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Micro-Nanostructured Plasmonic TiN layer produced using Rapid Thermal Nitridation of Nanoimprinted TiO₂ sol-gel
Abstract
Titanium nitride (TiN) is a very promising new plasmonic material to replace traditional plasmonic materials like gold and silver, especially thanks to its thermal and chemical stability. However, its chemical resistance and its hardness make TiN difficult to microstructure. An alternative approach is to micro-nanostructure a titanium dioxide (TiO 2 ) coating and then to use a nitridation reaction to obtain a micro-nanostructured TiN coating. This is an easy, rapid and cost-effective structuring process. In this paper, we demonstrate that rapid thermal nitridation (RTN) can be combined with nanoimprint lithography (NIL) to rapidly micro-nanostructure a TiN layer. This innovative approach is applied to a micro-nanostructured TiN layer for plasmonic response in the near infrared range. Experimental and theoretical approaches are compared.
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This study reports the optical, electrical and mechanical properties of TiN films prepared by direct rapid thermal nitridation process from a photo-patternable TiO2 sol-gel layer. The sol-gel approach is compatible to non-planar and large substrates and allows the micro-nanotexturing of crystallized TiN surfaces in a significantly short time, large scale and at a lower cost compared to TiN layer deposition from existing and conventional processes (CVD, PVD, ALD…). In this paper, the optical measurements are carried out by optical spectroscopy in the UV, visible and near-IR region and by ellipsometry. The resistivity and the conductivity are estimated by four-point probe method, while hardness is characterized by nano-indentation experiments. The results indicate that the TiN thin film made by sol-gel method and Rapid Thermal Nitridation are very promising for the manufacturing of optical metasurfaces devices or new plasmonic materials.
Refractory plasmonic materials that have optical properties close to those of noblemetals and at the same time are environmentally friendly, commercially viable and CMOScompatible could lead to novel devices for many thermo-photonic applications. Recently developed TiN thin films overcome some of the limitations of noble-metals, as their optical loss is larger than noble metals and conventional methods to deposit TiN films are not compatible for its integration with other semiconductors. In this work, high-quality epitaxial single-crystalline TiN thin films are deposited with plasma-assisted molecular beam epitaxy (MBE) that exhibit optical losses that are less than that of Au in most part of the visible (300 nm - 580 nm) and near-IR spectral ranges (1000 nm - 2500 nm). In addition, a large figure-of-merit for surface plasmon polariton (SPP) propagation length compared to the previously reported TiN films is achieved with the MBE-deposited films. © 2020 Optical Society of America under the terms of the OSA Open Access Publishing Agreement.
Titanium nitride (TiN) has recently emerged as an attractive alternative material for plasmonics. However, the typical high-temperature deposition of plasmonic TiN using either sputtering or atomic layer deposition has greatly limited its potential applications and prevented its integration into existing CMOS device architectures. Here, we demonstrate highly plasmonic TiN thin films and nanostructures by a room-temperature, low-power, and bias-free reactive sputtering process. We investigate the optical properties of the TiN films and their dependence on the sputtering conditions and substrate materials. We find that our TiN possesses one of the largest negative values of the real part of the dielectric function as compared to all other plasmonic TiN films reported to date. Two-dimensional periodic arrays of TiN nanodisks are then fabricated, from which we validate that strong plasmonic resonances are supported. Our room-temperature deposition process can allow for fabricating complex plasmonic TiN nanostructures and be integrated into the fabrication of existing CMOS-based photonic devices to enhance their performance and functionalities.
Titanium nitride (TiN) is an interesting refractory metallic compound which could replace gold as an alternative plasmonic material, especially for high temperature and semiconductor compatible applications. However, reported plasmonic properties of TiN films are so far limited by conventional growth techniques such as reactive sputtering. In this work, we adopt the nitrogen-plasma-assisted molecular-beam epitaxy (MBE) to grow single-crystalline, stoichiometric TiN films on sapphire substrates. The properties of as-grown TiN epitaxial films have been fully characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), spectroscopic ellipsometry (SE), and surface plasmon polariton (SPP) interferometry. We have confirmed that MBE-grown TiN films exhibit excellent plasmonic properties to replace gold in the visible and near-infrared spectral regions. Measuring the real and imaginary parts of dielectric function by SE, it is also found that TiN is better than gold in the short-wavelength range (<500 nm), where gold suffers from strong loss due to interband transition. Contrary to the recent theoretical prediction that air is not able to stabilize SPP modes at the TiN surface, our surface plasmon interferometry data clearly show the presence of propagating SPP modes at the TiN/air interface. To demonstrate the unique plasmonic properties of MBE-grown stoichiometric TiN, we have fabricated TiN metasurfaces for the visible-spectrum applications.
