Metal-insulator thin films have been studied for making self-patterning nano-templates and for controlling attachment strength on template surfaces. These films can form a phase segregated structure where the metal separates into independent, - PowerPoint PPT Presentation

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Metal-insulator thin films have been studied for making self-patterning nano-templates and for controlling attachment strength on template surfaces. These films can form a phase segregated structure where the metal separates into independent,

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Dependence of Crystal Orientation on Composition in Silver-Silicon Composite Thin Films Don Carlson, Dana Filoti, Amanda Brown, James M.E. Harper – PowerPoint PPT presentation

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Title: Metal-insulator thin films have been studied for making self-patterning nano-templates and for controlling attachment strength on template surfaces. These films can form a phase segregated structure where the metal separates into independent,


1
Dependence of Crystal Orientation on
Composition in Silver-Silicon Composite Thin
Films Don Carlson, Dana Filoti, Amanda Brown,
James M.E. Harper
Resistivity A plot of film resistivity versus
composition shows that between 46 and 64
silicon there is an exponential rise in
resistivity. This indicates tunneling conduction
with the silver no longer interconnected at these
compositions. This exponential increase in
resistivity is evidence of phase segregation and
shows that the silver is forming independent
islands in the insulating silicon. Electron
Microscopy Transmission electron microscopy
(TEM) offers a direct look at this behavior. The
TEM images below show films with increasing
silicon from left to right. The silver (dark
spots) loses its interconnectedness and forms
small independent regions, showing a change to
more distinct silver segregation. This is
consistent with the exponential rise in
resistivity from 46 to 64. The TEM images also
show that with increasing silicon, the silver
regions become smaller.
INTRODUCTION
RESULTS
Metal-insulator thin films have been studied for
making self-patterning nano-templates and for
controlling attachment strength on template
surfaces. These films can form a phase segregated
structure where the metal separates into
independent, non-adjoining regions within the
insulator. X-ray diffraction pole figure
analysis of these composite films has suggested
that the texture quality of the film
microstructure varies with changes in the ratio
of insulator to metal. This study examines
silver-silicon thin films to verify phase
segregation and to track the changes in
microstructural silver crystal orientation over a
range of silicon/silver compositional ratios.
EXPERIMENTAL METHODS
A dual source magnetron sputtering system was
used to deposit silver and silicon onto a
stationary substrate. Variations in deposition
rate due to distance from the sources created a
compositional gradient across the substrate.

XRD/Pole Figure Analysis XRD measurements of
films with compositions ranging from 20-80
silicon confirmed the presence of crystalline
silver with 111 planes producing the most intense
diffraction peak. Pole figure analysis of the 111
diffraction peak shows that for films mostly
composed of silver (lt 35 Si) the 111 planes are
consistently oriented parallel to the substrate
surface (intense peak at the center of the polar
pole figure plot). However, for increasingly
higher percentages of silicon, the orientation
becomes more random. This is likely due to
smaller islands of phase segregated silver buried
in the amorphous silicon. Without access to the
substrate surface, they have no preferred
orientation. This loss of consistent texture
between 37 and 47 is supported by the
resistivity measurements and TEM images covering
the same compositional region.
The completed films were analyzed using three
methods
  • The resistivity of the composite film was
    measured at 2 mm intervals along the substrate
    using a 4-point probe, and film composition was
    calculated from the thicknesses of separate
    silver and silicon calibration films. An
    exponential rise in resistivity versus
    composition indicates tunneling conduction.
  • Electron Microscopy provided a picture of how the
    silver was distributed through the silicon
    insulator.
  • X-ray diffraction (XRD)/pole figure analysis was
    used to study the crystal structure of the
    composite films. XRD identifies any crystalline
    substance in the film while pole figure analysis
    of a diffraction peak is used to measure the
    orientation of the associated crystal planes with
    respect to the substrate. Sputter deposited
    poly-crystalline silver films typically form with
    their 111 planes parallel to the substrate. This
    consistent orientation shows up as an intense
    peak on a pole figure plot. If the silver
    crystallites have a random orientation, then the
    pole figure plot would be fairly homogenous with
    no strong peaks.

CONCLUSION
Measurement of resistivity and electron
microscopy images are both used to confirm phase
segregation and the formation of independent
metal islands in metal-insulator composite thin
films. Measurements of polycrystalline
orientation using pole figure analysis has shown
that it can identify the same behavior. In the
silver-silicon films studied, resistivity
measurement showed independent silver islands
forming at 46 silicon and TEM images showed
increasingly distinct silver segregation for
compositions above 35 Si. Pole figure analysis
agreed with these results by suggesting island
formation between 37 and 47 Si. Use of
resistivity to measure phase segregation only
works with metal-insulator films. Pole figure
analysis could potentially verify phase
segregation and island formation in metal-metal
composite films. Since each crystalline material
would have a unique diffraction signature, pole
figure analysis could be used to measure the
polycrystalline orientation of each component
individually. This is an avenue for further
study on the use of pole figure analysis for
composite film characterization.
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