This PDF file contains the front matter associated with SPIE Proceedings Volume 10731, including the Title Page, Copyright information, Table of Contents, Author and Conference Committee lists.

Self-shadowing effect is elucidated as a simple means without “nanotechnology” to realize nanostructured thin films and layers in two typical prominent nanostructure effects, that is, birefringence of obliquely deposited thin films and intense visible photoluminescence of porous Si. In oblique deposition, the self-shadowing effect takes place in ballistic deposition and accumulation of materials on a vacuum / substrate interface. In porous Si, the drift diffusion of positive holes from an anode thorough Si to Si/HF solution interface causes a modified diffusion limited aggregation of positive holes which leads directly to formation of pores.

The development of active photonic devices with quantum dots (QDs) as active media in the visible wavelength range promises a large improvement in a wide variety of areas from biochemical sensing to quantum computing. Novel active photonic devices including nanolasers and light emitting diodes have been demonstrated over the last years, but are primarily limited to research laboratories owing to the expensive and complex fabrication of nanoscale features with high fidelity and precision. In particular, active photonic devices which operate in the visible region impose additional challenges as the dimensions of the features are smaller or around λ/4n (λ, wavelength, n, the refractive index). At these length scales, standard nanofabrication methods such as photolithography, e-beam lithography, and molecular beam epitaxy are either prohibitively expensive, very slow or not compatible with optically active materials. Some processes require dry etching steps with plasma exposure or operating at elevated temperature, which can easily be detrimental to preserving the optical properties of active materials. Solving these issues will be the key to developing a new path towards a high throughput and large scale manufacturing of active nanophotonic devices. Here we report a dramatically simplified method to fabricate passive and active photonic devices in the visible region by direct nanoimprinting of high-refractive index materials integrated with colloidal quantum dots, demonstrated on active one (1-D) and two (2-D) dimensional photonic crystals. The direct patterning of functional materials, while preserving the properties of the active materials, represents a robust and practical solution to fabricate active photonic devices. It is a powerful strategy as it enables to fabricate photonic devices in a single step processing with the ability to tailor specific properties (e.g. emission wavelength) of a device starting at the molecular level. Active media colloidal CdSe/CdS quantum dots (QDs) QDs were applied in two different ways: embedded inside a printable high-refractive index matrix to form an active printable hybrid nanocomposite, and used as a uniform coating on top of printed photonic devices. As a proof of demonstration for printed active photonic devices, two-dimensional (2-D) photonic crystals as well as 1D and 2D photonic nano-cavities were successfully fabricated following a simple reverse-nanoimprint process. We observed enhanced photoluminescence from the 2D photonic crystal and the 1D nano-cavities. The process presented in this study is fully compatible with large-scale manufacturing where the patterning areas are only limited by the size of the corresponding mold. This work shows that the integration of active media and functional materials is a promising approach to the realization of integrated photonics for visible light using high throughput technologies. We believe that this work represents a powerful and cost-effective route for the development of numerous nanophotonic structures and devices that will lead to the emergence of new applications.

Experimental study and simulation analyses have been implemented in creation of an asymmetric metalinsulator- metal (MIM) on surface of glass. All of the metallic layers are composed of metallic nitrides or ceramics. Among recently reported alternative plasmonic materials, titanium nitride (TiN) and zirconium nitride (ZrN) are candidates for the metallic layers because they have plasmonic characteristic in visible region and chemically-stable. On the other hand, aluminum nitride (AlN) is used for the insulating layer because of its transparency, high refractive index, and high thermal conductivity. In this study, thin-film deposition of the ceramics is done by pulsed laser deposition (PLD) with high power UV Nd:YAG laser at 355nm. The PLD targets are hot-pressed pellets of microcrystalline powder. The asymmetric MIM structure is going to be applied to an end of optical fiber probe as an exciter of surface plasmon polariton.

