Inorganic Thin Films Research Articles

Highly Efficient Full‐Color Inorganic LEDs on a Single Wafer by Using Multiple Adhesive Bonding

AbstractMonolithic integration is a promising way to realize full‐color high‐resolution displays. However, it is still a challenge to realize a highly efficient full‐color light‐emitting diode (LED) adopting color conversion layer. In this work, red, green, and blue inorganic LED thin films grown on respective substrates for high‐quality epitaxial layers are integrated on a single substrate using a multiple adhesive bonding technique. It is verified that the stacked thin films are structurally stable. After the multiple bonding, respective subpixels are formed by using standard photolithography only without a mass transfer process, showing the possibility of applying them to a high‐resolution micro‐LED display. Even after the bonding, the device still maintains high efficiency without deteriorating performance. The integrated subpixels are not only independently operated by controlling input power, but the light emission can also cover a wide range of the color space, about 83% compared to Rec.2020 color space.

Morphological and mechanical characterization of chitosan/gelatin/silica-gentamicin/bioactive glass coatings on orthopaedic metallic implant materials

Metals are the most widely used materials for orthopedics and dentistry due to their high mechanical properties. However, for certain uses like fixation plates and screws, dental implants, and osseo-articular prosthesis, their surface characteristics such as non-toxic and non-corrosive behavior, good cell adhesion and proliferation, and resistance to bacterial biofilm formation should be accompanied with high mechanical performance. One way to improve metallic implant performance in vivo is to coat them with biopolymer or inorganic thin films. This work describes two multifunctional coating systems for orthopedic titanium and stainless steel implants. Titanium implants were coated with a system consisting of a base hybrid sol-gel layer with bioactive glass particles (applied via spraying) and a top chitosan/gelatin layer with silica-gentamicin nanoparticles (applied via electrophoretic deposition, EPD). Stainless steel implants, which are designed to be removable, were coated only with the top chitosan/gelatin/ silica-gentamicin nanoparticles layer with the aim of providing a temporal attachment to bone and to combat possible bacterial adhesion. The microstructural and mechanical characterization of the coatings was conducted by optical microscopy, transmission and scanning electron microscopy, digital image processing, as well as nanoindentation and nanoscratch tests to advance the understanding of their elastic-plastic, morphologic and adhesive behavior. The coatings were homogeneous, providing good coverage to both substrates. Their surface properties, such as roughness and wettability, indicate that they represent excellent substrates for cell attachment. Bioactive glass particles can be added to titanium implant systems as bioactive components without affecting adhesion or mechanical performance of the chitosan/gelatin/silica-gentamicin nanoparticle EPD coatings. The increase in both hardness and elastic modulus of the coated systems could be due to the presence of the silica-gentamicin nanoparticles and their compaction during the penetration of the indenter. When the samples are subjected to scratch tests, the critical load increases with the reinforcement of the coatings by the silica-gentamicin nanoparticles absorbing the applied load and maintaining the elastic properties of the coatings.

Review of flexible microelectromechanical system sensors and devices

Today, the vast majority of microelectromechanical system (MEMS) sensors are mechanically rigid and therefore suffer from disadvantages when used in intimately wearable or bio-integrated applications. By applying new engineering strategies, mechanically bendable and stretchable MEMS devices have been successfully demonstrated. This article reviews recent progress in this area, focusing on high-performance flexible devices based on inorganic thin films. We start with the common design and fabrication strategies for flexibility and stretchability, summarize the recent application-oriented flexible devices, and conclude with criteria and opportunities for the future development of flexible MEMS sensors.

First Principles Study of Reactions in Hybrid Film Growth: The Role of the Organic Precursor

