Pulsed Direct Current Sputtering Research Articles

Nanoimprint Lithography for Next-Generation Carbon Nanotube-Based Devices.

This research reports the development of 3D carbon nanostructures that can provide unique capabilities for manufacturing carbon nanotube (CNT) electronic components, electrochemical probes, biosensors, and tissue scaffolds. The shaped CNT arrays were grown on patterned catalytic substrate by chemical vapor deposition (CVD) method. The new fabrication process for catalyst patterning based on combination of nanoimprint lithography (NIL), magnetron sputtering, and reactive etching techniques was studied. The optimal process parameters for each technique were evaluated. The catalyst was made by deposition of Fe and Co nanoparticles over an alumina support layer on a Si/SiO2 substrate. The metal particles were deposited using direct current (DC) magnetron sputtering technique, with a particle ranging from 6 nm to 12 nm and density from 70 to 1000 particles/micron. The Alumina layer was deposited by radio frequency (RF) and reactive pulsed DC sputtering, and the effect of sputtering parameters on surface roughness was studied. The pattern was developed by thermal NIL using Si master-molds with PMMA and NRX1025 polymers as thermal resists. Catalyst patterns of lines, dots, and holes ranging from 70 nm to 500 nm were produced and characterized by scanning electron microscopy (SEM) and atomic force microscopy (AFM). Vertically aligned CNTs were successfully grown on patterned catalyst and their quality was evaluated by SEM and micro-Raman. The results confirm that the new fabrication process has the ability to control the size and shape of CNT arrays with superior quality.

Mechanical properties of VC/ZrC and VC/HfC superlattices

Face-centered cubic transition metal carbides exhibit high melting points and hardness, making them prominent candidates for protective coating applications. Vanadium carbide (VC) has typical characteristics of transition metal carbides. It serves as model material in this study, in which we showcase the effect of superlattice architecture on mechanical properties and fracture toughness. While beneficial effects of superlattice arrangement have been demonstrated for a series of nitride-based coatings, transition metal carbides remain largely unexplored territory. Following density functional theory based ab initio predictions on lattice and shear modulus mismatch, we develop VC/ZrC and VC/HfC superlattice coatings synthesized via pulsed DC sputter deposition. The bilayer periods (Λ) of our fully fcc-structured polycrystalline coatings range between 2–50 nm (indicated by X-ray diffraction, transmission and scanning electron microscopy). The chemical composition is close to 1:1 stoichiometry (from X-ray fluorescence, elastic back-scattering spectrometry and elastic recoil detection analysis). Both superlattice series exhibit a strong dependence of hardness, elastic modulus, and fracture toughness on their bilayer periods, which can only be correlated with the in-plane stress variations for VC/ZrC. The VC/HfC superlattices provide their peak-hardness of 36.0 ± 1.6 GPa for Λ = 6 nm and their peak in fracture toughness of 3.5 ± 0.5 MPa√m for Λ = 10 nm.

Cu-doped lithium oxide films with high mobility and bandgap prepared by pulsed direct-current sputtering

In this study, Cu-doped lithium carbonate (Cu:Li2O2) films are prepared by pulsed direct-current (DC) magnetron sputter using a lithium carbonate and copper oxide mixed target. The oxygen flow rate is varied during the sputtering process to systematically investigate its effect on structural, electrical and optical properties of the films. The experimental results show that all the Cu:Li2O2 films are mainly amorphous as confirmed by X-ray diffraction. Cu incorporation is able to reduce the aggregated clusters of the lithium oxides. At the oxygen flow rate of 20 sccm the film with a Cu content of ∼0.7 at.% has a low p-type resistivity of 0.82 Ω-cm, hole concentration of 1.1 × 1017 cm−3 and the highest mobility of 73 cm2V−1s−1, which is at least twice higher than those of other p-type metal oxides prepared at similarly low temperatures. The film also has a high optical band gap of 2.87 eV. Moreover, the Cu:Li2O2/ZnO heterojunction demonstrating a clear diode rectification supports the p-type nature of Cu:Li2O2 films. The pulsed DC Cu:Li2O2 films with these remarkable optoelectronic properties demonstrate great potential to be adopted as transparent oxide semiconductors in high-performance optoelectronics.

