Thin Films Of Various Thicknesses Research Articles

Unification of insertion and supercapacitive storage concepts: Storage profiles in titania

Insertion storage in battery electrodes and supercapacitive storage are typically considered to be independent phenomena and thus are dealt with in separate scientific communities. Using tailored experiments on titanium oxide thin films of various thicknesses, we demonstrate the simultaneous occurrence of both processes. For the interpretation of the entire storage profile encompassing both contributions, the (free) energies of the charge carriers in the mixed conductor and the neighboring phase are the only materials parameters required. The experimental results enable no less than a unification of insertion and supercapacitive storage, the first being dominant for thick films, the latter for thin films or negligible electronic conductivity. Therefore, the size of the storage medium and the nature of the current collecting phases can be used to tune power density versus energy density.

Using femtosecond laser pulses to investigate the thickness-dependent nonlinear optical properties of nickel oxide thin films and their potential use as optical limiters

In this study, the Z-scan technique was used to investigate the nonlinear optical properties of nickel oxide (NiO) thin films of various thicknesses. Direct current (DC) sputtering was used to deposit single-phase NiO thin films with thicknesses of 280, 350, and 470 nm onto a soda-lime glass substrate. The film structure was measured using X-ray diffraction (XRD) and scanning electron microscopy (SEM), while the linear optical properties were measured using a UV-Vis spectrophotometer. NiO thin films were irradiated with 100 fs laser pulses at various excitation wavelengths and excitation powers to determine the nonlinear absorption coefficient and nonlinear refractive index. The NiO films were found to have reverse saturable absorption and self-focusing behavior. As the thickness of the NiO film increases, both the nonlinear absorption coefficient and nonlinear refractive index decrease. Additionally, the investigation of the optical limitations of NiO thin films revealed a definite association with the thickness of the NiO thin film.

Synthesis of thermochromic CdHgI4 thin film: Insight into the thickness-dependent structural, morphological, linear, and nonlinear spectroscopic properties

This study introduces an in-depth exploration of structural, morphological, linear, and nonlinear optical properties of CdHgI4 thin films deposited by the thermal evaporation technique. In this study, cadmium tetra iodomercurate (CdHgI4) nanopowder was synthesized by fusion method from which thin films of various thicknesses (150 to 450 nm) were deposited on glass substrates by thermal evaporation technique. The Structural investigation conducted by X-ray diffractometer (XRD) established that both CdHgI4 nanopowder and thin film formed in a single phase with a tetragonal crystallographic system. However, the CdHgI4 nanopowder and films display a different preferred orientation as corroborated by texture coefficient determination (Tc). The microstructural features obtained by High-resolution transmission electron microscopy (HRTEM) revealed that the powder particles were agglomerated; however, the particles of thin film were well-defined with high compactness and uniform size. The purity as well as stoichiometry were judged by energy dispersive X-ray analysis confirming the absence of any impurities and samples adopted near stoichiometry features. The surface morphology done by field emission scanning electron microscope revealed that films constituted of nanostructured grains with noticeable growth particles with increasing thickness. The CdHgI4 nanopowder had a direct optical transition of band gap of about 1.41 eV evaluated from diffuse reflectance spectroscopy. The band gap of thin films determined from specular optical spectroscopy varied from 2.20 to 1.58 eV, as the thickness changed from 150 to 450 nm. The thickness dependence of other linear optical parameters, such as Urbach energy (Eu), refractive index (n), optical dielectric constants (ε1, ε2), the surface and volume energy loss (SELF, VELF), were elaborately discussed. The nonlinear optical properties including first-order linear susceptibility, third-order susceptibility (χ(1), χ(3)), NL refractive index (n2), and two-photon absorption coefficients (βc) were greatly dependent on the film thickness.

Evaluating Free Thermal Expansion and Glass Transition of Ultrathin Polymer Films on Heated Liquid.