Polycyclic aromatic compounds (PACs) are known due to their mutagenic activity. Among them, 2-nitrobenzanthrone (2-NBA) and 3-nitrobenzanthrone (3-NBA) are considered as two of the most potent mutagens found in atmospheric particles. In the present study 2-NBA, 3-NBA and selected PAHs and Nitro-PAHs were determined in fine particle samples (PM 2.5) collected in a bus station and an outdoor site. The fuel used by buses was a diesel-biodiesel (96:4) blend and light-duty vehicles run with any ethanol-to-gasoline proportion. The concentrations of 2-NBA and 3-NBA were, on average, under 14.8 µg g⁻¹ and 4.39 µg g⁻¹, respectively. In order to access the main sources and formation routes of these compounds, we performed ternary correlations and multivariate statistical analyses. The main sources for the studied compounds in the bus station were diesel/biodiesel exhaust followed by floor resuspension. In the coastal site, vehicular emission, photochemical formation and wood combustion were the main sources for 2-NBA and 3-NBA as well as the other PACs. Incremental lifetime cancer risk (ILCR) were calculated for both places, which presented low values, showing low cancer risk incidence although the ILCR values for the bus station were around 2.5 times higher than the ILCR from the coastal site.
Optical metasurfaces are judicously engineered electromagnetic interfaces that can control and manipulate many of light’s quintessential properties, such as amplitude, phase, and polarization. These artificial surfaces are composed of subwavelength arrays of optical antennas that experience resonant light-matter interaction with incoming electromagnetic radiation. Their ability to arbitrarily engineer optical interactions has generated considerable excitement and interest in recent years and is a promising methodology for miniaturizing optical components for applications in optical communication systems, imaging, sensing, and optical manipulation. However, development of optical metasurfaces requires progress and solutions to inherent challenges, namely large losses often associated with the resonant structures; large-scale, complementary metal-oxide-semiconductor-compatible nanofabrication techniques; and incorporation of active control elements. Furthermore, practical metasurface devices require robust operation in high-temperature environments, caustic chemicals, and intense electromagnetic fields. Although these challenges are substantial, optical metasurfaces remain in their infancy, and novel material platforms that offer resilient, low-loss, and tunable metasurface designs are driving new and promising routes for overcoming these hurdles. In this review, we discuss the different material platforms in the literature for various applications of metasurfaces, including refractory plasmonic materials, epitaxial noble metal, silicon, graphene, phase change materials, and metal oxides. We identify the key advantages of each material platform and review the breakthrough devices that were made possible with each material. Finally, we provide an outlook for emerging metasurface devices and the new material platforms that are enabling such devices.
We report the fabrication of titanium nitride (TiN) films with the “best” plasmonic behavior reported so far by pulsed laser deposition (PLD) method. Even though the deposition is done at room temperature and grown on an amorphous native oxide of a silicon wafer, the plasmonic property of the TiN is comparable to that of gold that is a conventional plasmonic material in the visible to near infrared region. Because of the highly plasmonic nature of the TiN, the near-field around the TiN nanostructure can be as high as that of gold nanostructure. Room temperature process without strict requirement on substrate allows depositing a TiN film even on a flexible polymer film without degrading its property. Our results pave a way for using TiN as a truly practical plasmonic material replacing the use of noble metals.
We have synthesized gyroidal TiN metamaterials, studied their optical properties, and compared them with the optical properties of the TiN thin films fabricated using reactive magnetron sputtering. The plasma frequency, ωp, and the corresponding free carrier concentration, N, in the gyroid samples were found to be much lower than those in thin films. Furthermore, the plasma frequency in TiN gyroids was comparable to or smaller than the damping rate, γD. This makes the studied TiN gyroid a poor plasmonic material. At the same time, TiN gyroidal samples have demonstrated bright rainbow pattern in the optical microscopy reflectance study. This phenomenon is tentatively explained by different orientations of the gyroid domains.
We have reviewed the deposition of titanium nitride (TiN) thin films on stainless steel substrates by a DC magnetron sputtering method and annealing at different annealing temperatures of 500, 600, and 700°C for 120 min in nitrogen/argon atmospheres. Effects of annealing temperatures on the structural and the optical properties of TiN films were investigated using X-ray diffraction (XRD), atomic force microscope (AFM), field emission scanning electron microscopy (FESEM), and UV-VIS spectrophotometer. Our experimental studies reveal that the annealing temperature appreciably affected the structures, crystallite sizes, and reflection of the films. By increasing the annealing temperature to 700°C crystallinity and reflection of the film increase. These results suggest that annealed TiN films can be good candidate for tokamak first wall due to their structural and optical properties.
