Optimum Film Thickness Research Articles

Ultraviolet-sensitive and power-efficient oxide phototransistor enabled by nanometer-scale thickness engineering of InZnO semiconductor and gate bias modulation

Amorphous oxide semiconductor photodetectors (PDs) are promising ultrasensitive and power-efficient ultraviolet (UV) PDs because they generate low dark current in the dark and exhibit high photoresponse under UV irradiation owing to their superior UV absorption and photocarrier transport characteristics. Herein, we demonstrate UV-sensitive and power-efficient oxide phototransistors through the nanometer-scale engineering of oxide semiconductors and appropriate modulation of gate bias conditions. The dark current and photocurrent of an oxide phototransistor exhibit a trade-off relationship in terms of the thickness of the oxide semiconductor film. Ultrathin InZnO is disadvantageous for fabricating UV-sensitive PDs because of its low photoresponse. In contrast, excessively thick InZnO is disadvantageous for fabricating power-efficient UV PDs owing to its high dark current. However, the InZnO film with an optimal film thickness of 8 nm can simultaneously provide the advantages of both ultrathin and excessively thick cases owing to its low intrinsic carrier concentration and sufficient UV absorption depth. Consequently, an InZnO phototransistor with high UV-sensing performance (Smax = 1.25 × 106), low-power operation capability (Idark = ∼10−13A), and excellent repeatability is realized by using an 8-nm-thick InZnO semiconductor and applying appropriate gate bias modulation (constant gate bias for maximized photosensitivity and temporal positive bias pulse for persistence photocurrent elimination).

Simple and additive-free synthesis of highly reflective thin silver films and their application on large-scale surfaces

There is a growing demand for highly reflective coatings especially on non-conducting surfaces for use in various industries. Additionally, focus is arising on green production and cost reduction in terms of energy, time, etc., which require detailed investigation of coating process parameters. Therefore, in this work, silver thin films with high reflectance were synthesized on glass substrates in short durations at room temperature by electroless plating (ELP) method in one-step and without using any additives. Effects of deposition time, concentration of the reactants (AgNO3, Glucose, NaOH), and also the surface pretreatment and activation steps were investigated in detail to improve the reflectance and structural properties of silver films. Contact angle measurements were realized to examine the effects of each surface modification step. Surfaces subjected to etching, sensitization and Ag activation were found to yield more homogeneously distributed nanoparticles in short deposition period. Scanning electron microscopy (SEM) also showed smaller-sized spherulite-shaped crystals, forming a close packed structure with an optimum film thickness of ∼110 nm. The continuity of the silver coatings on the surface was verified by the low sheet resistance of 0.18 Ωsq−1. Atomic force microscopy (AFM) analysis revealed a smoother film structure with an RMS of 10.7 nm after sensitization. X-ray diffraction analysis (XRD) and X-ray photoelectron spectroscopy analysis (XPS) analysis proved the growth of highly crystalline silver nanoparticles with high purity. All these morphological improvements led to high values of light (∼97%), near-infrared (99%) and solar (96%) reflectance for the coatings. Finally, based on the optimized concentrations and bath conditions, large-scale (700×500 mm2) first-surface mirrors were successfully produced (96.2%R and 0.25 Ωsq−1) by spray coating technique combined with ELP. Overall, the results indicate that the obtained films have potential usage in applications such as solar energy, electronics and aeronautics.

Development and Investigation of Non-Destructive Detection Drive Mechanism for Precision Type Cylindrical Roller Dynamic Unbalance

In the process of dynamic unbalance detection for precision cylindrical rollers, challenges such as difficulty in achieving effective driving and susceptibility to surface damage during driving significantly impact the accuracy of unbalance detection. This hinders the industry’s ability to achieve the non-destructive detection of cylindrical rollers. Therefore, this paper proposes a novel driving method to enable non-destructive driving of precision cylindrical rollers. The structural principles of the driving mechanism are presented, and a mechanical model for the cylindrical roller is established to analyze the force distribution. Subsequently, a mathematical model for the air film bearing the cylindrical roller is developed to study the variation characteristics of the air film’s load-bearing capacity. The optimal air film thickness is determined, and the rationality of the mathematical model is validated through simulation analysis. Finally, an experimental platform for non-destructive driving is constructed to further verify the effectiveness of the proposed method. This research provides a prerequisite for the non-destructive detection of dynamic unbalance in precision cylindrical rollers.

