Original Anisotropic Growth Mode of Copper Nanorods by Vapor

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Original anisotropic growth mode of copper nanorods by vapour phase deposition Hélène Prunier, Christian Ricolleau, Jaysen Nelayah, Guillaume Wang, and Damien Alloyeau Cryst. Growth Des., Just Accepted Manuscript • DOI: 10.1021/cg5010825 • Publication Date (Web): 17 Oct 2014 Downloaded from http://pubs.acs.org on October 27, 2014

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Crystal Growth & Design

Original anisotropic growth mode of copper nanorods by vapour phase deposition

H. Prunier, C. Ricolleau, J. Nelayah, G. Wang, D. Alloyeau*

Laboratoire Matériaux et Phénomènes Quantiques CNRS-UMR 7162, Université Paris Diderot - Paris 7 75205 Paris Cedex 13 Corresponding author e-mail: [email protected]

KEYWORDS: copper nanorod, structure, growth by physical vapor deposition, electron tomography, electron diffraction.

ABSTRACT We report on a thermal evaporation method to synthesize copper nanorods, up to several microns long. The synthesis parameters that control the size and aspect ratio are studied to understand their influence on this anisotropic growth mode. We exploit the multifunctionalities of electron microscopy for studying the structural properties of these nanorods, in particular their growth morphology. By analyzing the face-centered cubic structure of the nanorods along several orientations, we demonstrate that their anisotropic axis is parallel to the [110] direction. The precise 3D shape of the nanorods is determined by using electron tomography, evidencing morphology with a two-fold symmetry and rectangular facets. This unusual faceting for metal nanorods is actually consistent with energetic considerations and arises from a growth mode that is different from the one of chemically prepared nanorods.

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1. Introduction One dimensional nanostructures such as nanorods (NRs) and nanowires have recently attracted much attention, from both experimental and theoretical points of view. In such systems, it is possible to enhance or to obtain new properties that cannot be obtained in 0D nanostructures giving rise to promising applications in electronic and optoelectronic nanodevices.1-10 In addition to a strong confinement effect due to the high aspect ratio, one can expect new properties as soon as the diameter of the nanorods is similar or smaller than the characteristic length of a physical phenomenon. For the applications of nanorods and nanowires, copper is the most commonly used metal because of its better thermal and electrical conductivity.11 Since the birth of electronic age, copper has been used as interconnects in circuits as it is an excellent conductor. For such interconnection, copper plays the role that no other metal can assume. Moreover, it has been recently shown that the electron emission characteristics of Cu nanorods are good enough to envisage using them as electron emitters.12,13 In the work by Kim et al.,12 an array of Cu NRs was used in a proof-ofprinciple experiment to demonstrate a field emission display. For both fundamental and technological purposes, new developments are strongly dependent on the ability to fabricate NRs with high aspect ratios and an accurate control on the growth parameters. In particular, it is essential to control their size and shape because these parameters influence electrical properties.14 Copper NRs have been synthesized by a variety of chemical routes such as the reverse micelles,15-21 electrochemical methods with organic22 or inorganic template23,24, wet chemical methods involving surfactant templating, 25-27 or not11 as well as metal-organic chemical vapor deposition technique (MOCVD).12,13,28 The main disadvantage of these approaches is the surface passivation of the produced nanorods. Although surface is of primary importance to regulate stability, solubility, and targeting of NRs in liquid environment, the presence of organic molecules at the NR surface is a drawback


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for the investigation of physical phenomena such as quantized conductance as well as the study of their optical properties. Among physical vapor phase deposition techniques, thermal evaporation is one of the most flexible because it offers a good control over the nucleation and growth kinetics, by tuning both atoms flux and the substrate temperature. This technique has been widely and successfully used in the preparation of metallic and semiconductor nanoparticles on amorphous or crystalline substrates. In the past, several research groups have tried to prepare Cu or Ag NRs from in situ beam-induced heating experiments in an electron microscope.23,2932

