Thickness Of Cu Layer Research Articles

Tribological behaviour of a-C:H films with Cu cover layers: Formation and influence of tribo-induced Cu/Cu2O nanograins

This study focuses on the tribological behaviour of Cu-layer covered a-C:H films and the transfer film formation mechanisms, by means of tribological test, surface profiling, Raman spectroscopy and in-depth transmission electron microscopy, etc. Results showed that introducing a Cu cover layer with proper thickness would significantly enhance the tribological performance of a-C:H films at low sliding speed. The CoF of a-C:H was reduced to 0.004 (superlubricating) at the optimal Cu-layer thickness of ∼32 nm. The transferred material on counterpart was composed of a dense Cu layer and an a-C/(nc-Cu/Cu2O) composite layer, which promoted the formation of a similar layer on a-C:H wear track. The strength and durability of a-C/(nc-Cu/Cu2O) composite layer was double-reinforced by “physical pinning” and Cu-O-C “chemical bonding”.

Investigation of the effects of Cu layer thickness and annealing temperature under air atmosphere on the properties of Co/Cu multilayer films

In this study, the suitability of Co/Cu multilayer films with different physical conditions (varying thickness values and systematic annealing processes) in magnetic technology applications is discussed. Co/Cu films were deposited by the sputtering technique. The effects of different thicknesses of non-magnetic (Cu) layers and annealing temperature on magneto-structural properties were investigated. Different thicknesses of Cu layers were determined as 34 nm, 10 nm, 4 nm. Additionally, two annealed situations were considered to investigate the annealing effect. While the first one is exposing the films to 80 °C and 130 °C for 240 s, second one is annealing the films at 180 °C for different exposure times (50 s and 150 s). All films that have different thicknesses of Cu layers crystallized in (111) plane of the face centered cubic (fcc) structure. The intensity of this peak increased with increasing Cu layers thickness. Variation in the thickness of Cu layers has an important effect on the film surface. Saturation magnetization (Ms), coercivity (Hc) and squareness (Mr/Ms, Mr: remanent magnetization) were considerably affected by variation of the Cu content and film surface caused by the change in the thickness of the Cu layers. The film with 4 nm Cu layer thickness has the highest Ms, lowest Hc values and high Mr/Ms ratio. This indicates magnetically high efficient compared to the other films in the same series. The fcc structure continued to exist for the films annealed at 80 °C and 130 °C for 240 s. It was found that the annealing procedure transfigured the film surface and the differences in Ms and Hc values can be mostly attributed to this transfiguration because of the same film content revealed. An increase in Ms value, and a slight decrease in Hc and Mr/Ms values were detected for the annealed film at 130 °C, compared to the film annealed at 80 °C. It was also seen that the film structure was damaged at 180 °C because of excessive heat transfer.

Current-perpendicular-to-plane giant magnetoresistance in Co/Cu multilayered nanocylinders electrodeposited into anodized aluminum oxide nanochannels with ultra-large aspect ratio

An anodized aluminum oxide (AAO) thick film with numerous nanochannels was synthesized by a cathodic exfoliation technique from a metallic aluminum rod. The nanochannel diameter D and length L were about 60 nm and 60 µm, respectively. The aspect ratio L/D reached ~ 1000. A rectangular pulsed potential deposition technique was applied to electrochemically grow the multilayered nanocylinders with alternating Cu and Co thin layers in the AAO nanochannels. The Co/Cu bilayer thickness was decreased to around 7 nm at the minimum by controlling the pulsed potential and duty cycle during the electrodeposition process. An electrochemical in situ single contact process was demonstrated by monitoring the observed current until a Co/Cu multilayered nanocylinder reached the nanoporous Au film on the AAO thick film. The resistance of the Co/Cu multilayered nanocylinder was determined to range from 1 to 2 kΩ, which corresponded well with a theoretical estimation. Current-perpendicular-to-plane giant magnetoresistance (CPP-GMR) of a Co/Cu multilayered nanocylinder with ~ 6000 bilayers (Cu = 2.4 nm, Co = 7.1 nm) reached up to 31.5% at room temperature. Valet–Fert model agreed well with the present study concerning the effect of Cu-layer thickness on CPP-GMR.