Significance
Plasmonic and metamaterial devices require high-performance material building blocks, both plasmonic and dielectric, to be useful in any real-world application. Here, we develop both plasmonic and dielectric materials that can be grown epitaxially into ultrathin and ultrasmooth layers with sharp interfaces. We show that a superlattice consisting of titanium nitride as a plasmonic component behaves as an optical hyperbolic metamaterial and exhibits extremely high photonic density of states.
The search for alternative plasmonic materials with improved optical properties, easier fabrication and integration capabilities over those of the traditional materials such as silver and gold could ultimately lead to real-life applications for plasmonics and metamaterials. In this work, we show that titanium nitride could perform as an alternative plasmonic material in the visible and near-infrared regions. We demonstrate the excitation of surface-plasmon-polaritons on titanium nitride thin films and discuss the performance of various plasmonic and metamaterial structures with titanium nitride as the plasmonic component. We also show that titanium nitride could provide performance that is comparable to that of gold for plasmonic applications and can significantly outperform gold and silver for transformation-optics and some metamaterial applications in the visible and near-infrared regions.
A variety of configurations and formats have been devised to exploit the phenomenon of surface plasmon on metal dielectric interfaces for sensing a variety of significant analytes, such as pesticides and explosives, pathogens and toxins, and diseased tissue. Researchers continue to aim at detecting lower concentrations in smaller volumes of samples in real time. A new research field, called nanoplasmnonics, has emerged in this regard.
The growth of ultrathin TiN films by plasma-assisted atomic layer deposition (PA-ALD) was studied by in situ spectroscopic ellipsometry (SE). In between the growth cycles consisting of TiCl4 precursor dosing and H2–N2 plasma exposure, ellipsometry data were acquired in the photon energy range of 0.75–5.0 eV. The dielectric function of the TiN films was modeled by a Drude-Lorentz oscillator parametrization, and the film thickness and the TiN material properties, such as conduction electron density, electron mean free path, electrical resistivity, and mass density, were determined. Ex situ analysis was used to validate the results obtained by in situ SE. From the in situ spectroscopic ellipsometry data several aspects related to thin film growth by ALD were addressed. A decrease in film resistivity with deposition temperature between 100 and 400 °C was attributed to the increase in electron mean free path due to a lower level of impurities incorporated into the films at higher temperatures. A change in resistivity and electron mean free path was observed as a function of film thickness (2–65 nm) and was related to an increase in electron-sidewall scattering for decreasing film thickness. The TiN film nucleation was studied on thermal oxide covered c-Si substrates. A difference in nucleation delay was observed on these substrates and was related to the varying surface hydroxyl density. For PA-ALD on H-terminated c-Si substrates, the formation of an interfacial SiNx film was observed, which facilitated the TiN film nucleation.
Titanium nitride (TiN) films were grown by CVD (Chemical Vapor Deposition) from titanium chlorides generated in situ by direct chlorination of titanium metal, ammonia (NH3) and hydrogen (H2) as carrier gas on single crystal c-plane sapphire, WCCo, stainless steel and amorphous graphite substrates. Kinetic pathways involving four surface reactions has been proposed to simulate the growth rate. The proposed model has been validated by experiments performed at different temperatures (650-1400 °C), pressures (300-1000 Pa), with different amount of precursors (N/Ti ratio in gas phase) and on different substrates. The study shows that on polycrystalline materials, the crystal orientation depends on supersaturation while (111) preferred orientation is forced by underlying c-plane sapphire whatever the supersaturation. The low N/Ti ratio in gas phase leads to low growth rate and dense TiN film which is the key to obtain golden TiN. The high growth rate corresponds to brown TiN. Globally, the study shows that golden color is independent from texture and is just the natural aspect of a dense stoichiometric TiN layer.
Superconducting titanium nitride (TiN) thin films were deposited on magnesium oxide, sapphire and silicon nitride substrates at 700 °C, using a pulsed laser deposition (PLD) technique, where infrared (1064 nm) pulses from a solid-state laser were used for the ablation from a titanium target in a nitrogen atmosphere. Structural studies performed with x-ray diffraction showed the best epitaxial crystallinity for films deposited on MgO. In the best films, superconducting transition temperatures, T C, as high as 4.8 K were observed, higher than in most previous superconducting TiN thin films deposited with reactive sputtering. A room temperature resistivity down to ∼17 μΩ cm and residual resistivity ratio up to 3 were observed in the best films, approaching reported single crystal film values, demonstrating that PLD is a good alternative to reactive sputtering for superconducting TiN film deposition. For less than ideal samples, the suppression of the film properties were correlated mostly with the unintended incorporation of oxygen (5-10 at%) in the film, and for high oxygen content films, vacuum annealing was also shown to increase the T C. On the other hand, superconducting properties were surprisingly insensitive to the nitrogen content, with high quality films achieved even in the highly nitrogen rich, Ti:N = 40/60 limit. Measures to limit oxygen exposure during deposition must be taken to guarantee the best superconducting film properties, a fact that needs to be taken into account with other deposition methods, as well.
