13 research outputs found
Temperature mapping of stacked silicon dies from x-ray diffraction intensities
Increasing power densities in integrated circuits has led to an increased
prevalence of thermal hotspots in integrated circuits. Tracking these thermal
hotspots is imperative to prevent circuit failures. In 3D integrated circuits,
conventional surface techniques like infrared thermometry are unable to measure
3D temperature distribution and optical and magnetic resonance techniques are
difficult to apply due to the presence of metals and large current densities.
X-rays offer high penetration depth and can be used to probe 3D structures. We
report a method utilizing the temperature dependence of x-rays diffraction
intensity via the Debye-Waller factor to simultaneously map the temperature of
an individual silicon die that is a part of a stack of dies. Utilizing beamline
1-ID-E at the Advanced Photon Source (Argonne), we demonstrate for each
individual silicon die, a temperature resolution of 3 K, a spatial resolution
of 100 um x 400 um and a temporal resolution of 20 s. Utilizing a sufficiently
high intensity laboratory source, e.g., from a liquid anode source, this method
can be scaled down to laboratories for non-invasive temperature mapping of 3D
integrated circuits
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Multiple rare-earth ion environments in amorphous (Gd2O3)(0.230)(P2O5)(0.770) revealed by gadolinium K-edge anomalous x-ray scattering
A Gd K-edge anomalous x-ray scattering (AXS) study is performed on the rare-earth (R) phosphate glass, (Gd2O3)0.230(P2O5)0.770, in order to determine GdâŻGd separations in its local structure. The minimum rare-earth separation is of particular interest given that the optical properties of these glasses can quench when rare-earth ions become too close to each other. To this end, a weak GdâŻGd pairwise correlation is located at 4.2(1)Ă
, which is representative of a metaphosphate RâŻR separation. More intense first-neighbor GdâŻGd pairwise correlations are found at the larger radial distributions, 4.8(1), 5.1(1), and 5.4(1)Ă
. These reflect a mixed ultraphosphate and metaphosphate structural character, respectively. A second-neighbor GdâŻGd pairwise correlation lies at 6.6(1)Ă
which is indicative of metaphosphate structures. Meta- and ultraphosphate classifications are made by comparing the RâŻR separations against those of rare-earth phosphate crystal structures, R(PO3)3 and RP5O14, respectively, or difference pair-distribution function (ÎPDF) features determined on similar glasses using difference neutron-scattering methods. The local structure of this glass is therefore found to display multiple rare-earth ion environments, presumably because its composition lies between these two stoichiometric formulae. These GdâŻGd separations are well-resolved in ÎPDFs that represent the AXS signal. Indeed, the spatial resolution is so good that it also enables the identification of RâŻX(X=R, P, O) pairwise correlations up to râŒ9Ă
; their average separations lie at râŒ7.1(1), 7.6(1), 7.9(1), 8.4(1), and 8.7(1)Ă
. This is a report of a Gd K-edge AXS study on an amorphous material. Its demonstrated ability to characterize the local structure of a glass up to such a long range of r heralds exciting prospects for AXS studies on other ternary noncrystalline materials. However, the technical challenge of such an experiment should not be underestimated, as is highlighted in this work where probing AXS signal near the Gd K edge is found to produce inelastic x-ray scattering that precludes the normal AXS methods of data processing. Nonetheless, it is shown that AXS results are not only tractable but they also reveal local structure of rare-earth phosphate glasses that is important from a materials-centered perspective and which could not be obtained by other materials characterization methods.J.M.C. is grateful to the Royal Commission of the Great Exhibition 1851 for a 2014 Design Fellowship hosted by Argonne National Laboratory (ANL) where work done was supported by the U.S. Department of Energy (DOE) Office of Science, Office of Basic Energy Sciences, and X-ray 1-BM beam line of the Advanced Photon Source, which is a DOE Office of Science User Facility, all under Contract No. DE-AC02-06CH11357. J.M.C. and R.J.N. are also indebted to the Engineering and Physical Sciences Research Council Grant No. GR/L41035 for funding
3D Atomic Arrangement at Functional Interfaces Inside Nanoparticles by Resonant High-Energy Xâray Diffraction
With current science and technology
moving rapidly into smaller scales, nanometer-sized materials, often
referred to as NPs, are produced in increasing numbers and explored
for numerous useful applications. Evidence is mounting, however, that
useful properties of NPs can be improved further and even new NP functionality
achieved by not only controlling the NP size and shape but also interfacing
