Energetic Condensation Research Articles

High entropy alloy thin films on SS304 substrates: Evolution of microstructure and interface modulated by energetic condensation in nanoscale

High entropy alloys (HEAs), as a novel material in the 21st century, possess several advantages, such as excellent corrosion & oxidation resistance and high mechanical properties. HEA thin films show these favourable properties with lower material costs than their bulk counterparts. Studying the HEA film-substrate interface represents challenges but is of extreme importance for the understanding of growth mechanisms with important implications for film adhesion. However, most HEA films were deposited on monocrystalline silicon substrates with limited practical applicability. Further, where commercial stainless steel, aluminium or titanium alloy substrates were used, the microstructure and chemistry at the interface were neglected. Here, we deposited AlCrFeCoNiCu0.5 HEA thin films on stainless steel 304 (SS304) substrates using cathodic arc deposition with different substrate biases. The crystallography and microstructure were investigated using an X-ray and electron-microscopy based chatacterization. A transition of an incoherent to semi-coherent interface was observed from 0 V to -50 V of the substrate bias. Energy dispersive spectroscopy demonstrated a transition of Cr2O3 to aluminum oxide across the interface. The nanoindentation tests revealed the significant improvement of mechanical properties of SS304 with HEA coatings. High-strength HEA (8.0 ± 0.2 GPa) thin films with semi-coherent interfaces were manufactured on SS304.

HiPIMS deposition of superconducting Nb thin films onto Cu substrates

The use of energetic condensation techniques, such as HiPIMS, has the potential to significantly improve the superconducting performance of coated Cu cavities by producing bulk-like Nb thin films. However, in order to benefit from these techniques, a deeper understanding of the effects of, and the relationship between, the different deposition parameters, the physical properties of the deposited films and the superconducting performance of the films, is still required. This contribution details the effects of different HiPIMS deposition parameters on the morphological, crystallographic and superconducting properties of Nb thin films deposited onto electropolished Cu substrates. Higher duty cycles (8 – 20 %) than previous HiPIMS investigations were used in the majority of the coatings. The films displayed more bulk-like crystallographic properties, indicated here by the lattice parameter, with a “transition zone” apparent in the early stages of film growth. A reduction in the surface roughness as well as interfacial voids, compared to typical DC MS Nb films, was also observed. The superconducting performance of the films, specifically the first magnetic flux entry field, showed a marked reliance on the substrate bias and the film thickness. Conversely, the HiPIMS duty cycle appears to have a comparatively insignificant effect.

Impact of a Relativistic Electron Beam on Cast Aluminized Energetic Condensed Systems

Impact of a Relativistic Electron Beam on Cast Aluminized Energetic Condensed Systems

Impact of a Relativistic Electron beam on Aluminized Cast Energetic Condensed Systems

Impact of a Relativistic Electron beam on Aluminized Cast Energetic Condensed Systems

To the Question of Detonation of Multicomponent Energetic Condensed Systems by a Nanosecond Electron Beam

An experimental study was made of the initiation of detonation of a polymer-bonded energetic condensed system containing glycerol trinitrate, ammonium perchlorate, and aluminum powder by a nanosecond relativistic electron beam with a flux density of 200 J/cm2. It has been found that the velocity of dispersion of gas–plasma formations from the surface of the energetic condensed system is ∼22 km/s. It has been shown that the detonation of the studied energetic condensed system by the nanosecond relativistic electron beam is reached at much lower pressures than in the case of initiation by an explosive charge.

Combustion Hotspots of Energetic Condensed Systems

The conditions of occurrence, nature, size, and shape of combustion hotspots of energetic condensed systems and the spatial dynamics of the hotspot combustion wave are discussed. A model for the propagation of hotspot combustion waves in condensed systems is briefly described based on the cellular automata method. A possible explanation for the occurrence of unsteady effects in the combustion of solid rocket propellants is proposed.