Titanium nitride (TiN) is a new plasmonic material with advantages due to greater thermal and chemical stability, compared to traditional metallic materials, i.e. gold and silver. TiN fabrication methods generally require reactive sputtering, which limits and complicates patterning capabilities. In this work, we demonstrate the fabrication of TiN films, as well as nano-patterned surfaces and three-dimensional (3D) structures by nitridation of crystalline titanium dioxide (TiO2) nanoparticle-based structures. TiO2 films are created by spin coating nanoparticle-based solutions, and TiO2 patterns are fabricated directly via solvent-assisted soft nanoimprint lithography. TiO2 films and structures were annealed in air and then reacted with ammonia gas at 1000oC for 0, 2, 4, or 6 hours. SEM analysis shows that patterned TiO2 surfaces and 3D structures retain their structural integrity after treatment, allowing for a convenient method of fabricating patterned TiN nanopatterned surfaces and structures. Treated samples demonstrate the crystalline transition from tetragonal to cubic, which is consistent with the transition from anatase TiO2 to TiN. Additionally, using spectroscopic ellipsometry, we observe a change in the real permittivity from positive to negative. For 0 and 6 hour treatments, the real permittivity changes from 3.1 to –9.6 (at 1000 nm). TiN has potential use for many plasmonic and metamaterial applications. In this work, we demonstrate the excitation of surface plasmon polaritons (SPPs) via grating coupling using 1 µm-period TiN line gratings.
High aspect ratio titanium nitride (TiN) grating structures are fabricated by the combination of deep reactive ion etching (DRIE) and atomic layer deposition (ALD) techniques. TiN is deposited at 500 °C on a silicon trench template. Silicon between vertical TiN layers is selectively etched to fabricate the high aspect ratio TiN trenches with the pitch of 400 nm and height of around 2.7 μm. Dielectric functions of TiN films with different thicknesses of 18 – 105 nm and post-annealing temperatures of 700 – 900 °C are characterized by an ellipsometer. We found that the highest annealing temperature of 900 °C gives the most pronounced plasmonic behavior with the highest plasma frequency, ωp = 2.53 eV (λp = 490 nm). Such high aspect ratio trench structures function as a plasmonic grating sensor that supports the Rayleigh-Woods anomalies (RWAs), enabling the measurement of changes in the refractive index of the ambient medium in the wavelength range of 600 – 900 nm. We achieved the bulk refractive index sensitivity (BRIS) of approximately 430 nm/RIU relevant to biosensing liquids.
Plasmonic titanium nitride nanostructures are obtained via nitridation of titanium dioxide. Results show that complex nano- and microscale designs of refractory plasmonic nitrides can be realized by utilizing the well-understood oxide material synthesis. Large-scale 3D nanoarchitectures will enable the use of refractory plasmonic materials in a variety of areas including spectrally and angularly selective metamaterials, plasmon-enhanced photocatalysis, and photothermal systems.
The plasmonic properties of titanium nitride (TiN) films depend on the type of substrate when using typical deposition methods such as sputtering. Here we show atomic layer deposition (ALD) of TiN films with very weak dependence of plasmonic properties on the substrate, which also suggests the prediction and evaluation of plasmonic performance of TiN nanostructures on arbitrary substrates under a given deposition condition. Our results also observe that substrates with more nitrogen-terminated (N-terminated) surfaces will have significant impact on the deposition rate as well as the film plasmonic properties. We further illustrate that the plasmonic properties of ALD TiN films can be tailored by simply adjusting the deposition and/or post-deposition annealing temperatures. Such characteristics and the capability of conformal coating make ALD TiN films on templates ideal for applications that require the fabrication of complex 3D plasmonic nanostructures.
