Ultrathin Ag Films Research Articles

Magnetic surface anisotropies of Co(0001)-based interfaces from in situ magnetometry of Co films on Pd(111), covered with ultrathin films of Pd and Ag

Magnetic surface anisotropies (MSA) of Co(0001) interfaces with Ag(111) and Pd(111), and of the free Co(0001) surface, were determined as a function of the thickness of Ag or Pd coverage, respectively, by torsion oscillation magnetometry in situ in UHV. Both second- and fourth- order contributions were considered. Whereas the free surface supports in-plane magnetization, the metal interfaces support perpendicular magnetization, with a pronounced maximum in the magnitude of MSA for 1 monolayer Ag, but a monotonic dependence on Pd thickness.

Magnetic surface anisotropies of Co(0001)-based interfaces from in situ magnetometry of Co films on Pd(111), covered with ultrathin films of Pd and Ag

Magnetic surface anisotropies of Co(0001)-based interfaces from in situ magnetometry of Co films on Pd(111), covered with ultrathin films of Pd and Ag

Layer-by-layer-resolved quantum-well states in ultrathin silver islands on graphite: A photoemission study.

Layer-resolved quantum-well states (QWS's) corresponding to islands of different thicknesses for ultrathin Ag films on graphite have been observed by angle-resolved ultraviolet photoemission. The spectral linewidth dependence on island thickness and on binding energy is well described within a phase-accumulation model, taking into account the specific quantum-well barriers involved. Thus high-resolution photoemission of QWS's provides an interesting tool to investigate the morphology and island-height distribution of ultrathin metal films.

Low-temperature scanning tunneling microscopy study of nucleation, percolation, and growth of ultrathin Ag films on Si(111)7×7

We have studied the growth of ultrathin Ag films on Si(111)7×7 between 80–100 K with low-temperature scanning tunneling microscopy. Nucleation of Ag in both halves of the 7×7 is observed. Corner holes and dimer sites are not occupied. Percolation occurs at submonolayer coverage through contact between the nucleated 2D Ag islands. This results in a honeycomb random site percolation problem. Upon completion of the first monolayer, 2D layer-like growth is observed.

Mössbauer studies of Fe(100)/Ag(100) multilayers grown on NaCl(100) by molecular beam epitaxy

Fe(100)/Ag(100) heterostructures, with varying Fe bilayer thicknesses equal to 3, 6 and 9 monolayers (ML) and a constant Ag bilayer thickness equal to 40 ML, were grown on suitably prepared monocrystalline NaCl(100) substrates by molecular beam epitaxy. The multilayer moncrystallinity was verified with in situ reflection high energy electron diffraction. Transmission Mössbauer measurements revealed a perpendicular surface anisotropy for the Fe(100) bilayers at 4.2 K. This behavior is unlike that of Fe(100)/Ag(111) ultrathin films of about the same thickness.

The structure and morphology of Ag film growth on Cu(110)

Low-energy electron diffraction (LEED), Auger electron spectrometry (AES), and workfunction change measurements have been used to characterize the structure and morphology of ultrathin Ag films grown on Cu(110). The LEED data show pronounced differences in diffraction arrays for multilayer deposition at 120 and ⩾ 300 K that are, respectively, consistent with disordered layering and layer-cluster growth morphologies deduced from AES. Following the initial growth of Ag in-registry with the substrate troughs, a split c(2 × 4) monolayer structure is observed that to first order is interpreted in terms of a distorted Ag(111) overlayer with a seventh-order superlattice periodicity normal to the substrate troughs. At 120 K, postmonolayer deposition reconstructs the monolayer template, producing a p(8 × 1) → p(8 × 3) → p( 8 7 × 3 ) sequence of diffraction features. These data are consistent with development of a heavily corrugated and strained Ag(110) film that grows from a configuration where the first atomic layer of Ag is captured in the Cu troughs. Multilayer coverages at ⩾ 300 K give LEED features that are indicative of clusters, which gradually coalesce to produce {111} microfacets in a geometry that is consistent with the 120 K structural observations. In agreement with trends seen in bulk binary properties of Ag and Cu, the film development appears to be driven by dominant Ag-Ag bonding as modulated by the row-trough substrate corrugation. The clustering is viewed as the most energetically favorable way to relieve the interfacial strain and attain a bulk Ag film in the absence of low-temperature kinetic limitations.

Mass transport of a Ag thin film on a stepped Si(111) surface

The mass transport of Ag on stepped Si(111) surfaces was investigated by a scanning Auger microscope (SAM). A highly anisotropic surface diffusion of Ag ultra-thin films was observed on 0°, 0.5°, 3° and 6° vicinal Si(111). The mass transport parallel to the step edge is overwhelmingly greater than that perpendicular to the edge. The preferential mass transport toward the cathode due to DC current heating was also observed. This increased with the resistivity of the Si(111) substrate. The anisotropic mass transport is correlated with the difference of the binding energies at the step edge sites and at the terrace sites.