Obtaining nanoparticles of Cu2O by means of a pulsed discharge of CH3CH2OH-N2

CH3CH2OH-N2 plasma mixture was used to synthesize cuprous oxide (Cu2O) micro-particles in a pulsed DC sputtering system, using a ethanol pressure of 1.5 Torr and a current of 400 mA at a frequency of 30 kHz. The plasma mixture was used successfully to obtain the micro-particles of Cu2O using a copper (Cu) target and a stainless steel substrate. The Cu2O products are characterized by the scanning electron microscope (SEM), the results show that the morphology of the Cu2O microparticles have a spherical shape which are randomly distributed on the stainless steel substrate. Raman results show that from the CH3CH2OH-N2 plasma mixture it is possible to obtain one of the Cu oxidation phases which corresponds to Cu2O due to the fact that within the sample analyzed by means of Raman it is possible to observe only the peaks that correspond to the Cu2O phase. The analysis by energy dispersive spectroscopy (EDS) serves to determine the stoichiometric balance present in the substrate, from which the presence of the characteristic peaks of stainless steel was confirmed, along with the characteristic peaks of Cu and O which exhibit an atomic ratio of 2:1 respectively. Atomic force microscopy (AFM) was used to again determine the morphology of the microparticles, finding a spherical morphology. In addition, the value of roughness and grain size was determined, finding values of 20 nm and 45 nm respectively. The images 3-D show the presence of peaks and valleys within the substrate and an non-homogeneous distribution of spherical micro-particles on the surface of the stainless steel.

Optical properties of plasmonic titanium nitride thin films from ultraviolet to mid-infrared wavelengths deposited by pulsed-DC sputtering, thermal and plasma-enhanced atomic layer deposition

We present a comparative study of the optical properties of 50 nm-thick titanium nitride (TiN) films deposited on a silicon substrate by pulsed-DC sputtering, thermal, and plasma-enhanced atomic layer deposition. Silicon was chosen as the optimal material for the complementary metal–oxide–semiconductor (CMOS) integration. Using ellipsometry and Fourier-transform infrared (FTIR) spectroscopy, broadband permittivity of the films was obtained from a series of free-space reflection measurements in the wavelength range of 210 nm to 20.0μm (∼47619–500 cm−1). Our particular focus is on the influence of the deposition method and its process temperature on the TiN plasmonic properties. We used grazing incidence X-ray diffraction, X-ray photoelectron spectroscopy, X-ray reflectometry, atomic force microscopy, and electrical resistivity measurements to analyze the composition of thin films and to elucidate the effect of different deposition parameters on their optical properties. All measurements were carried out at room temperature and the thickness of all film samples was fixed to 50 nm to exclude the influence of these factors on the optical properties. We demonstrate that PEALD-deposited films have smoother surfaces than those deposited by the sputtering technique, while sputtered films have higher densities. In addition, by changing the temperature of both processes, it is possible to influence the stoichiometry and crystal orientation of the layers. Based on this characterization, we found out that TiN thin film deposited by pulsed-DC at 600 °C gives the best plasmonic response (high negative permittivity ϵ1 and relatively low losses associated with ϵ2, where ϵ1 and ϵ2 are the real and imaginary parts of permittivity, respectively) among all samples for the entire wavelength range under study. The same film also exhibits the excellent resistivity of 29 μΩcm. These results suggest that there is a direct relationship between stoichiometry, structural quality, and oxygen incorporation in TiN films and their plasmonic response.

Antibacterial Effects of a Carbon Nitride (CN) Layer Formed on Non-Woven Polypropylene Fabrics Using the Modified DC-Pulsed Sputtering Method.

