Thin Films Of Various Thicknesses Research Articles

Optical and electrical properties of indium tin oxide (ITO) nanostructured thin films deposited on polycarbonate substrates “thickness effect”

In this research, indium tin oxide (ITO) thin films of various thickness (200, 250, 300, 350, 400nm) were deposited on polycarbonate polymer substrates using a magnetron sputtering technique. The structure, morphology, surface composition, optical and electrical properties of the thin films were investigated by X-ray diffraction (XRD), Field Emission Scanning Electron Microscopy (FE-SEM), X-ray Photoelectron Spectroscopy (XPS), UV-VIS-NIR spectrophotometer and four point probe method, respectively. The results indicated that grain size increased as the thickness increased. The transmittance and sheet resistance of the ITO thin films showed that ITO thin films with 200nm thickness had the highest transmission whereas ITO thin film with 400nm had the best conductivity.

Properties of Sb2S3 and Sb2Se3 thin films obtained by pulsed laser ablation

The properties of Sb2S3 and Sb2Se3 thin films of variable thickness deposited onto Al2O3, Si, and KCl substrates are investigated by the method of pulsed laser ablation. The samples are obtained at a substrate temperature of 180°C in a vacuum chamber with a residual pressure of 10−5 Torr. The thickness of the films amounted to 40–1500 nm. The structure of the bulk material of the targets and films is investigated by the methods of X-ray diffraction and transmission high-energy electron diffraction, respectively. The electrical properties of the films are investigated in the temperature range of 253–310 K. It is shown that the films have semiconductor properties. The structural features of the films determine their optical parameters.

Experimental evidence of correlation between 1/f noise level and metal-to-insulator transition temperature in epitaxial La0.7Sr0.3MnO3 thin films

The relation between lattice deformation, dc electrical properties and 1/f noise at room temperature was investigated experimentally in two series of high epitaxial La0.7Sr0.3MnO3 (LSMO) thin films of various thicknesses. The first series was deposited on SrTiO3 (0 0 1) single crystal substrates by pulsed laser deposition and the second one on SrTiO3-buffered Si (0 0 1) substrates by reactive-molecular-beam epitaxy. A clear correlation was found between 1/f noise level and the temperature of the metal-to-insulator transition. These findings are important in view of the optimization of LSMO thin films for applications in sensors.

Thickness dependent supercapacitor behaviour of sol-gel spin coated nanostructured vanadium pentoxide thin films

Vanadium pentoxide thin films of various thicknesses have been prepared by sol-gel spin coating method on glass and conducting substrates. X-ray diffraction analysis reveals crystalline nature for the 6–12 layered films (170–310 nm). The crystalline films indicate a preferential orientation of the crystallites along the (200) plane. FTIR studies of the V2O5 xerogel show the presence of V–O–V and V= O bond confirming the formation of V2O5. The scanning electron microscope images reveal formation of nanostructures in the 6–12 layered films. Optical absorption studies indicate a band gap of 2.2–2.5 eV. Pseudocapacitance behaviour of the V2O5 films was studied using cyclic voltammetric technique and impedance analysis. V2O5 films of thickness 202 nm (8 layers) exhibit a specific capacitance of 346 F/g at a scan rate of 5 mV/s.

Metal-insulator transition induced in CaVO3 thin films

Stoichiometric CaVO3 (CVO) thin films of various thicknesses were grown on single crystal SrTiO3 (STO) (001) substrates using a pulsed electron-beam deposition technique. The CVO films were capped with a 2.5 nm STO layer. We observed a temperature driven metal-insulator transition (MIT) in CVO films with thicknesses below 4 nm that was not observed in either thick CVO films or STO films. The emergence of this MIT can be attributed to the reduction in effective bandwidth due to a crossover from a three-dimensional metal to a two-dimensional insulator. The insulating phase was only induced with a drive current below 0.1 μA. X-ray absorption measurements indicated different electronic structures for thick and very thin films of CVO. Compared with the thick film (∼60 nm), thin films of CVO (2–4 nm) were more two-dimensional with the V charge state closer to V4+.

