Reactive multilayers fabricated by vapor deposition: A critical review

Reeves R.V., Adams D.P.

The reaction front dynamics of Co/Al reactive nanolaminates were studied as a function of the initial temperature of the unreacted material. Sample geometries that exhibit stable reaction fronts as well as geometries that present “spinning” reaction front instabilities were investigated at initial temperatures ranging from room temperature to 200 °C. It was found that reactions in samples with small reactant periodicities (<66.4 nm) were stable at all temperatures, reaction in large periodicity samples (≥100 nm) were unstable at all temperatures, and reactions in samples with intermediate periodicities transitioned from unstable behavior to stable behavior with increasing initial temperature. The results suggest that behaviors typical of two types of reaction kinetics are present in unstable reaction fronts: slow, diffusion-limited kinetics in the regions between transverse reaction bands, and a faster mechanism at the leading edge of the transverse bands.

Sraj I., Specht P.E., Thadhani N.N., Weihs T.P., Knio O.M.

The initiation of chemical reaction in cold-rolled Ni/Al multilayered composites by shock compression is investigated numerically. A simplified approach is adopted that exploits the disparity between the reaction and shock loading timescales. The impact of shock compression is modeled using CTH simulations that yield pressure, strain, and temperature distributions within the composites due to the shock propagation. The resulting temperature distribution is then used as initial condition to simulate the evolution of the subsequent shock-induced mixing and chemical reaction. To this end, a reduced reaction model is used that expresses the local atomic mixing and heat release rates in terms of an evolution equation for a dimensionless time scale reflecting the age of the mixed layer. The computations are used to assess the effect of bilayer thickness on the reaction, as well as the impact of shock velocity and orientation with respect to the layering. Computed results indicate that initiation and evolution of the reaction are substantially affected by both the shock velocity and the bilayer thickness. In particular, at low impact velocity, Ni/Al multilayered composites with thick bilayers react completely in 100 ms while at high impact velocity and thin bilayers, reaction time was less than 100 μs. Quantitative trends for the dependence of the reaction time on the shock velocity are also determined, for different bilayer thickness and shock orientation.

Barron S.C., Kelly S.T., Kirchhoff J., Knepper R., Fisher K., Livi K.J., Dufresne E.M., Fezzaa K., Barbee T.W., Hufnagel T.C., Weihs T.P.

High temperature, self-propagating reactions are observed in vapor-deposited Al/Zr multilayered foils of overall atomic ratios 3 Al:1 Zr and 2 Al:1 Zr and nanoscale layer thicknesses; however, the reaction velocities do not exhibit the inverse dependence on bilayer thickness that is expected based on changes in the average diffusion distance. Instead, for bilayer thicknesses of 20-30 nm, the velocity is essentially constant at ∼7.7 m/s. We explore several possible explanations for this anomalous behavior, including microstructural factors, changes in the phase evolution, and phase transformations in the reactant layers, but find no conclusive explanations. We determine that the phase evolution during self-propagating reactions in foils with a 3 Al:1 Zr stoichiometry is a rapid transformation from Al/Zr multilayers to the equilibrium intermetallic Al3Zr compound with no intermediate crystalline phases. This phase evolution is the same for foils of 90 nm bilayer thicknesses and foils of bilayer thicknesses in the range of 27 nm to 35 nm. Further, for foils with a bilayer thickness of 90 nm and a 3 Al:1 Zr overall chemistry, the propagation front is planar and steady, in contrast to unsteady reaction fronts in foils with 1 Al:1 Zr overall chemistry and similar bilayer thicknesses.

Lee D., Sim G., Xiao K., Seok Choi Y., Vlassak J.J.

The reaction of Zr/B multilayers with a 50 nm modulation period has been studied using scanning AC nanocalorimetry at a heating rate of approximately 103 K/s. We describe a data reduction algorithm to determine the rate of heat released from the multilayer. Two different exothermic peaks are identified in the nanocalorimetry signal: a shallow peak at low temperature (200–650 °C) and a sharp peak at elevated temperature (650–800 °C). TEM observation shows that the first peak corresponds to heterogeneous inter-diffusion and amorphization of Zr and B while the second peak is due to the crystallization of the amorphous Zr/B alloy to form ZrB2.