Thermomechanical properties of ultrathin films are crucial for fabrication and use of reliable thin electronic devices. Due to the lack of precise measurement techniques, the thermal deformation behavior of ultrathin films has not yet been clarified. Here, we propose a film on heated liquid (FOHL) method to simultaneously measure the coefficient of thermal expansion (CTE) and glass transition temperature (Tg) of multiple ultrathin polymer films. Free thermal expansion of thin films without substrate interaction can be guaranteed when the thin films are afloat on a liquid surface. To investigate the thermal behavior in a wide temperature range, glycerol is adopted as a thermally stable heating platform owing to its high boiling point of 290 °C. The thin films are transferred onto the glycerol surface from the water surface using the hygroscopic properties of glycerol. Highly accurate and high-throughput thermal strain measurement is achieved using three-dimensional digital image correlation (3D-DIC). The thermomechanical properties of ultrathin polystyrene thin films of various thicknesses (25-400 nm) are precisely characterized utilizing the FOHL and 3D-DIC method.

Direct-Contact Seebeck-Driven Transverse Magneto-Thermoelectric Generation in Magnetic/Thermoelectric Bilayers.

Transverse thermoelectric generation converts temperature gradient in one direction into an electric field perpendicular to that direction and is expected to be a promising alternative in creating simple-structured thermoelectric modules that can avoid the challenging problems facing traditional Seebeck-effect-based modules. Recently, large transverse thermopower has been observed in closed circuits consisting of magnetic and thermoelectric materials, called the Seebeck-driven transverse magneto-thermoelectric generation (STTG). However, the closed-circuit structure complicates its broad applications. Here, STTG is realized in the simplest way to combine magnetic and thermoelectric materials, namely, by stacking a magnetic layer and a thermoelectric layer together to form a bilayer. The transverse thermopower is predicted to vary with changing layer thicknesses and peaks at a much larger value under an optimal thickness ratio. This behavior is verified in the experiment, through a series of samples prepared by depositing Fe-Ga alloy thin films of various thicknesses onto n-type Si substrates. The measured transverse thermopower reaches 15.2 ± 0.4µVK-1, which is a fivefold increase from that of Fe-Ga alloy and much larger than the current room temperature record observed in Weyl semimetal Co2MnGa. The findings highlight the potential of combining magnetic and thermoelectric materials for transverse thermoelectric applications.

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

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

Highly Sensitive and Selective Hydrogen Gas Sensor with Humidity Tolerance Using Pd-Capped SnO2 Thin Films of Various Thicknesses

Detecting and identifying hydrogen gas leakage before a potential disaster is a critical safety concern. To address this issue, a low-cost and simple-design sensor is required with high response and fast sensing time, capable of detecting hydrogen gas even at low concentrations of 5–500 ppm. This study investigates the use of magnetron-sputtered SnO2 thin films with palladium as a catalytic layer to achieve better sensing output. The developed Pd-caped SnO2 thin film sensors showed increased sensitivity with increasing thickness, up to 246.1 nm at an operating temperature of 250 °C. The sensor with a thickness of 246.1 nm exhibited excellent selectivity for H2 gas, even in humid conditions, and was able to distinguish it from other gases such as CO, NH3, and NO2. The sensor demonstrated high response (99%) with a response/recovery time of 58 s/35 s for (5–500 ppm) hydrogen gas. The sensor showed linear response to H2 gas concentration variation (5–500 ppm) at 250 °C. The sensor was found to be mechanically stable even after 60 days in a high-humidity environment. The LOD of sensor was 151.6 ppb, making it a suitable candidate for applied sensing applications. The Pd-caped SnO2 thin film sensor with thickness of ~245 nm could potentially improve the safety of hydrogen gas handling.

