Layered Al/Cuo Thin Films for Tunable Ignition and Actuations Ludovic Salvagnac, Sandrine Assié-Souleille, Carole Rossi

Layered Al/CuO Thin Films for Tunable Ignition and Actuations Ludovic Salvagnac, Sandrine Assié-Souleille, Carole Rossi

To cite this version:

Ludovic Salvagnac, Sandrine Assié-Souleille, Carole Rossi. Layered Al/CuO Thin Films for Tun- able Ignition and Actuations. Nanomaterials, MDPI, 2020, 10 (10), 10.3390/nano10102009. hal- 02964404

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Communication Layered Al/CuO Thin Films for Tunable Ignition and Actuations

Ludovic Salvagnac, Sandrine Assie-Souleille and Carole Rossi * CNRS, LAAS, University of Toulouse, 7 Avenue du Colonel Roche, F-31400 Toulouse, France; [email protected] (L.S.); [email protected] (S.A.-S.) * Correspondence: [email protected]

Received: 20 August 2020; Accepted: 8 October 2020; Published: 12 October 2020

Abstract: Sputter-deposited Al/CuO multilayers are used to manufacture tunable igniters and actuators, with applications in various ﬁelds such as defense, space and infrastructure safety. This paper describes the technology of deposition and the characteristics of Al/CuO multilayers, followed by some examples of the applications of these energetic layers.

Keywords: nanothermite; pyroMEMS; nanoenergetics; reactive thin ﬁlm

1. Introduction Energetic materials are widely used to suddenly generate high amounts of thermal or mechanical energy under an electrical, mechanical or thermal stimulus. As typical energetic materials, nanothermites, which contain Al and oxide, have attracted much attention as they exhibit not only better combustion efficiencies and better ignitability compared to traditional explosives, but also their reaction outputs can be tuned, thanks to the selections of fuels, oxidizers, architectures and reactant size, allowing multiple actions. Among nanothermites, sputter-deposited Al/CuO multilayers represent interesting energetic thin film nanomaterials for tunable ignition, to replace old hot-wire ignitors. In that context, our research group demonstrated several miniature pyrotechnical ignition devices integrating Al/CuO multilayers within microelectromechanical systems (MEMS) based microheaters, called pyroMEMS, for civilian and military applications such as triggering the inflation of airbags, micro-propulsion systems, and arm and fire devices. This paper briefly reviews the technological process, focusing on the sputter-deposition technique, presents the properties of Al/CuO multilayered films, details the fabrication process flow of a micro-igniter, and present examples of applications of pyroMEMS.

2. Al/CuO Multilayered Nanothermites Two decades ago, the introduction of nanotechnologies enabled the emergence of a new class of energetic materials called nanothermites that could play a great role in future society. Nanothermites use raw materials that can be found in abundance, are low-cost and non-polluting (green materials). They also exhibit better combustion eﬃciencies and better ignitability compared to typical CHNO energetic mixtures, while being safer. Importantly, the reactions and ability to trigger speciﬁc actions can be tailored by varying the size and composition of the oxide, allowing multiple applications. Focusing on thermite multilayers, the overwhelming majority of works concern Al/CuO systems, as they feature an exceptionally high-energy release with gaseous production.

2.1. Multilayers Deposition Al/CuO thermite multilayers are mainly produced by the sputter-deposition technique [1–5], as this provides excellent control over the layering and stoichiometry. Cupric oxide thin ﬁlm is synthesized

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2.1. Multilayers Deposition

NanomaterialsAl/CuO2020 thermite, 10, 2009 multilayers are mainly produced by the sputter-deposition technique [1–5],2 ofas 6 this provides excellent control over the layering and stoichiometry. Cupric oxide thin film is synthesized using the direct current (DC) reactive magnetron sputtering technique in an oxygen- enrichedusing the environment. direct current To (DC)produce reactive Al/CuO magnetron multilayered sputtering films, layers technique of Al inand an CuO oxygen-enriched are deposited onenvironment. top of each other To produce in an alternating Al/CuO multilayeredfashion (see Figure ﬁlms, 1) layers without of venting Al and the CuO chamber. are deposited However, on aftertop of each each layer other of in deposition, an alternating the fashionsample (seestage Figure is cooled1) without at ambient venting temperature the chamber. for However, 600 s. At aftereach interfaceeach layer between of deposition, the cupric the sampleoxide and stage Al islayers, cooled an at intermixing ambient temperature layer of 4–8 for nm 600 is s.present At each that interface forms duringbetween the the deposition cupric oxide itself. and Al layers, an intermixing layer of 4–8 nm is present that forms during the depositionDepositions itself. parameters have been published several times and can be found in [6,7].

