Search

In this paper, the scientific progress in the field of thin film materials and their associated sensing technologies are described comprehensively to address the directions for future research and developments as per the need of modern-day technologies. To begin with, we briefly discussed the fundamental synthesis approaches for advanced thin films with an emphasis on the properties necessary for controlled fabrication (e.g., the elemental ratio and spatial arrangement). Subsequently, we explored the control, characterization, and optimization of hybrid porous thin films with respect to diverse sensing applications. The application of hybrid porous thin film materials has also been discussed in relation to the mechanisms used for biological, optical, electrical, acoustic, and other advanced sensing techniques (e.g., surface-enhanced Raman scattering (SERS)). Finally, conclusions are drawn to highlight the current status of thin film-based sensing technology along with its opportunities and challenges.

This work was supported by Spanish MINECO (FIS2013-45469 and FIS2016-76058 (AEI/FEDER,EU)).

The structure and thickness of the chemiresistive thin films can significantly affect their gas sensing performances for the heating-typed sensors. Under light irradiation, however, their influences are still to be addressed. In present paper, the multilayered ZnO porous thin films with different (three types) micro/nanostructures and controllable thickness are fabricated via layer by layer construction of the self-assembled colloidal-layers. The structural and thickness effects of such films on the gas sensing performances to NO2 under ultraviolet (UV) illumination are experimentally studied. It has been found that under UV irradiation, the responses of the ZnO porous thin films to NO2 increase upto the maxima with the rising film thickness. Further increasing the thickness would lead to the insignificantly or gradually decreasing responses. The film thicknesses corresponding to the maximal responses are associated with the porous structures and the porosity of the thin films. The films with the higher porosity would lead to the higher maximal responses and the larger corresponding film-thicknesses, or vice versa. Such thickness and porous-structure dependences of the responses are attributed to the ever-decaying light intensity (and hence ever-decreasing photo-generated carrier concentration) in the films along the depth from the films’ surface. This study is of importance in design and development of the light illuminating-typed gas sensing devices with high performances.

Here, pure ZnO, WO3 and Pd/WO3–ZnO composite porous thin films were successfully synthesized directly on porous silicon by a reactive DC magnetron sputtering technique. A sensor based on the Pd/WO3–ZnO composite porous thin films showed remarkably improved H2 sensing performance with good stability and excellent selectivity compared to that of pure WO3 and ZnO, at a relatively lower operating temperature (200 °C) and with a low detection range of 10–1000 ppm. The enhanced response can be attributed to the heterojunction formed between two dissimilar materials. The underlying mechanism behind their good performance for H2 gas was discussed in detail.

We report a new methodology based on glancing angle deposition (GLAD) of an organic molecule in combination with perpendicular growth of a second inorganic material. The resulting thin films retain a very well-defined tilted columnar microstructure characteristic of GLAD with the inorganic material embedded inside the columns. We refer to this new methodology as growth assisted by glancing angle deposition or GAGLAD, since the material of interest (here, the inorganic) grows in the form of tilted columns, though it is deposited under a nonglancing configuration. As a >proof of concept>, we have used silver and zinc oxide as the perpendicularly deposited material since they usually form ill-defined columnar microstructures at room temperature by GLAD. By means of our GAGLAD methodology, the typical tilted columnar microstructure can be developed for materials that otherwise do not form ordered structures under conventional GLAD. This simple methodology broadens significantly the range of materials where control of the microstructure can be achieved by tuning the geometrical deposition parameters. The two examples presented here, Ag/Alq3 and ZnO/Alq3, have been deposited by physical vapor deposition (PVD) and plasma enhanced chemical vapor deposition (PECVD), respectively: two different vacuum techniques that illustrate the generality of the proposed technique. The two type of hybrid samples present very interesting properties that demonstrate the potentiality of GAGLAD. On one hand, the Ag/Alq3 samples present highly optical anisotropic properties when they are analyzed with linearly polarized light. To our knowledge, these Ag/Alq3 samples present the highest angular selectivity reported in the visible range. On the other hand, ZnO/Alq3 samples are used to develop highly porous ZnO thin films by using Alq3 as sacrificial material. In this way, antireflective ZnO samples with very low refractive index and extinction coefficient have been obtained.

