Thin Films Of Various Materials Research Articles

Measurement of information content of Perovskite solar cell’s synthesis descriptors related to performance parameters

AbstractPerovskite solar cells (PSC) are formed by different layers composed of thin films of various materials, in which the properties of every thin layer affect the performance of the cell. The identification of those most relevant properties (or descriptors) has a significant impact on the optimization and cost reduction of the Perovskite solar cell. This relevance is typically evaluated by adjusting a model using subsets of features, but in the present work, we propose to use the mutual information measure to quantify the statistical association between input descriptors and Perovskite solar cell performance parameters (Voc, Jsc, FF, PCE). As a result, it is found that ion X is the factor that most impacts the performance of the solar cell. On the other hand, variables such as band gap, Perovskite layer thickness, and A and B ions are also important. In this work, we identify some of the most important factors affecting Perovskite solar cells’ performance, and it could help to improve the efficiency of Perovskite solar cells. In addition, this proposed method could also be applied to other types of functional coatings, thin films, and surfaces.

Thermal atomic layer deposition of aluminum oxide, nitride, and oxynitride: A mechanistic investigation

Atomic layer deposition (ALD) has been proven to be a versatile method for the deposition of thin films of various materials. It yields films with exceptional conformality and allows tunable film compositions with control of film thickness at the atomic level. Thin films of Al oxide, nitride, and oxynitride are deposited via ALD using Al(CH3)3 (TMA)/AlCl3 with H2O/NH3. Herein, surface chemical reactions are examined using density functional theory calculations to elucidate the adsorption, oxidation, and nitridation of precursors [TMA and AlCl3] as well as the mechanism controlling the composition of Al oxynitride thin films obtained through ALD. The hydrogen-terminated substrate surface is transformed into a CH3/Cl-terminated surface after the reaction with the TMA/AlCl3 precursors. The molecular adsorption of TMA occurs through a spontaneous reaction, whereas that of AlCl3 requires a slight energy input. Although the adsorption energy of AlCl3 is higher than that of TMA, the activation energy and energy change of AlCl3 adsorption are higher and lower than those of TMA, respectively; furthermore, the use of AlCl3 results in the generation of a corrosive by-product (HCl). A similar tendency is observed in the second ALD half reaction, which is oxidation. Nitride formation is endothermic for molecularly adsorbed AlCl3 but exothermic for TMA. Furthermore, the investigation of the exchange reactions between surface moieties and excess gaseous reactants reveals a preference for the substitution of N by O, which is attributed to differences in bond energies between the surface moieties and the surface metal atom, as well as between H2O and NH3.

When magnetron sputtering deposition meets machine learning: Application to process anomaly detection

This paper demonstrates how the application of machine learning techniques can be used in Magnetron Sputtering (MS) processes, to detect anomalies and reduce their failure rate. Magnetron Sputtering is a widely used technique in materials science and engineering to deposit thin films of various materials for a range of applications. However, the process is complex and can be prone to various anomalies that can lead to defects in the deposited films, resulting in a non-negligible waste of coated objects. In this paper, we focus on the use of machine learning algorithms for both online and offline anomaly detection, which can help identify and diagnose process anomalies in real-time or post-process. Our results demonstrate that machine learning techniques can be used to develop anomaly detection systems, to limit failure in magnetron sputtering processes.

New Approaches to Produce Large-Area Single Crystal Thin Films.

Wafer-scale growth of single crystal thin films of metals, semiconductors, and insulators is crucial for manufacturing high-performance electronic and optical devices, but still challenging from both scientific and industrial perspectives. Recently, unconventional advanced synthetic approaches have been attempted and have made remarkable progress in diversifying the species of producible single crystal thin films. This review introduces several new synthetic approaches to produce large-area single crystal thin films of various materials according to the concepts and principles.

Resonant toroidal metasurface as a platform for thin-film and biomaterial sensing.