In this talk, full time-domain hydrodynamic description of nonlinear electron dynamics in metallic nanostructures will be presented together with some vivid examples of its applications to harmonic generation on the nanoscale. The robust non-perturbalive numerical model implemented and solved, without any simplification reveals a key contribution to the nonlinear effects defined by the interplay between the topology of the nanostructure and the nonlocal response of the metal at the nanoscale. The quantum pressure term of the Fermionic gas responsible for nonlocal effects in the nonlinear hydrodynamic model leads to the emergence of fractional nonlinear harmonics and results in broadband coherent white-light generation. The investigation of Archimedean spirals, lacking any reflection and rotational symmetries, illuminated by 50 fs pulses, provides the clear signature of 6 nonlinear harmonics, favoring this structure over cylinders, as well as coherent white light generation. The described processes present a novel class of nonlinear phenomena in metallic nanostructures determined by nonlocality of electron response.

Carbon-Titan (C-Ti) multilayer films were deposited on silicon substrates by means of Thermionic Vacuum Arc (TVA) method. The final thickness of the multilayer structures was up to 400nm. The coated layers consisted of a base layer of about 100nm of Carbon deposited at low evaporation rates in order to ensure its stability on the substrate. Subsequently, seven Carbon and Titanium layers were deposited alternatively on top of Carbon base layer, each of them has a final thickness up to 40nm. For this study we obtained different batches of samples by variation of the substrate temperature between 0°C and 400°C, and the ion acceleration voltage applying a negative substrate bias voltage up to -700V . A low deposition rate 0.14nm/s for C and 0.18nm/s for Ti respectively was used in order to obtain the precise thickness.

The characterization of microstructure properties of as prepared C-Ti multilayer structures were done using Electron Microscopy techniques (TEM, SEM, STEM), and Raman Spectroscopy. TEM and STEM studies were performed on Philips Tecnai F30G2 at 300kV setup. Identification of the structure of the material was based on the data obtained from diffraction pattern with a Philips CM120ST using CRISP2 application, with crystalline material module (ELD). The morphology and thickness of the samples were also determined by SEM techniques with Quanta FEG450 setup. The thickness thus measured are between 155.4nm and 393.9nm. Raman spectra were measured at room temperature on a Jobin Yvon T6400 spectrometer using 514.5nm line of an Ar+ laser as the excitation source. The measurements reveal the content of diamond-like sp³ and graphite-like sp²; the ratio sp³/sp² increases when the bias voltage increases. For tribological characteristics determination, systematic measurements were performed using a ball-on-disk tribometer made by CSM Switzerland with normal force of 0.5, 1, 2, 3N respectively. The coefficient of friction depends on the substrate temperature and on the bias voltage. To characterize the electrical conductive properties, the electrical surface resistance versus temperature have been measured using drop voltage between two ohmic contacts on the sample and drop voltage on a standard resistance in a constant current regime. Owing to metallic layer of titanium in multilayer films, mechanical and electrical properties can be improved.

Several aspects of photonics, such as laser cavities, random lasing, plasmonics, strong coupling with matter etc. requires the description of a medium exhibiting gain. A very simple model consists in using an effective permittivity with a sign changing imaginary part, as compared to a non-active material. Using this model, we investigate the possibility of controlling the closing or opening of a band-gap inside a dielectric metamaterial. Further, we question the model itself and show that it leads to non-physical effects. The conclusion is that the model is not reliable for more than a short time description of the physics at stake.

The planewave reflection/transmission characteristics of two nanostructured thin films were investigated numerically. The thin films are: (i) a columnar thin film and (ii) a periodic multilayer whose unit cell consists of two different columnar thin films. The nanocolumns of these thin films were taken to be made from dissipative materials while the intercolumnar regions were filled with an active material. A combination of inverse and forward homogenization formalisms was employed to estimate the constitutive parameters of the thin films. By computing reflectances and transmittances, it was found that the thin films can simultaneously amplify s-polarized incident light and attenuate p-polarized incident light, or vice versa. This polarization-state-dependent attenuation and amplification phenomenon depends upon the angle of incidence and the thickness of the thin film. Furthermore, the periodic multilayer was found to exhibit the Bragg phenomenon in two generally distinct polarization-dependent spectral regimes for incident linearly polarized light. The presence of both dissipative and active materials allows the high reflectance to generally exceed unity for incident light of one linear polarization state but not for incident light of the other polarization state, in their respective Bragg regimes; however, transmittances are low in both Bragg regimes. That is, the chosen periodic multilayer is at best a good Bragg mirror for one linear polarization state and a Bragg supermirror for the other linear polarization state.