Introduction The sensing performance of mixed-potential gas sensors is highly dependent on the electrode microstructure. Recently, much effort has been made to improve the sensor performance by engineering of the electrode microstructure [1, 2]. Nevertheless, the different microstructure parameters, such as thickness, porosity, and three phase boundary (TPB), contribute jointly to the sensing response, and their respective contributions are usually difficult to identify. Thus, deviation of the apparent sensor behavior from the reality is usually unable to judge due to the uncertain effect of electrode catalytic reaction. In order to unravel the true response behavior, it would be necessary to reduce or minimize impact of the electrode diffusion-reaction process and control the microstructure, which could be achieved by using a very thin electrode with well-defined and controllable morphology. Herein, we fabricated thin ordered SnO2 sensing electrodes on YSZ substrate by employing a Polystyrene (PS) sphere-template method [3]. By varying the PS sphere diameter, three sensors of different electrode thickness and electrode/electrolyte interface were obtained. The gas sensing characteristics of the sensors were systematically studied. The sensing behavior was discussed in relation to variation of the electrode process and TPB density. Sensor fabrication and characterization As depicted in Figure 1, highly-ordered porous thin film sensors were prepared by using PS sphere templates in 200 nm, 500 nm and 1000 nm diameters. SEM, TEM and AFM images of SnO2 porous film electrodes were presented in Figure 2. Periodically ordered films of inverse opal structure were observed, with uniform circular pore openings and interconnected walls as the skeleton. Each film was porous and a homogenous assembly of 10-20 nm sized particles. The wall height was roughly half of the PS sphere size, which increased from 121 nm to 248 nm and 448 nm for the three PF films. Sensing performance Figure 3a and b show the response values and response time of the three PF sensors as a function of hydrogen concentration at 500 °C. Obviously, the response significantly increased, i.e., became more negative, with decreasing template diameters, while the response time of the three sensors was short and generally rather close to each other, with a value of 4.5 s-6 s for 500 ppm H2 at 500 °C. Figure 3c displays the cross-sensitivities of the PF sensors to 100 ppm various gases at 450 °C. The PF sensors exhibited much poorer H2 selectivity than regular thick film sensors [4]. The small film thickness and porous nature of the PF SE are highly favorable for the gas transport from the gas phase to the TPB, which are beneficial to the response kinetics. That the three PF sensors exhibited very close response time despite their minor difference in the film thickness, suggesting absence of significant electrode process and large H2 concentration reduction. This may allow us to study the effect of the TPB density on the sensing response. The TPB length was thus estimated for the PF sensors (Figure 4a). Clearly, the TPB density increased from 56.8 μm-1 to 89.7 μm-1 with the decreasing template diameters. It can also be seen that for each H2 concentration, the response increased (became more negative) monotonically with increasing TPB density (Figure 4b-c). It should be noted that thin film favors fast response kinetics and large response but may be disadvantageous to the selectivity. To achieve good overall sensing performance, e.g., fast response kinetics, large response, and high selectivity, careful tuning of the film thickness and TPB density would be demanded. References [1] N. Miura, T. Sato, S.A. Anggraini, H. Ikeda, S. Zhuiykov, A review of mixed-potential type zirconia-based gas sensors, Ionics. 20(2014) 901-25. doi.org/10.1007/s11581-014-1140-1. [2] G. Lu, Q. Diao, C. Yin, S. Yang, Y. Guan, X. Cheng, et al., High performance mixed-potential type NOx sensor based on stabilized zirconia and oxide electrode, Solid State Ionics. 262(2014) 292-7. doi:10.1016/j.ssi.2014.01.037. [3] L. Jia, W. Cai, H. Wang, Layer-by-layer strategy for the general synthesis of 2D ordered micro/nanostructured porous arrays: structural, morphological and compositional controllability, Journal of Materials Chemistry. 19(2009) 7301-7. doi: 10.1016/j.snb.2011.02.051. [4] J. Yi, H. Zhang, Z. Zhang, D. Chen, Hierarchical porous hollow SnO2 nanofiber sensing electrode for high performance potentiometric H2 sensor, Sensors and Actuators B: Chemical. 268(2018) 456-64. doi.org/10.1016/j.snb.2018.04.086. Figure 1

The selective incorporation of deposition species with preferential directionality is analyzed during the growth of TiO thin films by magnetron sputtering. Using wisely-designed collimators, tilted nanocolumnar morphologies are grown in a ballistic deposition regime, i.e. when most deposition species arrive at the film surface along well-defined preferential directions, and also in a thermalized deposition regime, when these species follow an isotropic momentum distribution in the plasma gas. The obtained results suggest that the use of particle collimators may promote the growth of porous thin films even in the classical magnetron sputtering configuration, when the target and the substrate are parallel. General insights are given on this approach and, as a proof of concept, its principles applied for the synthesis of nanostructured films in a laboratory-size reactor.

