16 research outputs found
Broadband Coherent Absorption in Chirped-Planar-Dielectric Cavities for 2D-Material-Based Photovoltaics and Photodetectors
Atomically
thin materials such as graphene and transition metal
dichalcogenides are being developed for a range of optoelectronic
devices, but their applications are currently limited by low light
absorption. Here, we describe a dielectric cavity design with chirped
Bragg reflectors for broadband coherent absorption. The chirped cavity
absorption is calculated by the transfer matrix method and optimized
using the Nelder–Mead optimization protocol. We numerically
demonstrate that with cavity enhancement, a monolayer MoS<sub>2</sub> photodetector absorbs as much as 33% of incident visible light over
a 300 nm bandwidth, and the external quantum efficiency of an atomically
thin monolayer graphene/monolayer MoS<sub>2</sub> solar cell can be
enhanced 3.6 times to a predicted value of 7.09%. The proposed layered
dielectric structures operate across a wide range of incident angles
and could enable applications for atomically thin photodetectors or
solar cells
Wide-Field Multispectral Super-Resolution Imaging Using Spin-Dependent Fluorescence in Nanodiamonds
Recent advances in fluorescence microscopy
have enabled spatial
resolution below the diffraction limit by localizing multiple temporally
or spectrally distinguishable fluorophores. Here, we introduce a super-resolution
technique that <i>deterministically</i> controls the brightness
of uniquely addressable, photostable emitters. We modulate the fluorescence
brightness of negatively charged nitrogen-vacancy (NV<sup>–</sup>) centers in nanodiamonds through magnetic resonance techniques.
Using a CCD camera, this “deterministic emitter switch microscopy”
(DESM) technique enables super-resolution imaging with localization
down to 12 nm across a 35 × 35 μm<sup>2</sup> area. DESM
is particularly well suited for biological applications such as multispectral
particle tracking since fluorescent nanodiamonds are not only cytocompatible
but also nonbleaching and bright. We observe fluorescence count rates
exceeding 1.5 × 10<sup>6</sup> photons per second from single
NV<sup>–</sup> centers at saturation. When combined with emerging
NV<sup>–</sup>-based techniques for sensing magnetic and electric
fields, DESM opens the door to rapid, super-resolution imaging for
tracking and sensing applications in the life and physical sciences
Nanoscale Engineering of Closely-Spaced Electronic Spins in Diamond
Numerous theoretical protocols
have been developed for quantum information processing with dipole-coupled
solid-state spins. Nitrogen vacancy (NV) centers in diamond have many
of the desired properties, but a central challenge has been the positioning
of NV centers at the nanometer scale that would allow for efficient
and consistent dipolar couplings. Here we demonstrate a method for
chip-scale fabrication of arrays of single NV centers with record
spatial localization of about 10 nm in all three dimensions and controllable
inter-NV spacing as small as 40 nm, which approaches the length scale
of strong dipolar coupling. Our approach uses masked implantation
of nitrogen through nanoapertures in a thin gold film, patterned via
electron-beam lithography and dry etching. We verified the position
and spin properties of the resulting NVs through wide-field super-resolution
optically detected magnetic resonance imaging
LNoS: Lithium Niobate on Silicon Spatial Light Modulator
Programmable spatiotemporal control of light is crucial for advancements in optical communications, imaging, and quantum technologies. Commercial spatial light modulators (SLMs) typically have megapixel-scale apertures but are limited to ~kHz operational speeds. Developing a device that controls a similar number of spatial modes at high speeds could potentially transform fields such as imaging through scattering media, quantum computing with cold atoms and ions, and high-speed machine vision, but to date remains an open challenge. In this work we introduce and demonstrate a free-form, resonant electro-optic (EO) modulator with megapixel apertures using CMOS integration. The optical layer features a Lithium Niobate (LN) thin-film integrated with a photonic crystal (PhC), yielding a guided mode resonance (GMR) with a Q-factor>1000, a field overlap coefficient ~90% and a 1.6 GHz 3-dB modulation bandwidth (detector limited). To realize a free-form and scalable SLM, we fabricate the PhC via interference lithography and develop a procedure to bond the device to a megapixel CMOS backplane. We identify limitations in existing EO materials and CMOS backplanes that must be overcome to simultaneously achieve megapixel-scale, GHz-rate operation. The `LN on Silicon' (LNoS) architecture we present is a blueprint towards realizing such devices
Supplement 1: Bright and photostable single-photon emitter in silicon carbide
