chaPter 7 nanomaterials: Properties
232
An important effect of shape is related to whether the nanomaterial is 2-D, 1-D, or 0-D. In the case of a 2-D nanomaterial there are
longitudinal plasmons along the plane of the sheet and a transverse
plasmon across the thickness of the sheet. For a 1-D nanomaterial, there is a longitudinal plasmon along the long axis, whereas
transverse plasmons exist across the diameter of the material. As we
reduce the diameter, a shift toward the blue is expected. In the case
of 0-D nanomaterials, the production of well-defined nonspherical
shapes is usually quite challenging but of great interest. However,
another alternative is to create core-shell nanoparticles. In this
fashion, shells with thinner metal layers produce localized surface
plasmon resonance toward lower frequencies, that is, longer wavelengths and a shift toward the red. Another optical plasmon effect
associated with metallic nanoparticles occurs when agglomeration
takes place. Under these conditions, a shift toward lower plasmon
frequencies occurs, leading to a red shift.
Finally, it is important to consider the environment surrounding
the nanoparticles. When the refractive index or dielectric constant
of the material embedding the nanoparticles increases, the plasmon
frequency decreases, generating a red shift. Using the aforementioned surface plasmon properties associated with metallic nanoparticles, light absorption and light emission can be significantly
enhanced. As a result, metallic nanoparticles can be used as structural and chemical labels, photothermal therapy, and colorimetric
chemical sensors.
7.6 acoustic ProPerties
As initially discussed in Section 4.8, materials interact strongly with
radiation that has a wavelength comparable with their internal
structure and/or dimensions. Therefore, in the case of nanomaterials for which the characteristic structure and dimensions are below
100 nm, there is a wide range of electromagnetic radiation within
the visible, ultraviolet, and X-rays regimes that are affected by
the nanoscale. On the other hand, acoustic waves, which exhibit
wavelengths that range from microns to kilometers, have little or
no direct effect on the properties of nanomaterials. As a result, the
discussion of acoustic properties is limited for the case of nanomaterials. However, it should be pointed out that sound waves are
used to produce nanomaterials. In addition, since the properties
of nanomaterials are in many cases very different from traditional
materials, acoustic waves can have a distinct indirect effect, such as
in the case of seismic waves.
232
An important effect of shape is related to whether the nanomaterial is 2-D, 1-D, or 0-D. In the case of a 2-D nanomaterial there are
longitudinal plasmons along the plane of the sheet and a transverse
plasmon across the thickness of the sheet. For a 1-D nanomaterial, there is a longitudinal plasmon along the long axis, whereas
transverse plasmons exist across the diameter of the material. As we
reduce the diameter, a shift toward the blue is expected. In the case
of 0-D nanomaterials, the production of well-defined nonspherical
shapes is usually quite challenging but of great interest. However,
another alternative is to create core-shell nanoparticles. In this
fashion, shells with thinner metal layers produce localized surface
plasmon resonance toward lower frequencies, that is, longer wavelengths and a shift toward the red. Another optical plasmon effect
associated with metallic nanoparticles occurs when agglomeration
takes place. Under these conditions, a shift toward lower plasmon
frequencies occurs, leading to a red shift.
Finally, it is important to consider the environment surrounding
the nanoparticles. When the refractive index or dielectric constant
of the material embedding the nanoparticles increases, the plasmon
frequency decreases, generating a red shift. Using the aforementioned surface plasmon properties associated with metallic nanoparticles, light absorption and light emission can be significantly
enhanced. As a result, metallic nanoparticles can be used as structural and chemical labels, photothermal therapy, and colorimetric
chemical sensors.
7.6 acoustic ProPerties
As initially discussed in Section 4.8, materials interact strongly with
radiation that has a wavelength comparable with their internal
structure and/or dimensions. Therefore, in the case of nanomaterials for which the characteristic structure and dimensions are below
100 nm, there is a wide range of electromagnetic radiation within
the visible, ultraviolet, and X-rays regimes that are affected by
the nanoscale. On the other hand, acoustic waves, which exhibit
wavelengths that range from microns to kilometers, have little or
no direct effect on the properties of nanomaterials. As a result, the
discussion of acoustic properties is limited for the case of nanomaterials. However, it should be pointed out that sound waves are
used to produce nanomaterials. In addition, since the properties
of nanomaterials are in many cases very different from traditional
materials, acoustic waves can have a distinct indirect effect, such as
in the case of seismic waves.