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and A. M. Basilio, Hsu YK, Wei PC, Ganguly A, Shih HC, Chen YT, Chen LC, Chen* KH.  2010.  Electrochemical Characterization of InN Thin Film for Biosensing Applications. J. New Mat. Electrochem. Systems. 13:337-343.
Bayikadi, KS, Imam S, Ubaid M, Aziz A, Chen K-H, Sankar R.  2022.  Effect of aliovalent substituted highly disordered GeTe compound's thermoelectric performance, 2022. 922:166221. AbstractWebsite

As a lead-free high-performance thermoelectric material, germanium telluride (GeTe) has recently been extensively studied for mid-temperature (500–800 K) applications. The carrier concentration and the thermal conductivity are reduced for vacancy-controlled GeTe compounds compared with pristine GeTe. We explored and optimized the Ge0.9−xSb0.1PxTe (x = 0.01–0.05) material's highest thermoelectric performance at elevated temperatures. Intrinsic Ge vacancy control and manipulation of Ge (+2) with Sb/P (+3) increased the charge contribution to power factor improvement to ∼42 µWcm−1 K−2 while minimizing the lattice thermal contribution to ∼0.4 W/mK. This resulted in an increase in thermoelectric performance of ∼2.4 @ 773 K for the Ge0.88Sb0.1P0.02Te sample. The inclusion of atomically disordered Sb/P ions considerably increases the scattering effects caused by the point defect, whereas stretched grain boundaries reveal the decreased lattice thermal contribution. The current work demonstrates the effectiveness of phosphorus as a co-dopant in increasing the average thermoelectric performance (ZTavg) value over the GeTe operating temperature range.

Bayikadi, KS, Sankar R, Wu CT, Xia C, Chen Y, Chen L-C, Chen K-H, Chou F-C.  2019.  Enhanced thermoelectric performance of GeTe through in situ microdomain and Ge-vacancy control, 2019. Journal of Materials Chemistry A. 7(25):15181-15189.: The Royal Society of Chemistry AbstractWebsite

A highly reproducible sample preparation method for pure GeTe in a rhombohedral structure without converting to the cubic structure up to ∼500 °C is reported to show control of the Ge-vacancy level and the corresponding herringbone-structured microdomains. The thermoelectric figure-of-merit (ZT) for GeTe powder could be raised from ∼0.8 to 1.37 at high temperature (HT) near ∼500 °C by tuning the Ge-vacancy level through the applied reversible in situ route, which made it highly controllable and reproducible. The enhanced ZT of GeTe was found to be strongly correlated with both its significantly increased Seebeck coefficient (∼161 μV K−1 at 500 °C) and reduced thermal conductivity (∼2.62 W m−1 K−1 at 500 °C) for a sample with nearly vacancy-free thicker herringbone-structured microdomains in the suppressed rhombohedral-to-cubic structure phase transformation. The microdomain and crystal structures were identified with HR-TEM (high-resolution transmission electron microscopy) and powder X-ray diffraction (XRD), while electron probe micro-analysis (EPMA) was used to confirm the stoichiometry changes of Ge : Te. Theoretical calculations for GeTe with various Ge-vacancy levels suggested that the Fermi level shifts toward the valence band as a function of increasing the Ge-vacancy level, which is consistent with the increased hole-type carrier concentration (n) and effective mass (m*) deduced from the Hall measurements. The uniquely prepared sample of a near-vacancy-free GeTe in a rhombohedral structure at high temperature favoured an enhanced Seebeck coefficient in view of the converging L- and Σ-bands of the heavy effective mass at the Fermi level, while the high density domain boundaries for the domain of low carrier density were shown to reduce the total thermal conductivity effectively.

Bhusari, DM, Yang JR, Wang TY, Chen KH, Lin ST, Chen LC.  1998.  Effect of Substrate Pretreatment and Methane Fraction on the Optical Transparency of Nano-crystalline Diamond Thin Films. J. Mater. Res.. 13:1769.
and C.H. Lin, KH, Chattopadhyay S, Hsu CW, Wu MH, Chen WC, Wu CT, Tsen SC, Lee JH, Chen CH, Chen CW, Chen LC, Chen* KH.  2009.  Enhanced charge separation by sieve-layer mediation in high efficiency inorganic-organic solar cell. Adv. Mater.. 21:259-263.
Chang, YK, Hsieh HH, Pong WF, Tsai MH, Lee KH, Dann TE, Chien FZ, Tseng PK, Tsang KL, Su WK, Chen LC, Wei SL, Chen KH, Bhusari DM, Chen YF.  1998.  Electronic and Atomic Structures of SiCN Thin Film by X-ray Absorption Spectroscopy and Theoretical Calculations. Phys. Rev.. B58:9018.
Chang, CY, Lan TW, Chi GC, Chen* LC, Chen KH, Chen JJ, Jang S, Ren F, Pearton SJ.  2006.  Effect of ozone cleaning and annealing on Ti/Al/Pt/Au ohmic contacts on GaN nanowires. Electrochemical and Solid-State Lett.. 9:G155-G157.
Chang, CC, Lin CF, Chiou JM, Ho TH, Tai Y, Lee JH, Chen YF, Wang JK, Chen LC, Chen* KH.  2010.  Effects of cathode buffer layers on the efficiency of bulk-heterojunction solar cells. Appl. Phys. Lett.. 96:263506.
Chang, CY, Tsao FC, Pan CJ, Chi GC, Wang HT, Chen JJ, Ren F, Norton DP, Pearton* SJ, Chen KH, Chen LC.  2006.  Electroluminescence from ZnO nanowire/polymer composite p-n junction. Appl. Phys. Lett.. 88:173503-(1-3).
Chang, H-C, You H-J, Sankar R, Yang Y-J, Chen L-C, Chen K-H.  2019.  Enhanced Thermoelectric Performance via Oxygen Manipulation in BiCuTeO, 2019. MRS Advances. 4(8):499-505.: Materials Research Society AbstractWebsite