Supplemental document Originally published in Optica on 20 July 2016 (optica-3-7-768
Reliable Exfoliation of Large-Area High-Quality Flakes of Graphene and Other Two-Dimensional Materials
Mechanical exfoliation has been a key enabler of the exploration of the properties of two-dimensional materials, such as graphene, by providing routine access to high-quality material. The original exfoliation method, which remained largely unchanged during the past decade, provides relatively small flakes with moderate yield. Here, we report a modified approach for exfoliating thin monolayer and few-layer flakes from layered crystals. Our method introduces two process steps that enhance and homogenize the adhesion force between the outermost sheet in contact with a substrate: Prior to exfoliation, ambient adsorbates are effectively removed from the substrate by oxygen plasma cleaning, and an additional heat treatment maximizes the uniform contact area at the interface between the source crystal and the substrate. For graphene exfoliation, these simple process steps increased the yield and the area of the transferred flakes by more than 50 times compared to the established exfoliation methods. Raman and AFM characterization shows that the graphene flakes are of similar high quality as those obtained in previous reports. Graphene field-effect devices were fabricated and measured with back-gating and solution top-gating, yielding mobilities of ∼4000 and 12 000 cm<sup>2</sup>/(V s), respectively, and thus demonstrating excellent electrical properties. Experiments with other layered crystals, <i>e.g.</i>, a bismuth strontium calcium copper oxide (BSCCO) superconductor, show enhancements in exfoliation yield and flake area similar to those for graphene, suggesting that our modified exfoliation method provides an effective way for producing large area, high-quality flakes of a wide range of 2D materials
Strong Enhancement of Light–Matter Interaction in Graphene Coupled to a Photonic Crystal Nanocavity
We demonstrate a large enhancement in the interaction
of light
with graphene through coupling with localized modes in a photonic
crystal nanocavity. Spectroscopic studies show that a single atomic
layer of graphene reduces the cavity reflection by more than a factor
of one hundred, while also sharply reducing the cavity quality factor.
The strong interaction allows for cavity-enhanced Raman spectroscopy
on subwavelength regions of a graphene sample. A coupled-mode theory
model matches experimental observations and indicates significantly
increased light absorption in the graphene layer. The coupled graphene–cavity
system also enables precise measurements of graphene’s complex
refractive index
Surface Structure of Aerobically Oxidized Diamond Nanocrystals
We investigate the aerobic oxidation
of high-pressure, high-temperature
nanodiamonds (5–50 nm dimensions) using a combination of carbon
and oxygen K-edge X-ray absorption, wavelength-dependent X-ray photoelectron,
and vibrational spectroscopies. Oxidation at 575 °C for 2 h eliminates
graphitic carbon contamination (>98%) and produces nanocrystals
with
hydroxyl functionalized surfaces as well as a minor component (<5%)
of carboxylic anhydrides. The low graphitic carbon content and the
high crystallinity of HPHT are evident from Raman spectra acquired
using visible wavelength excitation (λ<sub>excit</sub> = 633
nm) as well as carbon K-edge X-ray absorption spectra where the signature
of a core–hole exciton is observed. Both spectroscopic features
are similar to those of chemical vapor deposited (CVD) diamond but
differ significantly from the spectra of detonation nanodiamond. The
importance of these findings to the functionalization of nanodiamond
surfaces for biological labeling applications is discussed
Fiber-Coupled Diamond Micro-Waveguides toward an Efficient Quantum Interface for Spin Defect Centers
We
report the direct integration and efficient coupling of nitrogen vacancy (NV) color centers in diamond
nanophotonic structures into a fiber-based photonic architecture at
cryogenic temperatures. NV centers are embedded in diamond micro-waveguides
(μWGs), which are coupled to fiber tapers. Fiber tapers have
low-loss connection to single-mode optical fibers and hence enable
efficient integration of NV centers into optical fiber networks. We
numerically optimize the parameters of the μWG-fiber-taper devices
designed particularly for use in cryogenic experiments, resulting
in 35.6% coupling efficiency, and experimentally demonstrate cooling
of these devices to the liquid helium temperature of 4.2 K without
loss of the fiber transmission. We observe sharp zero-phonon lines
in the fluorescence of NV centers through the pigtailed fibers at
100 K. The optimized devices with high photon coupling efficiency
and the demonstration of cooling to cryogenic temperatures are an
important step to realize fiber-based quantum nanophotonic interfaces
using diamond spin defect centers