Toroidal resonances with weak free-space coupling have recently garnered significant research attraction toward the realization of advanced photonic devices. As a natural consequence of weak free-space coupling, toroidal resonances generally possess a high quality factor with low radiative losses. Because of these backgrounds, we have experimentally studied thin-film sensing utilizing toroidal resonance in a subwavelength planar metasurface, whose unit cell consists of near-field coupled asymmetric dual gap split-ring resonators (ASRRs). These ASRRs are placed in a mirrored configuration within the unit cell. The near-field coupled ASRRs support circulating surface currents in both resonators with opposite phases, resulting in excitation of the toroidal mode. In such a way, excited toroidal resonance can support strong light-matter interactions with external materials (analytes to be detected) placed on top of the metasurface. Further, our study reveals a sensitivity of 30GHz/RIU while sensing AZ4533 photoresist film utilizing the toroidal mode. Such detection of thin films can be highly beneficial for the development of sensing devices for various biomolecules and dielectric materials that can be spin coated or drop casted on metasurfaces. Hence, the toroidal mode is further theoretically explored towards the detection of avian influenza virus subtypes, namely, H5N2 and H9N2. Our study reveals 6 and 9GHz of frequency redshifts for H5N2 and H9N2, respectively, in comparison to the bare sample. Therefore, this work shows that toroidal metasurfaces can be a useful platform to sense thin films of various materials including biomaterials.

Growth of nano-branches on 1-D WO3 nanotrees by flame process and its photoelectrochemical performances

Flame vapor deposition (FVD) is a powerful method to prepare rapidly and economically the nanostructured thin film with high purity and high crystallinity. One-dimensional (1-D) nanostructured tungsten oxide (WO 3 ) thin film has high potential for various applications as photocatalytic material and, in this study, was prepared from tungsten wire as a precursor by FVD process. The nucleation and growth rates in FVD process could be controlled by changing the precursor supply rate in flame instantaneously by installing additional wire traverse feeder and the nanotree structured WO 3 thin film was prepared successfully. The concentration of nano-branches at nanotree structured WO 3 thin films could be controlled by adjusting wire traversing speed. The proper wire traverse feeding speed could increase surface area and allow more light absorption by additional growth of nano-branches, but too low wire traverse feeding speed could make random and dense growth of nano-branches to reduce the electrical properties and total surface area. The proper growth of nano-branches could increase the photoelectrochemical (PEC) performance of WO 3 /BiVO 4 heterojunction thin film by providing the larger interfacial contact area for heterojunction, but too much growth of nano-branches could reduce the PEC performance because of non-uniform loading of BiVO 4 in WO 3 thin film during spin-coating process. This study can be a basis to prepare by FVD process not only the nanotree structured WO 3 thin film for its PEC application but also many nanostructured thin films of various materials for their suitable applications. • Nanotree structured WO 3 thin film was successfully prepared by 1-step flame process. • The precursor concentration could be changed sharply by the wire traversing feeder. • Nucleation and growth rates were controlled to prepare nano-branches on nanotrees. • Nanotree structured WO 3 /BiVO 4 film improved photoelectrochemical performance. • Proper growth of nano-branch is important for high photoelectrochemical performance.

Transparent, Conducting Self‐Assembled CuS Nanostructures at and beyond Liquid‐Liquid Interface and their Electrocatalytic Properties

AbstractThe liquid‐liquid interface (LLI) technique has been used to form thin films of various materials parallel to the interface. In this report, by taking CuS as an example, we show that CuS not only adopts thin film structures at the liquid‐liquid interface parallel to the interface but can also utilize beyond the interface to form self‐supported vertically aligned CuS thin films by controlling the precursor concentration. We also report the formation of a self‐assembled monolayer of CuS nanoparticles in the dichlorobenzene‐water interface at a lower concentration of copper. Thin films generated at LLI show p‐type conductivity with a sheet resistance of ∼350 Ω/□ and transparency up to 72 % at 550 nm. CuS also show electrocatalytic activity towards glucose sensing with a sensitivity of 3958 μA mM−1 cm−2, which is among the best in copper‐based materials.

Universal micro-trench resonators for monolithic integration with silicon waveguides

We present a systematic study of micro-trench resonators for heterogeneous integration with silicon waveguides. We experimentally and numerically demonstrate that the approach is compatible with a large variety of thin film materials and that it does not require specific etching recipe development, thus making it virtually universal. The microresonators are fabricated through in-foundry silicon-on-insulator processing and in-house backend processing. We also report ultra-compact chalcogenide microresonators with radius as small as 5µ and quality factors up to 1.8 × 105. We finally show a proof-of-concept of a novel multilayer waveguide using the micro-trench technique.