We propose to combine a few known technologies to print TiOxNy quasi-sinusoidal grating using a direct photo-patternable TiO2 sol-gel thin layer, enabling the conversion of a pure dielectric grating to a metallic one. An expanded laser beam illuminates a photosensitive TiO2 sol-gel layer through a photo-mask grating, creating illuminated and non-illuminated areas in the sol-gel layer, which act as a negative photoresist and leads to a TiO2 based grating. Nitridation is made by heat treatment under NH3 flow to convert TiO2 in TiOxNy grating. This process shows that the sol-gel technology can be extended from a dielectric to metallic layer. The derived meta-material offers an alternative for plasmonic effects in the near-infrared region. This paper describes the experimental processes from the photochemistry of the TiO2 sol-gel layer to its nitridation. Thanks to the optical properties of the obtained micrometric period TiOxNy grating, surface plasmon resonance at TiOxNy-air interface has been excited in the NIR range (around 1500 nm), demonstrating the metallic behavior of the grating and its ability to be used as a plasmonic component.
CMOS-compatible fabrication of plasmonicmaterials and devices will accelerate the development of integrated nanophotonics for information processing applications. Using low-temperature plasma-enhanced atomic layer deposition (PEALD), we develop a recipe for fully CMOS-compatible titanium nitride (TiN) that is plasmonic in the visible and near infrared. Films are grown on silicon,silicon dioxide, and epitaxially on magnesium oxide substrates. By optimizing the plasma exposure per growth cycle during PEALD, carbon and oxygen contamination are reduced, lowering undesirable loss. We use electron beam lithography to pattern TiN nanopillars with varying diameters on silicon in large-area arrays. In the first reported single-particle measurements on plasmonic TiN, we demonstrate size-tunable darkfield scattering spectroscopy in the visible and near infrared regimes. The optical properties of this CMOS-compatible material, combined with its high melting temperature and mechanical durability, comprise a step towards fully CMOS-integrated nanophotonic information processing.
We have fabricated two-dimensional periodic arrays of titanium nitride (TiN) nanoparticles from epitaxial thin films. The thin films of TiN, deposited on sapphire and single crystalline magnesium oxide substrates by a pulsed laser deposition, are metallic and show reasonably small optical loss in the visible and near infrared regions. The thin films prepared were structured to the arrays of nanoparticles with the pitch of 400 nm by the combination of nanoimprint lithography and reactive ion etching. Optical transmission indicates that the arrays support the collective plasmonic modes, where the localized surface plasmon polaritons in TiN nanoparticles are radiatively coupled through diffraction. Numerical simulation visualizes the intense fields accumulated both in the nanoparticles and in between the particles, confirming that the collective mode originates from the simultaneous excitation of localized surface plasmon polaritons and diffraction. This study experimentally verified that the processing of TiN thin films with the nanoimprint lithography and reactive ion etching is a powerful and versatile way of preparing plasmonic nanostructures.
The nitridation of hollow TiO2 nanoshells and their layered assembly into electrodes for electrochemical energy storage are reported. The nitridated hollow shells are prepared by annealing TiO2 shells, produced initially using a sol–gel process, under an NH3 environment at different temperatures ranging from 700 to 900 °C, then assembled to form a robust monolayer film on a water surface through a quick and simple assembly process without any surface modification to the samples. This approach facilitates supercapacitor cell design by simplifying the electrochemical electrode structure by removing the need to use any organic binder or carbon‐based conducting materials. The areal capacitance of the as‐prepared electrode is observed to be ≈180 times greater than that of a bare TiO2 electrode, mainly due to the enhanced electrical conductivity of the TiN phase produced through the nitridation process. Furthermore, the electrochemical capacitance can be enhanced linearly by constructing an electrode with multilayered shell films through a repeated transfer process (0.8 to 7.1 mF cm–2, from one monolayer to 9 layers). Additionally, the high electrical conductivity of the shell film makes it an excellent scaffold for supporting other psuedocapacitive materials (e.g., MnO2), producing composite electrodes with a specific capacitance of 743.9 F g–1 at a scan rate of 10 mV s–1 (based on the mass of MnO2) and a good cyclic stability up to 1000 cycles. Hollow shells of TiO2 are nitridated by annealing in NH3, assembled into a monolayer film on water surface, and stacked layer‐by‐layer into electrodes for electrochemical energy storage. This approach facilitates supercapacitor cell design by simplifying the electrode structure and avoiding the use of any organic binder or carbon‐based conducting materials. The increased electrical conductivity due to the formation of TiN greatly enhances the electrochemical performance.
Nanocrystalline anatase (TiO2) thin films prepared by a physical vapour deposition method were nitrided by annealing in flowing NH3 at temperatures ranging between 650°C and 700°C. It was established that there was a narrow window of temperatures which allowed both incorporation of interstitial nitrogen into the films with retention of the anatase phase without chemical reduction and preservation of the characteristic nanocrystalline morphology. These optimally modified films responded to visible light in photowetting tests and showed the ability to degrade an organic dye under visible light irradiation.
