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Large-scale CO2 capture through membrane separation is the only viable method for cost-effective emission reduction. However, the fabrication of CO2 separation membranes with sufficient flux and se...

Tunable mid-wave infrared (MWIR) filters are highly desirable in a wide variety of imaging and spectroscopic applications; with the waveband containing numerous invaluable spectral absorption signatures. We demonstrate spectrally-tunable, all solid-state, thin-film bandpass filters operating across the MWIR by utilizing the phase-change material (PCM) Ge2Sb2Te5 as a tunable cavity medium between two Bragg mirrors. The induced PCM refractive index modulation increases the cavity’s optical path length, thereby tuning the filter passband. Our filters have 300 nm spectral tunability, ~70% transmission efficiencies, and ~60 nm passbands. We further show multispectral thermal imaging and dynamic CO2 gas plume sensing using the filters.

We demonstrate spectrally-tunable Fabry-Perot bandpass filters operating across the MWIR by utilizing the phase-change material GeSbTe (GST) as a tunable cavity medium between two (Ge:Si) distributed Bragg reflectors. The induced refractive index modulation of GST increases the cavity's optical path length, red-shifting the passband. Our filters have spectral-tunability of ~300 nm, transmission efficiencies of 60-75% and narrowband FWHMs of 50-65 nm (Q-factor ~70-90). We further show multispectral thermal imaging and gas sensing. By matching the filter's initial passband to a CO$_{2}$ vibrational-absorption mode (~4.25 $\mu$m), tunable atmospheric CO$_{2}$ sensing and dynamic plume visualization of added CO$_{2}$ is realized., Comment: 13 pages, 5 figures

This work reports on Mueller matrix spectroscopic ellipsometry characterization of various flexible plastic substrates that are optically anisotropic with varying degrees of birefringence. The samples are divided into three groups according to the suggested characterization strategy: low birefringence, high birefringence, and twisted birefringence. The first group includes poly(methyl methacrylate) and cyclic olefin copolymer substrates. These are modeled with biaxial anisotropy for the real part of the refractive index while the imaginary part is approximated as isotropic due to small light absorption. The second group includes polyethylene terephthalate and polyethylene naphthalate substrates, which are modeled with biaxial anisotropy for both real and imaginary refractive indices. Lastly, a polyimide substrate is described as two birefringent layers with twisted in-plane orientation.

We report the optical constants of graphene oxide and reduced graphene oxide determined by spectroscopic ellipsometry. The dynamic changes in optical properties and thickness of a drop-cast graphene oxide layer during reduction by long-term exposure to focused broad-band white light are monitored in situ. The anisotropic optical constants of the graphene oxide layer and the isotropically averaged optical constants of the reduced layer are precisely determined from a multiple-location analysis of spatially resolved data across the exposed location and a multiple-time-step analysis of the dynamic data, respectively. Observed inter-band transitions in the graphene oxide layer are discussed in relation to theoretical predictions for different coverage levels of the graphene oxide sheets with oxygen containing functional groups. The derived optical constants of the reduced graphene oxide layer are compared to reported values of graphene and thermally reduced graphene oxide.

The growing demand for multifunctional nanophotonic devices has led to the exploration, and utilization, of a plethora of exotic electro-optical materials. Recently, chalcogenide glass based phase change materials (PCMs) have shown utility as a tuning material for a range of nanophotonic devices. Owing to their low loss, ultrafast switching speeds and wide waveband operation, PCMs are integrated in an increasing number of next-generation tunable components, including integrated photonic switches, metasurface optics and tunable spectral filters. Nonetheless, modelling of PCM-based devices is challenging—both in terms of accurate representation of experimentally derived material properties in different phase states, and standardization of results across the research community. Further, as each device requires optimization of specific performance metrics dependent on their respective application, any inaccuracies will lead to erroneous outcomes. In this work, we introduce PCM-net (http://nekocloud.com/pnet/): an online database of the complex refractive indices of a variety of chalcogenide glass PCMs (such as GeSbTe), as an accessible and indexed repository for data sharing across the PCM community. Refractive indices (n) and extinction coefficients (k) between amorphous and crystalline states are directly extracted from experimentally derived data in numerous academic research articles, and collated into the material resource database. Due to the inaccuracies associated with our data collection methods, this data is supplemented with additional computationally generated data, obtained through WVASE® —a commercial ellipsometry analysis software package. To demonstrate the utility of PCM-net, we provide a NASA application-driven device optimization example using the optical properties of PCMs collected with our database. We anticipate the database providing great use to the PCM community and coordinated research efforts enabled by PCM-net will promote the shared repository for the selection of appropriate PCMs for tunable nanophotonic device design for a range of applications.