Although these TEM experiments allow observing the growth of NRs, they show a limited

control over the growth parameters, since atom diffusion is activated by electron beam irradiation of material already present on the surface and the temperature of the substrate is fixed by modifying the brightness of the condenser lens system of the electron microscope. Finally, Cu NRs were successfully grown from a vapor phase deposition on nano-structured surfaces by a self-organized monolayer of polystyrene spheres by using glancing angle deposition.33,34 In this paper, we report for the first time, the physical synthesis of Cu nanorods by using thermal evaporation on amorphous carbon. This simple method allows fabricating Cu nanorods with variable aspect ratio and surfactant-free surfaces. For exploring this new way to synthesize Cu nanorods, we took advantage of the multi-functionalities of the last generation TEM to study their structural properties in order to understand their growth mechanisms.



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2. Experimental section The Cu nanorods were prepared by using classical thermal evaporation in a high vacuum chamber (< 10−7 mbar). The source was a Knudsen type cell containing high purity Cu pellets heated by Joule effect in order to ensure an evaporation rate of 0.1 nm.min−1. Cu vapor phases deposit on a substrate placed in front of the Knudsen cell. The distance from cell to substrate was approximately 20 cm and the substrate temperature is tuneable to vary Cu atoms mobility. Cu deposition rate was controlled by an in situ quartz crystal monitor, which indicates the nominal thickness of deposited materials on the quartz surface in a continuous thin film approximation. Two commercial TEM supports were used as a substrate: holey amorphous carbon films (Agar®) and amorphous silicon films (SIMPore®). After each synthesis, samples were stocked under high vacuum conditions to prevent contamination or air oxidation. TEM experiments were performed by using the newly developed JEOL ARM 200F microscope equipped together with a CEOS aberration corrector of the objective lens, a cold field emission gun and a Gatan Imaging Filter (GIF Quantum ER®).35 Electron tomography was used to study the 3D morphology of the Cu nanorods. The tomography data set consisting of 184 STEM HAADF images collected between −70° and +65° using the Saxton scheme, where the tilt increment depends on the cosine of the overall tilt angle. After a fine alignment of all projections, the volume reconstruction was calculated using the simultaneous iterative reconstruction technique (SIRT) with 10 iterations. Volume rendering and slices of the tomogram were generated using the Amira module included in the tomography package of the Digital Micrograph software (Gatan). These TEM investigations were complemented by scanning electron microscopy analyses (FEG Zeiss Supra 40) which are very convenient to determine the size and the shape of long anisotropic nano-object.


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3. Results and discussion 3.1 Influence of the growth parameters The temperature dependence of the anisotropic growth of Cu nanostructures was studied and reveals that the activation temperature of this mechanism is about 500°C. Indeed, when the substrate temperature is below this activation temperature we only observed large facetted nanoparticles. On the contrary from 500°C to 600°C many NRs are found together with facetted particles (Figure 1). In the present work, we will only pay attention to nanostructures with relevant shape anisotropy, i.e. aspect ratio > 3. Tilt series of TEM images (Figure 1b-d) reveal that the angle between the anisotropy axis of the NRs and the substrate differs from one rod to another and varies from 45° to 90°. Due to this geometry, single TEM or SEM images, in which the depth dimension is unclear, are difficult to interpret and can even be counterintuitive when the observer is interested in the shape of the analyzed material. This issue is illustrated in Figure 1, in which many spherical particles observed with the electron beam perpendicular to the substrate (Figure 1c) turn out to be NRs on high tilt angle images (Figures 1b and 1d). By using tilt series experiments, we deduced that the length of the NRs ranges from 300 nm to 7 µm. Their width is more monodisperse and varies from 80 to 300 nm. Therefore, Cu NRs with an aspect ratio up to 56 can be obtained with this vapor phase deposition protocol. Note that the nominal thickness of the Cu film must be between 3 and 5 nm to obtain such NRs and no anisotropic nanostructures were observed when depositing a smaller Cu thickness on the substrate.