High-performance chemiresistive sensors were made using a porous thin film of single-walled carbon nanotubes (CNTs) coated with a carbazolylethynylene (Tg-Car) oligomer for trace vapor detection of nitroaromatic explosives. The sensors detect low concentrations of 4-nitrotoluene (NT), 2,4,6-trinitrotoluene (TNT), and 2,4-dinitrotoluene (DNT) vapors at ppb to ppt levels. The sensors also show high selectivity to NT from other common organic reagents at significantly higher vapor concentrations. Furthermore, by using Tg-Car/CNT sensors and uncoated CNT sensors in parallel, differential sensing of NT, TNT, and DNT vapors was achieved. This work provides a methodology to create selective CNT-based sensors and sensor arrays.

Developing inexpensive and efficient electrocatalysts without using precious metals for the hydrogen evolution reaction (HER) is essential for the realization of economical clean energy production. Here we demonstrate a facile approach to access interconnected three-dimensional (3-D) porous tungsten-based (WS2 and WC) thin-films without using any templates. Benefiting from the 3-D open frameworks of these highly porous thin-films, there are enormous amounts of exposed active sites and efficient mass transport in favor of the HER. Both electrodes exhibit excellent catalytic activity towards HER with onset overpotentials of ∼100 mV for WS2 and ∼120 mV for WC, and similar Tafel slopes of ∼67 mV per decade. The long-term operation of these thin-film electrodes is confirmed by their electrochemical stability test. With the low loading mass (∼80 and ∼160 μg cm−2 for WS2 and WC, respectively), these porous thin-films are among the best tungsten-based HER electrocatalysts.

In this work we have developed an infiltration methodology to incorporate metal nanoparticles (NPs) of controlled size and shape into the open voids available in oblique angle deposited thin films. These NPs exhibited well-defined surface plasmon resonances (SPRs). The nanometric confined space provided by their porous microstructure has been used as a template for the growth of anisotropic NPs with interesting SPR properties. The fabrication methodology has been applied for the preparation of films with embedded Ag and Au NPs with two associated plasmon resonance features that developed a dichroic behaviour when examined with linearly polarized light. A confined alloying process was induced by near IR nanosecond laser irradiation yielding bimetallic NPs with SPR features covering a large zone of the electromagnetic spectrum. The possibilities of the method for the tailored fabrication of a wide range colour palette based on SPR features are highlighted.

Open porous and transparent microcolumnar structures of TiO2 prepared by physical vapour deposition in glancing angle configuration (GLAD-PVD) have been used as host matrices for two different fluorescent cationic porphyrins, 5-(N-methyl 4-pyridyl)-10,15,20-triphenyl porphine chloride (MMPyP) and meso-tetra (N-methyl 4-pyridyl) porphine tetrachloride (TMPyP). The porphyrins have been anchored by electrostatic interactions to the microcolumns by self-assembly through the dip-coating method. These porphyrin/TiO2 composites have been used as gas sensors for ammonia and amines through previous protonation of the porphyrin with HCl followed by subsequent exposure to the basic analyte. UV–vis absorption, emission, and time-resolved spectroscopies have been used to confirm the protonation–deprotonation of the two porphyrins and to follow their spectral changes in the presence of the analytes. The monocationic porphyrin has been found to be more sensible (up to 10 times) than its tetracationic counterpart. This result has been attributed to the different anchoring arrangements of the two porphyrins to the TiO2 surface and their different states of aggregation within the film. Finally, there was an observed decrease of the emission fluorescence intensity in consecutive cycles of exposure and recovery due to the formation of ammonium chloride inside the film., We thank the Junta de Andalucía (Project: FQM-2310), the European Regional Development Funds program (EU-FEDER) and the Spanish Ministry of Economy and Competitiveness (Projects: MAT2013-40852-R, MAT2013-42900-P, MAT2014-57652-C2-2-R, MAT2015-69035-REDC, MINECO-CSIC 201560E055, PCIN-2015-169-C02-02 under a 2014 M-Era.Net project and RECUPERA 2020), for financial support. We acknowledge support by the CSIC Open Access Publication Initiative through its Unit of Information Resources for Research (URICI).