Optimization of Large-Area PM6:D18-CL:Y6 Ternary Organic Solar Cells: The Influence of Film Thickness, Annealing Temperature, and Connection Configuration

This research focuses on the fabrication and optimization of large-area PM6:D18-CL:Y6 ternary organic solar cells, with a particular emphasis on film thickness, annealing temperature, and the connection configuration’s impact on device performance. The experimental findings indicate that an optimal film thickness of approximately 105 nm fosters the formation of a well-interconnected network, reducing defects and significantly improving both the fill factor, which reaches 46.2%, and the power conversion efficiency (PCE) at 7.2%. An annealing temperature of 110 °C stands out as the ideal condition, resulting in the highest PCE of 8.15%. Notably, excessively high annealing temperatures lead to material aggregation, compromising device performance. Regarding the connection configurations, the study demonstrates that the 5-series 4-parallel arrangement surpasses traditional setups, achieving an impressive output power of 0.11 W. In conclusion, the meticulous control of the film thickness and annealing temperature is paramount for achieving a high PCE in large-area PM6:D18-CL:Y6 ternary organic solar cells. The 5-series 4-parallel configuration exhibits considerable promise for an enhanced power output, offering valuable insights into the development and industrialization of large-area organic solar cells.

Low-Pressure Deuterium Storage on Palladium-Coated Titanium Nanofilms: A Versatile Model System for Tritium-Based Betavoltaic Battery Applications.

Deuterium (D2(g)) storage of Pd-coated Ti ultra-thin films at relatively low pressures is fine-tuned by systematically controlling the thicknesses of the catalytic Pd overlayer, underlying Ti ultra-thin film domain, D2(g) pressure (PD2), duration of D2(g) exposure, and the thin film temperature. Structural properties of the Ti/Pd nanofilms are investigated via XRD, XPS, AFM, SEM, and TPD to explore new structure-functionality relationships. Ti/Pd thin film systems are deuterated to obtain a D/Ti ratio of up to 1.53 forming crystallographically ordered titanium deuteride (TiDx) phases with strong Tix+-Dy- electronic interactions and high thermal stability, where >90% of the stored D resides in the Ti component, thermally desorbing at >460 °C in the form of D2(g). Electronic interaction between Pd and D is weak, yielding metallic (Pd0) states where D storage occurs mostly on the Pd film surface (i.e., without forming ordered bulk PdDx phases) leading to the thermal desorption of primarily DOH(g) and D2O(g) at <265 °C. D-storage typically increases with increasing Ti film thickness, PD2, T, and t, whereas D-storage is found to be sensitive to the thickness and the surface roughness of the catalytic Pd overlayer. Optimum Pd film thickness is determined to be 10 nm providing sufficient surface coverage for adequate wetting of the underlying Ti film while offering an appropriate number of surface defects (roughness) for D immobilization and a relatively short transport pathlength for efficient D diffusion from Pd to Ti. The currently used D-storage optimization strategy is also extended to a realistic tritium-based betavoltaic battery (BVB) device producing promising β-particle emission yields of 164 mCi/cm2, an open circuit potential (VOC) of 2.04 V, and a short circuit current (ISC) of 7.2 nA.

Sulfonate-Grafted Metal–Organic Framework─A Porous Alternative to Nafion for Electrochemical Sensors

Nafion, a polymer containing negatively charged sulfonate groups, is commonly used as a thin film cast on the electrode to adjust the selectivity of complicated electrochemical reactions involving charged reactants or analytes in the electrochemical sensing and electrolytic systems. Herein, a highly porous and chemically stable metal–organic framework (MOF) with enriched sulfonate groups in its pores is synthesized by performing the postsynthetic immobilization of the sulfonate-based ligand within a zirconium-based MOF, MOF-808, and the resulting sulfonate-grafted MOF (SO3-MOF-808) is proposed as a “porous Nafion”─an appealing alternative to the conventional Nafion coating for modulating the selectivity of electrochemical reactions. As a demonstration, the electrochemical sensing of dopamine (DA), which usually suffers from interference caused by the oxidation of the coexisting negatively charged ascorbic acid (AA) and uric acid (UA), is implemented. With the use of the SO3-MOF-808 thin film deposited on the active electrode surface, both the current signal for DA oxidation and the selectivity toward the oxidation of DA against those of AA and UA remarkably outperform those achieved by the Nafion thin film with an optimized film thickness. Findings here suggest the new role of such sulfonate-grafted MOFs as an advanced alternative to Nafion in a range of electrochemical sensing systems and other complicated electrochemical reactions.