Microstructure and mechanical properties of Ni/Ti/Al/Cu composite produced by accumulative roll bonding (ARB) at room temperature

In this work, the Ni/Ti/Al/Cu composite was produced by accumulative roll bonding (ARB) technology at room temperature. The microstructure evolution and mechanical properties of the composite in the ARB process were investigated by scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), transmission electron microscope (TEM), X-ray diffraction (XRD), micro-hardness and tensile tests. The results showed that a uniform microstructure of the Ni/Ti/Al/Cu composite could be produced by an eight passes ARB process, and no intermetallics were generated at the interfaces. As the ARB pass increased, the thickness of the layers decreased, and the average thickness of Cu layers was 8.5μm after eight passes. In the ARB process, the average micro-hardness of Ni, Ti, Al, Cu improved from 157.9, 161.3, 23.8, 59.3HV to 284.3, 254.4, 60.4, 162.2HV, respectively. Moreover, the micro-hardness was linearly related to the actual equivalent strain. The tensile strength of the composites increased, but the elongation decreased in the ARB process. After eight passes, the tensile strength reached the maximum, which was 298.2MPa.

Cu/graphene interdigitated electrodes with various copper thicknesses for UV-illumination-enhanced gas sensors at room temperature.

Effective detection of NO2 and NH3 gases at room temperature (RT) is critical for environmental monitoring and protection. Here, graphene-based gas sensors (Cu/Gr device) of single layer graphene decorated by 6, 8 and 10 nm thick Cu layers with graphene instead of conventional metal as interdigital electrodes are designed and fabricated. The RT performance for both NO2 and NH3 detection can be greatly enhanced by UV light illumination which is closely related to the thickness of Cu layers in which the device with 8 nm thickness (8 nm Cu/Gr device) exhibits the best performances. Analysis of XPS reveals that Cu is partly oxidized to Cu+ and Cu2+ for 6 nm with extra Cuδ+ (1 < δ < 2) for 8 and 10 nm. The contents and distributions of copper oxides and copper in Cu layers influence the catalytic effects and the heterojunction barrier and thus the performances. The RT responses of -30.9% and -8.1% for 5 and 0.3 ppm NO2, and of +29.1% and +5.9% for 105 and 10 ppm NH3 are achieved for the 8 nm Cu/Gr device, respectively. The limits of detection (LODs) for NO2 and NH3 are 12 ppb and 17 ppb, respectively. The sensing mechanisms are discussed in terms of density functional theory (DFT) calculations and energy band diagrams. The study demonstrates an effective solution of improving the device performance by modifying the device configuration and incorporating combined oxides naturally oxidized, which provides the novel design alternatives for high performance sensors.

Phase pure CuSbS2 thin films by heat treatment of electrodeposited Sb2S3/Cu layers

In this work, we report the fabrication of CuSbS2 (CAS) thin films from Sb2S3/Cu multilayer developed by using electrodeposition. Sb2S3 thin films of approximately 250 nm were deposited by pulse electrodeposition from a bath containing SbCl3 and Na2S2O3 precursors onto which Cu was electrodeposited. In order to optimize the formation of pure chalcostibite phase of CuSbS2, the thickness of Cu layer was varied from 55 to 130 nm. The Sb2S3/Cu multilayer was heat treated at 250 °C under N2/S atmosphere for 30 min for its conversion into CuSbS2 and to enhance the crystallinity. XRD spectra showed orthorhombic phase for all CAS samples. Raman analysis confirmed that the sample with 100 nm of Cu thickness has the highest phase purity. SEM image demonstrated a homogeneous thin film with spherical grains. The chemical states of the elements in the phase pure CuSbS2 film were obtained from X-ray photoelectron spectroscopy evidencing the oxidation states as Cu+Sb3+S2−. The optical characterization demonstrated a band gap of 1.45 eV. Furthermore, the results showed that the CuSbS2 thin film is photosensitive and p-type. The energy level band diagram reaffirms its potential as a good absorber layer in thin film solar cells with suitable charge transport pathways.