We present optical simulations for a tandem solar cell consisting of a nanostructured thin-film perovskite top cell and a silicon heterojunction (SHJ) wafer bottom cell. The absorption and related current density are calculated using the rigorous simulations in the form of the finite element method for the nanostructured perovskite cell and a semi-empirical method for the SHJ cell. In order to reach the optimal value for the perovskite layer thickness we employ Newton’s method using derivatives obtained directly from the rigorous simulation. Using this we obtain an optimal layer thickness using typically one iteration step and eliminate the need for a parameter scan. We compare the results for different sinusoidal nanotextures applied to different layers in the multilayer thin-film perovskite top cell. The nanotextures lead to a gain in absorption and power conversion efficiency in comparison to an optimized planar reference. We also present experimental results towards a realisation of the proposed structure. These results give valuable insight for the emerging field of high efficiency perovskite/SHJ tandem solar cells.

Inspired by the mechanism of the wings of Morpho butterfly, here we propose biomimicry designs which have the potential to be used for radiative cooling purposes. We numerically analyzed the spontaneous emission at near-field and determined radiative heat flux at nano-scale in order to investigate the impact of geometric variations and material selection in these systems. Our findings suggest that these metasurfaces which support phononic surface waves, can be used to tailor radiative heat transfer at nano-scale in the atmospheric transparency window (8-13 μm) within the infrared regime.

Carbon nanotubes, and more specifically single walled carbon nanotubes (SWNTs), possess unusual properties which are valuable for nanotechnology and other fields of materials science and technology, owing to their extraordinary thermal, electrical, and in particular mechanical properties. Most of the desirable mechanical properties, including a high tensile strength, result from the covalent sp²-bonds formed between individual carbon atoms. However, SWNTs are much softer in their radial compared to their axial direction, which results in a reversible elastic deformation of the cross section when applying sufficiently strong hydrostatic pressures. This article provides further evidence, via time dependent Raman spectroscopy, that a stable deformed state exists as a result of van-der-Waals-interactions within individual tubes and specifically that these tubes can fully recover from this deformed state on surprisingly long time scales on the order of tens of minutes. In order to distinguish inter-tube from intra-tube effects, all experiments have been performed with densely packed, vertically aligned, free-standing SWNT arrays in comparison to individual, de-bundled SWNTs. These insights lead to far reaching conclusions regarding the mechanical properties and binding energies of the found stable state and, via a detailed analysis of D-mode, enable the distinction of fully reversible deformations from defect induced states.¹

Standard high reflectivity coatings consist of materials with high and low refractive indexes. Typically, optical resistivity of such elements is limited by the threshold value of material with high index. Combination of two deposition methods, namely ion-beam sputtering and oblique angle deposition, was used to form high reflectivity coatings for the wavelength of 355 nm. Variation of the design of standard coating and the number of top layers, deposited at oblique angle have been investigated. Laser induced damage thresholds, optical scattering, surface roughness, spectral performance etc. were tested for the experimental samples. Analysis indicate that combination of both deposition methods allows to enhance the optical resistivity of typical high reflictivity mirrors. Introducing standard method also allows to stabilize the spectra and reduce the losses of total optical component.

This paper describes digital printing of optical metasurfaces for ink-free colour decoration and flat optics, by holographic laser post-writing on nano-textured, metal-coated optical metasurfaces. Our optical metasurfaces are based on the concepts of both localized surface plasmon resonances (LSPR) and high-index dielectrics compatible with technologies for high volume manufactured plastic products. The optical metasurfaces are formed by nanoimprinting a surface texture comprising nanoscale cylinders. By subsequent deposition of a thin film of metal or high index dielectric, isolated nano-discs are formed on top of the cylinders, while a continuous film is formed on the substrate surface in between the cylinders. The nano-scale disks and corresponding holes in the continuous film form optical resonators. The master-original for the square-centimeter nano-texture is realized by means fast e-beam writing. The nanotextured plasmonic metasurface may be covered with a transparent protective coating, which can withstand the daily life handling. Laser post-writing can modify disks and holes, and hence the optical resonances. Laser pulses induce transient local heat generation that leads to melting and reshaping of the imprinted nanostructures. This enables flexible definition and alignment of optical components on high volume manufactured plastic products. Our approach offers a printing speed of 1 ns per pixel (in raster scan), resolution up to 127,000 dots per inch (DPI) and power consumption down to 0.3 nJ per pixel. References J. S.Clausen et al., Nano Letters, 14, 4499-4504, (2014). A. Kristensen et al., Nature Reviews Materials 2,16088, (2016). X. Zhu et al., Science Advances, 3(5), e1602487, (2017). E. Højlund-Nielsen et al., Adv. Mater. Technol., 1600054, (2016). E. Højlund-Nielsen et al., Microelectronic Engineering, 121, 104-107, (2014). X. Zhu et al., Nature Nanotechnology, 11, 325-329, (2016). M. S. Carstensen et al., ACS Photonics, in press (2018).

