pressure compression of cdse nanoparticles into ... · fig. 1. cdse nanowires synthesized by...

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1Sandia National Laboratories, Albuquerque, NM 87185, USA. 2Cornell High EnergySynchrotron Source, Cornell University, Ithaca, NY 14853, USA. 3Department ofChemical and Biological Engineering, Center for Micro-Engineered Materials, Uni-versity of New Mexico, Albuquerque, NM 87106, USA.*These authors contributed equally to this work.†Corresponding author. Email: [email protected]

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Pressure compression of CdSe nanoparticlesinto luminescent nanowiresBinsong Li,1* Kaifu Bian,1* Xiaowang Zhou,1 Ping Lu,1 Sheng Liu,1 Igal Brener,1 Michael Sinclair,1

Ting Luk,1 Hattie Schunk,1 Leanne Alarid,1 Paul G. Clem,1 Zhongwu Wang,2 Hongyou Fan1,3†

Oriented attachment (OA) of synthetic nanocrystals is emergingas aneffectivemeans of fabricating low-dimensionalnanoscale materials. However, OA relies on energetically favorable nanocrystal facets to grow nanostructuredmaterials. Consequently, nanostructures synthesized through OA are generally limited to a specific crystal facet intheir final morphology. We report our discovery that high-pressure compression can induce consolidation of spheri-cal CdSe nanocrystal arrays, leading to unexpected one-dimensional semiconductor nanowires that do not exhibitthe typical crystal facet. In particular, in situ high-pressure synchrotron x-ray scattering, optical spectroscopy, andhigh-resolution transmission electron microscopy characterizations indicate that by manipulating the coupling be-tween nanocrystals through external pressure, a reversible change in nanocrystal assemblies and properties can beachieved atmodest pressure.Whenpressure is increased above a threshold, these nanocrystals begin to contact oneanother and consolidate, irreversibly forming one-dimensional luminescent nanowires. High-fidelity molecular dy-namics (MD) methods were used to calculate surface energies and simulate compression and coalescence mecha-nisms of CdSe nanocrystals. The MD results provide new insight into nanowire assembly dynamics and phasestability of nanocrystalline structures.

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INTRODUCTIONOriented attachment (OA) of synthetic nanocrystals is emerging as aneffective means of fabricating low-dimensional nanoscale materials(1–7). Through OA, nanostructures such as nanowires and nano-sheets have been fabricated. Important applications in energy con-version have been successfully demonstrated (8–10). OA crystalgrowth formaterial synthesis occurs in solutions where activemobileclusters such as ions, clusters, or nanocrystals are self-assembledthrough direction-specific interparticle forces, such as dipole-dipoleinteractions found in several material systems (2, 11–14). Alternatively,capping agents or organic ligands (15, 16) have been used to modify orblock certain crystal surface facets to inhibit their growth so thatcontrolled growth of specific architectures, such as nanorods and nano-wires, through unblocked crystal facets is achieved.More recently, blockcopolymer and surfactant self-assembly (13, 14, 17–21) have beenused to confine oriented consolidation of necklace structures, includ-ing nanowires and bundles. Evolving toward theminimum free energy,OA leads to alignment of energetically favorable nanocrystal facetswhen the nanocrystals are coalesced to form various nanostructures(for example, nanowires) under ambient pressure (2, 11, 12, 22, 23).As a consequence, these nanostructures are generally limited to a spe-cific crystal facet in their finalmorphology. AlthoughOA is conductedat ambient conditions, our method, by application of external pres-sure, provides an additional processing parameter to change materialstructures viamanipulating system energy. This enables the formationof new material configurations that affect new chemical and physicalproperties. In contrast to OA in solutions, pressure-induced synthesisis conducted by applying pressure to solid-state self-assembled arraysof spherical CdSe nanocrystals. When the external pressure isincreased, the nanocrystal separation distance initially decreases. At

