Research

Thermal Radiation Coatings

*Paints and thin films*Engineered coatings are crucial under extreme temperature surroundings. For example, the Sun (T = 5800 K or 10,000

^{o}F) can make an untreated car exterior exceedingly hot. Conversely, deep space (T = 3 K or -450^{o}F) can help cool spacecraft electronics and living systems. Our interest is in developing coatings using nano- or microscopic features to mitigate or control thermal radiation in various environments.Metamaterials

*Unconventional optics*Metamaterials consist of engineered features typically smaller than the wavelength of light. In that sense, electromagnetic waves interact with metamaterials in an unusual manner. Applications where metamaterials are found include thin flat lenses, thermal cloaking, and molecular sensing. The group is designing metamaterials consisting of 2D materials and topological insulators.

Near-Field Transport

*Bridging the gap*What is "near-field" thermal radiation? When two surfaces are separated by a nanoscale-size gap (order of 1 billionth of a meter), energy transport between the gap exceeds that between two perfect emitters. This is because photons and electrons can tunnel through the gap. The group is investigating how nanomaterials can improve and control energy transport in this near-field domain.

Bottom-Up Transport Quantification

*Quantum transport*In nanomaterials, such as 2D materials, nanowires, nanoparticles, etc., movement of energetic particles have nowhere to go. In this segment, the group is uncovering the theoretical link between mechanical and electrical properties in confined atomic geometries. We employ numerical methods of coupled non-linear and non-thermodynamic equilibrium phonon transport equations to understand why certain materials can induce thermoelectricity and extraordinary thermal conductivity.

*Partially funded by the US AFOSR - AFRL*Thermoelectric Generation

*Harvesting heat*Thermoelectric devices convert a temperature gradient to usable electrical power, by means of the Peltier effect. The primary challenge of making efficient thermoelectric materials is low thermal conductivity while maintaining high electrical conductivity. The group is researching the thermal and electric properties of nanopatterned topological insulators, materials that behave as an insulator in volume but conductor on the surface.

Thermal Properties Testing

*Qualifying materials*Under sunlight or in space, how does a material or coating absorb and transfer heat with the environment? The group can help perform measurements on novel materials, for thermal conductivity, optical response, electronic properties, and more. Characterization techniques at the nanoscale level are being developed, including probe microscopy and near-field tunneling sensors.

Research Capabilities

Finite-Difference Solver

**Lumerical FDTD**We use a finite-difference time domain (FDTD) solver to model electromagnetic wave propagation for visualizing the optics and dispersion in metamaterials. Example metamaterials include nanowire arrays, graphene layers, quantum well heterostructures, etc.

Modeling Tools

**Numerical Methods**The group is developing code used in common engineering software to model thermal transport processes. Example applications include thin film spectral radiative properties calculator in Excel, 3D temporal thermal mapping on MATLAB, and thermal properties of various materials using molecular dynamics.

*See Useful Links > Modeling Tools for links (Under Construction)*Nanomaterials Facilities

The UNT Materials Research Facility is a collaborative interdisciplinary engineering facility containing $11 million and growing characterization and micro-fabrication equipment. Faculty, students, and outside collaborators can receive training and access to the facility. The group is experienced with SEM, FTIR, ellipsometry, and more.

Spectroscopy Facility

**FTIR**We have a Fourier-Transform Infrared Spectrometer (FTIR) for infrared (2 to 40 micron wavelength) spectroscopy to measure thin-film coatings' response to temperature change.

Thermal Simulation Package

A complex system in extreme environments may run the risk of overheating or component failure. Thermal Desktop/SINDA is a 3D finite-difference node modeler for predicting temperature profiles for electronics, pipe networks, and structures. The software contains built-in orbital and flight mechanics definitions for modeling solar loading on spacecraft. (can be ITAR enforced)

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