Information and program support of the analysis and processing of holographic information

The research of thin films of various materials on nano- and microlevel is undoubtedly topical. Three-dimensional images of thin films can significantly increase the level of the received results. Intellectual computer support of researches assumes the existence or creation of mathematical and the software that implements the experimental program. Such support can most effectively be realized with the help of an information and expert system, based on a holographic electron microscope. In this work we presented an information and expert system for solving this problem. When creating instrumental, hardware and software tools for non-destructive research of the 3D structure of objects, we proceeded from the assumption that the most complete information about the object of research can be obtained only with a comprehensive approach to the analysis of the structure of the object using complementary techniques that allow obtaining data as a 3D image.

Multifunctional Nanostructures and Nanopocket Particles Fabricated by Nanoimprint Lithography.

Nanostructured surfaces and nanoparticles are already widely employed in many different fields of research, and there is an ever-growing demand for reliable, reproducible and scalable nanofabrication methods. This is especially valid for multifunctional nanomaterials with physical properties that are tailored for specific applications. Here, we report on the fabrication of two types of nanomaterials. Specifically, we present surfaces comprising a highly uniform array of elliptical pillars as well as nanoparticles with the shape of nanopockets, possessing nano-cavities. The structures are fabricated by nanoimprint lithography, physical and wet-chemical etching and sputter deposition of thin films of various materials to achieve a multifunctional nanomaterial with defined optical and magnetic properties. We show that the nanopockets can be transferred to solution, yielding a nanoparticle dispersion. All fabrication steps are carefully characterized by microscopic and optical methods. Additionally, we show optical simulation results that are in good agreement with the experimentally obtained data. Thus, this versatile method allows to fabricate nanomaterials with specific tailor-made physical properties that can be designed by modelling prior to the actual fabrication process. Finally, we discuss possible application areas of these nanomaterials, which range from biology and medicine to electronics, photovoltaics and photocatalysis.

Analytical Optimization of the Design of Film-Laminated Thermoelectric Power Generators

Thermoelectric generators directly convert heat into electricity, typically made from bulk solid thermoelectric materials. They are a widely used technology in exhaust gas heat recovery from automotive vehicles or radioisotope power generation in space satellites. We propose a film-laminated device structure for lower cost and higher volume production. The film-laminated thermoelectric generator design includes a wide variety of thin-film materials and insulator polymer films. Despite the simple fabrication process, the challenges in the bypass heat leak across the insulator film would increase in a film-laminated device structure. The insulator films in the device exhibit low thermal conductivities but cannot be neglected compared to the thermoelectric materials. Comprehensive analysis is conducted on laminated film-based thermoelectric power generators. The study includes the impacts of the geometry design and thermal conductivity to the power output. The sensitivity of design parameters and material properties is investigated. Cost of the power ($/W) from the available heat is estimated. Both of the above are influenced by the effective heat transfer coefficient of the external thermal contacts. The normalized power as a function of the thermal conductivity ratio of the laminate to the thermoelectric materials is determined for a given ZT value. This relationship can be utilized to measure the impact of the laminating material for any material combination. The power output monotonical decreases as the thermal conductivity ratio gets closer to unity. It is highly desirable to use a one order of magnitude lower thermal conductivity for the insulator, especially for thin thermoelectric layer design.

Flexible and low-cost fabrication of optical waveguides by UV laser resist-mask writing

We report on UV laser photoresist mask writing as a tool for fabricating integrated optical waveguides and devices. Using 375 nm laser light and a pneumatically controlled direct writing stage, we defined mask features into a 250-nm-thick negative photoresist layer on a silicon nitride film on an oxidized silicon substrate. We investigated the feature size and edge roughness for different laser powers. Using the photoresist mask layer and reactive ion etching, we patterned high-refractive-index-contrast silicon nitride strip waveguides and devices with varying waveguide widths and gaps. We report on the structural and transmission characteristics of a directional coupler, Sagnac interferometer, and ring resonator and demonstrate 50/50 coupling at 1510 nm, 20 dB transmission drop at 1580 nm, and a Q factor of ∼13,000 at 1576 nm, respectively. These results demonstrate that this technique can be applied to a variety of thin film materials and substrates for inexpensive and rapid prototyping of integrated photonic devices.

