He scattering study of the nucleation and growth of Cu(100) from its vapor

Abstract

The nucleation and growth of layers of Cu deposited in ultrahigh vacuum on Cu(100) has been studied by He scattering. The intensity of the specular beam shows oscillations as a function of coverage, with maxima occurring at the completion of successive monolayers. The amplitude of these oscillations depends on both temperature and angle of incidence. An analysis of the dependence with the incident angle at fixed coverage, combined with the Bragg conditions for interference, provides an accurate method for determining the height of the two-dimensional islands formed in the process of crystal growth. %'e find a 0 value of 1.80+0.06 A in excellent agreement with x-ray determination of interlayer spacing of (100) planes. Measurements of the angular profile of the specular peak give an estimation of the average island size at different temperatures.The understanding of the processes involved in epitaxial growth of a crystal from its vapor has been a topic of permanent interest for 40 years. ' Many surface-sensitive techniques have been applied in the past years to characterize the series of atomic steps involved in growth phenomena, e.g. , condensation, migration, and nucleation. Whereas imaging techniques able to visualize individual adatoms, such as field ion microscopy (FIM), provide detailed information of small areas of the sample, diffraction techniques give the average over larger areas. As a typical example of the last type of techniques, the process of crystal growth has been recently studied by means of low-energy electron diffraction (LEED), ' " which, however, presents some problems due to the finite penetration of electrons in the solid. On the other hand, the scattering of atomic beams of He by surfaces is known to be sensitive only to the outer charge corrugation, thus, being especially suited to give average terrace size or step density of a growing crystal. Some of the advantages of using atomic beams for this purpose are their high sensitivity to detect disordered structures (adatoms, steps) at very low concentration, and their capability to provide information on the state of aggregation of the adsorbates.In this Rapid Communication we report on the first results of a study of nucleation and growth of copper evaporated on the (100) surface of the same metal using atomic beam scattering.The experiments were carried out in a UHV chamber equipped with standard surface-science techniques: Auger spectroscopy, low-energy electron diffraction, and Ar-ion sputterin . A supersonic He nozzle beam of 63 meV (k = 11 ') entered the chamber and impinged upon the crystal surface at a selected angle of incidence @. The scattered He intensity was measured by p movable quadrupole mass spectrometer. A more detailed description of the experimental setup has been already published.A copper wrapped tungsten filament placed near the crystal surface was used as a source of Cu vapor. The rate of Cu deposition was calibrated by measuring the peak heights of selected substrate and adsorbate Auger transitions in a cobalt foil ...

Photon-stimulated layer-by-layer desorption from NaCl(001) surfaces monitored by helium-atom scattering

“…The wave vector of the incident He beam (la = 5.58 A -1 ) satisfies nearly an out-of-phase condition for which waves scattered from terraces separated by an odd number of monatomic steps (step height: 2.81 A) interfere destructively. But, as expected [19], similar results were also observed for in-phase conditions, since the intensity of the specularly scattered He beam is mostly As seen in Fig. 1, as soon as the photon excitation is switched on the He intensity decreases sharply and oscillates with a constant frequency afterwards.…”

“…The observed damped oscillations clearly indicate an incomplete layerby-layer removal of the crystal in which several subsequent layers are involved. Layer-by-layer removal has not been previously observed in PSD and ESD [20], but is well known from studies on ion sputtering of metal surfaces [21] and for the reverse process of epitaxial growth observed with RHEED [22] and HAS [19,23,24]. It is interesting to note the very close similarity between the oscillations in Fig.…”

Initial growth morphology in a heteroepitaxial system at low temperature: Fe on Ag(100)

“…12 The monitoring of the intensity of an appropriate diffraction spot ͑''deposition curve''͒ represents a meaningful and direct method to control epitaxy. 13,14 Layerby-layer ͑LBL͒ growth induces oscillations in the deposition curve that reflect the oscillations of the surface step density consequent to cyclical nucleation and coalescence of twodimensional islands. Instead, in the case of three-dimensional growth the deposition curve decreases exponentially.…”

Surface phonon dispersion curves of thin Pb films on Cu(111)

“…The final characterization of the substrate surface, the newly prepared film surface, as well as the layer thickness were provided by HAS drift spectra, 45 diffraction patterns, and specular peak intensity oscillations during growth. 10,46 The substrate and film surfaces were of the same good quality as other surfaces prepared in our laboratory with a surface coherence length of several tens of nanometers.…”