7402. Growth of ultrathin Au and Ag films on a modified Ru surface: H Blud et al, Vacuum, 41, 1990, 1106–1108

7402. Growth of ultrathin Au and Ag films on a modified Ru surface: H Blud et al, Vacuum, 41, 1990, 1106–1108

Growth of ultrathin Au and Ag films on a modified Ru surface

Using TDS, LEED and AES we have studied the adsorption of Ag and Au on an oxygen precovered Ru(001) surface in comparison with the growth mechanisms of these adsorbates on the non-modified substrate. Oxygen desorbs from Ru at higher temperatures than Ag and causes even the smallest detectable Ag coverage to sublimate like bulk silver (in contrast to the layer-by-layer growth on pure Ru). In turn, the TD-spectrum of Au is hardly affected because oxygen desorbs partially before gold. However, a quantitative analysis of AES intensities, taken at room temperature, as well as simple model calculations support a 3D island growth mode of Au on the oxygen precovered Ru surface as well.

Growth and thermal stability of Ag or Au films on Nb(110).

The growth and thermal stability of ultrathin (<50-A-thick) Ag and Au films on Nb(110) was investigated with use of photoemission spectroscopy and low-energy electron-diffraction (LEED) patterns. The LEED results show that Ag or Au forms a monolayer which is commensurate with the substrate, but also show that the structure of this overlayer reverts to a more close-packed structure after three monolayers (ML) have been deposited. Photoemission spectra show trends that suggest the evolution of the Ag or Au band structure with coverage and also show that a surface deposit of at least 2 ML of Ag or Au is required to observe valence-band states characteristic of the bulk metal. Further examination of the photoemission spectra suggests that the Ag or Au d-band states play only a small role in the chemical bonding that occurs between the noble metals and Nb(110), and this can be contrasted with the extensive d-band involvement in chemisorption bonds formed between Pd or Pt and Nb(110). Heating does not cause substantial change in the electric structure of 12.8-ML-thick Ag films and they thermally desorb from Nb when heated above 830 K. Similar Au films intermix with Nb to form a disordered surface phase when heated beyondmore » 750 K. Desorption or complete in-diffusion of Au occurs when the substrate is heated beyond 1100 K. Implications for the formation of strained surface layers and surface chemical properties of noble metals on Nb(110) are discussed.« less

Surface phonon dispersion of ultrathin epitaxial Ag films on Ni(100) and Cu(1OO) substrates

Inelastic scattering of electrons has been applied successfully to study the surface phonon dispersion of ultrathin (111) oriented Ag films epitaxially grown on Ni(100) and Cu(1OO) substrates. Films with thickness of 1, 2, 3 and 50 ML have been investigated. For Ag monolayers strong hybridization of the vertically polarized Ag adlayer mode with the substrate Rayleigh wave is observed. For the bi- and trilayer the influence of the substrate on the dispersion of the adlayer mode is only small; a good data fit is achieved utilizing bulk Ag force constants. The transition from two-dimensional to three-dimensional Ag which is realized for the 50 ML film is reflected in the dispersion curves.

Growth and electronic structure of ultra-thin Pd and Ag films on Al(111)

Pd and Ag films vapor-deposited onto Al(111) were studied by AES, LEED and angle-resolved UPS. Both metals grow in the Stranski-Krastanov mode. With the substrate at 520 K Ag grows epitaxially. For Pd no ordered structures were found in the monolayer region. For Ag mainly two bands were found for the 4d states showing a maximum dispersion of 0.4 eV and a splitting into three bands in the outer parts of the two-dimensional Brillouin zone. In the monolayer the Pd4d emission lies 4 eV below the Fermi edge, which means that it maintains its atomic 4d 105s 0 configuration.

Growth and electronic structure of ultra-thin Pd and Ag films on Al(111)

Abstract Pd and Ag films vapor-deposited onto Al(111) were studied by AES, LEED and angle-resolved UPS. Both metals grow in the Stranski-Krastanov mode. With the substrate at 520 K Ag grows epitaxially. For Pd no ordered structures were found in the monolayer region. For Ag mainly two bands were found for the 4d states showing a maximum dispersion of 0.4 eV and a splitting into three bands in the outer parts of the two-dimensional Brillouin zone. In the monolayer the Pd4d emission lies 4 eV below the Fermi edge, which means that it maintains its atomic 4d 10 5s 0 configuration.