A one-dimensional, single-material polarizing photonic bandgap structure is designed and fabricated using e-beam PVD and oblique angle deposition technique. In order to obtain high- and low-index layers, we deposited alternate layers of titanium dioxide (TiO₂) at deposition angles of 0° and 70°on top of a fused silica substrate. This approach is chosen since at deposition angle of zero degree, deposited TiO₂ using e-beam PVD, show a negligible birefringence while the obliquely deposited TiO₂ acts as a biaxial material with significant birefringent behavior. As a result, deposition of a bilayer film at two angles is analogous to using two different materials with the advantage of simplifying fabrication and modeling this polarizing device. The bandgap of the bilayer structure is modeled in a way that only a specific wavelength with certain polarization, p polarization, could pass through while the s polarization is reflected. For modeling we used Transfer Matrix Method and numerical FDTD analysis to simulate behavior of the 1D photonic band gap structure. The simulations produce better than 98% reflection for s polarization and almost no reflection for p polarization for the center wavelength of 632.8 nm. The fabricated device shows 94% reflection for s polarization and less than 6% reflection for p polarization at the red HeNe laser wavelength at an incident angle of 70°. The results demonstrate that a 1D multi-layer photonic crystal, fabricated from a single material, can be designed to selectively reflect or transmit p or s polarization of an incident light beam.

Aluminum-nickel nano-alloys were prepared by successive evaporation of nickel and aluminum ultra-thin films on silicon and glass substrates at room temperature. Alloying was obtained through the spontaneous intermixing of the ultra-thin layers at room temperature. The shift in the X-ray photoelectron spectroscopy (XPS) peaks of the pure metals indicated the alloying process in the films. Using spectroscopic ellipsometry from the UV to near infrared spectral range, the optical properties of these films were investigated. The effective pseudo-dielectric functions obtained by direct inversion of the ellipsometry spectra reveled a surface plasmon resonance at 364 nm in the prepared alloys. The resonance peak was pronounced for the pure nickel films and it did not suffer any spectral shift when the films were alloyed with aluminum. Interpretations of this behavior is presented.

Recently, the so-called perfect absorbers, which are light-trapping nanostructures absorbing almost 100% of incident light with a designed wavelength, have attracted significant attention. The perfect absorbers consist of multilayers (absorption, dielectric, and mirror layers), which can be theoretically realized by any combination of materials. However, in order to achieve properties useful for a specific purpose, it is necessary to tune the optical properties of the absorption and dielectric layers by introducing metamaterials into the layered structures. Oblique-angle deposition (OAD) is one of the most powerful techniques to tailor metamaterials, which include well-controlled nanomorphologies significantly smaller than the wavelength of visible light, enabling the control of optical properties of various materials in different wavelength regions, from ultraviolet to infrared, at low costs. In this paper, we present several types of perfect absorbers fabricated by the OAD technique and their applications to photocatalysts, biochemical sensors, optical elements, and thermoplasmonic control of microfluidics.

We studied the optimization of an ultrathin CuIn_1-ξGa_ξSe₂ (CIGS) solar cell with a nonhomogeneous CIGS absorber layer and backed by a 1D metallic periodically corrugated back-reflector (PCBR) with a rectangular profile. Nonhomogeneity in the CIGS absorber layer was modeled through either a sinusoidal or a linear bandgap variation along the thickness direction. The maximum power density for the AM1.5G spectrum was determined from the spectrum of the useful solar absorptance computed using the rigorous coupled-wave approach. Ultrathin solar cells with optimized PCBR and homogenous bandgap depending on the thickness of the CIGS layer were found to deliver the best photonic absorption characteristics. The open-circuit voltage, efficiency, and fill factor were calculated for the optimal designs using values of the reverse-saturation current density, ideality factor, and the series resistance density obtained from experimental results. The overall trend is that the effect of the PCBR becomes less prominent as the thickness of the CIGS absorber layer increases. Higher efficiency and fill factor can be achieved with a solar cell containing as 400-nm-thick CIGS layer compared to the conventional solar cell with a 2200-nm-thick CIGS layer.