Makino A.

Relevant to the self-propagating high-temperature synthesis (SHS) process, an analytical study has been conducted to investigate the effects of electric field on the combustion behavior because the electric field is indispensable for systems with weak exothermic reactions to sustain flame propagation. In the present study, use has been made of the heterogeneous theory which can satisfactorily account for the premixed mode of the bulk flame propagation supported by the nonpremixed mode of particle consumption. It has been confirmed that, even for the SHS flame propagation under electric field, being well recognized to be facilitated, there exists a limit of flammability, due to heat loss, as is the case for the usual SHS flame propagation. Since the heat loss is closely related to the representative sizes of particles and compacted specimen, this identification provides useful insight into manipulating the SHS flame propagation under electric field, by presenting appropriate combinations of those sizes. A fair degree of agreement has been demonstrated through conducting an experimental comparison, as far as the trend and the approximate magnitude are concerned, suggesting that an essential feature has been captured by the present study.

Zaporozhets T.V., Gusak A.M., Korol’ Y.D., Ustinov A.I.

Suggested is a semi-analytical solution to the inverse SHS problem for determining the thermodynamic driving force and parameters of reactive diffusion in a multilayer nanofoil. The method is based on measurements of front temperature and front velocity as a function of the time of isothermal aging. In order to estimate the front velocity of single-stage SHS reaction with account of foil aging and heat sink, improved analytical formula were suggested. The scheme takes into account the influence of initial vacancy supersaturation in the foils on the growth kinetics for the product layer.

Alawieh L., Weihs T.P., Knio O.M.

A multiscale inference analysis is conducted in order to infer intermixing rates prevailing during different reaction regimes in Ni/Al nanolaminates. The analysis combines the results of molecular dynamics (MD) simulations, used in conjunction with a mixing measure theory to characterize intermixing rates under adiabatic conditions. When incorporated into reduced reaction models, however, information extracted from MD computations leads to front propagation velocities that conflict with experimental observations, and the discrepancies indicate that our MD simulations over-estimate the atomic intermixing rates. Thus, using only insights gained from MD computations, a generalized diffusivity law is developed that exhibits a sharp rise near the melting temperature of Al. By calibrating the intermixing rates at high temperatures from experimental observations of self-propagating fronts, and inferring the intermixing rates at low and intermediate temperatures from ignition and nanocalorimetry experiments, the dependence of the diffusivity on temperature is inferred in a suitably wide temperature range. Using this generalized diffusivity law, one obtains a generalized reduced model that, for the first time, enables us to reproduce measurements of low-temperature ignition, homogeneous reactions at intermediate temperatures, as well as the dependence of the velocity of self-propagating reaction fronts on microstructural parameters.

Simões S., Viana F., Ramos A.S., Vieira M.T., Vieira M.F.

This study investigated the interfacial structure of solid state diffusion bonding of TiNi to Ti6Al4V using reactive Ni/Ti multilayer thin films. The TiNi and Ti6Al4V surfaces were modified by sputtering, by deposition of alternated Ni and Ti nanolayers, to increase the diffusivity at the interface. Bonding experiments were performed at 750, 800 and 900 °C at a pressure of 10 MPa with a dwell time of 60 min. The reaction zone was characterized by high-resolution scanning and transmission electron microscopy. Joints free from porosity and cracks were produced with Ni/Ti reactive multilayer thin films. Several phases formed at the interface, ensuring the bonding of these alloys. The reaction zone was constituted by columnar grains of Ti2Ni and AlNi2Ti, close to the Ti6Al4V base material, and by alternate layers of Ti2Ni and TiNi equiaxed grains. The grain size decreased from Ti6Al4V to TiNi base materials. Nanometric grains were observed in the layers closest to the TiNi base material.

Swaminathan P., Grapes M.D., Woll K., Barron S.C., LaVan D.A., Weihs T.P.

