Thick Amorphous Films Research Articles

Growth of thick amorphous carbon films on alumina for improved tribological properties

Alumina, as a pivotal ceramic material extensively utilized in contemporary applications, the surface modification and enhancement of tribological properties are crucial. In this study, reactive magnetron sputtering was employed to deposit Ti, Si co-doped hydrogen-free (TiSi/a-C), and hydrogenated amorphous carbon films (TiSi/a-C:H) with a thickness exceeding 7 μm onto the surface of alumina ceramic substrates. Utilizing the design of the film structure, the difficulty of film-substrate adhesion was resolved by controlling the deposition time to influence the growth rate of the film, thereby enabling the reliable fabrication of thick films. The adhesion of the TiSi/a-C film exhibits the highest value, with an Lc1 value of 36.7 N. The hardness of the TiSi/a-C:H reaches a maximum of 15.2 GPa, and the hardness is closely correlated with the reaction gas utilized during its depositional process. The wear rate of amorphous carbon film decreases by 34 times compared to alumina substrate. During the dissociation of CH4 at a high hydrogen-to-carbon ratio, more hydrogen atoms are involved in the chemical reaction. The introduction of hydrogen elevates the H/E and sp3/sp2 ratios within the film, thereby favoring the generation of low-friction surfaces and refining the tribological performance of alumina ceramics.

Tolerance to deformation and flux pinning in superconducting amorphous molybdenum nitride thin films grown on flexible polyimide

We investigate the superconducting properties of 80 nm thick amorphous MoNx films fabricated via reactive sputtering on silicon and flexible commercial polyimide substrates. The samples are grown at room temperature using reactive sputtering with a gas mixture of N2 and Ar. The mechanical deformation tolerance for films on polyimide is evaluated by comparing the superconducting critical temperature (Tc) and critical current density (Jc) when the films are attached to cooper surfaces with varying curvatures. The amorphous films exhibit a Tc of 8.2 K on silicon and 7.9 K on polyimide. Our results demonstrate a significant enhancement in flux pinning for the thin films grown on polyimide, with the Jc at self-field and 3 K increasing from approximately 0.5 MA/cm2 to around 1 MA/cm2. Analyses of Jc as a function of the magnetic field, angle, and temperature reveal that the films on polyimide exhibit remarkable resilience to deformation. Interestingly, comparable Jc values are observed when the samples are affixed to both flat and cylindrical surfaces with diameters of 2.5 cm. This observation suggests that vortex dissipation predominantly occurs through flux motion in the region experiencing the maximum Lorentz force. Furthermore, the films maintain Tc without any discernible changes in resistivity when fixed to cylindrical surfaces with 1.2 cm diameters. However, there is a significant drop in vortex pinning, indicating reduced pinning capability in the stressed regions. The high deformation tolerance of amorphous MoNx renders it highly suitable for cryogenic electronics applications, providing a viable alternative to the commonly utilized metallic Nb.

Ferromagnetism of Nanometer Thick Sputtered Fe3GeTe2 Films in the Absence of Two-Dimensional Crystalline Order: Implications for Spintronics Applications

The discovery of ferromagnetism in two-dimensional (2D) monolayers has stimulated growing research interest in both spintronics and material science. However, these 2D ferromagnetic layers are mainly prepared through an incompatible approach for large-scale fabrication and integration, and moreover, a fundamental question of whether the observed ferromagnetism actually correlates with the 2D crystalline order has not been explored. Here, we choose a typical 2D ferromagnetic material, Fe3GeTe2, to address these two issues by investigating its ferromagnetism in an amorphous state. We have fabricated nanometer thick amorphous Fe3GeTe2 films approaching the monolayer thickness limit of crystallized Fe3GeTe2 (0.8 nm) through magnetron sputtering. Compared to crystallized Fe3GeTe2, we found that the basic ferromagnetic attributes, such as the Curie temperature which directly reflects magnetic exchange interactions and local anisotropic energy, do not change significantly in the amorphous states. This is attributed to the short-range atomic order, as confirmed by valence state analysis, being almost the same for both phases. The persistence of ferromagnetism in the ultrathin amorphous counterpart has also been confirmed through magnetoresistance measurements, where two unconventional switching dips arising from electrical transport within domain walls are clearly observed in the amorphous Fe3GeTe2 single layer. These results indicate that the long-range ferromagnetic order of crystallized Fe3GeTe2 may not correlate to the 2D crystalline order, and the corresponding ferromagnetic attributes can be utilized in an amorphous state which suits large-scale fabrication in a semiconductor technology-compatible manner for spintronics applications.