Nucleation of gold nanoclusters in PMMA during energetic plasma deposition: A molecular dynamics and tfMC-Monte Carlo study

We have explored the nucleation of gold nanoclusters in PMMA (Poly[methyl methacrylate]) using theoretical simulations. The nanoclusters are formed from energetic condensation of gold ions in the polymer from the very first deposition pulse. Three gold ion energy values are considered (50 eV, 100 eV and 150 eV). The influence of ion energy on sputtering, nucleation, diffusion and depth profile is discussed. For energetic plasma deposition techniques, including Filtered Cathodic Vacuum Arc (FCVA) deposition, the arrival of ions to the system can be considered as rare events. Therefore, to access a complete description of the nucleation process, Molecular Dynamics simulation is combined with time stamped force bias Monte-Carlo (tfMC) for the first pulse of deposition.

Combustion Hot Spots of Energetic Condensed Systems

Combustion Hot Spots of Energetic Condensed Systems

Spontaneous wrinkling of soft matter by energetic deposition of Cr and Au

Wrinkling of stiff thin films deposited on compliant substrates is an effect that has been broadly investigated. However, wrinkling consequent to metal ion implantation has been less studied. In the work described here, we have explored the sub-micron wrinkling phenomena that spontaneously occur when metal ions (Au and Cr) are implanted with energy of a few tens of electron volts (49 eV for Au and 72 eV for Cr) into a compliant material (PDMS). This very low energy ion implantation was performed using a Filtered Cathodic Vacuum Arc technique, a process often referred to as energetic deposition or energetic condensation. For comparison, Au and Cr depositions with similar doses were also done using a sputtering technique (with lower particle energy of approximately 2 eV), and no wrinkle formation was then observed. In this way, we can discuss the role of ion energy in wrinkle formation. Depth profiles of the implanted material were calculated using the Tridyn computer simulation code for each metal, for several implantation doses. UV-vis absorption spectroscopy analysis confirmed the presence of metal nanoparticles. Atomic Force Microscopy imaging with spectral processing was used to compare the wrinkle morphology for each case investigated.

Characterization of nanostructured zinc oxide thin films synthesized at room temperature using low energy plasma focus device

Nanocrystalline zinc oxide (ZnO) thin films were synthesized on glass substrates under extremely non-equilibrium conditions of energetic ion condensation during the focus phase in a low energy plasma focus (PF) device. The samples were deposited using multiple focus shots (5, 10 and 20), at constant axial and angular positions with respect to the tip of anode and anode axis (8cm and 0°), respectively. The argon:oxygen admixture (in 7:3 ratio) was used as a working gas. The structural, morphological, electrical and optical properties of the ZnO deposited thin films were investigated. The results obtained from XRD and SEM analyzes indicated that the size of nanoparticles/agglomerates and the thickness of the ZnO thin films strongly depend on number of shots. AFM analysis revealed that the size of grains and surface roughness of ZnO samples increase with the number of shots. Measurement of the electrical parameters indicated that electrical resistivity is reduced and carrier mobility enhanced with increasing the shots, with no noticeable variations in the carrier concentration. Moreover, the results from optical transmission patterns revealed that optical transmittance and band gap energy decrease with more shots.

Boron Particles Agglomeration and Slag Formation During Combustion of Energetic Condensed Systems

Boron is a promising component of energetic condensed systems due to its high gravimetric heat value, which is significantly higher than that one of aluminum. In the present work, two non-equilibrium processes, i.e., boron particles agglomeration and framework (slag) formation during combustion of high-energy compositions were investigated experimentally. The quench particle collection bomb technique was used to collect the condensed combustion products formed under nitrogen pressures of 0.1 – 4MPa. The formation of a framework was visualized using high-speed video registration (1200 fps). Particle size, morphology, and surface structure of collected condensed products were evaluated using laser diffractometry and scanning electron microscopy. In the experiments, the weight of the collected condensed combustion products was about 30% of the initial sample weight, where 26% belonged to the products collected from the gas phase and 4% were remained in a highly-porous framework. The initial amorphous boron powder consisted of 1-micron particles, whereas agglomerated particles, which were collected from the gas phase, were 10μm in diameter. The burning rate of compositions without binder was 4 times higher and the diameter of collected agglomerates was 10 times larger than those for compositions with binder.

