Fourier transform approximation is used to synthesize continuously changeable refractive index filters on a substrate. Its performance is sensitive to small variations of the involved deposition parameters. We study this dependence, numerically and experimentally.

Carbon quantum dots (CQD) have received significant attention in recent years due to their potential applications in optics and sensing. In this study, the authors report on the first characterization of the optical activity and broad absorption spectrum covering from short‐wave ultraviolet, at 200 nm, to mid‐infrared, at 1600 nm, of CQD synthesized using the “low‐molecular‐weight alcohols electrochemical carbonization” method. The CQD are analyzed using spectroscopic techniques, optical activity in the infrared, and high‐resolution transmission electron microscopy. Results show a CQD size distribution of 5±3 nm and spherical morphology. The absorption spectra show increased absorption at both, high and low frequency. Additionally, the specific rotation of the CQD solution is significantly higher than that of pure ethanol, by three orders of magnitude. These findings suggest that CQD may have potential applications in polarized infrared filters and/or sensors due to their ability to rotate the polarization state of light at 1550 nm. The results of this study provide valuable insights into the optical properties of CQD and their potential for infiltration into hollow core photonic crystal fibers, making them a promising material for future research and development in the field of optics and sensing.

In this work we design and fabricate from n(lambda) and k(lambda) experimental data for both Al2O3 and TiO2 single layer materials, an optical coating as "dielectric-mirror" following the non-quarter-wave stack formula (HxLy)H-8(x). Optical coating based on multilayer film on BK7 glass and Si(1 0 0) wafer substrates, was grown by thermal atomic layer deposition at 150 degrees C. Optical constants and optical properties of the TiO2-Al2O3 multilayer stack, before and after thermal treatment at 450 degrees C, were studied via spectroscopy ellipsometry and UV - Vis measurements in the spectral range from 200 to 1100 nm. Also, similar samples were studied by means of TEM, SEM and AFM at room temperature in order to obtain information about the morphological properties. From optical studies, we found absorption due to carbon impurities related with organometallic precursor used in ALD process; to reduce carbon related absorption, samples were submitted to an annealing process at 450 degrees C under air atmosphere. A reject zone or "stopband region" between 381 and 451 nm, with maximum reflection around of 99.9%, cut-off points at 371 and 455 nm after thermal treatment. This reject zone presents an acceptable bandwidth at lambda(0) = 420 nm reference wavelength. Results open the possibility to fabricate dielectric-mirrors on complex geometry substrates without the restriction of direct evaporate exposed-view, due to the conformality advantage of ALD technology and its affinity with nanophotonics and integrated optics.

A good Low-Emissivity (Low-E) filter coated on glass reduces the amount of heat coming from solar light into the building, thus the expenses in electricity for air conditioning are reduced. Standard Low-E filters contain a Silver layer between two dielectric thin films due to its high reflectance of infrared wavelengths: however, one of the major silver drawbacks are its chemical and mechanical weakness which reduces the filter mean lifetime. In this paper, we investigate alternative materials to be a substitution of Ag, and they were compared with commercial filters. It was found that an aluminum-based filter has a good cost-benefit performance with peak transmittance better than 80% in the visible, while having less than 20% transmittance for wavelengths longer than 1500nm. A simulation of the filters construction was made providing a tolerance of each layer thickness, so the filter keeps its optical performance (C) 2019 Elsevier B.V. All rights reserved.

We present a thorough study of the target-cleaning phase to estimate the healthiness of the target in a direct current (DC) magnetron sputtering deposition. The study is based on real-time plasma monitoring by means of optical emission spectroscopy during a traditional cleaning phase in an Ar atmosphere. In this work we demonstrate that intensities of Ar emission lines are sufficient indicators of the target cleanliness degree. To derive these results SiOxNy thin films were grown by reactive DC magnetron sputtering on silicon wafers for different deposition configurations of Ar, O-2 and N-2 fluxes. Refractive index of the resulting films is measured by in-situ spectroscopic-ellipsometry. A simple but robust estimator is used to determine the time when the target is ready to start deposition. Hence, this approach can be suited for an industrial environment since the time invested in the cleaning phase can be minimized avoiding the waste of material and time.

Nanolaminate multilayers made of Al2O3 and Y2O3 bilayer slabs were grown at 250 C by means of thermal Atomic Layer Deposition (ALD). Several samples were prepared, where the number of ALD cycles for the Al2O3 slab was kept constant at 17 ALD cycles, while the number for the Y2O3 slabs was varied from 1 to 100. An optical model was built and adapted for each sample considering the Cauchy relationship, which was used to simulate the optical response for transparent materials. The thickness obtained from the optical model was in agreement with the thickness of cross-sectional SEM images. The optical band gap, obtained from single-effective-oscillator model, varied from 5.45 to 4.24 eV as a function of the Y2O3 slab thickness. The refractive index as well as the optical band gap can be modulated systematically using the Al2O3:Y2O3 ratio as control parameter. By means of simulated propagation modes it is shown that there is a multimode behavior for thickness around 200 nm at wavelengths between 300 and 1550 nm. This study reveals the possibility of using Al2O3-Y2O3 nanolaminates as the core of optical waveguides. It also shows the potential of ALD technique for fabrication of submicron waveguides useful in miniature optical circuits. (C) 2017 Elsevier B.V. All rights reserved.

