Bogdan Palosz

1
Institute of High Pressure Physics Polish Academy
of Sciences Warsaw, Poland
Bogdan Palosz
diffraction studies of nano-crystalline
diamond in real and spaces
reciprocal
American Crystallograhic Association, Honolulu,
Hawaii, July 22-26 2006. Session PDF Analysis
of Industrially Relevant Materials
2
Diffraction studies of nanocrystalline diamond
and SiC in real and reciprocal spaces B.Palosz,
E.Grzanka, S.Stelmakh, W.Zerda, C.Pantea,
Th.Proffen, W.Palosz Institute of High Pressure
Physics, Polish Academy of Sciences, Warsaw,
Poland Nanocrystals have a non-uniform
structure, where the arrangement of atoms in the
grain interior (the core) is different than that
at the surface (the surface shell). This
difference may be very small and missed in a
conventional diffraction experiment. We show
that the key in a quantitative characterization
of the atomic structure of nanocrystals is
acquiring a diffraction data in a very large
range of the reciprocal space (gtQ 20-30 Å-1),
what requires high energy X-rays or hot neutrons.
Only such data can provide the accuracy needed
for a meaningful description of the atomic
structure of nano-grains. It concerns the
analysis in real (Bragg) as well as in reciprocal
spaces (PDF). With application of very large-Q
neutron diffraction at LANSCE (HIPPO and NPDF
stations, Q up to 50Å-1) we were able to examine
distribution of strains in nano- diamond and SiC
as a function of the grain size, and trace their
evolution in nano-ceramics sintered under high
pressures. Also, using the Wilson method,
different atomic thermal vibrations of the inner
and surface atoms were evaluated. We thank
LANSCE for access to beamlines HIPPO and NPDF.
This research is supported by the Polish Ministry
of Education and Science, grant 3 T08A 020 29,
and NSF grant DMR 0502136.
3
reciprocal versus real space analysis (PDF)
do we see the same ?
application to nano-crystalline diamond
4
PDF
Bragg
Bragg ?
Bragg ?!
5
relationship between

reciprocal space
real space
?
?
?
unit cell
inter-atomic distances
coherent scattering ONLY ! information on
long-range atomic order
total scattering total structural
information
6
crystal structures of diamond and graphite
reciprocal space
real space
ao 3.5667 Å
ao 2.456 Å
co 6.696 Å
unit cell diagonal cross-section
7
tentative model of nano-diamond, UDD
8
specific
how much of crystalline diamond is in
nano-diamond ?
1
questions
what is the specific atomic structure of the
diamond lattice in nano-diamond ?
2
4
in which form is non-diamond carbon present in
nano-diamond ?
what are the characteristic dimensions of
nano-diamond ?
3
9

• outline
• Experimental method large-Q powder neutron
  diffraction, NPDF
• The examined materials nano-diamond UD90
  UD96
• annealed up to 1200oC
• Bragg scattering reciprocal space
• - phase composition
• lattice parameters
• PDF analysis real space
• - phase composition
• interatomic bonds
• Result a tentative model of a nano-diamond NEW
  !