BiCuTeO is a potential thermoelectric material owing to its low thermal conductivity and high carrier concentration. However, the thermoelectric performance of BiCuTeO is still below average and has much scope for improvement. In this study, we manipulated the nominal oxygen content in BiCuTeO and synthesized BiCuTeOx (x = 0.94–1.06) bulks by a solid-state reaction and pelletized them by a cold-press method. The power factor was enhanced by varying the nominal oxygen deficiency due to the increased Seebeck coefficient. The thermal conductivity was also reduced due to the decrease in lattice thermal conductivity owing to the small grain size generated by the optimal nominal oxygen content. Consequently, the ZT value was enhanced by ∼11% at 523 K for stoichiometric BiCuTeO0.94 compared to BiCuTeO. Thus, optimal oxygen manipulation in BiCuTeO can enhance the thermoelectric performance. This study can be applied to developing oxides with high thermoelectric performances.

Chang, CY, Chi GC, Wang WM, Chen* LC, Chen KH, Ren F, Pearton SJ.  2006.  Electrical transport properties of single GaN and InN nanowires. J. Electronic Materials. 35:738-743.
Chang, H-C, You H-J, Sankar R, Yang Y-J, Chen L-C, Chen K-H.  2019.  Enhanced thermoelectric performance of BiCuTeO by excess Bi additions, 2019. 45(7, Part A):9254-9259. AbstractWebsite

Thermoelectric (TE) devices used to convert waste heat directly into electricity are highly desirable for alleviating the prevailing energy crisis and global climate-change issues. Among the various TE materials available, metal oxides exhibit high thermal and chemical stabilities in air, and are hence, preferred for use in many TE applications. However, most of them possess TE figures of merit (ZT) that are below the applicable value of 2, in the mid-temperature region (from 250 to 600 °C). In a previous work, the removal of a small amount of Bi from BiCuSeO was found to improve the ZT of BiCuSeO. In this work, we pursue another track and study the TE performance of BiCuTeO after the addition of up to 6% excess Bi. Bi1+xCuTeO (x = 0.00–0.06) samples were prepared by solid-state reactions, followed by hot-pressing to form pellets. By adding a stoichiometric excess of Bi into BiCuTeO, 16% enhancement in power factor was achieved at 450 °C. This enhancement can be attributed to the increase in the Seebeck coefficient because of the appearance of secondary phases. Detailed characterizations and discussions of the effect of the nominal excess Bi in BiCuTeO are presented in this paper. The findings of this study can be applied in the investigation of novel high-performance TE materials.

Chattopadhyay, S, Chen LC, Chen KH.  2011.  Energy production and conversion applications ofone-dimensional semiconductor nanostructures. NPG Asia Mater.. 3:74-81.
Chen, TT, Hsieh YP, Wei CM, Chen* YF, Chen LC, Chen KH, Peng YH, Kuan CH.  2008.  Electroluminescence enhancement of SiGe/Si multiple quantum wells through nanowall structures. Nanotechnology. 19:365705.
Chen, KH, Wu JY, Chen LC, Juan CC, Hsu T.  1995.  Epitaxial Growth of Diamond Films for Electronic Applications. the 188th Meeting of the Electrochemical Society. :Vol95-21,p55-69., Chicago
Chen, JT, Hsiao CL, Hsu HC, Wu CT, Yeh CL, Wei PC, Chen LC, Chen* KH.  2007.  Epitaxial growth of InN films by molecular-beam epitaxy using hydrazoic acid (HN3) as an efficient nitrogen source. J. Phys. Chem. A. 111:6755-6759.
Chen, KH, Wen CY, Wu CT, Chen LC, Wang CT, Ma KJ.  2001.  Electron beam induced formation of carbon nanorods. J. Phys. Chem. of Solids. 62:1561-1565.
Chen*, LC, Lin HY, Wong CS, Chen KH, Lin ST, Yu YC, Wang CW, Lin EK, Lin KC.  1999.  Ellipsometric study of carbon nitride thin films with and without silicon addition. Diamond & Related Materials. 8:618-622.
Chiou, JW, Jan JC, Tsai HM, Pong* WF, Tsai MH, Hong IH, Klauser R, Lee JF, Hsu CW, Lin HM, Chen CC, Shen CH, Chen LC, Chen KH.  2003.  Electronic structure of GaN nanowire studied by X-ray-absorption spectroscopy and scanning photoelectron microscopy. Appl. Phys. Lett.. 82:3949-3951.
Chiou, JW, Yueh CL, Jan JC, Tsai HM, Pong* WF, Hong IH, Klauser R, Tsai MH, Chang YK, Chen YY, Wu CT, Chen KH, Wei SL, Wen CY, Chen LC, Chuang TJ.  2002.  Electronic structure at the carbon nanotube tips studied by X-ray-absorption spectroscopy and scanning photoelectron microscopy. Appl. Phys. Lett.. 81:4189-4191.
Chou, CT, Tang WL, Lin CH, Liu CH, Chen LC, Chen KH.  2012.  Effect of substrate temperature on orientation of subphthalocyanine molecule in organic photovoltaic cells. Thin Solid Films. 520:2289-2292.
Ciao-WeiYang, Chin-ChangChen, Chen K-H, SoofinCheng.  2017.  Effect of pore-directing agents in SBA-15 nanoparticles on the performance of Nafion®/SBA-15n composite membranes for DMFC. Journal of Membrane Science. 526:106-117.
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.
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.