Posts: 1
Threads: 1
Joined: Sep 2010
hello,am an engineering student and i selected the topic "plasmonics technology"also i want some mathematical proofs including electromagnetic theory
the rest is given below
Plasmons are density waves of electrons, created when light hits the surface of a metal under precise circumstances. Because these density waves are generated at optical frequencies, very small and rapid waves, they can theoretically encode a lot of information, more than what's possible for conventional electronics.
Plamonics is thought to embody the strongest points of both optical and electronic data transfer. Optical data transfer, as in fiber optics, allows high bandwidth, but requires bulky "wires," or tubes with reflective interiors. Electronic data transfer operates at frequencies inferior to fiber optics, but only requires tiny wires. Plasmonics, sometimes called "light on a wire," would allow the transmission of data at optical frequencies along the surface of a tiny metal wire, despite the fact that the data travels in the form of electron density distributions rather than photons.The main limitation to plasmonics today is that plasmons tend to dissipate after only a few millimeters, making them too short-lived to serve as a basis for computer chips, which are a few centimeters across. For sending data even longer distances, the technology would need even more improvement. The key is using a material with a low refractive index, ideally negative, such that the incoming electromagnetic energy is reflected parallel to the surface of the material and transmitted along its length as far as possible. There exists no natural material with a negative refractive index, so nanostructured materials must be used to fabricate effective plasmonic devices. For this reason, plasmonics is frequently associated with nanotechnology.
Posts: 2,300
Threads: 878
Joined: Sep 2010
Posts: 5,362
Threads: 2,998
Joined: Feb 2011
[attachment=11359]
1.INTRODUCTION:
Currently, two of the most daunting problems preventing significant increases in processor speed are thermal and signal delay issues associated with electronic interconnection. Optical interconnects, on the other hand, possess an almost unimaginably large data carrying capacity, and may offer interesting new solutions for circumventing these problems. Unfortunately, their implementation is hampered by the large size mismatch between electronic and dielectric photonic components. Dielectric photonic devices are limited in size by the fundamental laws of diffraction to about half a wavelength of light and tend to be at least one or two orders of magnitude larger than their nanoscale electronic counterparts. This obvious size mismatch between electronic and photonic components presents a major challenge for interfacing these technologies. Further progress will require the development of a radically new chip- scale device technology that can facilitate information transport between nanoscale devices at optical frequencies and bridge the gap between the world of nanoscale electronics and microscale photonics.
We discuss a candidate technology that has recently emerged and has been termed ‘plasmonics’. This device technology exploits the unique optical properties of nanoscale metallic structures to route and manipulate light at the nanoscale. By integrating plasmonic, electronic, and conventional photonic devices on the same chip, it would be possible to take advantage of the strengths of each technology. We present some of the recent studies on plasmonic structures and conclude by providing an assessment of the potential opportunities and limitations for Si chip-scale plasmonics.
2.Plasmonics as a new device technology:
Metal nanostructures may possess exactly the right combination of electronic and optical properties to tackle the issues outlined above and realize the dream of significantly faster processing speeds. The metals commonly used in electrical interconnection such as Cu and Al allow the excitation of surface plasmon- polaritons (SPPs). SPPs are electromagnetic waves that propagate along a metal-dielectric interface and are coupled to the free electrons in the metal (Figure 1).
Figure1. A SPP propagating along a metal-dielectric interface. These waves are transverse magnetic in nature. From an engineering standpoint, an SPP can be viewed as a special type of light wave propagating along the metal surface.
The metallic interconnects that support such waves thus serve as tiny optical waveguides termed plasmonic waveguides. The notion that the optical mode (‘light beam’) diameter normal to the metal interface can be significantly smaller than the wavelength of light has generated significant excitement and sparked the dream that one day we will be able to interface nanoscale electronics with similarly sized optical (plasmonic) devices.