Electron transport properties and free electron density evolution during the phase change in VO2 thin films

The experimental results on the phase change behavior of vanadium dioxide (VO2) as a function of temperature are invariably examined in the light of the strong electron correlation-based Mott-Hubbard model or the periodic lattice distortion based Peierls model with limited success. Further, the experimental conditions-based nanostructure imparted to the VO2 thin films also plays an important role. Hence, it has been suggested that the theoretical model that best suits the experimental conditions needs to be applied. In this work, we have examined the electron transport properties of VO2 thin films of various thicknesses all along the reversible phase change cycle. These results have led us to carefully examine the free electron density (ne) evolution all along the phase transition cycle and to establish for the first time the reversible hysteresis cycles of this important parameter. The intimate correlation between the degree of change in ne and the resistance seen in our samples leads us to believe that our results may be in favor of the Mott-Hubbard model of phase transition.

Thickness dependence of magnetic properties of Ir/FeV-based systems

Ir-buffered ${\mathrm{Fe}}_{0.7}{\mathrm{V}}_{0.3}$ (FeV) thin films of variable thickness ($1.4\phantom{\rule{0.28em}{0ex}}\mathrm{nm}\ensuremath{\le}{t}_{\mathrm{FeV}}\ensuremath{\le}10\phantom{\rule{0.28em}{0ex}}\mathrm{nm}$) were sputtered on thermally oxidized Si substrate and capped with Cu or MgO films. Vibrating sample magnetometery measurements allowed deducing their magnetization at saturation and the magnetic dead layer thickness, found to be capping layer independent. Microstrip line ferromagnetic resonance measurements under in-plane and perpendicular to the film plane applied magnetic fields are employed to investigate the perpendicular magnetic anisotropy (PMA) and damping. PMA is found to result from a uniaxial interfacial contribution which is slightly capping layer dependent. In contrast, the second-order PMA constant, which could result from the inhomogeneous distribution and the spatial fluctuations at the nanoscale of the uniaxial PMA at interface, is significantly stronger for Ir/FeV/Cu films. The damping dependence on the inverse of FeV effective thickness revealed a low Gilbert damping constant for FeV $({\ensuremath{\alpha}}_{\mathrm{FeV}}=1.7\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3})$ and allowed concluding that damping enhancement is mainly induced by Ir/FeV. The zero frequency linewidth for in-plane configuration is attributed to two magnon scattering contribution, found to be higher for Cu capped FeV. The investigation of the FeV thickness dependence of interfacial Dzyaloshinskii-Moriya interaction (iDMI) of both systems via Brillouin light scattering allowed to conclude to the zero iDMI constant of FeV/Cu. It also led to deduce iDMI constants of Ir/FeV and FeV/MgO, estimated to be ${D}_{\mathrm{s}}^{\mathrm{Ir}/\mathrm{FeV}}=(0.13\ifmmode\pm\else\textpm\fi{}0.02)\phantom{\rule{0.28em}{0ex}}\mathrm{pJ}/\mathrm{m}$ et ${D}_{s}^{\mathrm{FeV}/\mathrm{MgO}}=(\ensuremath{-}0.07\ifmmode\pm\else\textpm\fi{}0.02)\phantom{\rule{0.28em}{0ex}}\mathrm{pJ}/\mathrm{m}$, respectively.

Analysis of current-voltage curves of ZnO thin films under dark and optical stimulus

In this work, we are reporting the current conduction mechanism in ZnO thin films of various thicknesses under the dark and optical stimulus. The ZnO thin films of different thicknesses (45, 70, 110, 160, 220 nm) were grown on a glass substrate at 250 °C using the spray pyrolysis method. For photoconductivity measurements, electrodes were made using silver paste by putting a ∼1 mm gap between the electrodes. The photocurrent under UV illumination increases with increasing film thickness. Linear fitting of the data suggests the major role of space charges in the film for the rise in the photocurrent. Therefore the obtained conduction mechanism is found to be space charge-limited conduction in ZnO thin films under UV illumination.

