Materials Science and Engineering

Materials Science and Engineering

• MSE-1 Scaling Up A Topochemical Fluorination Reactor

  Bryce J. Babarsky, Annibale J. DeLorenzo
  Advisor: Dr. Steven May

  Topochemical fluorination is a burgeoning process in research wherein fluorine is substituted for oxygen within an epitaxial metal oxide thin film without changing the parent crystal structure. The novelty of this process lies in the resulting changes in the electronic, ferroic, and optical properties of the resulting films. Leveraging engineering design criteria from the chemical vapor deposition (CVD) industry, an enclosed reactor was designed and constructed to scale up the fluorination process for epitaxial thin films to support ongoing NSF-funded research (NSF Award #1562223). Topochemical fluorination had previously been performed using a one-inch glass tube furnace. This method was limited by small sample size and slow production rate due to geometrical constraints. The new reactor design addressed the geometrical constraint that limited the previous method, being designed to accept up to four 2-inch single crystal wafers located on a resistively heated substrate holder. Silicon wafers were successfully fluorinated from a heated PVDF source and characterized using x-ray photoelectron spectroscopy (XPS) and ellipsometry to verify that fluorine was being deposited onto the sample surfaces. Results confirmed that the new reactor design was capable of topochemical fluorination. A strontium ferrite (SrFeO2.5) sample has also been trialed to investigate the scaled-up reactor’s capability relative to the glass tube furnace process.

• MSE-2 Quantum Materials Properties Characterization Using Computational Models

  Caroline Costello, Engy Khoshit, Elliot Sayles
  Advisor: Dr.Yong-Jie Hu, Dr. Jörn Venderbos

  Quantum materials are a class of materials whose properties and phenomena fundamentally rely on the quantum nature of the electronic structure. Material properties originate from the interactions between atoms and electrons on a quantum scale. Density Functional Theory (DFT) is a reliable and accurate first-principles computational method to predict electronic structures and can be used as an approach to understand the electronic properties and behaviors of materials. In Topological Insulators versus Topological Dirac Semimetals in Honeycomb Compounds, Zhang et al. identified 22 Dirac semimetals with ABC honeycomb structures that have the potential to be thermodynamically stable. In this work, the actual feasibility of these compounds was investigated using DFT calculations, aimed at determining formation energies and structural distortions. In particular, the presence of structural distortions away from perfect symmetry, caused by buckling within the honeycomb layers of the ABC structure, was considered. The buckling of the stable compounds was determined by performing DFT relaxation calculations to optimize ionic positions. After discarding the unstable compounds from further testing, electronic properties of the remainder were determined by evaluating the band-gap energies of the compounds obtained through DFT calculations. These electronic properties indicated which of the 22 ABC structures recommended by Zhang et al. would be worth exploring in a physical laboratory.

• MSE-3 Synthesis of MXenes from Novel MAX Phases

  Samantha Covell, Cathy Dang, Yuzhe Jin
  Advisor: Dr. Yury Gogotsi

  MAX phases, Mn+1AXn, are bulk ternary transition metal carbides and nitrides where M is an early transition metal, A an A-group element from Groups 13 and 14, X a carbon (C) or nitrogen (N), and n generally a number between 1 and 4 that defines the stoichiometric ratios. At Drexel University, MAX phases are well known as the precursor materials for the synthesis of MXenes, a family of multilayered two-dimensional materials created by selectively chemically etching MAX phases to remove the A layer atoms. Non-Al MAX phases were explored, focusing primarily on Sn- or Si-based MAX phases as they are the basis for potentially forming new MXenes that were not previously accessible from established Al-based MAX phases. Non-HF etching chemistries have also been explored to selectively remove either the Sn or Si from these phases to produce MXenes without the use of HF. A standard set of synthesis conditions (n values of 1, 2, and 3, in addition to these same ratios with increased amounts of the A element, using a high and low synthesis temperature), were studied to explore novel non-Al MAX phases. X-ray diffraction (XRD) was used characterize the materials produced and determine the resulting structures and compositions. The XRD results, in combination with simulated MAX phase diffraction patterns of the material systems explored, showed indications of the presence of MAX phases, but not as the majority product. Common industry-etching chemistries have also been used on known MAX phases for indications of the presence of MXenes.

