1. The document discusses using computational sciences to identify promising subspaces within the large design space of designer materials that exhibit rich phenomena. 2. It proposes researching nanolayered composites containing a large volume fraction of interfaces that act as obstacles to radiation-induced defects. 3. The research aims to provide insight into the morphological stability and radiation damage tolerance of these materials compared to bulk materials.

1. Enabling designer materials using computational sciences
Kedarnath Kolluri, Ph.D. UMass, Amherst
Small Scale Mechanical Behavior 1130
temperature by 33 keV He+ ions with a dose of 6 · 1016/
X. Zhang et al. / Nucl. Instr. and Meth. in Phys. Res. B 261 (2007) 1129–1132
were simulated. Case 1 represents ion-irradiation experi-
Research Summary
The Radiation Damage Tolerance National Lab, NM 87545
cm2 (referred to as case 2 hereafter), whereas annealed ments performed recently in Cu/Nb multilayers [23]. The
1 mm thick Cu sheet, Cu 2.5 nm/Nb 2.5 nm (referred to simulation parameters for case 2 and 3 are used for current
Los Alamos
as Cu/Nb 2.5 nm hereafter) and Cu/Nb 100 nm multilayers experiments. Fig. 1 shows the variation of He concentra-
with a total film thickness of around 500–600 nm were tion versus implantation depth. The peak He concentration
implanted by 150 keV He+ ions with a dose of 1 · 1017/ for the first case is about three times higher than that of the
cm2 (referred to as case 3 hereafter). Evolution of micro- other two cases. The simulation shows that implantation in
of Ultra-High Strength Nanolayered
structures before and after ion-irradiation was examined the last two cases will produce similar peak He concentra-
by cross-section transmission electron microscopy tion. The peak He concentration occurs much deeper under
(XTEM). TEM and high-resolution TEM (HRTEM) were film surface, 425 nm, at 150 keV, compared to approxi-
performed on a JEOL 3000F microscopes operated at mately 150 nm under surface for He ion-irradiated at
300 kV. 33 keV. Implantation of the first two cases will generate
Composites*
Bottom line Experience and expertise Proposed research
He peak concentration at similar depth under film surface
due to the usage of same implantation energy (33 keV).
F7∕2 ðCe3þ Þ and I ðHo Þ þ F ðCe Þ → 5 I7 ðHo3þ Þþ
2
3. Results and discussions 5 3þ 2 3þ
XTEM reveals radiation induced He bubbles and inter-
stitial 6 5∕2
loops in Cu thin sheet irradiated in case3, as shown
2
F multilayer films Þ a(38). layerThe as-synthesized NaYF : Yb/Ce/Ho
formed on Cu/Nb7∕2 ðCe
3þ
SRIM calculation of He ion-irradiation has been per-
with nominal in Fig. 2(a). These types of defects are typical in ion-irradi-
4
ated bulk fcc Cu. He bubbles with diameter on the order of
(20∕11∕2 mol%) spherical NCs (Fig. 1C) and hexagonal nano-
thickness of 80 nm each layer. Three ion-irradiation cases
• Designer materials exhibit very rich phenomena(Fig. 1L) display predominantly red emission under plates 16
2–3 nm were observed in 500 nm thick Cu films irradiated
in case 2, as shown in Fig. 2(b). Theoretical calculations
of contrast from cavities and gas bubbles have been carried Structure-transport relationships Superionic conductors for solid oxide fuel cells
A. Misra, M.J. Demkowicz, X. Zhang and excitation although the total intensity of emission is much
980 nm R.G. Hoagland
He concentration (1021ions/cm3)
33keV
17
1.5 x10 /cm
2 out by a number of researchers [24–26]. Experimentally
12 small cavities and gas bubbles are easily visible with the
• But the design space is large
images slightly out of focus and under kinematical diffrac-
weaker than other UCNPs (SI Appendix: Fig. S15). Powder XRD 8
33keV tion conditions. Generally in an underfocus condition the e- e-
patterns confirm that both samples are of pure hexagonal phase
16
6 x10 /cm
2
150keV cavities or gas bubbles is bright relative to background
1017/cm2
KEDARNATH KOLLURI AND MICHAEL J. DEMKOWICZ PHYSICAL REVIEW B 85, 205416 (2012)
Ea
and the image has a dark rim [26,27], as shown in
(SI Appendix: Figs. S16 and S17). The systematic peak shifts to
Fig. 2(b). The reverse is true of an overfocus condition
• We will identify most promising sub-space lower angles compared sinks forstandard XRD KEDARNATHof copper and niobium led
4
Interfaces act as obstacles to slip using computationalto the radia-
interfaces are to act as sciences and single-layer
pattern KOLLURI AND MICHAEL J. DEMKOWICZ
when the void is a dark image with a faint bright rim.
PHYSICAL REVIEW B 85, 205416 (2012)
For all TEM studies in this research, both underfocus O2-
O 2-
e- e- O2- e- e- O2- O2- O2-
one in the negative direction and the other in the positive
and overfocus conditions have been examined, but only To better understand the origin of this temperature de- O2- e- e-
0
0 200 400 600 800 O2- 64 e- e- O2- O2- O2-
β-NaYF4 imply the partial substitution of Y to considerable insight into the morpho-
tion-induced defects. Studies conducted ions by larger
underfocus conditions are presented in this paper. We also
and sinks for radiation-induced defects. Depth (nm)
L
3þ
direction. The number of distinct end states is also listed in
examined the microstructure of Cu/Nb 100 nm multilayers pendence, we revisit harmonic TST. In 2- formalism, the
O this e- e- e- e- O2- O2- O2-
Enhanced properties by tuning materials structure onein the negative direction and the other in the positive To better understand the origin of this temperature de- O2- O2-
Ce3þ ions in the REPORTS β-NaYF lattice (Y , r ¼ logical stability of of distinct end states2is also listed inTable I. The ratesrevisit harmonictransitions this formalism, the initial state (A) is Oxygen from2-the final state -by- a unique Oxygen
1.159 Å; Ce3þ ,number these nanolayered of individual are determined separated
(600 nm total film thickness) ion-irradiated in case 3, as
3þ
Hence, nanolayered composites that on sputter-deposited Cu-Nb multilayers
Fig. 1. SRIM calculations that simulate the variation of He concentration
Fuel Fuel O 2-
2- O2- O2-
Cathode
Cathode
shown in4Fig. 3(a). Magnified images of two boxes in 64 O 2-
e - e-
direction. The using the harmonic approximationTST. In
pendence, we
Anode
rate is given by e e
Anode
hypersurface (S) and the escape O
versus irradiation depth at various irradiation conditions. Case 1: 33 keV/
of transition state theory
r ¼ 1.283 Å) (39), which results in the expansion of the unit L1 I. cell.
