Applied Surface Science 307 (2014) 736–743 Contents lists available at ScienceDirect Applied Surface Science journal h om epa ge: www.elsevier.com/locate/apsusc Structural/spectroscopic analyses and H 2 /O 2 /CO responses of thulium(III) oxide nanosquare sheets Sung Woo Lee a , Seong Kyun Park b , Bong-Ki Min c , Jun-Gill Kang d , Youngku Sohn e,∗ a Center for Research Facilities, Chungnam National University, Daejeon 305-764, Republic of Korea b Bruker AXS Korea, 15F KINS Tower, 25-1 Jeongja-dong, Bundang-gu, Seongnam-si, Gyeonggi 463-847, Republic of Korea c Center for Research Facilities, Yeungnam University, Gyeongsan 712-749, Republic of Korea d Department of Chemistry, Chungnam National University, Daejeon 305-764, Republic of Korea e Department of Chemistry, Yeungnam University, Gyeongsan, Gyeongbuk 712-749, Republic of Korea a r t i c l e i n f o Article history: Received 28 March 2014 Accepted 18 April 2014 Available online 30 April 2014 Keywords: Tm(III) oxide Nanosquare sheet Spectroscopy Reduction Oxidation a b s t r a c t Cubic (space group Ia-3, a = 10.49 ˚ A) bixbyite two-dimensional thulium(III) oxide nanosquare struc- ture was first prepared, and then fully characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction crystallography (XRD), thermogravimetric analysis/differential scanning calorimetry (TGA/DSC), UV–vis-near IR absorption, Raman, X-ray photo- electron spectroscopy, temperature-programmed reduction and oxidation experiments. The crystal structure was fully refined, and detailed structural parameters were determined on the basis of the Rietveld analysis. High resolution TEM image revealed interplanar distances of 0.26 nm and 0.31 nm cor- responding to the (4 0 0) and (2 2 2) planes, respectively. The structure projections of the (4 0 0) and (2 2 2) planes were imaged along [0 1 1] and [1 1 -2] directions, respectively. A broad H 2 reduction peak and a sharp O 2 oxidation peak were found at 688 ◦ C and 123 ◦ C, respectively. CO oxidation activity started to appear at 400–500 ◦ C. The new results of this study further highlight the characteristics and the actual applications of Tm(III) oxide. © 2014 Elsevier B.V. All rights reserved. 1. Introduction Thulium (Tm) oxide has attracted a great deal of interest as a candidate material for gate dielectric oxide applications due to its high dielectric constant of 12–13 and its energy band gap of 5 eV [1–3]. Moreover, Tm is known to suppress an equivalent oxide thickness as an interfacial layer [1]. Tm 2 O 3 films were grown by molecular beam epitaxy using metallic Tm, where the preferen- tial growth orientations from (1 1 0) to (1 1 1) planes could be controlled by varying the oxygen pressure during the deposition [3]. Tm(III) has a high potential for IR laser application because it exhibits 1.4 and 1.8 m infrared emission [4,5]. In addition, Tm(III) oxide has recently been applied to sensors [6,7]. Li et al. prepared a glucose oxidase–Tm 2 O 3 nanoparticle-modified electrode and used this for a glucose electrochemical sensor [6]. Pan et al. fabricated a Tm 2 O 3 pH-sensing membrane using its high-k property [7]. Tm 2 O 3 was also shown to have a catalytic effect on the reversible absorp- tion and desorption of hydrogen in NaAlH 4 [8]. ∗ Corresponding author. Tel.: +82 53 810 2354; fax: +82 53 810 4613. E-mail address: youngkusohn@ynu.ac.kr (Y. Sohn). The nanostructure of Tm 2 O 3 appears far from that desired by the scientific community; however, it has high potential applica- bility and has been used extensively as a dopant material owing to its luminescence [9–22] and dielectric oxide layer [1–3,9–16,23]. Including the nanoplates containing lanthanide ions, the lan- thanide oxide nanoplates have been reported [24–30]. However, although Geng et al. reported a 2D-layered nanostructure with Tm 8 (OH) 20 Cl 4 ·nH 2 O [31], no investigations of two-dimensional Tm 2 O 3 nanostructures have been conducted to date. Therefore, we synthesized Tm 2 O 3 nanosquare sheets, revealed their new struc- tural and fundamental spectroscopic properties, and tested their hydrogen reduction, oxygen oxidation and CO oxidation activities. The results presented herein will stimulate fundamental studies and actual applications of Tm(III) oxide in the future. 2. Experimental 2.1. Materials and instrumentations Briefly, the nanosquare sheets were synthesized as follows. Ten mL of 0.1 M Tm(III) nitrate pentahydrate (Sigma–Aldrich, 99.9%) and 15 mL of Millipore water (18.2 M cm resistivity) were mixed, http://dx.doi.org/10.1016/j.apsusc.2014.04.149 0169-4332/© 2014 Elsevier B.V. All rights reserved.