1. GUIDED BY SUBMITTED BY
UDAY VEER SIR VISHAL SINGH
00320903613
MAE-2SEMESTER
INTRODUCTION & APPLICATION
NANOPHOTONICS
APPLIED PHYSICS

2. INTRODUCTION

3. Nanophotonics or Nano-optics is the study of the behavior of light on
the nanometer scale. It is considered as a branch of optical engineering which
deals with optics, or the interaction of light with particles or substances, at
deeply sub wavelength length scales. Technologies in the realm of Nano-optics
include near-field scanning optical microscopy (NSOM), photo assisted
scanning tunneling microscopy, and surface Plasmon optics. Traditional
microscopy makes use of diffractive elements to focus light tightly in order to
increase resolution. But because of the diffraction limit (also known as the
Rayleigh Criterion), propagating light may be focused to a spot with a
minimum diameter of roughly half the wavelength of the light. Thus, even with
diffraction-limited confocal microscopy, the maximum resolution obtainable is
on the order of a couple of hundred nanometers.
Electrons play crucial role of information carriers between light and
matter in various photonic devices. Electrons have the split personality of

4. wave properties in terms of wavelength and corpuscular properties in terms of
mass and charge. Thus by proper manipulation of the interaction of light with
matter, information processing speed can be increased substantially. The
interaction of light with matter can be effectively modified when the spatial
inhomogeneities that are present in the medium of various photonic devices
are not negligible when compared to the electron wavelength. Variations in
the electric and magnetic fields or inhomogeneity in electronic charge or
electronic mass displacement can contribute to the spatial inhomogeneities
for electrons.
When the spatial inhomogeneities can be extended to the atomic or sub
atomic level, the interaction of light with matter becomes the prerogative of
various processes that are involved in the electron subsystem of atoms. The
atoms in turn may form molecules and solids. Hence Nanophotonics can be
characterized as the science and technology of confined light waves in
complex media and confined electron waves in various nanostructured solids
that in turn determine a plethora of versatile physical phenomena.
ADVANTAGES/USES
 Enormous data transmission rate
Trans-oceanic fibre optic caller have been deployed in the Pacific and
Atlantic oceans for long distance communication technology. They are also
being used as local area networks. Thus owing to the speed by which various
data types can be sent from one place to another with minimal loss, electronic
technology has been replaced by photonics technology. Photonic integrated
circuits are devices that are similar to electronic integrated circuits which
integrate multiple photonic functions. Photonic integrated circuits are
replacing electronic integrated circuits owing to their higher capability and
performance in signal processing. This can be attributed mainly due to high
switching speeds offered by photonic integrated circuits. Hence with photonic

5. integrated circuit technology, one can achieve high-speed data processing
with an average processing speed of the order of tera bits per second.
 High optical memory storage density
An optical disk memory has the capacity for storing enormous amount
of digital signals in numerous small pits present on its surface, where each pit
stores one bit of data. The stored digital signals are read by illuminating the
disk surface by a focused laser beam and by detecting the laser light reflected
from the disk surface Nanophotonics devices, which are capable of large-scale
data storage and processing and thereby lay the foundation for the
fabrication, measurement, control and functional requirements of novel
optical science and technology.
Diffraction limited Nanophotonics
Diffraction limited nanophotonics, as a broader perspective, encompasses
photonic crystals, plasmonics, silicon photonics and quantum dot lasers, that
employ conventional propagating light.
 Photonic crystals
Photonic crystals are mainly used for controlling optical interference and light
scattering by devising a sub wavelength-sized periodic structure in the photonic
device material. Hence they are mainly used as filter device. The principal laying
behind the working of a photonic crystal is that at the centre of the device
material, constructive interference occurs between scattered light. Thus optical
energy is concentrated. In order to filter out the scattered light, it is made to
interference destructively at the edge of the device material. Constructive
Interference is maintained at the centre of the device material only when the
rim of the material is made sufficiently larger than the wave length of the
conventional propagating light. Otherwise, light that is concentrated at the
centre leaks to the rim, thereby playing a spoil sport for constructive
interference to occur. As photonic crystals employs conventional propagating
light and as its size cannot be reduced beyond a certain values, the spatial
dimensions of the photonic crystal is limited by diffraction.