Tuning structural, electrical, linear, and nonlinear optical properties of cadmium zinc telluride quantum dot thin films

Quantum dots of Cd0.18Zn0.14Te0.68 thin films of various thicknesses are deposited on a glass substrate using inert gas condensation and characterized using many techniques. Structural analysis confirms the cubic polymorph of the thin films. The particle size increased from 5.7 to 10.35 nm as the film thickness increased from 10 to 100 nm. Bandgap calculations show two direct allowed transitions, one of which is 1.8 eV for different thicknesses. The other transition changes from the ultra-violet region (3.7 eV) for 10 nm thickness to yellow (2 eV) for 100 nm thickness, depending on the particle size. This result suggests that this material is suitable for use in multiple absorption layers of the same material rather than multilayers of different materials in tandem solar cells. The optical linear and nonlinear parameters highly depend on the particle size. Electrical conductivity shows intrinsic conduction with low activation energies from ambient temperature to 336 K.Graphical abstract

Room temperature tunability of ferroelectricity and dielectricity in La and Mn codoped BiFeO3 nanoflakes: Implications for electronic devices applications

This study sheds a light on the in-situ growth of nanoflakes structure in Bi0.9La0.1Fe0.5Mn0.5O3 (BLFMO) thin film. The BLFMO thin films of various thicknesses were grown on LaNiO3 (LNO) coated Si (100) substrates using pulsed laser deposition technique. A long-range crystal structure of the as prepared BLFMO thin films was studied by X-ray diffraction measurements, which shows that the LNO buffer layer allows growth for a specific orientation. The compact and densely packed nanoflake structures in BLFMO thin film samples were confirmed by surface morphological investigations. To measure the polarization versus electric field (p-E) loop of BLFMO chip samples, a standard bipolar sinusoidal waveform with its magnitude of 250 kV/cm was applied at the frequency of 1 kHz. The maximum saturation and remnant polarizations of 104.50 μC/cm2 and 86.24 μC/cm2 respectively were probed for a critical thickness (420 nm) of the BLFMO layer. The voltage polarity-dependent leakage current behavior of Ag/BLFMO/LNO thin-film capacitor is thoroughly explored in detail. The value of leakage current density was observed from 1.16 × 10−4 to 2.24 × 10−5 J/cm2 for BLFMO thin films at an external applied electric field of 300 kV/cm. The highest tunability ∼60.20% and minimum temperature capacitance coefficient ∼1.23 × 10−3 were also observed for the same critical thickness of proposed chip element. The present study may open up a new opportunity to fabricate thin film based ferroelectric memory devices.

Effect of SnS thin film thickness on visible light photo detection

In this study, SnS thin films of various thicknesses (500 nm–700 nm) were prepared by the thermal evaporation technique for potential photodetector application. High purity SnS prepared at 1000 °C is used to deposit thin films at room temperature. The prepared SnS thin films were characterized to assess the thickness effect on the crystallite size, morphology, transmittance, band gap, and photo-sensing properties. SnS pure phase confirmed through XRD and Raman spectral analysis. Among the fabricated SnS thin films, the sample having a thickness of 650 nm showed better crystallinity with higher crystallite size and preferred orientation of crystallites. SnS grew plate-like-columnar grain morphology of different widths and thicknesses which is confirmed by FESEM results. The UV–Vis studies showed a minimum band gap value obtained for 650 nm thickness film. The 650 nm thickness SnS films have a highest photo response of 6.72 × 10−1 AW−1, external quantum efficiency (EQE) of 157%, and detectivity of 14.2 × 109 Jones. The transient photo-response analysis showed the 650 nm SnS thin film has a 5.3 s rise and 5.1 s fall duration, which is better suitable for photodetector applications compared to other samples.

