Other theoretical simulations showed that the mechanical strain exerted is extremely high, corresponding to a pressure of several Gpa [ 40 ]. Because atoms on the surface are under high strain, they can undergo large-amplitude molecular-like vibrations to relieve the strain [ 41 ]; and hence can also couple efficiently to thermal and mechanical stimuli. Second-order nonlinearity in silicon opens up other prospective applications in optics, including modulation, amplification, gain and laser action, and signal processing [ 42 ].
See a Problem?
Not only miniaturization afforded silicon strong luminescence and optical nonlinearity, but there are also some preliminary reports indicating optical gain and laser action in films of silicon nanoparticles [ 43 ]. The slab acted as an optical amplifier of weak light beams. In other reports 1-nm silicon nanoparticles were reconstituted into microcrystallites [ 45 ]. The crystallites were irradiated by infrared femtosecond pulses of a laser beam with high peak power.
Microscopic directed blue emission was observed. Microscopic red emission was also observed from clusters of 2. Miniaturization has triggered strong light—matter interactions. Nanotechnology allowed researchers to study light—matter interactions at the nanoscale and to launch the subfield of nano-optics. A considerable amount of basic knowledge as well as novel functions of nanomatter has accumulated over the past 20 years. Some applications have already reached the practical level, while others are futuristic. In this section we briefly present some practical applications of optics in nanotechnology in service of fields as diverse as electronics, opto- and photo-electronics, elementary particles, biomedicine, energy harvest and lighting, and art as in stained glass and lusterware pottery.
Bulk semiconductors, especially silicon, form the backbone of modern electronics and computing. Bulk silicon, however, is a very dull material, being an especially poor emitter of light, turning added energy into heat.
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This makes integrating electronic and photonic circuits a challenge. There have been several proposals to alleviate this problem. One approach involves doping silicon with other materials. However, the emitted light is not in the visible rather in deep infrared. Moreover, the emission is not very efficient and can degrade the electronic properties of silicon. Another approach is to use nanotechnology by making silicon devices that are very small, such as using luminescent nanoparticles, five nanometers in diameter or less as introduced above. As we have seen above, at that size quantum confinement effects allow the device to emit light.
But making electrical connections at that scale is not currently feasible and may compromise the optical activity of the nanomaterial [ 47 ], as well as afford very low electrical conductivity. Schematic of a hybrid silicon—silver nanowire system. From [ 48 ]. Understanding interactions between strong light and matter is central to many fields. Deeper understanding of strong light coupling with matter is expected to afford the creation of advanced tailored applications [ 50 ].
Present-day laser technology as well as light enhancement due to plasmonic effects has made it possible to study the behavior of atoms and molecules in fields that have peak electric field strength of the order of atomic fields inside atoms or molecules. Under these conditions, even tightly bound ground states must be greatly altered by the presence of the field [ 51 , 52 ].
Understanding interactions between light and nanomatter is central to many fields, providing invaluable insights into the nature of matter as well as the nature of light. Indeed, greater understanding of light—matter coupling has enabled creation of tailored applications, resulting in a variety of devices such as microscopic lasers, switches, sensors, modulators, fuel and solar cells, and detectors.
As discussed above, hybrid-plasmonic monolithic nanowire optical cavities highlight recent progress made in tailoring light—matter coupling strengths. From [ 53 ]. Thus the confined light to nanometal spaces is short range dies out exponentially and does not propagate to large distances. Thus it provides spatial nanoresolution. This opens up many applications, especially those optical processes or phenomena that depend very sensitively on the magnitude of the electric field, such as fluorescence, Raman scattering, and infrared absorption, resulting in plasmon-enhanced fluorescence, surface-enhanced Raman scattering, and surface-enhanced infrared absorption spectroscopy.
The Raman scattering effect, for example, depends on the fourth power of the field; thus they are enhanced if scattering is performed with the confined light near a metal nanoparticle rather than with ordinary propagating light. The Raman scattering effect is used for sensing and identification of substances.
When a substance is irradiated with light, it scatters light called Raman light at a wavelength or frequency slightly shifted from the wavelength of the original irradiated light by an amount equal to the natural frequency of molecules that make up the substance. So, detecting the Raman light and analyzing its spectrum allows the identification of the substance.
Since Raman light is usually very weak, detecting its intensity directly is quite difficult. If the electrical field strength is increased 10 times by surface plasmon resonance, then the Raman light is intensified 10 4 times so the intensity becomes 10, times higher.