Effect of Strain Rates on the Mechanical Behavior of Cu Thin Films of Various Thicknesses

The objective of this study is to investigate the mechanical behavior of copper thin film with different thicknesses subjected to varying strain rates. A micro-force tensile testing machine (MTS Tytron 250) was used to test the polyimide samples coated with different thicknesses of copper (500 nm, 750 nm, 1000 nm, and 1500 nm). The experiments were conducted by applying test vehicles to different strain rates (1.6×10-4 s-1, 1.6×10-3 s-1, and 1.6×10-2 s-1). The experimental results showed the strain rate and the thickness have obvious influence upon the mechanical properties of Cu thin film. The yield stress increases as increasing the strain rate or decreasing the thickness of Cu film. For considering the strain rate sensitivity m, the strain rate sensitivity m is found that it increases as decreasing the thickness to imply that Cu film has high strain-rate response at low thickness.

Thickness dependence of structural and electrical properties of electron-doped Sr1−xLaxCuO2 infinite-layer thin films grown by pulsed laser deposition

As the building blocks for all of the high-Tc cuprate superconductors, infinite layer (IL) compounds have the simplest structures and the highest Tc of electron-doped superconductors. However, IL structure is one of the high-pressure forms, which makes it difficult to synthesize a single crystal. Therefore, it is highly desirable to obtain high-quality epitaxial thin films making use of epitaxial effect. Although there are many reported attempts to grow IL thin films on different substrates, no one has systematically studied the thickness dependence of structural and electrical properties of IL thin films. In this report, electron-doped Sr1−xLaxCuO2 thin films of various thicknesses were deposited on (001) KTaO3 substrate by pulsed laser deposition. It is shown that IL peak shifts to a lower angle with increase of film thickness, indicating the reduction of the tensile strain. With further increase of thickness, there emerges an impurity phase. Transport measurements showed strong influence of the sample thickness on resistivity and Tc. For a certain thickness range we have demonstrated that superconductivity will occur. The resistive superconducting transition with Tc onset = 14.2 K and Tc (ρ =0) = 10 K has been observed. A moderate thickness is required to obtain IL thin films with superconductivity.

Effect of Thermal Treatments on the Structural and Optical Properties of Thermally Deposited Polycrystalline Cu Thin Films

Copper thin films are potentially used in optical and laser applications due to their intrinsic reflective indexes in visible and infrared region of the spectrum. The reflective properties of the thin films are mainly driven by their thickness, structure, and residual strain induced during the processing stages. Copper thin films of various thicknesses were deposited on glass slides using a thermal evaporation unit. The deposited substrates were thermally treated, in inert environment for 30 minutes, for various temperatures. Further, the substrates were characterized using various techniques. Structural studies of the thin films were carried out using XRD on the as deposited and heat treated films to study the phases, the crystallographic preferred orientation, residual strain and crystallite size. The polycrystalline Cu phase was revealed and no oxide phases were identified. The films were preferentially oriented along (111). The crystallite size increases while the residual strain decreases as the film thickness increases. The crystallite sizes were very small as compared to the film thickness. The optical properties of these coatings were investigated by double beam spectrophotometer. It was found that reflectance of these coatings strongly depends upon the film thickness and post deposition heat treatment. The optimum deposition procedure was established to obtain the enhanced reflecting power.