It is important to realize that, with the latest advances in electromagnetic simulations and current complementary metal-oxide semiconductor (CMOS)-compatible fabrication techniques, a variety of functional plasmonic structures can be designed and fabricated in a Si foundry right now. Current Si-based integrated circuit technology already uses nanoscale metallic structures, such as Cu and Al interconnects, to route electronic signals between transistors on a chip. This mature processing technology can thus be used to our advantage in integrating plasmonic devices with their electronic and dielectric photonic counterparts. In some cases, plasmonic waveguides may even perform a dual function and simultaneously carry both optical and electrical signals, giving rise to exciting new capabilities.
3.Imaging SPPs with a photon scanning tunneling microscope:
In order to study the propagation of SPPs, a photon scanning tunneling microscope was constructed (PSTM) by modifying a commercially available scanning near-field optical microscope. PSTMs are the tool of choice for characterizing SPP propagation along extended films as wellas metal stripe waveguide. Figure 2a shows how a microscope objective at the heart of our PSTM can be used to focus a laser beam onto a metal film at a well-defined angle and thereby launch a SPP along the top metal surface.
Figure2. (a) Schematic representation of the operation of a PSTM that enables the study of SPP propagation along metal film surfaces. The red arrow shows how a SPP is launched from an excitation spot onto a metal film surface using a high numerical aperture microscope objective. (b) Scanning electron microscopy (SEM) image of the near-field optical cantilever probe used in the experiments. The tip consists of a microfabricated; hollow glass pyramid coated with an optically thick layer of Al. Light can be collected or emitted through a 50 nm hole fabricated in the Al film on the top of the pyramid. © A cross-sectional view of the same hollow pyramidal tip after a large section was cut out of the sidewall with a focused ion beam (FIB). In close proximity to the surface, the pyramidal tip can tap into the propagating SPP and scatter out a little bit of light through the 50 nm hole (shown pictorially). The scattered light is detected in the far-field, providing a measure of the local field intensity right underneath the tip. By scanning the tip over the sample and measuring the intensity at each tip position, images of propagating SPPs can be created. (d) SEM image of an Au film into which a Bragg grating has been fabricated using a FIB. (e) PSTM image of an SPP wave launched along the metal film toward the Bragg grating. The back reflection of the SPP from the Bragg grating results in the observation of a standing wave interference pattern.
A sharp, metal-coated pyramidal tip (Figure 2b and 2c) is used to tap into the guided SPP wave locally and scatter light toward a far-field detector. These particular tips have a nanoscale aperture at the top of the pyramid through which light can be collected. The scattered light is then detected with a photomultiplier tube. The signal provides a measure of the local light intensity right underneath the tip and, by scanning the tip over the metal surface, the propagation of SPPs can be imaged The operation of the PSTM can be illustrated by investigating the propagation of SPPs on a patterned Au film (Figure 2d). Here, a focused ion beam (FIB) was used to define a series of parallel grooves, which serve as a Bragg grating to reflect SPP waves. Figure 2e shows a PSTM image of a SPP wave excited with a 780 nm wavelength laser and directed toward the Bragg grating. The back reflection of the SPP from the grating results in the standing wave interference pattern observed in the image. From this type of experiment the wavelength of SPPs can be determined in a straightforward manner and compared to theory.
4. Experiments and simulations on plasmonic waveguides
The valuable information about plasmonic structures provided by PSTM measurements allows us to evaluate the utility of plasmonics for interconnection. Plasmonic stripe waveguides provide a natural starting point for this discussion as such stripes very closely resemble conventional metal interconnects.
Electron beam lithography has been used to generate 55 nm thick Au stripes on a SiO2 glass slide with stripe widths ranging from 5 μm to 50 nm. Au stripes are ideal for fundamental waveguide transport studies as they are easy to fabricate, do not oxidize, and exhibit a qualitatively similar plasmonic response to Cu and Al. Figure 3a shows an optical micrograph of a typical device consisting of a large Au area from which SPPs can be launched onto varying width metal stripes. A scanning electron microscopy (SEM) image of a 250 nm wide stripe is shown as an inset. The red arrow shows how light is launched from a focused laser spot into 1 μm wide strip