Corrosion protection with hard coatings on steel: Past approaches and current research efforts

This work gives a review on published results on the corrosion behavior of hard coatings deposited on steel substrates by mainly physical vapor deposition (PVD) or in some cases by plasma-assisted chemical vapor deposition (PACVD). Corrosion investigations of our own lab have been added at several sites to complete missing knowledge or to introduce new non-published data. A detailed discussion of thin film growth, microstructure and the kind of defects inherent in hard coatings has been given. Then the influence of coating thickness and some processing parameters on the corrosion resistance of coated steel is demonstrated. After this incipient part, the corrosion behavior of hard nitride coatings, multilayer coatings, alloyed or modified nitride coatings, insulating nitride, oxide or oxynitride coatings and duplex treated steel is being presented. Own investigations and published results show that single layered, conducting nitride coatings can protect steel to some extent only if very thick coatings (≥10μm) are applied or if energetic deposition methods (e.g. ion-assisted deposition) are used. Distinct improvements of the corrosion behavior of hard coatings can be obtained by a proper multilayer structure deposited by deposition methods allowing energetic condensation, i.e. possessing a high ion-to-atom flux ratio. Alloying TiN by a sacrificial element, like magnesium, is also capable of significantly improving the corrosion resistance of low alloyed steel. Amazing improvements have also been reported for insulating coatings like AlN, oxynitride coatings or oxide coatings. However, the most significant improvement seems to be the application of duplex treatments. Plasma nitriding+PVD coating or PVD coating+atomic layer deposition (ALD) prolonged the time to red rust in neutral salt spray test for >2days up to one week, respectively. The only disadvantage of the duplex treatments is the higher cost. Recently, mapping by a confocal microscope of TiN coating surfaces before and after salt spray testing showed that open porosities in micro- and macro-scale growth defects mainly govern the corrosion behavior of hard coatings on steel. The coating microstructure – i.e. the submicron-scale morphology – seems to play only a secondary role in the corrosion behavior.

Investigating crystal microstructure of niobium materials by an x-ray diffraction reciprocal space mapping technique

An x-ray diffraction reciprocal spacing mapping (RSM) technique was applied to investigate crystal quality of Nb films and bulk materials, relevant to superconducting radio frequency applications. The RSM study used different x-ray penetration depths to study material processes after two different surface treatments: mechanical polishing or energetic condensation (a plasma process). The study revealed the material's microstructure evolution for the two different processes. The RSM plots revealed crystal quality of the materials at different thickness. The novel, differential-depth RSM technique presented in this study substantiated the following facts: (1) For a heteroepitaxial Nb film $\mathrm{Nb}(100)/\mathrm{MgO}(100)$, a film thickening process, via a cathodic arc-discharge Nb ion deposition (energetic condensation), created a near-perfect single crystal Nb on the surface top layer. (2) For a fine mechanically polished single-crystal bulk Nb material, the microstructure on the top surface layer is more disordered than that at a greater depth.

Stardust silicate nucleation kick-started by SiO+TiO 2

Dust particles are quintessential for the chemical evolution of the Universe. Dust nucleates in stellar outflows of dying stars and subsequently travels through the interstellar medium, continuously evolving via energetic processing, collisions and condensation. Finally, dust particles are incorporated in the next-generation star or its surrounding planetary system. In oxygen-rich stellar outflows, silicates are observed in the condensation zone (1200-1000 K), but, in spite of several decades of experimental and theoretical study, the stardust nucleation process remains poorly understood. We have previously shown that under these conditions ternary Mg-Si-O clusters may start forming at high enough rates from SiO, Mg and H₂O through heteromolecular association processes. In this reaction scheme, none of the possible initial association reactions was thermodynamically favourable owing to the large entropy loss at these temperatures. Here, we follow a previous idea that the incorporation of TiO₂ could help to initiate stardust nucleation. In contrast to these studies, we find that there is no need for TiO₂ cluster seeds-instead, one molecule of TiO₂ is sufficient to kick-start the subsequent nucleation of a silicate dust particle.