• MSE-4 Designing Sustainable Plastics

  Hunter Banavage, Dalton Wright
  Advisor: Dr. Christopher Li

  Plastic production and disposal are increasingly creating waste products and pollution in the environment, with plastic waste taking exceptionally long times to degrade while creating harmful waste. One sustainable solution for current plastic production is the use of polylactic acid (PLA) as a material. Specifically, the “shish-kebab” nanofiber morphology (NFSK) has shown promise in improving the properties of crystalline PLA, which are currently not suitable for use as a large-scale plastic due to its poor plasticity and degradation resistance. Processing of the NFSK materials is challenging due to their relatively low melting temperature, resulting in degradation of the PLA during processing. To combat these challenges, samples of PLA nanofibers were annealed before incubation to allow for widespread and complete formation of the NFSK structure. PLA samples were produced using various ratios of PLLA to PDLA, which are both chiral monomers of PLA. Incubated samples were characterized using scanning electron microscopy (SEM) and differential scanning calorimetry (DSC) to determine their thermodynamic properties. Mechanical analysis was performed on incubated samples to compare the resulting properties among the various PLA ratios with those of other traditional plastic materials.

• MSE-5 Near-Infrared Photodetector for Future Use in an Imaging Wand

  Anjiao Wetherhold, Maxene Kohler, Frankie Lau
  Advisor: Dr. Wei-Heng Shih

  Current methods of in vivo cancerous tumor imaging have low specificity. Recent research using quantum dot (QD)-based immunofluorescence (IF) showed higher specificity. While promising, its use within a surgical setting is limited by the bulky set-up used to detect IF-stained tissue. An alternative design of a handheld imaging wand using a near infrared (NIR) semiconductor photodetector on a transparent conducting substrate with a narrow gap has been proposed. Multiple imaging wand concepts have been explored: ambient-stable cubic MAPbI3 rods placed across the gap to absorb in the NIR directly, and conducting poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) with embedded MAPbI3 and lead sulfide (PbS), acting as an NIR harvesting material. The semiconductors were assembled on an indium tin oxide (ITO) substrate with a scribed gap. Wires were attached to the semiconductors using conductive glue to measure I-V characteristics. MAPbI3 rods were dropped onto ITO glass with a gap and allowed to evaporate and microscopy used to verify MAPbI3 rods spanning the gap. PEDOT:PSS with PbS was drop-cast onto ITO glass to embed MAPbI3 or PbS in the polymer matrix. Data was collected under dark conditions with no light and with an NIR lightbulb to compare the characteristic I-V curves. In the case of PEDOT:PSS with MAPbI3 or PbS, the current increased more than for pure MAPbI3 microrods, with embedded MAPbI3 showing a larger response than PbS. Results showed that NIR photodetectors made using a simple design could be made into hand-held devices to detect fluorescence images in immunofluorescence staining of cancer cells.

• MSE-6 Continuously Aligned Track-Spun Polymer Fiber Collection Device

  Joseph Michalowicz
  Advisor: Dr. Reva Street

  Generating 2D and 3D nanofiber structures with a layer-by-layer, aligned, or crisscrossed pattern for current tissue engineering research requires complex and expensive tooling that is often bottlenecked by polymer precursor type and fiber generation technique. An automated polymer fiber collection device, in conjunction with a novel mechanical fiber drawing technique known as track-spinning, has been designed, built and tested to control the end-to-end fiber placement and porosity in arranged structures, and to determine which process parameters had the largest influence on the spatial resolution, orientation, and degree of crystallinity of polymer nanofibers produced. The challenges with the devices included accurate control of the collection platform translation speed, and establishing the track-spinning control parameters required to reliably produce nanofibers with consistent average diameter and length from polyacrylonitrile (PAN) and dimethylformamide (DMF) precursor solutions. The prototype collection device design and associated programming moves and rotates the collection platform through multiple axes at the required speeds using programmable commercially available hardware. The accuracy and precision of nanofiber deposition and design effectiveness was determined via a series of trials. This collection device, in conjunction with the novel track-spinning technique, could greatly enhance the development of tissue engineering technology and other nanofiber applications currently limited by materials and costly equipment.