pressures above a threshold, adjacent nanocrystals come into contactand then consolidate, enabling the formation of new classes of me-chanically stable one-dimensional (1D) nanowires. To explore thehigh pressure–induced synthesis, we prepared films of self-assembledspherical CdSe nanocrystal arrays by solvent evaporation and loadedthem into a diamond anvil cell (DAC) to allow reversible compressionunder controlled and continuously monitored pressure conditions(see experimental details in Materials andMethods). Electronmicros-copy, in situ high-pressure synchrotron x-ray scattering, and opticalspectroscopy were performed to investigate the formationmechanismof nanowires and the associated structure and structural evolutionduring increasing degrees of compression.

RESULTSStructure of CdSe nanowiresFigure 1A and its inset show a representative transmission electronmi-croscopy (TEM) image of the 1D CdSe nanowires and bundles in thenanowire arrays formed after high-pressure compression of the spheri-cal nanocrystal arrays. The CdSe nanowire array consists of individualCdSe nanowires with 2D hexagonal packing. These nanowire arrayswere collected directly from the DAC and then dissolved in organicsolvents, such as toluene, to form stable homogeneous colloidal solu-tions. The nanowires have an average diameter of 5 nm, with an SD of10%, consistent with the diameter of the starting spherical nanoparti-cles. The nanowires display uniform lengths roughly on the scale of~600 nm and an aspect ratio of ~120. High-resolution scanningTEM (HR-STEM) images shown in Fig. 1B reveal an unusual nano-wire morphology, both polycrystalline and twisted. Along the nano-wire c axis, each nanowire consists of connected individual CdSenanocrystal domains. The nanocrystal domains retain the faceted na-ture of the starting spherical CdSe nanocrystals, which aids crystal-lographic indexing of the nanocrystal facets. This analysis indicatesthat nanowires are formed through direct coalescence of spherical nano-crystals along the c axis. From the lattice spacings seen in HR-STEMimaging, we found that the nanocrystal coalescence leads to several

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nanocrystal lattice orientations,which are summarized inFig. 1 [B (inset)and C]. The CdSe nanocrystals primarily coalesce along <111>/<111>orientations, with some other types of interface. This solid-state coa-lescence contrasts with OA growth in solutions, where freely mobilemoieties, such as ions, small clusters, and nanocrystals, are typicallylocked in through specific facets (1, 2, 5, 12, 22, 23). During solutionnucleation and growth, these free nanocrystals can rotate under thedriving force of the favorable facet interactions. Structural relaxationis possible through solution-mediated mass redistribution or atomicrearrangement to eliminate defects, such as the neck structures be-tween nucleated nanocrystals, leading to the formation of smoothand single crystalline nanowires (12, 22). In situ synchrotron x-rayresults indicate that the compressive stress induces neither nanocrystalrotation nor preferential nanoparticle alignment during compressionand pressure release (fig. S2 and Fig. 2).We propose that this accountsfor the observed random coalescence, the lack of neck structures be-tween adjacent nanocrystals, and a twisted morphology instead ofsmooth single crystalline nanowires. This randomcoalescence occurredregardless of CdSe nanocrystal size, as shown in Fig. 1D.

In situ high-pressure small- and wide-angle synchrotronx-ray scattering characterizationsThe consolidation of CdSe nanocrystals and the formation of CdSenanowires were further explored using in situ high-pressure small-