Hybrid materials are a special class of materials with tunable features. This is related to their diphasic structures that leads to multifunctional materials with a wide range of applications. Molecular layer deposition (MLD) enables the fabrication of ultrathin and conformal hybrid films using sequential, selflimiting reactions, similar to ALD. Despite growing interest in these materials, there is little understanding of the atomistic mechanism of MLD film growth.In this contribution, we explore the molecular mechanisms of the growth of different hybrid organic−inorganic thin films by using density functional theory (DFT). The prototype for MLD organic−inorganic hybrids are composed of thin films of aluminium alkoxides, known as ”alucones”. We investigate the MLD reaction products between the post-TMA Monomethyl-Al2O3 (Al-CH3-Al2O3) and Dimethyl-Al2O3 (Al(CH3)2-Al2O3) surface and the organic precursors ethylene glycol (EG) and glycerol (GL). The DFT calculations show that while the organic precursors can bind to the TMA fragments via formation of Al-O bonds and loss of CH4, it is most favorable for the organic precursors to lie flat and create so-called double reactions through two terminal hydroxyl groups with the surface fragments, where the terminal groups bind to Al. For EG this potentially removes all the active sites and growth will be less favorable. For GL the third hydroxyl group is available and growth can proceed. We also showed that the TMA in the next pulse reacts favourably with this OH from GL.We also explored the growth mechanism of magnesium containing hybrid films known as “magnesicone” from the reaction of EG and GL at MgCp-terminated MgO(100) as a model system. Interaction energies presented some clear differences in reaction mechanism of films grown with EG and GL. While the ligand elimination process is favorable for both precursors, EG prefers to orient in a flat configuration and interacts at the MgO(100) surface and GL species prefers to lie in an upright position. As a consequence the change in thickness for GL-based process is larger than for EG-based process, resulting in a thicker GL-based magnesicone compared to the EG-based magnesicone.Finally we use DFT to explore the growth mechanism of titanium-containing hybrid organic−inorganic films known as “titanicones”. We investigate the reaction mechanism of titanicones grown using titanium tetrachloride (TiCl4) as metal source and either ethylene glycol (EG) or glycerol (GL) as organic reactants. This investigation contributes to the understanding of growth process of EG and GL based hybrid films at the molecular level and is valuable in supporting experimental data on hybrid film growth.

(Invited) Novel Chemistries for Layer-by-Layer Etching of 2D Semiconductor Coatings and Organic-Inorganic Hybrid Materials

Here we report two new advances in atomic layer etching (ALEt) that extend our range of capabilities in nanoscale device fabrication. Semiconductor device manufacturing is limited by our ability to precisely deposit and remove thin film layers at the various levels of multistep device fabrication processes. Consequently, innovations in atomic layer deposition (ALD) and etching methods are essential. ALD-based methods have matured significantly and are now used extensively in semiconductor fabs. Recently, there has been an intense focus on developing ALEt methods. In particular, thermal ALEt has been shown to precisely remove ALD inorganic thin films selectively and on complex structures. These capabilities have opened new possibilities for nanoscale device design. Here, we report a new thermal etching process similar to ALEt for removing hybrid inorganic-organic layers that we call molecular layer etching (MLEt). This MLEt process uses vapor phase lithium organic salts in combination with trimethyl aluminum to perform layer-by-layer etching of molecular layer deposition (MLD) coatings.Ultra-thin layers of two dimensional (2D) transition metal dichalcogenide (TMD) semiconductors can exhibit exceptional electrical, optical, magnetic, mechanical and chemical properties. This allows the exploration of internal quantum degrees of freedom of electrons and their potential application in optoelectronic, energy, and sensor devices. Among the various 2D-TMDs, MoS2 has shown exciting material properties and this has stimulated the exploration of a variety thin film synthesis methods such as physical vapor deposition (PVD), chemical vapor deposition (CVD), and solution based methods. In addition, the ALD community is investigating ALD methods for MoS2 growth. Here we report the thermal ALEt of ALD MoS2 thin films. We believe the successful combination of both ALD and ALEt of MoS2 and other TMDs can pave the way to control the synthesis of 2D-TMD layers over large areas. Combining ALD and ALEt will allow MoS2 interface engineering and enable MoS2 integration into the large-scale manufacturing of future complex device structures.

Quaternary Oxidized Carbon Nanohorns—Based Nanohybrid as Sensing Coating for Room Temperature Resistive Humidity Monitoring

