Electron-beam Sputtering Research Articles

CONDUCTIVITY OF HAFNIUM OXIDE LMS OBTAINED BY ELECTRON BEAM SPUTTERING

Films of hafnium oxide HfOx with a thickness of about 40 nm were obtained by electron beam sputtering at di erent oxygen ow rates in the chamber. The electrophysical properties of lms in air and vacuum were studied. It is shown that the temperature dependences of lm conductivity, measured in vacuum inthe temperature range from 20 to 180 ◦C, have an activation character with an activation energy of 0.82 ±0.02 eV. It has been suggested that charge transfer in the resulting lms is determined by the activation of electrons into the conduction band from the donor level associated with oxygen vacancies. It was found that the conductivity of lms in air changes greatly with varying oxygen ow, while in vacuum the conductivity is practically independent of the oxygen ow. This indicates signi cant di erences in the surface properties of lms obtained at di erent oxygen ows in the chamber during the deposition process.

Conductivity of Hafnium Oxide Films Obtained by Electron-Beam Sputtering

Conductivity of Hafnium Oxide Films Obtained by Electron-Beam Sputtering

High‐Quality NiFe Thin Films on Oxide/Non‐Oxide Platforms via Pulsed Laser Deposition at Room Temperature

AbstractSoft ferromagnetic permalloy (NiFe) thin films are promising for applications in spintronic devices because of their constituent electrical and magnetic properties. Electron beam evaporation and sputtering techniques have been used to deposit NiFe thin films. For in situ stacking of NiFe with functional complex oxides, the pulsed laser deposition (PLD) method is highly desirable. However, the growth of high‐quality NiFe (and non‐oxide thin films in general) by PLD remains a formidable task. Here, high‐quality NiFe thin films of various thicknesses on oxide/non‐oxide substrates with desirable magnetic properties by PLD at room temperature are reported. The magnetic properties are found to be strongly dependent on the laser fluence of the deposition process. The laser fluence of 4 J cm−2 produces the highest magnetization of ≈547 emu cc−1. The small coercivity (few Oersted) and sharp ferromagnetic switching behavior indicate uniaxial anisotropy with an easy axis along the in‐plane direction. In addition, thickness‐dependent magnetodynamics characterizations are studied via ferromagnetic resonance. These results offer significant insight into the PLD‐based development of thin metal magnetic films.

Композиционные мембраны для обессоливания воды

Methods of coatings forming on the surface of a poly(ethylene terephthalate) track-etched membrane by magnetron and electron-beam sputter deposition of polytetrafluoroethylene in vacuum are considered. It is established that the involve of these modification methods leads to the formation of composite membranes consisting of two layers, one of which is the original track-etched membrane, characterized by an average level of hydrophilicity. The second layer has a hydrophobic nature. The contact angle of wettability by water of this layer varies depending on its thickness and the modification method used. It is shown that deposition of coatings by magnetron sputtering of polytetrafluoroethylene leads to smoothing of structural inhomogeneities of the surface of the initial membrane. Deposition of coatings by electron-beam dispersion of polymer, on the contrary, causes an increase in surface roughness. The observed differences in the morphology of the composite membranes surface layer are related to the size of the deposited polymer nanostructures. Nanostructures formed on the surface of track-etched membranes, when polytetrafluoroethylene is dispersed under the action of electron beam, have greatly large sizes. A significant increase in roughness due to the increase in the size of nanostructures makes it possible to obtain coatings with high- and superhydrophobic properties. It is shown that composite membranes consisting of a hydrophilic base with a hydrophobic coating deposited on the surface provide higher separation selectivity during desalination of an aqueous solution of sodium chloride by membrane distillation compared with the initial poly(ethylene terephthalate) track-etched membrane. In addition, the performance of two-layer composite membranes in the process of membrane distillation due to low resistance to mass transfer is higher in comparison with a track-etched membrane made of polypropylene.

Model experiments with Auger electron and X-ray photoelectron spectroscopy at lithiated graphite material: Surface changes related to ion- and electron-beam effects

Li-based batteries as a key element for green energy economy should be permanently improved in their performance. Therefore, the complex electrochemical processes in such batteries have to be understood in detail. For their characterization beside (electro-)chemical methods also electron spectroscopic methods such as X-ray photoelectron spectroscopy (XPS) and Auger electron spectroscopy (AES) are used to get more insight into the chemical processes at the surfaces. One crucial point is stability of the solid electrolyte interface (SEI) upon measurements, especially at the (graphite-)anodes. In this paper, we use highly oriented pyrolytic graphite (HOPG) as a model anode material, which was lithiated in a molten metal intercalation process. Strong beam damage effects at the lithiated HOPG under electron and ion beam radiation are observed and described. These effects are important for using of local electron beam investigations and sputter depth profiling, often applied also for SEI characterization.