Transmission-path dependent electron hopping transport in thin films and nanorods of NiO

The present study demonstrates how the length and dimensionality of electron transmission-paths and temperature impact the electron hopping transport in NiO thin films and nanorods. The NiO nanorods and thin films of varying thicknesses were synthesized using physical vapor deposition techniques. The thin films of various thicknesses offer two-dimensional (2D) transmission-paths of varying lengths, whereas nanorods provide confined one-dimensional (1D) transmission-paths for the conduction of electrons. Also, the current-voltage characteristics of 2D and 1D transmission-paths in thin films and nanorods are measured at varying temperatures. The thin films and nanorods of NiO display a characteristic transition in conduction of electrons at a temperature of ∼180 K, which distinguishes the two kinds of electron conduction mechanisms, viz., the nearest-neighbor hopping (NNH) and variable range hopping (VRH). The analysis of the NNH and VRH mechanism quantifies the activation energy, localization lengths, probable hopping distance, and hopping energy of electrons through 2D and 1D transmission-paths at various temperatures. The quantification of these various figure-of-merits proves that the electron hopping transport in nanorods and thin films is quintessentially influenced due to the lengths and dimensionality of transmission-paths and temperature.

Thin Ni/Al Metal Films Characterization Using a High-Frequency Electromagnetic Field

The paper presents methods of obtaining and studying new materials - thin metal films of the Ni/Al system. The technique and main parameters of the resistive method of thermal evaporation of the alloy using a vacuum universal station are briefly presented. Samples of thin films of various thicknesses were obtained. The thickness of the material was determined both using a scanning electron microscope and a developed eddy-current gage system operating under a hardware-software complex. In the course of the research, the limit the film thickness gauging capabilities of the developed gage system was established (400 nm). The ability of the gage system to detect differences in the thickness of the same film was shown using the developed method. Also, the possibility of determining the thickness of an undoubtedly unknown thin film by an eddy-current transducer signal amplitude has been demonstrated.

Humidity Sensing Ceria Thin-Films.

Lowering the constitutive domains of semiconducting oxides to the nano-range has recently opened up the possibility of added benefit in the research area of sensing materials, in terms both of greater specific surface area and pore volume. Among such nanomaterials, ceria has attracted much attention; therefore, we chemically derived homogeneous ceria nanoparticle slurries. One set of samples was tape-casted onto a conducting glass substrate to form thin-films of various thicknesses, thereby avoiding demanding reaction conditions typical of physical depositions, while the other was pressed into pellets. Structural and microstructural features, along with electrical properties and derivative humidity-sensing performance of ceria thin-films and powders pressed into pellets, were studied in detail. Particular attention was given to solid-state impedance spectroscopy (SS-IS), under controlled relative humidity (RH) from 30%–85%, in a wide temperature and frequency range. Moreover, for the thin-film setup, measurements were performed in surface-mode and cross-section-mode. From the results, we extrapolated the influence of composition on relative humidity, the role of configuration and thin-film thickness on electrical properties, and derivative humidity-sensing performance. The structural analysis and depth profiling both point to monophasic crystalline ceria. Microstructure analysis reveals slightly agglomerated spherical particles and thin-films with low surface roughness. Under controlled humidity, the shape of the conductivity spectrum stays the same along with an increase in RH, and a notable shift to higher conductivity values. The relaxation is slow, as the thickness of the pellet slows the return of conductivity values. The increase in humidity has a positive effect on the overall DC conductivity, similar to the temperature effect for semiconducting behavior. As for the surface measurement setup, the thin-film thickness impacts the shape of the spectra and electrical processes. The surface measurement setup turns out to be more sensitive to relative humidity changes, emphasized with higher RH, along with an increase in thin-film thickness. The moisture directly affects the conductivity spectra in the dispersion part, i.e., on the localized short-range charge carriers. Moisture sensitivity is a reversible process for thin-film samples, in contrast to pellet form samples.

