Pulsed Electron Beam Deposition Research Articles

Comparative Study on Structural Differences in Monosaccharide Layers Using PLD and PED Techniques.

To demonstrate the feasibility of obtaining low-molecular-weight organic films (below 200 Da) using non-solvent PVD processes, glucose layers were produced via pulsed laser deposition (PLD) and pulsed electron beam deposition (PED) methods. Glucose was chosen due to its fundamental role in various biological processes, and because this low-molecular-weight compound is a solid at room temperature, which is required for both techniques. The physical and chemical structures of the deposited glucose layers were characterized by optical, scanning electron, and atomic force microscopy, as well as by X-ray diffraction, X-ray photoelectron, and infrared spectroscopy. Both PLD and PED methods resulted in glucose layers with good chemical structure preservation (with minor oxidation observed in PED) while yielding films with distinct physical properties. This opens up the possibility of tailoring organic layers with specific characteristics depending on the application, by choosing the deposition method.

Rubber-like PTFE Thin Coatings Deposited by Pulsed Electron Beam Deposition (PED) Method.

PTFE coatings were manufactured using the pulsed electron beam deposition (PED) technique and deposited on Si substrates. The deposition was carried out at constant parameters: temperature 24 °C, discharge voltages 12 kV, and 5000 electron pulses with a pulse frequency of 5 Hz. Nitrogen was used as the background gas. The gas pressure varied from 3 to 11 mTorr. The coating adhesion was evaluated using micro scratch testing and the residual scratch morphology was characterized by atomic force microscopy. Detailed studies of the chemical and physical structure were conducted using infrared spectroscopy and X-ray diffraction. These analyses were then correlated with the mechanical response of the coatings observed during the scratch tests. Drawing upon a review of the literature concerning energetic beam interactions with PTFE material, hypotheses were posed to explain why only specific conditions of the PED process yielded PTFE coatings with rubber-like properties.

Angular distribution of species in pulsed electron beam deposition of BaxSr1-xTiO3

The angular thickness and composition profiles of thin films obtained by irradiating a BaxSr1-xTiO3 (x = 0.2) target with a pulsed electron beam were investigated by Rutherford backscattering spectrometry for argon and oxygen background gases at a pressure of about 10-2 mbar. A “semi-sphere” holder was used, resulting in a fixed target to substrate distance of about 40 mm. The film thickness profiles have forward shaped peaks, with measurable thickness up to 80-90° for major axis and 25° for minor axis, and presents similar trend for both argon and oxygen background gas. The analysis of the congruent transfer of the elements from the target as a function of the angle showed that the film composition is not uniform over this wide angular range and differs with respect of the ablated target depending on the element used and on background gas.

Transparent Structures for ZnO Thin Film Paper Transistors Fabricated by Pulsed Electron Beam Deposition.

Thin film transistors on paper are increasingly in demand for emerging applications, such as flexible displays and sensors for wearable and disposable devices, making paper a promising substrate for green electronics and the circular economy. ZnO self-assembled thin film transistors on a paper substrate, also using paper as a gate dielectric, were fabricated by pulsed electron beam deposition (PED) at room temperature. These self-assembled ZnO thin film transistor source-channel-drain structures were obtained in a single deposition process using 200 and 300 µm metal wires as obstacles in the path of the ablation plasma. These transistors exhibited a memory effect, with two distinct states, "on" and "off", and with a field-effect mobility of about 25 cm2/Vs in both states. For the "on" state, a threshold voltage (Vth on = -1.75 V) and subthreshold swing (S = 1.1 V/decade) were determined, while, in the "off" state, Vth off = +1.8 V and S = 1.34 V/decade were obtained. A 1.6 μA maximum drain current was obtained in the "off" state, and 11.5 μA was obtained in the "on" state of the transistor. Due to ZnO's non-toxicity, such self-assembled transistors are promising as components for flexible, disposable smart labels and other various green paper-based electronics.