Nanolaminates formed by several bilayers of Al2O3 and ZnO (AZA), grown by atomic layer deposition from Trimethyl aluminum, Diethyl zinc and water as co-reactants, were deposited on n-type (100) silicon substrates. A set of 5 nanolaminates with a total thickness of about 100 nm, containing several Al2O3/ZnO bilayers with thicknesses of 0.28, 0.38, 2, 10 and 20 nm, were prepared. XRD shows an evolution from amorphous to crystalline structure as a function of bilayer thickness. Capacitance-Voltage (C-V) and Current-Voltage (I-V) electrical characterization was carried out in order to evaluate the potential of the nanolaminates for microelectronic applications. Dielectric constant values between 8.3 and 9.6 were obtained, depending on bilayer thickness. The MOS capacitors exhibited net equivalent oxide thickness values between 44 and 38 nm.

The fundamental emission of a Nd: YAG laser (1064 nm), with an energy 0.1 J/pulse and a repetition rate of 10 Hz was employed to synthesize silver nanoparticles by ablation method confined in methanol and ethanol. The experimental setup allows synthesizing materials immersed in flammable solvents using an Argon atmosphere to prevent combustion, making the process safer when high fluence and high repetition rates of laser pulses are used. Transmission electron micrographs were taken for methanol and ethanol samples. The analysis of the methanol sample the day of synthesis and one month later, show that nanoparticles obtained were more dispersed, corresponding to better suspension stability. On the contrary, the images of nanoparticles in ethanol show a strong agglomeration, resulting in a fast sedimentation and less stability.

In this work silver nanoparticles suspension of 4.5nm average size and narrow size distribution was obtained for the first time in a deep eutectic solvent (DES) by using laser ablation targeting a silver metal blank immersed in choline chloride-urea DES. Luminescence properties in both DES and aqueous media of as-synthesized silver nanoparticles are discussed.

This research focuses on the study of the refractive index and bandgap behavior in ultrathin multilayer films of Al2O3-ZnO bilayers grown via atomic layer deposition (ALD) technique on Si(100) substrates. The multilayer configuration stack consists in alternate layers of constant thickness Al2O3 (2 nm) and varying thickness ZnO films in order to obtain a total thickness of similar to 100 nm. A set of 10 samples based on bilayers with various 2:X thickness ratios were prepared, where X refers to the ZnO layer thickness. X is proportional to the number of cycles (N) of the ZnO precursor, varying from 1 to 100. The sample morphology was studied via Atomic Force Microscopy and the results show that the surface roughness of the multilayers varies from 0.2 to 1.2 nm, as the ZnO layer thickness increases. In all cases, the roughness values remain below 2% of the total thickness of the multilayer. The refractive index n(lambda) and optical bandgap, E-g, of each multilayer sample were studied via spectroscopic ellipsometry (SE). A General Oscillator optical model was utilized to fit the experimental data in order to obtain the total thickness, refractive index and absorption coefficient. Cross-sectional mode scanning electron microscope images verified the multilayer total thickness and corroborated the accuracy of the optical model. The refractive index varies significantly from values close to the Al2O3 refractive index when the bilayer thickness is small, up to values corresponding closely to ZnO for thicker bilayers. The refractive index, as a function of bilayer thickness, varies between 1.63 and 2.3, for lambda = 370 nm (UV region), showing high sensitivity. In addition, the optical bandgap energy, Eg, determined using the Tauc model, decreases when the bilayer thickness increases, with a maximum variation of Delta E-g similar to 1.6 eV. These results reveal that the refractive index and optical bandgap of Al2O3-ZnO material can be modulated systematically as a function of the bilayer thickness. Such behavior is of great importance for optoelectronics applications, in particular for the development of devices with response in the UV spectral range. (C) 2016 Elsevier B.V. All rights reserved.

This work focuses on the study of the optical properties of nanolaminate films of Al2O3-Y2O3 bilayers. Nanolaminates were grown by means of thermal atomic layer deposition (ALD). The multilayer thickness, refractive index and optical bandgap were studied via spectroscopic ellipsometry. Ellipsometric data revealed an increase of the refractive index from 1.9 to 2.2 at 190 nm wavelength when the bilayer thickness varies between 4 and 10 nm. These results demonstrate that the refractive index can be modulated by varying the nanolaminate thickness. Optical bandgap values, obtained by the Wemple and DiDomenico model, indicate that the bilayer thickness decrease leads to an increase of the optical bandgap (AE(g) = 0.8 eV), as well as Eg modulation as a function of the bilayer thickness. The optical properties show that this material could be exploited for designing optical multilayered coatings suitable for nanoscale optoelectronic devices. (C) 2016 Elsevier Ltd. All rights reserved.