In the present study, the surface of non-woven polypropylene (NW-PP) fabric was modified to form CN layers using a modified DC-pulsed (frequency: 60 kHz, pulse shape: square) sputtering with a roll-to-roll system. After plasma modification, structural damage in the NW-PP fabric was not observed, and the C-C/C-H bonds on the surface of the NW-PP fabric converted into C-C/C-H, C-N(CN), and C=O bonds. The CN-formed NW-PP fabrics showed strong hydrophobicity for H2O (polar liquid) and full-wetting characteristics for CH2I2 (non-polar liquid). In addition, the CN-formed NW-PP exhibited an enhanced antibacterial characteristic compared to NW-PP fabric. The reduction rate of the CN-formed NW-PP fabric was 89.0% and 91.6% for Staphylococcus aureus (ATCC 6538, Gram-positive) and Klebsiella pneumoniae (ATCC4352, Gram-negative), respectively. It was confirmed that the CN layer showed antibacterial characteristics against both Gram-positive and Gram-negative bacteria. The reason for the antibacterial effect of CN-formed NW-PP fabrics can be explained as the strong hydrophobicity due to the CH3 bond of the fabric, enhanced wetting property due to CN bonds, and antibacterial activity due to C=O bonds. Our study presents a one-step, damage-free, mass-productive, and eco-friendly method that can be applied to most weak substrates, allowing the mass production of antibacterial fabrics.

A multi-step deposited AlN films in a DC pulsed sputtering and film characteristics classification with principal component analysis of OES data

A multi-step deposited AlN films in a DC pulsed sputtering and film characteristics classification with principal component analysis of OES data

Fabrication of Mg/Al2O3 Nanolaminates using DC/PDC Magnetron Sputtering to Evaluate the Effect of Oxygen Content and Total Pressure for Deposition of Thin-Films

Thin films have always shown high sensitivity to its deposition parameters and surface morphology. Magnetron sputtering is known for its high level of consistency in deposition and repeatability. In this study Mg/Al2O3 nanolaminates in a range of 10 to 40 nm were synthesized using Direct current and Pulsed DC sputtering techniques at room temperature on glass substrates and silicon substrate using different oxygen flow rates and varying total pressure conditions to understand its effect on deposition rates and roughness of thin films. It is observed that more power and resources consumed for higher deposition time. Roughness of the film is very sensitive for certain applications like corrosion, Lenses, Implants. Scanning electron microscopy (SEM), Atomic force microscopy (AFM) were used to characterize the morphology, structure of the thin films. Optical microscopy and X-ray reflectometry (XRD-XRR) techniques confirmed the optical density and thickness of the nanolaminates respectively. It is confirmed that as total pressure and oxygen flow rate rises deposition rate significantly goes down, that impacts deposition time and roughness of thin films.

Broadband infrared absorber based on a sputter deposited hydrogenated carbon multilayer enhancing MEMS-based CMOS thermopile performance.

Based on pulsed DC sputter deposition of hydrogenated carbon, an absorber optical coating with maximized broadband infrared absorptance is reported. Enhanced broadband (2.5-20µm) infrared absorptance (>90%) with reduced infrared reflection is achieved by combining a low-absorptance antireflective (hydrogenated carbon) overcoat with a broadband-absorptance carbon underlayer (nonhydrogenated). The infrared optical absorptance of sputter deposited carbon with incorporated hydrogen is reduced. As such, hydrogen flow optimization to minimize reflection loss, maximize broadband absorptance, and achieve stress balance is described. Application to complementary metal-oxide-semiconductor (CMOS) produced microelectromechanical systems (MEMS) thermopile device wafers is described. A 220% increase in thermopile output voltage is demonstrated, in agreement with modeled prediction.

