bio sensoring
Post on 07-Feb-2017
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CONTENTS:- WHAT IS MOS2?
WHY MOS2?
PROPERTIES OF MOS2
ENERGY BAND STRUCTURE
ENERGY BAND ENGINEERING
CARRIER MOBILITY
PREPARATION TECHNIQUES
FUNCTIONALIZATION
BIOSENSORING
CONCLUSIONS AND OUTLOOK
INTRODUCTION:-SINCE THE INVENTION OF THE FIRST TRANSISTOR, SILICON HAS BEEN
AT THE HEART OF ELECTRONICS BUT AS THE DEMANDS INCREASES ,
WE ARE ASKING WAY TOO MUCH OUT OF SILICON THUS FOR ALL ITS
DRAWBACKS SCIENTISTS BEGAN SEARCHING FOR FUTURISTIC
ELEMENTS THAT CAN REPLACE AND EVEN OUTPERFORM SILICON.
THIS SEARCH LED US TO MOS2- SINGLE LAYER AND FEW
MONOLAYER THICK 2-DIMENSIONAL SEMICONDUCTOR.
ITS UNIQUE PHYSICAL PROPERTIES OUTPERFORMS SILICON AND ITS
CLOSEST COMPETITOR GRAPHENE.
WHAT IS MOS2?MOS2 IS CLASSIFIED AS A METAL DICHALCOGENIDE. IT IS A SILVERY
BLACK SOLID THAT OCCURS AS THE MINERAL MOLYBDENITE, THE
PRINCIPAL ORE FOR MOLYBDENUM.
IN APPEARANCE AND FEEL, MOLYBDENUM DISULPHIDE IS SIMILAR TO
GRAPHITE.
WHY MoS2?EXCELLENT GATE CONTROL
SATURATION
SCALABILITY
HIGH CURRENT CAPABILITY
VERY LOW NOISE
WIDE DIRECT BAND GAP
IT EXHIBITS GOOD ELECTRICAL AND TRANSPORT PROPERTIES
CHEMICALLY AND THERMALLY STABLE
TRANSPARENT AND flEXIBLE
RELATIVELY INEXPENSIVE
These properties include large surface area, tunable energy band
diagrams, a comparatively high electron mobility,
photoluminescence, liquid media stability, relatively low toxicity
make it of great interest for developing biosensors .
PROPERTIES OF MoS2
ATOMIC STRUCTURE:-
MOS2 BELONGS TO THE GROUP OF TMDS WITH THE COMMON
FORMULA MX2, WHEREIN M REPRESENTS A TRANSITION METAL.
WITHIN A SINGLE X-M-X LAYER, THE M AND X ATOMS FORM A 2D HEXAGONAL SUB-LATTICE
FIG.1 ARRANGEMENT OF MOS2 ATOMS
MECHANICAL PROPERTIES:-
THE YOUNG’S MODULUS OF MOS2 CAN BE ENHANCED BY A
FACTOR OF FIVE BY SANDWICHING IT BETWEEN TWO GRAPHEME
LAYERS.
MOS2 SANDWICHED BETWEEN GRAPHENE LAYERS
MECHANICAL PROPERTIES:-MOS2 ALSO HAS THE ADVANTAGE THAT IT IS AS STIFF AS STAINLESS STEEL
BUT IS ALSO CAPABLE OF BEING FLEXIBLE.
IT CAN BE BENT TO LARGE ANGLES AND CAN BE STRETCHED UPTO 10%
OF ITS LENGTH.
IT HAS A KEY ADVANTAGE OVER GRAPHENE- IT CAN AMPLIFY
ELECTRONIC SIGNALS AT ROOM TEMPERATURE, WHILE GRAPHENE MUST
BE COOLED TO 70 KELVIN- COLD ENOUGH FOR NITROGEN TO TURN INTO
LIQUID.
ENERGY BAND STRUCTURE:- ALONG WITH THE OTHER GROUP-VI LAYERED COMPOUNDS, MOS2
EXHIBITS SEMICONDUCTING BEHAVIOR.
THE ELECTRONIC ENERGY STATES OF 2D MOS2 CAN BE ADJUSTED
RANGING FROM SEMICONDUCTING, IN ITS INTRINSIC STATE, TO FULLY
CONDUCTING WHEN IT IS TRANSFORMED INTO THE 1T MOS2 PHASE (WITH OCTAHEDRAL UNIT CELLS , MAKING THIS MATERIAL SUITABLE FOR MANY
BIOSENSING CONDITIONS. IN PARTICULAR, LAYERED 2D MOS2 IS
COMPATIBLE WITH STANDARD ELECTROCHEMICAL SYSTEMS, WHICH ARE
COMMONLY USED AS THE WORKING ELECTRODES OF BIOSENSORS. IN
CONTRAST, MANY OF THE OTHER 2D MATERIALS DO NOT OFFER SUCH
CONCOMITANT ELECTRONIC AND CHEMICAL PROPERTIES.
