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Lee, YY, Tu KH, Yu CC, Li SS, Hwang JY, Lin CC, Chen KH, Chen LC, Chen HL, Chen CW.  2011.  Top laminated graphene electrode in a semitransparent polymer solar cell by simultaneous thermal annealing/releasing method. ACS Nano. 5:6564-6570.
Wang, J, Chen KH, Mazur E.  1986.  Time-resolved Spontaneous Raman Spectroscopy of Infrared-multiphoton-excited SF6. Phys. Rev.A. 34:3892.
Huang, Y-F, Liao K-W, Fahmi FRZ, Modak VA, Tsai S-H, Ke S-W, Wang C-H, Chen L-C, Chen K-H.  2021.  Thickness-Dependent Photocatalysis of Ultra-Thin MoS2 Film for Visible-Light-Driven CO2 Reduction. Catalysts. 11, Number 11 AbstractWebsite

The thickness of transition metal dichalcogenides (TMDs) plays a key role in enhancing their photocatalytic CO2 reduction activity. However, the optimum thickness of the layered TMDs that is required to achieve sufficient light absorption and excellent crystallinity has still not been definitively determined. In this work, ultra-thin molybdenum disulfide films (MoS2TF) with 25 nm thickness presented remarkable photocatalytic activity, and the product yield increased by about 2.3 times. The photocatalytic mechanism corresponding to the TMDs’ thickness was also proposed. This work demonstrates that the thickness optimization of TMDs provides a cogent direction for the design of high-performance photocatalysts.

Lin, Y-K, Chen R-S, Chou T-chin, Lee Y-H, Chen Y-F, Chen K-H, Chen L-C.  2016.  Thickness-Dependent Binding Energy Shift in Few-Layer MoS2 Grown by Chemical Vapor Deposition, 2016. ACS Applied Materials & InterfacesACS Applied Materials & Interfaces. 8(34):22637-22646.: American Chemical Society AbstractWebsite
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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.

Tran Nguyen, NH, Nguyen TH, Liu Y-ren, Aminzare M, Pham ATT, Cho S, Wong DP, Chen K-H, Seetawan T, Pham NK, Ta HKT, Tran VC, Phan TB.  2016.  Thermoelectric Properties of Indium and Gallium Dually Doped ZnO Thin Films, 2016. ACS Applied Materials & InterfacesACS Applied Materials & Interfaces. 8(49):33916-33923.: American Chemical Society AbstractWebsite
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Prem Kumar, DS, Tippireddy S, Ramakrishnan A, Chen K-H, Malar P, Mallik RC.  2019.  Thermoelectric and electronic properties of chromium substituted tetrahedrite, 2019. Semiconductor Science and Technology. 34(3):035017.: IOP Publishing AbstractWebsite

Cr substituted tetrahedrites with the chemical formula Cu12−xCrxSb4S13 (x = 0.15, 0.25, 0.35, 0.5, 0.75, 1.0) have been synthesised for thermoelectric study. Cr substitutes at the Cu site to optimize the thermoelectric properties and achieve a higher figure of merit (zT). X-Ray diffraction (XRD) analysis revealed that the tetrahedrite is the major phase with minor impurity phases. Electron probe microanalysis (EPMA) shows the formation of tetrahedrite main phase with near stoichiometry and the presence of Cu3SbS4, CuSbS2 and Sb as secondary phases. X-ray photoelectron spectroscopy (XPS) shows the oxidation state of Cu, Sb and S as +1, +3 and −2, respectively, whereas for Cr, it could not be identified. Temperature-dependent magnetic susceptibility of sample x = 0.75 shows antiferromagnetic correlation originating from the Cr ion. The calculated effective magnetic moment of 2.83 μB per Cr atom indicates the presence of Cr+4 in this sample. The decrease in the electrical resistivity upon doping indicates the compensation of holes due to the substitution of Cr at the Cu site. But the x = 0.35 sample is not following the trend due to larger compensation of holes with an activation energy of 124.6 meV. The temperature-dependent behaviour of electrical resistivity shows the shift in the Fermi level from the valance band towards the band gap. The absolute Seebeck coefficient is positive throughout the temperature range and follows a similar trend as that of electrical resistivity, with the exception of the x = 0.35 sample. The electronic thermal conductivity reduces due to hole compensation caused by Cr substitution. Moreover, the substitution of Cr effectively reduces the lattice thermal conductivity due to point defect scattering of phonons. A maximum zT of 1.0 is achieved for sample x = 0.35 at 700 K.