Influence of the upper electrode material on the electrophysical properties of MDM structures based on ferroelectric films

Ferroelectric films of the composition Ba0.8Sr0.2TiO3 (BST) were synthesized on platinized silicon substrates by RF sputtering. Top electrodes made of nickel, aluminum, copper and chromium were formed on the grown films by electron beam sputtering. The results of studies of the electrophysical properties of the obtained metal-dielectric-metal (MDM) heterostructures (Me-BST-Pt-Si) are presented. Keywords: ferroelectric BST films, metal-dielectric-metal (MDM) structures, microstructure, electrophysical properties.

The Critical Temperature of Superconducting Aluminum Films

The R(T) dependences of thin superconducting aluminum films deposited on leucosapphire and gallium arsenide substrates by electron beam sputtering and molecular beam epitaxy have been experimen-tally studied. Regardless of morphology, a noticeable increase in the critical temperature of the supercon-ducting transition with a decrease in the film thickness is found. The effect is interpreted as a manifestation of the quantum size effect.

Microwave Plasma-Enhanced Parylene-Metal Multilayer Design from Metal Salts.

In this paper, a new approach for the synthesis of Parylene–metal multilayers was examined. The metal layers were derived from a metal salt solution in methanol and a post-drying plasma reduction treatment. This process was designed as a one-pot synthesis, which needs a very low amount of resources and energy compared with those using electron beam sputtering processes. The Parylene coatings were obtained after reduction plasma treatments with Parylene C. Therefore, a Parylene coating device with an included plasma microwave generator was used to ensure the character of a one-pot synthesis. This process provided ultra-thin metal salt layers in the range of 1–2 nm for layer thickness and 10–30 nm for larger metal salt agglomerates all over the metal salt layer. The Parylene layers were obtained with thicknesses between approx. 4.5 and 4.7 µm from ellipsometric measurements and 5.7–6.3 µm measured by white light reflectometry. Tensile strength analysis showed an orthogonal pulling stress resistance of around 4500 N. A surface roughness of 4–8 nm for the metal layers, as well as 20–29 nm for the Parylene outer layer, were measured. The wettability for non-polar liquids with a contact angle of 30° was better than for polar liquids, such as water, achieving 87° on the Parylene C surfaces.

Dark electron tunneling current in metal–insulator–metal structures: modeling, fabrication, and measurement

Metal–insulator–metal (MIM) structures have been proposed for infrared photodetectors, optical rectennas, and alternative choices to conventional solar cells. Generally, if two dissimilar electrodes are separated by a sufficiently thin insulator, electrons can travel through the insulating gap region due to the quantum tunneling effect. This tunneling through the insulating gap can be driven by an electromagnetic field or an external bias voltage. In our work, we incorporate the contributions of the Poole–Frenkel (PF) effect on the energy barrier of the MIM junction and the effect of Coulomb interaction between the electron charge and its virtual image charges. Using this modified PF-Coulombic barrier, we perform quantum calculations for electron tunneling using the transfer matrix method and Wentzel–Kramers–Brillouin approximations. This, along with the density of states, the Fermi occupation probability, and the quantum confinement effect is used to derive the dark current density for the MIM diode. To test the theory, MIM Au-TiO2-Ti diodes are designed and fabricated in-house using photolithography, along with electron beam evaporation and sputter depositions. The dark current–voltage (I − V) characteristics of the fabricated MIM photodiodes are measured and show good agreement with theoretical predictions.

Defect-Free Metal Deposition on 2D Materials via Inkjet Printing Technology.

2D materials have many outstanding properties that make them attractive for the fabrication of electronic devices, such as high conductivity, flexibility, and transparency. However, integrating 2D materials in commercial devices and circuits is challenging because their structure and properties can be damaged during the fabrication process. Recent studies have demonstrated that standard metal deposition techniques (like electron beam evaporation and sputtering) significantly damage the atomic structure of 2D materials. Here it is shown that the deposition of metal via inkjet printing technology does not produce any observable damage in the atomic structure of ultrathin 2D materials, and it can keep a sharp interface. These conclusions are supported by abundant data obtained via atomistic simulations, transmission electron microscopy, nanochemical metrology, and device characterization in a probe station. The results are important for the understanding of inkjet printing technology applied to 2D materials, and they could contribute to the better design and optimization of electronic devices and circuits.