From transparent to black amorphous zinc oxide thin films through oxygen deficiency control

Despite the fact that zinc oxide is a well-known transparent oxide, several recent studies on “black” ZnO have renewed its potential for photocatalytic applications. We report on the control of oxygen deficiency in ZnO thin films grown at 300 °C on c-cut sapphire single-crystal substrates by pulsed electron beam deposition (PED) through a slight variation of argon pressure in PED. At a pressure of 2 × 10−2 mbar transparent, stoichiometric (ZnO) and crystalline films are obtained, while at 9 × 10−3 mbar black, oxygen-deficient (ZnO0.85) and amorphous films result. Stoichiometry, structural, and optoelectronic properties of transparent and black ZnO thin films were comparatively analyzed as a function of oxygen deficiency. Black ZnO thin films exhibit enhanced absorption in the visible and near-infrared due to oxygen deficiency, thus extending the range of applications of zinc oxide thin films from transparent electronics to solar absorbers and photocatalysis.

Crystallization of GeTe phase change thin films grown by pulsed electron-beam deposition

In this work, a technique for crystallization of Germanium Telluride (GeTe) thin films was experimentally studied. The GeTe phase change material was grown by a novel high vacuum physical deposition method called pulse electron-beam deposition (PED). To evaluate the quality of the PED growth method, crystallized GeTe thin films were investigated by contemplating the crystallite quality and the electrical conductivity performance. X-ray diffractometer (XRD) spectrum and resistivity were used to evaluate the crystal quality. Alternative material characterization methods, like field emission scanning electron microscope (FESEM) and energy-dispersive X-ray spectroscopy (EDX), were used to explore the crystallization parameters further. Our previous study observed that the as-grown GeTe thin film was amorphous. In order to convert the GeTe thin film into a crystalline formation, post treatment annealing was performed. To optimize the post annealing procedure, several annealing parameters were experimentally investigated. The thin film resistivity dropped by six orders of magnitude upon the crystallization process.

Tailorable properties of Nd-doped ZnO epitaxial thin films for optoelectronic and plasmonic devices

Transparent conductive oxides with both low resistivity and high transparency in the visible and near-infrared wavelengths are required for solar cells and plasmonic applications. In this work we demonstrate that highly conducting and transparent Nd:ZnO thin films have been grown on c-cut sapphire single crystal substrates by pulsed electron beam deposition under argon (10−2 mbar). At 2% at. Nd doping, these films crystallize in the wurtzite structure at T > 300 °C, with well-defined epitaxial relationships with the c-cut sapphire as a function of the substrate temperature. The improvement of the film structural quality with increasing growth temperature led to the lowest resistivity value of 5.12 × 10−4 Ωcm and highest transparency that were maintained more than 36 months under ambient conditions. X-ray photoelectron valence band measurements revealed that the dominant Zn-polar face of Nd:ZnO thin films explains the improved electrical properties. The dielectric functions of films were determined and show that these films are suitable as transparent contact electrodes for solar cell devices or tunable epsilon-near-zero materials for plasmonics.

Nd-doped ZnO films grown on c-cut sapphire by pulsed-electron beam deposition under oblique incidence

Nd-doped ZnO thin films were grown by pulsed-electron beam deposition (PED) on c-cut sapphire substrates under oblique angle incidence, at 10-2 mbar oxygen pressure and for a substrate temperature of 500 °C. The films were smooth, compact and constituted with columnar grains inclined at about 17°±4° from the normal to the substrate surface. From X-ray diffraction and transmission electron microscopy experiments, it was found that the wurtzite phase of Nd-doped ZnO thin films is observed with the c-axis inclined around 35° with respect to the normal axis of the substrate, with a three-fold azimuthal symmetry. Epitaxial relationships between Nd-doped ZnO films and sapphire substrate were determined from the asymmetric X-ray diffraction and are presented compared with those obtained for the films grown by non-oblique PED. The tilt of the ZnO c-axis has been explained by the epitaxy of the (2 2 9) ZnO plane on the (0 0 l) sapphire plane, such particular epitaxial growth having never been reported previously.

Charge Compensation Mechanism of Li2MnO3 Cathode in All-Solid-State Thin Film Battery Investigated By Using Operando HAXPES