(b)

(a)

(c)

4 µm


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Figure 1. Cu nanorods obtained by thermal evaporation on an amorphous carbon film heated at 500°C. (a) SEM image in secondary electrons mode. TEM images of the same area acquired at different tilt angle (α) : (b) α = − 65°C, (c) α = 0°, (d) α = + 65°.

To determine the influence of the substrate on the growth of Cu NRs, we applied the same experimental protocol on an amorphous silicon film heated at 500°C. Surprisingly, this synthesis generates very small nanoparticles and large non-facetted aggregates with random shapes (see Figure 1 in supplementary materials). Thus, the amorphous carbon substrate seems to play an important role in the formation of Cu NRs although we cannot exclude that, in the case of silica, the activation temperature of this anisotropic growth mode is higher than 500°C. Finally, we have also highlighted the kinetic aspects of the nanorod growth. We have realized a synthesis on amorphous carbon at room temperature. This sample was then heated at 500°C for 30 minutes, corresponding to the synthesis time. This protocol does not allow the formation of NRs and leads to spherical nanoparticles with large size dispersion (see Figure 2 in supplementary materials). This result demonstrates that the non conventional anisotropic shape of the Cu nanostructures prepared on amorphous carbon is not strictly imposed by thermodynamics. It is also stabilized by kinetic effects at the early stage of the vapor phase deposition processes.

3.2 Structural analyses Electron diffractions acquired on individual nanorods reveal their face-centered cubic (FCC) structure, as expected from the bulk copper phase diagram. These structural analyses also evidenced that the majority of the rods are monocrystals (Figure 2). The crystallographic direction of anisotropy is of primary importance to understand the growth mode and the shape


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of elongated nano-objects. However, the determination of the anisotropy axis by electron microscopy is not trivial since their axis does not lie in the plane of the substrate. Consequently, the angle between the anisotropy axis and the substrate cannot be determined on the bright field image and, it is then impossible to deduce the crystallographic direction of anisotropy from the image and the diffraction of a nanorod. This limitation can be overcome by using the following geometric approach, which can be applied to the TEM structural study of any crystalline anisotropic nano-objects. As shown in Figures 2a and 2b, this methodology consists in acquiring two images and two diffractions of the same nanorod oriented along two different zone axes. We have checked that the rotation of the projector lenses system of the JEOL ARM 200F microscope is well compensated at any magnification and that there is no rotation between images and diffractions. Therefore, a given direction on the image is parallel to the same direction in the diffraction plane. The diffraction pattern in Figure 2a shows that the nanorod structure is oriented along the [001] zone axis and the projection of the anisotropy axis observed on the corresponding image, is parallel to the [200] direction a). The condition for having a [uvw] direction included in a (hkl) plane is:

hu + kv + lw = 0

Taking into account this condition and the geometry of electron diffraction, the anisotropy axis is obviously contained in the (020) plan which includes the [200] and [002] directions. Similarly, in Figure 2b, the nanorod structure is in [112] zone axis orientation and the projection of the anisotropy axis is along the [ 2 20] direction. Therefore, the rod anisotropy

a)

Strictly speaking, this is the [200] direction of the reciprocal lattice. But, since copper crystallizes in the face centered cubic Bravais lattice, the basis vectors a, b and c of the unit cell are parallel to those of the reciprocal lattice. There is thus no need to distinguish directions between direct and reciprocal lattices.



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axis is also contained in the (11 ) plan. It is then possible to conclude that the crystallographic direction of anisotropy is [101], which corresponds to the intersection of the (020) and (11 ) planes. Applied to many nanorods, this method has evidenced that the anisotropy axis is always a [110]-type direction.