Figure 1. Cross-sectional transmission electron micrographs of the Al/CuO multilayer obtained by Figure 1. Cross-sectional transmission electron micrographs of the Al/CuO multilayer obtained by magnetron sputtering. magnetron sputtering.

2.2. IgnitionDepositions and Reaction parameters Properties have been published several times and can be found in [6,7]. Applying an external source of energy locally on the multilayer results in an increase in the 2.2. Ignition and Reaction Properties temperature of the multilayer section directly in contact with the heated surface. This can be done by electrostaticApplying discharge an external [8], mechanical source of energyimpact locally[9], laser on irradiation the multilayer [10], electrical results in heating an increase (spark) in [11] the ortemperature thermal hot of points the multilayer [12], the sectionlatter of directly which is in the contact widest with used. the After heated being surface. ignited, This the can multilayers be done by reactelectrostatic by a self-sustained discharge [8 ],propagating mechanical reaction impact [9 following], laser irradiation the chemistry [10], electrical of Equation heating (1). (spark) [11] or thermal hot points [12], the latter of which is the widest used. After being ignited, the multilayers react 2Al + 3CuO → Al2O3 + 3Cu (+ ∆H) (1) by a self-sustained propagating reaction following the chemistry of Equation (1). In other words, after the temperature is raised locally and rapidly to a characteristic onset reaction temperature, the reaction2Al enthalpy+ 3CuO (∆H)Al spreads2O3 + 3Cu into ( +neighboring∆H) unreacted portions of the (1) → film, leading to a self-sustained reaction wave, which is highly luminous. AsIn otherthe exothermic words, after chemical the temperature reactions is are raised contro locallylled by and the rapidly outward to a migration characteristic of oxygen onset reaction atoms fromtemperature, the CuO thematrix reaction towards enthalpy the aluminum (∆H) spreads layers, intothe reaction neighboring rate strongly unreacted depends portions on the of thereactant ﬁlm, spacingleading to(bilayer a self-sustained thickness). reaction The sustained wave, which combustion is highly luminous.rate is commonly characterized with a standardAs the high-speed exothermic camera chemical under reactions ambient are pressure controlled [5,7]. by the outward migration of oxygen atoms fromThe the CuOcombustion matrix towardsvelocity theincreases aluminum for thinner layers, thebilayers, reaction with rate a strongly maximum depends at ~90 on m/s the for reactant free- standingspacing (bilayer foils (see thickness). Figure 2a). The However, sustained combustionthe reaction rate stops is commonly suddenly characterizedfor extremely with small a standard bilayer thicknesses,high-speed camerawhich is under due to ambient the presence pressure of interfacial [5,7]. layers, as described earlier, which reduces the amountThe of combustion stored energy, velocity i.e., increases reaction forenthalpy, thinner ∆ bilayers,H. with a maximum at ~90 m/s for free-standing foils (see Figure2a). However, the reaction stops suddenly for extremely small bilayer thicknesses, which is due to the presence of interfacial layers, as described earlier, which reduces the amount of stored energy, i.e., reaction enthalpy, ∆H.

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Figure 2. (a) Sustained combustion velocity in air of free-standing multilayers as a function of bilayer thickness (total thickness t = 2 µm); (b) ignition time as a function of the electrical power sent through the micro-heater for 5 bilayers of Al/CuO.

