The growth of cubic CdS on InP(110) studied in situ by Raman spectroscopy

CdS was deposited onto clean cleaved InP(110) by molecular beam epitaxy (MBE) using a growth rate of 0.2 monolayers/min and a substrate temperature of 440 K (510 K). Raman spectra were taken in situ of the clean InP surface and after each evaporation step using an Ar+ ion laser as a light source. Due to this resonant excitation scattering signals originating from the CdS deposition are observed at coverages as low as 2 monolayers (ML). The number of phonon peaks observed and their selection rules reveal that the cubic modification is present. The spectra are dominated at all coverages by the longitudinal optical (LO) and 2LO phonon scattering intensities and the variation of the 2LO/LO intensity ratio with CdS deposition indicates changes in the electronic structure of the growing CdS. Another spectral feature in the Raman spectra is attributed to a chemically reacted layer at the interface most likely consisting of an In–S compound. The intensity of this feature is found to depend critically on the growth parameters, in particular the substrate temperature, but also on the operating time of the MBE cell. The amount of reaction at the interface also influences the critical CdS film thickness and the development of the 2LO/LO ratio. The results are discussed taking complementary photoluminescence, x‐ray diffraction, and photoemission data into account

Field desorption of H₃ and field dissociation of H⁺₃

Ab-initio calculations using a non-local spin-density approximation have been done for linear and triangular H+3 ions in an external homogenous electric field. From these calculations it is predicted that linear H+3 is not stable above 2 V/Å if its molecular axis is parallel to the field vector, whereas triangular H+3 resists field dissociation up to at least 3.1 V/Å. Linear H3 is formed at kink sites on the surface of the field emitter. Laser-stimulated field desorption of that H3 could lead to linear H+3. In spite of the rotation of the H+3 ion, a majority should field-dissociate in fields greater than 2.4 V/Å. However, if the linear H3 is bending during laser-stimulated field desorption the more stable triangular H+3 will be formed upon field ionization. The H+3 field dissociation for fields between 2.4 and 3.1 V/Å was experimentally investigated using laser pulse correlated ion pair spectroscopy in combination with a pulsed-laser atom probe. During these measurements a total of 605 H+3 ions arrived at the time-of-flight detector, but only one event occurred which could be attributed to H+3 field dissociation. However, H+2, formed by field ionization of the H+3 field dissociation product H2, could have been field-dissociated also. Therefore the H+2 field-dissociation probability has been calculated for the case where the H+2 molecular axis is parallel to the field vector. Taking this maximum dissociation probability of H+2 into account, it followed from processing of the measured yields that the H+3 field-dissociation probability is smaller than that of field-desorbed H+2 for fields up to 3.1 V/Å. Hence, it is inferred that linear H3 bends during laser-stimulated field desorption, resulting in a more stable triangular H+3 after field ionization