A novel molecularly imprinted conducting polymer (MICP) system with porous thin films of electropolymerized polypyrrole (Ppy) derivatives was successfully developed to detect a specific target molecule (e.g. theophylline). The porous MICP films grown on gold pore arrays through cyclic voltammetry showed increased sensing response in detecting theophylline compared to a conventional planar MICP film due to its improved sensing capacity.

Minimization of helices opens a door to impose novel functions derived from the dimensional shrinkage of optical, mechanical and electronic devices. Glancing angle deposition (GLAD) enables one to deposit three-dimensional helical porous thin films (HPTFs) composed of separated spiral micro/nano-columns. GLAD integrates a series of advantageous features, including one-step deposition, wafer-scale production with mono-handedness of spirals, flexible engineering of spiral materials and dimensions, and the adaption to various kinds of substrates. Herein, we briefly review the fabrication of HPTFs by GLAD, specific growth mechanisms, physical properties in structures, mechanics and chiral optics, and the emerging applications in green energy. A prospective outlook is presented to illuminate some promising developments in enantioselection, bio-dynamic analyses, wirelessly-controlled drug delivery and mass production.

Porous thin films grown at oblique angles by evaporation techniques are formed by tilted nanocolumnar structures which, depending on the material type and growth conditions, associate along certain preferential directions, giving rise to large domains. This arrangement, commonly denoted as bundling association, is investigated in the present work by performing fundamental experiments and growth simulations. It is proved that trapping processes of vapor species at the film surface, together with the shadowing mechanism, mediate the anisotropic widening of the nanocolumns and promote their preferential coalescence along certain directions, giving rise to domains with different shape and size. The role of these two processes is thoroughly studied in connection with the formation of these domains in materials as different as SiO and TiO., The authors thank the Junta de Andalucía (P12-FQM-2265) and the Spanish Ministry of Economy and Competitiveness (Projects, MAT2013-40852-R, MINECO-CSIC 201560E055) for financial support.

TiO(2) and SiO(2) porous thin films consisting of tilted nanocolumns prepared by glancing angle evaporation (GLAD) have been infiltrated with guest derivatives belonging to the family of perchlorinated trityl radicals, novel guest molecules presenting an open-shell electronic configuration associated with paramagnetism, fluorescence, and electroactivity. The main driving forces for infiltration from aqueous solutions of the carboxylate-substituted radical derivatives are the electrostatic interactions between their negative charge and the net positive charges induced on the film pores. Positive charges on the internal surface of the films were induced by either adjusting the radical solution pH at values lower than the point of zero charge (PZC) of the oxide or passivating the nanocolumns oxide surface with a positively charged aminosilane. The infiltrated composite thin films are robust and easy to handle thanks to the physical protection exerted by the film columns. They also keep the multifunctionality of the used guests, as confirmed by electron paramagnetic resonance (EPR), UV-vis spectroscopy, and fluorescence spectroscopy. To prove the electroactivity of the infiltrated porous films, a porous TiO(2) host layer was supported onto conductive indium tin oxide (ITO). By application of an appropriate redox potential, the guest radical molecules have been reversibly switched from their open-shell electronic configuration to their diamagnetic state and hence changed their optical properties. On the basis of these results, it is herein proposed that the appropriate surface functionalization of the pore internal surface of GLAD thin films can be used to prepare novel radical-oxide composite thin films usable for the development of robust switchable electrically driven photonic and magnetic devices.

Eine physikalische Deposition unter den Bedingungen eines schrag einfallenden Partikelflusses und begrenzter Adatom-Diffusion fuhrt zu Schichten mit einer saulenartigen Mikrostruktur. Diese Saulen sind in Richtung der Partikelquelle orientiert. Eine zusatzliche Substratrotation kann genutzt werden, um diese Strukturen in unterschiedlicher Gestalt (senkrechte und geneigte Saulen, Zick-Zack-Strukturen, Schrauben, Spiralen) zu entwickeln. Mit der Deposition unter schragem Partikeleinfall (GLAD) konnen porose dunne Schichten von isolierenden, halbleitenden und metallischen Materialien konstruiert werden. In dieser Arbeit werden die physikalischen Grundlagen der GLAD-Technologie vorgestellt, die Herstellung von Mikro- und Nano-Struktruren unterschiedlichen Habitus auf nicht strukturierten und vorstrukturierten Substraten demonstriert und auf einige potentielle Anwendungen dieser neuen Depositionstechnologie hingewiesen. Micro- and nanostructured thin films by Glancing angle deposition Physical vapour deposition under conditions of obliquely incident flux and limited adatom diffusion results in films with a columnar microstructure. These columns will be oriented toward the vapour source. An additional substrate rotation can be used to sculpt the columns into various morphologies (slanted and vertical posts, chevrons, screws or spirals). With this glancing angle deposition (GLAD) technique can prepared porous thin films with engineered structures from a variety of dielectric, semiconducting and metallic materials. The paper presents the In this paper the physical fundamentals of the GLAD technique are introduced, the production of micro- and nanostructures of different morphology on non-patterned and patterned substrates is demonstrated and some possible applications of this new deposition technique are introduced.