Figure 2. Nanorod structural analysis: Bright field images and diffraction patterns (indexed according to the FCC structure) of the same nanorod acquired along different zone axis. The white dotted line presents the projection of the anisotropy axis observed on the bright field images. (a) The nanorod is oriented along the [001] zone axis. (b) The nanorod is oriented along the [112] zone axis. Aberration-corrected high resolution transmission electron microscopy (HRTEM) was used to characterize the nanorods surface state, which is a very important parameter for understanding their physical properties. As shown on Figure 3, the nanorod surface is quasi-atomically smooth both on the side (Figure 3a) and the tip (Figure 3b). Moreover, these atomic-scale observations unambiguously show that the surface of the rods is not oxidized. Indeed, Cu


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oxidation would have induced a substantial change of the crystal lattice parameters near the surface of the nanorod. This result was confirmed by electron energy loss spectroscopy (EELS) (insert of Figure 3b). The shape of the spectrum is typical from non-oxidized copper since, in the range of energy from 520 to 540 eV, there is no peak corresponding to the oxygen K edge (532 eV). In addition, in the range from 920 to 990 eV, the spectrum exhibits clearly a copper L2,3 edge corresponding to the reference of metallic copper given by Ahn and Krivanek, with a smooth edge located at 925 eV.36 In the case of copper oxide, the Cu L2,3 edge is characterized by two peaks (also known as white line edges) centered at 931 and 951 eV which are not observed here. Single atoms detection by EELS has been already realized with a cold FEG electron microscope.37 This level of sensitivity allows excluding the presence of a small layer of copper oxide.

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(b)

8,0x105 6,0x105 4,0x105 2,0x105 0,0 520 530 540 920 930 940 950 960 970 980 990

Energy loss (eV)

Figure 3. High resolution images of the side (a) and the tip (b) of a copper nanorod. In insert, the Fourier transform of the image shows the face centered cubic crystal structure, oriented along the [220] zone axis direction. The insert shows the EELS spectrum of the copper NR in the energy range of oxygen K edge(520 – 540 eV, black line) and copper L2,3 edge (920 – 990 eV, red line).



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3.3 3D morphology analysis by tomography Among the TEM techniques developed to obtain three-dimensional information on a nanometer scale, tomography is without any doubt the simplest and the most effective.38,39 We performed electron tomography in STEM HAADF mode in order to minimize artifacts due to diffraction contrast which could be important on micron-long Cu nanorods. The 3D reconstruction observed on Figure 4a clearly shows the parallelepiped form of the nanorods. Indeed, the nanorods present four well defined rectangular facets, parallel to the [110] anisotropy axis. This two-fold symmetry is confirmed by the rectangular shape observed on both the cross section of the nanorod extracted from the tomogram (i.e. 2D slice perpendicular to the nanorod anisotropy axis, left insert in Figure 4a) and the high resolution SEM images (Figure 4b).

0.255 nm

0.361 nm

(b)

[001]

20 nm

(a)

[110]

100 nm 200 nm

Figure 4. (a) Nanorod tomogram. Left insert: slice of the tomogram in a plane perpendicular to the anisotropy axis showing the 2-fold symmetry of the rectangular section of the nanorod. Right insert: Projection along the 2-fold [110] direction of the FCC structure of copper. (b) SEM imaging of a Cu nanorod. The edges of the NR have been highlighted with red dotted lines.


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To determine the indexes of the NRs lateral facets, diffraction experiments were performed on NRs oriented with the projection of their anisotropy axis along the tilt axis of the tomography TEM sample holder. In such configurations, NRs with their long axis lying parallel or almost parallel to the tilt axis of the microscope were rotated along the tilt direction until their lateral size is the smallest so that the largest lateral facets are almost edge on with respect to the electron beam. In all the analyzed NRs, the lateral facets are parallel to the {002} planes. A typical example is shown in Figure 5 where the NR is oriented near the [3 5 0] zone axis (Figure 5b). It would have been possible to confirm this result by acquiring electron diffraction on NRs with their anisotropy axis parallel to the electron beam. However, due to their very long size, up to several microns, it is quite difficult to acquire electron diffraction in such configuration, the pattern being mostly dominated by strong inelastic scattering. According to the direction of the anisotropy axis of the NRs, namely [110], and the direction perpendicular to the large lateral facets ([002]), we can deduce that the planes parallel to the small facets are perpendicular to the [2 2 0] direction, i.e. the (2 2 0) planes. Hence the NRs have rectangular section bounded by the {002} and {220} planes for large and small lateral facets respectively (Figure 5c).