3. PyroMEMS Integration and Characterization When integrated onto a device/substrate, the widest and simplest ignition method for igniting an Al/CuO multilayered thin film is using hot-wire, which functions via local metallic thin film resistance.FigureFigure A 2. pyroMEMS2.(a ()a Sustained) Sustained is combustion mainlycombustion composed velocity velocity in ofin air aair ofsubstrate, of free-standing free-standing thin multilayersmetallic multilayers resistance as as a functiona function and of theof bilayer bilayer Al/CuO nanothermitesthicknessthickness (total (see (total thicknessFigure thickness 3a). t = t =2 2µ m);µm); (b ()b ignition) ignition time time as as a a function function of of the the electrical electrical power power sent sent through through Tothethe minimize micro-heater micro-heater the for ignition for 5 bilayers5 bilayers energy, of of Al Al/CuO./ CuO.the substrate must be a good thermal insulator. We chose 500 µm thick 4-inches glass substrates AF32 (Schott AG, Mainz, Germany). After being cleaned in oxygen 3. PyroMEMS Integration and Characterization plasma3. PyroMEMS to remove Integration surface contaminants, and Characterization 300 nm thic k titanium followed by 300 nm thick gold layers are evaporatedWhen integrated onto the onto glass a device substrate,/substrate, and the widestfilament and is simplestpatterned ignition using methodthe lift-off for technique. igniting an When integrated onto a device/substrate, the widest and simplest ignition method for igniting ThenAl/CuO the multilayeredgold is chemically thin ﬁlm etched is using and hot-wire, patterned which to define functions the Ti via resistance local metallic and Au thin electrical ﬁlm resistance. pads. an Al/CuO multilayered thin film is using hot-wire, which functions via local metallic thin film Finally, Al/CuO multilayers are sputter-deposited through a silicon shadow mask. A photo of a Aresistance. pyroMEMS A is pyroMEMS mainly composed is mainly of a composed substrate, thinof a metallicsubstrate, resistance thin metallic and the resistance Al/CuO and nanothermites the Al/CuO pyroMEMS thus manufactured is presented in Figure 3b. (seenanothermites Figure3a). (see Figure 3a). To minimize the ignition energy, the substrate must be a good thermal insulator. We chose 500 µm thick 4-inches glass substrates AF32 (Schott AG, Mainz, Germany). After being cleaned in oxygen plasma to remove surface contaminants, 300 nm thick titanium followed by 300 nm thick gold layers are evaporated onto the glass substrate, and the filament is patterned using the lift-off technique. Then the gold is chemically etched and patterned to define the Ti resistance and Au electrical pads. Finally, Al/CuO multilayers are sputter-deposited through a silicon shadow mask. A photo of a pyroMEMS thus manufactured is presented in Figure 3b.

FigureFigure 3. 3. (a(a) )3D 3D schematic schematic representa representationtion of of a a pyroMEMS; pyroMEMS; (b (b) )photo photo of of the the pyroMEMS; pyroMEMS; ( (cc)) photo photo duringduring the the nanothermite nanothermite reaction. reaction.

WeTo minimizecharacterized the ignition that, for energy, any heating the substrate surface mustareas be(micro-heater a good thermal sizes), insulator. the ignition We chose time 500(delayµm betweenthick 4-inches the time glass of application substrates of AF32 the electrical (Schott AG, power Mainz, and the Germany). emission After of the being light) cleanedrapidly decreases in oxygen whenplasma the to removeignition surfacepower contaminants,density increases, 300 nm un thicktil an titanium asymptotic followed value, by defining 300 nm thick the goldminimum layers are evaporated onto the glass substrate, and the filament is patterned using the lift-off technique. Then response ignition time, which is a characteristic of the multilayered film itself. the goldAs an is illustration, chemically etchedFigure and2b provides patterned the to igniti defineon the time Ti resistanceversus the andigniti Auon electrical power for pads. a thermite Finally, Figure 3. (a) 3D schematic representation of a pyroMEMS; (b) photo of the pyroMEMS; (c) photo madeAl/CuO of multilayers15 300 nm thick are sputter-deposited 1:1 Al/CuO bilayers. through Below a silicona certain shadow electrical mask. powe A photor, no ignition of a pyroMEMS occurs, during the nanothermite reaction. regardlessthus manufactured of the duration is presented of applic ination Figure of3 theb. power. This is simply explained by the fact that, below this ignitionWe characterized power threshold, that, for the any electrical heating surfaceenergy areassupplied (micro-heater to the micro-heater sizes), the ignitionis not sufficient time (delay to We characterized that, for any heating surface areas (micro-heater sizes), the ignition time (delay compensatebetween the for time the of energy application lost by of theconduction electrical through power and the thesubstrate, emission by of radiation the light) from rapidly the decreasesexposed between the time of application of the electrical power and the emission of the light) rapidly decreases surface,when the or ignitionby convection power densityin the air. increases, The multilayer until an cannot asymptotic reach value, its ignition defining temperature, the minimum also response known when the ignition power density increases, until an asymptotic value, defining the minimum asignition the onset time, reaction which temperature. is a characteristic of the multilayered film itself. response ignition time, which is a characteristic of the multilayered film itself. ThisAs an threshold illustration, highly Figure depends2b provides on the theheating ignition surface time area, versus and the detailed ignition results power can for be a found thermite in As an illustration, Figure 2b provides the ignition time versus the ignition power for a thermite [12].made of 15 300 nm thick 1:1 Al/CuO bilayers. Below a certain electrical power, no ignition occurs, made of 15 300 nm thick 1:1 Al/CuO bilayers. Below a certain electrical power, no ignition occurs, regardless of the duration of application of the power. This is simply explained by the fact that, below regardless of the duration of application of the power. This is simply explained by the fact that, below this ignition power threshold, the electrical energy supplied to the micro-heater is not sufficient to this ignition power threshold, the electrical energy supplied to the micro-heater is not sufficient to compensate for the energy lost by conduction through the substrate, by radiation from the exposed compensate for the energy lost by conduction through the substrate, by radiation from the exposed surface, or by convection in the air. The multilayer cannot reach its ignition temperature, also known surface, or by convection in the air. The multilayer cannot reach its ignition temperature, also known as the onset reaction temperature. as the onset reaction temperature. This threshold highly depends on the heating surface area, and detailed results can be found in [12].