Dip-coated sol–gel-derived TiO2 films on an alumina substrate were converted to nonstoichiometric titanium nitride (TiNx (x≦ 1)) films by heating at approxmately 1000°C in NH3 gas. TiO2 films made from TiO2 sols prepared from Ti(O–i-C3H7)4 and stabilized by diethanolamine were more easily nitrided than those from sols containing HCl as a deflocculant reagent. This appears to be a result of the more porous structure of the former films.
A series of PVD ceramic hard coatings (TiN, ZrN, TiAlN, TiZrN and TiCN) were deposited on steel substrates using the cathodic arc/unbalanced magnetron deposition technique. These coatings were characterised using Raman microscopy to elucidate the behaviour of the optic and acoustic phonon modes of the (cubic) crystalline lattices. Defect-induced first- (and second-) order spectra have been observed in the 200–300 and 500–800cm−1 regions and these have been assigned and correlated with coating composition. Changes in the position, intensity and shape of the principal TO band (640–560cm−1) have been interpreted.Raman microscopy has been shown to be a very useful non-destructive complementary technique to XRD for the characterisation of PVD hard coatings.
TiO2 films were deposited by a new sol-gel process, based on the polymerization of an ultrasonically generated alkoxide aerosol onto a silicon substrate. Tetrabutyl titanate (TBT) was used as titanium precursor, and was diluted in an ethanol/diethanolamine (DEA) solution. Films were deposited in cycles of 15–30 s, alternated with a thermal treatment at 600°C in air. Different thicknesses were achieved by several numbers of cycles. The films were then annealed for 30 min at a temperature of 600°C in order to avoid carbon contamination from the solvent. These films were treated for different times, at temperatures ranging from 650 to 1100°C in ammonia gas. This kind of treatment leads to a nitrogen incorporation and oxygen loss. The process is controlled by oxygen out-diffusion through the film. The grown films were analyzed by resistivity measurements, RBS and NRA (C, O and N quantification). The nitridation of TiO2 films results in TiN formation, whose characteristics depend critically on treatment temperature.
Titanium nitride (TiN) deposited by chemical vapor deposition (CVD) techniques has been the premier wear-resistant coating in many applications for the last several decades. This review presents a history of developments in the technology of CVD TiN coatings. The CVD processes and equipment are discussed and the current knowledge on the thermodynamics and kinetics of the deposition process is presented. Various properties of CVD TiN coatings, such as hardness, adhesion, morphology and frictional properties, are discussed in the context of applications where wear resistance is required. Particular emphasis is given to applications in metal cutting where TiN has remained the mainstay of the various new and recent developments in coating design for cutting tools. Recent results of correlation between machining performance, deposition parameters, coating morphology and properties are presented. Throughout the paper, gaps in the existing understanding of the technology are pointed out. Finally, the paper presents a glimpse into the future of CVD TiN technology for wear-resistant applications.
We have investigated the formation of titanium nitride (TiN) thin films on (001) MgO substrates by molecular beam epitaxy and radio frequency acitvated nitrogen plasma. Although cubic TiN is stabile over a wide temperature range, superconducting TiN films are exclusively obtained when the substrate temperature exceeds 710 °C. TiN films grown at 720 °C show a high residual resistivity ratio of approximately 11 and the superconducting transition temperature (Tc) is well above 5 K. Superconductivity has been confirmed also by magnetiztion measurements. In addition, we determined the upper critical magnetic field (μ0Hc2) as well as the corresponding coherence length (ξGL) by transport measurements under high magnetic fields. High-resolution transmission electron microscopy data revealed full in plane coherency to the substrate as well as a low defect density in the film, in agreement with a mean-free path length ℓ ≈ 106 nm, which is estimated from the residual resistivity value. The observations of reflection high energy electron diffraction intensity oscillations during the growth, distinct Laue fringes around the main Bragg peaks, and higher order diffraction spots in the reciprocal space map suggest the full controlability of the thickness of high quality superconducting TiN thin films.
© 2012 American Institute of Physics
Raman scattering and superconductivity of titanium nitride with various N deficiencies have been investigated. While in stoichiometric superconducting TiN second-order Raman scattering is predominant, first-order Raman scattering increases with increasing N deficiency. The first-order Raman spectrum which agrees well with the phonon density of states shifts to higher frequencies when the N deficiency grows. This frequency shift is particularly strong at small N deficiencies (∼5%) and is coupled with a drastic drop of Tc. The shift of the phonon density of states indicates phonon anomalies in stoichiometric TiN at 200 cm-1 in close agreement with just performed neutron studies. In almost stoichiometric TiN the mean-square frequencies 〈ω2〉 from the Raman spectra are in good agreement with corresponding specific-heat data. The similarities between the nonstoichiometric TiN0.55 and TiC are discussed.
