The adsorbate-induced reconstruction of the room-temperature Ni(110)-H surface has been resolved by scanning tunneling microscopy. The structure, known as ‘‘streaky’’ (1×2) from LEED observations, is found to be primarily a (5×2) Ni reconstruction with small domain size along the 〈001〉. Top-layer Ni atoms are paired long the 〈001〉 by a 0.5-Å lateral displacement to form tetramers and every fifth 〈001〉 row is missing. The barrier height, measured simultaneously with a constant-current topograph, is found to be higher along the 〈001〉 missing rows.

• Received 10 July 1987

DOI:https://doi.org/10.1103/PhysRevLett.59.1452