Effects of Bitumen Thickness on the Aging Behavior of High-Content Polymer-Modified Asphalt Mixture.

The film thickness of asphalt mixtures is critical for determining their performance and aging durability. However, understanding of the appropriate film thickness and its influence on performance and aging behavior for high-content polymer-modified asphalt (HCPMA) mixtures is still limited. This research aims to examine the relationship between film thickness, performance, and aging behavior of HCPMA mixtures in order to establish an optimal film thickness that ensures satisfactory performance and aging durability. HCPMA specimens with film thicknesses ranging from 6.9 μm to 17 μm were prepared using a 7.5% SBS-content-modified bitumen. Various tests, including Cantabro, SCB, SCB fatigue, and Hamburg wheel-tracking tests, were conducted to evaluate raveling, cracking, fatigue, and rutting resistance before and after aging. The key findings indicate that insufficient film thickness negatively affects aggregate bonding and performance, while excessive thickness reduces mixture stiffness and resistance to cracking and fatigue. A parabolic relationship between the aging index and film thickness was observed, suggesting that increasing film thickness improves aging durability up to a point, beyond which excessive thickness adversely impacts aging durability. The optimal film thickness for HCPMA mixtures, considering performance before and after aging and aging durability, falls within the 12.9 to 14.9 µm range. This range ensures the best balance between performance and aging durability, offering valuable insights for the pavement industry in designing and utilizing HCPMA mixtures.

Design of Antireflection and Enhanced Thermochromic Properties of TiO2/VO2 Thin Films

AbstractVO2‐based thin films exhibit great potential applications in thermochromic smart windows. However, it is still a challenge to synergistically achieve the high luminous transmittance (Tlum) and large solar modulation (ΔTsol). In this paper, antireflective (AR) TiO2/VO2 thin films are designed through optical simulations, and the thin films with optimized film thickness are prepared by magnetron sputtering. The overall performances of the thin films are significantly improved. Compared with single‐layer VO2, the Tlum value of the TiO2/VO2 thin film is significantly increased from 29.03% to 46.29% by 59.5%, and the ΔTsol value is increased up to 16.03%. The Tlum and ΔTsol values of the TiO2/VO2/TiO2 sandwiched thin films can be further improved up to 50.49% and 20.11%, respectively, owing to the light interference at the interfaces between the multilayers. The results provide an effective strategy for improving the performance of smart windows.

Evaluation of asphalt-aggregate adhesive property and its correlation with the interaction behavior

The performance of the asphalt binder-aggregate interface is an essential guarantee of the stability and durability of asphalt pavements. The objectives of this paper are to investigate the effects of various factors (test conditions, material properties) on the interfacial adhesive properties of asphalt binder-aggregate systems and to analyze the correlation between the bond strength and interface interaction. For this purpose, the improved pull-off tests under various temperatures, loading frequencies and asphalt film thickness were carried out to determine the test conditions for interfacial adhesion failure. The interfacial bond strength of various asphalt binders-aggregates and the corresponding interaction values were tested according to the determined test conditions and the correlation between them was analyzed. The results show that the bond strength between asphalt binder and aggregate was negatively correlated with temperature and positively correlated with loading rate, and there was an optimal film thickness. Among the selected minerals and aggregates, calcite and limestone presented the best bonding properties with asphalt binder respectively. Asphaltenes and resins enhanced the bond strength of asphalt binder-aggregate, while saturates and aromatics weakened the bond strength of asphalt binder-aggregate. The short-term aging of asphalt binder was beneficial to the bonding of binder and aggregate, whereas the long-term aging of asphalt binder was detrimental. Among the material properties factors, the SARA composition had the most significant effect on interfacial bond strength. A significant correlation was found between the C value (the preferred interaction parameter) and the bond strength of the asphalt binder-aggregate interface.