The effects of molecular architecture and loading of a porogen material on the structural characteristics of methylsilsesquioxane (MSQ)-based porous films are examined using X-ray porosimetry (XRP)...

The sol-gel technology is being increasingly used for the development of optical sensors and biosensors, due to its simplicity and versatility. By this process, porous thin films incorporating different chemical and biochemical sensing agents are easily obtained at room temperature, allowing final structures with mechanical and thermal stability as well as good optical characteristics. In this article, an overview of the state-of-the-art of sol-gel thin films-based optical sensors is presented. Applications reviewed include sensors for determination of pH, gases, ionic species and solvents, as well as biosensors.

Several mixed oxide thin film series of samples (Si¿Co¿O, Si¿Ni¿O, Si¿W¿O) have been prepared by reactive magnetron sputtering at oblique angle geometries. The paper focuses on the description of microstructure of the films as a function of their stoichiometry. It is found that for identical process parameters (gas mixture, pressure, magnetron-substrate distance, incidence angle of the vapour flux, etc.) the tilt angle of the developed columnar microstructure and the film porosity is strongly dependent on the stoichiometry of the films. The results are discussed in the framework of several theoretical models on this topic., The authors thank Junta de Andalucia (Projects TEP8067, and FQM-2265) and Ministry of Science and Innovation (Projects MAT2013-42900-P, and MAT2013-40852-R) for financial support.

Transparent TiO2, WO3-TiO2, and MoO3-TiO2 films were prepared by spin-coating each colloidal suspension. The monolayer coverage of WO3 on the surface of TiO2 greatly increased the photocatalytic activity in the decomposition of gaseous 2-propanol, whereas the addition of MoO3 considerably decreased the photocatalytic reaction of TiO2. For the estimation of superhydrophilicity, the change of contact angles between the water drop and the film surface was measured as a function of UV-irradiation time. The measured contact angle of WO3-TiO2 film was considerably lower than that of TiO2 before the UV-irradiation, and it decreased to the minimum value about 4 times faster than that of pure TiO2 films with the irradiation of UV light. On the other hand, MoO3-TiO2 films showed a low contact angle at initial point, but their contact angle was very slowly decreased under the UV light. The initial low contact angles suggest the high hydrophilic character of WO3-TiO2 and MoO3-TiO2 films with high Lewis surface acidities. The observed trend suggests that the superhydrophilicity is closely related to the photocatalytic activity.

Highly porous thin films with columnar microstructures are applicable to many optical, chemical, and electronic devices, and can be fabricated using the glancing angle deposition method for physical vapour deposition onto tilted substrates. In a recent advancement of this method, it was shown that decoupling of the vapour incidence direction from the column growth direction provides significant flexibility to engineer the pore structure of the films. Here we elaborate on the decoupling principle by applying it to chiral thin films with a periodic microstructure, and demonstrating how it leads to improved film uniformity and the elimination of column broadening. We also show the effects of such depositions onto substrate seed layers with intentional defects. Substrate based defects normally transfer to thin films as air filled defects, but here we present for the first time that a simple adjustment of the deposition parameters can invert the normally air filled defects to become solid, evaporant filled defects. This defect engineering capability provides new opportunities for the deployment of glancing angle deposition thin films to photonic bandgap crystals and microfluidic devices.

A method of producing relatively monodisperse, small-diameter (sub-500 nm diameter) aerosol fibers is described. This method involves the separation of porous thin films from their substrate. It was found that fibers with diameters of less than several hundred nm and lengths of several micrometers can be formed that do not adhere to one-another. Two μ m thick columnar thin films were fabricated and processed, yielding aerosol fibers with lengths up to 2 μm and diameters up to 170 nm. Diameter and length distributions of a collected aerosol showed that a broad range of fiber lengths and diameters are formed by this method. Further modification of the method, however, is expected to greatly narrow the range of effective diameters and lengths obtained.