Modification of electrical properties of amorphous vanadium oxide (a-VOx) thin film thermistor for microbolometer

This work reports on the modification of electrical properties of amorphous vanadium oxide (a-VOx) thin film thermistor by growth temperature and its effects on the performances of a cooler-free microbolometer. The a-VOx thin films have been deposited by pulsed DC sputtering processes under various growth temperatures from 160 to 230 ℃. The sheet resistance of the samples at room temperature decreases from 330 to 70 kΩ/▢ with increasing growth temperature. This is due to the increase of oxygen vacancies at higher growth temperature, which have been confirmed by XPS analysis. Temperature dependence of resistance of a-VOx films shows non-hysteresis behaviors up to 120 ℃, which in turn shows clear activation energies. The activation energy of a-VOx films also decreases from 0.190 to 0.145 eV with increasing growth temperature, which confirms the decrease of temperature coefficient of resistance (TCR) from 2.80 to 2.44 (-%/K) at 25 ℃ and from 1.48 to 1.14 (-%/K) even at 120 ℃. The responsivities of fabricated microbolometers based on the a-VOx thin film thermistors have been measured from 3.04 × 103 to 1.14 × 103 V/W at room temperature and from 9.54 × 102 to 3.02 × 102 V/W even at 120 ℃ with increasing growth temperature.

Realization of ZnO microrods and Ag nanoparticles on glass and Si substrates by magnetron sputtering and near band edge photoluminescence enhancement from the exciton-plasmon system

• A dry method of fabrication of Ag nanoparticles and ZnO microrods heterostructure. • Preferential nucleation of Ag nanoparticles in proximities of ZnO microrods. • Seed assisted growth of ZnO microrods at higher gas pressure and shorter duration. • Near-UV (380 nm) emission enhancement possibly due to exciton-plasmon interaction. • Nearly 3-fold enhancement of near band edge photoluminescence from ZnO microrods. This work presents a physical vapour-based fabrication of an exciton-plasmon system via depositions of ZnO microrods (ZnOµRs) and Ag nanoparticles (AgNPs) on glass and p-type Si substrates. Pulsed DC sputtering of ZnO at a relatively higher Ar pressure and varying applied power enables deposition of ZnOµRs on ZnO seed layers. Sputtering of Ag ensures fabrication of AgNP/ZnOμR heterostructure with good adhesion suitable for device realization. Microstructural analyses confirm formations of wurtzite ZnOμRs and f.c.c. AgNPs. AgNPs are observed as isolated clusters due to preferential nucleation in the proximities of ZnOµRs. UV-Vis absorption spectroscopy reveals broad surface plasmon resonance (SPR) of Ag NPs around 538 nm, which experiences a bathochromic shift in AgNP/ZnOμR heterostructure. The photoluminescence (PL) spectra of AgNP/ZnOμR heterostructure suggest a 3-fold enhancement of narrow near band edge (NBE) emission attributed to the exciton-plasmon interaction.

Influence of Pulsed DC Sputtering Power on the Quality and Residual Stress of AlN Films on Si (100) Substrates

AbstractAluminum nitride (AlN) films are prepared on Si (100) substrates by pulsed direct current magnetron sputtering. The effect of sputtering power on the crystal quality, residual stress, surface morphology, and optical properties of AlN films is comprehensively studied using X‐ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), atomic force microscope, and ellipsometer. It is found that the AlN film quality is strongly impacted by the sputtering power. When the sputtering power increases to 3 kW, the full width at half maximum of the AlN (002) rocking curve decreases to 2.66°. And the film crystal quality does not change significantly when the sputtering power exceeds 3 kW. Fourier transform infrared spectrum analysis shows that with increasing sputtering power, the compressive stress of AlN films first increases and then decreases. The high sputtering power also results in smoother surface and better optical performance for the AlN films. This work can serve as an important reference for growing high‐quality AlN films on cost‐effective silicon (Si) substrates via sputtering, which can facilitate the development and commercialization of III‐nitride based photonics and electronics on AlN‐on‐Si substrates.

