Vapor Incidence Angle Research Articles

Effect of substrate rotational speed during deposition on the microstructure, mechanical and tribological properties of a-C:Ta coatings

Rotational speed has an important influence on the performance of coating materials. The a-C:Ta composite coatings were prepared by controlling the substrate rotational speed during deposition process using PVD technique. The results showed that the coating transformed from dense structure to columnar structure. Due to the changes of deposition time and the vapor incident angle of the sputtering ions, the sp2 hybrid structure increased and the C–Ta bonds contents decreased as a function of the rotational speed, which led to the improvement of adhesion force. The average friction coefficient of the composite coatings did not fluctuate significantly for the amorphous carbon matrix and the transfer films formed during friction, while the wear rates were gradually increased. The sample at 0.5 rpm possessed the lowest wear rate, which was mainly associated with the cooperative behavior of the dense structure and the formation of TaC nanoclusters in the composite coating.

Transition from discrete patches to plasmonic nanohole array by glancing angle deposition on nanosphere monolayers

By combining nanosphere lithography and glancing angle deposition, a morphological transition from disconnected patchy silver (Ag) coated nanosphere particles to a connected Ag nanohole sheet on close-packed nanosphere monolayers has been demonstrated, which significantly changes the optical property of the Ag nanostructure deposited. For different sized nanosphere monolayers, when the vapor incident angle was set to be 55°, the transmission spectra showed complicated features when the Ag deposition thickness was less than 60 nm. When the thickness was large enough (≥60 nm), a distinguished extraordinary optical transmission (EOT) peak was observed. The EOT peak wavelength position is independent of the Ag thickness deposited and is proportional to the nanosphere diameter. The obtained EOT peaks possess a high quality factor and have high transmission values compared to those reported in the literature for similar structures. The Monte Carlo growth simulations demonstrate the morphological transition from the patchy arrays to nanohole arrays while the electromagnetic numerical calculations confirm the change in the optical properties. Such a high quality EOT response could be used for constructing better sensors or developing other plasmonic applications.

Comparative study of TiAlN coatings deposited by different high-ionization physical vapor deposition techniques

In physical vapor deposition (PVD), the energy and incident angle of ions can be adjusted easily by applying an electromagnetic field so that coatings with different structures and properties can be produced. In this work, several high-ionization coating techniques are employed to deposit TiAlN coatings to compare the effectiveness of each technique and resulting coating properties. The continuous high-power magnetron sputtering (C-HPMS) technique shows advantages in the deposition rate and coating performance. In addition, a deposition rate of 400 nm/min is achieved by C-HPMS, whereas those of high power impulse magnetron sputtering (HiPIMS) and arc ion plating (AIP) are 85 nm/min and 225 nm/min, respectively. The coating also shows a particle-free and dense morphology with a smaller surface roughness of 22.4 nm. Owing to efficient ionization, the TiAlN coating deposited by C-HPMS has a high hardness of 33.2 GPa which is comparable to those prepared by AIP and HiPIMS but with small residual stress. The results provide valuable information on how to choose the proper techniques and parameters to produce coatings with the desirable adhesion strength, tribological properties, as well as corrosion resistance.

Optical filters for linearly polarized light using sculptured nematic thin flim of TiO2

A study of optical filters using sculptured nematic thin films is presented in this article. A central 90◦ twist-defect between two sculptured nematic thin films (SNTFs) sections transmit light of same polarization state and reflect other in the spectral Bragg regime. The SNTFs reflect light of both linearly polarized states in the Bragg regime if the amplitude of modulation of vapor incident angle is increased. A twist-defect in a tilt-modulated sculptured nematic thin films as a result produces bandpass or ultra-narrow bandpass filter depending upon the thickness of the SNTFs. However, both the bandpass or/and ultra-narrow bandpass filters can make polarization-insensitive Bragg mirrors by the appropriate modulation of the tilted 2D nanostructures of a given sculptured nematic thin films. Moreover, it is also observed that the sculptured nematic thin films are very tolerant of the structural defects if the amplitude of modulating vapor incident angle of the structural nano-materials is sufficiently large. Similarly, we observed the affect of incident angles on Bragg filters.

Morphology of Thin Films Formed by Oblique Physical Vapor Deposition

Physical vapor deposition is a fundamental tool to create thin films for countless applications. Deposition at oblique vapor incidence angles can lead to the growth of thin films with dramatically changed morphological features. Techniques such as oblique angle deposition (OAD) and glancing angle deposition (GLAD) utilize this fact to create self-organized nanostructures on surfaces. The changed columnar microstructure of such thin films significantly influences the film properties. The film density, for instance, influences the refractive index and therefore has impact for optical applications, like filters or antireflection coatings. Understanding the influence of the incidence angle in physical vapor deposition is an important step that allows tailoring the nanostructured surfaces for specific applications not only in optics, but also for catalysis or biosensing usage. To investigate thin film growth at oblique deposition conditions, silicon, germanium, and molybdenum nanostructured thin films were dep...