A pulsed slow-positron beam has been constructed for applications to polymer films. A new setup of the moderator system and a new design for the bunching signal waveform are introduced. The results show that such a kind of moderator appears to be good one, and that a new waveform for the bunching is very practical. The current pulsed slow-positron beam can be used to characterize polymer films or porous thin films.

We report the preparation of mesoporous thin films with bright pyrene excimer emission and their application in visual and rapid detection of nitroaromatic explosive vapors. The fluorescent films were produced by physically encapsulating pyrene molecules in the organically modified silica (ormosil) networks which were prepared via a facile template-free sol-gel method. Formation and stability of pyrene excimer emission were investigated in both porous and nonporous ormosil thin films. Excimer emission was significantly brighter and excimer formation ability was more stable in porous films compared to nonporous films. Rapid and selective quenching was observed in the excimer emission against vapors of nitroaromatic molecules; trinitrotoluene (TNT), dinitrotoluene (DNT), and nitrobenzene (NB). Fluorescence quenching of the films can be easily observed under UV light, enabling the naked-eye detection of nitro-explosives. Furthermore, excimer emission signal can be recovered after quenching and the films can be reused at least five times. © 2014 American Chemical Society.

Porous thin films with engineered microstructures have been fabricated using glancing angle deposition (GLAD). GLAD films with chiral microstructures have been previously shown to exhibit unique chiral optical response. The pores of these films were embedded with (non-chiral) nematic liquid crystals (LCs) to produce a new composite optical material wherein the GLAD film induces chiral nematic-like LC orientation. We demonstrate here reversible electro-optic switching of the LC component of these hybrid films. Unaddressed, cells of GLAD/LC hybrid films show enhanced chiral optic response compared with the unfilled GLAD film. When addressed, the chiral optic response vanishes.

Porous thin films with memory for imprinted metals have been prepared by casting water-THF mixed solutions of a poly(vinyl chloride- co -acylic acid) / poly(propylene glycol) blend. When Cu 2+ and Pb 2+ ions are imprinted in the cast process, the films retain a memory for the original Cu 2+ and Pb 2+ ions. The imprinting processes can be thoroughly monitored by FT-IR spectroscopy.

Porous thin films have been prepared by casting water–THF mixed solutions of poly(vinyl chloride-co-acrylic acid): when Cu2+ ion is imprinted in the casting process, the film obtains a memory for the original Cu2+ ion. The imprinting processes can be closely monitored by FTIR spectroscopy.

The chemiresistive thin film gas sensors with fast response, high sensitivity, low power consumption and mass-produced potency, have been expected for practical application. It requires both sensitive materials, especially exquisite nanomaterials, and efficient substrate chip for heating and electrical addressing. However, it is challenging to achieve repeatable microstructures across the films and low power consumption of substrate chip. Here we presented a new sensor structure via the fusion of metal-oxide nanoporous films and micro-electro-mechanical systems (MEMS)-based sensing chip. An interdigital-electrodes (IDEs) and microheater integrated MEMS structure is designed and employed as substrate chip to in-situ fabricate colloidal monolayer template-induced metal-oxide (egg. SnO2) nanoporous sensing films. This fused sensor demonstrates mW-level low power, ultrafast response (~1 s), and parts-per-billion lever detection for ethanol gas. Due to the controllable template strategy and mass-production potential, such micro/nano fused high-performance gas sensors will be next-generation key miniaturized/integrated devices for advanced practical applications.

Take a metal powder and add aqueous hydrogen peroxide and a small amount of acetic acid (10:1 ratio) under ambient conditions and, in one simple step, colloidally stable dispersions of nanoparticle (NP) metal oxides of the respective metals form with diameters in the range approx. 3–8 nm. No complex work-up or time-consuming purification is required, just simple filtration and spin-coating to make a nanopar ticle metal oxide thin film. Furthermore, this straightforward approach avoids expensive organic surfactants, capping ligands and solvents, metal salts, coordination compounds, and sol–gel precursors commonly used in prior reported syntheses of metal oxide nanoparticles that often contaminate and therefore complicate their subsequent utilization. [1,2] This facile synthetic strategy provides a universal, clean, green, and simple approach to metal oxide nanoparticles, as well as single and multilayer metal oxide nanoparticle porous films perceived to provide diverse applications such as lithium batteries, solar and photoelectrochemical cells, electrochromics and sensors, photocatalysts, and photonic crystals. [3−7] Metal oxide nanoparticles and thin films thereof offer distinctive and desirable properties that make them attractive candidates for materials science and biomedical applications. [8] The synthesis begins with micrometer-scale metal powders exemplified by W, Mo, Ni, Co, Fe, Zn, and Mg (purity 99.5 to 99.95%) which dissolve in aqueous/H 2 O 2 (30 wt%) and acetic acid, AcH. (DANGER: Very exothermic reaction, instant ice-bath cooling is necessary in a well ventilated fumehood. Protective glasses, gloves, and a lab coat must be worn all the time during this synthetic procedure.) Contingent upon the choice of metal(s), this results in highly stable, single (M 1 O x ), binary Spinel (M 1 M 2 O 4 ) and ternary multi-metallic (M1M2M3Oz) aqueous dispersions of colloidally stable metal