Synthesis and Characterization of CN Thin Films Produced by DC-Pulsed Sputtering in an CH3CH2OH-N2 Atmosphere

Synthesis and Characterization of CN Thin Films Produced by DC-Pulsed Sputtering in an CH3CH2OH-N2 Atmosphere

Wafer-sized WS2 monolayer deposition by sputtering.

We demonstrate that tungsten disulphide (WS2) with thicknesses ranging from monolayer (ML) to several monolayers can be grown on SiO2/Si, Si, and Al2O3 by pulsed direct current-sputtering. The presence of high quality monolayer and multilayered WS2 on the substrates is confirmed by Raman spectroscopy since the peak separations between the A1g-E2g and A1g-2LA vibration modes exhibit a gradual increase depending on the number of layers. X-ray diffraction confirms a textured (001) growth of WS2 films. The surface roughness measured with atomic force microscopy is between 1.5 and 3 Å for the ML films. The chemical composition WSx (x = 2.03 ± 0.05) was determined from X-ray Photoelectron Spectroscopy. Transmission electron microscopy was performed on a multilayer film to show the 2D layered structure. A unique method for growing 2D layers directly by sputtering opens up the way for designing 2D materials and batch production of high-uniformity and high-quality (stochiometric, large grain sizes, flatness) WS2 films, which will advance their practical applications in various fields.

Si–Sn Codoped N-Gan Film Grown on an Amorphous Glass Substrate with Dc-Pulse Sputtering

Si–Sn Codoped N-Gan Film Grown on an Amorphous Glass Substrate with Dc-Pulse Sputtering

Highly precise multi-cathode pulsed-DC sputtering employing digital processing–application to layer–by–layer synthesis of cubic (Er0.1Y0.9)2Zr2O7 thin film

A digitally processed DC reactive sputtering (DPDRS) system employing field-programmable gate-array has been developed. In this report, atomically precise pulsed-DC sputtering of a metal oxide compound, cubic (Er0.1Y0.9)2Zr2O7 (c-EYZO), is demonstrated by using DPDRS. An alternating process of pulsed metal sputtering and reactive gas pulsing was applied in order to realize layer-by-layer reactive sputtering. The pulsed metal sputtering separated from the oxidation process results in a stable and high deposition rate of c-EYZO at 1.9 μm h−1, which corresponds to 1.56 nm/cycle. By adjusting the deposition rate to the d-spacing of 0.26 nm corresponding to the (200) diffraction, layer-by-layer synthesis of a highly oriented c-EYZO thin film showing the d-spacing was achieved. X-ray diffraction and photoluminescence measurements indicate drastic improvement of the crystalline properties and the emission properties due to the layer-by-layer synthesis. It is expected that DPDRS enables arbitrarily designed atomically precise deposition of the metal oxide compound synthesis.

Development of digitally processed DC reactive sputtering and its application to the synthesis of (Er0.1Y0.9)2SiO5 layered crystalline thin film

We have developed a digitally processed DC reactive sputtering (DPDRS) system that enables synthesis of arbitrarily designed atomically precise deposition of metal oxide compounds. Pulsed-DC sputtering employing a digital pulse pattern generator can perform the temporally alternating process of multiple metal sputtering and oxidation. High-speed switching of the pulsed-DC sputtering process driven by the digital signal processing was confirmed from time-resolved plasma emission spectroscopy. Metal sputtering, which was temporally separated from the oxidation process, resulted in a deposition rate higher than 1 μm/h. It was also found that the temporally separated radical oxidation at the deposited metal surface could control the oxidation process. The DPDRS was applied to layer-by-layer synthesis of (Er0.1Y0.9)2SiO5 (EYSO) films oriented to the ⟨100⟩ direction. The deposition rate for each metal target (Er and Y) was adjusted to 0.86 nm/cycle corresponding to a d-spacing of the (100) plane by changing independently the duty ratio of the base pulse for plasma generation. X-ray diffraction measurements indicated a formation of ⟨100⟩ highly oriented (Er0.1Y0.9)2SiO5 crystalline thin films. Photoluminescence spectra and the decay characteristics also showed synthesis of high crystalline quality EYSO films better than those obtained by pulsed laser deposition.