Heats of reaction and heat capacity changes were measured using scanning nanocalorimetry for a nickel and aluminum bilayer where initial heating rates of 104 K/s were achieved. Multiple exotherms were observed on the initial heating, but the number of intermediate exotherms decreased with increasing heating rate. The final phase was the B2 NiAl intermetallic. Results from the nanocalorimeter were compared with a conventional differential scanning calorimeter (operating at 0.7 K/s) to understand the effect of significant (10 000×) increases in heating rate on the phase transformation sequence. The high heating rate in the nanocalorimeter delays reaction initiation, causes the exothermic peaks to shift to higher temperatures, and appears to suppress the formation of intermediate, metastable phases. Potential explanations for this apparent suppression are discussed.

Ustinov A., Falchenko Y., Melnichenko T., Shishkin A., Kharchenko G., Petrushinets L.

In the diffusion welding (DW) of difficult-to-deform materials (such as composites and intermetallics), the application of intermediate multilayer foils (MF), which have alternating layers of elements that form intermetallics, allows for production of a permanent joint under milder conditions. In this paper, the processes occurring in the joint zone (JZ) during DW of Al–5 wt.%Mg+27 wt.%Al 2 O 3 composite material through the Al/Cu interlayer were studied. It was shown that, while heating of such a foil, phase transformations that are due to the reaction diffusion of elements, run in it. At MF heating under a continuously applied external load, the materials are plastically deformed. It is established that the intensity of foil plastic deformation at a specified load non-monotonically depends on temperature. It is shown that welding temperature is determined by the temperature at which MF can undergo superplastic flow under the impact of applied pressure. A mechanism of formation for a solid-phase joint of high-strength materials through interlayers based on the MF of intermetallic-forming elements is proposed.

Braeuer J., Besser J., Tomoscheit E., Klimm D., Anbumani S., Wiemer M., Gessner T.

This paper introduces a method that uses a specific form of local heat generation, which is based on nano scale reactive multilayer systems. Such systems consist of several layers of minimum two different materials with nano scale thicknesses. These layers generate heat based on a self-propagating exothermic reaction during their intermixing. The resulting heat can be used as heat source for bonding processes at chip and wafer-level.

McDonald J.P., Reeves R.V., Jones E.D., Chinn K.A., Adams D.P.

Vapor-deposited, equiatomic Ni/Ti multilayer foils exhibit low-speed, self-propagating formation reactions that are characterized by a spin-like reaction front instability. In addition to the intermetallic reaction between Ni and Ti, reactions performed in air can also exhibit a discrete combustion wave associated with the oxidation of Ti. In general, the oxidation wave trails the complex intermetallic reaction front. Multilayers that have a large reactant layer periodicity (≥200 nm) exhibit a decrease in net reaction speed as air pressure is reduced. Oxidation has a much smaller effect on the net propagation speed of multilayers with small layer periodicity (<100 nm). The net propagation speed of the multilayers is increased when air is present, due to the added energy release of Ti oxidation. High-speed optical microscopy shows that the increased front speed is associated with an increased nucleation rate of the reaction bands that typify the spinning reaction instability of the Ni/Ti system.

Peruško D., Čizmović M., Petrović S., Siketić Z., Mitrić M., Pelicon P., Dražić G., Kovač J., Milinović V., Milosavljević M.

Multilayered 5×(Al/Ti) structures, deposited on a Si substrate to a total thickness of 130 nm, were treated by unfocused Nd:YAG laser pulses (150 ps) with energies of 85 and 65 mJ. Irradiations were performed in air with 10, 50 and 100 successive laser pulses. Characterizations were done by using Rutherford backscattering spectrometry (RBS), elastic recoil detection analysis (ERDA), x-ray diffraction (XRD) and transmission electron microscopy (TEM). The results obtained show that laser irradiation, at either energy, induced almost full intermixing of deposited layers and formation of intermetallic compounds, but this was more pronounced for the applied laser pulses with a higher energy. The intermixed layer–silicon interface remains intact for all numbers of applied laser pulses and for both energies. The formation of an oxide layer on the sample surfaces was also observed, the thickness of which is greater for the higher laser beam energy.

Kwon J., Ducéré J.M., Alphonse P., Bahrami M., Petrantoni M., Veyan J., Tenailleau C., Estève A., Rossi C., Chabal Y.J.

