains its highly insulative properties and it was observed that an increase in compressive stress is correlated to an increase in film ordering quality. Importantly, the thermal conductivity of vertically ordered h-BN is considerably high at 5.1 W m(-1) K(-1). The favourable thermal conductivity coupled with the dielectric properties of this novel material and the low temperature growth could outperform SiO2 in high power density electronic applications.
Material jetting bioprinting is a highly promising three-dimensional (3D) bioprinting technique that facilitates drop-on-demand (DOD) deposition of biomaterials and cells at pre-defined positions with high precision and resolution. A major...
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