Strong Intermixing Research Articles

Adsorption and compound formation of Yb on Ni(100)

The adsorption and compound formation of Yb on Ni(100) is studied by AES, ISS, LEED and XPS. The deposition of Yb is followed at two substrate temperatures, room temperatures and 670 K. Yb deposition at 670 K results in the formation of ordered structures. An incommensurate structure is attributed to adsorbed Yb, a c(10 × 2) and a slightly distorted hexagonal structure result from the formation of ordered Yb Ni compound layers. Intermixing between Yb and Ni occurs only above a certain Yb threshold coverage. Different valence states of the Yb atoms are revealed by XPS. Divalent Yb is found at the surface for all Yb depositions. Trivalent Yb is located in the bulk of the compound and, in certain coverage regions, also at the surface. Room temperature deposition of Yb does not lead to any ordered structures. At low coverages the room temperature structures can in many respects be considered as disordered versions of the 670 K structures. At higher Yb deposition no strong intermixing with the Ni occurs. Instead an Yb film starts growing.

Diffusion-induced disordering of Ga0.47In0.53As/InP multiple quantum wells with zinc

Diffusing zinc into Ga0.47In0.53As/InP MQW layers is found to cause strong intermixing of the group III elements, which changes the composition in the quantum wells and barriers. As a result of this disordering the MQW bandgap is reduced in energy and the photoluminescence emission peak moves to longer wavelength.

V/Ge(111): Temperature dependent intermixing studied with high resolution photoemission and quantitative modeling

High resolution, temperature dependent core level photoemission results for the V/Ge(111) interface show the interplay between atomic diffusion and trapping in the boundary layer. Room temperature results show strong intermixing, and core level analysis allows us to identify well‐defined chemical environments for Ge atoms (chemical shifts of −0.5 and −0.95 eV). Through modeling of the interface, we have determined the composition and extent of each reacted species. Studies at higher temperature showed that the extent and composition of the reacted overlayer could be varied. Indeed, by increasing the substrate temperature, we could produce an overlayer which became chemically homogeneous by 475 K. In this range, we find a diffusion activation energy of 5 kcal/mol which controls the width of the reacted layer.

7 × 7 Si(111)Cu interfaces: Combined LEED, AES and EELS measurements

CuSi(111) interfaces have been examined as a function of substrate temperature and deposition time using different surface sensitive techniques. At room temperature a layer by layer growth was found. Strong intermixing of Cu and Si takes place and beyond 10 monolayers an ordered α Si phase in Cu was found. At high temperature, the growth follows the layer plus island or Stranski-Krastanov growth mode. Three-dimensional crystallites, probably consisting of Cu 3Si, grow epitaxially on an ordered intermediate layer.

Photoemission studies of the Cu-InP(110) interface

The atomic and electronic structure of Cu-($n$-type) InP(110) interface has been studied by soft-x-ray photoemission spectroscopy and Auger spectroscopy for copper coverages ranging from 0.7 to 80 \AA{}. By monitoring the evolution of the P $2p$ and In $4d$ core-level spectra and the change of the Cu $3d$ level, which is degenerate with the substrate valence band, we provide evidence of strong intermixing taking place at the interface. A strong outward diffusion of phosphorous into the copper overlayer and indium segregation at the surface have been observed. A splitting of the phosphorous ${L}_{2,3}\mathrm{VV}$ Auger line has been observed for Cu coverages higher than 8 \AA{}. This splitting, similar to that observed for silicides, provides evidence of bond formation between Cu and P. On the basis of the P $2{p}_{\frac{3}{2}}$ line shift, a Schottky-barrier height of 0.6 eV has been established.

The band structure of polyferrocenylene

The band structure of polyferrocenylene is studied by means of crystal orbital calculations based on a semiempirical INDO model. The width for the highest filled bands is found between 0.40 to 2.61 eV. The closely spaced basis energies of ligand π and Fe 3d states lead to a strong metal-ligand intermixing in the k-space.

An INDO crystal orbital approach to the one-dimensional porphyrinatonickel(II) system

The band structure of the one-dimensional metallomacrocycle porphyrinatonickel(II), Ni(P), has been studied by means of the crystal orbital formalism based on a semi-empirical INDO Hamiltonian. The unoxidized Ni(P) polymer is an insulator, the highest occupied bands as well as the conduction band are localized in the ligand framework. Bands with significant Ni 3 d admixtures are predicted at lower energies. The dense manifold of ligand states in the vicinity of the Ni 3 d basis energies leads to a strong metal-ligand intermixing in Ni(P) bands in the outer valence region.

The interaction of thin Au and Al overlayers with the GaAs(110) surface

Abstract Different photoemission techniques using synchrotron radiation as the excitation source have been used to study the electronic structure of metal-semiconductor interfaces (in particular, Au/GaAs(110) and Al/GaAs(110)) and the formation of Schottky barriers. The Fermilevel pinning is complete at less than 0.2 monolayers, and it is proposed that defect states at, or close to, the interface are responsible for the barrier height. In the case of Au, there is a strong intermixing between the metal and the semiconductor, indicating a nonabrupt interface. Photoemission core level data provide evidence that, in the case of A1, a replacement interaction takes place between Al and Ga in the topmost GaAs surface layer.

Abstract: Application of MeV backscattering to thin film diffusion problems

The temperature at which mixing processes and compound formation between two metals occur in a thin film structure is strongly decreased with respect to bulk materials. The MeV He+ backscattering technique is well suited with its mass and depth perception to investigate the thermal kinetics of grain boundary diffusion in both miscible and nonmiscible couples of thin films. In the Cu−Pb thin film couple, a nonmiscible system as predicted by the phase diagram, a grain boundary migration of Pb occurs in the temperature range 200−300°C and Pb atoms accumulate at the Cu surface following a t1/2 dependence. In Al−In couples, another nonmiscible system, grain boundary diffusion takes place during deposition with filling of boundaries so that no accumulation is detected after annealing. In the completely miscible In−Pb couples, the slight increase of the substrate temperature during evaporation allows a strong intermixing so that backscattering spectra indicate the presence of both elements on the sample surface.

Excitation of Coupled Nuclear Antiferromagnetic Resonance Modes

The presence of a strong hyperfine coupling in the antiferromagnets KMn${\mathrm{F}}_{3}$ and CsMn${\mathrm{F}}_{3}$ leads to a strong intermixing of the nuclear magnetic resonance and antiferromagnetic resonance (AFR) modes at low temperatures. In the experiments described here, ${\mathrm{Mn}}^{55}$ resonance absorption is detected by monitoring the field for AFR while driving at appropriate nuclear frequencies. Such resonance absorption is observed for a range of frequencies many times larger than the nuclear linewidth. A spin-pinning model is proposed which provides nucleation centers for this off-resonance saturation.