6.  Plasmonics
In plasmonics technology, by exciting free electrons, resonant enhancement of
light takes place in a metal. As a result of strong interaction with the free
electrons, optical energy gets concentrated on the metal surface in the form of
a surface plasmon, which represents in general, the quantum mechanical
picture of plasmon oscillation of free electrons on the
metal surface. But this quantum mechanical picture is lost as the plasma
oscillation of electrons has a short phase relaxation time. Hence plasmonics is
essentially governed by wave optics in the metal and hence is limited by
diffraction.
 Silicon Photonics
In silicon photonics, narrow-striped optical wave guides that use high-refractive
index silicon crystals are employed to confine light effectively. As wave optics is
solely responsible for this light confinement, this is essentially an application of
wave optics in silicon and hence is limited by diffraction.
 Quantum dot lasers
Nanometre-sized semiconductor quantum dots are used as the gain media in a
quantum dot laser. Large number of quantum dot lasers are required in order
to confine light effectively because semiconductor quantum dots are much
smaller than the wavelength of light and hence an individual quantum dot
cannot be employed for effective light confinement due to scattering and
diffraction. This again leads to the scenario that the device size becomes limited
by diffraction. Thus all the above mentioned cases are based on diffraction
limited wave optics. Also, even if nanometre- sized materials are used for the
above mentioned cases in the future, as long as conventional propagating light
is used, the size of these photonic devices cannot be reduced beyond the
diffraction limit. Hence to go beyond the diffraction limit, the only other option
left is to use non-propagating or stationary nanometre-sized light to induce
primary excitations in a nanometre-sized material such that the spatial phase of
the excitation is independent of that of the incident light.

7. Electromagnetic radiation in vacuum
E denote the macroscopic electric field strength, D-the electric
displacement, H-the magnetic field strength, P-the electric polarization of the
macroscopic medium, M-the magnetization of the macroscopic medium, B-the
magnetic induction, r-the charge density and J-the electric current density.
For electric displacement are free charges
E and H are responsible for the generation of each other and that the
macroscopic current density J is responsible for the generation of the magnetic
field strength H can be represented by the following respective relations
Vacuum is represented by the following conditions
Solving,
Hence, the equation for plane wave is given by

8. Diffraction of light
Diffraction of light is generally formed as the encouragement of light on any
obstacle and is attributed to the wavelength of light. Huygens’ theory of light
states that as a point source is responsible for a spherical wavefront, any point
propagated by a light wave is solely responsible for the origin of secondary
spherical waves that spread out in all directions. By adding the concept of
interference to Huygens’ theory, Fresnel stated that the complex amplitude of
a light wave beyond the wavefront can be superimposed to that of all
elementary waves which propagate from each point of the wavefront to the
observed point
where A is the amplitude, r0 is the radius and k is the propagation constant of
the plane wave.
where K (q ) is termed as the obliquity factor such that 0 ≤ K(q ) ≤ M, where
K(q )→0 as q →1.57 and tends to a maximum value M, when q →0. q is the
angle subtended by a line between a points of the wavefront to the observed
point to a line normal to the wavefront in the amplitude of the elementary
waves in the plane wave. When there is no obstacle, the process of light
propagation is given by the equation
where ds is the infinitesimal area.