Morphology and crystal texture in tilted columnar micro-structured titanium thin film coatings

Titanium thin films deposited at various polar incidence angles by electron-beam evaporation are investigated by electron microscopy and X-ray diffraction pole-figures. The resulting film morphology and texture are shown to be strongly affected by the vapor flux direction. At normal incidence deposition angle, a fiber texture forms, with the c-axis of Ti crystallites aligned parallel to the surface normal with random in-plane (azimuthal) orientation. At off-normal deposition angles, porous morphologies with inclined micro-columns form. The texture of these films is an inclined fiber texture, where the texture tilt angle increases with increasing deposition angle. Biaxial texture is observed for films grown at polar incidence angles larger than 60°. The micro-column tilt axis, and the c-axis of the crystallites, both lie in the deposition plane but at different polar angles; the mechanism behind micro-column tilt is due to the shadowing effect, whereas the fiber texture tilt angle and the biaxial texture orientations of the films result from evolutionary crystal growth, determined by the kinetic growth habits of crystallites.Changes in the morphology of Ti films deposited at a vapor incidence angle of 84° and nominal thickness of 3μm at substrate temperatures corresponding to homologous temperatures of 0.15, 0.4, and 0.5 are studied, and compared to the Mukherjee and Gall structure zone model, proposed for high temperature glancing angle deposition. The observed morphology changes are consistent with their model of competition between shadowing length and adatom diffusion length. All the films were grown with homologous temperature lower than 0.5, and formed porous and inclined micro-column morphology, resulting from the dominance of shadowing over adatom surface diffusion.

Band-Limited Filters and Bragg Reflectors in Perturbed Defect Nanostructures of Chiral Sculptured Thin Films

Sculptured thin films (STFs) are engineered films having tailored morphology and high porosity. Henceforth, we can elicit desired optical responses upon light excitation in these films. The oblique deposition of the nanocolumns and the resulting anisotropic properties have been discovered over the past decade. Their discovery has lead to unique and predictable optical, mechanical, electrical, magnetic, thermal, and biological properties. To study the optical response of such STFs, we introduced a central defect in a perturbed chiral STF (CSTF), which transmits light of one circular polarization state and reflects the other in a spectral Bragg regime. The perturbed CSTF reflects light of both circular polarization states in the Bragg regime if the amplitude of modulation of vapor incident angle increases. A structurally chiral layer defect or either central twist defect in a perturbed matched CSTF fabricated a narrow bandpass (ultranarrow bandstop filter) and Bragg reflectors depending upon the thickness and periods of these nanostructures. However, both the ultranarrow bandstop filter and Bragg reflectors have become polarization insensitive by the appropriate modulation of the tilt nanohelixes of perturbed CSTFs. Moreover, simulation revealed that the polarization-insensitive Bragg mirrors, laser mirror, and Bragg reflector were fabricated using such CSTF structures having structural defect. These structural nanomaterials are very tolerant when the amplitude of modulation of vapor incident angle is sufficiently large. It has been also examined that different STFs structures of different refractive indices and porosity are fabricated by changing deposition angle and angle of inclination through modulation and glancing angle deposition.

Multiple excitations of a surface-plasmon-polariton wave guided by a columnar thin film deposited on a metal grating

Surface-plasmon-polariton (SPP) wave excitation in a composite structure obtained by depositing a columnar thin film (CTF) on a metal (silver) substrate decorated periodically by an array of rectangular grooves was analyzed using the rigorous coupled-wave approach. The SPP wave is excited as a Floquet harmonic of different orders by light incident from different directions, the incidence plane being the same as the grating plane. But, in some instances, the SPP wave appears to be excited as a doublet, i.e., a Floquet harmonic of the same order at two closely spaced angles of incidence, the excitation being less efficient for one angle of incidence than for the other. The characteristics of the SPP wave are affected by the vapor incidence angle chosen to deposit the CTF.