Lithium battery has been used as a power source for not only small devices but also large equipment like an electric vehicle because of its potentially high energy density and high rate performance. All-solid-state battery is a promising battery form to achieve high energy density. Since solid-electrolyte has a wider potential window than a liquid one, high voltage cathode material can be implemented. Among novel cathode materials, we focus on a Li-rich manganese oxide Li2MnO3, which has a layered rock-salt structure with a honeycomb-ordered LiMn2 layer. Although having a high theoretical capacity of ~459 mAh g-1, the cathode delivers a smaller reversible capacity than the theoretical value. Recently, we have found that an all-solid-state battery with a Li2MnO3 thin film can deliver a reversibly capacity of 270 mAh g-1, and the rate and cyclic performance are extremely high [1]. However, the redox species of the Li2MnO3 during the electrochemical charge/discharge reactions are still unknown for this battery system. In this study, the charge compensation mechanism of the Li2MnO3 cathode in an all-solid-state thin film battery was investigated by using an operando hard X-ray photoelectron spectroscopy (HAXPES) method. Although X-ray photoelectron spectroscopy is a powerful method to investigate the electronic structure of the cathode, there is an issue that the probing depth is about a few nm when using Al or Mg Ka source. On the other hand, HAXPES has a high probing depth of several 10 nm, which makes it possible to detect a signal from the buried region of the battery. Solid-electrolyte supported thin film batteries were developed for HAXPES measurement as illustrated in Fig (a). Using solid-electrolyte as substrate, cathode, and anode layers can be separated on the front and the back of the substrate, respectively, which enables us to detect the HAXPES signal of the cathode layer. The battery composed of a polycrystalline Li2MnO3 cathode, an amorphous Li3PO4 buffer layer, a lithium anode, an Al current collector, and a LICGC glass-ceramics solid-electrolyte substrate (manufactured by Ohara Inc.) was prepared by using pulsed laser deposition, magnetron sputtering, and thermal or electron-beam vapor deposition methods. Charge-discharge experiments were performed galvanostatically at a 0.2 C rate between 2.0 and 5.0 V (vs. Li/Li+) at room temperature. After the cell voltage reached at 5.0 V, the voltage was kept for 30 minutes.An operando HAXPES measurement was conducted at BL28XU in SPring-8. The incident photon energy of 7940 eV was used. The operando O1s, Mn3s, and Li1s spectra were measured during the 1st and the 5th charge-discharge processes. The charge-discharge curves showed a plateau at 4.6 V in the 1st charge and slope-like curves from the 1st discharge. Since these characteristics are also identified in the case of the battery using the Li2MnO3 epitaxial thin film [1], the prepared battery is suitable to conduct a HAXPES measurement for the purpose. The figures (b, c) show O1s operando spectra during the 1st charge-discharge process. During the 1st charge, a new peak at 531.1 eV is generated from 3.7 V in addition to a lattice oxygen O2- at 529.8 eV. According to previous reports, the new peak can be assigned as higher oxidized lattice oxygen such as O- [2]. After 3.7 V, the area of the new peak increases while that of O2- decreases as the voltage increases. During the 1st discharge, the new peak gradually decreases and then disappears at 3.3 V. Therefore, the reversible oxygen redox could contribute the charge compensation for the battery reactions. The average valence state of Mn was analyzed from Mn3s operando spectra. Manganese is reduced from 4+ to 3.5+ during the 1st charge process then Mn is further reduced to 3.1+ from 3.3 V during 1st discharging process. Upon the 5th charge-discharge process, the Mn redox occurred reversibly below 3.5 V. These results indicate that the oxygen as well as Mn redox reactions occur reversibly in Li2MnO3 cathode. Furthermore, the oxygen redox occurs on the higher voltage region between ~3.3 and 5.0 V and the Mn redox occurs on the lower region between 2.0 and ~3.3 V. Therefore, it is evident that the large reversible capacity of Li2MnO3 thin film results from the oxygen redox activity. Realizing the stable oxygen redox reaction on batteries with a larger scale will be a key for practical application.[1] K. Hikima et al., Chem. Lett. 48, 192 (2019).[2] M. Sathiya et al., Nature Materials 12, 827 (2013). Figure 1

Synergistic Effect of Singly Charged Oxygen Vacancies and Ligand Field for Regulating Transport Properties of Resistive Switching Memories

The controlled incorporation of defect species in amorphous oxide (AO) for regulating charge transport properties is highly demanding and challenging, especially for resistive switching (RS) memories. Here, we use pulsed electron beam deposition technique to engineer the growth of AO films, which show a large decrease (∼33%) in the t2g–eg gap. Our collective experiments and density functional theory (DFT) based ab initio simulations reveal the presence of undercoordinated TiO5 units, causing a decrease in the t2g–eg gap. Further, the importance of TiO5 in facilitating excess electron localization is demonstrated, showing an evolution of a broad defect band within the energy gap. The origin of this band (singly charged oxygen vacancy) is resolutely established by X-ray photoelectron spectroscopy and electron paramagnetic resonance measurements and is also supported by calculated partial charge density and Bader charge analysis. The preeminence of singly charged oxygen vacancies cause a low-current level (u...

