Electronic and Optical Properties of Sillicon and Titanium Nanowires

8/13/2019 Electronic and Optical Properties of Sillicon and Titanium Nanowires

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lectronic and optical properties ofSillicon and titanium Nanowires

Ab- intio study

Project Report

By

FlorinaRegius

SRM UNIVERSITY

Under the guidance of

Dr.AnuragSrivastav

Computational Nano Science and Technology Lab CNTL

ABV- Indian Institue of Information Technology and Management , Gwalior


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Acknowledgement

I would like to take this opportunity to express my sincere thanks

to Dr.AnuragSrivastav for his valuable guidance and support

through out my project. I have been benefitted a lot from his

erudite Academic levels and conscientious Research Institute.

I would like to extend my gratitude to Sumit Jain for his dynamic

guidance , sharing valuable experiences , discussions , opinions and

also giving valuable reviews to my project and study.

I additionaly thank Mr.Vikas for all his help . I am also grateful to

my parents . Without their support and encouragement , I would

have not able to come so far. I also acknowledge the ABV Indian

Institue of Information Technology and Management , Gwalior for

the Infrastructural support provided to the project work .

FlorinaRegius

Date:


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Declaration

I hereby declare that the work which is being

presented in this report entitled Electronic and

optical properties of Sillicon and titanium

Nanowires : Ab initio study is an authentic

record of my own work carried out under the

guidance of Dr.AnuragSrivastava , ComputationalNano Science and technology Lab (CNTL) ,ABV-

IIITM, Gwalior.

I further declare that the matter embodied in this

report has not been submitted by me as a whole

or in part at any other Institution /University.

FlorinaRegius

(Btech 4 semnanotech)

Registration Number = 1231210022

SRM university


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Certificate

This is to certify that Miss. FlorinaRegius , a student of Btech (Nanotech ) from

SRM UNIVERSITY , Chennai , Registration Number 1231210022 has successfully

completed her winter training /project on the topic Electronic and Optical

properties of Sillicon and titanium nanowire : Ab initio study under the

guidance of my supervision from 1/12/13 to 25/12/13 . During her stay , I

personally found her very sincere , dedicated and always keen to learn newer

things , this qualities may lead to build her career as a great researcher.

The declaration made by Miss. FlorinaRegius in her report is correct to the best

of my knowledge and the report is bonafide work done by her at the

Computational Nano Science and Technology lab (CNTL) , ABVIndian Institue

Of Information Technology and Management , Gwalior .

I wish her success in all her endeavours.

Dr.AnuragSrivastava

Computational Nanosicence and technology Lab (CNTL)

ABV- Indian Institute of Information Technology and Management

Gwalior - 474010

ATAL BIHARI VAJPAYEEIndian

Institue of Information

Technology and Management ,

Gwalior


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Introduction

Sillicon Nanowire

Silicon nanowires can enhance broadband optical absorption and reduce radial

carrier collection distances in solar cell devices. Arrays of disordered nanowiresgrown by vapor-liquid-solid method are attractive because they can be grown

on low-cost substrates such as glass, and are large area compatible. Here, we

experimentally demonstrate that an array of disordered silicon nanowires

surrounded by a thin transparent conductive oxide has both low diffuse and

specular reflection with total values as low as < 4% over a broad wavelength

range of 400 nm < < 650nm. These anti-reflective properties together with

enhanced infrared absorption in the core-shell nanowire facilitates enhancement

in external quantum efficiency using two different active shell materials:amorphous silicon and nanocrystalline silicon. As a result, the core-shell

nanowire device exhibits a short-circuit current enhancement of 15% with an

amorphous Si shell and 26% with a nanocrystalline Si shell compared to their

corresponding planar devices.

Titanium Nanowire

The structures of free-standing titanium nanowires are studied by using a

genetic algorithm with a tight-binding potential. Helical multi-walledcylindrical structures are obtained and pentagonal packing is found for these

thin wires with diameters from 0.747 to 1.773 nm. The angular correlation

functions and vibrational properties of nanowires are discussed. We have

further calculated the electronic structures of the titanium nanowires with the

plane-wave pseudopotential method. Bulk-like continuous electronic bands are

found in the Ti wires thicker than 1 nm. The vibrational and electronic

properties of titanium nanowire are significantly dependent on the multi-walled

structure of the nanowire.