Ultrasonic-Assisted Spin-Coating: Improved Junction by Enhanced Permeation of a Coating Material within Nanostructures.

Over the last decades, the spin-coating (SC) technique has been widely used to prepare thin films of various materials in the liquid phase on arbitrary substrates. The technique simply relies on the centrifugal force to spread a coating solution radially outward over the substrate. This mechanism works fairly well for solutions with low surface tension to form thin films of reasonable junctions on smooth substrates. Here, we present a modified SC technique, namely, ultrasonic-assisted spin-coating (UASC), to form thin films of coating solution having high surface tension on rough substrates with excellent junctions. The UASC technique couples SC with an external ultrasonic wave generator to provide external perturbation to locally break down big drops of the coating material into smaller droplets via Rayleigh instability. Because of their lower mass, these tiny droplets gain low momenta and move slowly both in radial and azimuthal directions, giving them an enough time to effectively permeate within pores, thereby yielding excellent junctions. Furthermore, we also investigated the effect of junction improvement on conventional and inverted bulk heterojunction organic solar cells. Intriguingly, the organic solar cells fabricated by the UASC method showed an improved efficiency compared to typical SC owing to efficient charge transfer across the junction. These results clearly imply that UASC is a simple and powerful technique which can significantly enhance the device performance by improving the junction. Moreover, we believe that UASC can be more effective for the preparation of devices composed of multilayers of different materials having complicated nanostructures.

Thermal Properties of Anisotropic and/or Inhomogeneous Suspended Thin Films Assessed via Dual-Side Time-Domain Thermoreflectance: A Numerical Study

ABSTRACTTime-domain thermoreflectance (TDTR) is a powerful method for measuring thermal properties, such as thermal conductivity and thermal boundary resistance, of a broad variety of thin-film materials and interfaces. Dual-side TDTR, in which measurements are performed on the top and bottom sides of a suspended region of a thin film of interest, has recently emerged as an effective way to investigate the thermal properties of a film that is thermally anisotropic and/or inhomogeneous. Despite its experimental versatility, dual-side TDTR has yet to be fully interrogated. In this work, we examine the thermal conductivity and boundary resistance of anisotropic and/or inhomogeneous suspended thin films, extracted by dual-side TDTR on these films via numerical simulation. We start from a simple case of an anisotropic or inhomogeneous suspended membrane and then consider the combined case where the suspended membrane is both anisotropic and inhomogeneous. Taken together with analysis of measurement sensitivity, we aim to provide a general guideline for data extraction methodologies for dual-side TDTR on anisotropic and/or inhomogeneous suspended thin films.

Atomic Layer Deposition of Iridium Thin Films Using Sequential Oxygen and Hydrogen Pulses

Atomic layer deposition (ALD) is an advanced thin-film deposition method based on self-limiting surface reactions that allows for the controlled deposition of conformal, high-quality thin films of various materials. In this study, we aimed to explore how modifying the deposition chemistry affects the growth and properties of iridium films. We demonstrated a new ALD process using sequential pulses of iridium acetylacetonate [Ir(acac)3], oxygen (O2), and hydrogen (H2) and compared this to the established Ir(acac)3 + O2 process in the wide temperature range of 200–350 °C. A reaction scheme is proposed to explain how both oxygen and hydrogen affect the film growth. Comprehensive information on film properties was obtained for both processes. In particular, the strong (111) texture seen in this study has not been reported before for ALD iridium films. Changes in film properties, especially lowered resistivity, stronger (111) texture, and faster nucleation compared to the Ir(acac)3 + O2 process, should motivate...

Fabrication of multilayered nanofluidic membranes through silicon templates.

We present a new fabrication method for solid-state nanoporous membranes based on sacrificial template structures made of silicon. The process consists of creating membranes by evaporating thin-films on sacrificial templates which, after their selective removal, opens the nanopores and releases the free-standing membranes. This way it is possible to define the geometry of the pore by design and to build the membrane by stacking thin-films of various materials through evaporation. Such a membrane with controlled porosity, pore geometry, thickness and nano-channel composition provides new opportunities for selective chemical functionalization, gating, electrical sensing or electrical stimulation inside the nanopore.