Chemical Structure of EVA Films Obtained by Pulsed Electron Beam and Pulse Laser Ablation.

Poly(ethylene-co-vinyl acetate) (EVA) films were deposited for the first time using physical methods. The chemical structure of the films obtained using two techniques, pulsed electron beam deposition (PED) and pulsed laser deposition (PLD), was studied by attenuated total reflection Fourier infrared spectroscopy (ATR-FTIR) and X-ray photoelectron spectroscopy (XPS). Whilst significant molecular degradation of the EVA films was observed for the PLD method, the original macromolecular structure was only partially degraded when the PED technique was used, emphasizing the superiority of the PED method over PLD for structurally complex polymers such as EVA. Optical and scanning electron microscopic observations revealed compact and smooth EVA films deposited by pulsed electron beam ablation as opposed to heterogeneous films with many different sized particulates obtained by PLD.

Ultraviolet photodetector based on a ZnS–ZnO structure with a surface acoustic wave

The structural properties of a thin ZnO film synthesized by a reactive ion-plasma method have been studied. It is shown that a combination of reactive ion-plasma sputtering and pulsed electron beam deposition methods allows the formation of a thin-film ZnS–ZnO heterostructure with few structural defects. The results of a study of the optical and photoelectric properties of ZnS–ZnO in the wavelength range from 0.26 to 0.45 μm are presented. The spectral dependence of the frequency shift of surface acoustic waves under the influence of ultraviolet radiation on the surface of the ZnS–ZnO heterostructure of a photodetector, based on an acoustoelectronic amplifier, has been studied.

Growth study of GeTe phase change material using pulsed electron-beam deposition

Thin film growth of chalcogenides composition is an exciting field, owing to the interesting optical and electrical properties of them. In this work, a novel, physical vapor deposition (PVD) method called pulse electron-beam deposition (PED) experimentally studied to investigate the requirements for ablation of phase change materials (PCM). To evaluate the qualifications of the PED method, thin films of Germanium Telluride (GeTe) are grown and investigated by contemplating the surface morphology and the material composition. High-quality GeTe thin films with thicknesses from 30 to 200 nm, were successfully grown on top of silicon wafers at room temperature to demonstrate the ability of PED. To optimize the growth procedure, several growth parameters were thoroughly investigated, including background pressure, pulse energy, and growth temperature. A series of material characterization methods were adopted to study the GeTe material quality after the growth. These methods include field emission scanning electron microscope (FESEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), and thickness profilometer. It was found that higher material growth rate can be obtained in lower background pressure (∼ 2.6 mTorr), lower temperature (room temperature) but higher pulse energy (e.g., 15 kV). Besides, by increasing the target-to-substrate distance, the surface quality (e.g., smoothness) was improved substantially, but the growth rate decreased linearly. Finally, after the growth optimization, FESEM images revealed that the as-grown GeTe films were of high smoothness and uniformity. EDX analysis indicated that the compositions of the GeTe films were pressure dependent. Through the XRD spectrum, it is found that the as-grown GeTe films were amorphous. In order to convert them into crystalline formation, further post-treatment approaches (e.g., annealing) will be required.

Degenerate and non-degenerate In2O3 thin films by pulsed electron beam deposition

Pulsed electron beam deposition (PED) was used to grow indium oxide thin films on c-cut sapphire single crystalline substrates between room temperature and 500 °C under oxygen gas. A slight difference in oxygen pressure during the PED growth (from 2 × 10−2 to 1.3 × 10−2 mbar) has strong effects on the electrical and optical film properties. The indium oxide thin films grown in these conditions changed from a non-degenerate semiconducting behaviour (at 2 × 10−2 mbar) to a degenerate semiconductor one (at 1.3 × 10−2 mbar), with a metal-insulator transition at 149 K. This crossover from strong to weak localization, evidenced in the temperature dependent resistivity curves, may be due to the effects of a structural disorder in such films. The direct optical band gap was estimated from transmission spectra taking into account non-degenerate/degenerate behaviour.