O O2- O2-
1.5 · 1017/cm2; case 2: 33 keV/6 · 1016/cm2; case 3: 150 keV/1017/cm2. Fig. 3(a) are shown in Fig. 3(b) and (c). Region 1, close
contain a large volume fraction withdisplays a epitaxial growth of 3þ YSZ on top ofdiffers from previous reports whereTable theThe rates of individual transitions areastate theory(TST) due to Vineyard64act the escape rate final each transition
trolyte material. So far, yttria-stabilized zirconia thick STO films with YSZ layers of inter- 0.3905 (19) and 0.514 nm (20), respectively, the
(Y2O3)x(ZrO2)1–x (YSZ) is the material mostly nanoplates 1 nm (18). Figure nanoplates
thickness
This Ce the doping the STO
materials. Copper approximation of transition determined initial state (A) is separated from the is of state by a unique
lanthanide
using harmonic
and niobium have hypersurface (S) − E and
where the frequency
given by source
O2-
ES O
2- e- e- source
O2- e- e- O2- O2- O2-
Er between 62 and Tm 1A −
e2-
kB T SO kB T dS e- e- O2- e- e- O2- O2- O2-
used in SOFCs because of its mechanical sta- over an order of magnitude ensures a large, expansive strain in the thin YSZ
faces provide low-magnification (inset) and a high-resolution with large thick- positive due notof mixing, very limited Cu-Mo KS
(TST) heat
elements plane. Increasing the ionic radii (e.g., La3þ ¼ 1.300 Å) could to VineyardKS the frequency of each transitionis given by = ν0 e
Cu-Nb − kEactT
64
where kB T
. We assume Eν0 =Cu-V KSof −1
1ns for all = 2- E
O− A O .
2- e - e- (2) O 2-
e - e- O2- O2- O2-
bility, chemical compatibility with electrodes, and annular dark field (or Z-contrast) image of a layers of 7% in the ab the transitions in Table I, which allowsT us to determine the
− S 2π
increase in strength and enhanced radia-
high oxygen ionic conductivity. It is well known [YSZ1nm/STO10nm]9 superlattice (with nine ness of YSZ incorporated into the β-NaYF4 lattice (23). In given by
be (for constant STO thickness) results solid solubility,ν0 e B . no assume ν0 = 1ns for all oftemperature dependence of kB T effective migration rate, but(2)
is addition, = and We tendency to −1
= the S e kB dS
. AOe2- Electrolyte - -
kB T
dA
e e O 2- Electrolyte
e - e-
O2- O2- O2-
that doping ZrO2 with Y2O3 stabilizes the cubic repeats), showing the excellent crystalline quality in a loss of structural coherence, as reflected by a 2π
uniform undoped β-NaYF4 NRs can also be synthesized by thein Table I, whichK. Kolluri and M. J. Demkowicz, Phys. Rev. B., 82, T193404 (2010)
form intermetallic compounds. us to determine butnot the absolute value of the rate itself.kB dA
the transitions allows
Thus, rate, the
EA
−
fluorite structure of ZrO2 attion damage tolerance compared to bulk reduction of superlattice satellites in XRD. Elec-
room temperature and of the sample. The layers appear continuous and A e Here, the numerator is the configurational partition function
temperature dependence of the effective migration
present method (SI Appendix: Fig. S19).
supplies the oxygen vacancies responsible for flat over long lateral distances (a few microns). tron microscopy observations confirm that the
the interfaces between copper and nio- shown as partition function of the saddle-point hypersurface, while theelectrolyte
The results numerator is the configurationalthe black points
Here, the of our calculation are 85, 205416 (2012) Current: Bulk denominator is Future: Nano-structured electrolyte
the ionic conduction, resulting in high values Thepaper between the theand the YSZ release of strain results in a granular morphology,
materials.STO. interfaces shows STO experi-
This not the absolute value of the rate itself. Phys.line shows the temperature dependence the configurational partition function of the hyperspace (A)
Rev. B.,
der building up in of thetruly at the interfaces between temperatures nanorodsbe atomically flat. From the high- although the growth remains textured.composed of anisotropic NCs have attracted
Fig. 1. TEM images of the β-NaYF -based UCNPs. (A, D, G, J) NaYF : Yb/Er (20∕2 mol%) UCNPs. (B,Superlattices The results of our calculation are shown as the black pointsin Fig. 16(a). The gray hypersurface, while the denominator is
inate oxygen conductivity at high YSZ and Er are seen to Tm nanorods of the saddle-point
mentaltwo (C, L) atomistic modeling results Wegreat interest due to the rich phase behaviors and the Fig. 16(a).are gray line shows the temperature dependencethat would be expected had the effective defect migration rate corresponding to the initial state. For a system with N degrees
of and 4 E, H, K) NaYF : Yb/Tm (22∕0.2 mol%) UCNPs. (F, I) NaYF : Yb/
The experimental (5–7). A maximum Ho superposition UCNPs. 1 S = NaYF : Yb/Ce/Ho image it is possible to count the bars represent 100the lateral electrical conductivity
Our results indicate a (20∕2 mol%) (where parallel magnification (20∕11∕2 mol%) UCNPs. All scale
value of 0.1 S/cm 4 plotted nm.
