Tuesday 1 January 2013

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This perspective presents and assesses the development and capabilities of tip-enhanced Raman scattering (TERS) since its discovery in 2000. So far, this technique has proven to be valuable for studies of a variety of inorganic, organic and biochemical specimens. Due to its ability to provide chemical and topographic characterization in a single experiment at a sub-100 nm resolution, TERS has gained importance in super-resolution structural analysis. In this contribution the focus is set on applications with relevance in the biology and medical fields. The potential and challenges of this near-field technique are discussed with respect to state-of-the-art microscopic and spectroscopic imaging methods. Furthermore, possible ways to surpass current boundaries and an outlook to future projects are presented.
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 Abstract— Previous attempts have been devoted to mimic
biological vision intelligence at the architectural system level. In
this paper, a novel imitation of biological visual system
intelligence is suggested, at the device level with the introduction
of  novel photodiode morphology. The proposed bio-inspired
nanorod photodiode puts the depletion region length on the path
of the incident photon instead of on its width, as the case is with
the planar photodiodes. The depletion region has a  revolving
volume to increase the  photodiode responsivity, and thus its
photosensitivity. In addition, it can virtually boost the pixel fill
factor (FF) above the 100% classical limit due to decoupling of
its vertical sensing area from its limited planar circuitry area.
Furthermore, the suggested nanorod photodiode
photosensitivity is analytically proven to be higher than that of
the planar photodiode. We also show semi-empirically that the
responsivity of the suggested device varies linearly with its
height; this important feature has been confirmed using
Sentaurus simulation. The proposed nano-photorod is believed
to meet the increasingly stringent High-Resolution-Low-Light
(HRLL) detection requirements of the camera-phone and
biomedical imaging markets.
Electronic imaging technologies have tremendously
progressed in the last three decades for the maturing CoupledCharge Devices (CCD) technology and in the last two decades
for the emerging  Complementary-Metal-OxideSemiconductor Active  Pixel  Sensor imaging (CMOS-APS)
technology [1]-[4]. Enhancing the resolution of CMOS image
sensors  is always an important factor of this imaging
technology evolution [4]. However, the progress is likely to
face a great obstacle for CMOS APS as the Signal-to-Noise
Ratio (SNR) and Dynamic Range (DR) go inversely with the
pixel pitch [4]. These constraints are, however, not faced in
CCD’s due to minimal dielectric stack layers over the pixels
and the larger full well capacity of the CCD’s MOS structure.
These technological constraints have led to hybridizing CCD’s
image sensing elements with CMOS low power, mixed signal
processing and faster readout to achieve sub-micron pixelresolution  [5]. However, combining CCD within  CMOS
technology does not import the former high charge transfer,
lower dark current and surface traps into the latter single
polysilicon limitation and surface traps [6].
At the technological level, CMOS imaging is based on the
vertical PN junction adopted from the planar standard CMOS
technology.  The small depletion region and its short
intersection with incident photons,  which limits the photosignal, inhibit smaller photodiode design and higher resolution
CMOS imagers. The  matter becomes worse in low light
conditions where fewer photons impinge on  the active area.
To tackle  these device constraints, photo-generation of
charges has to take place in a 3D surface area instead of the
current 2D planar photodiodes. In fact, biological smart visual
systems use non-planar photocells of conic and cylindrical
morphologies  [7] to  maximize vision resolution without
compromising low light vision. Figure 1 shows the anatomy of
a human retina and its cross section. Biological photocells
sense the light along their elongations; this enhances their light
sensitivity and relaxes their footprint area constraints.
Free High Resolution Images
Free High Resolution Images
Free High Resolution Images
Free High Resolution Images
Free High Resolution Images
Free High Resolution Images
Free High Resolution Images
Free High Resolution Images
Free High Resolution Images
Free High Resolution Images
Free High Resolution Images

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