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(a)

1 µm (b)

[002]

(c) 531 _

002

531

Figure 5. Bright field (BF) image of a Cu NR oriented near the [3 5 0] zone axis direction (a) and 3D model (b). (c) Corresponding electron diffraction showing the [002] direction perpendicular to the large facets of the NR. To determine the direction perpendicular to the large facets, we have selected on the BF a NR with its long axis parallel to the tilt axis of the sample holder then the NR was rotated along the tilt direction until the section of the NR is the smallest.

4. Discussion Remarkably, the shape of nanorods revealed by electron tomography is different than those observed in chemically prepared Cu NRs. This result is original since nobody reports yet this anisotropic growth mode by using controlled physical evaporation technique to synthesize Cu NRs. Moreover, it worth noting that the growth mechanism observed here is completely


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different than the one that has already been reported in the literature for the NRs prepared by chemical routes.12,19,40-42 In all these works, the NRs growing is induced on 5-fold symmetry nanoseeds (icosahedra, decahedra), which are commonly obtained in metallic FCC nanoparticles with small size. The NRs have their anisotropy axis parallel to the [110] direction and are formed by a cyclic penta-twinned FCC structure bounded by five {111} twinned boundaries at both NR edges and five {200} side surfaces. The formation of highly anisotropic Cu nanostructures is then induced by two phenomena. At first, the twin boundaries on the edges of the NRs are the highest energy sites on the surface resulting in a preferential attachment of the Cu atoms on those sites. This leads to a unidirectional elongation of decahedron into a pentagonal nanorod limited by {200} facets. The mechanism involving crystal defects in the growth of anisotropic NRs has been very well explained by Lofton and Sigmund.43 This mechanism cannot be envisaged here since we don’t observed such defect in the NRs produced by the thermal evaporation technique. Secondly, it has been proposed that surfactants (PEG and CTAB,25 polyols,26 tetradecylamine (TDA)27) or chemical reagents, in the case of surfactant-less synthesis, (glucose at a particular concentration11) are face-blocking agents. These molecules will stick preferentially on the {200} surfaces rather than on the {111} ones in order to reduce the total surface energy of the system. This gives rise to the passivation of the {200} surfaces preventing their further growth. Once the rodshaped structure has been formed, it can readily grow into longer NR because their side surfaces are completely passivated whereas their tip facets are uncovered. They remain to be reactive sites toward new copper atoms inducing consequently the preferential growth on the {111} facets only.12,15,27 The same mechanisms have been also proposed to explain the anisotropic growth of silver and gold nanowires.42,44-47 The copper NRs prepared by vapor phase deposition exhibit a two-fold symmetry around their [110] anisotropy axis. This symmetry reflects the intrinsic one of the face centered cubic



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lattice of the Cu crystal as illustrated in the right insert of Figure 4a and can be explained by thermodynamic considerations. Even if the observed morphology is stabilized by kinetic effects during the early stage of the nucleation step, the different free energies of the crystal facets are responsible for the anisotropic growth mode of the Cu NRs. The equilibrium shape of nanocrystals is determined by the Wulff construction.48 The Wulff theorem expresses that the ratio of the different surface free energies and the corresponding distance between a given facet and the centre of the NPs is constant. As a consequence, metallic FCC Cu nanoparticles tend to minimize their free energy by developing facets with the lowest surface energies: (111), (200) and (220), i.e. the densest atomic planes of the FCC structure. In such a case, the equilibrium shape of a NP formed with copper is a truncated octahedron bounded by large {111} and small {200} facets. However, as the energy landscape of NPs varies with the synthesis conditions (composition, size, pressure in the vacuum chamber, temperature and nature of the substrate) and kinetic effects, morphologies that are not predicted by the Wulff construction can be formed during the growth. Nucleation of the Cu nanostructures takes place on preferential sites of the amorphous carbon substrate. On an amorphous carbon substrate, local atomic arrangement with various symmetries: pentagons, hexagons, heptagons, etc…49 exist and can act as nucleation site. Depending on the local symmetry of these nucleation sites, the Cu seeds can have different morphology. Then, the further growth of the anisotropic morphology is favored by both the direct growth of the NRs from the atoms coming from the vapour phase and by the highly diffusive Cu atoms, directly deposited on the carbon surface, towards the already formed Cu NRs. Metals are known to diffuse very rapidly on carbon substrates since the energy barrier for diffusion is very low, a few hundredth of electron volt.51 During the growing process, the nanocrystal tends to develop a 3D morphology that minimizes its surface energy. The final shape exhibits surfaces with the slowest growth rate