9. APPLICATIONS

10. NEMS
Nanoelectromechanical systems (NEMS) are a class of devices integrating
electrical and mechanical functionality on the nanoscale. NEMS form the logical
next miniaturization step from so-called microelectromechanical systems, or
MEMS devices. NEMS typically integrate transistor-like nanoelectronics with
mechanical actuators, pumps, or motors, and may thereby form physical,
biological, and chemical sensors. The name derives from typical device
dimensions in the nanometre range, leading to low mass, high mechanical
resonance frequencies, potentially large quantum mechanical effects such as
zero point motion, and a high surface-to-volume ratio useful for surface-based
sensing mechanisms. Uses include
accelerometers, or detectors of chemical
substances in the air.
A key application of NEMS is atomic
force microscope tips. The increased
sensitivity achieved by NEMS leads to
smaller and more efficient sensors to detect
stresses, vibrations, forces at the atomic
level, and chemical signals. AFM tips and
other detection at the nanoscale rely heavily
on NEMS. If implementation of better
scanning devices becomes available, all of
nanoscience could benefit from AFM tips.
FABRICATION
Two complementary approaches to fabrication of NEMS can be found.
The top-down approach uses the traditional micro fabrication methods,
i.e. optical and electron beam lithography, to manufacture devices. While being
limited by the resolution of these methods, it allows a large degree of control
over the resulting structures. Typically, devices are fabricated from metallic thin
films or etched semiconductor layers.
Bottom-up approaches, in contrast, use the chemical properties of single
molecules to cause single-molecule components to
(a) Self-organize or self-assemble into some useful conformation
(b) Rely on positional assembly. These approaches utilize the concepts of
molecular self-assembly and/or molecular recognition. This allows fabrication of
much smaller structures, albeit often at the cost of limited control of the
fabrication process.

11. Nanotube nanomotor
A device generating linear or rotational motion using carbon nanotube(s) as the
primary component, is termed a nanotube nanomotor. Nature already has
some of the most efficient and powerful kinds of nanomotors. Some of these
natural biological nanomotors have been re-engineered to serve desired
purposes. However, such biological nanomotors are designed to work in
specific environmental conditions (pH, liquid medium, sources of energy, etc.).
Laboratory-made nanotube nanomotors on the other hand are significantly
more robust and can operate in diverse environments including varied
frequency, temperature, mediums and chemical environments. The vast
differences in the dominant forces and criteria between macro scale and
micro/nanoscale offer new avenues to construct tailor-made nanomotors. The
various beneficial properties of carbon nanotubes makes them the most
attractive material to base such nanomotors on.
 NEMS nanomotor
The nanoactuator consists of a gold plate rotor, rotating about the axis of a
multi-walled nanotube (MWNT). The ends of the MWNT rest on a SiO2 layer
which form the two electrodes at the contact points. Three fixed stator
electrodes (two visible 'in-plane' stators and one 'gate' stator buried beneath
the surface) surround the rotor assembly. Four independent voltage signals
(one to the rotor and one to each stators) are applied to control the position,
velocity and direction of rotation. Empirical angular velocities recorded provide
a lower bound of 17 Hz (although capable of operating at much higher
frequencies) during complete rotations.
Arrays of nanoactuators
Due to the minuscular magnitude of output generated by a single
nanoactuator the necessity to use arrays of such actuators to accomplish a
higher task comes into picture. Conventional methods like chemical vapor
deposition (CVD) allow the exact placement of nanotubes by growing them
directly on the substrate. However, such methods are unable to produce very
high qualities of MWNT. Moreover, CVD is a high temperature process that
would severely limit the compatibility with other materials in the system. A Si
substrate is coated with electron beam resist and soaked in acetone to leave
only a thin polymer layer. The substrate is selectively exposed to an low energy
electron beam of an SEM that activates the adhesive properties of the polymer
later. This forms the basis for the targeting method. The alignment method