Damage resistance of B4C reflective mirror irradiated by X-ray free-electron laser

In this paper, a simple theoretical model combining Monte Carlo simulation with the enthalpy method is provided to simulate the damage resistance of B4C/Si-sub mirror under X-ray free-electron laser irradiation. Two different damage mechanisms are found, dependent on the photon energy. The optimum B4C film thickness is determined by studying the dependence of the damage resistance on the film thickness. Based on the optimized film thickness, the damage thresholds are simulated at photon energy of 0.4–25 keV and a grazing incidence angle of 2 mrad. It is recommended that the energy range around the Si K-edge should be avoided for safety reasons.

Precise Design of VO2Thin Films for Smart Windows by Employing Thickness‐Dependent Refractive Index

Vanadium dioxide (VO2) is an adjustable refractive index material and has capability of behaving as semiconductor or conductor depending on its temperature. Such a condition makes it as a material which can be employed in fabricating thermochromic smart windows. The transmission characteristics of these type of windows strongly depend on the thickness of the film. Therefore, some calculations are required to optimize the VO2thickness. Since the refractive index of VO2thin film is thickness dependent, therefore, in calculating the transmission of light spectrum from VO2thin films, a unique refractive index cannot be utilized. Herein, using three theoretical models (Lorentz–Drude oscillator, Lorentz oscillator, and Tauc–Lorentz) and employing experimental results from previous reports, a collection of thickness‐dependent refractive indexes of VO2films is provided. More precise transmission can be achieved using this set of refractive index data in the calculations which agree with those of experiments. These results also make capable to determine optimized film thickness for any desired transmission performance. This method is useful for design of VO2‐based thermochromic smart windows.

Designed and Produced the Rotary Substrate Holder and Its Optimized in Angular DC Magnetron Co-Sputtering System

We report the design approach of a home-built rotary substrate holder on simple rotation stages for low-pressure vacuum applications. The result of designing and fabricating the rotary substrate holder that it can be successfully used to rotate the substrate in a low-pressure vacuum application without pressure fl uctuations and leakage. Then we investigated the suitable thin fi lm deposition by fabricating optimal multilayer coatings under three variable operating conditions: Speed of substrate, deposition time, and discharge voltage. The thin film deposition result of three copper targets was mounted on each magnetron gun, providing a total of three magnetron guns. The thin fi lm was deposited on a glass slide at room temperature using a custom-built angular DC magnetron co-sputtering system. Analysis of variance for the response surface regression model of film thickness as a function of the three independent variables shows that substrate rotation speed, sputtering time, sputtering voltage, and coeffi cient of squared sputtering time are the most signifi cant factors in determining the optimum film thickness. The optimum thin-film deposition with substrate rotation speed, sputtering time, and sputtering voltage of 10 rpm, 8.61 min, and 200%V, respectively, maximizes the thickness of 72.036 nm.

Cobalt oxide nanoparticles embedded in borate matrix: A conduction mode atomic force microscopy approach to induce nano-memristor switching for neuromorphic applications

Herein, a cobalt borate (CoBi) based synaptic device (nano-memristor) was fabricated via solution process electrochemical deposition technique, in which equally spaced nanocrystalline cobalt oxide particles were embedded in an amorphous borate (B-O) mesh. The synaptic properties across the fabricated film were investigated with the help of conductive mode atomic force microscopy (CAFM). The structural and chemical analysis of the prepared synaptic device revealed that the presence of ultrathin (≤ 2 nm) interstitial amorphous mesh of B-O is critical to introducing the reproducible analog switching characteristics caused by the gradual formation and dissolution of thermodynamically unstable filament at the confined sub-nanometer scale. The prepared device is analyzed by device flux, device charge, and charge-flux relation, confirming CoBi as an emerging material for neuromorphic computing and emulation of Hebbian learning rules. Hence, the optimized pulse stimuli were used to emulate the brain functions like spike rate-dependent plasticity, spike time-dependent plasticity, and learning and forgetting characteristics in the device. The CoBi synaptic device with the optimized film thickness of 100 nm showed analog switching characteristics with low energy consumption of 42 fj and the current in the range of ∼pA at the applied voltage sweeps of ±3.0 V. From the potentiation and depression characteristics, the nonlinearity factor (NL) for long-term potentiation (LTP) and long-term depression (LTD) are calculated as 3.15 and 3.25, respectively indicating the device's high accuracy performance. This work opens up a new avenue to engineer low-power and cost-effective nanoscale memristors to mimic brain functions.