4
bium layers The atomically sharp, with
in potential
4 4
the configurational partition function of the hyperspace (A)
TO/YSZ interface 1 A/V) at 1000°C is observed forbulk8and one at- number of unit cells of STO and YSZ, nomi- (real part s′) of the thinnest YSZ trilayer versus
contributions—one due to the the to 9 mole
ionic conductivity percent (mol the interface—and(2–4). A Cu-Nb nanolayered YSZ. Most impor- frequency inemergent collective properties (40). Here weno evidence of mixing. Furthermore,
tributable to %) yttria content the colossal ionic nally 25 of STO and 2 of composite
from a severe for a double logarithmic plot (Fig. 2). explore the beKOLLURI had the effective J. DEMKOWICZ ratebeencorresponding to the initial state. For a systemenergy event of freedom, the energy surfaces near the saddle point and initial
that would in- governed only by the highest activation with N degrees
ly because the first drawback toward shapesas implementation of are shown YSZ is perfectly the case with the The characteristic electrical Appendix: ionic S4). In addition, quan-
conductivity is observed and compositions tantly, the in Fig. 1. For coherent of
the final long as the interface from the TEM images (SI response of Fig. con-
triguing structural diversity of ordered nanocrystal assemblies
NaYF4 : that of the bulk. The the optimized of nanostructur- ductors (21–23) is observed based on inductively coupled plasma
to room temperature STO, in agreementcomposition for effi- titative elemental analyses in the figure. The long
Yb/Er (20∕2 mol%)-an roles with x-ray diffraction (XRD)
highlight
KEDARNATH
expected AND MICHAEL defect migration
boundaries rates obtained from
act PHYSICAL REVIEW B 85, kMC
initialAnalytical models of observed phenomena
= 0.4 eV). The migration rates obtained from 205416 (2012) states may be approximated with Taylor expansions in phase
been governed only by the highest activation energy event(Eeffof freedom, the energy surfaces near the saddle point and dip
unlike graineV). The migrationin single-ele- kMC dipbelow thismay be approximated high temperatures, indicating space, parametrized through modal coordinates qj and qj : Nano-structured materials for nuclear reactors
from the others as SOFCs is theis larger than
conductance relatively low 100 nm
trate. This scaling, ionic conductivity of this material, which imposes the morphologies of the UCNPs can layer range using spectrometry ofNRs and the the propor- -based UCNPs. We 0.55 negative direction and the other in the positive
act
(Eeff = 0.4 states simple prediction at with Taylor expansions in phase
ment in employ prediction at highinterfaces indicatingthat space,multiplicity of transitions occurring temperature de-
cient upconversion (36),
abrupt conductivity decrease when the thickness results (fig. S1), meaning that the ultrathin optical emission β-NaYF (ICP-OES) indicate β-NaYF Fig. 2. Underfocused XTEM micrograph of bulk Cu sheet ion-irradiated with He ions of 150 keV at a dose of 1 · 1017/cm2 (a), and 33 keV with a dose of
be temperatureslength to aNCs (Fig. 1A), to nanorods (NRs)c axis obtained from the of precursor in s′ versus elements into the
tuned most likely 800°Cscales grows rotated by 45° around the of
ing around due of YSZ and the response tional incorporationconductivity 4 the material is
from spherical
or sdc ionic
lanthanide
one polycrystals, Cu-Nb temperatures,
below the simple 0.5To parametrized through modal coordinates qj aand q :
the better understand the origin of this in
6 · 1016/cm2 (b). Vacancy clusters, interstitial loops and He bubbles were observed in (a) and mostly He bubbles with 2–3 nm in diameter were seen in (b).
4 this single
f the conductance rather high operational nm is
changes from 30 to 62 N
hows that Fig. 2. (1–4). Theinterface(Fig. 1D), toelectrolytes layers and strains to match the STO lattice. Because the frequency plots. Appendix: Table S2). By increasing the sodiumcan produce continuousmultiplicity of distinct end occurring also a singlemigration eventwe revisit harmonic TST. In this formalism, the
an (SI Zhang et. al,
interfacial assembly strategy that that the and
plateau found 64 j
1
Structural andYeinterfaceshas ion of the β-NaYF4 -based UCNPs. UCNPs X. In the presence of blocking effects
the large degraded search for alternative hexagonal nanoprisms (Fig. 1G), and finally to hex- final direction. The number of transitions states is in listed in 0.45 pendence, reduces the overall point defect migration rate.
optical al.,YSZ to
structure whencharacterization
et. the
collision STO and
Xingchen in reaching the conduc- by adjusting22430 (2010) YSZ are lanthanide ratio andnanocrystalfurther 0.5
areTable The rates constrained against
compositionally the overall point defect migration rate. reduction may is separated as a1 the final 2state by a unique
PNAS, 107, constants of cascades in due touniform the reaction time, hexagonal nanoplates (41). When 15 μL I.of hex- of individual transitions are determinedThis initial state (A)be representedfrom temperature-dependent EA ≈ E(A) + (2π νj )2 qj , 2
(3)
Downloaded from www.sciencemag.org on September 17, 2011
N
erostructures orig- not yet been successful nanoplates (Fig. 1J) bulk lattice the reaction time and/or
exceed the criticalagonal
thickness. to grain boundaries or electrodes, a superlattice films migration event reduces
0.45 2
(A) Powdervalue of 0.01 S/cm desired for room tem- 4 : Yb/Er (20∕2 mol%) UCNPs with an edge length of 133 Æ 5 Meth. thickness of 104 Æ 261 (2007)
XRD patterns of sodium to lanthanide trifluoroacetates. Powder X-ray with
of the NaYF Nucl. Inst. nm and Phys. Res. 8 nm 0.4 ≈ the escape rate νis)2 qj , by
EAandE(A) + (2π j given (3) j =1
tivity the ratiodesigning composite materials with high obtained (Fig. 1J and SI Appendix:aFig. S5). HRTEM image a migration.harmonic approximation of transition state theory hypersurface (S)
using reduction may
This the
ane solution of the β-NaYF4 NRs with an aspect ratio (AR) of be represented as a temperature-dependenteffective attempt frequency. 2
CHEMISTRY
different shapes. The peaks(XRD)indexedconfirm that all the NaYF4 : Yb/Er XRD
diffraction are patterns according to the standard are
perature operation (1–4). 0.4 N−1
garithm of the 64
(TST) due attempt frequency. the frequency of each transition
to Vineyard where
effective gly- 0.35 j =1 1
! E (eV)
pattern of β-NaYF4
f the trilayers (20∕2 radiation are of pure β-NaYF4 phase (Fig. correspond- from the is drop-cast onto its high crystallinity weakly polar Some nanolayered materials are
reductions in UCNPs damage tolerance.
mol%) number:
Only modest (JCPDS filethe operation 28-1192). Insets are the2A). The taken ∼1.4 edge region confirms the viscous and ethylene 0.35 act N−1 − ES ES ≈ E(S) + (2π νj )2 qj2 . (4)
E
−k T 0.3 1
e kB T dS2 2 2
mperature.ing geometricalofmodels.patterns of the be
The temperature SOFCs (500° to 700°C) can spherical NCs and the NRs exhibit en-
XRD (Fig. 2E). Although the present results do not rule out the pos-
(B) HRTEM image of(002)spherical whereas :a Yb/Er of col (EG) surface β) phase transition very earlyallowed to slowly given0.3and the solvent is is evaporate, ν0 e B . We assume ν0 = 1ns for all of
by = −1
ES ≈= E(S) B
k T S
+ (2π νj ) . j . (4)
anticipated with the recently (h00) as optimizeddiminished
hanced proposed well as a reflections NaYF4 sibility cubic to hexagonal (α → known to exhibit spheroidization upon 2
q (2) j =1
is 1 to 62 nm.