The thermal stability and melting behavior of ultrathin titanium nanowires with

multi-shell cylindrical structures are studied using molecular dynamic

simulation. The melting temperatures of titanium nanowires show remarkable

dependence on wire sizes and structures. For the nanowire thinner than 1.2 nm,

there is no clear characteristic of first-order phase transition during the melting,

implying a coexistence of solid and liquid phases due to finite size effect. An

interesting structural transformation from helical multi-shell cylindrical


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Literature Survey

1.1: Sillicon Nanowire

It is well-known that one-dimensional nanostructures reduce pulverization of

silicon (Si)-based anode materials during Li ion cycling because they allow

lateral relaxation. However, even with improved designs, Si nanowire-based

structures still exhibit limited cycling stability for extended numbers of cycles,

with the specific capacity retention with cycling not showing significant

improvements over commercial carbon-based anode materials. We have found

that one important reason for the lack of long cycling stability can be the

presence of milli- and microscale Si islands which typically form under

nanowire arrays during their growth. Stress buildup in these Si island

underlayers with cycling results in cracking, and the loss of specific capacity forSi nanowire anodes, due to progressive loss of contact with current collectors.

We show that the formation of these parasitic Si islands for Si nanowires grown

directly on metal current collectors can be avoided by growth through anodized

aluminum oxide templates containing a high density of sub-100 nm nanopores.

Using this template approach we demonstrate significantly enhanced cycling

stability

Sinanowire-based lithium-ion battery anodes, with retentions of more than

1000 mAh/g discharge capacity over 1100 cycles.

Silicon nanowires can enhance broadband optical absorption and reduce radial

carrier collection distances in solar cell devices. Arrays of disordered nanowires

grown by vapor-liquid-solid method are attractive because they can be grown

on low-cost substrates such as glass, and are large area compatible. Here, we

experimentally demonstrate that an array of disordered silicon nanowires

surrounded by a thin transparent conductive oxide has both low diffuse andspecular reflection with total values as low as < 4% over a broad wavelength

range of 400 nm < < 650nm. These anti-reflective properties together with

enhanced infrared absorption in the core-shell nanowire facilitates enhancement

in external quantum efficiency using two different active shell materials:

amorphous silicon and nanocrystalline silicon. As a result, the core-shell

nanowire device exhibits a short-circuit current enhancement of 15% with an

amorphous Si shell and 26% with a nanocrystalline Si shell compared to their

corresponding planar devices.


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The fiftieth anniversary of silicon-wire research was recently commemorated, agood occasion to take a look back and attempt to review and discuss some ofthe essential aspects of silicon-wire growth, of the growth thermodynamics, andof the electrical properties of silicon nanowires. The statement of a fiftieth

anniversary refers to the publication of Treuting and Arnold of 1957,[1] which,to the best of our knowledge, represents the first publication on Si wire growth.Therein, the authors report on the successful synthesis of silicon whiskers withh111i orientation. At these times, the term whisker was most commonly used inreference to grown filamentary silicon crystals, often times still havingmacroscopic dimensions (see, e.g., the impressively large wires shown in[2]). Inaddition to the terms whisker or wire, nanorod is also sometimesused.[3,4]Throughout this work, the traditional name whisker will not be used,even when referring to the works of old times. Instead, we will use the termsilicon wire for filamentary crystals of diameters larger than about hundrednanometers. The term nanowire will be employed in reference to wires ofdiameters smaller than about hundred nanometers. When general aspects notrestricted to a certain size range are discussed, we will use the more generalterm wire. We will try to stick to thisconvention, albeit not with uttermost strictness. Going back to the 1960s, onlyseven years after the work of Treuting and Arnold was published[1] didresearch on silicon wires start to really gain momentum, a process clearlycatalyzed by the pioneering work of Wagner and Ellis.[5] In this paper, theyclaimed their famous vaporliquidsolid (VLS) mechanism of single-crystal

growth, which set the basis for a new research field and which until todayrepresents the mostcommon way to synthesize silicon wires. As shown inFigure 1, research on silicon wires basically started with the publication ofWagner and Ellis, flourished for about 10 years, and then ebbed away.

Nevertheless, this time was sufficientfor the discovery of many of the fundamental aspects of VLS silicon-wiregrowth.[6]The second phase in silicon-wire research started in the mid1990s,when advances in microelectronics triggered a renewedinterest in siliconnownanowireresearch. Morales and Lieber[7] managed to synthesize nanowires

of truly nanoscopicdimensions and introduced laser ablation as a new methodforand its implications for the silicon-nanowire growth velocity. Last,we will turn our attention to the electrical properties of silicon nanowires anddiscuss the different doping methods. Then, three effects essential for theconductivity of a silicon nanowire are treated. These are the diameterdependence of the dopantionization efficiency, the influence of surface traps on the charge-carrierdensity, also causing a diameter dependence, andthe charge-carrier mobility in silicon nanowires.


