Multi-Functional Materials and Devices

Projects:

Electrical-Mechanical Coupling in Multi-functional Architectures

Personnel: Max Lifson (Ph.D. student in Materials Science)

Piezoelectric materials are a class of materials that exhibit a charge separation due to an anisotropy in the electron distribution of the atoms with applied strain. To characterize this property and to understand how it changes at small dimensions, we design and fabricate nanolattices out of piezoelectric materials, i.e. ZnO and quartz, and perform nanomechanical experiments to determine the piezoelectric coefficients d or e. These coefficients describe the extent to which these materials deform with an applied electric field or create a charge separation with an applied strain, and how effective the material can be when used in sensors, actuators, and other devices.

Vertical type nanotruss capacitor
Vertical type nanotruss capacitor

Another aspect of electrical-mechanical coupling is realized through studying dielectric materials, which are electrical insulators that alter the capacitance of the material stack by affecting the permittivity of the electric field through it. Through our collaboration with the Gwangju Institute of Science and Technology (GIST), we are studying the effect of nanoarchitecture on the dielectric constant κ (sometimes written as the permittivity ε). For semiconductor applications, it is particularly important to decrease the capacitance of the device stack, so as to decrease the signal delay. This has led to an industry-wide push to discover and characterize new low-k materials, to help further speed the electronic devices we use every day.


Ultra-Thin Si Nanopillar Arrays for Polarization-Independent Spectral Filters in the Near-IR

Personnel: Ryan Ng (Ph.D. student in Chemical Engineering)

Spectral filters have a wide range of sensing applications ranging from environmental (hazardous waste, oil, etc) to surveillance. In sensing, detectors are sensitive to anywhere from several to hundreds of electromagnetic bands. Based on the number of bands and bandwidth, these systems are separated into multispectral and hyperspectral imaging systems with multispectral systems capturing under 10 bands and hyperspectral imaging capturing hundreds to thousands of bands of narrow width (around 10-20 nm) that allow for a continuous measurement across a spectrum.

Hyperspectral Filters - Pillar Array
Pillar Array

Subwavelength dielectric nanopillar arrays have potential for such spectral filtering applications as band pass and notch filters. In these arrays, rapid spectral variations in reflectivity and transmission are observed when incident light couples via a grating vector to a leaky waveguide mode propagating perpendicular to the surface and are reradiated, leading to sharp near-unity reflectivity resonances. The band width, amplitude, and peak wavelength are easily controlled through array fabrication parameters such as the pillar height, radius, and array periodicity.


Fog Harvesting and Solar Steam Generation in a Single Architect Device

Personnels: Dr. Ye Shi (post-doc)