MOS2:A NEW MATERIAL

FOR biosensor

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.

THANK YOU!

FATEMEH KARIMI