Structural and magnetic tunability of Co/Cu multilayer nanowires induced by electrolyte acidity and spacer layer thickness

Co/Cu multilayer nanowires (MNWs) were ac pulsed electrodeposited into the 50 nm diameter nanopores of anodic aluminum oxide (AAO) templates in 2.5, 3.8 and 5.25 pH values using the single bath technique. In each acidity, thickness of the Co magnetic layers (tCo) was kept constant (∼45 nm) and that of the non-magnetic Cu layers (tCu) was changed (3, 15, 32, 65, 160 and 260 nm) by adjustment of pulse numbers. Structural and magnetic properties of the samples were studied by X-ray diffraction (XRD) patterns, transmission electron microscope (TEM), field emission scanning electron microscope (FESEM), hysteresis loops and first order reversal curve (FORC) diagrams. TEM images confirm the formation of multilayer structure and uniformity in thickness of the layers. XRD patterns show strong effect of the acidity and Cu-layer thickness on crystallographic characteristics. The acidity along with Cu-layer thickness caused the c-axis direction to change from parallel to perpendicular to the wires axis. A strong relation between crystalline features as preferred orientation and magnetic properties of the samples was also observed by hysteresis loops and FORC diagrams. As shown, both the acidity and tCu affect magnetic response of the magnetic system. FORC diagrams also showed that magnetostatic interactions between the magnetic layers significantly decrease with the increase in tCu, regardless of the electrolyte acidity. The coercivity distribution was also seen to vary through both crystalline structure and magnetostatic interactions.

MODEL OF TRANSMISSION OF MULTILAYER COATINGS BASED ON THE Cu-ZrO2 SYSTEM IN THE OPTICAL WAVELENGTH RANGE

The transmission model for optical diapason was developed for multilayer coatings consisting of alternating layers of copper and zirconium dioxide deposited on K8 glass substrates. The model is based on the laws of light interference. It was shown that the transmission in the optical range of a 60 nm thick Cu layer with a surface resistance ρ = 1 Ohm/sq is 4–5 %, and the transmission of the ZrO2/Cu/ZrO2/Cu/К8 coating obtained by dividing a 60 nm thick copper layer into two sublayers at 30 nm with the application of antireflection layers of ZrO2 on them, at ρ = 1.2 Ohm/sq it reaches 25 %. The thicknesses and the number of layers of the Cu-ZrO2 system were calculated, which ensure a transmission in the wavelength range of 400–700 nm of at least 45 %. The permissible thickness of Cu layers (≥ 20 nm) was determined, below which, due to their insular structure and partial oxidation with the formation of Cu2O, the electrical conductivity of the multilayer coating sharply decreases (ρ ≥ 100 Ohm/sq).

Effect of Inserting a Transition Metal Cu Layer on the Spin‐Orbit Torque‐Induced Magnetization Switching in Pt/Co/Ta Structures

Current induced spin‐orbit torque (SOT) in perpendicularly magnetized heavy metal/ferromagnetic metal/heavy metal trilayers has been widely studied to achieve the current‐induced magnetization switching. Decreasing the critical switching current‐density (JC) is a primary factor in the performance of memory or logic devices because JC directly affects the power consumption of the devices. This work demonstrates the influences of inserting a transition metal copper (Cu) layer between the Co/Ta interface in the Pt/Co/Ta structures with perpendicular magnetic anisotropy (PMA) on the JC, SOT, coercive field, and perpendicular magnetic anisotropy field (Han). The results show that JC decreases significantly when the thickness of Cu layer is above 3 nm, compared with the Pt/Co/Ta control sample, under consideration of the shunting effect of Cu layer. The decrease of JC is the result of the competition between the modified SOT and Han due to the insertion of Cu. The study suggests that the critical switching current‐density of SOT‐switching can be decreased by inserting a transition metal Cu layer.

