Al/CuO nanothermites were fabricated by thermal oxidation of copper layer at 4501C for 5 hand by aluminum thermal evaporation: thermal evaporation allows producing thin layer less than 2 mminsize. The copper has been deposited by electroplating or thermal evaporation depending on the required thickness. The obtained diameter of Al/CuO nanowiresis 150–250nm. Al/CuO nanowires composite were characterized by scanning electronmicroscopy (SEM), X-raydiffraction (XRD), differential scanning calorimetry (DSC) and differential thermal analysis (DTA). Two distinct exothermicreactions occurred at 515 and 6671C and total energy release of this thermite is 10kJ/cm

Alphonse, Pierre

Bourrier, David

Conédéra, Véronique

Petrantoni, Marine

Rossi, Carole

Tenailleau, Christophe

English

International audienceAl/CuO nanothermites were fabricated by thermal oxidation of copper layer at 4501C for 5 hand by aluminum thermal evaporation: thermal evaporation allows producing thin layer less than 2 mminsize. The copper has been deposited by electroplating or thermal evaporation depending on the required thickness. The obtained diameter of Al/CuO nanowiresis 150–250nm. Al/CuO nanowires composite were characterized by scanning electronmicroscopy (SEM), X-raydiffraction (XRD), differential scanning calorimetry (DSC) and differential thermal analysis (DTA). Two distinct exothermicreactions occurred at 515 and 6671C and total energy release of this thermite is 10kJ/cm

Scientific Publications of the University of Toulouse II Le Mirail

Synthesis process of nanowired Al/CuO thermite.