angle (HP-SAXS) and high-pressure wide-angle (HP-WAXS) syn-chrotron x-ray scattering characterization. Figure 2 shows the SAXSand WAXS data collected from the same specimens during compres-sion and pressure release. The results reveal pressure-induced phasetransitions at both the atomic scale and mesoscale. Figure 2A indi-cates that at the atomic scale, the initial wurtzite (WZ) CdSe nanocrys-tals remained as WZ with increasing pressure up to ~7 GPa. At about7 to 8 GPa, phase transformation from WZ to rock salt (RS) occurred(24). The nanocrystals then remained as RS with increasing pressureup to about 15 GPa. When pressure was released from 15 GPa, thenanocrystals remained in the RS structure until 0.7 GPa, only revert-ing to the zinc blende (ZB) structure when pressure was released toambient pressure. The atomic phase transition of CdSe nanocrystalsunder pressure uniquely differs from the formation of metallic na-nowires, such as gold nanowires, that do not exhibit atomic phasetransition (25, 26). The WAXS peak intensity as a function of azi-muthal angle, measured during the entire compression and releasecycle, exhibits only characteristics of powders (see fig. S2) (27). Nopreferential alignment of the nanoparticles was observed in eitherthe starting nanoparticle arrays or those formed during compressionand pressure release. At the mesoscale, the SAXS patterns shown inFig. 2B indicate that before compression, the nanocrystals were ar-ranged in a standard face-centered cubic (fcc) lattice (fm�3m) with aunit cell parameter afcc = 9.8 nm (also see fig. S3). Upon continuous

Fig. 1. CdSe nanowires synthesized by pressure-induced assembly. (A) Representative TEM image of CdSe nanowires synthesized by pressure-induced assembly.The nanowire samples were collected after releasing the pressure from 15 GPa. Inset: CdSe nanowire bundles. More TEM images are provided in fig. S1. (B) HR-STEMimage of the CdSe nanowires. Inset: Statistical analyses of crystallography of interfaces between nanocrystals. (C) Schematic model showing the coalescence of CdSenanocrystals in random crystal orientations, as marked by the arrows. (D) Nanowires synthesized by compression of 6- and 8-nm nanoparticle arrays.

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increase of pressure, the SAXS peaks continuously shifted to higherangles (lower d-spacing), indicative of shrinkage of interparticledistances. This shrinkage is more directly revealed in Fig. 2C, wherethe d-spacing of the first Bragg peak is plotted as a function of pres-sure. It can be seen from this compression curve that the d-spacingcontinuously decreased and the nanocrystals continuously approachedeach other with increasing pressure. The nanocrystals were in contactat a threshold pressure of ~9.5 GPa, where a minimal d-spacing wasreached.When the pressure was released from 9.5 GPa to ambient con-dition, the SAXS peaks and the d-spacing returned to the originalpositions of startingmaterials, indicating that the change of the unit cellwas reversible in the pressure range between 0 and 9.5 GPa. However,Fig. 2B indicates that when the pressure was increased above 9.5 GPa,the contacting nanocrystals began to consolidate, accompanied by a


transformation of the mesophase from fcc packing to 2D hexagonalpacking. This change in the phase and the corresponding unit celldimension appears irreversible. Thismesophase transition is illustratedin Fig. 2D, which shows the d-spacing ratio R during compression andrelease. For pressures below 9.5 GPa, the nanocrystal array displays anfcc mesophase, where R (= d311/d111) was nearly constant and close tothe ideal fcc value of d311/d111 = 0.52. After pressure release, the ratio Rbecame ~0.5, was close to the theoretical ratio of d20/d10 for a 2Dhexagonal mesophase, and was consistent with SAXS indexing andTEM results.

Optical property and correlation to structureThe results of optical absorption experiments shown in Fig. 3 indi-cate that the optical properties of nanocrystals correlate with the

Fig. 2. Pressure-induced structural evolution of CdSe nanocrystal mesophase during compression and release. (A) Representative integrated data from WAXSimages of CdSe nanocrystal arrays at varied pressures. (B) Representative integrated data from SAXS images of CdSe nanocrystal arrays at varied pressures. r is used todisplay the releasing pressure. Below 9.5 GPa, the HP-SAXS patterns are consistent with fcc mesophase. Mesophase transformation of the nanocrystal arrays starts at~9.5 GPa, followed by an intermediate phase, where the overall distorted structures cannot be indexed by either fcc or 2D hexagonal mesophase. After releasing theapplied pressure, the HP-SAXS patterns are consistent with 2D hexagonal mesophase. (C) The d111-spacings change with the pressure during compression and release.(D) d-spacing ratios (R) at different pressures. In the fcc nanocrystal mesophase, R = d311/d111; in the 2D hexagonal mesophase, R = d20/d10.

