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Daichakomphu, N, Abbas S, Chou T-L, Chen L-C, Chen K-H, Sakulkalavek A, Sakdanuphab R.  2022.  Understanding the effect of sputtering pressures on the thermoelectric properties of GeTe films. Journal of Alloys and Compounds. 893:162342. AbstractWebsite

In this work, we study the effect of sputtering pressures on the thermoelectric properties of GeTe films. The working pressures were differentiated from 3 to 30 mTorr, and the as-deposited films were annealed at 623 K for 10 min in Ar atmosphere. The results show that the working pressure has a significant effect on the Ge content and crystalline size. The turning trend of the Seebeck coefficient with different sputtering pressures corresponds to the Ge content. The surface morphology of annealed film will change from cracks to voids with increasing sputtering pressure. This behavior can be explained by the growth mechanisms model. The voids and relatively low crystalline size of GeTe films affect to the reduction of the electrical conductivity. In addition, the void content decreased as film thickness was increased. Therefore, controlling the working pressures in the sputtering process and film thickness is important for the thermoelectric performance of GeTe thin film. In our work, we prove that the thermoelectric properties of GeTe films could be optimized effectively by simply tuning different sputtering conditions.

Das, CR, Dhara S, Hsu HC, Chen LC, Jeng YR, Bhaduri AK, Raj B, Chen KH, Albert SK.  2009.  Mechanism of recrystallization process in epitaxial GaN under dynamic stress field : Atomistic origin of planar defect formation. J. Raman Spect.. 40:1881-1884.
Das, CR, Hsu HC, Dhara S, Bhaduri AK, Raj B, Chen LC, Chen KH, Albert SK, Ray A, Tzeng Y.  2010.  A complete Raman mapping of phase transitions in Si under indentation. J. Raman Spectroscopy. 41:334.
Das, S, Valiyaveettil SM, Chen K-H, Suwas S, Mallik RC.  2019.  Thermoelectric properties of Mn doped BiCuSeO, 2019. Materials Research Express. 6(8):086305.: IOP Publishing AbstractWebsite

BiCuSeO is a promising thermoelectric material having earth-abundant non-toxic constituents and favourable thermoelectric properties like ultra-low thermal conductivity. In this study, Mn+2 has been introduced at the Bi+3 site to increase hole concentration as well as Seebeck coefficient, through aliovalent doping and magnetic impurity incorporation respectively. Samples were prepared through two-step solid state synthesis with the composition Bi1-xMnxCuSeO (x = 0.0, 0.04, 0.06, 0.08, 0.10 and 0.12). X-ray diffraction patterns confirmed the tetragonal (space group: P4/nmm) crystal structure of BiCuSeO as well as phase purity of the samples. The Seebeck coefficient and electrical resistivity had a decreasing trend with increasing doping fraction owing to the generation of charge carriers. The samples with x = 0.04 and 0.06 showed temperature independent Seebeck coefficient above 523 K, which is a signature of small polaron hopping. While the Seebeck coefficient of the samples with x = 0.08, 0.10 and 0.12 increased above 523 K due to the combination of localized and extended states. The thermal conductivity was dominated by the lattice part of the thermal conductivity. As a result of moderate Seebeck coefficient and low electrical resistivity, the highest power factor of 0.284 mW m−1-K2 was obtained for the Bi0.92Mn0.08CuSeO at 773 K, leading to a maximum zT of 0.4 at 773.