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Open Archive Toulouse Archive Ouverte (OATAO)OATAO is an open access repository that collects the work of Toulouse researchers andmakes it freely available over the web where possible.  This is an author-deposited version published in: http://oatao.univ-toulouse.fr/ Eprints ID: 3822To link to this article: doi:10.1016/j.jpcs.2009.07.020 URL: http://dx.doi.org/10.1016/j.jpcs.2009.07.020To cite this version: Petrantoni, M. and Rossi, Carole and Conédéra, V. and Bourrier, D. and Alphonse, Pierre and Tenailleau, Christophe ( 2010) Synthesis processofnanowiredAl/CuOthermite. Journal of Physics and Chemistry of Solids, vol.71 (2). pp. 80-83. ISSN 0022-3697 Any correspondence concerning this service should be sent to the repository administrator: staff-oatao@inp-toulouse.fr Synthesis process of nanowired Al/CuO thermiteM. Petrantoni a,b,, C. Rossi a,b, V. Conedera a,b, D. Bourrier a,b, P. Alphonse c, C. Tenailleau b,ca CNRS, LAAS, 7 Avenue du Colonel Roche, F-31077 Toulouse, Franceb Universite de Toulouse, UPS, INSA, INP, ISAE, LAAS , F-31077 Toulouse, Francec CIRIMAT, 118 route de Narbonne, 31062 Toulouse Cedex 04, FranceArticle history:Received 2 June 2009Accepted 22 July 2009Keywords:A. NanostructuresC. X-ray diffractiona b s t r a c tAl/CuO nanothermites were fabricated by thermal oxidation of copper layer at 450 1C for 5 h and byaluminum thermal evaporation: thermal evaporation allows producing thin layer less than 2mm in size.The copper has been deposited by electroplating or thermal evaporation depending on the requiredthickness. The obtained diameter of Al/CuO nanowires is 150–250 nm. Al/CuO nanowires compositewere characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), differentialscanning calorimetry (DSC) and differential thermal analysis (DTA). Two distinct exothermic reactionsoccurred at 515 and 667 1C and total energy release of this thermite is 10 kJ/cm3.1. IntroductionIn recent years researchers have found that energetic materialswhich are produced on the nanoscale show significantly improvedperformances, especially in the area of sensitivity. Metastableintermolecular composites (MICs) or nanothermites represent oneexample of such materials. These systems consist of metals (e.g.aluminum) and oxidizers [1]. For MEMS applications, Al/CuOsystem is particularly interesting because aluminum and copperare commonly used in a microelectronic process and Al/CuOreaction can reach up to 4 kJ/g. However, produced at macroscale,composite reaction is relatively slow [2,3]. Produced at nanoscale,as the specific surface area increases, the intimacy betweenthe reactants (Al and CuO) also increases and therefore thereaction rate increases, making Al/CuO nanothermite very inter-esting. Our team members, Zhang et al., have developed a simpleprocess to produce array of nanowires of CuO covered by a thinlayer of Al [4,5]. This paper describes an optimized thermaloxidation process to produce an auto organized array of CuOnanowires of 40–90nm diameter from a Cu thin layer. Here,we also compare the effects of two kinds of copper depositionmethods on the nanowires growth. Finally, the energetic perfor-mances of the optimized Al/CuO nanowired thermite arecharacterized using DSC and DTA to determine experimentallythe heat of reaction.2. Experiment2.1. Al/CuO sample preparation2.1.1. Cu depositionA 30-nm-thick layer of titanium is thermal evaporated undersecondary vacuum (3.7510–7 Torr) on the clean 400 silicon sub-strate to serve as an adhesion layer between copper and silicon.After this stage two kinds of copper deposition methods are usedelectroplating and thermal evaporation.For the electroplated copper, a 50-nm-thick layer of copper isevaporated to serve as a conducting layer for the second step,which is the electroplating of Cu film at 25 1C in a microfabCU200bath (25 g(Cu)/L(H2SO4)—Enthone Omi). The current density is2A/dm2. Copper thickness is 1mm.For the thermal evaporated copper, the step following thetitanium evaporation is the thin film copper evaporation. Copperthicknesses tested for the nanowires growth are 50, 300 and1000nm to determine the critical thickness below which there isno nanowire growth.2.1.2. Cu thermal oxidationNext step is the removal of the native copper oxide using adiluted solution of hydrochloric acid (HCl). Then, the as-preparedwafers are cleaned, dried by nitrogen