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phase transition during compression and pressure release. In partic-ular, the absorption peak continuously shifted to blue for pressuresup to ~7 GPa. When the pressure was released from ~7 GPa, the ab-sorption peak returned reversibly (see fig. S4). Considering that theabsorption peak reflects the direct gap specific to a crystal structure,this result is consistent with the complete recovery of WZ observedfrom the HP-WAXS results shown in Fig. 2A. However, when thepressure was increased above ~7 GPa, the sharp absorption edgeabruptly disappeared in Fig. 3. We believe that this is caused by theobserved phase transition from the direct bandgapWZ to the indirectbandgap RS, indicated by the WAXS results in Fig. 2A. Pressure wasthen released after reaching a maximum value of ~14.8 GPa. Uponcomplete release of the pressure, a new absorption peak appeared at594 nm. According to the TEM and HP-SAXS results, CdSe nano-wires were formed when pressure was completely released, and thisnew peak can be attributed to the CdSe nanowires. The red shiftand broadening of the excitonic peak of the nanowires were probablycaused by the incomplete fusion (or growth) of the nanoparticles intonanowires, which is consistent with results on the nanowires synthe-sized from OA. Increased grain size through more complete fusion ofnanoparticles would enable stronger delocalization, thereby narrowingof bandgaps (6, 28). The nanowires exhibited a quantumyield of about1.6% immediately after the pressure release, with a slowly increasingquantum yield over time thereafter. This is attributed to relaxation ofresidual stresses within CdSe quantum dots after pressure release (29).To validate this, we relaxed residual stresses further by annealingsamples at 200°C (fig. S5). As indicated in fig. S5, the quantum yieldof annealed samples significantly increased from 1.6 to 17%. Thecrystal structure remains the same after annealing (fig. S5). Comparedto a luminescence quantum yield of less than 1% in typical chemically


synthesized CdSe nanowires, the high luminescence quantum yieldsobtained here are indicative of high crystalline quality nanowires(11), which also has been observed to increase nanowire mechanicalstrength (30, 31).

Molecular dynamics simulation of CdSe coalescenceTo understand the energetics of phase transformations describedabove, molecular dynamics (MD) simulations were performed tocompress a synthetic bulk crystal composed of half ZB and half WZstructures. The initial configuration, projected along a <111> ZB or<0001> WZ direction, is shown in Fig. 4A, where the hexagonal{111} ZB or {0001} WZ plane is indicated by a hexagon. The systemwas then compressed for 1.2 ns at a temperature of 1500 K and apressure of about 5 GPa. The same projected configuration is shownin Fig. 4B, where a square indicates that the initial hexagonal con-figuration transforms to a square plane. Examination of the unit cellof the square confirms that the system corresponds to an RS crystalstructure. The MD simulation was continued for another 1.3 ns torelease the stress, and the final projected image is shown in Fig. 4C,in which the system recovered back to a hexagonal symmetry char-acteristic of {111} ZB or {0001} WZ. More detailed analysis indicatedthat the system after pressure release also contains a mixture of ZBand WZ. However, different ZB and WZ domains are stacked alongthe direction normal to the image, as opposed to the left and the rightbicrystals shown in Fig. 4A. Hence, Fig. 4 (A and C) appears different.The modeling results in Fig. 4 are consistent with the experimentalfindings that, during compression, the initial WZ nanocrystals weredriven to RS structure and were recovered to a stable ZB structureupon pressure release. Further, the simulation illustrates how theRS structure acts as an intermediate phase without a change in theinitial and final crystallographic orientations. For example, the initialWZ {0001} and the final {111} ZB planes shown in Fig. 4 (A and C)are essentially the same hexagonal plane.