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This threshold highly depends on the heating surface area, and detailed results can be found Nanomaterialsin [12]. 2020, 10, x FOR PEER REVIEW 4 of 6

4.4. Examples Examples of of Applications Applications ToTo date, date, igniters igniters are are the the widest widest investigated investigated ap applicationsplications and and are are widely widely used used to to trigger trigger the the inflationinflation of of airbags, airbags, micro-propulsi micro-propulsionon systems, systems, and and the the arm arm and and fire fire devices devices used used in in missiles, missiles, rockets rockets andand any otherother ordnanceordnance systems. systems. Traditionally, Traditionally, igniter igniter technology technology consists consists of a metallicof a metallic hot-wire hot-wire (Ni/Cr, (Ni/Cr,et al.) or etbridge al.) or wirebridge in contactwire in withcontact a secondary with a secondary or primary or explosive. primary explosive. The fabrication The fabrication and integration and integrationof explosives of inexplosives igniters requiresin igniters extreme requires precaution extreme dueprecaution to their due high to sensitivitytheir high tosensitivity electrostatic to electrostaticdischarge, friction discharge, or shock. friction or shock. Al/CuOAl/CuO multilayersmultilayers can can effi efficientlyciently replace replace the hot-wirethe hot-wire and primary and explosive.primary explosive. Other advantages Other advantagesof replacing of traditional replacing hot-wire traditional with hot-wire pyroMEMS with are pyroMEMS as follows: (1)are The as overallfollows: integration (1) The isoverall easier, integrationrequiring only is easier, the electrical requiring connections only the electrical of the pyroMEMS, connections whereas of the pyroMEMS, traditional pyrotechnical whereas traditional igniters pyrotechnicalrequire at least igniters two steps require (hot-wire at least and primarytwo steps pyrotechnic (hot-wire compositionand primary deposition). pyrotechnic (2) composition The Al/CuO deposition).multilayers are(2) The safe Al/CuO and less multilayers sensitive to theare environment.safe and less sensitive (3) Ignition to the threshold environment. and reaction (3) Ignition output threshold(flame temperature and reaction and gaseousoutput (flame products) temperature can be easily and tuned gaseous by changing products) the Alcan/CuO be easily bilayer tuned thickness by changingand stoichiometry the Al/CuO (bilayer bilayer thickness thickness ratio). and stoichiometry (bilayer thickness ratio). TatonTaton et et al. al. [13] [13] first first reported reported the the design, design, realization realization and and characterization characterization of of hot-wire hot-wire ignition ignition integratingintegrating Al/CuO Al/CuO multilayers multilayers (see (see Figure Figure 4)4) for for us usee in in pyrotechnical pyrotechnical systems systems for for space space applications. applications. TheThe reactive reactive Al/CuO Al/CuO multilayered multilayered thin thin film film reside residess on on a a 100 100 µmµm thick thick epoxy/polyethyleneterephtalate epoxy/polyethyleneterephtalate (PET)(PET) membrane membrane to to insulate insulate the the reactive reactive layer layer from from the the bulk bulk substrate. substrate. When When current current is is supplied, supplied, Al/CuOAl/CuO reacts andand the the products products of theof the reaction reaction produce produce sparks sparks that can that ignite can anyignite secondary any secondary energetic energeticcomposition, composition, such as RDXsuch (hexogen).as RDX (hexogen). The authors The authors demonstrated demonstrated a 100% a success 100% success of ignition of ignition over a over0.25–4 a 0.25–4 A firing A currentfiring current range, correspondingrange, correspondi to 80–244ng to µ80–244J, and withµJ, and response with response times ranging times fromranging 2 to from260 µ 2s. to Then, 260 µs. Glavier Then, et Glavier al. [14] usedet al. this [14] igniter used this to cut igniter and propel to cut aand thin propel metallic a thin foil andmetallic ignite foil RDX and in ignitea detonation. RDX in Authorsa detonation. showed Authors that a showed stainless-steel that a flyerstainless-steel of 40 mg canflyer be of properly 40 mg can cut andbe properly propelled cut at andvelocities propelled calculated at velocities from 665 calculated to 1083 m /froms, as a665 function to 1083 of them/s, RDX’s as a function extent of compactionof the RDX’s and extent ignition of compactioncharge. The and impact ignition of the charge. flyer can The directly impact initiateof the fl theyer detonationcan directly of initiate an RDX the explosive, detonation which of an is RDX very explosive,promising which in terms is ofvery removing promising primary in terms explosives of removing from detonators. primary explosives A schematic from view detonators. and photo A of schematicone miniature view detonatorand photo is of given one miniat in Figureure4 .detonator is given in Figure 4.