Poly(propylene)/carbon composite thin films obtained by pulsed electron‐beam deposition

For the first time pulsed electron beam deposition (PED) was used to deposit thin films composed of polymer‐carbon composite material. The targets were polypropylene‐carbon (PP/C) composites, with different carbon fillers: carbon black, nanotubes, or graphene. It was confirmed that coatings with composite structure were obtained – the PED method enables complex structures, including nanotubes, to be ablated whole from the target, transported toward substrate, and incorporated into the polymer matrix. These breakthrough results can contribute significantly to improved understanding of the mechanism of electron beam ablation of polymer and composite materials, and open up new possibilities for the deposition of complex composite thin films for use in, for example, advanced sensor applications.

Transport phenomena in SrVO3/SrTiO3 superlattices

Epitaxial [(SrVO3)7/(SrTiO3)4]r (SVO/STO) superlattices were grown on (0 0 1)-oriented LSAT substrates using a pulsed electron-beam deposition technique. The transport properties of the superlattices were investigated by varying the number of repetitions of the SVO/STO bilayers r (1 ⩽ r ⩽ 9). A single SVO/STO bilayer (r = 1) was semiconducting, whereas an increase in the number of repetitions r resulted in metallic behavior in the superlattices with r ⩾ 3. The transport phenomena in the SVO/STO superlattices can be regarded as conduction through parallel-coupled SVO layers, the SVO layer embedded in the superlattices showed a great enhancement in the conductivity compared with the single SVO layer. This work provides further evidence of electronic phase separation in the SVO ultrathin layer that has been recently discovered, the SVO ultrathin layer is considered as a 2D Mott insulator with metallic and insulating phases coexisting, the coupling between SVO layers embedded in the SVO/STO superlattices creates more conduction pathways with increasing number of repetitions r, resulting in a crossover from insulating to metallic behavior.

Polytetrafluoroethylene thin films obtained by the pulsed electron beam deposition method at different gas pressures

Polytetrafluoroethylene thin films obtained by the pulsed electron beam deposition method at different gas pressures

Deposition Of Oxide And Intermetallic Thin Films By Pulsed Laser (PLD) And Electron Beam (PED) Methods

Abstract In this work the pulsed laser deposition (PLD) and the pulsed electron beam deposition (PED) techniques were used for fabrication of Mo-Bi2O3, La1−xSrxCoO3, La1−xCaxCoO3 and Al-Mg thin films. An influence of ablation process basic parameters on the coatings structure and properties was discussed. Two types of laser ablation systems were applied: one equipped with a KrF excimer and second with a Q-switched Nd:YAG. Films were deposited on Si and MgO substrates. Scanning (SEM) and transmission (TEM) electron microscopy, atomic force microscopy (AFM) as well as X-ray diffraction (XRD) were used for structural analysis. Investigations focused on structure and chemical composition showed that smooth and dense thin films with nanocrystalline structure, preserving the composition of the bulk target, could be obtained by the both PLD and PED techniques. Research study showed that by a proper selection of PLD and PED process parameters it was possible to deposit films with significantly decreased amount and size of undesirably nanoparticulates.

GaN growth on silicon based substrates using pulsed electron beam deposition (PED) process

ABSTRACTGrowth of GaN on Si(111) and Ge coated Si(111) using pulsed electron beam deposition (PED) process is reported. GaN was deposited on Si(111) and Ge/Si(111) at 600°C in an N2 environment without any surface pre-treatment such as pre-nitridation. X-ray diffraction confirmed that c-plane oriented GaN was grown. Photoluminescence showed near-band-edge emission, the intensity of which was improved with hydrogen passivation. Electrical characterization showed n-type conductivity with room temperature electron mobilities in the range of 300 cm2/V-sec.

Defect characterization and magnetic properties in un-doped ZnO thin film annealed in a strong magnetic field

Highly c-axis oriented un-doped zinc oxide (ZnO) thin films, each with a thickness of ∼ 100 nm, are deposited on Si (001) substrates by pulsed electron beam deposition at a temperature of ∼ 320 °C, followed by annealing at 650 °C in argon in a strong magnetic field. X-ray photoelectron spectroscopy (XPS), positron annihilation analysis (PAS), and electron paramagnetic resonance (EPR) characterizations suggest that the major defects generated in these ZnO films are oxygen vacancies. Photoluminescence (PL) and magnetic property measurements indicate that the room-temperature ferromagnetism in the un-doped ZnO film originates from the singly ionized oxygen vacancies whose number depends on the strength of the magnetic field applied in the thermal annealing process. The effects of the magnetic field on the defect generation in the ZnO films are also discussed.