Interface layers between reactive and energetic materials in nanolaminates or nanoenergetic materials are believed to play a crucial role in the properties of nanoenergetic systems. Typically, in the case of Metastable Interstitial Composite nanolaminates, the interface layer between the metal and oxide controls the onset reaction temperature, reaction kinetics, and stability at low temperature. So far, the formation of these interfacial layers is not well understood for lack of in situ characterization, leading to a poor control of important properties. We have combined in situ infrared spectroscopy and ex situ X-ray photoelectron spectroscopy, differential scanning calorimetry, and high resolution transmission electron microscopy, in conjunction with first-principles calculations to identify the stable configurations that can occur at the interface and determine the kinetic barriers for their formation. We find that (i) an interface layer formed during physical deposition of aluminum is composed of a mixture of Cu, O, and Al through Al penetration into CuO and constitutes a poor diffusion barrier (i.e., with spurious exothermic reactions at lower temperature), and in contrast, (ii) atomic layer deposition (ALD) of alumina layers using trimethylaluminum (TMA) produces a conformal coating that effectively prevents Al diffusion even for ultrathin layer thicknesses (∼0.5 nm), resulting in better stability at low temperature and reduced reactivity. Importantly, the initial reaction of TMA with CuO leads to the extraction of oxygen from CuO to form an amorphous interfacial layer that is an important component for superior protection properties of the interface and is responsible for the high system stability. Thus, while Al e-beam evaporation and ALD growth of an alumina layer on CuO both lead to CuO reduction, the mechanism for oxygen removal is different, directly affecting the resistance to Al diffusion. This work reveals that it is the nature of the monolayer interface between CuO and alumina/Al rather than the thickness of the alumina layer that controls the kinetics of Al diffusion, underscoring the importance of the chemical bonding at the interface in these energetic materials.

Miikkulainen V., Leskelä M., Ritala M., Puurunen R.L.

Atomic layer deposition (ALD) is gaining attention as a thin film deposition method, uniquely suitable for depositing uniform and conformal films on complex three-dimensional topographies. The deposition of a film of a given material by ALD relies on the successive, separated, and self-terminating gas–solid reactions of typically two gaseous reactants. Hundreds of ALD chemistries have been found for depositing a variety of materials during the past decades, mostly for inorganic materials but lately also for organic and inorganic–organic hybrid compounds. One factor that often dictates the properties of ALD films in actual applications is the crystallinity of the grown film: Is the material amorphous or, if it is crystalline, which phase(s) is (are) present. In this thematic review, we first describe the basics of ALD, summarize the two-reactant ALD processes to grow inorganic materials developed to-date, updating the information of an earlier review on ALD [R. L. Puurunen, J. Appl. Phys. 97, 121301 (2005)], and give an overview of the status of processing ternary compounds by ALD. We then proceed to analyze the published experimental data for information on the crystallinity and phase of inorganic materials deposited by ALD from different reactants at different temperatures. The data are collected for films in their as-deposited state and tabulated for easy reference. Case studies are presented to illustrate the effect of different process parameters on crystallinity for representative materials: aluminium oxide, zirconium oxide, zinc oxide, titanium nitride, zinc zulfide, and ruthenium. Finally, we discuss the general trends in the development of film crystallinity as function of ALD process parameters. The authors hope that this review will help newcomers to ALD to familiarize themselves with the complex world of crystalline ALD films and, at the same time, serve for the expert as a handbook-type reference source on ALD processes and film crystallinity.

Wiss E., Jaziri N., Müller J., Wiese S.

Reactive bonding can overcome the issues associated with conventional soldering processes, such as potential damage to heat-sensitive components and the creation of thermomechanical stress due to differing coefficients of thermal expansion. The risk of such damage can be reduced by using localized heat sources like reactive multilayer systems (RMS), which is already a well-established option in the field of silicon or metal bonding. Adapting this process to other materials, such as low temperature co-fired ceramics (LTCC), is difficult due to their differing properties, but it would open new technological possibilities. One aspect that significantly affects the quality of the bonding joints is the pressure applied during the bonding process. To investigate its influence more closely, various LTCC samples were manufactured, and cross-sections were prepared. The microscopical analysis reveals that there is an optimum range for the bonding pressure. While too little pressure results in the formation of lots of voids and gaps, most likely in poor mechanical and electrical properties, too high pressure seems to cause a detachment of the metallization from the base material.

