<p>The demand for
the faster information transport and better computational abilities is ever
increasing. In the last few decades, the electronic industry has met this
requirement by increasing the number of transistors per square inch. This lead
to the scaling of devices to tens of nm. However, the speed of the electronics
is limited to few GHz. Using light, the operating speed of photonic devices can
be much larger than GHz. But the photonic devices are diffraction limited and
hence the size of photonic device is much larger than the electronic
components. Plasmonics is an emerging field with light-induced surface
excitations, and can manipulate the light at nanoscale. It can bridge the gap
between electronics and photonics. </p>
<p>With the present scaling of devices to few
nm, the scientific community is looking for alternatives for continued progress.
This has opened up several promising routes recently, including two-dimensional
materials, quantum computing, topological computing, spintronics and
valleytronics. The discovery of graphene has led to the immense interest in the
field of two-dimensional materials. Two dimensional-materials have
extraordinary properties compared to its bulk. This work discusses the
applications of plasmonics in this emerging field of two-dimensional materials
and for heat assisted magnetic recording.</p>
<p>Black phosphorus is an emerging low-direct
bandgap two-dimensional semiconductor, with anisotropic optical and electronic
properties. It has high mobility and is promising for photo detection at
infrared wavelengths due to its low band gap. We demonstrate two different
plasmonic designs to enhance the photo responsivity of black phosphours by
localized surface plasmons. We use bowtie antenna and bowtie apertures to
increase the absorption and polarization selectivity respectively. Plasmonic
structures are designed by numerical electromagnetic simulations, and are
fabricated to experimentally demonstrate the enhanced photo responsivity of
black phosphorus. </p>
<p>Next, we look at another emerging
two-dimensional material, bismuth telluride selenide (Bi<sub>2</sub>Te<sub>2</sub>Se).
It is a topological insulator with an insulating bulk but conducting electronic
surface states. These surface states are Dirac like, similar to graphene and
can lead to exotic plasmonic phenomena. We investigated the optical properties
of Bi<sub>2</sub>Te<sub>2</sub>Se and found that the bulk is plasmonic below
650 nm wavelength. We study the distinct surface plasmons arising from the bulk
and surface state of the topological insulator, Bi<sub>2</sub>Te<sub>2</sub>Se.
The propagating surface plasmons at a nanoscale slit in Bi<sub>2</sub>Te<sub>2</sub>Se
are imaged using near-field scanning optical microscopy. The surface state
plasmons are studied with a below band gap excitation of 10.6 µm wavelength and the surface
plasmons of the bulk are studied with a visible wavelength of 633 nm. The
surface state plasmon wavelength is 100 times shorter than the incident
wavelength in sharp contrast to the plasmon wavelength of the bulk. </p>
<p>Next, we look at the application of
plasmonics in heat assisted magnetic recording (HAMR). HAMR is one of the next
generation data storage technology that can increase the areal density to
beyond 1 Tb/in<sup>2</sup>. Near-field transducer (NFT) is a key component of
the HAMR system that locally heats the recording medium by concentrating light
below the diffraction limit using surface plasmons. In this work, we use
density-based topology optimization for inverse design of NFT for a desired
temperature profile in the recording medium. We first perform an inverse
thermal calculation to obtain the required volumetric heat generation (electric
field) for a desired temperature profile. Then an inverse electromagnetic
design of NFT is performed for achieving the desired electric field. NFT designs
for both generating a small heated spot size and a heated spot with desired
aspect ratio in recording medium are demonstrated. The effect of waveguide,
write pole and moving recording medium on the heated spot size is also
investigated. </p>
| Identifer | oai:union.ndltd.org:purdue.edu/oai:figshare.com:article/14125349 |
| Date | 01 March 2021 |
| Creators | Prabhu Kumar Venuthurumilli (10203191) |
| Source Sets | Purdue University |
| Detected Language | English |
| Type | Text, Thesis |
| Rights | CC BY 4.0 |
| Relation | https://figshare.com/articles/thesis/Applications_of_plasmonics_in_two_dimensional_materials_thin_films/14125349 |
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