Ag and Cu nanoparticles supported in mordenite structure have been formed applying reduction temperatures in the range 100-400 C and varying Ag/Cu atomic ratios. Absorbance spectra of samples exhibit signature features consistent with absorption via localized surface plasmons propagating in metallic nanoparticles. The formation of binary Ag-Cu nanoparticles is inferred. Theoretical calculations within an average field Maxwell-Garnett model modified for a three component composite system are used to interpret resonance shifts and relative intensities of plasmon peaks in the experimental findings. Within the applied model the relative volume occupied by each metallic species can be changed. This permits the simulation of experimental conditions of the samples. It is experimentally found that the simultaneous presence of two metal species during the synthesis affects reduction temperatures, stability and relative concentration of embedded nanoparticles. Furthermore the observed optical spectra of the supported bimetallic nanoparticles is contrasted with that of single metal nanoparticles studied previously. Our study represents a contribution to the possibility of optical monitoring of synthetic pathways in zeolite + metal nanoparticle systems.

In this work, we studied the optical and morphological properties of ultrathin nano laminate films based on Al2O3/ZnO (AZ) bilayers stack. The films were deposited on Si (100) by means of thermal atomic layer deposition (ALD) technique. The bilayer thicknesses (ratio = 1:1) were 0.2,1, 2, 4,10 and 20 nm. Refractive index (n) and band gap (E-g) of each nanolaminate were studied via spectroscopic ellipsometry (SE), and spectral reflectance ultraviolet-visible spectroscopy (UV-vis). Surface morphology and roughness parameters of the nanolaminates were measured by Atomic Force Microscopy (AFM). The optical and morphological properties were shown highly dependent on the bilayer thickness. Ellipsometric data treated through the Cody-Lorentz optical model revealed that the refractive index decreases for thinner bilayers. A sharp intensity decay of refractive index and peaks at the UV region (200-400 nm) indicated increased transparency for thinner bilayers. It is also shown that the band gap is tunable. The maximum band gap value was 4.8 eV. These results reveal that ZnO combined with Al2O3 as bilayers stack can be converted into a dielectric material with enhanced band gap, opening the possibility for new optical and dielectric applications. (C) 2015 Elsevier Ltd. All rights reserved.

Atomic layer deposition (ALD) provides a method for coating conformal, pinhole-free, chemically bonded, and ultra-thin films on particle surfaces. ALD is based on one or more cycles, each cycle comprising two half-reactions. As such, ALD is a process inherently discrete in time, where the coating thickness can be controlled as a function of number of cycles. A popular scheme for achieving uniform coats on powders is to combine ALD reactors with fluidization conditions. However, fluidization is not easy to attain because it is strongly dependent on particle size, density, morphology, and surface roughness. This article proposes that a pulsed-bed, instead of a continuous fluidization, is easier to achieve in most ALD reactors. Taking advantage of the discrete nature of the ALD process, with simple changes in the configurations of purge and carrier gases, the pulsed-bed mode can be completed. An adaptation made to a regular ALD reactor to work in this mode is presented. The inclusion of a capsule for powder, valve relocations, and control of times were all necessary modifications. It was found that the pulsed-bed is a very convenient alternative for research purposes, since it can coat powders of different morphological characteristics, such as carbon nanotubes, flower-like ZnO micro-arrays, and YCrO3 particles.

Optical spectra of noble metal nano-particles supported on different types of zeolites are studied and compared. The absorbance spectra of Cu, Ag and Au nanoparticles supported on mordenite, beta-zeolite, Na/Y and H/Y zeolites respectively are reported. Spectra for pre-exchanged Au-Cu/Na/Y, Au-Ni/Na/Y and Au-Fe/Na/Y are also studied. A simple effective medium approach (Maxwell-Garnett) is used to obtain a theoretical complex effective dielectric function of the composite and to asses the sensibility of the plasmon resonance to the sample characteristics. The knowledge of these properties can hopefully be applied to the development of optical tools to monitor the synthetic path.

Gold nanoparticles supported on Y-zeolite were prepared using the [Au(NH3)(4)](NO3)(3) complex as gold precursor. The differences in the formation of gold nanoparticles in the presence of various co-cations (Na, Cu, Ni or Fe) were discussed in this work. The shift in the plasmon peak observed in the UV-vis spectra for different sample compositions was linked with variation in Au nanoparticle size, as well as changes in the sample chemical composition under thermal treatment. Theoretical spectra for Au nanoparticles supported on modified zeolites were obtained applying an average field model. Qualitative comparison of the data with the theoretical spectra yields insight into the role of distinct co-cations in the system. (C) 2014 Elsevier B.V. All rights reserved.

Measurements of line intensity ratios have been used in astronomy to determine physical properties of plasmas such as density and temperature. Herein, this procedure was applied to monitor thin film growth during plasma-assisted deposition and useful information about the plasma was obtained. The aim of this study was to monitor plasma variations during deposition, using wide field optical spectroscopy, and to establish a relationship with thin film stoichiometry using spectroscopic ellipsometry. With this purpose, inhomogeneous SiOxNy thin films were grown by dc magnetron sputtering.