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i.e. those having the lowest surface energy. These surfaces have the higher importance in the nanocrystal morphology. Assuming the surface free energy is only due to the energy required to break first neighbor bonds,52,53 we can determine the surface energy from the simple following model. In a face centered cubic structure, each atom has 12 first neighbors. We first calculate the number nB of unsaturated bonds (dangling bonds) in the first three surfaces with lowest indexes. In the (111) planes, each atom has 6 first neighbors. Hence the 6 others are distributed symmetrically on both sides of the surface so there are 3 dangling bonds. In the (200) planes, each atom has 4 first neighbors, hence there are 4 dangling bonds. Finally, in the (220) planes, each atom has 2 first neighbors and then there are 5 dangling bonds in these planes. To evaluate the bond energy, we use the latent heat of sublimation, Lsub, by assuming it needs to break 12 bonds per atom to go through the solid → vapor transition. The surface energy per atom is thus equal to nB Lsub / 12. For copper, Lsub is equal to 3.534 eV.atom−1 48 and the surface energy for the (111), (200) and (220) surfaces are respectively: ES(111) = 3/12 Lsub = 0.883 eV.atom−1, ES(200) = 4/12 Lsub = 1.178 eV.atom−1, ES(220) = 5/12 Lsub = 1.472 eV.atom−1. These values are overestimated since Lsub is not a free enthalpy and a term –T∆S, T being the temperature and ∆S the entropy difference between the vapor phase and the crystalline one, must be added which lower Lsub because the entropy of the vapor phase is higher than the one of the crystal. At 500°C, the entropy difference between the vapor and the crystalline phase is equal to 0.00135 eV.atom−1.54 By taking into account this contribution in the model, the values of the surface energies are the following: ES(111) = 0.623 eV.atom−1, ES(200) = 0.830 eV.atom−1, ES(220) = 1.038 eV.atom−1. These values of surface energies obtained with this very simple model are in good agreement with the ones calculated by Vito et al.55 These authors have computed the surfaces energy of copper by using the density functional theory and they



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found respectively for the (111), (200) and (220) surfaces: ES(111)= 0.707 eV.atom−1, ES(200)= 0.906 eV.atom−1 and ES(220) = 1.323 eV.atom−1. As a consequence, for morphology with twofold symmetry, like the one of the Cu nanorods studied in this paper, the (200) surface is the most important with respect to the (220) one. The anisotropic growth mode observed in this work can then proceeds in two steps. In the first step, the Cu seeds are formed very rapidly during the nucleation process due to the very low energy of the diffusion barrier of Cu on carbon. Some of the seeds would exhibit two-fold symmetry with {200} and {220} facets due to local symmetry arrangement of the carbon atoms in the substrate. In the second step, these seeds can grow and they will develop morphology which obeys to the thermodynamic rules of the growth rates of crystal facets as a function of their surface energy. The facets with the lowest surface energy have a slower growth rate and will be highly developed in the final morphology. At the opposite, the facets with a high surface energy, for which the growth rate is high, tend to disappear in the 3D shape of the nanostructure. The NRs tends therefore to develop a parallelepiped shape bounded by large (200) surfaces and small (220) facets.