single crystal electrolytes such reversed trend image
(C) HRTEM observed INTRODUCTION
(20∕2 mol%) UCNP.as gadolinia-dopedis ceria andofinathe case 4of Yb/Er (20∕2 mol%) NR. the growth, no definitive superlattices comprised of monolayer and double-
NaYF : hexagonal nanoprisms during large-area NR signature of α phase is observed the transitions in Table I, which allows us to determine the 0.25
0.25
2π j =1 e− kEAT dA
B
700 nm thick HRTEM image of a NaYF : These the(20∕2 mol%) hexagonal nanoprism. the high reaction temperature (∼330 °C) favors the formation
lanthanum gallates and nanoplates. hand, results imply that the majority of spherical
(8–11). On the other and thermal annealing. Similarly, radiation rate, but 0.2
temperature dependence of the effective migration A
νj and νj are normal mode vibration frequencies about
layer domains are obtained depending on the concentration ofvalue of the rate itself. νj I ν are normal mode vibration frequencies about
I 0.15 andthe jnumerator is the configurational partition function the initial and the saddle points, respectively. The normal
(D) Yb/Er
one to two orders NCs and NRs4are lyingthe a preference for the [0001] direction 0.2
ame nominal of magnitude increase of with of β-NaYF4 UCNPs. not the absolute Here, Collision cascade Defect kinetics
(E) HRTEM image taken from the nano-glassof a NaYFof Yb/Er (20∕2 mol%) NaYF4 : Yb/Er (20∕2 mol%) UCNPs(Fig. 3 A and B). The NRs preferentially
The toperformance used for XRD while in The NRs in the dispersion exhibit intense up-
edge substrates 4 : materials may The0.15 of our geometrical arrange- points the the saddle-pointsaddle points, respectively. The normalis mode perpendicular to the saddle-point hypersurface has an
destroy the calculation are shown as the black
Downloaded from www.sciencemag.org on September 17, 2011
K conductance electrical conductivity reported (12–14) in the
(c-axis) parallel initial and the hypersurface, while the denominator
results of
hexagonal nanoplate. comparednanoprismsenvironments of emission spectra
rlattices as a as (F) Room temperature upconversion
crystalline samples hexagonal with single crys- nanoplates are generally sitting with
extreme as an and conversion luminescence under 980 nm excitation (Fig. 2F and
irradiation Appendix: Fig. S6). Three visible emission bands centered the substrate, mentFig. 16(a). The gray line shows the temperature dependence mode perpendicular partition function of the hyperspace an imaginary vibration frequency and is not part of the sum in
align with their c-axis parallel to at exhibiting both morphologies because
in of 0.1 layered 0.1
the configurational to the saddle-point hypersurface has (A) (picoseconds) (up to several years)
Dislocation model
corresponding to the initial state. For system of the b
nterfaces, ni. tals outlines the importance ofperpendicular to the substrates (similar trends are con-
processing SI
of the NaYF4 : route to the c-axisconductivity valuesNaYF4 : Yb/Tm (22∕0.2 mol%) UCNPs
alternative Yb/Erfirmed separately by TEM). High-resolution TEM (HRTEM) im-
increasing mol%) and
(20∕2 imaginary vibration frequency and is anot part with Nsum in Eq. (4). Therefore, only N − 1 degrees of freedom are taken
degrees
f the conduct- 525, 542, positional and orientation order on the scale of tens of0.05of expected had the effective defect migration rate
and temperature clear lattice fringes associated mol%) UCNPs.from H, K) NaYF : Yb/Tm (22∕0.2 mol%)and from I)the 4 F: Yb/
must be J)significantly and 655 nm are observed, attributable to the radiative that would be radiation-induced point
flow a micro-
thebeen governed only by the highest activationin CuNb
0.05
dispersed in the desiredFig. 1. TEMPhotographs of theUCNPs. (A, D, G, NaYFluminescence
nm] trilayers at toward hexane.levels. a single spherical NC shows upconversion : Yb/Er (20∕2 transitions (B, E, the (2 H
Inset: images of the β-NaYF -based
age of Because modern thin 11∕2 , S3∕2 ) (green)
4 UCNPs. (F, NaYF Point defect MEP energy event Eq. (4). Therefore, only N − 1 near the saddle pointare taken into account when computing the configurational partition
of0 freedom, the energy surfaces degrees of freedom and initial
Atomistics
film growth techniques allow a precise control of and (0001) crystalYb/Tm respectively scale barsexcited states nm. confirmed by the , respectively.
represent 100 to as 4 I
meters, the 15∕2 ground state of Er3þ sharp small-angle electron act into an interface changes its
diffraction
4 4 4 4
0
Error barsfrom the NaYF : Yb/Er (20∕2 mol%) ¯ to extend the planes, (22∕0.2 life-
improved(left) and NaYF4 : reliability, mol%) defects= 0.4 eV). The migration rates obtained from kMC dip into account when computing theTaylor expansions in phase function for the saddle point.
9∕2
are Ho (20∕2 mol%) UCNPs. (C, L) NaYF : Yb/Ce/Ho (20∕11∕2 mol%) UCNPs. All
4 with the ð10 10Þ, ¯ ð10 11Þ, 4 (red) (Eeff states may be approximated with configurational partition
ty of the con- layer thickness and morphology, they provide a corresponding to the (0001) planes ap-
(right) NR dispsersions under 980 fringes
(Fig. 2B). Lattice nm diode laser patterns (SAED). The striking in-plane ordering of the NR super-
The activator Yb 3þ , capable of absorbing the 980 nm near-infra-
time, al.spectra of the NaYF grow along thenuclear 3þ lattices is also revealed by the selected-area wide-angle electron0.1prediction at 0.4 0.5 0.6 its indicating 1 function 0.1 the saddle point. 0.5 as coordinates q0.9 (4), jthe When energies are expressed as in Eqs. (3) and (4), the
pathway for the production of the NRs, indicating that the excitation. (G) Room tem- light efficiently, transfers its energy sequentially to nearby
and efficiency of: Yb/Ho (20∕2 mol%)
solid electrolytes NRs future c-axis
pear along compositions are shown in Fig. 1. For the case of red the TEM images (SI Appendix: Fig. S4). In addition, quan-
shapes and from
perature upconversion emission Appendix: Fig. S2A). HRTEM analysis also re- Er through the 2 F ðYb3þ Þ → 4 I ðEr3þ Þ process, pumping
with optimized properties. Maier et found a
atomic this simple 0.2 0.3 perturbing 0.7 0.8 0.9
below configuration,
0 high temperatures, 0 for 0.2 0.3 0.4
space, parametrized through modal
When energies are expressed
0.6 0.7 0.8 j and q :
in Eqs. (3) and
1
that the multiplicity of transitions occurring in a single configurational integrals in Eq. (2) become
NaYF2CYb/Er conductivity
(Fig. 4 : and SI(20∕2 1
(20∕1 and BaF when the the reactor environments,
dc ionic
4
mol%)-an optimized composition for effi- titative elemental analyses based on inductively coupled plasma
and NaYFsuperlattices ofveals that the “cube-like”In morphologieshexane. hexagonal the Er3þ diffraction patterns (SAWED), whose spots are due to diffraction
substantial increase of thereactors.