FigureFigure 4. ((aa)) SchematicSchematic and and (b )( photob) photo of the of reactive the reactive electro-thermal electro-thermal initiator oninitiator Epoxy /onPET Epoxy/PET membrane. Chip dimension is 4 mm 2 mm. (c) Schematic and (d) photo of one miniature detonator integrating membrane. Chip dimension× is 4 mm × 2 mm. (c) Schematic and (d) photo of one miniature detonator integratingAl/CuO multilayers Al/CuO multilayers as the initiator. as the initiator.

MoreMore recently, recently, Nicollet Nicollet et et al. al. [1 [122]] developed developed the the Al/CuO Al/CuO multilay multilayerer igniter igniter concept concept for for several several substrates,substrates, and simpliﬁedsimplified thethe fabrication fabrication process process to to adapt adapt it toit airbagto airbag initiation. initiation. Additionally, Additionally, our teamour teamhas demonstrated has demonstrated miniature miniature one-shot one-shot circuit breakers circuit breakers [15], based [15], on thebased combustion on the combustion of a nanothermite. of a nanothermite.Each device is Each simply device made is from simply two made assembled from printedtwo assembled board circuits printed (PCBs) board to circuits deﬁne a(PCBs) hermetic to µ definecavity a in hermetic which an cavity Al/CuO in which multilayer an Al/CuO initiator multilayer chip ignites—in initiator less chip than ignites—in 100 s—a less few than milligrams 100 µs—a of few milligrams of nanothermite, to cut a thick copper connection (see Figure 5). The authors demonstrated the good operation (100% success rate) with a response time of 0.57 ms, which is much lower than the response time of classical mechanical circuit breakers (>ms).

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nanothermite, to cut a thick copper connection (see Figure5). The authors demonstrated the good operation (100% success rate) with a response time of 0.57 ms, which is much lower than the response Nanomaterialstime of classical 2020, 10 mechanical, x FOR PEER circuitREVIEW breakers (>ms). 5 of 6

FigureFigure 5. ((aa)) 3D 3D schematic schematic of of the the nanothermite-based nanothermite-based circuit circuit breaker breaker with with exploded exploded views views and and ( (bb)) snapshotssnapshots of of high high speed speed images images taken taken for for the the tested tested circuit circuit breaker. breaker. The The time time between between each each picture picture is is 100 µs.µs. Taken Taken from [15]. [15].