12. exploits the surface velocity obtained by a fluid as it flows off a spinning
substrate. MWNTs are suspended in orthodicholrobenzene (ODCB) by
ultrasonication in an aquasonic bath that separates most MWNT bundles into
individual MWNTs. Drops of this suspension are then pipetted one by one onto
the center of a silicon substrate mounted on a spin coater rotating at 3000 rpm.
Arc-discharge evaporation technique
This technique is a variant of the standard arc-discharge technique used
for the synthesis of fullerenes in an inert gas atmosphere. The experiment is
carried out in a reaction vessel containing an inert gas such as helium, argon,
etc. flowing at a constant pressure. A potential of around 18 V is applied across
two graphite electrodes (diameters of the anode and cathode are 6 mm and 9
mm) separated by a short distance of
usually 1–4 mm within this chamber. The
amount of current (usually 50–100 A)
passed through the electrodes to ensure
nanotube formation depends on the
dimensions of the electrodes, separation
distance and the inert gas used. As a result,
carbon atoms are ejected from the anode
and are deposited onto the cathode hence
shrinking the mass of the anode and
increasing the mass of the cathode. The
black carbonaceous deposit (a mixture of
nanoparticles and nanotubes in a ratio of
1:2) is seen growing on the inside of the
cathode while a hard grey metallic shell
forms on the outside. The total yield of nanotubes as a proportion of starting
graphitic material peaks at a pressure of 500 torr at which point 75% of graphite
rod consumed is converted to nanotubes. The nanotubes formed range from 2
to 20 nm in diameter and few to several micrometres in length. There are
several advantages of choosing this method over the other techniques such as
laser ablation and chemical vapor deposition such as fewer structural defects
(due to high growth temperature), better electrical, mechanical and thermal
properties, high production rates (several hundred mg in ten minutes), etc.
Applications
1. The rotating metal plate could serve as a mirror for ultra-high-density
optical sweeping and switching devices as the plate is at the limit of

13. visible light focusing. An array of such actuators, each serving as a high
frequency mechanical filter, could be used for parallel signal processing
in telecommunications.
2. The plate could serve as a paddle for inducing or detecting fluid motion
in microfluidic applications. It could serve as a bio-mechanical element in
biological systems, a gated catalyst in wet chemistry reactions or as a
general sensor element.
3. A charged oscillating metal plate could be used as a transmitter of
electromagnetic radiation.
 Thermal gradient driven nanotube actuators
Fabrication
The MWNT are fabricated using the standard arc-discharge evaporation
process and deposited on an oxidized silicon substrate. The gold plate in the
centre of the MWNT is patterned using electron-beam lithography and Cr/Au
evaporation. During the same process, the electrodes are attached to the
nanotube. Finally, electrical-breakdown technique is used to selectively remove
a few outer walls of the MWNT. This enables low friction rotation and
translation of the shorter nanotube along the axis of the longer tube. The
application of the electrical-breakdown technique does not result in the
removal of the tube(s) below the cargo. This might be because the metal cargo
absorbs the heat generated in the portion of the tube in its immediate vicinity
hence delaying or possibly even preventing tube oxidation in this part.
Principle
The interaction between the longer and shorter tubes generates an
energy surface that confines the motion to specific tracks – translation and
rotation. The degree of translational and rotational motion of the shorter tube
are highly dependent on the chirality’s of the two tubes as shown in Figure 2.3.
Motion in the nanoactuator displayed a proclivity of the shorter tube to follow
a path of minimum energy. This path could either have a roughly constant
energy or have a series of barriers. In the former case, friction and vibrational
motion of atoms can be neglected whereas a stepwise motion is expected in
the latter scenario.
Mechanism for actuation
Many proposals were made to explain the driving mechanism behind the
nanoactuator. The high current (0.1 mA) required to drive the actuator is likely

