19-07-2011, 02:12 PM
NANO SENSORS.ppt (Size: 3.18 MB / Downloads: 118)
INTRODUCTION
LIMITATIONS OF CNTs AND SINWs :
DISADVANTAGES IN EXISTING FABRICATION METHODS
IMPROPER SURFACE MODIFICATION METHODS
INTRINSIC DRAWBACKS OF SILICON NANOWIRES
TEDIOUS AND EXPENSIVE POSTGROWTH ASSEMBLY PROCESS
COMPARISION OF STATE-OF-THE ART NANO SENSOR MATERIALS
Cyclic Voltamamogram of Pd electrodeposition
Fig shows a cyclic voltammogram of Pd p-salt plating solution using a two electrode configuration.
The reduction peak of Pd ions to Pd is observed at –1.7 V. When a more negative potential than –1.7 V is applied to the electrode, a significant increase in the current density is observed which is due to H2 gas evolution.
A computer controlled potentiostat/galvanostat is used to grow Pd wires in galvanostatic mode.
The applied currents are –10 nA, -20 nA, –100 nA, and –1000 nA and corresponding potentials are monitored.
Electrode arrays with e-beam patterned electrolyte channels
(a)1 um width and 3 um length wires (2 electrodes)
(b) 1um width and 3 um length (3 electrodes)
© 500 nm width and 3 um length (2 electrodes)
(d) 500 nm width and 3 um length (3 electrodes).
Measured electrical properties during deposition
(a) Cathode potential responses as a function of deposition time deposition potential versus deposition time
(b) Resistance change between anode and cathode as a function of time: Deposition current was kept at –1000 nA
OPTICAL IMAGES OF ELECTRODEPOSITED Pd WIRES GROWN BETWEEN ELECTRODES
Fig (a) Single wire
Fig (b) Double wires
BIOCHEMICAL SENSORS
OPERATING PRINCIPLE :
DETECTION OF LOW MOLECULAR CONCENTRATIONS BY MEASURING CHANGES IN THE ELECTRICAL CONDUCTANCE OF NANO WIRES
TYPES :
AMPEROMETRIC BIOSENSORS :
ELECTRONICALLY COUPLING APPROPRIATE REDOX ENZYMES TO A METAL ELECTRODE
CONDUCTOMETRIC BIOSENSORS :
ENTRAPPING THE RELEVANT ENZYMES IN CONJUGATED POLYMER NANOWIRES (Eg : POLYANILINE) ON AN ELECTRODE
GLUCOSE SENSOR :
BUNDLED Pt NANOWIRES HAVE A HIGH ROUGHNESS FACTOR i.e.,iT HAS A HIGH EFFECTIVE SURFACE AREA
GAS SENSORS
BASIC PRINCIPLE :
DETECTION OF SMALL CONCENTRATIONS BY MEASURING CHANGES IN ELECTRICAL CONDUCTANCE IN NANOWIRES
PROPERTIES :
FAST RESPONSE
HIGHER SENSITIVITY
MORE SELECTIVITY
Pd NANOWIRES :
LOW RESISTANCE AND HIGH SENSITIVITY TO HYDROGEN
FAST RESPONSE TIME (<75ms)
LOW POWER (<100nw)
RESISTANT TO POISONOUS REACTIVE GASES LIKE O2,CO
Ph SENSORS
WIDELY USED SOLID-STATE METAL OXIDES – Sb2O3 SENSORS
FAST RESPONSE TIME
DRIFT FREE BEHAVIOUR
GOOD STABILITY IN HIGHLY ACIDIC AND ALKALINE ENVIRONMENTS
ADVANTAGES
Electrodeposition allows a high degree of specificity in location and chemical identity of a deposit, as well as control of thickness.
It avoids post growth assembly process which is very tedious.
Multiple species can be simultaneously detected.
Power consumption in nano watts.
High sensitivity and high speed
CONCLUSION
CAPABILITY OF PRODUCING ARRAYS OF INDIVIDUALLY ADDRESSABLE NANOWIRE SENSORS WITH CONTROLLED DIMENSIONS, POSITIONS, ALIGNMENTS AND CHEMICAL COMPOSITIONS
REDUCTION IN WIDTH OF E-BEAM PATTERNED CHANNELS
CAPABILITY OF DETECTING MULTIPLE CHEMICAL SPECIES
POSSIBILITY OF LARGE SCALE ARRAYS