Critical current modulation induced by an electric field in superconducting tungsten-carbon nanowires

The critical current of a superconducting nanostructure can be suppressed by applying an electric field in its vicinity. This phenomenon is investigated throughout the fabrication and electrical characterization of superconducting tungsten-carbon (W-C) nanostructures grown by Ga^+ focused ion beam induced deposition (FIBID). In a 45 nm-wide, 2.7 upmu m-long W-C nanowire, an increasing side-gate voltage is found to progressively reduce the critical current of the device, down to a full suppression of the superconducting state below its critical temperature. This modulation is accounted for by the squeezing of the superconducting current by the electric field within a theoretical model based on the Ginzburg–Landau theory, in agreement with experimental data. Compared to electron beam lithography or sputtering, the single-step FIBID approach provides with enhanced patterning flexibility and yields nanodevices with figures of merit comparable to those retrieved in other superconducting materials, including Ti, Nb, and Al. Exhibiting a higher critical temperature than most of other superconductors, in which this phenomenon has been observed, as well as a reduced critical value of the gate voltage required to fully suppress superconductivity, W-C deposits are strong candidates for the fabrication of nanodevices based on the electric field-induced superconductivity modulation.

Ti3SiC2 irradiation damage at electron beam energy levels of 120 keV and 200 keV

Irradiation damage response under electron beam irradiation energies of 120 keV and 200 keV on Ti3SiC2 was investigated in this study. The surface of material became rough under 120 keV caused by the electron beam sputtering. Under 200 keV electron irradiation, the surface damage was more serious. Diffraction spots with low intensity of some crystal planes due to the displacement of Si atoms at 200 keV. Point defects caused by irradiation reduced the a-axis lattice constant by 1.8%. However, even after irradiation for 600 s, no amorphous ring was observed.

XPS study of Rh/In2O3 system

The effect of surface modification of In2O3 films by rhodium atoms deposited by electron beam sputtering on the XP spectra is considered. The surface coverage with rhodium ranged from 0 to 0.1 ML. It was shown that the main changes in the XP spectra occur in the Rh3d region and are caused by the dimensional effect of rhodium particles. With an increase in the surface coverage with rhodium, Rh particles grow from an atomically dispersed state to relatively large clusters. As the particle size increases, its electronic structure tends to approach the state corresponding to the bulk Rh. Such a process is accompanied by a decrease in BE Rh3d5/2 by 0.3–0.6 eV, which behaviour depends on the surface structure of the used In2O3 films.

The Use of Silicon Dioxide Films as Anti-Reflective Coating of Thermoelectric Single-Photon Detector

Antireflection layers are an important part of the sensitive elements of high performance single photon detectors. We have obtained amorphous silicon dioxide films by electron-beam sputtering on Al2O3, AlN, Si substrates as well as CeB6, LaB6, and W coatings. The elemental composition, microstructure and surface roughness, as well as optical characteristics of the samples obtained under various conditions of spraying are investigated. It is shown that SiO2/Al2O3 and SiO2/AlN two-layer coatings can provide high detection efficiency under registration of the radiation in the near IR region, which is used in telecommunication systems and devices for quantum information processing.

Structure and magnetoresistive properties of three-layer thin films of spin-valve type

Three-layer thin films of spin-valve type Co/Сu/NixFe100-x at x = 20–80 at.% were prepared by electron-beam sputter deposition. The investigated phase state and magnetoresistive properties were done for as-deposited and annealed to 400, 550, and 700 K films. The measurements of field dependences of magnetoresistance were held at different temperatures. It was demonstrated that phase state, crystal structure, and magnetoresistive properties of Co/Сu/NixFe100-x systems strongly dependent on both NixFe100-x composition NixFe100-x and heat treatment conditions.

Versatile nanodot-patterned Gore-Tex fabric for multiple energy harvesting in wearable and aerodynamic nanogenerators