Schematic of a large molecule in the proximity of metal nanoparticle. It shows the profile of the plasmonic electric field. Different parts of the molecule experience different electric field strengths, introducing strong distortion within the molecules From [ 16 ]. Left top Schematic of a tungsten tip of a scanning electron microscope bathed with a laser beam in a chamber with a certain pressure of a molecular gas.
Molecules, in the gap or near the gap, are subjected to the combined effect of the laser field and the localized field of the metal tip excites, dissociates, ionizes, and pins down ions on the counter surface. A single molecule of trimethyl aluminum is picked on a graphite surface. Left Report in search and discovery of Physics Today about the use of intense light combined with an electric field to identify and selectively detect single atoms From [ 57 ].
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Right cover of The Sciences displaying Alhazen conducting some laboratory experiments. Inside, the issue reports on the detection of single atoms using the process described in the Fig.
One hot area involving the interaction of light with nanosemiconductor in the presence of an external electric field is the generation of voltage that can be stored. A thin film of silicon nanoparticles or capsules of silicon nanoparticles, for example, are placed on top of a silicon-based p-n junction amorphous, polycrystalline, or monocrystalline silicon solar cell. When light strikes the nanoparticles some light is absorbed. As a result, electron hole e—h pairs excitons are produced in the nanoparticles. If the electron and hole are separated from each other completely before they could recombine to produce light luminescence or recombine non-radiatively to produce vibrations and heat then the electrons and holes may be transported, collected, and stored on two external electrodes appropriately constructed and positioned.
The voltage difference between the electrodes can be harnessed at a later time as a battery. The electric field in a p-n junction plays a pivotal role in charge separation and collection. This architecture using 2. In another development, silicon nanowire arrays were used [ 64 ]. Efficient procedures for fabrication of nanowires were recently developed [ 65 , 66 ]. Hemispherical gold deposits are made on the end of the wires. When a near-infrared optical field falls onto the gold deposits, it excites plasmon resonances, which remarkably amplify the intensity, effectively making them like antennas.
The same gold deposit can form a p-n like Schottky junction with the nanowire, which enhances charge collection. Thus the system acts as an effective near-infrared photodetector [ 64 ]. Silicon-based sensitive UV photodetectors have military as well as commercial applications. Military applications include missile warning systems, biological attack warning systems, and jet engine sensors. Schematic of a plasmon solar cell.
It consists of a thin silicon-based active layer on a glass substrate. Gold nanoparticles are placed on the active layer. The novel optical properties of nanomaterial discussed above in Sect. However, due to their direct nature, luminescence of a given nanoparticle size is sharply dependent on its size, which requires the use of an appropriate size distribution to produce broadened emission.
Demonstration of 2. Normalized spectrum of pure RTV in light blue. Another advantage of using nanomaterial as a component in the phosphor mixture stems from the fact that nanomaterial reduces the reflectivity of the mixed composite material so as not to harm the pumping LED chip. Also nanomaterial improves heat dissipation, thus prolonging the lifetime of the bulb.
Thus current manufacturing process of white light can be developed further using the novel interaction of light with nanomatter to produce better efficiency bulbs that cover smoothly the solar white light range, as well as handle larger areas. Schematic of plasmonic nanoparticle-based photothermal therapy for cancer treatment.
A non-consequential weak infrared light gets concentrated in gold nanoparticles, heating them enough to kill cells Adapted from [ 69 ]. Improvement of the sensitivity of Raman analysis due to the enhanced electric field in the proximity of gold nanoparticles as discussed above in Sect. The extra sensitivity allows following changes in the molecular content inside cells, including destruction or formation of molecules in cancerous cells during their death [ 70 ].
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As was discussed above in Sect. When white light shines only the G green component resonates with the electrons in the gold nanoparticles and is absorbed, hence removed. The B blue light is weakened by suffering scattering in all direction. The remaining R red component passes through. A nineth century CE lusterware from Mesopotamia Susa. Top left Lusterware appears red.
Optics Optical Instruments Introduction by Johnson
Micrographs, courtesy D. Chabanne , right TEM image showing the presence of metal nanoparticle Adapted from [ 77 , 78 ]. Several material analysis studies [ 80 , 81 , 82 , 83 ] confirmed that the color of the luster decorations come from metallic nanoparticles. For instance, the presence of metal particles was directly confirmed by conducting high resolution transmission electron microscopy and imaging TEM along with material analysis using electron energy loss spectroscopy.
Generally, copper and silver clusters were incorporated by applying a mixture of a paint, which contained copper and silver salt powders onto a glazed ceramic. This was followed by annealing in a reducing atmosphere.