: Yb/Ho cient upconversion (36), projections arein of the UCNPs can optical emission emitting levels. The multiphonon the propor-
mol%) UCNPs dispersed coming from Inset: Photo-
5∕2 11∕2
b image of the STO/YSZ interface of
to its spectrometry (ICP-OES) indicate relaxation shape from flat to the overall point Such
migration event reduces meandering.
s defect migration rate. configurational integrals in Eq. (2) 1 s become 2 2
N
 
of 4 CaF2 2 Fig. 1.rectangular f10 ¯ transmission electron microscopy (STEM)
(A) Z-contrast scanning side facets EA ≈ E(A) + (2π νj ) qj , (3)
of the individualdamage introducedfrom to9 nanorods (NRs) processesobtained in thethe different lanthanide elements into thehelp bridge precursor excited states of Er 3þ , giving
graphs thickness of the upconversion spherical NCsor 1nmin 10nm]the10g of4 radia-
prisms composed luminescence
of six square (Fig. 1A),
be tuned from decreased the [YSZ /STOthe form (with nine tional incorporation of VG Microscopes HB603U
superlattice (2008)repeats), of crystallographic lattice 59, 62 (2007)
NaYF : Yb/Ho undulations provide an opportunity for
planes. Specifically, the This reduction may be represented as a temperature-dependent
strong (002)  2 k T  E(S) N−1 1 kB T
emission peakset. al., JOM,
A. Misra (SI S2). Fig.
Modifications to existing models
E(S)
layers was
J. Garcia-Barriocanal et. al., microscope. the1G),arrowplanes the position riseYSZ distinct (SI Low-magnification image obtained S8). The NaYF4 :
belonging (Fig. 321, 676
Science,
down to 16 nm, assigned to hexagonal basesYb/Ho (20∕2 {0001} marks (center) the to layer. (Inset) Appendix: TableAppendix:increasing
(Fig. two a size effect due nanoprisms to A yellow and finally to hex-
with (Fig. 2D N−1=1j 1  kB T j =1 νj 2π  e B
−k T
(20∕2 mol%) nanoprism1D), to hexagonal:to The formationmol%)and hexagonal ofand UCNPs mol%) UCNPs obtainedBy arising the sodium anisotropic rod-shape of frequency.
final effective attempt −k T
B
(left), NaYFS2B). NR (5)
the space charge regions being smallerFig. the by the VG Microscopes HB501UX column. In both cases a whitediffraction growth direction. (B) EEL
agonaltion-induced in adjusting the reaction time and/or Yb/Er (20∕2 ratio and the reaction time, hexagonal from the
defects and980between the laser properties (Fig.the spots Appendix: Fig.size-dependent
helium from lanthanide indicates 2F and SI are display S9):nanoplates  kB T j =1 νj 2π  e =  − E(A) .
and SI Appendix: than4 1J) of NRs
adjacent nanometer-spaced interfaces to
B
nanoplates (Fig. to arrow = N−1
1  2 − E(A) . (5) 2π 1
For example,{0001} andspectradelicate the Oat different growth total an theof emission and the intensitynm of green to red
N kB T
NaYF4 : Yb/Ho (20∕1the16). Kosacki (right) dispersions underK edge obtainedX-ray STO unit cell at thelength of 133 (red5circles) and a thickness of 104 Æ 8the
mol%) NR et al. lanthanide showing interplay nm diode with
layer thickness (15, ratio of sodium tohave by a trifluoroacetates. Powder from the optical edge interface plane Æ nm and and their mutual alignment along the c-axis.
nanoprisms is determined Both nm ES ≈ 2π + 1 (2π νj )eqj2B.T e kB T
individual NCs 4.5 E(S) N kB T (4) j =1 νj 2π
reported enhancedgrowth rates in highly tex- into the STO layer (black squares). 4 : embrit- for the same positions,and SI Appendix: spectra
transmutation reactions results in where emission increase as NCs get larger. These relationships can be react and pinch off. Because the stability
High-capacity anodes for batteries
k
excitation. conductivity of f10 ¯ planes
diffraction (XRD) patterns confirm that all the NaYF (Inset) Ti L2,3 edges obtained (Fig. 1J same color code. All Fig.ratio HRTEM image
10g Yb/Er are intensity S5). j =1 νj 2 2π
tured thin films of YSZ withThis observation contrastsresult ofprevious four individual spectrataken from the edge region time of 3 s each. high crystallinity and simultaneous absence
Interestingly, the appearance of (h00)
stages. thicknesses between pure with studies j =1
60 and • nm, reaching 0.6 S/cm at 800°C (17). dimensional NRs exhibit en- ofemissionthat as the size of thedo not rule out the pos-
(20∕2 mol%) UCNPs are of are theβ-NaYFaveraging (Fig. 2A). The
4 phase at these positions, with an acquisition confirms its The terms in parentheses on the right-hand side of Eq. (5)
15 Particle shapeβ-NaYF4 NCs was upconversion(Fig. 2E). Although spectra
shape tlement the controls the instability
XRD patterns of the spherical NCs anddominated by control- ascribed to the fact the present resultsspots, together with the recognitionlayered structure relies upon the
evolution of and NCs decreases, surface of the that the The terms in parentheses on the right-hand side of Eq. (5)
ling thickness as therefore process (35). Furthermore, dynamic
film the Ostwald-ripening Fig. 2. (002) reflections whereas a
Because reducing hanced (h00)(and well as diminishedReal part of the lateral defects-ofof ligands-induced quenching of upconversion become
sibility and
(110) diffraction
cubic to hexagonal (α → β) phase transition very early ¯ νj and νj are effective attempt frequency ν . Simplifying together form the effective attempt frequency νo . Simplifying
together form the normal mode vibration frequencies about
reversed trend is observed electrical conductivity the fre- size of can important, whichdefinitive signature of α phase isthe f10 10g facets, planarity of the interfaces, such reactions
increasing the fraction of both near the in- in theprobe offuel versus nanoprisms
light scattering experiments that and the hydrodynamic
material structural case components.