5.5. Conclusions Conclusions Sputter-depositedSputter-deposited AlAl/CuO/CuO multilayers, multilayers, composed composed of of alternating alternating Al andAl and CuO CuO nanolayers nanolayers with with total totalthicknesses thicknesses ranging ranging from 1from to tens 1 to of tensµm, presentof µm, present an opportunity an opportunity for tunable for ignitiontunable andignition actuation. and actuation.The interest The in andinterest integration in and integration of igniter applications of igniter applications have been demonstrated have been demonstrated for diﬀerent for applications, different applications,such as in inﬂators, such as aerospace in inflators, or actuators.aerospace or actuators.

Author Contributions: L.S.L.S. developed developed the the sputter-deposition sputter-deposition proce processss and and assisted assisted in in py pyroMEMSroMEMS development. development. S.A.-S.S.A.-S. developed developed all all the experimental benches and assisted in the characterizationcharacterization part. C.R. C.R. supervised the the researchresearch and and wrote the paper. All authors have read and agreed to the published version of the manuscript.

Funding:Funding: C.R. receivedreceived funding funding from from the the European European Research Research Council Council (ERC) (ERC) under under the European the European Union’s Union’s Horizon 2020 research and innovation program (grant agreement No 832889—PyroSafe). L.S. received funding for Horizon 2020 research and innovation program (grant agreement No 832889—PyroSafe). L.S. received funding sputter-deposition equipment from FEDER/Region Occitanie program Grant THERMIE. for sputter-deposition equipment from FEDER/Region Occitanie program Grant THERMIE. Acknowledgments: The authors acknowledge support from the European Research Council (H2020 Excellent Acknowledgments:Science) Researcher AwardThe authors (grant acknowledge 832889—PyroSafe) support and from the Occitaniethe European Region Research/European Council Union (H2020 for their Excellent FEDER Science)support Researcher (THERMIE Award grant). (grant The authors 832889—PyroSafe) thank Séverine and Vivies the Occitanie from LAAS-CNRS Region/European and Teresa Union Hungria-Hernandez for their FEDER supportfrom “Centre (THERMIE de Micro grant). Caract Theérisation authors Raymond thank CastaingSéverine (UMS Vivies 3623)” from for LAAS-CNRS their great support and Teresa with theHungria- sample preparation and TEM experiments. Hernandez from “Centre de Micro Caractérisation Raymond Castaing (UMS 3623)” for their great support with theConﬂicts sample of preparation Interest: The and authors TEM experiments. declare no conﬂict of interests.