Response to “Comment on ‘Twin symmetry texture of energetically condensed niobium thin films on sapphire substrate’ ” [J. Appl. Phys. 112, 016101 (2012)

Welander is correct about the misidentified crystal-directions in the top-view sapphire lattice (Fig. 4 [Zhao et al., J. Appl. Phys. 110, 033523 (2011)]). He is also correct about the misorientation of the pole figures in Fig. 4. In Fig. 1 of this response, we have corrected these errors. Perhaps because of these errors, Welander misconstrued our discussion of the Nb crystal growth as claiming a new 3D registry. That was not our intention. Rather, we wished to highlight the role of energetic condensation that drives low-defect crystal growth by a combination of non-equilibrium sub-plantation that disturbs the substrate lattice and thermal annealing that annihilates defects and promotes large-grain crystal growth.

Energetic condensation growth of Nb thin films

This paper describes energetic condensation growth of Nb films using a cathodic arc plasma, whose 60--120 eV ions penetrate a few monolayers into the substrate and enable sufficient surface mobility to ensure that the lowest energy state (crystalline structure with minimal defects) is accessible to the film. Heteroepitaxial films of Nb were grown on $a$-plane sapphire and MgO crystals with good superconducting properties and crystal size ($10\text{ }\text{ }\mathrm{mm}\ifmmode\times\else\texttimes\fi{}20\text{ }\text{ }\mathrm{mm}$) limited only by substrate size. The substrates were heated to temperatures of up to $700\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$ and coated at $125\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$, $300\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$, $500\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$, and $700\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$. Film thickness was varied from $\ensuremath{\sim}0.25\text{ }\text{ }\ensuremath{\mu}\mathrm{m}$ to $>3\text{ }\text{ }\ensuremath{\mu}\mathrm{m}$. Residual resistivity ratio ($⟨\mathrm{RRR}⟩$) values (up to a record $⟨\mathrm{RRR}⟩=587$ on MgO and $⟨\mathrm{RRR}⟩=328$ on $a$-sapphire) depend strongly on substrate annealing and deposition temperatures. X-ray diffraction spectra and pole figures reveal that RRR increases as the crystal structure of the Nb film becomes more ordered, consistent with fewer defects and, hence, longer electron mean-free path. A transition from Nb(110) to Nb(100) orientation on the MgO(100) lattice occurs at higher temperatures. This transition is discussed in light of substrate heating and energetic condensation physics. Electron backscattered diffraction and scanning electron microscope images complement the XRD data.

Twin symmetry texture of energetically condensed niobium thin films on sapphire substrate (a-plane Al2O3)

An energetic condensation technique, cathodic arc discharge deposition, is used to grow epitaxial Niobium (Nb) thin films on a-plane sapphire (hexagonal-closed-packed Al2O3) at moderate substrate heating temperature (<400 °C). The epitaxial Nb(110)/Al2O3(1,1,-2,0) thin films reached a maximum residual resistance ratio (RRR) value 214, despite using a reactor-grade Nb cathode source whose RRR was only 30. The measurements suggest that the film’s density of impurities and structural defects are lower when compared to Nb films produced by other techniques, such as magnetron sputtering, e-beam evaporation or molecular-beam-epitaxy. At lower substrate temperature, textured polycrystalline Nb thin films were created, and the films might have twin symmetry grains with {110} orientations in-plane. The texture was revealed by x-ray diffraction pole figures. The twin symmetry might be caused by a combination effect of the Nb/Al2O3 three-dimensional epitaxial relationship (“3D-Registry” Claassen’s nomenclature) and the “Volmer-Weber” (Island) growth model. However, pole figures obtained by electron backscattering diffraction (EBSD) found no twin symmetry on the thin films’ topmost surface (∼50 nm in depth). The EBSD pole figures showed only one Nb{110} crystal plane orientation. A possible mechanism is suggested to explain the differences between the bulk (XRD) and surface (EBSD) pole figures.