Gas sensing characteristics of Fe-doped tungsten oxide thin films

This study reports on the gas sensing characteristics of Fe-doped (10at.%) tungsten oxide thin films of various thicknesses (100–500nm) prepared by electron beam evaporation. The performance of these films in sensing four gases (H2, NH3, NO2 and N2O) in the concentration range 2–10,000ppm at operating temperatures of 150–280°C has been investigated. The results are compared with the sensing performance of a pure WO3 film of thickness 300nm produced by the same method. Doping of the tungsten oxide film with 10at.% Fe significantly increases the base conductance of the pure film but decreases the gas sensing response. The maximum response measured in this experiment, represented by the relative change in resistance when exposed to a gas, was ΔR/R=375. This was the response amplitude measured in the presence of 5ppm NO2 at an operating temperature of 250°C using a 400nm thick WO3:Fe film. This value is slightly lower than the corresponding result obtained using the pure WO3 film (ΔR/R=450). However it was noted that the WO3:Fe sensor is highly selective to NO2, exhibiting a much higher response to NO2 compared to the other gases. The high performance of the sensors to NO2 was attributed to the small grain size and high porosity of the films, which was obtained through e-beam evaporation and post-deposition heat treatment of the films at 300°C for 1h in air.

DSMC Scheme for Phonon Transport in Solid Thin Films

Analysis of phonon dynamics based on a linearized Boltzmann transport equation is widely used for thermal analysis of solid thin films, but couplings among various phonon modes appear in some situations. We propose a direct simulation Monte Carlo (DSMC) scheme to simulate the phonon gas starting without the conventional linearization approximation. This requires no relaxation time as an input parameter, and we can investigate the couplings among phonons with different modes. A prototype code based on a simple phonon model was developed, and energy flux was evaluated for thin films of various thickness as a test calculation.

Thermal properties of TiO2 films grown by atomic layer deposition

We study the thermal properties of amorphous TiO2 thin films of various thicknesses t, grown by atomic layer deposition. The thermo-optic coefficient dn/dT and the temperature coefficient dρ/dT of film density ρ are determined from ellipsometric data in wavelength range 380<λ<1800nm with the Cauchy model and the Lorentz–Lorenz relation. It is found that dn/dT exhibits negative values for films with t<150nm and positive values for thicker films, while no significant changes in the two coefficients take place if t<200nm. A qualitative physical explanation based on porosity of the thin films is suggested. Films with t=60nm are illustrated in detail at λ=640nm: the room-temperature values of the coefficients are found to be dn/dT=−3.1×10−5°C−1 and dρ/dT=−4.8×10−5gcm−3°C−1.

Effect of support materials on platinum lattice strain and its oxygen reduction activity

The oxygen reduction activities of sputter-deposited platinum (Pt) thin films of various thicknesses on amorphous carbon (a-C), tungsten oxide (WO3), and titanium oxide (TiO2) were examined to investigate the effect of the support materials. An X-ray diffraction analysis showed that the Pt lattice constant clearly increased with decreasing Pt thickness on the a-C, while it did not change on the WO3 and TiO2. The oxygen reduction activity of the catalysts was measured electrochemically in 0.5mol/L sulfuric acid at 308K. The measurements showed that the activity of Pt/a-C catalysts decreased with the Pt thickness. However, decrease of activity was not observed in the Pt/WO3 and Pt/TiO2 catalysts. The correlation between catalytic activity and Pt lattice strain was obtained from these results; Pt lattice expansion, which was observed on the a-C support, resulted in the decrease of catalytic activity for an oxygen reduction reaction. The metal-oxide support, such as the WO3 and TiO2, suppresses the Pt lattice expansion and maintains the Pt catalytic activity in the case of decreasing Pt thickness compared to the a-C support.

Thickness dependent surface electrical conductivity in copper (II) phthalocyanine thin films

The electrical dark conduction properties of surface cells of copper (II) phthalocyanine (CuPc) thin films of various thicknesses have been studied as a function of voltage at different sample temperatures by using a specially designed conductivity chamber. The results have been analyzed on the basis of the space charge limited conduction theory. The trap distribution in the film surface has been found to be exponential type. Action spectra for the surface photoconductivity in CuPc films for various thicknesses have been performed at room temperature (303 K). The dependence of surface photoconductivity was studied as a function of intensity of the photoexciting light at different sample cell temperatures. The distribution of traps in this thin film surface has been determined from the intensity dependence of surface photocurrent and the results have been compared with the results of dark conductivity measurement.