Investigation of ultra-thin Ag films on Ni with the photoelectron emission microscope

In combination with an ultra-high vacuum system the photoelectron emission microscope (PEEM) was used for observations of silver layers (thickness range between 0.01 and 2.5 nm) deposited on thermally recrystallized polycrystalline Ni substrates as well as Ni(100) and (111) surfaces. These investigations have proved the strong influence of thin surface coverages of metallic atoms on the photoelectron current; the high sensitivity can be explained to be due to changes in the work function as was previously done for gas adsorption on Ni. Here also qualitative information is obtained about the initial steps of Ag surface diffusion induced by both thermal treatment and interaction of the exciting photons with the specimen. Measurements of the photoelectron emission versus the Ag film thickness indicate a rapidly increasing intensity up to about 1 ML coverage, implying a decrease in the electron work function. In some respects PEEM imaging is complemented by AES and SAM as well as by TEM surface imaging, giving some insight into the observed strong PEEM orientation contrast and the morphology of the Ag coverages.

The adsorption of Ag on the Si(111) 7×7 surface at room temperature studied by medium energy ion scattering, LEED and AES

We have studied the morphology and reactivity of ultrathin Ag films deposited on the Si(111) 7×7 surface at room temperature, employing the high depth resolution of Medium Energy Ion Scattering. In addition, LEED and AES measurements have been made. For coverages from zero to 5×10 14 Ag atoms cm −2 we have observed the formation of a two-dimensional Ag layer, followed by the nucleation and growth of three-dimensional Ag islands for higher coverages (Stranski-Krastanov growth mode). Detailed analysis of the measured peak shapes in the energy spectra shows the presence of very high densities (≈ 10 12 cm −2) of islands with height to width ratios less than 0.2. For the coverage range studied (zero to 1 × 10 16 Ag atoms cm −2), the number of Si atoms, displaced from lattice sites does not increase above the value for the clean Si(111) 7×7 surface. This shows that no substantial mixing of Ag and Si occurs. The crystallographic relation between the Ag(111) crystallites and the Si substrate has been determined from LEED and Ion Blocking measurements, showing that part of the Ag crystallites have a preferential orientation, 180° rotated around the surface normal, with respect to that of the underlying substrate.

Electrical, optical, and structural properties of semitransparent metallic layers

Electrical, optical, and structural properties of ultrathin films of Ag, Au, and Al were investigated. MOS solar cells were fabricated with Ag, and Au barrier metals on n-type and with Al barrier metal on p-type silicon. The short-circuit current density Jsc was measured as a function of the average metal layer thickness tm. The film structure was examined under a transmission electron miscroscope. The optical transmittance T was measured as a function of the wavelength λ with tm as a parameter. The transmission electromicrographs indicated that, in the Ag and Au case, the film network structure attained electrical continuity at a lower value of tm than in the case of Al. Also, in the Ag and Au case, surface covered by the film was lower. Largely due to this, optical transmittance was higher in the Ag and Au case than in the case of Al. The T(λ) characteristics exhibited strong features in the Ag and Au case but not in the Al case. The profiles of Jsc(tm) were found to be peaked with the maximum occuring around 55 Å for Ag and Au and around 70 Å for Al. Furthermore, the peaks were sharp in the Al case, but were broad in the Ag and Au case. Also, the peak values were larger in the Ag and Au case. The higher rate of degradation of Ag and Au MOS cells than Al MOS cells can be related to the presence of large discontinuity in Ag and Au films.

On the mechanism of degradation in Si/SiOx/Ag metal oxide semiconductor solar cells

The mechanism of degradation in metal oxide semiconductor solar cells with Ag as the barrier metal has been investigated. Si/SiOx /Ag cells were fabricated with different oxide thicknesses but with no protective or antireflection coating. These cells were aged in the atmosphere and their current-voltage and capacitance-voltage characteristics were monitored. These electrical measurements and transmission electron micrographs of the ultrathin Ag films indicate the following mechanisms to be responsible for degradation. The ultrathin Ag films are discontinuous and consist of interconnected islands. Lateral migration of Ag takes place as the cells age, leading to disruption of interconnections between the islands. Consequently, the active area of the cell decreases and the series resistance increases resulting in poorer fill factor and a decrease in the short-circuit current. Ag may also be diffusing to the interface, creating interface states, which may be contributing to the reduction in open-circuit voltage. Oxygen/water vapor also diffuses to the interface, as the cells age, leading to a growth of the interfacial oxide layer. If the initial oxide is thinner than the optimal, the open-circuit voltage will increase; however, when the oxide becomes thicker, drastic photocurrent suppression will occur with a simultaneous decrease in fill factor and open-circuit voltage.

Optical properties of ultrathin Ag films

Reflection and transmission measurements from 1.8 to 4.4 eV have been made on evaporated Ag films with mass thicknesses less than 8 nm on fused silica substrates. The data were analyzed using approximative techniques. The results are discussed in terms of both the Maxwell–Garnett theory and the two-dimensional sphere model. Results indicate that the properties of specially heat-treated films are predicted very closely by the Maxwell–Garnett theory.

Optical properties of ultrathin ag films

Optical properties of ultrathin ag films