Das, D, Raha D, Chen WC, Chen KH, Wu CT, Chen LC.  2012.  Effect of substrate bias on the promotion of nanocrystalline silicon growth from He-diluted SiH4plasma at low temperature. J. Mater. Res.. 27:1303.
Das*, D, Jana M, Barua AK, Chattopadhyay S, Chen LC, Chen KH.  2002.  Electrical, thermal and structural properties of microcrystalline Si thin films. Jpn.Appl. Phys. Lett.. 41:L229-232.
Das*, D, Chen KH, Chattopadhyay S, Chen LC.  2002.  Spectroscopic studies of nitrogenated amorphous carbon films prepared by ion beam sputtering. J. Appl. Phys.. 91:4944-4955.
Datta, A, Dhara* S, Muto S, Hsu CW, Wu CT, Shen CH, Tanabe T, Maruyama T, Chen KH, Chen LC, Wang YL.  2005.  Formation and in-situ dynamics of metallic nanoblisters in self-ion-implanted GaN nanowires. Nanotechnology. 16:2764-2769.
Deliwala, S, Goldman J, Chen KH, Lu C-Z, Mazur E.  1994.  Coherent Anti-Stokes Raman Spectroscopy of Infrared Multiphoton Excited Molecules. J. Chem. Phys.. 101:8517-8528.
Dhara, SK, Datta A, Lan ZH, Chen* KH, Wang YL, Shen CS, Chen LC, Hsu CW, Lin HM, Chen CC.  2004.  Blue shift of yellow band in self-ion beam irradiated GaN nanowires. Appl. Phys. Lett.. 84:3486-3488.
Dhara, S, Chang CW, Tsai HM, Chen* LC, Chen KH.  2010.  Direct observation of amophization in load rate dependent nanoindentation studies of crystalline Si. Appl. Phys. Lett.. 96:253113.
Dhara, S, Datta A, Wu CT, Lan ZH, Chen* KH, Wang YL, Hsu CW, Shen CH, Chen LC, Chen CC.  2004.  Hexagonal-to-cubic phase transformation in GaN nanowires by Ga+ implantation. Appl. Phys. Lett.. 84:5473-5475.
Dhara, SK, Datta A, Wu CT, Lan ZH, Chen* KH, Wang YL, Chen LC, Hsu CW, Lin HM, Chen CC.  2003.  Enhanced dynamic annealing in self-ion implanted GaN nanowires. Appl. Phys. Lett.. 82:451-453.
Dhara, SK, Magudapathy P, Kesavamoorthy R, Kalavathi S, Nair KGM, Hsu GM, Chen LC, Chen* KH, Santhakumar K, Soga T.  2006.  Nitrogen ion beam synthesis of InN in InP(100) at elevated temperature. Appl. Phys. Lett.. 88:241904-(1-3).
Dhara, S, Yao LC, Wu CT, Hsu CW, Tu WS, Chen KH, Wang YL, Chen LC.  2010.  Focused ion beam induced nanowelding and defect doping as building block for nanoscale electronics in GaN nanowires. J. Phys. Chem.. C114:15260.
Dhara*, S, Wu JJ, Mangama G, Bera S, Magudapathy P, Wu CT, Nair KGM, Kamaruddin M, Yu CC, Yang MH, Liu SC, Tyagi AK, Narashiman SV, Chen LC, Chen KH.  2007.  Long-range ferromagnetic ordering at room temperature in Co+ implanted TiO2 nanorods. Nanotechnology. 18:325705.
Dhara*, S, Kesavamoorthy R, Magudapathy P, Premila M, Panigrahi BK, Nair KGM, Wu CT, Chen KH, Chen LC.  2003.  Quasiquenching size effects in gold nanoclusters embedded in silica matrix. Chem. Phys. Lett.. 370:254-260.
Dhara*, S, Das CR, Hsu HC, Chen KH, Chen LC, Raj B, Bhaduri AK, Albert SK, Ray A.  2008.  Recrystallization of epitaxial GaN under indentation. Appl. Phys. Lett.. 92:143114.
Dhara*, S, Sundaravel B, Nair KGM, Kesavamoorthy R, Valsakumar MC, Rao CTV, Chen LC, Chen KH.  2006.  Ferromagnetism in cobalt doped n-GaN. Appl. Phys. Lett.. 88:173110-(1-3).
Dhara*, S, Sundaravel B, K.H. Chen, et al.  2004.  Spillout effect in gold nanoclusters embedded in c-Al2O3(0001) matrix. Chem. Phys. Lett.. 399:354-358.
Dhara*, S, Chandra S, Magudapathy P, Kalavathi S, Panigrahi BK, Nair KGM, Sastry VS, Hsu CW, Wu CT, Chen KH, Chen LC.  2004.  Blue luminescence of Au nanoclusters embedded in silica matrix. J. Chem. Phys.. 121:12595-12599.
Dhara*, S, Lu C-Y, Nair KGM, Chen KH, Chen C-P, Huang Y-F, David C, Chen LC, Raj B.  2008.  Mechanism of bright red emission in Si nanoclusters. Nanotechnology. 19:395401-(1-5).
Du, HY, Yang CS, Hsu H-C, Huang HC, Chang ST, Wang C-H, Chen J-C, Chen KH, Chen LC.  2015.  Pulsed electrochemical deposition of Pt NPs on polybenzimidazole-CNT hybrid electrode for high-temperature proton exchange membrane fuel cells. International Journal of Hydrogen Energy. 40:14398.
Du, HY, Wang CH, Yang CS, Hsu HC, Chang ST, Huang HC, Lai SW, Chen JC, Yu LT, Chen LC, Chen KH.  2014.  A high performance polybenzimidazole-CNT hybrid electrode for high-temperature proton exchange membrane fuel cells. J. of Mater. Chem. . 2:7015-7019.
Du, HY, Wang CH, Hsu HC, Chang ST, Yen SC, Chen LC, Viswanathan B, Chen* KH.  2011.  High performance of catalysts supported by directly grown PTFE-free micro-porous CNT layer in a proton exchange membrane fuel cell. J. Mater. Chem.. 21:2512-2516.