Pseudomorphy, surface alloys and the role of elementary clusters on the domain orientations in the Cu/Al13Co4(100) system

We have used the pseudo-tenfold surface of the orthorhombic Al13Co4 crystal as a template for the adsorption of Cu thin films of various thicknesses deposited at different temperatures. This study has been carried out by means of low energy electron diffraction (LEED), scanning tunnelling microscopy (STM), x-ray photoelectron spectroscopy (XPS) and x-ray photoelectron diffraction (XPD). From 300 to 573 K, Cu adatoms grow pseudomorphically up to one monolayer. At 300 K, the β-Al(Cu, Co) phase appears for coverages greater than one monolayer. For higher temperature deposition, the β-Al(Cu, Co) phase further transforms into the γ-Al4Cu9 phase. Both β and γ phases grow as two (110) domains rotated by 72° ± 1° from each other. Instead of following the substrate symmetry, it is the orientations of the bipentagonal motifs present on the clean Al13Co4(100) surface that dictate the growth orientation of these domains. The initial bulk composition and structural complexity of the substrate have a minor role in the formation of the γ-Al4Cu9 phase as long as the amount of Al and the Cu film thickness reach a critical stoichiometry.

Anomalous Hall effect and electron transport in ferromagnetic MnBi films

The electron transport properties of highly c-axis oriented MnBi thin films of various thicknesses have been investigated. Samples are metallic but the low temperature resistivity shows an unusual T3 dependence. Transverse Hall effect measurements show that both the ordinary and anomalous Hall coefficients decrease with decreasing temperature below 300 K, but the ordinary Hall coefficient (R0) undergoes a sign reversal around 105 K, where the magnetic anisotropy also changes sign. Analysis of the Hall data for various samples shows that the anomalous Hall coefficient (Rs) exhibits a strong ρ2 dependence, where ρ is the longitudinal resistivity.

Microstructural and domain effects in epitaxial CoFe2O4 films on MgO with perpendicular magnetic anisotropy

CoFe2O4 (CFO) epitaxial thin films of various thicknesses were grown on MgO substrates using the pulsed electron-beam deposition technique. The films have excellent in-plane coherence with the substrate, exhibit layer-by-layer growth and have well-defined thickness fringes in x-ray diffraction measurements. Atomic force microscopy (AFM) measurements indicate that misfit dislocations form in thicker films and the critical thickness for the dislocation formation is estimated. Perpendicular magnetic anisotropy in CFO due to epitaxial in-plane tensile strain from the substrate was found. A stripe-like domain structure in the demagnetized state is demonstrated using magnetic force microscopy (MFM), in agreement with previous predictions. Coercivity increased in thicker films, which is explained by domain wall pinning due to misfit dislocations at the CFO/MgO interface.

Influence of 150 MeV Ni 11+ swift heavy ion irradiation on CuFe 2O 4 thin films prepared by radio frequency magnetron sputtering: Modification on structure and surface morphology

The bulk copper ferrite nanomaterials are synthesized by co-precipitation technique. The vibrating sample magnetometer measurement for bulk CuFe 2O 4 reveals its unsaturated superparamagnetic behavior. The crystallites of the synthesized nanomaterial are in cubic form having an average size of ~ 100 Å and are used as target to prepare thin films of various thicknesses (600, 900 and 1100 nm) by radio frequency magnetron sputtering technique. X-ray peaks arise only when films are annealed at 1200 °C and also they are found to be in tetragonal structure. The magnetic characteristics of 900 nm unirradiated CuFe 2O 4 thin film exhibit superparamagnetic behavior and have an unsaturated magnetic moment at high field. Magnetic force microscopy images of unirradiated CuFe 2O 4 thin films confirm the soft nature of the magnetic materials. The 150 MeV Ni 11+ swift heavy ion irradiation on these thin films at the fluence of 1 × 10 14 ions/cm 2 modifies the polycrystalline nature due to electron–phonon coupling. Atomic force microscopy image shows that the swift heavy ion irradiation induces agglomeration of particles in 600 and 900 nm thin films and increases rms surface roughness from 33.43 to 39.65 and 69.7 to 102.46 nm respectively. However, in 1100 nm film, holes are created and channel-like structures are observed along with a decrease in the rms surface roughness from 75.12 to 24.46 nm. Magnetic force microscopy images of 900 nm irradiated thin film explain the formation of domains on irradiation and are also supported by the ferromagnetic hysteresis observed using vibrating sample magnetometer.