Amorphous to Polycrystalline Phase Transition in La2O3 Films Grown on a Silicon Substrate Forming Si‐Doped La2O3 Films

Herein, La2O3 films are fabricated on a Si substrate without a La–Sr intermixing layer at the La2O3/Si interface using a pulsed laser deposition method. X‐ray diffraction data shows only two discernible peaks of the La2O3 films: hexagonal La2O3 (10‐1) and cubic La2O3 (222), indicating polycrystalline character. During film growth, the reflection high‐energy electron diffraction pattern from the La2O3 surface changes from an initial column shape to a complicated distributed dot pattern with narrow lines, suggesting possible structural property changes in the La2O3 film. The occurrence of a structural transition is confirmed by high‐resolution transmission electron microscopy (HRTEM), which exhibits a clear crystalline phase change from an initial ≈10 nm thick amorphous La2O3 film to polycrystalline La2O3 film on Si. Rutherford backscattering shows a reduced La–Si intermixing between La2O3 and Si. Furthermore, the results of X‐ray photoelectron spectroscopy atomic depth profile analysis show that observation of La‐silicate over the whole La2O3 film indicates that Si diffuses through whole thick La2O3 films forming Si‐doped La2O3 films. This study of the well‐defined structural characteristics and sharp interface of La2O3/Si will enable further understanding of high dielectric constant materials grown on Si by the introduction of advanced film growth technique.

Nanometric Amorphous TiO2 As an Extrinsic Pseudo-Capacitive Electrode for All-Solid-State Asymmetric Hybrid Micro-Supercapacitors: Effects on the Electrochemical Performance

On-chip solid-state micro-supercapacitors (MSCs) have gained widespread attention owing to their versatile benefits, including high power density and long cycle life1,2. Recently asymmetric hybrid microsupercapacitors (AsHMSCs) introducing a charge storage mechanism based on both faradaic reaction and electric double-layer phenomena have been considered to increase the energy density. Within this context, the selection of electrode materials and their interaction at the interface with the electrolyte is a key issue to optimize the AsHMSC electrochemical performance.In this work, nanometric (5-20 nm thick) amorphous TiO2 films have been elaborated and characterized in liquid and solid-state electrolyte (LiPON) half-cell configurations. Interestingly, TiO2 films after LiPON deposition exhibited a constant initial amount of intercalated lithium ions for all considered thicknesses and did not require a first activation process, in comparison to the liquid electrolyte configuration. For all considered configurations, the specific capacity extracted from cyclic voltammetry and galvanostatic cycling within [0.5-3V] potential range correspond to the theoretical value expected for the Lix=1TiO2 phase at low current density. Furthermore, the cooperative effects of high Li ion intercalation kinetics and Low interfacial charge transfer resistance for 5nm TiO2 electrode (extracted from electrochemical impedance spectroscopy analysis) exhibit an outstanding specific capacity of 2mC.cm-2 at 1µA.cm-2, and high rate performance with 60% capacity holding ratio at 100µA.cm-2, thus highlighting the extrinsic pseudo-capacitive behavior of the sub 10nm electrodes.A TiO2 5nm/LiPON 100nm/Pt AsHMSC is successfully fabricated, which achieves an operating voltage window of 3V and a specific capacity of 0.3mC.cm-2 at 1mA.cm-2.In addition, the device also exhibited a 100% coulombic efficiency even after cycling for 6000 continuous charge-discharge cycles. This work offers an approach to tune the Li ion storage properties of TiO2 by nano-engineering and gives insights into the enhancement of pseudocapacitance-assisted lithium-storage capacity.References Kyeremateng et al., Nature Nanotech 12, 7–15 (2017). https://doi.org/10.1038/nnano.2016.196Sallaz et al., J. Power Sources 451, 227786 (2020), doi: 10.1016/j.jpowsour.2020.227786. Figure 1