and oxidized in static air.The optimized oxidation process to get only CuO is as follows: a thermal ramp from room temperature to 450 1C with aheating rate of 2 1C/min a plateau at 450 1C during 5h under static air (see Fig. 1) a cooling ramp from 450 1C to room temperature with a rate of2 1C/minARTICLE IN PRESSCorresponding author at: LAAS–CNRS, Groupe N2IS, 7 avenue du ColonelRoche, 31077 TOULOUSE Cedex 4-France. Tel.: +330 561336418;fax: +330561336208.E-mail address: mpetrant@laas.fr (M. Petrantoni).ARTICLE IN PRESSFor nanoenergetic application, it is important to have only CuObecause Al/CuO exhibits the highest heat of reaction [6].3CuO+2Al-3Cu+Al2O3, DH ¼ 21kJ/cm3 or 4.1 kJ/g (5)3Cu2O+2Al-Al2O3+6Cu, DH ¼ 13kJ/cm3 or 2.5 kJ/g2.1.3. Al/CuO nanothermite finalizationA 1mm aluminum is thermally evaporated on and inside theCuO nanowires array obtained from the evaporated or electro-plated Cu (see Fig. 2).The Al/CuO samples preparation are illustrated in Fig. 2.2.2. CharacterizationThe Al/CuO nanowires are observed using scanning electronmicroscopy (SEM); S-4800.Oxide nanowires are also characterized by X-ray diffraction(XRD). Thermal analyses are performed by differential scanningcalorimetry (DSC) and differential thermal analysis (DTA). For DSCmeasurements, each sample undergoes a temperature increasefrom 300 to 1000K with a heating rate of 5K/min under anitrogen flow (99.999% purity). DTA measurements allow us towork on a widest temperature range (up to 1200 1C (1473K) with aspeed of 5 1C/min under a 4.5 argon flow (99.995% purity)).3. Results3.1. Copper oxide natureAfter copper oxidation, a large area of copper oxide nanowiresis observed by SEM on the surface of the silicon wafer. Theobserved diameter of the nanowires is between 40 and 90nm.The XRD pattern shows only CuO peaks (see Fig. 3).After aluminum deposition, the nanowire diameters are inthe range 150–250nm. As shown in Fig. 4, the aluminum coats allthe copper oxide nanowires surface and even penetrates betweeneach nanowire. The specific Al growth on the nanowires could beobserved in Fig. 4b.Fig. 1. Thermal oxidation cycle parameters.Native oxide removing-Thermal oxidation(450°C –5h –static air)SiSiTi (30 nm)Cu (50 nm)ElectroplatingSiTi (30nm)Cu (50 + 1000 nm)SiTiCuOSiTi (30 nm)Cu (≤1000 nm)SiTiAl film on CuOThermal evaporationThermal evaporationThermal evaporationFig. 2. Schematic view of the nanowired Al/CuO process.Fig. 3. (a) X-ray diffraction analysis of a CuO sample and (b) SEM image of CuOnanowires.Fig. 4. SEM images of Al/CuO nanowires: (a) top view and (b) cut view.M. Petrantoni et al. / Journal of Physics and Chemistry of Solids 71 (2010) 80–83ARTICLE IN PRESS3.2. Thermal evaporation vs. electroplatingSEM observations and XRD analyses of CuO grown from 1mmcopper evaporated or 1mm electroplated showed that (see Fig. 5):1. The chemical composition between the two samples is thesame with only CuO present.2. Nanowires are present in both samples.As a consequence, in order to have dense nanowires array with aless risk of impurity, it is preferable to start with a thermalevaporated copper thin film. But it is limited to copper thicknessless than 1–2mm.3.3. Critical copper thicknessWe have also characterized the nanowires density for differentthicknesses of evaporated oxidized Cu (50, 300 and 1000nm) inorder to determine the critical thickness to form CuO nanowires(see Fig. 6a).In Fig. 6, it can be seen that the nanowires growth begins witha metal grain swelling (Fig. 6a), afterwards nanowires grow(Fig. 6b) with an inhomogeneous repartition on the samplesurface. The critical copper thickness to get nanowires in our caseis 300nm.Fig. 6. SEM images of evaporated Cu film surface after thermal oxidation. Copperthickness is: (a) 50nm and (b) 300nm.Fig. 7. Measurements of the heat of reaction in Al/CuO sample by: (a) DSC and(b) DTA.Fig. 5. SEM images of CuO nanowires: (a) from a 1-mm-thick thermal evaporatedthin Cu film and (b) from a 1-mm-thick electroplated Cu thin film.M. Petrantoni et al. / Journal of Physics and Chemistry of Solids 71 (2010) 80–83ARTICLE IN PRESS3.4. Thermal decompositionDSC and DTA results on CuO/Al samples (with 1mm ofelectroplated Cu) are shown in Fig. 7a and b, respectively. Anexothermic reaction occurs before the aluminum melting point(630 1C). This can be explained by the first solid Al–solid CuOreaction that occurs in the nanowires region and between