Chen L., Xiao X., Yuan H., Chen H., Zhou Y., Ye Y., Shen R., Wu L.

AbstractWith the ongoing advancement of miniaturization and microfabrication, Micro‐Electro‐Mechanical Systems (MEMS) energetic devices are increasingly demanding higher output capabilities from energetic materials. This study investigates the incorporation of Titanium (Ti) into PVDF‐based energetic films to improve their performance. We fabricated five Al/Ti/CuO/PVDF energetic composite films with varying Ti contents by direct ink writing (DIW). The results indicate that the Al/Ti/CuO/PVDF films demonstrate superior performance compared to Al/CuO/PVDF(AT‐0). Notably, the 50 wt% Al/50 wt% Ti/CuO/PVDF (AT‐50) film achieved optimal performance, exhibiting a 68% increase in combustion rate compared to the AT‐0 film. Additionally, it showed a reduction in ignition delay time by 6 ms, an increase in flame temperature of 160.9 K, a 24% rise in maximum pressure, a pressurization rate enhancement of 117%, and an overall increase in heat release of 26.8%. This is attributed to the synergistic effect of the Al/Ti bimetallic fuels, where their close contact creates an alloying reaction that releases a large amount of heat and avoids the detrimental effects of Al sintering. This Al/Ti/CuO/PVDF energetic composite film, characterized by its exceptional synergistic mechanism and high energy output, holds significant promise for integration with MEMS devices, paving the way for innovative applications in micro‐ignition, micro‐propulsion, and micro‐startup technologies.Highlights Ti was added to the PVDF‐based energetic films to form the dual‐fuel system. The Al/Ti dual‐fuel has a synergistic effect to improve output performance. The 50wt%Al/50wt%Ti/CuO/PVDF film can achieve optimal output performance.

Kittell D.E., Abere M.J., Specht P.E., Adams D.P.

Continuum shock mixture models are reviewed and applied to determine the equations of state for five different compositions of NixAly, as well as bulk Ni+Al reactive multilayers, by combining the fundamental property data for elemental nickel and aluminum. From the literature, we down-select and evaluate two analytical models for the mixture Hugoniot, i.e., the well-known method of kinetic energy averaging (KEA) and a recent model proposed by Jordan and Baer [J. Appl. Phys. 111, 083516 (2012)]. Fundamentally, the former method assumes pressure equilibrium, whereas the latter assumes a common particle velocity and mixture sound speed from compressible two-phase cavitating flows. Additionally, we construct thermodynamically complete equations of state by fitting Einstein oscillator series models for the specific heat at constant volume. Finally, the solid solution approximation is invoked for intermetallic compositions, which are not strictly physical mixtures. Overall, the KEA model provides a better fit to the available NixAly and Ni+Al multilayer shock compression data; however, there are combinations of material properties where the performance of these two models is thought to be reversed. Moreover, the results of this work include the first analytical solution of Jordan–Baer that does not require numerical root finding, as well as proposed modifications to the Einstein oscillator series to incorporate some effects of local pressure–temperature equilibrium and reaction–diffusion. Future work is planned that will use these equations of state in mesoscale simulations to study shock-induced reaction in Ni+Al multilayers, and the intended application is illustrated with a brief 2D hydrocode example.

Chen Y., Chang Y., Hsiang C., Chiu Y., Su K., Chou Y.

Selecting freestanding bilayer thickness of Ni/Si reactive multilayers below 50 nm or above 170 nm could better control the final phases for practical applications.

Shekhawat D., Sulman M., Flock D., Ecke G., Glaser M., Döll J., Bergmann J.P., Pezoldt J.

Liu G., Chen K., Li J.

Tang T., Zhu Y., Yan S., Dong Y., Wang M., Zheng X.

Deng Z., Wang Y., Liu R., Li W., Gan Q.

Gaković B., Petrović S., Siogka C., Milovanović D., Momčilović M., Tsibidis G.D., Stratakis E.