Laser‐Induced Tuning and Spatial Control of the Emissivity of Phase‐Changing Ge2Sb2Te5 Emitter for Thermal Camouflage

AbstractThe tuning of a material's emissivity in the atmospheric window range of 8–13 µm is crucial for infrared (IR) adaptive applications such as thermal camouflage, IR stealth, and radiative cooling. A resonator structure comprising a phase‐changing Ge2Sb2Te5 (GST) film on a metal mirror is promising as a tunable thermal emitter because its long‐wavelength IR emissivity can be varied by adjusting the degree of crystallization of the GST film through annealing. However, the space‐selective tuning of the emissivity required for practical use remains a significant challenge. Herein, a hybrid method combining laser irradiation and heat treatment is presented for space‐selective and continuous tuning of the emissivity of a GST‐based resonator. The current study shows that a laser‐induced crystalline layer formed in the near‐surface region of a 400 nm thick amorphous GST film can act as heterogeneous nuclei for crystallization when the film is subsequently annealed, thereby increasing the crystallization rate of the GST film. This results in a large difference in emissivity between the irradiated and nonirradiated areas, and the emissivity difference can be tuned by changing the annealing temperature. Thermal camouflage is experimentally demonstrated by making high‐and low‐temperature regions with low and high emissivity, respectively.

Combine XPS- and AFM Study of Silicon Oxide Film with Zinc Impurity for ReRAM Devices

The composition, structure and properties, as well as the current-voltage characteristics of a layered structure consisting of two 50 nm thick amorphous SiO2 films deposited by electron beam evaporation, between which a Zn film with a thickness that varied from 100 nm to 50 nm was deposited. Then these structures were annealed in air in the temperature range from 300 up to 400oC with a step of 50oC for 30 min. Planar electrodes with different configuration were used. They were made from gold, platinum and aluminum. It was found that after deposition on the sample surface, a granular structure with a grain size of 50-100 nm of SiO2 composition was formed. After annealing at 400oC, the sample roughness decreases from 25 nm after deposition to 10 nm, and the grain size in plan increases to 100-200 nm. For films annealed at 400oC the current-voltage characteristics with hysteresis were obtained. Keywords: silicon oxide film, zinc impurity, electron beam evaporation, annealing, nanoclusters, ZnO.

Совместное XPS- и AFM-исследование пленок оксида кремния с примесью цинка для ReRAM устройств

The composition, structure and properties, as well as the current-voltage characteristics of a layered structure consisting of two 50 nm thick amorphous SiO2 films deposited by electron beam evaporation, between which a Zn film with a thickness that varied from 10 to 50 nm was deposited. Then these structures were annealed in air in the temperature range from 300 up to 450°C with a step of 50°C for 30 minutes. Planar electrodes with different configuration were used. They were made from gold, platinum and aluminum. It was found that after deposition on the sample surface, a granular structure with a grain size of 50-100 nm of SiO2 composition was formed. After annealing at 400°C, the sample roughness decreases from 25nm after deposition to 10 nm, and the grain size in plan increases to 100-200 nm. For films annealed at 400°C the current-voltage characteristics with hysteresis were obtained.

The combined use of wrinkling and cracking for the characterization of the mechanical properties of the laser-fabricated nanometer-thick amorphous carbon films