Tez (Yüksek Lisans) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 2011, Thesis (M.Sc.) -- İstanbul Technical University, Institute of Science and Technology, 2011, Lityum iyon pilleri uzun kullanım ve raf ömrü, geniş kullanım sıcaklık aralığı, hızlı şarj edilebilirlik, yüksek enerji verimliliği gibi özellikleriyle son zamanlarda öne çıkan güç kaynaklarındandır. Lityum iyon pilleri, elektronik cihazların sürekli olarak küçülmesi sebebiyle mikro güç kaynaklarına olan ihtiyacı karşılayabilecek özelliklere sahiptir. Ancak lityum metalinin ergime sıcaklığının düşük olması (181 ⁰C) ve çok reaktif bir malzeme olması sebebiyle anot malzemesi olarak üretilmesi zordur. Bu nedenle lityum iyon pillerinde alternatif anot malzemelerinin kullanılması araştırma konusudur. Bu alternatif anot malzemeleri arasında Sn, SnO2, Sn-bazlı sistemler öne çıkmaktadır. Çünkü kalay, lityum ile kolay ve tersinir olarak reaksiyona girebilmekte ve oldukça yüksek gravimetrik ve hacimsel teorik kapasiteye ulaşmaktadır. Ancak saf kalay oldukça aktif olduğundan, şarj/deşarj olayı sırasında hacim genleşmesine sebep olmaktadır. Bu durum pil ömrünün azalmasına neden olur. Bunun önüne geçebilmek için Li-Sn sistemine Ag eklemek ve anot malzemesini gözenekli ince film olarak üretmek mümkündür. Bu çalışmada, Li-iyon pillerinde anot malzemesi olarak kullanılmak üzere Sn, SnO2 ve Ag katkılı Sn-Ag malzemeleri elektron demeti ile fiziksel buharlaştırma (EB PVD) yöntemi ile Cu altlık malzeme üzerinde biriktirilerek düzenli nano gözenekli ve gözeneksiz ince film olarak üretilmiştir. Ag katkılı Sn-Ag sisteminde, Ag3Sn intermetalik bileşiği oluşturulmuştur. Üretilen ince film anot malzemelerinin yüzey morfolojisi, kimyasal kompozisyonu ve kristal yapısı sırası ile, SEM, EDS ve XRD cihazları ile karakterize edilmiştir., Li-ion batteries are the most studied power sources because of the properties of long cycle and shelf life, broad temperature range of operation, rapid charge capability and high coulombic and energy efficiency. The continuous miniaturization of electronic devices has led to the growing demands of micro power sources. Lithium ion batteries have the properties of satisfying the demand for thin power sources. However, it is difficult to produce lithium metal as an anode material because it has low melting point (181⁰C) and it is highly reactive with air. For this reason, alternative anode materials are investigated. Sn, SnO2 and Sn-based systems are the most attractive anodes among alternative anode materials since tin is easily and reversibly alloys with Li atoms and it has high gravimetric and volumetric specific theoretical capacities. However, it will be the volume expansion during the charge/discharge process because pure tin is highly reactive. Therefore, battery cycle life will be shorter. To prevent this volume expansion it is possible to dop Ag in the Sn-Li system and to produce anode material as a porous thin film. In this study, Sn, SnO2, Ag-Sn materials were deposited on the Cu substrate as nanoporous and nonporous thin film anodes by electron beam evaporator for lithium ion batteries. It was achieved that Ag3Sn intermetallic phase in the Sn-Ag system by dopping Ag. To characterize of the surface morphology, chemical composition and crystal structure of thin film anodes, SEM, EDS and XRD analyses were used respectively., Yüksek Lisans, M.Sc.