The interaction of ultra-short laser pulses (USLP) with Nickel/Titanium (Ni/Ti) thin film has been presented. The nano layer thin film (NLTF), composed of ten alternating Ni and Ti layers, was deposited on silicon (Si) substrate by ion-sputtering. A single and multi-pulse irradiation was performed in air with focused and linearly polarized laser pulses. For achieving selective ablation of one or more surface layers, without reaching the Si substrate, single pulse energy was gradually increased from near the ablation threshold value to an energy value that caused the complete removal of the NLTF. In addition to single-pulse selective ablation, the multi-pulse USLP irradiation and production of laser-induced periodic surface structures (LIPSSs) were also studied. In the presented experiment, we found the optimal combination of accumulated pulse number and pulse energy to achieve the LIPSS formation on the thin film. The laser-induced morphology was examined with optical microscopy, scanning electron microscopy, and optical profilometry. To interpret the experimental observations, a theoretical simulation has been performed to explore the thermal response of the NLTFs after irradiation with single laser pulses.

Chang Y., Sun Y., Chen Y., Chou Y.

Lorenzin G., Klimashin F.F., Yeom J., Hu Y., Michler J., Janczak-Rusch J., Turlo V., Cancellieri C.

The combination of the high wear resistance and mechanical strength of W with the high thermal conductivity of Cu makes the Cu/W system an attractive candidate material for heat sinks in plasma experiments and for radiation tolerance applications. However, the resulting mechanical properties of multilayers and coatings strongly depend on the microstructure of the layers. In this work, the mechanical properties of Cu/W nanomultilayers with different densities of internal interfaces are systematically investigated for two opposite in-plane stress states and critically discussed in comparison with the literature. Atomistic simulations with the state-of-the-art neural network potential are used to explain the experimental findings of Young’s modulus and hardness. The results suggest that the microstructure, specifically the excess free volume associated with porosity and interface disorder interconnected with the stress state, has a great impact on the mechanical properties, notably Young’s modulus of Cu/W nanomultilayers.

Goviazin G.G., Goldstein D.A., Ratzker B., Messer O., Sokol M., Rittel D.

Altunin R.R., Moiseenko E.T., Zharkov S.M.

Yuile A., Schulz A., Wiss E., Müller J., Wiese S.

Numerical computational fluid dynamics simulations have been performed on 2D sandwich models to compare the performance of low‐temperature cofired ceramics (LTCC)/LTCC and Si/Si sandwiches used in reactive bonding. In the sandwich model layers of solder, silver and a reactive multilayer used to bond the substrates are modeled. Additional to this, the surrounding air environment is also modeled. For simulating the heat released by the multilayer system, a user‐defined function in the form of a square wave is written for the heat source with a defined width, corresponding to the reaction width, and this propagates at a fixed speed. Two sandwiches, one with LTCC/LTCC, and the other with Si/Si, are simulated and their response analyzed in terms of the solidification/melting of the solder and their respective time–temperature histories.

Nnaji M.O., Tavakoli D.A., Hitchcock D.A., Vogel E.M.

Mn+1AXn-phase Ti2AlN thin-films were synthesized using reactive sputtering-based methods involving the deposition of single-layer TiAlN, and Ti/AlN and TiN/TiAl multilayers of various modulation periods at ambient temperature and subsequent annealing at elevated temperatures. Ex situ and in situ x-ray diffraction measurements were used to characterize the Ti2AlN formation temperature and phase fraction. During annealing, Ti/AlN multilayers yielded Ti2AlN at a significantly lower in situ temperature of 650 °C compared to TiN/TiAl multilayers or single-layer TiAlN (750 °C). The results suggest a reactive multilayer mechanism whereby distinct Ti and AlN layers react readily to release exothermic energy resulting in lower phase transition temperatures compared to TiN and TiAl layers or mixed TiAlN. With a modulation period of 5 nm, however, Ti/AlN multilayers yielded Ti2AlN at a higher temperature of 750 °C, indicating a disruption of the reactive multilayer mechanism due to a higher fraction of low-enthalpy interfacial TiAlN within the film.