The interfacial Cu–Sn intermetallic compounds (IMCs) growth behavior of Cu/Sn/Cu sandwich structure via induction heating method

Forming full IMC solder joint technology has become one of the leading candidates to replace conventional high temperature Pb-based solder for wide bandgap (WBG) power modules (SiC and GaN) due to its excellent thermo-stability and high electrical/thermal conductivity. Few studies were investigated the formation and growth mechanism of interfacial Cu–Sn IMCs layer of Cu/Sn(10 μm)/Cu system during induction heating method. The results showed that the growth behavior of Cu–Sn IMCs of the Cu/Sn interface by induction heating method was different from Cu–Sn IMCs growth behavior of the Cu/Sn interface by conventional soldering method. The Cu6Sn5 thickness increased by Cu/Sn solid–liquid interfacial reaction before the bonding time of 45 s and then decreased by Cu6Sn5/Cu solid–solid interfacial reaction within the bonding time of 60 s. The Cu3Sn thickness increased by solid Cu/liquid Sn interfacial reaction and solid Cu6Sn5/solid Cu interfacial reaction within the bonding time of 60 s. A formation mechanism model of Cu–Sn compounds was also presented. The mathematic model of Cu layer consumption at different temperature was also illustrated, which indicated that higher temperature is in favor of the consumption of Cu layer. By knowing the relationship between the thickness of Cu layer on SiC power device at different temperature could be designed when evaluating the reliability of device by induction heating process.

Stacking order-dependent sign-change of microwave phase due to eddy currents in nanometer-scale NiFe/Cu heterostructures

In the field of spintronics, ferromagnetic/nonmagnetic metallic multilayers are core building blocks for emerging technologies. Resonance experiments using stripline transducers are commonly used to characterize and engineer these stacks for applications. Up to now in these experiments, the influence of eddy currents on the excitation of the dynamics of ferromagnetic magnetization below the skin-depth limit was most often neglected. Here, using a coplanar stripline transducer, we experimentally investigated the broadband ferromagnetic resonance response of NiFe/Cu bilayers a few nanometers thick in the sub-skin-depth regime. Asymmetry in the absorption spectrum gradually built up as the excitation frequency and Cu-layer thickness increased. Most significantly, the sign of the asymmetry depended on the stacking order. Experimental data were consistent with a quantitative analysis considering the eddy currents generated in the Cu layers and the subsequent phase shift of the feedback magnetic field generated by the eddy currents. These results extend our understanding of the impact of eddy currents below the microwave magnetic skin-depth and explain the line shape asymmetry and phase lags reported in stripline experiments.

Structure and properties of TiSiN/Cu multilayer coatings deposited on Ti6Al4V prepared by arc ion plating

The TiSiN/Cu nano-multilayer coatings were deposited on Ti6Al4V substrate by multi-arc ion plating. The distribution and diffusion of Cu were controlled by the designed thickness of Cu layer and TiSiN barrier layer. Anti-bacterial behaviors and anti-fouling properties of TiSiN/Cu multilayer coatings were investigated. The TiSiN/Cu multilayer coating consists of nano-crystalline TiN and amorphous Si3N4. The metallic copper presents as nanosize clusters. When the copper layer thickness is 97.10 nm, the TiSiN/Cu coating with the maximum hardness 40.39 ± 0.77 GPa has the best antifouling behavior with the reduction rate of 79.36%, 66.21% and 41.37% for the P. triceratium, N. closterium and chlorella, respectively. Meanwhile, the TiSiN/Cu multilayer coatings have an excellent anti-bacterial behavior against Escherichia coli and Bacillus sp.