Photoelectrochemical Enhancement of Cu2O by a Cu2Te Hole Transmission Interlayer.

Cuprous oxide (Cu2O) films are electrodeposited on fluorinated tin oxide (FTO) substrates with controlled crystallographic orientation and optimized film thickness. The Cu2O films exhibit a (100)-to-(111) texture change and a pyramid-to-cuboidal crystallite morphology transformation by increasing the electrodeposition current density. The cuboidal crystallites enclosed by (100) sidewalls and (111) truncated surfaces demonstrate better photoelectrochemical property than the pyramid crystallites. By introducing a copper(I) telluride (Cu2Te) layer in between Cu2O and FTO, the photocurrent density increases 70% for the (111)-textured Cu2O film in a 1 M Na2SO4 solution under AM1.5 G illumination. The enhancement is mainly attributed to the improved separation of photocarriers in the illuminated Cu2O film by pumping hole carriers to the Cu2Te layer. In contrast to typical electron pathway management, this study provides an alternative route to improve the photoelectrochemical performance of Cu2O-based photocathodes through hole pathway modification.

Self-powered photodetector based on poly(3-hexylthiophene) / Zinc oxide quantum dots Organic-inorganic hybrid heterojunction

The ZnO quantum dots (QDs) was synthesized by the sol–gel method and spin-coated into films to prepare n-ZnO/p-poly(3-hexylthiophene) hybrid heterojunction ultraviolet photodetectors (PDs) with different film thicknesses. Under optimal critical film thickness, 0 bias voltage and ultraviolet light (360 nm) irradiation, the device yields a photo-dark current ratio of ∼ 990, the quantum efficiency of ∼ 1.05 %, the highest photoresponsivity of ∼ 3.04 mA/W, detectivity of ∼ 1010 Jones and fast rise/fall time of ∼ 23 ms. This work paves the way for the development of low-cost and high-performance PDs.

Preferential growth of (001)-oriented Bi2SiO5 thin films deposited on (101)-oriented rutile substrates and their ferroelectric and dielectric properties

Ferroelectric thin films are important because of their great potential for use in various electric devices such as ferroelectric random-access memory. It was expected that Bi2SiO5, a Si-containing ferroelectric material, would show improved ferroelectricity by targeting a film with the (001)-orientation (polar-axis) on the substrate. Although there was a narrow process window for the deposition of the (010)/(001)-oriented Bi2SiO5 thin film, it was successfully prepared on a (101)-oriented TiO2 single substrate using the pulsed layer deposition technique. The optimum film deposition conditions and film thickness were found, and in this material, the volume fraction of the (001)-oriented domain reached about 70%. By controlling film orientation to the polar axis, the remanent polarization value of this film was 4.8 μC cm−2, which is the highest value among reported Bi2SiO5.

Design and characterization of frog egg shaped CoFe2O4@C core-shell composite as a novel multi-functional counter electrode for low-cost energy devices

The electrical conductivity and catalytic activity of the electrode materials greatly affect the photoelectric conversion performance of DSSCs. However, the commonly used Pt electrodes no longer meet the needs of long-term development at present. Herein, based on the Kirkendall effect, CoFe 2 O 4 @C nanoparticles with core-shell structure are successfully prepared using the treatment of quasi-sol-gel method. The size of CoFe 2 O 4 @C nanoparticles is homogenized without agglomeration through adjusting the ratio of metal salt in the precursor. The composite exhibits excellent counter electrode properties in DSSCs, which attributes to the large specific surface area and superior electro-catalytic activity. With the optimized film thickness (12 µm) of CoFe 2 O 4 @C, an excellent photoelectric conversion efficiency of 7.80% is finally achieved, significantly higher than that of pure carbon (PC) electrode (6.36%) and even Pt counter electrode (7.05%) under the same conditions. The composite can additionally catalyze the recycling of I - /I 3 - redox couple steadily, providing more possibilities for the study of Pt-free materials about DSSCs counter electrode. Through the simple quasi sol-gel method, the carbon material with good conductivity and CoFe 2 O 4 with excellent catalytic activity are tactfully combined to form stabile CoFe 2 O 4 @C nanoparticles with core-shell structure, which are successfully applied to DSSCs counter electrodes. The photoelectric conversion performance of DSSCs is greatly improved by utilizing the sufficient specific surface area of the composite material and its stable catalytic ability to electrolyte cycle. A PCE of 7.80% is achieved literally with the further optimization of adjusting the carbon-transition metal oxide ratio and the film thickness of CoFe 2 O 4 @C-based CE, which is enhanced by 11% and 23% than that of Pt (PCE=7.05%) and pure carbon (PCE=6.36%). This attempt provides a new idea and reference for further optimization of DSSCs. • A core-shell structure CoFe 2 O 4 @C composite was prepared efficiently by quasi-sol-gel method based on the Kirkendall effect. • The composite combines the superior conductivity of the carbon shell with the good catalysis of the CoFe 2 O 4 core. • A PCE of 7.80% is achieved with the optimization of the ratio of C and CoFe 2 O 4 and the thickness of CoFe 2 O 4 @C-based CE.