DFT-GGA CALCULATED BAND STRUCTURES FOR (A) BULK MOS2, (B) 4-LAYER MOS2, (C) BI-LAYER MOS2, AND (D)MONOLAYER MOS2 . THE SOLID ARROWS INDICATE THE LOWEST
ENERGY TRANSITIONS.
Band gap engineering:-
MECHANICAL STRAIN:-
MECHANICAL STRAIN CAN STRONGLY AFFECT THE BAND STRUCTURE, CARRIER EFFECTIVE MASSES, AND TRANSPORT, OPTICAL,
AND MAGNETIC PROPERTIES OF MOS2 VIA CHANGING THE DISTANCE
BETWEEN THE ATOMS AND ALSO THE CRYSTAL SYMMETRY.
LARGER STRAIN CAN BE APPLIED TO LOW-DIMENSIONAL MOS2 DUE
TO ITS MECHANICAL flEXIBILITY, AND ITS PROPERTIES CAN BE TUNED BY
APPLIED STRAIN, WHICH OPENS POSSIBILITIES FOR DEVELOPING NEW
TUNABLE ELECTRONIC DEVICES.
THE ENERGY BAND GAP GRADUALLY DECREASES WITH INCREASING
TENSILE STRAIN, WHEREAS IT INITIALLY RISES AND THEN DECREASES
LINEARLY UNDER APPLIED COMPRESSIVE STRAIN.
A) TOP AND SIDE VIEWS OF MOS2 MONOLAYER LATTICE. B) CALCULATED BAND GAP OF MONOLAYER MOS2 VERSUS ISOTROPIC STRAIN. C) – G) ELECTRONIC BAND STRUCTURE OF MOS2 MONOLAYER UNDER ISOTROPIC COMPRESSIVE STRAIN OF C) –8% AND D) –2%,
E) UNSTRAINED MOS2 MONOLAYER, AND UNDER ISOTROPIC TENSILE STRAIN OF F) 2% AND G) 8%. THE RED DASHED LINE DENOTES THE FERMI LEVEL.
CARRIER MOBILITY:-
THE HOLE MOBILITY (96.62 CM2 V−1 S−1) IN MONOLAYER
SHEETS OF MOS2 IS ABOUT TWICE THAT OF THE ELECTRON
MOBILITY (43.96 CM2 V−1 S−1).
THE HIGHEST MOBILITY VALUE OF 700 CM2 V−1 S−1 WAS
REPORTED FOR A BACK-GATED FET BASED ON 10-NM-THICK
MULTILAYER MOS2 flAKE.
Preparation techniquesMethods for synthesizing 2D MoS2 compromise a wide range,
including those that exfoliate thin layers from bulk 2H MoS2 or
others that vapor/liquid phase deposit the single layers of MoS2
directly on a substrate.
[1]. MECHANICAL EXFOLIATION
TECHNIQUE:-
Single and multilayer MoS2 films are deposited
onto Si/SiO2 using the mechanical exfoliation technique.
The films were then used for the fabrication of
field-effect transistors.
These FET devices can be used as gas sensors to detect nitrous oxide (NO).
[2].SELECTIVE SOLUTION METHOD:-
SELECTIVE SOLUTION METHOD TO PREPARE MOLYBDENUM DISULFIDE (MOS2) THIN FILMS FOR FUNCTIONAL THIN FILM TRANSISTORS (TFTS).
THE SELECTIVE AREA SOLUTION-PROCESSED MOS2GROWS ON TOP AND AROUND THE GOLD (AU) SOURCE AND DRAIN ELECTRODES AND IN THE CHANNEL AREA OF THE TFT. MOS2 THICKNESSES IN THE CHANNEL AREA ARE IN THE ORDER OF 11 NM
[3].Chemical vapor deposition method:-
RECENT SUCCESS IN THE GROWTH OF MONOLAYER MOS2 VIA
CHEMICAL VAPOR DEPOSITION (CVD) HAS OPENED UP
PROSPECTS FOR THE IMPLEMENTATION OF THESE MATERIALS
INTO THIN FILM ELECTRONIC AND OPTOELECTRONIC DEVICES.
A SCHEMATIC OF THE CVD PROCESS FOR GROWING SINGLE-
LAYER MOS2
Device
applications:-MOS2 HAS A WIDE RANGE OF APPLICATIONS.