Fig. 3. In situ UV-vis absorption spectra of CdSe nanocrystal arrays duringcompression and pressure release. r is used to show the releasing pressure.

Fig. 4. MD simulation of pressure-induced nanocrystal phase transition andconsolidation. (A) Initial configuration. (B) Intermediate configuration at pressure~5 GPa. (C) Final configuration after pressure release. Two MD simulation cases ofsintering showing (D) the formation of the <111>/<111> interface and (E) theformation of the <111>/<210> interface.

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Direct MD simulations were also performed to study sintering oftwo CdSe ZB particles of 5.5 nm diameter (25, 26). Figure 4 (D and E)shows two representative cases, where the two particles were mis-aligned arbitrarily. After MD simulations at 800 K for 0.2 ns withthe cell dimension along the axis of the two particles shrinking at astrain rate of −3.75 × 10−5 ps−1, the two particles in the first case coa-lesced on a <111>/<111> interface, as shown in Fig. 4D, and the par-ticles in the second case coalesced on a <111>/<210> interface, asshown in Fig. 4E. Time-resolved observation indicates that duringsintering, the interface orientations are mostly random due to the lackof rotation before the contact.

MD simulations were further used to calculate energies of a varietyof CdSe ZB surfaces (see fig. S6) (32, 33), which indicated that {111}and {110} surfaces of CdSe nanocrystals have the lowest energies. As aresult, the nanocrystal facets were mostly composed of these twosurfaces before the compression. If sintering proceeds with little ad-justment of orientation, interfaces are most likely to contain one{111} plane or one {110} plane because of the high probability ofencountering such a surface when nanocrystals come into contact.Once such a {111} or {110} plane is present, we hypothesize that theother crystals find a matching plane when they come into contact.This process appears consistent with the atomistic coalescence processshown in Fig. 4 (D and E) and contrasts with the solution-processedOA, where interfaces tend to contain high-energy surface planes be-cause systems can remove these unfavorable planes by forming inter-faces through crystal rotation. Hence, the calculated surface energiesappear consistent with the conclusion drawn from the experimentalobservations that coalescence occurred nearly randomly with littlecrystal rotation. Finally, we point out that although the coalesced par-ticles were RS crystals, the RS structure only acted as an intermediatephase because it does not affect the initial and the final orientations.For example, Fig. 4 (A to C) indicates that the initial {111} ZB or{0001} WZ planes before compression were still {111} ZB or {0001}WZ planes after pressure release, despite intervening transformationto {100} RS under pressure.

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DISCUSSIONThe combined experimental characterization and simulation indicatethat mechanical compression can drive the formation of new micro-structures of CdSe nanowires. The CdSe nanoparticles are surface-stabilized by organic monolayers, which initially prevent nanoparticlesfrom aggregation or contact. At ambient pressure, ordered fcc nano-particle arrays are formed through balanced nanocrystal interactions,such as van der Waals forces, hydrophobic attraction, and charge-charge interaction, leading to alkane chain interdigitation that locksin the final fcc nanocrystal mesophase (34). The ligand-coated nano-particle assembly exhibits exponent force against external compres-sion. An external pressure is necessary to overcome the force toinduce nanoparticle coalescence (34). During compression at lowpressure, pressure is not sufficient to break the force balance betweenadjacent nanoparticles. Hence, the spherical nanoparticle arrays re-main in the fcc mesophase while shrinking and reversibly springingback when pressure is released, as verified by the SAXS results (Fig.2, B toD).However, when the pressure is higher, continuous compres-sion increasingly breaks the force balance between adjacent nano-particles and drives the nanoparticles to contact and ultimatelycoalesce, forming nanowires. In the fcc mesophase, the closest inter-particle spacings are between {220} planes. Consequently, particles