hexagonal UCNPs more the growth, no4 NRs are enclosed by observed
during β-NaYF modifies the relative population among allow us to con- o Anode in its Anode in its
centration • Nanostructured ceramics conduct colossal amount of phonon-assistedions
but also the surface functionalities majority of spherical various high reaction temperatureoxygen the formation
of the expression, the attempt frequency is found to be indepen- this expression, the attempt frequency is found to be indepen-
this initial and the saddle points, respectively. The normal discharge state charge state
terface) produces such a noticeable NRs and hexagonal nanoprisms show results con-
the dispersed conductivity quency that trilayer with 1-nm-
and nanoplates. These results implyof the the and the excited states throughNRs arefavors nonradiative aligned along their f10 ¯
be an effective the NCs and of the largest with a upconversionloginplot. radia- β-NaYF4 UCNPs. the clude that (∼330 °C) azimuthally can destabilize the structure and trigger dent of temperature:
sistentTherefore, dimensions of a for the NCs direction relaxations (36). Therefore, engineering not only the dopant con-
interfaces NRs are lying the preference double luminescence.
ability to remove dent ofperpendicular to the saddle-point hypersurface has an
10g mode temperature:
enhancement, meanswith tuning thethick YSZ inindividual[0001]measured
themselves would of imaginary vibration frequency and is not part of the sum in
tion-inducedof the357 to 531 K. Theand control The NaYF4 : Yb/Er (20∕2 (SIdefects Fig. S22). The superlattice formation
seem to play a determining role in the to the glass substrates measured XRD while
outstand- Isotherms were used for the
To demonstrate the generality nanoplates are generally method and
(c-axis) parallel point synthesis solid crystal facets mol%)
defectsremove radiation-induced 980 UCNPs exhibit(Fig. 2F and Appendix: intense up- the onset of recrystallization. There is N−1 1 Low capacity
• Internalwww.pnas.org/cgi/doi/10.1073/pnas.1008958107trytrends aregrowth Appendix:luminescence under bynmthe in-plane, dense packing ofcompetition4between restoring forces
hexagonal nanoprisms and line trap and
ing conductivity properties observed.
2 of 6 ∣ interfaces represents a NCL contribution with conversion accounted for
further tailor the upconversion emissions, wea temperature- con-other
0
range of
To search for interface effects, we fabricated the substrates (similar several
the c-axis perpendicular to (s′ ~ nucleation and
helium 8 bubble Aw, where A is
sitting
SI
is excitation
Fig. S6). Three visible emission bands centered at
Ye et al. the β-NaYF
a the interac-
N−1 1
Eq. (4). Therefore, only νN −E(S)−E(A)
j =1 j −
into account when N 1 e kBthe = ν0 e B .
=
1 degrees of freedom are taken
E act
−k T
computing T configurational partition (6)
j =1 νj − E(S)−E(A)
= N 1 e kB T
= ν0 e
E
−k T
act
B . (6) C Li C6
firmed separately by TEM). High-resolution TEMand Yb/Ho/Ce 542, NRs, possessing a attributable to the radiative
and 655 nm are observed, hexagonal cross section and also
heterostructures where YSZ layers (with mol % j =1 νj Mechanically
dopant combinationsa including Yb/Tm,is the lattice fringes associated transitions from the (2 H , 4 S ) (green) and from the 4 F
dependentYb/Ho, (HRTEM) im-
proportionality factor 525, function for the saddle νj
j =1point.
Design space is huge for interfaces and particles
nominal yttria content) in the thickness range from to improving the mechani-
of are crucial NC shows acting adjacent the interface and the
to flatten stable
age PROGRESS w clear angular frequency),
single spherical and
ARTICLEthe tion of ligands, 3∕2 contributing to the 9∕2 attractions between When energies are expressed as in Eqs. (3) and (4), the
for the nm down to layers ofthesandwichedð10 ¯ and (0001)images Stars iden- NaYF4 : excited states to the 11∕2 ground state of Er3þ , respectively.
62
β-NaYF4 -based UCNPs. TEM crystaltext. of respectively (red)
1 nm were ¯ between
with insulating10Þ, (STO). as explained in the planes, 4
I15∕2 This expression is only valid if the saddle-point configuration This expression is only valid if the saddle-point configuration
Cathode
two 10-nm-thick cal propertiestifydifferentthe (0001) planes ap- are activator c 3þ , capable of absorbing the 980 nm near-infra-the explanation is the lateral
ð10 SrTiO 11Þ,
of irradiated metals. This NRs. Further evidence that supports undulations induced by rapid adsorption configurational integrals in Eq. (2) become
Anode
Yb/Tm (22∕0.2 mol%) alternating 10-nm- ty ofthe valueNRsmeasurements the c-axis The light efficiently, transfers its energy sequentially to nearby
(Fig. 2B). Lattice fringes correspondingof sdc. The uncertain- partition function has just one degree of freedom less than the partition function has just one degree of freedom less than the
3
Also, superlattices were grown, UCNPs with conductance morphologies to Yb High capacity
Structure the NRs, indicating that the Point defects along is displacement (a) 4 No helium bubbleslayers in the β-NaYF4 NR
between3þneighboring are   Li4.4 Si
pear along
challenge callsnSfor Surface coverage Fig.also re-(hex- through Figure ðYb3þ Þ → I ðEr Þ process, pumping
−2 novel approaches to
in de Física de Materiales and SI Universidad Fig. 1Eshown, see error bar).