We report the relative humidity (RH) sensing response of a resistive sensor, employing sensing layers, based on a quaternary organic–inorganic hybrid nanocomposite comprising oxidized carbon nanohorns (CNHox), graphene oxide (GO), tin dioxide, and polyvinylpyrrolidone (PVP), at 1/1/1/1 and 0.75/0.75/1/1/1 mass ratios. The sensing structure comprises a silicon substrate, a SiO2 layer, and interdigitated transducer (IDT) electrodes. The sensing film was deposited via the drop-casting method on the sensing structure. The morphology and the composition of the sensing layers were investigated through Scanning Electron Microscopy (SEM), X-ray diffraction (XRD), and RAMAN spectroscopy. The organic–inorganic quaternary hybrid-based thin film’s resistance increased when the sensors were exposed to relative humidity ranging from 0 to 100%. The manufactured devices show a room temperature response comparable to that of a commercial capacitive humidity sensor and characterized by excellent linearity, rapid response and recovery times, and good sensitivity. While the sensor with CNHox/GO/SnO2/PVP at 0.75/0.75/1/1 as the sensing layer has the best performance in terms of linearity and recovery time, the structures employing the CNHox/GO/SnO2/PVP at 1/1/1/1 (mass ratio) have a better performance in terms of relative sensitivity. We explained each constituent of the quaternary hybrid nanocomposites’ sensing role based on their chemical and physical properties, and mutual interactions. Different alternative mechanisms were taken into consideration and discussed. Based on the sensing results, we presume that the effect of the p-type semiconductor behavior of CNHox and GO, correlated with swelling of PVP, dominates and leads to the overall increasing resistance of the sensing layer. The hard–soft acid–base (HSAB) principle also supports this mechanism.

Insights into the exceptional stability of the molecular precursor solution for Cu2ZnSnS4 solar absorber

Environment friendly molecular precursors are extensively studied for green, economical and scalable fabrication of inorganic thin films for various device applications. For compound semiconductors such as the chalcogenide solar absorber Cu2ZnSnS4 (CZTS), the stability of such precursor solution is highly sought after. The longer shelf life of the precursor could significantly improve the phase purity as well as the reproducibility of the resulting films, and also would aid the industrial scaling up of the fabrication process. Herein, the reason behind the exceptional stability shown by a precursor solution for CZTS is explored, by probing the nature of interaction between its various components. The unique combination of solvent and the sulfur source is shown as favorable for the stable bonds in the solution, especially the predominant bidentate bridging of sulfur source to the metal atoms. The insights elucidated through simple spectroscopic techniques can be handy when designing such sustainable precursors for other functional chalcogenides and technologically important inorganic compounds.

Silicone encapsulation of thin-film SiO x , SiO x N y and SiC for modern electronic medical implants: a comparative long-term ageing study

Objective. Ensuring the longevity of implantable devices is critical for their clinical usefulness. This is commonly achieved by hermetically sealing the sensitive electronics in a water impermeable housing, however, this method limits miniaturisation. Alternatively, silicone encapsulation has demonstrated long-term protection of implanted thick-film electronic devices. However, much of the current conformal packaging research is focused on more rigid coatings, such as parylene, liquid crystal polymers and novel inorganic layers. Here, we consider the potential of silicone to protect implants using thin-film technology with features 33 times smaller than thick-film counterparts. Approach. Aluminium interdigitated comb structures under plasma-enhanced chemical vapour deposited passivation (SiO x , SiO x N y , SiO x N y + SiC) were encapsulated in medical grade silicones, with a total of six passivation/silicone combinations. Samples were aged in phosphate-buffered saline at 67 ∘C for up to 694 days under a continuous ±5 V biphasic waveform. Periodic electrochemical impedance spectroscopy measurements monitored for leakage currents and degradation of the metal traces. Fourier-transform infrared spectroscopy, x-ray photoelectron spectroscopy, focused-ion-beam and scanning-electron- microscopy were employed to determine any encapsulation material changes. Main results. No silicone delamination, passivation dissolution, or metal corrosion was observed during ageing. Impedances greater than 100 GΩ were maintained between the aluminium tracks for silicone encapsulation over SiO x N y and SiC passivations. For these samples the only observed failure mode was open-circuit wire bonds. In contrast, progressive hydration of the SiO x caused its resistance to decrease by an order of magnitude. Significance. These results demonstrate silicone encapsulation offers excellent protection to thin-film conducting tracks when combined with appropriate inorganic thin films. This conclusion corresponds to previous reliability studies of silicone encapsulation in aqueous environments, but with a larger sample size. Therefore, we believe silicone encapsulation to be a realistic means of providing long-term protection for the circuits of implanted electronic medical devices.