Nanocrystalline fibrous TiO2 (anatase) was prepared by electrostatic spinning from ethanolic solution of Ti(IV) butoxide, acetylacetone, and poly(vinylpyrrolidone) employing the Nanospider industrial process. These titania fibers were smoothly converted into cubic titanium oxynitride, TiOxNy fibers (a = 4.1930 Å) during 4 h at 600 °C in ammonia atmosphere. The obtained material is convertible back into TiO2 fibers by heat treatment in air at 500 °C. The TiO2 fibers, which were reformed in this way, contain anatase as the main phase. Their follow-up reaction with NH3 at 600 °C/2 h leads to a less crystalline oxynitride material with a ≈ 4.173 Å, which is close to that of cubic TiO. Three subsequent cycles of this transformation were demonstrated. The described conversions are specific for electrospun anatase fibers only. At the same experimental conditions, other forms of nanocrystalline anatase do not react with ammonia yielding cubic phases. An almost perfectly stoichiometric titanium nitride, TiN (a = 4.2290 Å) containing only 0.2 wt % O, was prepared from TiOxNy fibers in NH3 at temperatures up to 1000 °C. This TiN material maintains the morphology of fibers and is composed of nanocrystals of a similar size as those of the precursor.
Titanium, zirconium, and hafnium nitride thin films were synthesized from tetrakis(dialkylamido)metal(IV) complexes and ammonia by atmospheric pressure chemical vapor deposition with high growth rates at low substrate temperatures (200-450-degrees-C). Depositions were successfully carried out on silicon, low-sodium glass, soda lime glass, vitreous carbon, and boron substrates. Stainless steel and polyester were also used as substrates for depositions of titanium nitride below 250-degrees-C. All of the films showed good adhesion to the substrates and were chemically resistant. The films were characterized by Rutherford backscattering spectrometry, X-ray photoelectron spectroscopy, ellipsometry, and transmission electron microscopy. Reflectance and transmission spectra were also recorded. Hydrogen in the films was estimated by hydrogen forward recoil scattering spectrometry. The titanium nitride coatings were slightly nitrogen-rich TiN (N/M ratio 1.05-1.15). These films displayed metallic properties and were crystalline as deposited. The zirconium and hafnium nitride films were Zr3N4 and nitrogen-rich Hf3N4 (N/M ratios 1.35 +/- 0.05 and 1.7 +/- 0.1, respectively). They were crystalline, yellow-colored, transparent, and insulating. The hydrogen content of the films diminished as the deposition temperature increased. For depositions carried out at 400-degrees-C the TiN films contained 9 atom % hydrogen and at 300-degrees-C the Zr3N4 and Hf3N4 films contained 10 and 16 atom % hydrogen, respectively. The hydrogen is proposed to be incorporated in the films as NH and NH2 groups in the amorphous portion of a mix composed of amorphous material and imbedded nitride crystallites.
TiN thin films were deposited on Si substrate using an R.F. sputter as a function of Ar / N2 ratio of 20 : 30, 10 :3 0 and 0 : 30. The average thickness of thin film was 0.7 μm, while the size of TiN nano-particles dispersed in the matrix was 5∼10 nm in diameter. The microstructure became fine as the flow rate of N2 to Ar gas increased. The hardness and elastic modulus measured by a nanoindentation method were also enhanced. It discussed the fracture pattern took placed at the TiN layer during the indentation.
The titanium nitride coating film was prepared on the SiO2 glass substrate by ammonolysis of titanium dioxide coating film formed by sol-gel method. The X-ray diffraction (XRD) pattern
indicated that it is cubic titanium nitride with a lattice parameter,a
o, of 0.4231 nm. The obtained titanium nitride is non-stoichiometric (TiN
x
x≤ 1) because the value, 0.4231 nm, is smaller than the stoichiometric one (0.4240 nm). The coating film show very high infrared
(i.r.) reflectance in the wavelength region of 2–8 μm.
Preparation of TiN fibres by ammonolysis of the sol-gel derived TiO2 fibres has been performed in the present study. TiO2 gel fibres were prepared from Ti(O-i-C3H7)4 by hydrolysis and polycondensation. As a result, TiN is found to form above 900C. A thermodynamic interpretation of the nitridation reaction of TiO2 was considered. Moreover, from the kinetic treatment, it is found that the nitridation reaction of TiO2 is controlled by diffusion of either reactant (NH3) or one of the products (H2O) through the reaction layer.
The conductivity and the Hall coefficient of nanostructured TiN films synthesized by nonreactive RF magnetron sputtering have
been experimentally studied. The mechanism of conductivity and the role of grain size are discussed.