Highly sensitive double-layered nanorod array gas sensors prepared by oblique angle deposition

ITO based nanorod arrays fabricated by oblique angle deposition (OAD) were designed as resistive gas sensors for NO2 detection, and the detection limit was found to reach as low as 50 ppb with a response time of 20 min. A comparative study shows that the ITO nanorod array has a higher sensing response than that of the ITO film, and a double-layered ITO nanorod array design could further improve the sensing response. By increasing the vapor incident angle during the nanorod fabrication, the sensing response also increases, due to the increased porosity and gas penetration. It is expected that OAD technique could become a versatile and scalable fabrication technique for gas sensors.

Sculptured platinum nanowire counter electrodes for dye-sensitized solar cells

Sculptured platinum nanowire thin films were formed by oblique angle electron beam evaporation with a 5° vapor incidence angle and incorporated as counter electrodes for dye-sensitized solar cells (DSSCs). For the comparison of the performance, bare fluorine doped tin oxide, planar Pt electrodes and counter electrodes treated with chloroplatinic acid were prepared. The sculptured Pt nanowire electrodes showed five times lower charge transfer resistance (0.121 [Ω∗cm2]) than that of Pt planar electrode (0.578 [Ω∗cm2]) and when the Pt nanowire electrodes are treated with an H2PtCl6 solution have more than ten times lower charge transfer resistance (0.04025 [Ω∗cm2]). Moreover, Pt nanowire films used as a counter electrode lead to enhancement in current density and efficiency in comparison with Pt planar counter electrodes. The conversion efficiency with planar electrodes was 5.1 [%] while the efficiency of DSSC with platinum nanowire counter electrodes reached to 5.63 [%] under AM 1.5 illumination.

Observations of self-assembled microscale triangular-shaped spikes in copper and silver thin films

We present observations on the formation of previously unreported self-assembled triangular-shaped morphological features in copper and silver thin films deposited at oblique and glancing vapor incidence angles by electron-beam evaporation in ultrahigh vacuum, and characterized them by using scanning electron microscopy (SEM). This systematic study investigates the morphology of 500nm thick copper and silver films, fabricated at vapor incidence angles between 0 and 85 degrees, from the substrate normal. Films fabricated at 50 degrees vapor incidence and greater exhibit triangular-shaped “microspikes” scattered seemingly randomly across the surface with areal densities on the order of 50 spikes per 10×10micrometer area. SEM analysis reveals that the microspikes increase in size with increasing vapor incidence angle. Films deposited at glancing vapor incidence angles (80 degrees and greater), are composed of inclined nanoscale columnar structures, with a high degree of interconnectivity between adjacent columns; where microspikes grow randomly from these tilted columns, and the spikes range in size from 100 to 2000nm in length.

Reflectance and surface enhanced Raman scattering (SERS) of sculptured silver films deposited at various vapor incident angles

By using e-beam evaporation at various oblique angles, silver nanorod arrays were produced on silicon and fused silica substrates. Reflectance of P and S polarizations was measured at an incident angle of 30°, with the data analyzed by using the appropriate optical dispersive model. The surface enhanced Raman scattering (SERS) was investigated using trans-1,2-bis(4-pyridyl)ethene (BPE) as a probe molecule at an excitation wavelength of 633 nm. The Ag-coated surface become rougher as the vapor incident angle is increased. Only the sample deposited at 85° shows clear oblique column structure. Reflectance fitting confirmed the positive rexlation between roughness and deposition angle and showed an increase of porosity in the film with increasing deposition angle. The reflectance measurements also indicate that the sample deposited at 85° has a very high anisotropic effect due to the inclined column structure. In the RS scans, only the 85° samples on Si and silica substrates gave strong SERS with a similar enhancement factor, with a higher background level and noise signal from the silica substrate.

Tilting angle of nanocolumnar films fabricated by oblique angle deposition

The tilting angle, β, of nanocolumns during oblique angle deposition (OAD) as a function of vapor incident angle, θ, has been investigated through both literature survey and systematic experiments. Most experimental data cannot be fit by either the tangent or cosine rule and show strong material dependence. The material-dependent fan angle, φ, can be extracted using the fan-out model proposed by Tanto et al. [J. Appl. Phys. 108, 026107 (2010)]. This fan angle, φ, depends closely on the melting temperature for single element materials, the heat of formation for compound materials, lattice structure, and the complexity of the materials, and is a critical parameter in understanding the fundamental growth mechanism of OAD.

Composition dependent nanocolumn tilting angle during the oblique angle co-deposition

During the oblique angle co-deposition of Si and Cu, the nanoculumn tilting angle β changes systematically with the relative composition of Si and Cu when the vapor incident angle θ is fixed. This result demonstrates that the β-θ relationship does depend closely on the material property and composition, which is very different from the predictions of the well-known “universal” models, such as tangent or cosine rules. A statistic model based on the size, spacing, and stacking of Si and Cu atoms has been proposed and the predicted result agrees well with the experimental data.