M.C. Kan, Huang* JL, Sung JC, Chen KH, Yau BS.  2003.  Thermionic emission of amorphous diamond and field emission of carbon nanotube. Carbon. 41:2839-2845.
Su, T-Y, Wang T-H, Wong DP, Wang Y-C, Huang A, Sheng Y-C, Tang S-Y, Chou T-chin, Chou T-L, Jeng H-T, Chen L-C, Chen K-H, Chueh Y-L.  2021.  Thermally Strain-Induced Band Gap Opening on Platinum Diselenide-Layered Films: A Promising Two-Dimensional Material with Excellent Thermoelectric Performance, 2021. Chemistry of MaterialsChemistry of Materials. 33(10):3490-3498.: American Chemical Society AbstractWebsite
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Wei, PC, Shih HC, Hsu CM, Lin FS, Chen KH, Chattopadhyay* S, Ganguly A, Hsu CW, Chen LC.  2008.  Thermal diffusivity study in supported epitaxial InN thin films by the Traveling-Wave technique. J. Appl. Phys.. 104:064920.
Chattopadhyay*, S, Chien SC, Chen LC, Chen KH, Lehmann G, Hess P.  2002.  Thermal diffusivity in diamond, SiCxNy and BCxNy. Diamond Relat. Mater. 11:708-713.
Chattopadhyay, S, Chen* LC, Wu CT, Chen KH, Wu JS, Chen YF, Lehmann G, Hess P.  2001.  Thermal diffusivity in amorphous silicon carbon nitride thin films by the traveling wave technique. Appl. Phys. Lett.. 79:332-334.
Sun, CL, Hsu YK, Lin YG, Chen KH, Bock C, MacDougall B, Wu X, Chen LC.  2009.  Ternary PtRuNi nanocatalysts supported on N-doped carbon nanotubes: deposition process, materials characterization, and electrochemistry. J. Electrochem. Soc.. 156:B1249-B1252.
Lin, DY, Li CF, Huang YS, Jong YC, Chen YF, Chen LC, Chen CK, Chen KH, Bhusari DM.  1997.  Temperature dependence of direct band gap of Si-containing carbon nitride crystalline films. Phys. Rev. B. 56:6498-6501.
Chen, KH, Chuang MC, Penney M, Banholzer WF.  1992.  Temperature and Density Distribution of H2 and H in Hot Filament CVD of Diamond Films. J. Appl. Phys.. 71:1485.
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Lee, S-W, Chen J-C, Wu J-A, Chen K-H.  2017.  Synthesis and Properties of Poly(ether sulfone)s with Clustered Sulfonic Groups for PEMFC Applications under Various Relative Humidity. ACS Appl. Mater. Interfaces. 9(11):9805–9814.
Lee, S-W, Chen J-C, Wu J-A, Chen K-H.  2017.  Synthesis and Properties of Poly(ether sulfone)s with Clustered Sulfonic Groups for PEMFC Applications under Various Relative Humidity, 2017. ACS Applied Materials & InterfacesACS Applied Materials & Interfaces. 9(11):9805-9814.: American Chemical Society AbstractWebsite
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Yang, M-J, Yusuf Fakhri M, Liao C-N, Chen K-H.  2022.  Synthesis and characterization of Ge-Ag-Sb-S-Se-Te high-entropy thermoelectric alloys, 2022. 311:131617. AbstractWebsite

Multielement alloying is an appealing approach for suppressing thermal conductivity of thermoelectric materials. In this study, we synthesized GeTe-based high-entropy alloys with notable (S, Se) substitution at Te sites and (Ag, Sb) at Ge sites. The Ge0.82Ag0.08Sb0.1S0.5Se0.1Te0.4 exhibits an extremely low thermal conductivity of ∼ 0.66 W/m⋅K and a high Seebeck coefficient (>250 μV/K) over a temperature range of 150 – 400 °C. The influence of lattice distortion on phase transformation and transport properties of Ge0.9-2xAg2xSb0.1S0.5Se0.1Te0.4 (x = 0 – 0.06) was investigated.

Wu, JT, Fang TH, Hsu CF, Yu YY, Wang GJ, Tang CW, Chen KH, Lii KH.  1998.  Synthesis and Characterization of an Organic-inorganic Hybrid Compound: [WO3(2,2’-bipyridine)]. J. Matter. Chem.. 8:2181.
Chiu, J-M, Chou T-chin, Wong DP, Lin Y-R, Shen C-A, Hy S, Hwang B-J, Tai Y, Wu H-L, Chen L-C, Chen K-H.  2018.  A synergistic “cascade” effect in copper zinc tin sulfide nanowalls for highly stable and efficient lithium ion storage. Nano Energy. 44:438-446. AbstractWebsite
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Bayikadi, KS, Wu CT, Chen L-C, Chen K-H, Chou F-C, Sankar R.  2020.  Synergistic optimization of thermoelectric performance of Sb doped GeTe with a strained domain and domain boundaries, 2020. Journal of Materials Chemistry A. 8(10):5332-5341.: The Royal Society of Chemistry AbstractWebsite

