Rajeev Gandhi, J, Nehru R, Chen S-M, Sankar R, Bayikadi KS, Sureshkumar P, Chen K-H, Chen L-C.
2018.
Influence of GeP precipitates on the thermoelectric properties of P-type GeTe and Ge0.9−xPxSb0.1Te compounds, 2018. CrystEngComm. 20(41):6449-6457.: The Royal Society of Chemistry
AbstractGermanium telluride (GeTe) is a very well known IV–VI group semiconducting material with the advantageous property of showing metallic conduction, which materializes from its superior carrier concentration (n) (high number of Ge vacancies). A systematic investigation into the thermoelectric properties (TEP) of GeTe was reported by way of carrier concentration (n) engineering. The present investigation focuses on studying the effects of doping (antimony – Sb) and co-doping (phosphorus – P) on the TEP of GeTe. In order to understand the system, we have prepared p-type GeTe and Ge0.9−xPxSb0.1Te (x = 0, 0.01, 0.03, or 0.05) samples via a non-equilibrium solid state melt quenching (MQ) process, followed by hot press consolidation. Temperature dependent synchrotron X-ray diffraction studies reveal a phase transition from rhombohedral to simple cubic in the Ge0.9−xPxSb0.1Te system at 573 K, which is clearly reflected in the TEP. Further high resolution transmission electron microscopy (HRTEM) studies reveal the pseudo-cubic nature of the sample. However, powder X-ray diffraction (PXRD) and field emission scanning electron microscopy (FESEM) images and energy dispersive X-ray spectroscopy (EDX) studies confirm the presence of germanium phosphide (GeP) in all P-doped samples. The presence of a secondary phase and point defects (Sb & P) enhanced the additional scattering effects in the system, which influenced the Seebeck coefficient and thermal conductivity of GeTe. A significant enhancement in the Seebeck coefficient (S) to ∼225 μV K−1 and a drastic reduction in thermal conductivity (κ) to ∼1.2 W mK−1 effectively enhanced the figure-of-merit (ZT) to ∼1.72 at 773 K for Ge0.87P0.03Sb0.1Te, which is a ∼3 fold increase for GeTe. Finally, P co-doped Ge0.9Sb0.1Te demonstrates an enhancement in ZT, making it a good candidate material for power generation applications.
Ray, SC, Palnitkar U, Pao CW, Tsai HM, Pong* WF, Lin I-N, Papakonstantinou P, Ganguly A, Chen LC, Chen KH.
2008.
Field emission effects of nitrogenated carbon nanotubes on chlorination and oxidation. J. Appl. Phys.. 104:063710.
Ray, SC, Tsai HM, Bao CW, Chiou JW, Jan JC, Kumar K, Pong* WF, Tsai M-H, Chattopadhyay S, Chen LC, Chien SC, Lee MT, Lin ST, Chen KH.
2004.
Electronic and bonding structures of B-C-N thin films by X-ray absorption and photoemission spectroscopy. J. Appl. Phys. . 96:208-211.
Ray, SC, Pao CW, Tsai HM, Chiou JW, Pong* WF, Chen CW, Tsai M-H, Papakonstantinou P, Chen LC, Chen KH.
2007.
A comparative study of the electronic structures of oxygen- and chlorinetreated nitrogenated carbon nanotubes by X-ray absorption and scanning photoelectron microscopy. Appl. Phys. Lett.. 91:202102.
Raym, SC, Pao CW, Tsai HM, Chiou JW, Pong* WF, Chen CW, Tsai MH, Papakonstantinou P, Chen LC, Chen KH, Graham WG.
2007.
Electronic structures and bonding properties of chlorine-treated nitrogenated carbon nanotubes: X-ray absorption and scanning photoelectron microscopy study. Appl. Phys. Lett.. 90:192107.
Roy, PK, Haider G, Lin H-I, Liao Y-M, Lu C-H, Chen K-H, Chen L-C, Shih W-H, Liang C-T, Chen Y-F.
2018.
Multicolor Ultralow-Threshold Random Laser Assisted by Vertical-Graphene Network, 2018. Advanced Optical MaterialsAdvanced Optical Materials. 6(16):1800382.: John Wiley & Sons, Ltd
AbstractAbstract Application of lasers is omnipresent in modern-day technology. However, preparation of a lasing device usually requires sophisticated design of the materials and is costly, which may limit the suitable choice of materials and the lasing wavelengths. Random lasers, on the other hand, can circumvent the aforementioned shortcomings with simpler fabrication process, lower processing cost, material flexibility for any lasing wavelengths with lower lasing threshold, providing a roadmap for the design of super-bright lighting, displays, Li-Fi, etc. In this work, ultralow-threshold random laser action from semiconductor nanoparticles assisted by a highly porous vertical-graphene-nanowalls (GNWs) network is demonstrated. The GNWs embedded by the nanomaterials produce a suitable cavity for trapping the optical photons with semiconductor nanomaterials acting as the gain medium. The observed laser action shows ultralow values of threshold energy density ≈10 nJ cm?2 due to the strong photon trapping within the GNWs. The threshold pump fluence can be further lowered to ≈1 nJ cm?2 by coating Ag/SiO2 upon the GNWs due to the combined effect of photon trapping and strong plasmonic enhancement. In view of the growing demand of functional materials and novel technologies, this work provides an important step toward realization of high-performance optoelectronic devices.
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