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Junaid, M, Lundin D, Palisaitis J, Hsiao CL, Darakchieva V, Jensen J, Persson POA, Sandstrom P, Lai WJ, Chen LC, Chen KH, Helmersson U, Hultman L, Birch J.  2011.  Two-domain formation during the epitaxial growth of GaN (0001) on c-plane Al2O3 (0001) by high power impulse magnetron sputtering. J. Appl. Phys.. 110:123519.
Huang, S-J, Muneeb A, Sabhapathy P, Bayikadi KS, Murtaza T, Raju K, Chen L-C, Chen K-H, Sankar R.  2021.  Two-Dimensional Layered NiLiP2S6 Crystals as an Efficient Bifunctional Electrocatalyst for Overall Water Splitting. Catalysts. 11, Number 7 AbstractWebsite

The quest of earth-abundant bifunctional electrocatalysts for highly efficient oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is essential for clean and renewable energy systems. Herein, directed by the experimental analysis, we demonstrate layered nickel lithium phosphosulfide (NiLiP2S6) crystal as a highly efficient water-splitting catalyst in alkaline media. With strained lattice due to stacked layers as observed by TEM and electronic structure analysis performed by XPS showed mixed Ni2+,3+ oxidation states induced by addition of Li as a cation, NiLiP2S6 displays excellent OER (current density of 10 mA cm–2 showed an overpotential of 303 mV vs. RHE and a Tafel slope of 114 mV dec–1) and HER activity (current density of −10 mA cm–2 showed an overpotential of 184 mV vs. RHE and a Tafel slope of 94.5 mV dec–1). Finally, an alkaline media was employed to demonstrate the overall water splitting using NiLiP2S6 as both the anode and the cathode, which attained a 50 mA cm−2 current density at 1.68 V. This bimetallic phosphosulfide, together with long-term stability and enhanced intrinsic activity, shows enormous potential in water splitting applications.

Chou, CT, Lin CH, Wu MH, Cheng TW, Lee JH, Liu CHJ, Tai Y, Chattopadhyay S, Wang JK, Chen KH, Chen LC.  2011.  Tuning open-circuit voltage in organic solar cells by magnesium modified Alq3. J. Appl. Phys.. 110:083104.
Lin, C-H, Yeh W-T, Sun C-L, Shen J-L, Lee J-H, Chen L-C, Wang J-K, Chen* K-H.  2011.  Tuning energy-level in magnesium modified Alq3. J. Appl. Phys.. 109:083541.
Chien, CT, Li SS, Lai WJ, Yeh YC, Chen HA, Chen LC, Chen KH, T.Nemoto, Isoda S, Chen M, Fujita T, Chhowalla M, Chen CW.  2012.  Tunable photoluminescence from graphene oxide. Angewandte Chemie. 51:6662-6666.
Bhusari, DM, Teng CW, Chen KH, Chen LC.  1997.  Traveling wave method for measurement of thermal conductivity of thin films. Rev. Sci. Instrum.. 68(11):4180-4183.
C. Y. Chang, Chi GC, Wang WM, Chen LC, Chen KH, Ren F, Pearton* SJ.  2005.  Transport properties of InN nanowires. Appl. Phys. Lett.. 87:093112-(1-3).
Liu, YL, Yu CC, Lin KT, Yang TC, Wang EY, Chen HL, Chen LC, Chen KH.  2015.  Transparent, broadband, flexible, and bifacial-operable photodetectors containing a large-area graphene-gold oxide heterojunction. ACS Nano . 9:5093-5103.
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.
Thang, NQ, Sabbah A, Huang C-Y, Phuong NH, Lin T-Y, Kamal Hussien M, Wu H-L, Wu C-I, Pham NNT, Viet PV, Lee C-H, Chen L-C, Chen K-H.  2024.  Tailoring atomically dispersed Fe-induced oxygen vacancies for highly efficient gas-phase photocatalytic CO2 reduction and NO removal with diminished noxious byproducts, 2024. Journal of Materials Chemistry A. 12(46):31847-31860.: The Royal Society of Chemistry AbstractWebsite

Single-atom-supported metal oxides have attracted extensive interest in energy catalysis, offering a promising avenue for mitigating greenhouse gas emissions and environmental pollution. This study presents a facile synthesis of single-atom Fe-modified Bi2WO6 photocatalysts. By carefully tuning the Fe ratios, the 1.5Fe-Bi2WO6 sample demonstrates exceptional photocatalytic efficiency in CO2 to CO reduction (36.78 μmol g−1). Additionally, an outstanding NO removal performance is also achieved through this photocatalyst with an impressively low conversion of toxic NO2 at just 0.37%. The reaction intermediates and mechanisms governing the photocatalytic reduction of CO2 into CO are elucidated using in situ DRIFTS and in situ XAS techniques. Regarding NO removal, the introduction of Fe single-atoms, along with induced oxygen vacancies, plays a pivotal role in facilitating the transformation of NO and NO2 into nitrate by stabilizing NO and NO2 species. Mechanistic insights into photocatalytic NO oxidation are garnered through scavenger trapping and EPR experiments employing DMPO. This study emphasizes single-atom-supported metal oxide's potential in sustainable chemistry and air purification, providing a promising solution for urgent environmental challenges.