14. to cause sufficient dissipation to clean the surface of contaminants; hence,
ruling out the possibility of contaminants playing a major role. The possibility of
electro migration, where the electrons move atomic impurities via momentum
transfer due to collisions, was also ruled out because the reversal of the current
direction did not affect the direction of displacement. Similarly, rotational
motion could not have been caused by an induced magnetic field due to the
current passing through the nanotube because the rotation could either be left
or right-handed depending on the device. Stray electric field effect could not be
the driving factor because the metal plate staid immobile for high resistive
devices even under a large applied potential. The thermal gradient in the
nanotube provides the best explanation for the driving mechanism.
Thermal gradient induced motion
The induced motion of the shorter nanotube is explained as the reverse
of the heat dissipation that occurs in friction wherein the sliding of two objects
in contact results in the dissipation of some of the
kinetic energy as phononic excitations caused by the
interface corrugation. The presence of a thermal
gradient in a nanotube causes a net current of
phononic excitations traveling from the hotter region
to the cooler region. The interaction of these
phononic excitations with mobile elements (the
carbon atoms in the shorter nanotube) causes the
motion of the shorter nanotube. This explains why
the shorter nanotube moves towards the cooler
electrode. Changing the direction of the current has no effect on the shape of
thermal gradient in the longer nanotube. Hence, direction of the movement of
the cargo is independent of the direction of the bias applied. The direct
dependence of the velocity of the cargo to the temperature of the nanotube is
inferred from the fact that the velocity of the cargo decreases exponentially as
the distance from the midpoint of the long nanotube increases.
Applications
Some of the main applications of the electron windmill include:
1. A voltage pulse could cause the inner element to rotate at a calculated
angle hence making the device behave as a switch or a nanoscale
memory element.

15. 2. Modification of the electron windmill to construct a nanofluidic pump by
replacing the electrical contacts with reservoirs of atoms or molecules
under the influence of an applied pressure difference.
 Electron windmill
Structure
The nanomotor consists of a double-walled CNT (DWNT) formed from an
achiral outer tube clamped to external gold electrodes and a narrower chiral
inner tube. The central portion of the outer tube is removed using the
electrical-breakdown technique to expose the free-to-rotate, inner tube. The
nanodrill also comprises an achiral outer nanotube attached to a gold electrode
but the inner tube is connected to a mercury bath.
Principle
Conventional nanotube nanomotors make use of static forces that
include elastic, electrostatic, friction and van der
Waals forces. The electron windmill model makes
use of a new "electron-turbine" drive mechanism
that obviates that need for metallic plates and
gates that the above nanoactuators require. When
a DC voltage is applied between the electrodes, a
"wind" of electrons is produced from left to right.
The incident electron flux in the outer achiral tube initially possesses zero
angular momentum, but acquires a finite angular momentum after interacting
with the inner chiral tube. By Newton's third law, this flux produces a tangential
force (hence a torque) on the inner nanotube causing it to rotate hence giving
this model the name – "electron windmill". For moderate voltages, the
tangential force produced by the electron wind is much greatly exceed the
associated frictional forces.
Applications
Some of the main applications of the electron windmill include:
1. A voltage pulse could cause the inner element to rotate at a calculated
angle hence making the device behave as a switch or a nanoscale
memory element.
2. Modification of the electron windmill to construct a nanofluidic pump by
replacing the electrical contacts with reservoirs of atoms or molecules
under the influence of an applied pressure difference.

16. Nanolithography
Nanolithography is the branch of nanotechnology concerned with the study
and application of fabricating nanometre-scale structures, meaning patterns
with at least one lateral dimension between the size of an individual atom and
approximately 100 nm. Nanolithography is used during the fabrication of
leading-edge semiconductor integrated circuits or Nanoelectromechanical
systems (NEMS).
Assisted photolithography
On employing a visible light source, the dressed photon-coherent phonon
assisted photolithography enhances the patterning of commercial
photoresists. The main highlight is that the propagating light does not pattern
the photoresist as the photoresist is sensitive only to UV propagating light.
However a dressed-photon coherent phonon gets generated at the
photoresist edge. The photoresist gets activated by the transfer of energy
from the dressed photon coherent phonon to the photoresist and thereby
gets patterned due to the phonon assisted process. Moreover, as the energy
gets transferred not only to the surface of the photoresist but also to its
interior, the photoresist gets effectively patterned within a short exposure
time. Thus by properly manipulating the exposure time, the photoresist can be
patterned to have a stable spatial profile. By employing a light source of
appropriate laser frequency, high resolution can be achieved when the
wavelength of the light source is greater than the wavelength of absorption
band edge of the photoresist. Hence phonon assisted photolithography is not
expensive as it does not require either short wavelength
X-ray or UV light source for patterning.