Extremely non-equilibrium synthesis of luminescent zinc oxide nanoparticles through energetic ion condensation in a dense plasma focus device

Luminescent ZnO nanoparticles have been synthesized on silicon and quartz substrates under extremely non-equilibrium conditions of energetic ion condensation during the post-focus phase in a dense plasma focus (DPF) device. Ar+, O+, Zn+ and ZnO+ ions are generated as a result of interaction of hot and dense argon plasma focus with the surfaces of ZnO pellets placed at the anode. It is found that the sizes, structural and photoluminescence (PL) properties of the ZnO nanoparticles appear to be quite different on Si(1 0 0) and quartz substrates. The results of x-ray diffractometry and atomic force microscopy show that the ZnO nanoparticles are crystalline and range in size from 5–7 nm on Si(1 0 0) substrates to 10–38 nm on quartz substrates. Room-temperature PL studies reveal strong peaks related to excitonic bands and defects for the ZnO nanoparticles deposited on Si (1 0 0), whereas the excitonic bands are not excited in the quartz substrate case. Raman studies indicate the presence of E2 (high) mode for ZnO nanoparticles deposited on Si(1 0 0).

Large crystal grain niobium thin films deposited by energetic condensation in vacuum arc

This article presents evidence for unprecedented, large crystal grain size in ∼1μm thick Nb films that were grown on sapphire and copper substrates using a vacuum arc process called coaxial energetic deposition CED™. Most other deposition techniques with low adatom energy produce amorphous or small crystal-grain films. Typically, high substrate temperatures and annealing steps are required to form the large, highly connected grains. The CED™ technique deposits from plasma consisting of a nonequilibrium, high energy (50–150eV) ion population produced from the ionized source material. At the substrate these fast ions break up columnar structures, intermix with the first few atomic layers of the substrate to improve adhesion, and form dense films at lower substrate temperatures than are typical for low adatom energy techniques, such as physical vapor deposition (PVD). Nanoscale features of the thin films were examined using electron backscatter diffraction (EBSD). The films’ cryogenic state electrical properties were characterized by their residual resistivity ratio (RRR) and superconducting transition temperature (Tc). RRR of ∼77 and Tc∼9.2K were measured on a Nb thin film deposited on a sapphire substrate. EBSD and x-ray diffraction measurements indicated that the sapphire substrate thin films have single crystal structure, with a Nb {110} crystal plane monolithically aligned and parallel to the sample surface. Nb thin films on an ∼400°C Cu substrate had average crystal grain size of 50μm, which is an order of magnitude larger than that which is typical of films grown by PVD. The crystal structure of CED™ thin films is comparable to that of polycrystalline bulk Nb material, which is the state of the art for superconducting radio frequency (SRF) particle accelerators such as at the Thomas Jefferson National Accelerator Facility (JLab). The films’ novel crystal features suggest that CED™ is a promising technique to coat Nb thin films for lower cost SRF particle accelerators. Further studies of the nanoscale grain boundary features would shed light on the role played by these features in determining the performance of SRF cavities using such thin films on Cu.

Nanopore processing in dielectric materials and dielectric template-assisted nanoarray synthesis: Using pulsed bias to enhance process throughput and precision

An effective technique to improve the precision and throughput of energetic ion condensation through dielectric nanoporous templates and reduce nanopore clogging by using finely tuned pulsed bias is proposed. Multiscale numerical simulations of ion deposition show the possibility of controlling the dynamic charge balance on the upper template’s surface to minimize ion deposition on nanopore sidewalls and to deposit ions selectively on the substrate surface in contact with the pore opening. In this way, the shapes of nanodots in template-assisted nanoarray fabrication can be effectively controlled. The results are applicable to various processes involving porous dielectric nanomaterials and dense nanoarrays.