(spherical NCs), the 0S2A). HRTEM analysis
0 1 (10
grow
shown0 Grupo Fig. 1B(Fig. 2C Complejos, Appendix: Fig. sampleS/cm in conductivity for 1H 0.53þ superlattices (SI 11∕2
(NRs),
red
Er the 2 F5∕2
1. of defects. initial state. In some cases, however, there mayE(S) additional initial state. In some cases, however, there may be additional
N−1 1 kB T be
Si
1
(patchiness)from1.4radiation Er3þ to detected in under-focused TEM image in
A Appendix: Fig. S23). Liquid crystalline order  kB T
−
modes that do not contributejtemperature-dependent terms to modes that do not contribute temperature-dependent terms to
2π  e kB T charge
1K square0.2 rectangular resisthexagonal processeshasitsbeen observed multiphononErrelaxation NR dispersions (42) and vacuum annealing stud-
agonalComplutense de Madrid, Madriddesigning materials that f10real part facets 0.45 Remarkably, =1 νj
28040, “cube-like”
nanoprisms), that theFig.ofNational projections are coming ¯ side respec-
veals and Spain. Materials
2
150 (hexagonal nanoplates), the emitting levels. The (5)
=  partition function, for  E(A) . when the the configurational partition function, for example, when the Mechanical
(Inset) Imaginary versus
0.2Science and Technology Division, Oak Ridge six
prisms composed 0.2 or
of the impedance (Nyquist)10g at
plots in concentrated
help bridgenm different excited states of 3þ ,multilayer
a 2.5 the layer thickness Cu-Nb giving the configurational 2π N 1 kB T example,
−k T nightmare
. The ADF image in theSuperior panel980withareaexcitation, these 511, and 531 K. Whereas1.2 (Fig. 2D
tively. Laboratory, Oakshows the 37831,hexagonal Universi-belonging to the {0001} high strength to distinctimplanted (SI Appendix: Fig. S8). The NaYF4 : (150
UponIngenieros TN Telecomunicaciones, bases 492, hexagonal planes UCNPs NRemission prepared by controlled evaporation (43,ies conducted on Cu-Nb nanolayered
Ridge, nm
twoused for EELS mapping maintaining phase
damage while e
3
USA. Escuela Técnica
saddle point contains rotations =1 translations not present in the saddle point contains rotations or translations not present in the
B
rise peaks j or νj
upper de
films 44) or by Lang-
0.4
de the at room temperature 2π
0.4dad Politécnica de Madrid,S12) emit brighthigh-frequency contribution is ahexagonalprocess characterized mol%) UCNPs obtained 0, the
green rectangle) in the [YSZ1nm/STO10nmand Madrid 28040, Spain. 100
]9 superlattice. The 0.4 S2B). The formation of NRs and Debye-like
SI Appendix:middle panel 0.4
Fig. Yb/Er (20∕2 by a conductivity exponent n = display 2size-dependent
(SI Appendix: Fig. image, showing the STO “grain boundary” term observed in the the 0.35 properties (Fig.from a Debye behavior, as Fig.). Here the have also employed polar-
*To nanoprisms toughness. Using 3 1 lumines- a clear deviation 2F and 1 Appendix: S9): Both we
with correspondence should be addressed. E-mail:
blue upconversion
acquired simultaneously whom the EEL spectrum andis determined by a delicate interplay between Nyquist plots shows muir-Blodgett assembly (45).Note that the
nanolayered
1 D → F andB 1 G →
optical keV helium, SI 1017/cm composites revealed their thermal sta- initial state. B¨ ttiker and Christen suggested that in some such initial state. B¨ ttiker and Christen suggested that in some such
u u
cases, the integration acrosson the right-hand be treated by (5) cases, the integration across the saddle cannot be treated by a
The terms in parentheses the saddle cannot side of Eq. a High capacity
(higher-intensity) layers. The lower from the Ti (red) {0001} thuliumbyplanes at different growth
cence jacsan@fis.ucm.es growththe trivalent(dark reflected the distorted impedance arcs. 4 0.3 intensitylayered morphology ratio wellstudy the ordering of NR films.
arising panel shows rates of 0.6 50 and f10 ¯ Aspect ratio 4
and Sr 0 total and the intensity is of preserved. Sandwiched
stages. metallic from contrasts with as
10g
are averaged composites previous studies where
2 model systems, izing emission get larger. These relationships canred
of
optical microscope togreen to be bility FIG. 16.no evidence between effective defect migration FIG. 16. (a)approximation,between effective defect migration
with (a) Comparison of spheroidiza- together form the effective in the usual case whereSimplifying Gaussian approximation, as in the usual case where the saddle
attempt frequency νo . the saddle
Transition between structures
0.6
several consecutive interfaces. These line traces This observationthe
0.6
Gaussian Comparison as discharge Si and Li4.4+ Si
emission increase as NCs
3
Hframed with the same color(Fig. for Ti, darkIn β-NaYF NCs was dominated 0.8 control- 0.25 to the fact that as the size of the(Fig. 3C image Appendix: Fig. S25) indicate 2
he insets, each 6 transitions shape (red 2F). of yellow for
code evolution the addition, predominantly green (b) High-resolution TEM and SI of a
ascribed Optical micrographs NCs decreases, surface this expression, the attempt frequency is found to be indepen- has positive curvatures in all directions not along the MEP. nc-Si Mechanical
by
this article highlightsthe hexagonal phase 2008 ligands-induced quenchingfrom 677
www.sciencemag.org SCIENCE tailoring1 the
4
how VOLdynamic AUGUST and Cu-Nb interface of upconversion become rates computed using kMC (black dots), a standard Arrhenius-typerates has positive curvatures in all directions not Arrhenius-type
tion up to 800°C. This finding formed computed using kMC (black dots), a standard along the MEP. stability possible
upconversion emissions are observed from Furthermore,
G Microscopes HB501UX.0.8 Because the STEM specimen was relatively thick
0.8
ling the Ostwald-ripening process (35). 0.8
he wide chemical interface profiles are most likely attributable 0 beam that probe the hydrodynamic size of
to
321 defects-
0.2 domains that are strongly birefringent due implanted region to the alignment ofonly the highest activation energy event (E act =
equation using
dent of temperature:of a saddle point in one direction act be Instead, the flatness of a saddle point in one direction can be
Instead, the flatness
equation using only the highest activation energy event (Eeff = can
the Appendix: Fig. S14) NaYF of the
1
length 1 and Yb/Ho (20∕2 show results con- 0.15 excited states through phonon-assisted nonradiative NR films isthe 0.4 eV, gray line),exploring the expression in Eq. (8) with a0.4 eV, gray line),aand the modified rate expression in Eq.accessible to modeled as a “translational” degree of freedom accessible to
light scattering experiments(layer thickness) and inter-
the dispersed NRs
scales 1
model of (SIYSZ/STO interface showing: (1) The compatibility 4 : hexagonal nanoprisms mol%) NRs and Faceting
0.6
C more important, which modifies the relative populationdetectable
various
showing sharp interface with no
NRs. The multidomain nature of the
among
alsobasis for and the modified rate stability
confirmed 3.5
eff
modeled as “translational” degree of freedom (8) with a
N−1 1
structures. (2) A side view of0.2 interface 0.6 betweenCu-Nb bottom)
STO the KS
nanoprismsthe positions in face properties0.4 0 of provide 0.6 measured1ratio
UCNPs (Figs. (atlargest dimensions 2G).0.80.4 1 intensityinto
sistent with the 1 0 and I and
1 F 0.2 0can0.6individual NCs 0.8 The insight 0.28 amorphous regions. (c) At dopant con-
not only the higher doses of nanolayered composite materials the system at the saddle point.65 line).