17. Advantages
1. Complicated patterns can be obtained with high resolution when subject
to multiple exposures as the photoresist is insensitive to incident visible
light. Phonon assisted photolithography has the ability to pattern even
an optically inactive film.
2. Photon-coherent phonons can be generated and applied to a nanometre
rough surface material, when illuminated with a light source. On
employing dressed photon technology, for repairing surface roughness,
namely, etching and desorption.

18. Near-field scanning optical microscope
Near-field scanning optical microscopy
(NSOM/SNOM) is a microscopy
technique for nanostructure
investigation that breaks the far field
resolution limit by exploiting the
properties of evanescent waves. This is
done by placing the detector very close
(distance much smaller than wavelength
λ) to the specimen surface. This allows
for the surface inspection with high
spatial, spectral and temporal resolving
power. With this technique, the resolution of the image is limited by the size of
the detector aperture and not by the wavelength of the illuminating light. In
particular, lateral resolution of 20 nm and vertical resolution of 2–5 nm have
been demonstrated. As in optical microscopy, the contrast mechanism can be
easily adapted to study different properties, such as refractive index, chemical
structure and local stress. Dynamic properties can also be studied at a sub-
wavelength scale using this technique.
Near-field spectroscopy
As the name implies, information is collected by spectroscopic means
instead of imaging in the near field regime. Through Near Field Spectroscopy
(NFS), one can probe spectroscopically with subwavelength resolution. Raman
SNOM and fluorescence SNOM are two of the most popular NFS techniques as
they allow for the identification of nanosized features with chemical contrast.
Some of the common near field spectroscopic techniques are:
 Direct local Raman NSOM: Aperture Raman NSOM is limited by very hot
and blunt tips, and by long collection times. However, apertureless
NSOM can be used to achieve high Raman scattering efficiency factors
(around 40). Topological artefact’s make it hard to implement this
technique for rough surfaces.
 Surface enhanced Raman spectroscopy (SERS) NSOM: This technique
can be used in an apertureless shear-force NSOM setup, or by using an
AFM tip coated with gold. The Raman signal is found to be significantly
enhanced under the AFM tip. This technique has been used to give local
variations in the Raman spectra under a single-walled nanotube. A highly

19. sensitive optoacoustic spectrometer must be used for the detection of
the Raman signal.
 Fluorescence NSOM: This highly popular and sensitive technique makes
use of the fluorescence for near field imaging, and is especially suited for
biological applications. The technique of choice here is the apertureless
back to the fibre emission in constant shear force mode. This technique
uses merocyanine based dyes embedded in an appropriate resin. Edge
filters are used for removal of all primary laser light. Resolution as low as
10 nm can be achieved using this technique.
 Near field infrared spectrometry and near field dielectric microscopy.

20. References
o davidkirkpatrick.wordpress.com/tag/nanophotonics/
o www.nanophotonics.de/Â
o www.ece.rice.edu/~halas/
o nanohub.org/courses/nanophotonics
o Hewakuruppu, Y., et al., Plasmonic “ pump – probe ” method to study
semi-transparent nanofluids
o A. Harootunian, E. Betzig, M. Isaacson, and A. Lewis (1986). "Super-
resolution fluorescence near-field scanning optical microscopy". Appl.
Phys. Lett. 49: 674. doi:10.1063/1.97565
o Nanosystems by K. Eric Drexler.