Processing-structure-property relationships in electron beam physical vapor deposited yttria stabilized zirconia coatings

The physical and mechanical properties of yttria stabilized zirconia (YSZ) coatings deposited by the electron beam physical vapor deposition technique have been investigated by varying the key process variables such as vapor incidence angle and sample rotation speed. The tetragonal zirconia coatings formed under varying process conditions employed were found to have widely different surface and cross-sectional morphologies. The porosity, phase composition, planar orientation, hardness, adhesion, and surface residual stresses in the coated specimens were comprehensively evaluated to develop a correlation with the process variables. Under transverse scratch test conditions, the YSZ coatings exhibited two different crack formation modes, depending on the magnitude of residual stress. The influence of processing conditions on the coating deposition rate, column orientation angle, and adhesion strength has been established. Key relationships between porosity, hardness, and adhesion are also presented.

Synoptic view of Dyakonov–Tamm waves localized to the planar interface of two chiral sculptured thin films

The Dyakonov-Tamm wave combines the features of the Dyakonov wave and the Tamm electronic state. Dyakonov-Tamm waves guided by the planar interface of two dissimilar chiral sculptured thin films (STFs) were systematically examined. The interfaces result from the chiral STFs being dissimilar in (a) orientation about the helical axis, (b) structural handedness, (c) structural period, (d) vapor incidence angle, (e) material, or (f) various combinations thereof. A boundary-value problem for the propagation of Dyakonov-Tamm waves was formulated and numerically solved. Up to three physical solutions were obtained for any specific combination of constitutive properties of the two chiral STFs. Each solution indicates the existence of a Dyakonov-Tamm wave. If more than one solution exists, the corresponding Dyakonov-Tamm waves differ in phase speed and degree of localization to the interface. Fewer solutions were found when the two chiral STFs differ in many attributes.

Determination of constitutive and morphological parameters of columnar thin films by inverse homogenization

A dielectric columnar thin film (CTF), characterized macroscopically by a relative permittivity dyadic, was investigated theoretically. The CTF was assumed, on the nanoscale, to be an assembly of parallel, identical, elongated ellipsoidal inclusions made of an isotropic dielectric material that has a different refractive index from the bulk material that was evaporated to fabricate the CTF. The inverse Bruggeman homogenization formalism was developed in order to estimate the refractive index of the deposited material, one of the two shape factors of the ellipsoidal inclusions, and the volume fraction occupied by the deposited material, from a knowledge of relative permittivity dyadic of the CTF. A modified Newton-Raphson technique was implemented to solve the inverse Bruggeman equations. Numerical studies revealed how the three nanoscale parameters of CTFs vary as functions of the vapor incidence angle.

Multiple trains of same-color surface plasmon-polaritons guided by the planar interface of a metal and a sculptured nematic thin film. Part III: Experimental evidence

The absorbance, reflectance, and transmittance of a linearly polarized, obliquely incident plane wave were calculated for the planar interface of a metal and a sculptured nematic thin film (SNTF) in the Kretschmann configuration, the wave vector of that plane wave being arbitrarily oriented with respect to the morphologically significant plane of the SNTF. The permittivity profile of the chosen SNTF was supposed to have been sculptured during physical vapor deposition by varying the vapor incidence angle sinusoidally about a mean value. Regardless of the orientation of the wave vector, multiple surface-plasmon-polariton (SPP) trains or waves of the same color but different phase speeds and guided by the metal/SNTF interface can be excited.

Erratum: Engineering the phase speed of surface plasmon wave at the planar interface of a metal and a chiral sculptured thin film

AbstractOriginally published Microwave Opt Technol Lett 50:1966–1970, 2008. © 2009 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 2524, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24663

Multiple trains of same-color surface plasmon-polaritons guided by the planar interface of a metal and a sculptured nematic thin film. Part II: Arbitrary incidence

The absorbance, reflectance, and transmittance of a linearly polarized, obliquely incident plane wave were calculated for the planar interface of a metal and a sculptured nematic thin film (SNTF) in the Kretschmann configuration, the wave vector of that plane wave being arbitrarily oriented with respect to the morphologically significant plane of the SNTF. The permittivity profile of the chosen SNTF was supposed to have been sculptured during physical vapor deposition by varying the vapor incidence angle sinusoidally about a mean value. Regardless of the orientation of the wave vector, multiple surface-plasmon-polariton (SPP) trains or waves of the same color but different phase speeds and guided by the metal/SNTF interface can be excited.