Atomic structure, chemical composition, and oxidation behavior of the (001) surface of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mtext>Ni</mml:mtext><mml:mn>2</mml:mn></mml:msub><mml:msub><mml:mtext>In</mml:mte

Intermetallic compounds have shown promising catalytic properties, exhibiting better selectivity and thermal stability than their metallic counterparts. Understanding their surface properties is crucial for optimizing catalytic performance. Here, we present an investigation of the atomic structure, chemical composition, and oxidation behavior of the previously unexplored binary intermetallic catalyst, <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"><a:mrow><a:msub><a:mi>Ni</a:mi><a:mn>2</a:mn></a:msub><a:msub><a:mi>In</a:mi><a:mn>3</a:mn></a:msub></a:mrow></a:math>, using various complementary techniques, including low-energy electron diffraction (LEED), scanning tunneling microscopy (STM), x-ray photoelectron spectroscopy (XPS), and low-energy ion scattering (LEIS), which provides elemental information from the topmost surface layer. We also calculated the surface energy of several possible bulk-terminated surfaces by density functional theory (DFT) to investigate surface stability. The <b:math xmlns:b="http://www.w3.org/1998/Math/MathML"><b:mrow><b:msub><b:mi>Ni</b:mi><b:mn>2</b:mn></b:msub><b:msub><b:mi>In</b:mi><b:mn>3</b:mn></b:msub></b:mrow></b:math>(100) surface was prepared by ion bombardment and annealing under ultrahigh vacuum conditions. We find that ion bombardment preferentially removes indium (In), while annealing promotes In segregation to the surface. After annealing, the surface exhibits a <c:math xmlns:c="http://www.w3.org/1998/Math/MathML"><c:mrow><c:mo>(</c:mo><c:mn>1</c:mn><c:mo>×</c:mo><c:mn>1</c:mn><c:mo>)</c:mo></c:mrow></c:math> LEED pattern. The surface develops a three-domain <d:math xmlns:d="http://www.w3.org/1998/Math/MathML"><d:mrow><d:mi mathvariant="normal">c</d:mi><d:mo>(</d:mo><d:mn>2</d:mn><d:msqrt><d:mn>3</d:mn></d:msqrt><d:mo>×</d:mo><d:mn>4</d:mn><d:mo>)</d:mo></d:mrow></d:math> rectangular structure upon exposure to ambient hydrogen present in the experimental chamber or hydrogen dosed from an external source, as evidenced by both STM and LEED. Both nickel (Ni) and In oxidize upon exposure to molecular oxygen. Based on STM and LEIS results along with surface energy calculations, we reveal that the surface planes contain In atoms bonded with Ni, the catalytically active constituent, suggesting that the surface may be stabilized by intermetallic bonding.