Direct laser writing carbonization has been recently developed to enable facile fabrication of patternable nanometer-thick two-dimensional amorphous carbon films, which may find promising applications in high-performance sensing, energy storage, catalysis, biomaterials etc. Given its nanometer-thick character and brittleness in nature, it is quite challenging to evaluate and characterize the mechanical properties of this novel material. With assistance of a sacrificial-layer transfer approach for sample preparation, herein, we rely on wrinkling metrology as a viable tool for characterizing the elastic modulus of the laser-fabricated nanometer thick amorphous carbon films. Moreover, upon combining the wrinkling metrology with channel cracking behavior investigation, the strength-related mechanical properties, including fracture toughness, fracture strength and fracture strain of the carbon thin films of varied thickness have been evaluated comprehensively. Within the experimental conditions being studied, the elastic modulus, fracture toughness, fracture strength and fracture strain of the laser-fabricated nanometer-thick carbon films respectively fall in a range of 23.1–34.9 GPa, 16.3–151.7 J/m2, 0.5–1.4 GPa, and 2.0–4.5%. The results and methodology presented in this study demonstrate the usefulness of combining wrinkling metrology and cracking technique as a simple but generally applicable approach for comprehensive characterization and evaluation of the mechanical properties of different types of brittle and nanometer-thick thin films.

Dual Electrochemical Treatments to Improve Properties of Ti6Al4V Alloy.

Surface treatments are considered as a good alternative to increase biocompatibility and the lifetime of Ti-based alloys used for implants in the human body. The present research reports the comparison of bare and modified Ti6Al4V substrates on hydrophilicity and corrosion resistance properties in body fluid environment at 37 °C. Several surface treatments were conducted separately to obtain either a porous oxide layer using nanostructuration (N) in ethylene glycol containing fluoride solution, or bulk oxide thin films through heat treatment at 450 °C for 3 h (HT), or electrochemical oxidation at 1 V for 3 h (EO), as well as combined treatments (N-HT and N-EO). In-situ X-ray diffraction and ex-situ transmission electron microscopy have shown that heat treatment gave first rise to the formation of a 30 nm thick amorphous layer which crystallized in rutile around 620 °C. Electrochemical oxidations gave rise to a 10 nm thick amorphous film on the top of the surface (EO) or below the amorphous nanotube layer (N-EO). Dual treated samples presented similar results with a more stable behavior for N-EO. Finally, for both corrosion and hydrophilicity points of view, the new combined treatment to get a total amorphous N-EO sample seems to be the best and even better than the partially crystallized N-HT sample.

A study on ultrafast laser micromachining and optical properties of amorphous polyether(ether)ketone (PEEK) films

Polyether(ether)ketone (PEEK) has been widely used in the electronics and biomedical industries due to excellent electrical, chemical and thermal stability. The ablation and optical properties of amorphous PEEK have been investigated using ultrahigh intensity fs laser pulses (180 fs/ 1 kHz) for precision manufacture. The single pulse ablation threshold was found to be 2.01±0.05 J cm-2 and 0.23±0.02 J cm-2 at 775 nm and 387 nm respectively. The significant difference has been attributed to the change in wavelength dependent nonlinear absorption order from multi-photon at 775 nm (via virtual states) to sequential 2-photon at 387 nm with photon energy within the material band edge. The 2-photon absorption coefficient at 387 nm was measured to be β ∼ 38 cm GW-1 at I ∼3 GW cm-2 leading to a strong light-matter coupling. Fs ablation quality is much superior at 387 nm with almost no melting and debris, allowing the observation of laser induced periodic surface structures (LIPSS) with pitch Λ < 0.4 µm. Large area LIPSS have been machined on 200 µm thick amorphous PEEK film with the direction of LIPSS parallel to the direction of linear polarisation.

Thick amorphous complexion formation and extreme thermal stability in ternary nanocrystalline Cu-Zr-Hf alloys

Building on the recent discovery of tough nanocrystalline Cu-Zr alloys with amorphous intergranular films, this paper investigates ternary nanocrystalline Cu-Zr-Hf alloys with a focus on understanding how alloy composition affects the formation of disordered complexions. Binary Cu-Zr and Cu–Hf alloys with similar initial grain sizes were also fabricated for comparison. The thermal stability of the nanocrystalline alloys was evaluated by annealing at 950 °C (>95% of the solidus temperatures), followed by detailed characterization of the grain boundary structure. All of the ternary alloys exhibited exceptional thermal stability comparable to that of the binary Cu-Zr alloy, and remained nanocrystalline even after two weeks of annealing at this extremely high temperature. Despite carbide formation and growth in these alloys during milling and annealing, the thermal stability of the ternary alloys is mainly attributed to the formation of thick amorphous intergranular films at high temperatures. Our results show that ternary alloy compositions have thicker boundary films compared to the binary alloys with similar global dopant concentrations. While it is not required for amorphous complexion formation, this work shows that having at least three elements present at the interface can lead to thicker grain boundary films, which is expected to maximize the previously reported toughening effect.

