Supplementary Information
Title: Physical assembly of Ag nanocrystals on enclosed surfaces in
monocrystalline Si
Michael S. Martin1, N. David Theodore2, Chao-Chen Wei3, and Lin Shao1,2*
1
Department of Nuclear Engineering, Texas A&M University, College Station, TX
77843
2
CHD-Fab, Freescale Semiconductor, Inc., Chandler, AZ 85224
3
Materials Science and Engineering Program, Texas A&M University, College
Station, TX 77843
*Correspondence to: lshao@tamu.edu
1
Supplementary Information:
Direct evidence of the 4:3 co-incident site lattice relationship between
Si(111) and Ag(111) is shown in Fig. S1. The nanocrystals are observed in a
specimen fabricated by irradiation with 5×1015/cm2 100 keV He ions, annealing for
60 minutes at 950°C in flowing UHP Ar gas, deposition of 100 nm Ag, and heat
treatment for one hour at 750°C in flowing UHP Ar gas. This specimen is also
displayed in Figs. 1f, 2d and 3. A nanocrystals with side lengths ~15 nm is imaged
near the [110] zone axis in Fig. S1a, and the portion in the white box is shown in
greater detail in Fig. S1b. Silver and silicon lattice planes in the nanocrystal are
marked by orange and red lines, respectively. Yellow dashed lines parallel to Ag
lattice planes (orange lines) extend to show the mis-alignment with Si lattice planes
(red lines). There are roughly three Si atomic plane spacings for every four Ag
atomic plane spacings.
Investigation of dislocations by TEM in three samples is shown in Fig. S2.
The investigated samples are prepared with varying defect annealing times at
950°C, 30, 60, and 90 minutes for a, b, and c, respectively, with fixed diffusion heat
treatment of one hour at 750°C. The total length of dislocations decreases with
increasing defect annealing. In the three samples shown in Fig. S2, trapped Ag
concentration increases from S2a to b before falling off precipitously in c,
according to Fig. 2e. The remaining small amount of trapped Ag in Fig. S2c appears
to be trapped in small nanoparticle clusters around dislocations or dislocation loops.
Additional investigation will be undertaken in the future in order to determine the
kinetics of Ag nanocrystal dissolution.
2
Fig. S1: Heteroepitaxial relationship between Si and Ag (111) atomic
planes. a Ag nanocrystal embedded in Si with b top corner showing four
atomic planes of Ag are aligned with three atomic planes of Si.
3
Fig. S2: A few areas of strain contrast indicating dislocations in the
region containing voids/nanocrystals. Samples prepared by void
formation annealing for a 30, b 60, or c 90 minutes at 950C and
diffusion heat treatment at 750C for one hour. Fewer dislocations are
observed with increasing void formation annealing time. In c, small
nanoparticles are clustered around some of the remaining dislocations.
4
Fig. S3 shows TEM and electron diffraction investigation of a large Ag
nanocrystal. The specimen was fabricated by 100 keV He ion irradiation to fluence
5×1015/cm2, followed by annealing at 950°C for 3.5 hours, followed by 100 nm Ag
film by physical vapor deposition, followed by diffusion heat treatment at 750°C
for two hours.
The striking double diffraction patterns in Fig. S2 show that Ag and Si exist
in their pure forms, and measured atomic spacings are within a few percent of
tabulated values. All observed planes of Ag and Si are parallel with the exception of
the Ag (100) atomic planes shown in Fig. S3c and d, which indicate the Ag unit cell
is slightly non-cubic. This figure is included because the slight increase in size
(from ~20 nm side lenghts in Figs. 3 and 4 to ~35 nm side lengths in Fig. S3)
roughly quintuples the volume of the nanocrystal, meaning there are a sufficient
number of Ag atoms to obtain a diffraction pattern from a low-index zone axis. The
authors refrain from drawing any conclusions from this isolated specimen other
than the inference that parallel Moire interference observed in Figs. 3 and 4 (of the
main article) sufficiently demonstrate that pure fcc Ag exists and that no Ag-Si
compounds are formed.
Figure S4 shows the portion of micrograph in Fig. S3c marked with white
dashed lines that has been Fourier filtered to show Moire interference fringe. The
observed fringe spacing of 5.6 agrees well with calculated fringe spacing for
parallel Si and Ag (110) atomic planes.
5
Fig. S3: a High-resolution transmission electron micrograph and b
diffraction pattern obtained with the electron beam along the [011]
zone axis, and c and d are of the same nanoparticle along the [100]
zone axis. Diffraction patterns b and d have brightness, contrast and
gamma slightly increased (to 0.55 or less from 0.50) to enhance lowintensity reflections. Dashed and solid circles indicate reflections
from Si and Ag, respectively, and yellow, red and blue indicate
reflections of (100), (110) and (111) families of planes, respectively,
in b and d.
6
Figure S4: Portion of high-resolution micrograph in Fig. S3c,
outlined by white dashed lines, filtered by Fourier transformation
and masking, showing interference fringes of Si and Ag(110) planes
with a spacing of 5.6 Å.
7