A Study on Formation of Aluminum-Doped Zinc Oxide Films by Pulsed-Direct Current Sputtering for CIGS Solar Cells.

Considering the relationship between thin film thickness of transparent conductive oxide (TCO) materials and the reversed pulse time in pulsed-direct current (DC) sputtering, aluminum-doped zinc oxide (AZO) films were deposited on glass substrates at different reversed pulse times by changing oxygen/argon (O₂/Ar) gas ratios for window layers of large area CuIn1-xGaxSe₂ (CIGS) solar cells. As a result of the reduced sputtering time, the thickness of AZO film was decreased when the reversed pulsed time was increased. The higher resistance and resistivity of the AZO film was obtained at a higher reversed pulse time. From the structural investigations of AZO such as transmittance and X-ray diffraction (XRD), it was possible to observe the relationship between the crystallinity of AZO and transmittance. Even at the short reversed pulse time of 0.5 µs, it can be concluded that the accumulated charges on the AZO target are completely cleared and the AZO layers show the highest figure of merit (FOM) with low sheet resistance and high transmittance.

Transfer matrix based reverse engineering approach to analyse annealing induced changes in optical transmission of TiO2/Ag/TiO2/Ag multilayer

Measured optical transmission spectrum of photonic structure comprising TiO2/Ag/TiO2/Ag multilayer is reverse engineered by employing transfer matrix method with three different multilayer models to analyse the factors responsible for the annealing induced changes in the transmission. The multilayer is made to have a single peak or a passband in the visible region, so that the spectral changes due to annealing can be observed more vividly. Prior to the multilayer deposition, single layer thin film of Ag and TiO2 are prepared using asymmetric bipolar pulsed dc sputtering and their optical constants such as refractive index and extinction co-efficient are determined. The multilayer is prepared by four-layer sequential deposition of Ag and TiO2 on BK7 glass substrate. The deposited TiO2/Ag/TiO2/Ag multilayer is annealed in the temperature range 100–300 °C. The optical transmission of the annealed multilayers is measured using spectrophotometer. The measured peak transmission and spectral bandwidth of the multilayer filter decreases with annealing, which is ascribed to inter-diffusion at the interfaces, and increasing absorption at the interfaces and in the silver layers of the multilayer. The ascription is resolved from the layers properties and interface parameters obtained by reverse engineering the measured transmission spectra. The rough interfaces in the multilayer are modeled as thin homogeneous layers following Bruggeman effective medium approximation, and the interface parameters are found to be varying with annealing.

Magnetic properties of (Bi1\u2212xLax)(Fe,Co)O3 films fabricated by a pulsed DC reactive sputtering and demonstration of magnetization reversal by electric field

(Bi1−xLax)(Fe,Co)O3 multiferroic magnetic film were fabricated using pulsed DC (direct current) sputtering technique and demonstrated magnetization reversal by applied electric field. The fabricated (Bi0.41La0.59)(Fe0.75Co0.25)O3 films exhibited hysteresis curves of both ferromagnetic and ferroelectric behavior. The saturated magnetization (Ms) of the multiferroic film was about 70 emu/cm3. The squareness (S) (= remanent magnetization (Mr)/Ms) and coercivity (Hc) of perpendicular to film plane are 0.64 and 4.2 kOe which are larger compared with films in parallel to film plane of 0.5 and 2.5 kOe. The electric and magnetic domain structures of the (Bi0.41La0.59)(Fe0.75Co0.25)O3 film analyzed by electric force microscopy (EFM) and magnetic force microscopy (MFM) were clearly induced with submicron scale by applying a local electric field. This magnetization reversal indicates the future realization of high performance magnetic device with low power consumption.