Al/CuOinterfaces. A second and more important exothermic reactiontakes place around 667 1C, so after the melting point of aluminum.In that case, the aluminum should diffuse into the CuO thicknessleading to a reaction in the volume.The total heat of reaction is calculated to be 2.5k J/g or10 kJ/cm3, which is less than the theoretical one (3.9 kJ/g). Thisdifference can be explained by the unoptimized stoichiometry ofthe reactants Al and CuO.After the DSC analysis, XRD pattern indicates that the finalproducts are Al and CuO (see Fig. 8a). This result could beinterpreted by a none reaction of the thermite sample. Butexothermic reaction has been observed and measured using theDSC method (see Fig. 7a). Therefore, we supposed that at 515 1C,which corresponds to a DSC maxima temperature is too low topermit a complete reaction in material bulk. At this temperatureonly interfaces reaction between Al and CuO may occur.In consequence, the products of the reaction are amorphous, orthickness is too low to be detected by the XRD method.After DTA measurements, XRD analyses were realized andshowed that the final products were CuO and CuAlO2 (see Fig. 8b).In that case, the thermite has completely reacted but there are nocopper and no Al2O3. The Cu formed by the Al/CuO reaction mayhave reacted with Al or Al2O3 to produce CuAlO2 or may haveformed CuO. Moreover, we should have excess of CuO in theAl/CuO stoichiometry.4. ConclusionAl/CuO nanowires were realised by thermal oxidation ofcopper thin film and the deposition of an aluminum thermalevaporated layer. The diameter of CuO nanowires is between 40and 90nm and the diameter of Al/CuO nanowires is between 250and 350nm. If the Cu layer thickness is less than 2mm, thermalevaporation deposition method is preferable to get denser CuOnanowires. For thicknesses greater than 2mm, electrodeposition isused and can also gives CuO nanowires. For Cu with thickness lessthan 300nm, no nanowire has grown. Finally, DTA and DSCanalyses estimated the heat of reaction to be 10kJ/cm3 andshowed two distinct exothermic reactions: one at 515 1C and asecond at 667 1C. The first exothermic peak corresponds Al/CuOreaction in the nanowires region, whereas the second exothermicpeak (slower but more energetic) corresponds to the Al/CuOreaction in the bulk layer (underneath the nanowires).This new nanosized energetic layer opens the door to manypyrotechnical applications such as micro-propulsion, pneumaticactivation and pyrotechnic initiation [7–10].AcknowledgementsThis work was realized thanks to the French military agencyDGA in collaboration with NEXTER MUNITIONS.References[1] D.E. Wilson, K.Kim, 43rd AIAA Aerospace Sciences Meeting and Exhibit, Reno,NV, 2005.[2] ‘‘Novel Energetic Materials’’, /http://www.globalsecurity.org/military/systems/munitions/novel-energetic-materials.htmS.[3] Michelle L. Pantoya, John J. Granier, Propellants, Exposives, Pyrotechnics 30(2005) 53.[4] K. Zhang, C. Rossi, G.A. Ardila Rodriguez, Applied Physics Letters 91 (2007)3117.[5] K. Zhang, C. Rossi, C. Tenailleau, P. Alphonse, J.Y. Chane-Ching, Nanotechnol-ogy 18 (2007) 8.[6] S.H. Fischer, M.C. Grubelich, in: Proceedings of 24th International Pyrotech-nics Seminar, Monterey, CA, USA, 1998.[7] K. Zhang, C. Rossi, M. Petrantoni, N. Mauran, Journal of Microelectromecha-nical Systems 17 (4) (2008) 832.[8] G. A Ardila Rodrı´guez, S. Suhard, C. Rossi, D. Esteve, P. Fau, S. Sabo-Etienne,A.F. Mingotaud, M. Mauzac, B. Chaudret, Journal of Micromechanics andMicroengineering 19 (2009) 8.[9] H. Laucht, H. Bartuch, D. Kovalev, in: Proceedings of the Seventh InternationalSymposium and Exhibition on Sophisticated Car Occupant Safety Systems,2004, p. 12.[10] D.S. Stewart, in: Proceedings of 21st the International Conference ofTheoretical and Applied Mechanics (ICTAM04), 2004.2-Theta (deg)2-Theta (deg)CuAlO2CuOCuOAl20 40 60 8020 40 60 80 100Intensity(a.u.)Intensity(a.u.)Fig. 8. XRD analyses: (a) after DSC measurement and (b) after DTA measurements.M. Petrantoni et al. / Journal of Physics and Chemistry of Solids 71 (2010) 80–83

K.Kim, 43rd AIAA Aerospace Sciences Meeting and Exhibit,

Novel Energetic Materials’’, /http://www.globalsecurity.org/military/sys tems/munitions/novel-energetic-materials.htmS.

Propellants, Exposives,

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Synthesis process of nanowired Al/CuO thermite.

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