A Model for Adsorption and Diffusion in Water Vapor Barrier Films

A model for describing the diffusion behavior of water vapor in barrier films is developed and applied to the cases of 1) pure polyethylene terephthalate (PET); 2) an inorganic thin film (ITF) with defects on a PET substrate (ITF/PET); and 3) PET/ITF/PET. The normalized concentration profile and the relative mass of water vapor in the ITF/PET and PET/ITF/PET barrier films are simulated as a function of diffusion time by considering the sorption and desorption of water vapor. The number of atoms penetrating the barrier films is quantitatively evaluated by the concentration gradient of water vapor, which is related to the water vapor transmission rate (WVTR). The simulated WVTR values in pure PET, PET/SiOx, and PET/SiOx/ORM layered structures are in good agreement with the experimental ones.

Ductile‐Metal Ag as Buffer Layer for Flexible Self‐Powered Ag2S Photodetectors

AbstractThe rigid nature of inorganic semiconductors makes them rarely use in flexible devices till now. For the first time, ductile‐metal Ag is used as buffering layer to bond the inorganic semiconductor thin films and polymer substrate forming a sandwich structure, which has outstanding flexible photoelectric character. The ductile thin Ag layer under Ag2S thin film acts as electrode and buffering material between the Ag2S and polyimide (PI) layers. The strong bonding interaction between Ag2S and Ag can reduce the stress force in Ag2S thin films that is generated during bending, which enhances its flexibility. The resulted Ag2S/Ag/PI film shows excellent electrical performance retentivity. After more than 104 cycles bending test, the conductivity of the Ag2S/Ag/PI films has almost not changed. The prepared Au/PEDOT:PSS/Ag2S/Ag/PI photodetectors are stable in air or N2. It can bear a small bending radius as low as 1.5 mm for ≈4000 bending cycles test without drastic performance decay. In addition, the Ag2S/Ag based flexible photodetectors show a wide spectral response from ultraviolet to near infrared.

Defect-passivation of organometal trihalide perovskite with functionalized organic small molecule for enhanced device performance and stability

Defects in solution-processed organic and inorganic halide perovskite thin films deteriorate their photovoltaic performance and stability. Here, a bisimidazole-based organic small molecular hole transport material (HTM) that can suppress interfacial defects of the perovskite with its functional groups working as Lewis bases is newly introduced. Surface passivation of perovskite film leads to the reduction in non-radiative recombination trap density as well as the improvement of its crystallinity, consequently enhancing the efficiency of perovskite solar cell (PSC) from 16.3% to 18.3% with superior stability, preserving 92% of its initial efficiency for 500 h in an atmosphere.

Black-Box Optimization for Automated Discovery.

In chemistry and materials science, researchers and engineers discover, design, and optimize chemical compounds or materials with their professional knowledge and techniques. At the highest level of abstraction, this process is formulated as black-box optimization. For instance, the trial-and-error process of synthesizing various molecules for better material properties can be regarded as optimizing a black-box function describing the relation between a chemical formula and its properties. Various black-box optimization algorithms have been developed in the machine learning and statistics communities. Recently, a number of researchers have reported successful applications of such algorithms to chemistry. They include the design of photofunctional molecules and medical drugs, optimization of thermal emission materials and high Li-ion conductive solid electrolytes, and discovery of a new phase in inorganic thin films for solar cells.There are a wide variety of algorithms available for black-box optimization, such as Bayesian optimization, reinforcement learning, and active learning. Practitioners need to select an appropriate algorithm or, in some cases, develop novel algorithms to meet their demands. It is also necessary to determine how to best combine machine learning techniques with quantum mechanics- and molecular mechanics-based simulations, and experiments. In this Account, we give an overview of recent studies regarding automated discovery, design, and optimization based on black-box optimization. The Account covers the following algorithms: Bayesian optimization to optimize the chemical or physical properties, an optimization method using a quantum annealer, best-arm identification, gray-box optimization, and reinforcement learning. In addition, we introduce active learning and boundless objective-free exploration, which may not fall into the category of black-box optimization.Data quality and quantity are key for the success of these automated discovery techniques. As laboratory automation and robotics are put forward, automated discovery algorithms would be able to match human performance at least in some domains in the near future.