Epitaxial strain-induced magnetic anisotropy in Sm3Fe5O12 thin films grown by pulsed laser deposition

Sm3Fe5O12 thin films of various thicknesses were grown on a (001)-oriented Gd3Ga5O12 substrate by pulsed laser deposition. The crystal structure of the films was strongly dependent on film thickness. The lattice was strained for thinner films due to a lattice mismatch between the film and substrate. This lattice strain was relaxed when the film thickness exceeded a critical thickness of around 660Å. It is suggested that the epitaxial strain induces uniaxial magnetic anisotropy with an out-of-plane magnetic easy axis.

Highly Mass-Sensitive Thin Film Plate Acoustic Resonators (FPAR)

The mass sensitivity of thin aluminum nitride (AlN) film S0 Lamb wave resonators is theoretically and experimentally studied. Theoretical predictions based on modal and finite elements method analysis are experimentally verified. Here, two-port 888 MHz synchronous FPARs are micromachined and subsequently coated with hexamethyl-disiloxane(HMDSO)-plasma-polymerized thin films of various thicknesses. Systematic data on frequency shift and insertion loss versus film thickness are presented. FPARs demonstrate high mass-loading sensitivity as well as good tolerance towards the HMDSO viscous losses. Initial measurements in gas phase environment are further presented.

Extreme Hardening of PDMS Thin Films Due to High Compressive Strain and Confined Thickness

Polymers confined to small dimensions and that undergo high strains can show remarkable nonlinear mechanics, which must be understood to accurately predict the functioning of nanoscale polymer devices. In this paper we describe the determination of the mechanical properties of ultrathin polydimethylsiloxane (PDMS) films undergoing large strains, using atomic force microscope (AFM) indentation with a spherical tip. The PDMS was molded into extremely thin films of variable thickness and adhered to a hard substrate. We found that for films below 1 μm in thickness the Young's modulus increased with decreasing sample thickness with a power law exponent of 1.35. Furthermore, as the soft PDMS film was indented, significant strain hardening was observed as the indentation depth approached 45% of the sample thickness. To properly quantify the nonlinear mechanical measurements, we utilized a pointwise Hertzian model which assumes only piecewise linearity on the part of the probed material. This analysis revealed three regions within the material. A linear region with a constant Young's modulus was seen for compression up to 45% strain. At strains higher than 45%, a marked increase in Young's modulus was measured. The onset of strain induced stiffening is well modeled by finite element modeling and occurs as stress contours expanding from the probe and the substrate overlap. A third region of mechanical variation occurred at small indentations of less than 10 nm. The pointwise Young's modulus at small indentations was several orders of magnitude higher than that in the linear elasticity region; we studied and ruled out causes responsible for this phenomenon. In total, these effects can cause thin elastomer films to become extremely stiff such that the measured Young's modulus is over a 100-fold higher than the bulk PDMS. Therefore, the mechanics of a polymer can be changed by adjusting the geometry of a material, in addition to changing the material itself. In addition to understanding the mechanics of thin polymer films, this work provides an excellent test of experimental techniques to measure the mechanics of other nonlinear and heterogeneous materials such as biological cells.