Parabolic Model for Optimum Dry Film Thickness (DFT) of Corrosion Protective Coatings

This study proposes a model for calculating the optimum dry film thickness of corrosion protective Coatings. It was assumed that the graph of coating thickness against corrosion rate is a parabola whose coordinates at turning point consists of optimum thickness and minimum corrosion rate. On this basis, equation of parabola was formed. Three equations of parabola were also formed with three assumed thicknesses, taking arbitrarily with their corresponding corrosion rates of the coated metals. From the equations, a 3x3 matrix was derived. From the solution of the matrix, equations for optimum thickness, minimum corrosion rates and corrosion rate of uncoated specimen were obtained. It is assumed that with this model a technical ground shall be established, upon which the optimum thicknesses of corrosion protective coatings shall be recommended.

Carbon nanotube-based, serially connected terahertz sensor with enhanced thermal and optical efficiencies

ABSTRACT Owing to their high thermal and optical performances, carbon nanotube (CNT) films are used in various photo-thermo-electric (PTE) applications, such as terahertz (THz) sensing and energy harvesting. To improve the performance of PTE devices, a device structure should be designed based on a deep understanding of the thermal and optical responses of the CNT film. However, the optical properties of CNT films in the THz frequency region remain unclear because of the difficulties associated with device processing and measurements. Herein, we report our findings on the thermal and optical characteristics of CNT films. The shape of the CNT film that maximizes the product of the thermal and optical factors (optimal structure of the PTE sensor) depends on the frequency of the irradiating electromagnetic wave. The optimal film thickness and width values for THz irradiation range from 300–600 nm and 50–70 µm, respectively. Subsequently, we fabricated a serially connected, multi-element PTE sensor with an optimal device structure and enhanced the detection sensitivity by approximately 13 times compared with a single-element PTE sensor. In addition, we demonstrated the first THz spectroscopy application using a PTE sensor. The findings of this study, thermal/optical factor enhancement, and micro-sized CNT film processing technology can be used to improve the performance of all CNT-based photothermal devices, including PTE sensors and thermoelectric generators.

Low-cost sedimentation deposition of boron nanoparticle films for thermal neutron detection applications

The stagnating supply of 3He, the essential material used in gas proportional counters for neutron detection, has recently motivated research activity in solid boron thin-film deposition. The isotope 10B can be used to replace 3He as the neutron reactive material that produces charged reactants to enable detection. In our research, we developed a process for depositing boron films via nanoparticle sedimentation out of a suspension solution. The simple process, in comparison to conventional vacuum deposition techniques, is expected to reduce processing cost and maximize material utilization during fabrication of large-area neutron detection systems. The work being reported here details the process for producing the boron film by the sedimentation method and analyzes the physical properties of the resulting films. Also, the neutron conversion efficiency of the film was evaluated, and the performance results compared favorably to a sputtered 10B4C conversion film employed in commercial large-area neutron straw detector systems, suggesting its potential to become an appealing option for use in large-area neutron detectors after further optimization. We also investigated the effect of boron nanoparticle films’ thickness on the neutron conversion efficiency. The optimal film thickness tends to be slightly larger than what is expected for pure B solid film, due to porosity in the film.