Conformal Nanoscale Zirconium Hydroxide Films for Decomposing Chemical Warfare Agents

Amorphous zirconium hydroxide (ZH) has attracted recent attention for its high decomposition reactivity with chemical warfare agents (CWA). Conformal, 50 nm thick amorphous ZH films were produced on arbitrarily shaped metallic substrates by cathodic electrodeposition from ZrOCl2 in aqueous solution, with nanoscale control of the film thickness. The films had a root-mean-square (rms) roughness of ∼6–8 nm, ∼2.4 nm nanoscale pores, and a high specific surface area of 132 m2 g–1. These rapidly grown, cost-effective, and scalable films may be more suitable for some in situ decontamination needs than post-event application of powders prepared by conventional wet-synthesis methods. The morphology and chemical properties of the electrodeposited films were characterized with scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis mass spectrometry (TGA-MS), and nitrogen-sorption porosimetry. The decomposition activity of ZH toward dimethyl methylphosphonate (DMMP), a CWA simulant, was probed with gas chromatography–mass spectrometry (GC-MS) and in situ attenuated total reflection infrared spectroscopy (ATR) by monitoring the evolution of gas-phase methanol and the coverage of surface-bound methoxy and phosphonate species during and after DMMP dosing. We compared the chemical activity of electrochemically synthesized ZH (EZ), commercial ZH (CZ) and ZrO2 nanopowders, and calcined EZ at 100–500 °C. The ATR, XPS, and XRD results indicate that calcination to 500 °C decreased DMMP decomposition due to the loss of hydroxyls and conversion to crystalline ZrO2 and that EZ and CZ had virtually identical surface reactions. This study provides a framework for characterizing the evolution of complex reactions during the transition from amorphous-to-crystalline material.

Notch tip fields in amorphous films resting on ductile substrates

The architecture consisting of films resting on a ductile substrate is ubiquitous in a wide variety of applications. A typical failure mechanism of such a structure is cracking of the films. In this study, the calculations for the notch tip fields in a metallic glass film deposited on a ductile substrate are carried out to explore the fracture mechanisms of the amorphous films. The amorphous film is characterized by an isotropic elastic-plastic model which captures the pressure sensitive yielding and post-yield strain softening behavior of metallic glasses, and the substrate is taken to be an elastic-plastic solid with the flow rule given by von-Mises flow theory. It is found that the thick amorphous films exhibit high opening stress and small plastic deformation, indicating that brittle cracking of the films tends to be the dominant fracture mode. Whereas, the low opening stress is observed and shear bands develop in the case of thin amorphous films, implying that the cracking caused by shear bands governs the fracture of films. We further revealed that the pressure sensitive yielding plays an important role in the fracture of amorphous films; large degree of pressure sensitivity enables low opening stress and enhanced plastic deformation in the films, increasing the propensity of formation of shear bands. The findings of this study provide plausible explanations for the experimentally observed fracture behavior of amorphous films on ductile substrates, and shed new light on the fracture mechanisms of such a structure.

Thick Amorphous Complexion Formation and Extreme Thermal Stability in Ternary Nanocrystalline Cu-Zr-Hf Alloys

Building on the recent discovery of tough nanocrystalline Cu-Zr alloys with amorphous intergranular films, this paper investigates ternary nanocrystalline Cu-Zr-Hf alloys with a focus on understanding how alloy composition affects the formation of disordered complexions. Binary Cu-Zr and Cu-Hf alloys with similar initial grain sizes were also fabricated for comparison. The thermal stability of the nanocrystalline alloys was evaluated by annealing at 950 °C (>95% of the solidus temperatures), followed by detailed characterization of the grain boundary structure. All of the ternary alloys exhibited exceptional thermal stability comparable to that of the binary Cu-Zr alloy, and remained nanocrystalline even after two weeks of annealing at this extremely high temperature. Despite carbide formation and growth in these alloys during milling and annealing, the thermal stability of the ternary alloys is mainly attributed to the formation of thick amorphous intergranular films at high temperatures. Our results show that ternary alloy compositions have thicker boundary films compared to the binary alloys with similar global dopant concentrations. While it is not required for amorphous complexion formation, this work shows that having at least three elements present at the interface can lead to thicker grain boundary films, which is expected to maximize the previously reported toughening effect.

