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Nanotechnology-Enabled Sensors

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288<br />

In three-dimensional reciprocal space, the volume of a cubic unit cell is<br />

defined as:<br />

V3D 3<br />

⎛ 2π ⎞<br />

= ⎜ ⎟⎠ , (6.11)<br />

⎝ L<br />

which is the volume of a single energy state.<br />

The vector k encompasses a volume of 4/3 πk 3 . As a result, with reference<br />

to (Fig. 6.3), the volume between the two shells which are infinitely<br />

close to each other, at a distance of k from the centre is found to be:<br />

⎛ 4 3 ⎞ 2<br />

d⎜<br />

π k ⎟ = 4πk<br />

dk . (6.12)<br />

⎝ 3 ⎠<br />

ky<br />

Chapter 6: Inorganic <strong>Nanotechnology</strong> <strong>Enabled</strong> <strong>Sensors</strong><br />

kz<br />

Fig. 6.3 The k-space (reciprocal space) in 3D. Calculation of the NOS for a<br />

wavenumber between k and k+dk.<br />

By dividing this volume by the volume of a single energy state (Eq.<br />

(6.11)), the density of states, D(k), in reciprocal space can be obtained as:<br />

2 2 3<br />

4πk<br />

dk k L dk<br />

D(<br />

k)<br />

dk = 2 × = . (6.13)<br />

2<br />

V π<br />

3D<br />

k<br />

dk<br />

kx

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