Surface modification and cathodic electrophoretic deposition of ceramic materials and composites using celestine blue dye

A new method has been developed for the surface modification of inorganic particles, which allowed their efficient electrostatic dispersion and cathodic electrophoretic deposition (EPD). The approach is based on the use of cationic celestine blue (CB) dye as a charging and dispersing agent. The key advantages of this approach are related to its applicability to different materials and strong adsorption of CB to the inorganic surfaces, which is of critical importance for efficient particle dispersion. Proof-of-concept studies involved the EPD of thin films of various materials, such as TiO2, MnO2, Mn3O4, BaTiO3, halloysite nanotubes, zirconia and yttria. The results of the deposition rate measurements, Fourier transform infrared spectroscopy, UV-vis and quartz crystal microbalance studies provided an insight into the mechanism of CB adsorption, which involved the interactions of the OH groups of the catechol ligand of CB and metal atoms on the particle surface. It was demonstrated that CB can be used as an efficient dispersing agent for the nanoparticle synthesis by chemical precipitation methods. The feasibility of EPD of various oxide materials paved the way to the EPD of various composites using CB as a co-dispersant for the individual components. Thin films of individual oxides and composites were investigated by electron microscopy and X-ray diffraction methods. The benefits of cathodic EPD for nanotechnology were demonstrated by the formation of nanostructured MnO2 films on commercial high surface area current collectors for energy storage in electrochemical supercapacitors. Testing results showed that the method allowed the fabrication of efficient electrodes with high capacitance and excellent capacitance retention at high charge–discharge rates. The new method paves the way for the deposition of other functional materials and composites for advanced applications.

Influence of atomic layer deposited coatings for MEMS applications: a review

This paper reviews the influence of coating MEMS devices using atomic layer deposition (ALD) to produce nanometer-thin films. It has recently become a subject of great interest for ultrathin film deposition in many various applications such as microelectronics, photovoltaic, dynamic random access memory (DRAM), and microelectromechanical system (MEMS). Atomic layer deposition (ALD) is a thin film growth technique that utilises alternating, self-saturation chemical reactions between gaseous precursors to achieve deposited nanoscale layers. The ALD process is capable of depositing a variety of thin-film materials to protect MEMS devices from electrical break down, mechanical wear and stiction failure. ALD ensures conformal film coverage on all sides of the MEMS device and can be performed at relatively low temperature. The ALD film thickness can be precisely controlled at the atomic level as each reaction cycle deposits approximately one atomic monolayer. It facilitates surface deposition on a variety of substrates that have low melting temperature. Eventually it could contribute to widen nanoscale MEMS applications and be advantageous in other emerging areas.

IR spectroscopic determination of the refractive index and thickness of hydrogenated silicon layers

IR spectroscopic techniques widely used to determine the thickness and refractive index of layers and thin films of various materials are adapted for determining those of hydrogenated silicon layers. Based on a literature analysis, three formulas are chosen which enable the refractive index and thickness of such layers to be determined from reflection and transmission spectra. The formulas are applicable, with some restrictions, to other samples in the form of relatively transparent layers (films) on transparent substrates. Experimental data are presented that illustrate the use of the formulas.

Silicon nanotips formed by self-assembled Au nanoparticle mask

The Au nanoparticle monolayer is formed by self-assembly technology on the Si substrates terminated with different functional groups. Silicon nanotips were fabricated by a self-assembled gold colloidal particle monolayer as an etch mask. The silicon nanotips with high density and uniformity in height and shape were obtained using reactive ion etching (RIE). The Si nanotips on the surface of the 3-aminopropyltrimethoxysilane (APTMS)-treated Si substrate are less-ordered array and uniformity than 3-mercaptopropyltrimethoxysilane (MPTMS)-treated Si substrate at the same etching conditions. The ordered array and uniformity of Si nanotips on the APTMS-modified Si substrate was improved through heat-treatment. This result is implied the different functional groups on the Si surfaces could affect the formation of the Si nanostructures during RIE process. The uniformly nanotip pattern with height of >20 nm is obtained on the etched nanoparticle-coated Si substrate. This method can be applied to patterning a wide variety of thin film materials into tip arrays.