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1. Plasmonic Response of Light-Activated, Nano-Gold Doped Polymers

   https://doi.org/10.1557/adv.2019.286  

   Andriolo, Jessica M.; Joseph, McKenzie L.; Brockway, Molly C.; Skinner, Jack L. (January 2019, MRS Advances)

   Abstract Incorporation of metallic nanoparticles (NPs) in polymer matrix has been used to enhance and control dissolution and release of drugs, for targeted drug delivery, as antimicrobial agents, localized heat sources, and for unique optoelectronic applications. Gold NPs in particular exhibit a plasmonic response that has been utilized for photothermal energy conversion. Because plasmonic nanoparticles typically exhibit a plasmon resonance frequency similar to the visible light spectrum, they present as good candidates for direct photothermal conversion with enhanced solar thermal efficiency in these wavelengths. In our work, we have incorporated ∼3-nm-diameter colloidal gold (Au c ) NPs into electrospun polyethylene glycol (PEG) fibers to utilize the nanoparticle plasmonic response for localized heating and melting of the polymer to release medical treatment. Au c and Au c in PEG (PEG+Au c ) both exhibited a minimum reflectivity at 522 nm or approximately green wavelengths of light under ultraviolet-visible (UV-Vis) spectroscopy. PEG+Au c ES fibers revealed a blue shift in minimum reflectivity at 504 nm. UV-Vis spectra were used to calculate the theoretical efficiency enhancement of PEG+Au c versus PEG alone, finding an approximate increase of 10 % under broad spectrum white light interrogation, and ∼14 % when illuminated with green light. Au c enhanced polymers were ES directly onto resistance temperature detectors and interrogated with green laser light so that temperature change could be recorded. Results showed a maximum increase of 8.9 °C. To further understand how gold nanomaterials effect the complex optical properties of our materials, spectroscopic ellipsometry was used. Using spectroscopic ellipsometry and modeling with CompleteEASE® software, the complex optical constants of our materials were determined. The complex optical constant n (index of refraction) provided us with optical density properties related to light wavelength divided by velocity, and k (extinction coefficient) was used to show the absorptive properties of the materials. 

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2. Machine learning enhanced characterization and optimization of photonic cured MAPbI ₃ for efficient perovskite solar cells

   https://doi.org/10.20517/jmi.2024.72  

   Allen, Cody R; Bhandari, Bishal; Xu, Weijie; Lee, Mark; Hsu, Julia_W P (December 2024, Journal of Materials Informatics)

   Photonic curing (PC) can facilitate high-speed perovskite solar cell (PSC) manufacturing because it uses high-intensity light pulses to crystallize perovskite films in milliseconds. However, optimizing PC conditions is challenging due to its many variables, and using power conversion efficiency (PCE) as the optimization metric is both time-consuming and labor-intensive. This work presents a machine learning (ML) approach to optimize PC conditions for fabricating methylammonium lead iodide (MAPbI3) films by quantitatively comparing their ultraviolet-visible (UV-vis) absorbance spectra to thermal annealed (TA) films using four similarity metrics. We perform Bayesian optimization coupled with Gaussian process regression (BO-GP) to minimize the similarity metrics. Refining PC conditions using active learning based on BO-GP models, we achieve a PC MAPbI3 film with an absorbance spectrum closely matching a TA reference film, which is further verified by its crystalline and morphological properties. Thus, we demonstrate that the UV-vis absorption spectrum can accurately proxy film quality. Additionally, we use an AI-based segmentation model for a more efficient grain size analysis. However, when we use the optimized PC condition to fabricate PSCs, we find that interaction between MAPbI3 and the hole transport layer (HTL) during PC critically degrades the PSC performance. By adding a buffer layer between the HTL and MAPbI3, the optimized PC PSCs produce a champion PCE of 11.8%, comparable to the TA reference of 11.7%. Using UV-vis similarity metrics instead of device PCE as the objective in our BO-GP method accelerates the optimization of PC processing conditions for MAPbI3 films. 