touch and coalesce along the close packing <110> direction first,forming 1D nanowires. During this process, partial dissociation of li-gands at the contact points of the nanocrystal surfaces likely occurs toallow particle connection (12). Because the starting CdSe nanocrystalarrays are in a solid-state phase that does not allow facile rearrange-ment of nanocrystals, this coalescence occurs in a random patternwithin adjacent nanocrystals, leading to unusually twisted polycrystal-line nanowires. The pressure-induced nanocrystal assembly mecha-nism discovered here may provide a flexible material synthesis routebecause morphology and architecture can be readily tuned to producedesired properties independent of crystal facet orientation.

In summary, we have developed a facile mechanical compressionmethod to fabricate luminescent semiconductor nanowires fromordered spherical CdSe nanoparticle arrays. The fabrication processrelies on pressure-induced phase transitions and coalescence fromboth atomic scale and mesoscale. The long-range ordering of startingnanoparticle assembly and its mesophase orientation are importantfor the formation of the nanowires. The fabrication method is simpleand convenient to be implemented for large-scale synthesis of newnanostructures. The ease of the compressive process facilitates fun-damental understanding of nanomaterial coupling through energytransfer. We envision that this method could apply to a variety ofother semiconductor and magnetic materials (35, 36).

MATERIALS AND METHODSSynthesis of CdSe nanocrystals and ordered arraysSe powder (14.7 mmol, 1.16 g) was dissolved in 7.22 g of trioctylphos-phine (TOP) to make a 1.70 M stock solution. CdO (1.88 mmol,0.24 g), octadecylphosphonic acid (3.76 mmol, 1.26 g), and trioctyl-phosphonic oxide (31 mmol, 12 g) were loaded into a three-neckflask, degassed, and purged with Ar. The mixture was heated to150°C and pumped for 1 hour before it was heated to 300°C underAr. TOP (6 g) was injected into the flask, and the mixture was heatedto 355°C. Se/TOP (1.72 ml) stock solution was quickly injected intothe flask. The heating mantle was removed after 20 s to 3 min. In thecase of 5-nm CdSe, 1-min reaction time was used. The reaction mix-ture was cooled to room temperature. The CdSe nanoparticles wereprecipitated using ethanol and centrifuged at 4000 rpm. The crudeproduct was further purified by dissolving in a small amount of tolueneand precipitated again. The CdSe nanoparticle solution was filteredthrough a 0.45-mm polytetrafluoroethylene filter before use. CdSe(100 mg/ml) nanoparticle (with or without 20 weight % polystyrene)solution in toluene was drop-casted on Si wafers to form thin films ofCdSe arrays. A small piece of film was peeled off and transferred tothe DAC for high-pressure measurement.

CharacterizationsTEM was performed on a JEOL 2010 TEM and an FEI Titan G2 80-200 STEM with a Cs probe corrector, operated at a 200-kV acceler-ation voltage. STEM images were recorded with a high-angle annulardark-field detector with the angular range of 60 to 150 mrad. SEMimages were taken using a Hitachi S-5200 FEG microscope at 5 kV.Ultraviolet-visible (UV-vis) spectra were obtained on a Lambda 950spectrophotometer (PerkinElmer). Photoluminescence (PL) spectrawere measured using a Horiba FluoroMax-4 fluorometer with an ex-citation wavelength of 450 nm. In situ HP-SAXS and HP-WAXSmeasurements were performed on B1 station at Cornell High EnergySynchrotron Source (CHESS) with monochromatic x-ray radiation

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wavelength l of 0.485946 Å (37). The distance between the sampleand a large-area MAR345 detector was 727.19 mm, as determinedusing both CeO2 and silver behenate powder standard. Several smallruby chips were loaded into the DAC chamber as internal pressureprobes to monitor the sample pressure by a standard pressure–dependent ruby fluorescence technique (38). Scattering images werecalibrated and integrated using the Fit2D software.

