氢气在 Cu(111)表面和次表面的吸附。

Adsorption of hydrogen on the surface and sub-surface of Cu(111).

机构信息

Chemistry Department, Brookhaven National Laboratory, Upton, New York 11973, USA.

出版信息

J Chem Phys. 2013 Jul 28;139(4):044712. doi: 10.1063/1.4816515.

PMID:23902008

Abstract

The interaction of atomic hydrogen with the Cu(111) surface was studied by a combined experimental-theoretical approach, using infrared reflection absorption spectroscopy, temperature programmed desorption, and density functional theory (DFT). Adsorption of atomic hydrogen at 160 K is characterized by an anti-absorption mode at 754 cm(-1) and a broadband absorption in the IRRA spectra, related to adsorption of hydrogen on three-fold hollow surface sites and sub-surface sites, and the appearance of a sharp vibrational band at 1151 cm(-1) at high coverage, which is also associated with hydrogen adsorption on the surface. Annealing the hydrogen covered surface up to 200 K results in the disappearance of this vibrational band. Thermal desorption is characterized by a single feature at ∼295 K, with the leading edge at ∼250 K. The disappearance of the sharp Cu-H vibrational band suggests that with increasing temperature the surface hydrogen migrates to sub-surface sites prior to desorption from the surface. The presence of sub-surface hydrogen after annealing to 200 K is further demonstrated by using CO as a surface probe. Changes in the Cu-H vibration intensity are observed when cooling the adsorbed hydrogen at 180 K to 110 K, implying the migration of hydrogen. DFT calculations show that the most stable position for hydrogen adsorption on Cu(111) is on hollow surface sites, but that hydrogen can be trapped in the second sub-surface layer.

摘要

采用红外反射吸收光谱、程序升温脱附（TPD）和密度泛函理论（DFT）相结合的实验理论方法研究了原子氢与 Cu(111) 表面的相互作用。在 160 K 下吸附的原子氢的特征在于在 754 cm(-1)处的反吸收模式和 IRRA 光谱中的宽带吸收，这与氢在三配位空穴表面位和亚表面位上的吸附以及在高覆盖率下出现的尖锐振动带在 1151 cm(-1)处有关，这也与表面上的氢吸附有关。将氢覆盖的表面退火至 200 K 会导致该振动带消失。热脱附的特征是在约 295 K 处出现单一特征，前沿在约 250 K 处。尖锐的 Cu-H 振动带的消失表明，随着温度的升高，表面氢在从表面解吸之前迁移到亚表面位。在 200 K 退火后，用 CO 作为表面探针进一步证明了亚表面氢的存在。当将在 180 K 下吸附的氢冷却至 110 K 时，观察到 Cu-H 振动强度的变化，这意味着氢的迁移。DFT 计算表明，氢在 Cu(111)上吸附的最稳定位置是在空穴表面位，但氢可以被困在第二亚表面层中。