(black kB T similar interpretation may the system at the saddle point. A similar interpretation may
A E act 65
A’ e
0 0.4 0.8 0 0.2 j =1
temperature-dependent prefactor (black line). (b) Fits of the modifiedtemperature-dependent prefactor νj − E(S)−E(A) (b) Fits − kB T modified
relaxations (36). Therefore, engineeringmicroscopy (AFM). We anticipate that NRs
by the keV helium, 1.5 1017 /cm2, 5 nm Cu- of the
(33 atomic force
ionic radius. The shaded oxygen
0 the interface plane are = N =ν (6)
Cu-Mo KS in this work. Abstracting away0 efrom .the detailed be applied in this work. Abstracting away from the detailed
be applied
rate expression to MD data (gray dots). Temperatures are plotted onrate expression to MD data (gray1 dots). Temperatures are plotted on
ecause of of green to red emission from the NRs increases as the Ho con- 3
Epitaxial growth of polydisperse particles
3þ 0.26
the design of radiation-damage-tolerant
volume constraints, enabling the high ionic conductivity. (3) A 1.4
with larger AR (3) would be better suited for the formation of
Nb multilayer), 1–2 nm diameterethelium underinverse scale.
an irradiation conditions, studied
j =1
MEPs illustrated in Fig. νj all the intermediate states in the MEPs illustrated in Fig. 9, all the intermediate states in the
9,
Formation energy (eV)
150
he ionic radius reduced by half to betterof 6 ∣ www.pnas.org/cgi/doi/10.1073/pnas.1008958107
2 visualize the plane of oxygen 0.2 an inverse scale.
erface. The square symbol in increases from 1% to 2%, owing to the enhanced
centration the legend indicates the empty positions 0.24 Ye al.
liquid crystalline phases using the present assembly methodology.
0.2
by He+ implantation overNW
2.5 Ag-V a broad range
0.2
structural materials. quantization 1.2 D3þ 0.22
interface.energy transfer from the Yb3þ sensitizers to adjacent Ho
Pattern
bubbles are detected as bright spots in This expression is only valid if the saddle-point configuration
0.4 100 ions
0.2
β-NaYF4 NRs with an images.∼2.0 dotted
under-focused TEM AR of The have also been used to study conditions and layer 205416-10
partition function has just one degree of freedom less than the 205416-10
0.4
(37). Furthermore, trivalent Ce Chemical0and morphological stability
0.4
3þ ions are introduced to modu- 1
0.18
thewhite line represents the end of range of
shape-directed assembly behavior: monolayer
of and double-2
irradiation initial state. In some cases, however, there may be additional
Energy (eV)
0.16
late the upconversionof interfaces is0.6 necessary factor Ein the a layer superlattices are obtained by depositing 15 μL of NR dis- The results presentedthicknesses.
CE www.sciencemag.org 3–6
0.6
profiles of the NaYF4 :Branching (20∕2 mol%)
0.6 50
Yb/Ho 0.8 0.14 implanted helium. 1.5
Cu-Nb KS do not contribute temperature-dependent terms to
modes that
UCNPs. The parity-allowed of nanolayered composites where
0.8 design 4f → 5d0.8
0.8 transition in the Ce ions 3þ 0.12
persion (Fig. 4 A and B). However, when 40 μL of NR dispersionto highlight the roles of
are organized B’
the configurational partition function, for example, when the
0
0.1
saddle point contains rotations or translations not present in the
can effectively depopulate the green-emitting 4∕ 2
5 F0.6 5 S states 0.08 is used, the NRs tend to orient vertically in the film with well1 initial state. B¨ ttiker and Christen suggested that in some such
u
of Ho 0 while increasing 1 the population of0.4the red-emitting
1 1 0.06
crystallized domains up to ∼200 μm 2 (Fig. 4C), as seen from
3þ 0.2 0.4 0.6 0.8 1
Cu-Fe NW
0 0.2 0.4 0 0.6 0.2 0.8 10.6 0.8
F
1 cases, the integration across the saddle cannot be treated by a
5 F state of Ho3þ through two cross-relaxation pathways (SI Chemical ordering 0.5
5 0 62 0 0 0.55 the corresponding SAWED pattern. Each domain is FIG. 16. (a) Comparison September 2007 migration Gaussian approximation, as in the usual case where the saddle
composed JOM • between effective defect
Appendix: Fig. S8): 5 F4 ∕5 S2 ðHo3þ Þ þ 0.2 5∕2 ðCe3þ Þ → 1.4F5 ðHo3þ0.5
0.2
150 2
F 5
Þþ
0.45
of hexagonally closed-packed perpendicularly aligned NRs0 kMC (black dots), a standard Arrhenius-type has positive curvatures in all directions not along the MEP.
rates computed using
0.2
1.2 0.4 equation using only the highest activation energy event (Eeff = act Instead, the flatness of a saddle point in one direction can be
0.4 0.4 100 0.4 Shape gradient G 0.35 0.4 eV, gray line), and the modified rate expression in Eq. (8) with a
-0.5 C’ 65
modeled as a “translational” degree of freedom accessible to
Ye et al.
0.6 0.6 50 0.6
1 0.3
0.25 PNAS Early Edition ∣ 3 of 6 B A
temperature-dependent prefactor (black line). (b) Fits of the modified C system at the saddle point. A similar interpretation may
the
0.8 0.2 rate expression to-1 data (gray dots). Temperatures are plotted on
MD be applied in this work. Abstracting away from the detailed
0.8 0.8
0
0.8 0.15 an inverse scale. -4 -2 0 2 4 MEPs illustrated in Fig. 9, all the intermediate states in the
6 8 10
H 0.1
0.6
Roughness
1 1
0 0.2 0.4
1
0.60.2 0.8 0.4 1
0.05 Size of point defect cluster at an MDI
0 0.2 0.4 0.6 0.8
Cu-V KS
1 0 0.6 0.8 1 205416-10
K. Kolluri et. al., Unpublished S. C. Glotzer et. al., Nat. Mater., 6, 557-562 (2007)
Figure 2 Anisotropy ‘dimensions’ used to describe key anisotropy attributes of particles. Homologous series of particles as the attribute corresponding to the anisotropy axis
is varied from left to right. A: Interaction patchiness via surface coverage, B: aspect ratio, C: faceting, D: interaction patchiness via surface pattern quantization, E: branching,
This material is based upon work supported as part of the Center for Materials at Irradiation and Mechanical
F: chemical ordering, G: shape gradient, H: roughness. Further dimensions, such as chirality, are not shown. Acknowledgments:
Extremes, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, UMass : Dimitrios Maroudas, Lakis Mountziaris, Rauf Gungor
we consider several of the particles in Fig. 1. The key anisotropy experiment, theory and simulation to fruitfully interact to explore
Office of Basic Energy Sciences under Award Numberfor anisotropic particle design and assembly.
dimension of the tetrapods in the top row is branching (axis E). the potential 2008LANL1026. MIT : Michael Demkowicz
However, the two tetrapods diVer in aspect ratio (axis B) because
the tetrapod on the left (which resembles a ‘plus’ sign) may be SEEKING DESIGN RULES FOR ASSEMBLY THROUGH ANISOTROPY LANL : Blas Uberuaga, Amit Misra, John Hirth, Richard Hoagland