Low temperature adsorption of hydrogen on Si(111) and (100) surfaces studied by elastic recoil detection analysis

Hydrogen adsorption on clean Si(111)-7×7 and Si(100)-2×1 surfaces at low temperatures (100 K) has been investigated by a combined use of high-energy ion-beam and LEED techniques. The effect of substrate temperatures on the absolute amount of adsorbed hydrogen atoms has been measured. When hydrogen is adsorbed at room temperature, the hydrogen coverage saturates at about 1.5 monolayer (ML) for Si(111)-7×7 and at about 2.0 ML for Si(100)-2×1, respectively. However, when the substrate temperature is kept at about 100 K during adsorption, such a saturation could not be observed. The hydrogen coverage gradually increases with the increase in hydrogen exposure. After 6000 langmuir (L) exposure, the coverage is 2 or 3 times larger than those at room temperature for Si(100) and Si(111) surfaces, respectively. LEED observation shows no ordered surface structure after hydrogen adsorption.