THIS MATERIAL IS HIGHLY ANISOTROPIC WITH
EXCELLENT NONLINEAR OPTICAL PROPERTIES AND
ALSO IS A VERY GOOD LUBRICANT.
THE LAYERED MATERIAL HELPS THE MEMBRANES
TO HAVE MECHANICAL STRENGTHS SOME 30 TIMES
HIGHER THAN THAT OF STEEL.
IT HAS STABILITY AT UP TO 1100 ◦C IN AN INERT
ATMOSPHERE.
TWO-DIMENSIONAL MOS2 MAY BE USED IN SENSORS AND
MEMORY AND PHOTOVOLTAIC DEVICES. DIRECT BAND GAP AND CONfiNEMENT EffECTS IN SINGLE-LAYER MOS2 MAKES THIS MATERIAL
ATTRACTIVE FOR OPTOELECTRONICS.
MOLYBDENITE (MOS2) HAS A NUMBER OF BENEFITS OVER SILICON
(SI) WHEN IT COMES TO CREATING A MICRO CHIP. FUTURE CHIPS USING MOS2 WILL BE SMALLER THAN SILICON CHIPS. REDUCED
ELECTRICITY CONSUMPTION IS ANOTHER BENEFIT, ALONG WITH
MECHANICAL FLEXIBILITY.
The obtained rMoS 2 can be used for glucosedetection. In addition, it can selectively detect
opamine in the presence of ascorbic acid and
uric acid. This novel material, rMoS 2 , is
Delieved to be a good electrode material for
ectrochemical sensing applications.
FUNCTIONALIZATION
For the development of biosensors, after the synthesis of 2D
MoS2, these thin sheets should be functionalized to respond
to specific bio targets. It has been suggested that basal planes of MoS2 can be functionalized using silane and thiol
based methods, which are commonly applied for modifying
oxide and chalcogenides surfaces. Many other methods such
as in situ reduction of metal ions,esterfication, ring-opening
polymerization, and free radical polymerization can also be
used.
BIOSENSORS
Current biosensors based on 2DMoS2 can be categorized intoseveral types including:
electrode based devices
electrodeless optical systems
reverse electroluminescent systems
Conclusions and outlook
TWO-DIMENSIONAL MATERIALS, PARTICULARLY THE TMD MONO
LAYERS, ARE EMERGING AS A NEW CLASS OF MATERIALS.
AMONG THEM, SEMICONDUCTING MOS2 IS GAINING INCREASING ATTENTION OWING TO AN ATTRACTIVE COMBINATION OF PHYSICAL
PROPERTIES, WHICH INCLUDE BAND GAP TUNABILITY AND
REASONABLY HIGH ELECTRON MOBILITY.
ON THE EXPERIMENTAL FRONT, RESEARCHERS HAVE FOCUSED ON S
PRACTICAL APPLICATIONS OF 2D MOS2, IN PARTICULAR THE
DEVELOPMENT OF fiELD-EffECT TRANSISTORS,AND NEGLIGIBLE OFF CURRENT.
ULTRASENSITIVE PHOTOTRANSISTORS, LOGIC CIRCUITS, AND
AMPLIfiERS BASED ON MONOLAYER MOS2 HAVE ALSO BEEN
DEMONSTRATED, WITH GOOD OUTPUT CURRENT SATURATION AND
HIGH CURRENTS.
THE flEXIBILITY, STRETCHABILITY, AND OPTICAL TRANSPARENCY OF MONOLAYER MOS2 MAKE IT PARTICULARLY ATTRACTIVE FOR
TRANSPARENT AND flEXIBLE ELECTRONICS.
SINCE THE PROPERTIES OF MOS2 DEPEND STRONGLY ON THE
NUMBER OF MONOLAYERS, TECHNIQUES PROVIDING CONTROL
OVER THE NUMBER OF DEPOSITED MONOLAYERS ARE HIGHLY
DESIRABLE.
FOR USE IN flEXIBLE ELECTRONICS, THE MAJOR CHALLENGE IS TO
fiND APPROACHES THAT WOULD PRODUCE ELECTRONIC-QUALITY
MATERIAL AT DEPOSITION TEMPERATURES BELOW 400 ◦C
NECESSITATED BY THE NEED FOR GROWTH DIRECTLY ON
TRANSPARENT PLASTIC SUBSTRATES.
DEVELOPMENT OF 2D MOS2-BASED DEVICES, IN PARTICULAR FETS,
FOR REAL APPLICATIONS ALSO REQUIRES FURTHER STUDIES OF
ELECTRODE AND GATE DIELECTRIC MATERIALS.
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