Role of Cu layer thickness on the magnetic anisotropy of pulsed electrodeposited Ni/Cu/Ni tri-layer

The Ni/Cu/Ni tri-layer film with different thickness of Cu layer was deposited using pulsed electrodeposition method. The XRD pattern of all the films show the formation of fcc structure of nickel and copper. This shows the orientated growth in the (2 2 0) plane of the layered films as calculated from the relative intensity ratio. The layer formation in the films were observed from cross sectional view using FE-SEM and confirms the decrease in Cu layer thickness with decreasing deposition time. The magnetic anisotropy behaviour was measured using VSM with two different orientations of layered film. This shows that increasing anisotropy energy with decreasing Cu layer thickness and a maximum of −5.13 × 104 J m−3 is observed for copper deposited for 1 min. From the Keff.t versus t plot, development of perpendicular magnetic anisotropy in the layered system is predicted below 0.38 µm copper layer thickness.

Study of the structure of interlayer boundaries in [Co/Cu]10 superlattices by methods of NMR and X-ray reflectometry

Methods of nuclear magnetic resonance and X-ray reflectometry have been used to investigate the state of interfaces in Co/Cu superlattices with different thicknesses of the nonmagnetic layers of Cu. It has been shown that, with an increase in the thicknesses of Cu layers, the perfection of the structure of the interfaces deteriorates.

Numerical Simulation on Optical Characteristics of ZnO/Cu/ZnO Thin Film.

This paper investigates optical characteristics of ZnO/Cu/ZnO multilayer optical thin film by numerical simulation and it is further verified by experiments. The influences of Cu and ZnO thickness on the optical characteristics of ZnO/Cu/ZnO thin films are studied. The results show that the transmittances of ZnO/Cu/ZnO thin film decrease with the increase of thickness of Cu layer but are nonlinear with the ZnO thickness. The maximal light transmission in the visible region is obtained by controlling the thickness of Cu and ZnO films.

Spin-dependent scattering of conduction electrons in Co/Cu multilayers

The magnetotransport properties of giant magnetoresistive Co/Cu multilayers with Cu layer thickness tCu varied from 8 to 27Å are studied using the magnetorefractive effect. Interfacial relaxation times τi↑(↓) and scattering probabilities Pi↑(↓), and interface scattering asymmetry γCo/Cu of conduction electron were obtained from the magnetoreflection in the intraband absorption region. The greatest changes of τi and Pi occur in a spin-up current channel with increasing tCu. Due to a size quantization of transverse component of a quasi-momentum of free electrons in Cu layers, the magnitude of τi↑ oscillates reaching the maximum values at tCu corresponding to the first two peaks of antiferromagnetic interlayer exchange coupling, while the τi↓ experiences only slight changes keeping low values at all thicknesses of Cu layer. It was found that condition τi↑≈τCu is critical to minimize the scattering of spin-up conduction electrons at Co/Cu interface. In this case, in the region of the first peak of antiferromagnetic interlayer exchange the spin asymmetry coefficient γ≈0.86, and the probability of electron scattering Pi↑ is approximately equal to 0.02, which ensures the maximum values of giant magnetoresistance and magnetorefractive effect.

Application Prospects of Multilayer Film Shields for Space Research Instrumentation

We have studied the magnetic properties of multilayer film cylindrical configuration shields (MFS) based on NiFe / Cu. The studied samples were prepared by electrode position. MFS were constituted by alternating layers of NiFe and Cu, deposited on an aluminum cylinder with diameter of 4cm, length of 13cm and 0.5cm thickness. The thickness of each ferromagnetic layer varied from 10 to 150μm, and the thickness of Cu layers was 5μm. Five-samples in which the number of ferromagnetic layers varied from 3 to 45 and copper – from 2 to 44 were tested. The best shielding efficiency was achieved at the maximum number of layers and comprised about 102. Permalloy multilayer foil shield at the same total thickness has several times less efficiency in comparison with MFS. The description of a prototype of the charged particles telescope for space application is presented. Results of its testing regarding sensitivity to the constant magnetic field are described.