Study and performance analysis of Perovskite solar cell structure based on organic and inorganic thin films

In this paper, the performance of (CuI/CH3NH3PbI3-xClx/ZnO/TCO) Perovskite solar cell (PSC) is studied using Solar Cell Capacitance Simulator (SCAPS-1D). In this solar cell structure, the absorber layer CH3NH3PbI3-xClx characterized by a highly efficient absorption, the CuI layer is used as a hole transporter material (HTM), and ZnO layer is used as an electron transporter material (ETM). They exhibit a good chemical stability and low cost of synthesis procedure compared with conventional layers 2,2',7,7'-Tetrakis [N,N-di(4-methoxyphenyl)amino]-9,9'-spirobifluorene (Spiro-OMETAD) and Phenyl-C61-butyric acid methyl ester (PCBM). The optimum configuration is obtained by varying the thickness of different layers, and the simulation results of the investigated PSC exhibit Voc = 1.256 V, Jsc = 25.06 mA/Cm2, FF = 80.67 % and a conversion efficiency of 25.40 %. The results are very promising and the proposed configuration performs better; it can be also considered as a good candidate for developing cheaper and efficient PSCs.

Chemical vapour deposition

Chemical vapour deposition (CVD) is a powerful technology for producing high-quality solid thin films and coatings. Although widely used in modern industries, it is continuously being developed as it is adapted to new materials. Today, CVD synthesis is being pushed to new heights with the precise manufacturing of both inorganic thin films of 2D materials and high-purity polymeric thin films that can be conformally deposited on various substrates. In this Primer, an overview of the CVD technique, including instrument construction, process control, material characterization and reproducibility issues, is provided. By taking graphene, 2D transition metal dichalcogenides (TMDs) and polymeric thin films as typical examples, the best practices for experimentation involving substrate pretreatment, high-temperature growth and post-growth processes are presented. Recent advances and scaling-up challenges are also highlighted. By analysing current limitations and optimizations, we also provide insight into possible future directions for the method, including reactor design for high-throughput and low-temperature growth of thin films. This Primer on chemical vapour deposition summarizes current and emerging experimental set-ups as well as common characterization approaches used to determine thin film formation and quality as applied to graphene and other novel 2D materials.

A TbPc2 sub-monolayer deposit on a titanium dioxide ultrathin film: magnetic, morphological, and chemical insights

Thin inorganic films (i.e., metal oxides) are often used as decoupling layers to optimize the interactions between the molecular magnetic layers and metallic surfaces.

Organic–inorganic hybrid thin film light-emitting devices: interfacial engineering and device physics

Organic–inorganic hybrid LEDs are reviewed from the perspectives of organic and inorganic functional materials, interfacial engineering, device structures and device physics.

Molecular layer deposition of photoactive metal-naphthalene hybrid thin films.

We here report on photoactive organic-inorganic hybrid thin films prepared by the molecular layer deposition (MLD) method. The new series of hybrid films deposited using 2,6-naphthalenedicarboxylic acid (2,6-NDC) and either hafnium chloride (HfCl4), yttrium tetramethylheptanedionate (Y(thd)3) or titanium chloride (TiCl4) were compared with the known zirconium chloride (ZrCl4) based system. All metal-naphthalene films are amorphous as-deposited and show self-saturating growth as expected for an ideal MLD process with varied growth rates depending on the choice of metal precursor. The growth was studied in situ using quartz crystal microbalance (QCM) and the films were further characterised using spectroscopic ellipsometry (SE), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), and UV-Vis and photoluminescence (PL) spectroscopy to obtain information on their physicochemical properties. The hybrid thin films display intense blue photoluminescence, except for the Ti-organic complex in which titanium clusters were found to be an effective PL quencher for the organic linker. We demonstrate how the optical properties of the films depend on the choice of metal component to make a foundation for further studies on these types of organic-inorganic hybrid materials for applications as photoactive agents.

Two-colour photoswitching in photoresponsive inorganic thin films

Herein we present two-colour photoswitching in a photoresponsive thin film based on a Ru-sulfoxide complex immobilized onto a ZrO2 surface.

Memory Devices via Unipolar Resistive Switching in Symmetric Organic–Inorganic Perovskite Nanoscale Heterolayers

Organic–inorganic hybrid perovskite thin films with nanostructured polycrystalline grains have shown great potential in various nanoscale optoelectrical applications. Among them, the field of elect...

Approach to Transparent Photovoltaics Based on Wide Band Gap Sb2S3 Absorber Layers and Optics-Based Device Optimization

Numerous methods have been employed for utilizing inorganic thin films to improve the stability of transparent photovoltaics (TPVs). However, the use of these methods was restricted due to limitati...