We report the optical properties and solar reflectance of catalyst-free vertical graphene (VG) sheets grown on two types of substrate, copper and silicon, over a wide range of wavelengths and for the first time, a method for the separation of the sheets from the substrate. The index of refraction of the VG sheets was close to unity in the visible and infrared range, while the coefficient of absorption was higher than those of forests of carbon nanotubes (CNTs). A total reflectance (diffuse and specular) of less than 10% was observed for the VG sheets in the visible range. For VG sheets grown on a copper substrate, the specific absorption (absorption divided by the areal density) at a wavelength of 633 nm was measured to be two times higher than previously reported results for VG sheets grown on a silicon substrate and much higher than that of a CNT forest.

The optical constants of various substrates and coating materials employed widely for solar-cell fabrication are summarized. The substrate materials described here include various SiO2 (soda-lime glass, borosilicate glass, fused silica, and quartz), metal (stainless) and plastic (polycarbonate, PEN, PET, PMMA, Kapton HN) substrates. For PEN, PET and Kapton HN substrates, which exhibit strong biaxial optical anisotropy, full data sets are provided. In solar cell devices, a protection coating (EVA) and anti-reflection (MgF2/LiF) layers are quite important, and the optical constants of these coating layers are also described here. The refractive index spectra of the transparent materials were parameterized using the Sellmeier model, whereas the parameterization of absorbing polymer substrates was carried out assuming several transition peaks calculated by the Tauc-Lorentz model. In this chapter, the model parameters for all the substrates and coating materials are summarized, together with the tabulated optical constants.

The development of novel neutron detectors requires an understanding of the entire neutron detection process, a process which depends strongly on material properties. Here we present accurate measurements of the neutron detection efficiency of an unenriched 640 nm thick boron carbide solid state neutron detector grown by plasma enhanced chemical vapor deposition as a function of the neutron wavelength at a time-of-flight facility. The data were compared to that obtained simultaneously by a calibrated nitrogen detector over the same wavelength range. The measured spectra of both detectors fit a Maxwell–Boltzmann wavelength distribution, thereby indicating that the boron carbide detector can be used as a reliable beam monitor. Measurements of the material properties (density, thickness and elemental composition) of the semiconducting boron carbide enable a precise calculation of the ideal expected neutron detection efficiency. The calculated neutron detection efficiency for the effective moderator temperature (obtained from a fit to the Maxwell–Boltzmann distribution) showed excellent agreement with the experimentally determined neutron detection efficiency of 1.25%. Higher efficiencies may be obtained either by increased film thickness and/or 100% 10B enrichment of the boron carbide source molecule.

Organic-based electronic devices are rapidly increasing in popularity, making it essential to understand and characterize the interface between organic materials and metallic electrodes. This work reports on the characterization of the interface between thin films of an emerging organic ferroelectric, vinylidene fluoride (VDF) oligomer, and Co, an important high Curie temperature ferromagnet. Using a wide battery of experimental techniques, it is shown that VDF oligomer thin films as thin as 15 nm can halt, or prevent, Co oxidization in atmospheric conditions, a necessary condition for device applications. Selectivity of magnetic properties, such as remanent magnetization, is enabled by the clarification of the time scale of Co oxidation, a topic on which there are many conflicting reports. Furthermore, this work shows evidence of chemical bonding at the interface between VDF oligomer and Co, a result with important implications for organic spintronic devices. These results establish the suitability of VDF oligomer for organic-based electronic devices.

The wide band gap, temperature stability, high resistivity, and robustness of semiconducting boron carbide make it an attractive material for device applications. Undoped boron carbide is p type; Ni acts as a n-type dopant. Here we present the results of controlled doping of boron carbide with Ni on thin film samples grown using plasma enhanced chemical vapor deposition. The change in the dopant concentration within the thin film as a function of the dopant flow rate in the precursor gas mixture was confirmed by x-ray photoelectron spectroscopy measurements; with increasing dopant concentration, current-voltage (I-V) curves clearly establish the trend from p-type to n-type boron carbide.