chemically or structurally distinct entities into single, so-called
âcompositeâ NPs. A typical example is coreâshell
NPs wherein the synergy of distinct atoms at the core\shell interface
endows the NPs with otherwise unachievable functionality. However,
though advantageous, the concept of functional interfaces inside NPs
is still pursued largely by trial-and-error. That is because it is
difficut to assess the interfaces precisely at the atomic level using
traditional experimental techniques and, hence, difficult to take
control of. Using the core\shell interface in less than 10 nm in size
Ru coreâPt shells NPs as an example, we demonstrate that precise
knowledge of the 3D atomic arrangement at functional interfaces inside
NPs can be obtained by resonant high-energy X-ray diffraction (XRD)
coupled to element-specific atomic pair distribution function (PDF)
analysis. On the basis of the unique structure knowledge obtained,
we scrutinize the still-debatable influence of core\shell interface
on the catalytic functionality of Ru coreâPt shell NPs, thus
evidencing the usefulness of this nontraditional technique for practical
applications
PtâAu Alloying at the Nanoscale
The formation of nanosized alloys between a pair of elements,
which
are largely immiscible in bulk, is examined in the archetypical case
of Pt and Au. Element specific resonant high-energy X-ray diffraction
experiments coupled to atomic pair distribution functions analysis
and computer simulations prove the formation of PtâAu alloys
in particles less than 10 nm in size. In the alloys, AuâAu
and PtâPt bond lengths differing in 0.1 Ă
are present
leading to extra structural distortions as compared to pure Pt and
Au particles. The alloys are found to be stable over a wide range
of PtâAu compositions and temperatures contrary to what current
theory predicts. The alloy-type structure of PtâAu nanoparticles
comes along with a high catalytic activity for electrooxidation of
methanol making an excellent example of the synergistic effect of
alloying at the nanoscale on functional properties
Resolving Atomic Ordering Differences in Group 11 Nanosized Metals and Binary Alloy Catalysts by Resonant High-Energy Xâray Diffraction and Computer Simulations
Resonant high-energy X-ray diffraction
coupled to atomic pair distribution
function analysis and computer simulations is used to study the atomic-scale
structure of group 11 nanosized metals and binary alloy catalysts.
We find that nanosized Cu is quite disordered structurally whereas
nanosized Ag and especially Au exhibit a very good degree of crystallinity.
We resolve CuâCu and AgâAg atomic correlations from
Au-involving ones in AuâCu and AuâAg nanoalloys and
show that depending on the synthetic route group 11 binary alloys
may adopt structural states that obey or markedly violate Vegardâs
law. In the latter case, Cu and Ag atoms undergo substantial size
expansion and contraction by as much as 0.3 and 0.03 Ă
, respectively,
while heavier Au atoms remain practically intact. The size change
of Cu and Ag atoms does not follow Paulingâs rule of electronegativity
predicting charge flow toward the more electronegative Au but occurs
in a way such that Cu/Au and Ag/Au atomic size ratios in the nanoalloys
become closer to one. Atomic size adjusting and the concurrent charge
redistribution result in a synergistic effect of oxygen inactive Au
and oxygen very active Cu and Ag leading to nanoalloys with very good
activity for low-temperature oxidation of CO
Resolving Atomic Ordering Differences in Group 11 Nanosized Metals and Binary Alloy Catalysts by Resonant High-Energy Xâray Diffraction and Computer Simulations
Resonant high-energy X-ray diffraction
coupled to atomic pair distribution
function analysis and computer simulations is used to study the atomic-scale
structure of group 11 nanosized metals and binary alloy catalysts.
We find that nanosized Cu is quite disordered structurally whereas
nanosized Ag and especially Au exhibit a very good degree of crystallinity.
We resolve CuâCu and AgâAg atomic correlations from
Au-involving ones in AuâCu and AuâAg nanoalloys and
show that depending on the synthetic route group 11 binary alloys
may adopt structural states that obey or markedly violate Vegardâs
law. In the latter case, Cu and Ag atoms undergo substantial size
expansion and contraction by as much as 0.3 and 0.03 Ă
, respectively,
while heavier Au atoms remain practically intact. The size change
of Cu and Ag atoms does not follow Paulingâs rule of electronegativity
predicting charge flow toward the more electronegative Au but occurs
in a way such that Cu/Au and Ag/Au atomic size ratios in the nanoalloys
become closer to one. Atomic size adjusting and the concurrent charge
redistribution result in a synergistic effect of oxygen inactive Au
and oxygen very active Cu and Ag leading to nanoalloys with very good
activity for low-temperature oxidation of CO