In addition to the Ge-vacancy control of GeTe, the antimony (Sb) substitution of GeTe for the improvement of thermoelectric performance is explored for Ge1−xSbxTe with x = 0.08–0.12. The concomitant carrier concentration (n) and the aliovalent Sb ion substitution led to an optimal doping level of x = 0.10 to show ZT ∼ 2.35 near ∼800 K, which is significantly higher than those single- and multi-element substitution studies of the GeTe system reported in the literature. In addition, Ge0.9Sb0.1Te demonstrates an impressively high power factor of ∼36 μW cm−1 K−2 and a low thermal conductivity of ∼1.1 W m−1 K−1 at 800 K. The enhanced ZT level for Ge0.9Sb0.1Te is explained through a systematic investigation of micro-structural change and strain analysis from room temperature to 800 K. A significant reduction of lattice thermal conductivity (κlat) is identified and explained by the Sb substitution-introduced strained and widened domain boundaries for the herringbone domain structure of Ge0.9Sb0.1Te. The Sb substitution created multiple forms of strain near the defect centre, the herringbone domain structure, and widened tensile/compressive domain boundaries to support phonon scattering that covers a wide frequency range of the phonon spectrum to reduce lattice thermal conductivity effectively.

Krishnamoorthy, V, Sabhapathy P, Raghunath P, Huang C-Y, Sabbah A, Kamal Hussien M, Syum Z, Muthusamy S, Lin M-C, Wu H-L, Chen R-S, Chen K-H, Chen L-C.  2024.  Synergistic Electronic Interaction of Nitrogen Coordinated Fe-Sn Double-Atom Sites: An Efficient Electrocatalyst for Oxygen Reduction Reaction, 2024. Small Methods. n/a(n/a):2301674.: John Wiley & Sons, Ltd AbstractWebsite

Abstract Double-atom site catalysts (DASs) have emerged as a recent trend in the oxygen reduction reaction (ORR), thereby modifying the intermediate adsorption energies and increasing the activity. However, the lack of an efficient dual atom site to improve activity and durability has limited these catalysts from widespread application. Herein, the nitrogen-coordinated iron and tin-based DASs (Fe-Sn-N/C) catalyst are synthesized for ORR. This catalyst has a high activity with ORR half-wave potentials (E1/2) of 0.92 V in alkaline, which is higher than those of the state-of-the-art Pt/C (E1/2 = 0.83 V), Fe-N/C (E1/2 = 0.83 V), and Sn-N/C (E1/2 = 0.77 V). Scanning electron transmission microscopy analysis confirmed the atomically distributed Fe and Sn sites on the N-doped carbon network. X-ray absorption spectroscopy analysis revealed the charge transfer between Fe and Sn. Both experimental and theoretical results indicate that the Sn with Fe-NC (Fe-Sn-N/C) induces charge redistribution, weakening the binding strength of oxygenated intermediates and leading to improved ORR activity. This study provides the synergistic effects of DASs catalysts and addresses the impacts of P-block elements on d-block transition metals in ORR.

Samireddi, S, Aishwarya V, Shown I, Muthusamy S, Unni SM, Wong K-T, Chen K-H, Chen L-C.  2021.  Synergistic Dual-Atom Molecular Catalyst Derived from Low-Temperature Pyrolyzed Heterobimetallic Macrocycle-N4 Corrole Complex for Oxygen Reduction. Small. 17:2103823., Number 46 AbstractWebsite

Abstract A heterobimetallic corrole complex, comprising oxygen reduction reaction (ORR) active non-precious metals Co and Fe with a corrole-N4 center (PhFCC), is successfully synthesized and used to prepare a dual-atom molecular catalyst (DAMC) through subsequent low-temperature pyrolysis. This low-temperature pyrolyzed electrocatalyst exhibited impressive ORR performance, with onset potentials of 0.86 and 0.94 V, and half-wave potentials of 0.75 and 0.85 V, under acidic and basic conditions, respectively. During potential cycling, this DAMC displayed half-wave potential losses of only 25 and 5 mV under acidic and alkaline conditions after 3000 cycles, respectively, demonstrating its excellent stability. Single-cell Nafion-based proton exchange membrane fuel cell performance using this DAMC as the cathode catalyst showed a maximum power density of 225 mW cm−2, almost close to that of most metal–N4 macrocycle-based catalysts. The present study showed that preservation of the defined CoN4 structure along with the cocatalytic Fe–Cx site synergistically acted as a dual ORR active center to boost overall ORR performance. The development of DAMC from a heterobimetallic CoN4-macrocyclic system using low-temperature pyrolysis is also advantageous for practical applications.

Huang, BR, Chen KH, Ke WZ.  2000.  Surface-enhanced Raman analysis of the diamond films by using different metals. Materials Letters. 42:162-165.
Wang, SB, Huang YF, Chattopadhyay S, Chang SJ, Chen RS, Chong CW, Hu MS, Chen LC, Chen KH.  2013.  Surface plasmon-enhanced gas sensing in single gold peapodded-silica nanowire. Asia Materials.