The optical properties of monolayer transition-metal dichalcogenides (1L-TMDs) are predominantly governed by excitonic effects even in room temperature because of two-dimensional confined nature. As the result of strong coulomb interaction in 1L-TMDs, non-radiative exciton-exciton annihilation (EEA) is one of key influence to their light emission at nominal excitation density. Therefore, the modulation of EEA can help to make higher photoluminescence (PL) quantum yeild and develop optoelectric devices using 1L-TMDs. Here, we observed reduced EEA rate in mechanically exfoliated monolayer tungsten disulfide (1L-WS2) by laser irradiation with improved light emission at the saturating optical excitation level. PL efficiency of 1L-WS2 in irradiated region increased with increasing the excitation intensity and finally it was 3 times higher at high excitation level compared to that in non-irradiated region, while the laser irradiated regions in 1L-WS2 have lower PL intensity at low excitation level than non-irradiation region. This kind of the excitation density dependence was confirmed by time-resolved PL measurement and EEA rate was reduced about 3 times by laser irradiation. Sulfur vacancies and lattice distortion might be formed by laser irradiation which can give rise to lower PL and shorter lifetime in laser irradiated region of 1L-WS2. But, we attribute these laser induced defects or adsorption of oxygen molecules in air to the origin of reduced EEA by hindering exciton diffusion. Our results could provide an idea for high performance opto-electric devices.

Three-dimensional chiral metamaterials, plasmonic nanohelixes, with chiroptical activity have attracted attention for many potential photonic applications. In previous works, glancing angle deposition (GLAD) has been applied to deposit various Ag nanohelix arrays on smooth substrates and the structure dependent circular dichroism has been measured and analyzed. In this work, two-turn SiO₂ nanohelixes are grown upon Ag nanohelixes to form a SiO₂-Ag nanohelix array. For the bottom Ag nanohelices, the average pitch length (P) and the radii of curvature (R) are 231nm and 137nm, respectively. P and R are 174nm and 118nm for the top SiO₂ nanohelices, respectively. Under left-handed (righthanded) circularly polarized light illumination, the transmittance, reflectance, and extinctance of the SiO₂-Ag nanohelix array are measured. The circular dichroism described with g-factor is also presented here as a function of wavelength. According to the measurement, the g-factor exhibits a shift phenomenon as the SiO₂ nanohelixes are capped upon Ag nanohelixes. This phenomenon leads to flexible control over the circular dichroism of SiO₂-Ag nanohelix arrays with respect to the resonance wavelength and amplitude of g-factor.

The planewave re ection/transmission characteristics of a chiral sculptured thin film (CSTF) were investigated numerically. The helical nanowires of the CSTF were taken to be made from a dissipative material while the void regions between the nanowires were filled with an active material. Theory showed that the CSTF can simultaneously amplify left-circularly-polarized incident light and attenuate right-circularly-polarized incident light, or vice versa depending upon the handedness of the CSTF. The presence of both dissipative and active materials allows the high reflectance to exceed unity for incident light of one circular polarization state across a substantial portion of the circular Bragg spectral regime but not for incident light of the other circular polarization state. That is, the chosen CSTF is a circular Bragg supermirror for one, and only one, circular polarization state.

Small scale magnets have very high technological importance today. We synthesized thin film magnets containing iron and nickel oxides using sol-gel and spin coating methods. Structural properties of iron particles were investigated using Mossbauer spectroscopy, X-ray absorption spectroscopy including Extended X-ray Absorption Spectroscopy. The variation in oxidation state and other structural parameters were deduced. It appears the oxidation state of iron particles prepared by sol-gel method is very stable up to annealing temperatures of 600° C. The iron particles prepared by spin coating method exist in two different chemical environments with slightly different oxidation states.