The microstructure and improved mechanical properties of Ag/Cu nanoscaled multilayer films deposited by magnetron sputtering

The Ag/Cu nanoscaled multilayer films, which had a constant thickness of Ag layer (about 15 nm) and various thicknesses of Cu layer from about 4 to 20 nm, have been deposited by magnetron sputtering technique. The phase composition, microstructure, surface topography and mechanical properties of these films were investigated, respectively. XRD results revealed that both Ag and Cu layers in multilayer films had a polycrystalline fcc structure with preferred growth of (1 1 1) orientation. The crystallite sizes decreased greatly compared with that of pure Ag film. High-resolution TEM analysis indicated that the multilayers exhibited obvious interfaces between Ag and Cu layers and had dense and columnar grain morphology. AFM analysis showed that all the multilayers with various thicknesses of Cu layers were much smoother than their constituent Ag and Cu pure films. As compared to that of pure Ag (1.7 GPa) and Cu (2.1 GPa) films, as well as, the hardness values calculated from the rule-of-mixtures, a remarkable increase of hardness was observed for all the multilayer films. The maximum hardness value of 4.3 GPa was obtained for the multilayer film with about 20 nm Cu layer. The vacuum ball-on-disk tribotest results suggested that the multilayer film with highest hardness showed a slight decrease in friction coefficient and notable increase in wear resistance. Especially, these results about mechanical and tribological properties were discussed as a function of the film microstructure.

Transparent conductive Ga2O3/Cu/ITO multilayer films prepared on flexible substrates at room temperature

Abstract Transparent conductive Ga2O3/Cu/ITO films were prepared on the polyethylene terephthalate (PET) substrates using radio frequency (RF) and direct current (DC) magnetron sputtering without substrates heating. The effects of Ga2O3 layer thickness and Cu layer thickness on the optical and electrical properties of the Ga2O3/Cu/ITO films were studied. Changes in the optoelectrical properties of Ga2O3/Cu (4.2 nm)/ITO (30 nm) films were investigated with respect to the Ga2O3 layer thickness. The maximum transmission of 86%, the sheet resistance of 45 Ω/sq and the figure of merit of 8.89 × 10−2 Ω−1 were achieved for Ga2O3 (15 nm)/Cu (4.2 nm)/ITO (30 nm) films. The optoelectrical properties of the Ga2O3/Cu/ITO films were also significantly influenced by the thickness of the Cu layer. When the thickness of Cu layer was 3.7 nm, the maximum transmission of 87.6%, the sheet resistance of 50 Ω/sq and the figure of merit of 9.26 × 10−2 Ω−1 were obtained for the Ga2O3 (15 nm)/Cu/ITO (30 nm) films.

Influence of precursor sulfur content on film formation and the properties of sulfurized Cu2ZnSnS4 thin films for solar cells

This is the Cu2ZnSnS4 (CZTS) films were fabricated on glass substrates by sputtering using compound material targets. The fabrication method combines the deposition of metallic precursors and the sulfurization annealing process using S vapor. The optimal precursor sequence for CZTS growth was Cu/SnS/ZnS/Mo. To optimize the composition and the thickness of CZTS, the thickness of Cu layer and precursor was varied. The best cell had an area of 0.185 cm2, Cu/(Zn + Sn) = 0.89, Zn/Sn = 1.04, and S/(metal) = 1.13 and showed an open‐circuit voltage (VOC) of 0.66 V, a short‐circuit current (JSC) of 13.60 mA cm−2, a fill factor of 43.14% and a conversion efficiency of 3.84%.