Thin TiN layers have been successfully produced on Si and SiO 2 by reactive evaporation combined with rapid thermal annealing. Results of composition, resistivity, and stress measurements on these layers are reported. The TiN layers have a resistivity around 40 μΩ cm and a high stress of between 1 and 6 GPa. The composition ratio of nitrogen to titanium, measured by elastic recoil detection (ERD), combined with time‐of‐flight, was found to vary between 0.8 and 1.0 depending on the deposition conditions. In addition to the stoichiometry determination, ERD also clearly shows the presence of a TiSi 2 layer between the TiN and the Si substrate. It is also shown that good TiN layers can be produced by reactive evaporation for nitrogen partial pressures between 1.0 and 2.0×10<sup>-5</sup> mbar and for titanium evaporation rates between 0.3 and 0.5 nm/s.
Interest in the development of surface plasmon resonance (SPR) based immunosensors for detection and monitoring of low-molecular-weight analytes of biomedical, food and environmental fields has been rapidly increasing over the last 10 years. By combining the advantages of the specific antigen–antibody immunoreaction and the high sensitivity and reliability of SPR signal transduction, SPR immunoassays offer exceptional performance capabilities with respect to sensitivity, specificity, speed and multianalyte detection in complex analytical matrices. Advancements in the technology of antibody production and the signal transduction provide a promising scope for SPR immunosensors to lead in the next generation biosensors. This review highlights the current state-of-the-art in SPR immunosensors and outlines briefly the important issues with regard to the development of SPR immmunosensors, such as preparation of the biomolecules, sensor fabrication, non-specific adsorption, surface regeneration and detection principles. Particular emphasis is given to the indirect competitive immunoassay principle which is compatible and highly promising for detection of small analytes with enhanced sensitivity. In addition, recent advancements and trends in the application of SPR immunosensors in biomedical, environmental and food-related analyses are discussed.
Since the first application of the surface plasmon resonance (SPR) phenomenon for sensing almost two decades ago, this method has made great strides both in terms of instrumentation development and applications. SPR sensor technology has been commercialized and SPR biosensors have become a central tool for characterizing and quantifying biomolecular interactions. This paper attempts to review the major developments in SPR technology. Main application areas are outlined and examples of applications of SPR sensor technology are presented. Future prospects of SPR sensor technology are discussed.
The growth, structure, surface morphology, optical properties and electrical resistivity studies on TiNx (0.4 < x ≤ 0.5) films is presented. The films of thickness 116–230 nm were grown on fused silica substrates by RF magnetron sputtering in 100% pure nitrogen atmosphere at ambient temperature and pressures from 12 to 25 mTorr. For the as-deposited films, the refractive index decreased from 1.86 to 1.6 with increasing N2 pressure from 12 to 25 mTorr. The absorption edge for the film deposited at 12 mTorr was 4.7 eV and it decreased to 3.5 eV on increasing the N2 pressure to 25 mTorr. Post-deposition annealing of the films at 873 K for 1 min did not cause any variation in the optical properties. The film deposited at 25 mTorr and annealed at 873 K showed a nanocrystalline peak corresponding to ɛ-Ti2N (3 1 1) with a crystallite size of 60 nm. Surface morphologies varied dramatically with N2 pressure. The electrical resistivity of the film deposited at 12 mTorr was 37 MΩ cm whereas it is 270 kΩ cm for the films deposited at 25 mTorr. Therefore, the current work provides signatures for the ɛ-Ti2N phase in terms of refractive index, optical absorption edge and electrical resistivity, that can be used to identify the presence of the sub-stoichiometric forms in a TiN film.
Novel cancer treatments, prevention of postmenopausal disorder, and prescription of oral contraceptives are the main developments in the design of synthetic estrogenic medication. The increasing consumption of these synthetic pharmaceuticals, in addition to human and animal natural estrogenic compound excretion, contribute to their environmental dissemination worldwide. Their assimilation as a result of consumption of food and water perturbs normal endocrine systems and leads to the emergence of human and animal diseases and malformations. These compounds are active in the organism at low concentrations. Accordingly, daily low-level exposure disrupts the natural equilibrium in the endocrine system. A method enabling quantification at such products at low levels (from pg L(-1) to ng L(-1)) is therefore required for these products. Surface plasmon resonance, essentially used for comprehension of molecular mechanisms and in drug discovery, can also be used for environmental pollutant monitoring. This technology has already been used for evaluation of the effects of chemical pollutants on specific nuclear receptors. It has been possible to determine the role of each individual compound on the disruption of the estrogen-activated cellular pathway. Development of SPR screening methods enables application of such an approach for quantification of these compounds in water.