The ongoing expedition to harvest ambient renewable energies from the environment by wearable fabric-based nanogenerators is a promising route to sustainably drive the small electronics with unprecedented opportunities in next-generation self-powered devices. Here, we report a simple method to fabricate a washable, breathable and wearable triboelectric nanogenerator that harvests the energy of triboelectricity through an enhanced friction surface area made of the gold nanodot-pattern crafted by electron-beam sputtering on an inexpensive polyurethane surface. The gold deposition which crops-up as regular small islands, under oxygen plasma is subsequently, etched into nanodot-pattern on a polyurethane surface to convert mechanical energy into an electrical signal via in-plane sliding mode with a maximum output of ~2 μW. The nanodot engineering plays an important role to improve the active sliding frictional area, as well as the corresponding output-performance of the triboelectric nanogenerator. To demonstrate the potential applications of our approach, we designed a self-powered wearable device integrated with clothes to harvest different kinds of mechanical energies from the human motion. To elevate the power output-performance, we fabricated waterproof fiber with flutter membrane and quantified triboelectric charge against airflow speed. At mild wind speed, the fabricated triboelectric nanogenerator shows a maximum output of 70 µW. Besides, as an example of practical application, the nanogenerator constructed can produce an improved capacitor charge voltage to drive dozens of light-emitting diodes and apply them to low power consumption devices. This technology is produced in a simple and cost-effective manner and reports an easy way to produce an energy harvesting system based on triboelectric effects using a sustainable and renewable energy source of body motions and air flows. This system is expected to be one of the best green energy sources for portable and wearable electronic devices in the near future.

Electrical Characterization of Charge Polarity in AlF₃ Anti-Reflection Layers for Complementary Metal Oxide Semiconductor Image Sensors.

In this study, the charge polarity of aluminum fluoride (AlF3) as a function of varying thickness (tAlF3 = 20, 35, 50, 65, and 80 nm) was discussed. AlF3 films were deposited onto p-Si wafers via electron beam sputtering. Thickness dependent charge polarity and reliability issues under bias-temperature stress conditions were identified using a capacitance-voltage (C-V) characterization method. AlF3 was found to possess negative fixed charges, leading to a C-V curve shift toward the positive gate bias direction as tAlF3 was increased up to 50 nm. On the contrary, the C-V characteristics were dominantly affected by the positive charges of mobile ions and/or fluorine vacancies when tAlF3 was increased to more than 50 nm. Additionally, negative bias temperature stress (1 MV/cm, 473 K for 10 mins) increased insulator trapped charges and decreased interface traps in 20 nm thick AlF3 films. These results could be attributed to positively charged fluorine vacancies introduced by broken Al-F bonds within AlF3 films and the passivation of Si dangling bonds due to broken fluorine ions at the interface, respectively. It was believed that 20 nm thick AlF3 films sufficiently attracted holes from the Si substrate, forming a hole accumulation layer on the surface due to total charge polarity of the AlF3 dielectric being entirely governed by negative fixed charges as the thickness of AlF3 decreased. Based on these results, AlF3 films are proposed for use as an anti-reflection layer to replace HfO2 in CMOS image sensors.

Investigation of Morphology and Chemical Structure of Nanosized Polytetrafluoroethylene Films Deposited on the Surface of Track-Etched Membranes by Plasma Processing

The morphology and chemical structure of nanosized polytetrafluoroethylene films deposited on the surface of track-etched poly(ethylene terephthalate) membranes by means of radiofrequency magnetron sputtering and electron-beam sputtering of the polymer in a vacuum have been studied using atomic force microscopy and X-ray photoelectron spectroscopy. It has been established that the morphology of films formed with the use of these coating techniques varies considerably. This is due to the size of the deposited polymer particles. The particles formed by the electron-beam sputtering of polytetrafluoroethylene are larger than those produced by magnetron sputtering of the polymer. It has been shown that the chemical composition of the films deposited by electron-beam sputtering in a vacuum is more in line with the composition and structure of the initial polymer than the films obtained by radiofrequency magnetron sputtering.

High sensitivity vanadium–vanadium pentoxide–aluminium metal–insulator–metal diode

This work reports on the fabrication of an improved sensitivity metal–insulator–metal (MIM) diode. They devise an asymmetric structure diode that cascades vanadium, vanadium pentoxide, and aluminium (V–V2O5–Al) thin film layers. The MIM diode is fabricated using electron-beam lithography, sputter deposition and metal liftoff techniques. X-ray photoelectron spectroscopy analysis is performed to determine the phase composition of the V2O5 insulating thin film. Electrical characterisation of the fabricated V–V2O5–Al shows a clear high sensitivity at −316 mV that reaches −8.52 V−1 with a dynamic resistance of 5.024 kΩ.

Atomic-Scale Insights into the Oxidation of Aluminum.

The surface oxidation of aluminum is still poorly understood despite its vital role as an insulator in electronics, in aluminum-air batteries, and in protecting the metal against corrosion. Here we use atomic resolution imaging in an environmental transmission electron microscope (TEM) to investigate the mechanism of aluminum oxide formation. Harnessing electron beam sputtering we prepare a pristine, oxide-free metal surface in the TEM. This allows us to study, as a function of crystallographic orientation and oxygen gas pressure, the full oxide growth regime from the first oxide nucleation to a complete saturated, few-nanometers-thick surface film.