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3. Extracting the Optical Constants of Partially Absorbing TiO2 ALD Films

   https://doi.org/10.3390/coatings14121555  

   Chowdhary, Nimarta Kaur; Gougousi, Theodosia (December 2024, Coatings)

   Typical titanium oxide (TiO2) films are transparent in the visible range, allowing for their index of refraction and thickness to be extracted by single-angle spectroscopic ellipsometry (SE) using a Cauchy model. However, TiO2 films grown by atomic layer deposition (ALD) from tetrakis(dimethylamino)titanium (IV) (TDMAT) and H2O at 350 °C absorb in the visible range due to the formation of Ti-O-N/Ti-N bonds. Single-angle SE is inadequate for extracting the optical constants of these films, as there are more unknowns (n, k, d) than measurable parameters (ψ, Δ). To overcome this limitation, we combined SE with transmission (T) measurements, a method known as SE + T. In the process, we developed an approach to prevent backside deposition on quartz substrates during ALD deposition. When applying a B-spline model to SE + T data, the film thicknesses on the quartz substrates closely matched those on companion Si samples measured via standard lithography. The resulting optical constants indicate a reduced refractive index, n, and increased extinction coefficient, k, when compared to purer TiO2 thin films deposited via a physical vapor deposition (PVD) method, reflecting the influence of nitrogen incorporation on the optical properties. 

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4. Thermodynamics of Protein-Surface Binding- the Model Makes all the Difference

   Nicholas C. Fitzkee, Kayla D (February 2020, Biophysical journal)

   null (Ed.)

   Gold nanoparticles (AuNPs) are now being used in such areas as diagnostics, drug delivery, and biological sensing. In these applications, AuNPs are frequently exposed to biological fluids. These fluids contain many different proteins, any of which may interfere with the intended function of the nanoparticle. In this work, we examine the thermodynamic consequences of proteinnanoparticle binding using a combined spectroscopic and calorimetric approach. We monitored binding using UV-Vis spectroscopy, differential scanning calorimetry (DSC), and isothermal titration calorimetry (ITC). Six proteins were studied based on their differing chemical properties, and both 15 nm and 30 nm citrate-coated AuNPs were investigated. We interpreted the UV-Vis data using two different models: the commonly-used Langmuir isotherm model and a more complex mass transport model. Both models can be used to determine Kd values for the 30 nm AuNP data; however, the mass transport model is more appropriate for 15 nm AuNPs. This is because, when fitting the Langmuir model, it is commonly assumed that most proteins are not surface-associated, and this assumption fails for 15 nm AuNPs. The DSC thermograms show two transitions for a globular protein adsorbed to a 15 nm AuNP: one high-temperature transition that is similar to global protein unfolding (68 C), and one low-temperature transition that may correspond to unfolding at the surface (56 C). Conversely, ITC experiments show no net heat of adsorption for GB3, even at high protein/AuNP concentrations. Together, the spectroscopic and calorimetric data suggest a complex, multi-step process for protein-nanoparticle adsorption. Moreover, for the proteins studied, both AuNP curvature and protein chemistry contribute to protein adsorption, with proteins generally binding more weakly to the larger nanoparticles. In the future, this work may lead to principles for improving the design of AuNPbased therapeutics and sensors. 

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5. Synthesis, Spectroscopic Characterization and Applications of Tin Dioxide

   https://doi.org/https://doi.org/10.1007/978-3-030-62761-4_11  

   Alghamdi, Hawazin; Concepcion, Benjamin; Baliga, Shankar; and Misra, Prabhakar (December 2020, Chapter in Book: Contemporary Nanomaterials in Material Engineering Applications)

   Mubarak, Nabisab M.; Walvekar, Rashmi; Arshid, Numan; and Khalid, Mohammad (Ed.)

   Metal oxides are useful for the detection and sensing of combustible and toxic gases, and for use in lithium batteries and solar cells. The present study focuses on the spectroscopic investigation of commercial and in-house laboratory synthesized tetragonal tin dioxide (SnO2), aimed at studying its physical and chemical properties at nanoscale levels and in bulk. We have investigated the pure powder form and thin films prepared on two different types of substrate, silicon and UV-Quartz, each with five different thicknesses (i.e. 41, 78, 96.5, 373, and 908 nm). Raman spectroscopy with two different laser excitation wavelengths, namely 780 and 532 nm, has been used to investigate the various SnO2 vibrational modes. Thermal effects on the primary vibrational features in the Raman spectra have been studied in the range 30–170 °C. X-ray diffraction (XRD) spectra have been recorded to confirm the rutile structure of tin dioxide and to obtain information on the spherical grain particle size of SnO2 with EDS analysis for the thin film samples. Scanning Electron Microscope (SEM) images have been recorded in order to understand the morphology of the particles of SnO2 at the nanoscale level. In addition, FT-IR spectra have been obtained to study the IR-active vibrational modes for the bulk and thin film samples on the two substrates. Moreover, UV-VIS spectra have been employed to determine the energy band gap for the SnO2 film samples by an efficient process facilitated by a Tauc plot technique utilizing an in-house developed python script. 

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