Investigation and improvement of atomization efficiency based on SAW device coated with amorphous fluoropolymer film for olfactory display

This paper reports on a method to realize the instant and high-efficiency atomization for liquid perfumes in an olfactory display system using surface acoustic wave device coated with amorphous fluoropolymer film. The liquid perfumes diluted with ethanol tend to spread into a thin film on LiNbO3 substrate before atomization, which causes low atomization efficiency and serious smell persistence. The proposed method employs a layer of 400 nm thick amorphous fluoropolymer film Cytop on SAW substrate to maintain the droplet’s sphere-like shape due to the excellent hydrophobicity. Amino-based silane coupling agent was used to enhance the adhesion. The difference of atomization process between hydrophilic and hydrophobic surfaces was clearly revealed. With the finer and more stable mists being generated on coated surface, the significant improvement of atomization efficiency was demonstrated. Sensory test results on three liquid perfumes show that the smell persistence was greatly reduced after the coating.

Protective amorphous carbon coatings on glass substrates

Thick amorphous carbon films were deposited by the Magnets-in-Motion (M-M) rf linear hollow cathode at varying acetylene contents in Ar in a hybrid PVD/PE-CVD process directly on glass substrates. The hollow cathode plates manufactured from graphite were used as the PVD target. The measurements show that the films can reach thickness of up to 50 μm at deposition rates of up to 2.5 μm/min. Scratch test measurements confirm that well adhering films several μm thick can be achieved at C2H2 contents of up to 0.5%.

Thermally stable amorphous tantalum yttrium oxide with low IR absorption for magnetophotonic devices

Thin film oxide materials often require thermal treatment at high temperature during their preparation, which can limit them from being integrated in a range of microelectronic or optical devices and applications. For instance, it has been a challenge to retain the optical properties of Bragg mirrors in optical systems at temperatures above 700 °C because of changes in the crystalline structure of the high–refractive-index component. In this study, a ~100 nm–thick amorphous film of tantalum oxide and yttrium oxide with an yttrium-to-tantalum atomic fraction of 14% was prepared by magnetron sputtering. The film demonstrated high resistance to annealing above 850 °C without degradation of its optical properties. The electronic and crystalline structures, stoichiometry, optical properties, and integration with magnetooptical materials are discussed. The film was incorporated into Bragg mirrors used with iron garnet microcavities, and it contributed to an order-of-magnitude enhancement of the magnetooptical figure of merit at near-infrared wavelengths.

Tailoring plasticity of metallic glasses via interfaces in Cu/amorphous CuNb laminates

Abstract

Mn-doped Ge self-assembled quantum dots via dewetting of thin films

In this study, we demonstrate an original elaboration route for producing a Mn-doped Ge self-assembled quantum dots on SiO2 thin layer for MOS structure. These magnetic quantum dots are elaborated using dewetting phenomenon at solid state by Ultra-High Vacuum (UHV) annealing at high temperature of an amorphous Ge:Mn (Mn: 40%) nanolayer deposed at very low temperature by high-precision Solid Source Molecular Beam Epitaxy on SiO2 thin film. The size of quantum dots is controlled with nanometer scale precision by varying the nominal thickness of amorphous film initially deposed. The magnetic properties of the quantum-dots layer have been investigated by superconducting quantum interference device (SQUID) magnetometry. Atomic force microscopy (AFM), x-ray energy dispersive spectroscopy (XEDS) and transmission electron microscopy (TEM) were used to examine the nanostructure of these materials. Obtained results indicate that GeMn QDs are crystalline, monodisperse and exhibit a ferromagnetic behavior with a Curie temperature (TC) above room temperature. They could be integrated into spintronic technology.