Simulation methodThe Cd-Se-Te analytical bond-order potential (BOP) (39) was usedin the MD code LAMMPS (Large-scale Atomic/Molecular MassivelyParallel Simulator) (40, 41) to perform the simulations. The BOP wastested through stringent MD simulations of crystalline growth. Com-pared with other simpler potentials (42), an additional advantage ofthe BOP is that it captures property trends of many metastable phasesand defects. Time-averaged energies obtained from MD simulationswere used to calculate surface energies. In addition to incorporatingthe finite temperature effects, time-averaged energies obtained fromMD simulations were found, somewhat surprisingly, to be much moreaccurate than the static energies calculated from energy minimizationsimulations (43).

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SUPPLEMENTARY MATERIALSSupplementary material for this article is available at http://advances.sciencemag.org/cgi/content/full/3/5/e1602916/DC1fig. S1. Representative TEM image of CdSe nanowires synthesized by pressure-inducedassembly.fig. S2. WAXS-azimuth analysis.fig. S3. TEM and small angle x-ray scattering images of starting CdSe nanoparticle arrays.fig. S4. Reversible optical absorption and microstructure of CdSe nanoparticle under pressure.fig. S5. Thermal annealing of compressed CdSe nanowires.fig. S6. MD calculations of energies of various ZB surfaces of CdSe.


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AcknowledgmentsFunding: This work is supported by the U.S. Department of Energy, Office of Basic EnergySciences, Division of Materials Sciences and Engineering. CHESS is supported by the NSF andNIH/National Institute of General Medical Sciences via NSF award DMR-0225180. Research wascarried out, in part, at theCenter for IntegratedNanotechnologies, aUSDepartment of Energy,Officeof Basic Energy Sciences user facility. Sandia is a multimission laboratory operated by SandiaCorporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Departmentof Energy’s National Nuclear Security Administration under contract DE-AC04-94AL85000.Author contributions: H.F. conceived the idea and designed the experiments. X.Z. performedthe simulation and modeling. P.L. performed STEM characterizations. K.B. and B.L. performed


statistical analysis of TEM images and optical characterizations. B.L., K.B., and Z.W. performedsynchrotron experiments and analysis. M.S. performed PL imaging. All authors commentedon the manuscript and contributed to the writing of the manuscript. Competing interests: H.F.and B.L. are inventors on U.S. patents 9,180,420 B1 (“Tuning and synthesis of metallicnanostructures by mechanical compression,” 10 November 2015) and 9,187,646 B1 (“Tuningand synthesis of semiconductor nanostructures by mechanical compression,” 17 November2015). All other authors declare that they have no competing interests. Data and materialsavailability: All data needed to evaluate the conclusions in the paper are present in thepaper and/or Supplementary Materials. Additional data available related to this paper maybe requested from the authors.

Submitted 21 November 2016Accepted 8 March 2017Published 5 May 201710.1126/sciadv.1602916

Citation: B. Li, K. Bian, X. Zhou, P. Lu, S. Liu, I. Brener, M. Sinclair, T. Luk, H. Schunk, L. Alarid,P. G. Clem, Z. Wang, H. Fan, Pressure compression of CdSe nanoparticles into luminescentnanowires. Sci. Adv. 3, e1602916 (2017).

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Pressure compression of CdSe nanoparticles into luminescent nanowires

Alarid, Paul G. Clem, Zhongwu Wang and Hongyou FanBinsong Li, Kaifu Bian, Xiaowang Zhou, Ping Lu, Sheng Liu, Igal Brener, Michael Sinclair, Ting Luk, Hattie Schunk, Leanne

DOI: 10.1126/sciadv.1602916 (5), e1602916.3Sci Adv

ARTICLE TOOLS http://advances.sciencemag.org/content/3/5/e1602916

MATERIALSSUPPLEMENTARY http://advances.sciencemag.org/content/suppl/2017/05/01/3.5.e1602916.DC1

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