Fluorescent tetracationic porphyrin (TMPyP) molecules have been incorporated into optically transparent TiO2 thin films acting as a host material. The films, with a columnar structure and open pores, were prepared by electron evaporation at glancing angles (GAPVD). The open porosity of the films has been estimated by measuring a water adsorption isotherm with a quartz crystal monitor. TMPyP molecules were infiltrated in the host thin films by their immersion into water solutions at controlled values of pH. The state of the adsorbed molecules, the infiltration efficiency, and the adsorption kinetics were assessed by analyzing the optical response of the films by UV?vis absorption and fluorescence techniques. The infiltration efficiency was directly correlated with the acidity of the medium, increasing at basic pHs as expected from simple considerations based on the concepts of the point of zero charge (PZC) developed for colloidal oxides. By a quantitative evaluation based on the analysis of the UV spectra, the infiltration process has been described by a Langmuir type adsorption isotherm and an Elovich-like kinetics. The accessibility of the infiltrated molecules in the TMPyP/TiO2 composite films is assessed by following the changes of their optical properties when exposed to the acid vapors and their subsequent recovery with time. © 2010 American Chemical Society.

Porous thin films made from a mesh of organic nanowires can detect explosives more efficiently and rapidly than other fluorescence-based sensors

Porous thin films with tailored chiral microstructure fabricated using glancing angle deposition (GLAD) have previously been shown to exhibit unique chiral optic response. Recently, the pores of chiral GLAD films were filled with liquid crystalline (LC) materials to produce a new class of hybrid materials which exhibit enhanced chiral optic response. We demonstrate here reversible electro-optic switching of the LC component in a cell structure composed of a chiral GLAD film embedded with a nematic LC. When the cell is addressed, the chiral optic response vanishes.

A preliminary TEM investigation of porous films fabricated by glancing angle deposition has shown the importance of surface diffusion and crystal structure in determining the final microstructure of the film. Although the process variables are extremely important in defining the morphology of the film, their effects are limited in terms of final microstructure.

Glancing angle deposition (GLAD) was used to fabricate optically active thin films with porous chiral microstructure. Liquid crystals added to the films result in enhanced optical properties.

A new fully three dimensional (3D) ballistic deposition simulator 3D-FILMS has been developed for the modeling of thin film deposition and structure. The simulator may be implemented using the memory resources available to workstations. In order to illustrate the capabilities of 3D-FILMS, we apply it to the growth of engineered porous thin films produced by the technique of GLancing Angle Deposition (GLAD).

Recent experimental work has demonstrated that unique high porosity thin films may be ob- tained in physical deposition systems by combining glancing angle deposition with in situ sub-strate motion control [1-7]. The microstructure of these films consists of isolated columns engineered into shapes such as helices, posts, or chevrons. Due to the isolated nature of the columns, the films present a unique opportunity to study fundamental thin film growth behaviour and, in particular, the influence of the self shadowing mechanism in three dimensions. Apart from this academic motivation, there is the need to characterize the physical constraints imposed on the engineering of these films. In particular, this study will have implications for the realization of isolated, periodically arranged nanostructures envisioned for certain applications. Preliminary results from an ongoing study of growth dynamics, morphology, porosity, and scaling behaviour, and the dependence of these features on deposition parameters are presented below.

Hybrid organic-inorganic xerogel films were deposited as porous thin films by spinning the precursor sol on silicon substrates. Films of various compositions were prepared using combinations of the following precursors: methyltrimethoxysilane, dimethoxydimethylsilane and tetramethoxysilane (TMOS). The hybrid films exhibited excellent gap-filling capabilities (0.45 micron trenches). Thermal desorption experiments indicate that heating to ∼130 C removes moisture and volatile organic constituents present in the as-cast film. Curing was found to increase the adhesion between the xerogel and the silicon substrate. Moisture was found to be responsible for an increase in the dielectric constant. That is, in ambient, the dielectric constant for a cured film was found to be 4.4; but in a dry atmosphere, it decreased to 2.5. Current-voltage measurements show the cured hybrid film possesses a breakdown field of 3.4 MV/cm.

We evaluate two thin-film microstructures in high-speed humidity sensor applications. The first sensing structure consists of high aspect ratio SiO posts between metal electrodes. Examples of this microstructure were found to respond to steplike changes in humidity with speeds as low as 35 ms as moisture diffuses inward and 25 ms as dry air is added. The second sensor is the negative image of the first, a polymer matrix perforated by networks of high aspect ratio pores. In this case, response times on the order of 75 ms were measured as moisture was added to the system and 175 ms when dry air was added.