Effect of thickness and reaction media on properties of ZnO thin films by SILAR

Zinc oxide (ZnO) is one of the most promising metal oxide semiconductor materials, particularly for optical and gas sensing applications. The influence of thickness and solvent on various features of ZnO thin films deposited at ambient temperature and barometric pressure by the sequential ionic layer adsorption and reaction method (SILAR) was carefully studied in this work. Ethanol and distilled water (DW) were alternatively used as a solvent for preparation of ZnO precursor solution. Superficial morphology, crystallite structure, optical and electrical characteristics of the thin films of various thickness are examined applying X-ray diffraction (XRD) system, scanning electron microscopy, the atomic force microscopy, X-ray photoelectron spectroscopy, ultraviolet–visible spectroscopy, photoluminescence spectroscopy, Hall effect measurement analysis and UV response study. XRD analysis confirmed that thin films fabricated using ethanol or DW precursor solvents are hexagonal wurtzite ZnO with a preferred growth orientation (002). Furthermore, it was found that thin films made using ethanol are as highly crystalline as thin films made using DW. ZnO thin films prepared using aqueous solutions possess high optical band gaps. However, films prepared with ethanol solvent have low resistivity (10–2 Ω cm) and high electron mobility (750 cm2/Vs). The ethanol solvent-based SILAR method opens opportunities to synthase high quality ZnO thin films for various potential applications.

Electron microscopy of the microstructure of antimony thin films of variable thickness

Thin Sb films with a thickness gradient deposited in vacuum were investigated by transmission electron microscopy. Microstructures in films with increasing thickness change from amorphous islands of increasing density and size to labyrinthine and continuous films with texturing, which also changes with increasing thickness. Based on the analysis of the patterns of bend extinction contours, a strong internal bending of the crystal lattice, up to 120 deg/μm, and the dependence of the crystallographic orientations in the structures of the film on the thickness were revealed. Keywords: Antimony, thin films, TEM, crystallography, extinction bend contours.

Microstrip Array Ring FETs with 2D p-Ga2O3 Channels Grown by MOCVD

Gallium oxide (Ga2O3) thin films of various thicknesses were grown on sapphire (0001) substrates by metal organic chemical vapor deposition (MOCVD) using trimethylgallium (TMGa), high purity deionized water, and silane (SiH4) as gallium, oxygen, and silicon precursors, respectively. N2 was used as carrier gas. Hall measurements revealed that films grown with a lower VI/III ratio had a dominant p-type conduction with room temperature mobilities up to 7 cm2/Vs and carrier concentrations up to ~1020 cm−3 for thinner layers. High resolution transmission electron microscopy suggested that the layers were mainly κ phase. Microstrip field-effect transistors (FETs) were fabricated using 2D p-type Ga2O3:Si, channels. They achieved a maximum drain current of 2.19 mA and an on/off ratio as high as ~108. A phenomenological model for the p-type conduction was also presented. As the first demonstration of a p-type Ga2O3, this work represents a significant advance which is state of the art, which would allow the fabrication of p-n junction based devices which could be smaller/thinner and bring both cost (more devices/wafer and less growth time) and operating speed (due to miniaturization) advantages. Moreover, the first scaling down to 2D device channels opens the prospect of faster devices and improved heat evacuation.

Ion tracks in ultrathin polymer films: The role of the substrate

Surface damage produced by single MeV-GeV heavy ions impacting ultrathin polymer films has been shown to be weaker than those observed under bulk (thick film) conditions. The decrease in damage efficiency has been attributed to the suppression of long-range effects arising from excited atoms lying deeply in the solid. This raises the possibility that the substrate of the films itself is relevant to the radiation effects seen at the top surface. Here, the role of the substrate on cratering induced by individual 1.1 GeV Au ions in ultrathin poly(methyl methacrylate) (PMMA) layers is investigated. Materials of different thermal and electrical properties (Si, SiO2, and Au) are used as substrates to deposit PMMA thin films of various thicknesses from ∼1 to ∼300 nm. We show that in films thinner than ∼40 nm craters are modulated by the underlying substrate to a degree that depends on the transport properties of the medium. Crater size in ultrathin films deposited on the insulating SiO2 is larger than in similar films deposited on the conducting Au layer. This is consistent with an inefficient coupling of the electronic excitation energy to the atomic cores in metals. On the other hand, the damage on films deposited on SiO2 is not very different from the Si substrate with a native oxide layer, suggesting, in addition, poor energy transmission across the film/substrate interface. The experimental observations are also compared to calculations from an analytical model based on energy addition and transport from the excited ion track, which describe only partially the results.