10
the experimental method neutron powder
diffraction (NPDF and HIPPO, LANL at LANSCE, Los
Alamos) reciprocal versus real space analysis
11
structural information contained in a
diffraction pattern
12
?
?
the effect of annealing of nano-crystalline
diamond on its atomic structure
300, 600, 800, 1000, 1200oC
?
UD90 UD96
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TEMs of nano-diamond UD90
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TEMs of nano-diamond UD96
15
reciprocal space phase analysis
phase composition of nano-diamond the diamond
but also non-diamond carbon graphite-like
? gas-like ? other ?
16
neutron powder diffraction patterns of
nano-diamond UD90
NPDF, LANSCE, Los Alamos
calculated pattern
graphite does not appear even at 1200oC
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neutron powder diffraction patterns of
nano-diamond UD96
NPDF, LANSCE, Los Alamos
calculated pattern
graphite appears as a phase only at 1200oC
18
non-diamond carbon
after annealing at 1200oC there is an increase of
Bragg-to-diffuse scattering ratio the
difference corresponds to approximately 3 wt. of
non-diamond non-crystalline carbon in the sample
19
non-diamond carbon
after annealing at 1200oC there is an increase of
Bragg-to-diffuse scattering ratio the
difference corresponds to approximately 8 wt. of
non-diamond non-crystalline carbon in the sample
20
?
the atomic structure of the core of
nano-diamond is it a small single crystal ?
?
21
the dimension of a diamond nano-crystal
is only several times larger than that of the
unit cell
22
limitations of the Bragg equation for
nanocrystalline materials
23
experimental apparent lattice parameters alp-Q
dependencies of nano-diamond powders annealed up
to 1200oC
UD90
UD96
Q lt 15Å
24
diamond
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theoretical alp-Q dependencies of 5 nm
nano-diamond crystals with a tensile strain in
the surface shell
a0T 2.5183 Å (0.9985 a0D) c0T 2.0644 Å
(1.0040 c0D) c0 a0 1.004
Q lt 15Å
30 vol. atoms in the surface shell !
26
theoretical alp-Q dependencies of 5 nm
nano-diamond crystals with a compressive strain
in the surface shell
Q gt 15Å
alp refined
27
evolution of nano-diamond lattice in the grain
core
upon annealing
c/a
c/a
c
c
a
a
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experimental alp-Q dependencies of 5 nm
nano-diamond powders
UD90
Q gt 15Å
4 GPa
Cu
Mo
at very large Q the measured alp values tend to
match the lattice parameter in the core of the
nano-diamond particle
29
experimental alp-Q dependencies of 5 nm
nano-diamond powders
Q gt 15Å
UD96
1 GPa
Cu
Mo
at very large Q the measured alp values tend to
match the lattice parameter in the core of the
nano-diamond particle
30
lattice parameter of the core of nano-diamond
crystal
(model)
c/a
cT
Qlt15Å-1
aT
Qgt15Å-1
acubic
31
?
?
real space phase analysis inter-atomic
distances ? (sp3 and sp2 bonds)
?
32
sp2
real-space phase analysis of nano-diamond
r4
r5
inter-plane, graphite
8
UD90
15
UD96
no indication of presence of sp2 bonds in the
samples annealed below 1200oC
33
?
the atomic structure of nano-diamond how does
it look like in real space ?
?
34
Experimental evolution of inter-atomic distances
in nano-diamond upon annealing
inter-lattice
intra-lattice
inter-lattice
intra-lattice
35
(no direct) correlation between description of
nano-diamond in reciprocal and real spaces
36
?
atomic model of nano-diamond ?
?
37
core-shell model of nano-diamond
the outer shell non-diamond, non-graphite
transforms from sp3 to sp2 at about
1200oC the shell with compressve
strain the core either under
compressive or a tensile strain
38
specific
how much of crystalline diamond is in
nano-diamond ?
1
questions
90 inner core diamond strained surface shell
(1 3)
what is the specific atomic structure of the
diamond lattice in nano-diamond ?
2
4
core shell structure with compressed (3)
surface deformed cubic lattice
what are the characteristic dimensions of
nano-diamond ?
in which form is non-diamond carbon present in
nano-diamond ?
3
core (? 4 nm) and surface shell (0.3 nm)
gas-like carbon with sp3 bonds sp2- bonds at
1200oC (graphite?)
39
Collaboration
E. Grzanka1, S. Stelmakh1, S.Gierlotka1 C.
Pantea2, Th. Proffen2, T.W. Zerda3, W. Palosz4
1Institute of High Pressure Physics, Polish
Academy of Sciences, Warsaw, Poland 2LANSCE at
LANL, Los Alamos, USA 3TCU, Physics Department,
Forth Worth, Texas, USA 4BAE Systems, NASA/MSFC,
Huntsville, Alabama, USA