Conflicts of Interest: The authors declare no conflict of interests. References

References1. Petrantoni, M.; Rossi, C.; Salvagnac, L.; Conédéra, V.; Esteve, A.; Tenailleau, C.; Alphonse, P.; Chabal, Y.J. Multilayered Al/CuO thermite formation by reactive magnetron sputtering: Nano versus micro. J. Appl. 1. Petrantoni, M.; Rossi, C.; Salvagnac, L.; Conédéra, V.; Esteve, A.; Tenailleau, C.; Alphonse, P.; Chabal, Y.J. Phys. 2010, 108, 084323. [CrossRef] Multilayered Al/CuO thermite formation by reactive magnetron sputtering: Nano versus micro. J. Appl. 2. Adams, D. Reactive multilayers fabricated by vapor deposition: A critical review. Thin Solid Films 2015, 576, Phys. 2010, 108, 084323, doi:10.1063/1.3498821. 98–128. [CrossRef] 2. Adams, D. Reactive multilayers fabricated by vapor deposition: A critical review. Thin Solid Films 2015, 576, 3. Fu, S.; Shen, R.; Zhu, P.; Ye, Y. Metal–interlayer–metal structured initiator containing Al/CuO reactive 98–128, doi:10.1016/j.tsf.2014.09.042. multilayer ﬁlms that exhibits improved ignition properties. Sens. Actuators A Phys. 2019, 292, 198–204. 3. Fu, S.; Shen, R.; Zhu, P.; Ye, Y. Metal–interlayer–metal structured initiator containing Al/CuO reactive [CrossRef] multilayer films that exhibits improved ignition properties. Sens. Actuators A Phys. 2019, 292, 198–204, 4. Manesh, N.A.; Basu, S.; Kumar, R. Experimental ﬂame speed in multi-layered nano-energetic materials. doi:10.1016/j.sna.2019.04.019. Combust. Flame 2010, 157, 476–480. [CrossRef] 4. Manesh, N.A.; Basu, S.; Kumar, R. Experimental flame speed in multi-layered nano-energetic materials. 5. Rossi, C. Engineering of Al/CuO Reactive Multilayer Thin Films for Tunable Initiation and Actuation. Combust. Flame 2010, 157, 476–480, doi:10.1016/j.combustflame.2009.07.011. Propellants Explos. Pyrotech. 2018, 44, 94–108. [CrossRef] 5. Rossi, C. Engineering of Al/CuO Reactive Multilayer Thin Films for Tunable Initiation and Actuation. 6. Lahiner, G.; Zapata, J.; Cure, J.; Richard, N.; Djafari-Rouhani, M.; Estève, A.; Rossi, C. A redox reaction Propellants Explos. Pyrotech. 2018, 44, 94–108, doi:10.1002/prep.201800045. model for self-heating and aging prediction of Al/CuO multilayers. Combust. Theory Model. 2019, 23, 700–715. 6. Lahiner, G.; Zapata, J.; Cure, J.; Richard, N.; Djafari-Rouhani, M.; Estève, A.; Rossi, C. A redox reaction [CrossRef] model for self-heating and aging prediction of Al/CuO multilayers. Combust. Theory Model. 2019, 23, 700– 715, doi:10.1080/13647830.2019.1584336. 7. Zapata, J.; Nicollet, A.; Julien, B.; Lahiner, G.; Esteve, A.; Rossi, C. Self-propagating combustion of sputter- deposited Al/CuO nanolaminates. Combust. Flame 2019, 205, 389–396, doi:10.1016/j.combustflame.2019.04.031.

Nanomaterials 2020, 10, 2009 6 of 6

7. Zapata, J.; Nicollet, A.; Julien, B.; Lahiner, G.; Esteve, A.; Rossi, C. Self-propagating combustion of sputter-deposited Al/CuO nanolaminates. Combust. Flame 2019, 205, 389–396. [CrossRef] 8. Weir, C.; Pantoya, M.L.; Ramachandran, G.; Dallas, T.; Prentice, D.; Daniels, M. Electrostatic discharge sensitivity and electrical conductivity of composite energetic materials. J. Electrost. 2013, 71, 77–83. [CrossRef] 9. Cheng, J.; Hng, H.H.; Lee, Y.; Du, S.; Thadhani, N. Kinetic study of thermal- and impact-initiated reactions in Al–Fe2O3 nanothermite. Combust. Flame 2010, 157, 2241–2249. [CrossRef] 10. Damm, D.; Maiorov, M. Thermal and radiative transport analysis of laser ignition of energetic materials. Opt. Eng. Appl. 2010, 7795, 779502. [CrossRef] 11. Hadjiafxenti, A.; Gunduz, I.; Doumanidis, C.; Rebholz, C. Spark ignitable ball milled powders of Al and Ni at NiAl composition. Vacuum 2014, 101, 275–278. [CrossRef] 12. Nicollet, A.; Lahiner, G.; Belisario, A.; Assié-Souleille, S.; Rouhani, M.D.; Estève, A.; Rossi, C. Investigation of Al/CuO multilayered thermite ignition. J. Appl. Phys. 2017, 121, 034503. [CrossRef] 13. Taton, G.; Lagrange, D.; Conedera, V.; Renaud, L.; Rossi, C. Micro-chip initiator realized by integrating Al/CuO multilayer nanothermite on polymeric membrane. J. Micromech. Microeng. 2013, 23, 105009. [CrossRef] 14. Glavier, L.; Nicollet, A.; Jouot, F.; Martin, B.; Barberon, J.; Renaud, L.; Rossi, C. Nanothermite/RDX-Based Miniature Device for Impact Ignition of High Explosives. Propellants Explos. Pyrotech. 2017, 42, 308–317. [CrossRef] 15. Nicollet, A.; Salvagnac, L.; Baijot, V.; Estève, A.; Rossi, C. Fast circuit breaker based on integration of Al/CuO nanothermites. Sens. Actuators A Phys. 2018, 273, 249–255. [CrossRef]

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