5. Conclusion We have shed light on the formation of Cu nanorods by vapor phase deposition on amorphous substrates. The copper nanorods growth is favored on carbon substrates with an optimal temperature of 500°C and with a 3 nm nominal thickness of Cu. The NRs are monocrystals with a face centered structure as the bulk copper. Their anisotropy axis is parallel to the [110] direction as demonstrated by using a geometrical approach that mixed direct and reciprocal information. We have shown that this anisotropic morphology results from an out-ofequilibrium shape stabilized during the growth that cannot be obtained by a thermal annealing at the same temperature after the synthesis.


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Electron tomography was used to determine the precise 3D morphology of the NRs. We evidenced non expected shapes with two-fold symmetry bounded by rectangular facets. Finally, we show that while the Cu NRs prepared by physical and chemical route have the same [110] anisotropy direction, their final 3D shape is different. For chemical route synthesis, the shape of the NRs, with a five-symmetry bounded by large {200} lateral facets, is imposed by the passivation of given faces by surfactants. On the contrary, the morphology of the NRs grown by physical vapor deposition exhibits a two-fold symmetry and can be explained by thermodynamic considerations.

Acknowledgements We are grateful to Region Ile-de-France for convention SESAME E1845, for the support of the JEOL ARM 200F electron microscope recently installed at the Paris Diderot University. The authors are also indebted to Hélène Lecoq (ITODYS, University Paris Diderot, Paris, France) for the SEM FEG experiments.

References (1) Andres, R. P.; Bielefeld, J. D.; Henderson, J. I.; Janes, D. B.; Kolagunta, V. R.; Kubiak, C. P.; Mahoney, W. J.; Osifchin, R. G. Science 1996, 273, 1690-1693. (2) Forster, S.; Antonietti, M. Adv. Mater. 1998, 10, 195-217. (3) Cui, Y.; Wei, Q.; Park, H.; Lieber, C.M. Science 2001, 293, 1289-1292. (4) Liu, S.; Yue J.; Gedanken, A. Adv. Mater. 2001, 13, 656-658. (5) Xia, Y.; Yang, P.; Sun, Y.; Wu, Y.; Mayers, B.; Gates, B.; Yin, Y.; Kim, F.; Yan, H. Adv. Mater. 2003, 15, 353-389.



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For Table of Contents Use Only Title of the manuscript: Original anisotropic growth mode of copper nanorods by vapour phase deposition

Authors : H. Prunier, C. Ricolleau, J. Nelayah, G. Wang, D. Alloyeau* Synopsis: Copper nanorods were obtained by thermal vapor deposition. Their structural properties and their growth morphology have been studied by a series of complementary transmission electron microscopy techniques. They are in the cubic face centered structure and they grow with their anisotropy axis parallel to the [110] direction. A model including both kinetic and thermodynamic aspects is proposed to explain the growth mechanism.

20 nm

100 nm


(b)

Page (a) 23 of 27 1 2 3 4 5 6 7 8

Crystal Growth(c) & Design


4 µm

(d)

(a)


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2-20

1 2 3 4 5 6 7 8 9 10 (b) 11 12 13 14 15 16 17 18 19 20 21

200

220

0-20 -2-20

020 -200

-220

[001]

-1-11

-311 -220 -13-1

1-31

ACS Paragon Plus Environment 2-20 3-1-1

11-1

[112]

(a)

002 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26

-

220

EELS intensity

6 Crystal Growth1,0x10 & Design

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(b)

8,0x105 5

6,0x10

4,0x105 2,0x105 0,0 520 530 540 920 930 940 950 960 970 980 990

Energy loss (eV)


1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21

(a)

[001]

20 nm

0.255 nm

0.361 nm

(b) Crystal Growth & Design

[110]


100 nm 200 nm

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(a)

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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39


1 µm

(b)

[002]

(c) 531 _

531

002


Original Anisotropic Growth Mode of Copper Nanorods by Vapor

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