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1.2 Titaniun Nanowire

The structures of free-standing titanium nanowires are studied by using a

genetic algorithm with a tight-binding potential. Helical multi-walled

cylindrical structures are obtained and pentagonal packing is found for thesethin wires with diameters from 0.747 to 1.773 nm. The angular correlation





properties of titanium nanowire are significantly dependent on the multi-walled

structure of the nanowire

One-dimensional single crystal nanostructures have garnered much attention,from their low-dimensional physics to their technological uses, due to their

unique properties and potential applications, from sensors to interconnects.

There is an increasing interest in metallic titanium nanowires, yet their single

crystal form has not been actualized. Vaporliquidsolid (VLS) and template-

assisted top-down methods are common means for nanowire synthesis;

however, each has limitations with respect to nanowire composition and

crystallinity. Here we show a simple electrochemical method to generate single

crystal titanium nanowires on monocrystallineNiTi substrates. This work is asignificant advance in addressing the challenge of growing single crystal

titanium nanowires, which had been precluded by titanium's reactivity.

Nanowires grew non-parallel to the surface and in a periodic arrangement along

specific substrate directions; this behavior is attributed to a defect-driven

mechanism. This synthesis technique ushers in new and rapid routes for single

crystal metallic nanostructures, which have considerable implications for

nanoscale electronics.A fluorescent erbium/ytterbium co-doped fluoride

nanocrystal glued at the end of a sharp atomic force microscope tungsten tipwas used as a nanoscale thermometer. The thermally induced fluorescence

quenching enabled observation of the heating and measurement of the

temperature distribution in a Joule-heated 80 nm wide and 2 m long titanium

nanowire fabricated on an oxidized silicon substrate. The measurements have

been carried out in an alternating heating mode by applying a modulated current

on the device at low frequency. The heating is found to be inhomogeneous

along the wire, and the temperature in its center increases quadratically with the

applied current. Heat appears to be confined mainly along the wire, with weak


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lateral diffusion along the substrate and in the lateral metallic pads. The lateral

resolution of this thermal measurement technique is better than 250 nm. It could

also be used to study thermally induced defects in nanodevices.

The structures of free-standing titanium nanowires are studied by using agenetic algorithm with a tight-binding potential. Helical multi-walled

cylindrical structures are obtained and pentagonal packing is found for these

thin wires with diameters from 0.747 to 1.773 nm. The angular correlation





properties of titanium nanowire are significantly dependent on the multi-walledstructure of the nanowire.

The thermal stability and melting behavior of ultrathin titanium nanowires with

multi-shell cylindrical structures are studied using molecular dynamic

simulation. The melting temperatures of titanium nanowires show remarkable

dependence on wire sizes and structures. For the nanowire thinner than 1.2 nm,

there is no clear characteristic of first-order phase transition during the melting,

implying a coexistence of solid and liquid phases due to finite size effect. An

interesting structural transformation from helical multi-shell cylindrical to bulk-like rectangular is observed in the melting process of a thicker hexagonal

nanowire with 1.7 nm diameter.


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Computational Method

The purpose of this tutorial is to show how to set up and perform calculations for a devicebased on a silicon nanowire. You will define the structure of a H-passivated silicon nanowirealong the (100) direction, and set up a field-effect transistor (FET) structure with a cylindricalwrap-around gate.

Note

We will primarily use the graphical user interface Virtual NanoLab (VNL) for setting upand analyzing the results. To familiarize yourself with VNL, it is recommended to gothrough theVNL Tutorial.

The underlying calculation engines for this tutorial are ATK-DFTand ATK-SE. A

complete description of all the parameters, and in many cases a longer discussion abouttheir physical relevance, can be found in theATK Reference Manual.

In order to run this tutorial, you must have a license for both ATK-SE and ATK-DFT. Ifyou do not have one, you may obtain a time-limited demo license by contactingQuantumWise viaour website.

Setting up the Si (100) nanowire geometry

Start VNL and create a new project and give it a name then click Open. Next launch the

Builder via the icon on the toolbar.

In the builder, click Add From Database.... Type silicon fcc in the search field to

locate the diamond phase of silicon. Click the icon in the lower right-hand corner of theDatabase window to add the structure to the Stash in the Builder.

Next unfold the Builders panel bar in the right-hand column of the Builder and open theSurface (Cleave)... tool.

In the surface cleave tool,

Keep the default (100) cleave direction, and press Next >.

Keep the default surface lattice, and press Next >.

Keep the default supercell, this will ensure that the wire direction is perpendicular tothe surface, and press Next >.

Press the Finish button to add the cleaved structure to the Stash.
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Next open Bulk Tools Repeatand enter A=2, B=2, C=1, and press Apply.

Press Ctrl+R to reset the view in the Builder.

To finalize the setup perform the following steps:

Open Bulk Tools Lattice Parametersand set the length of the A and Bvectors to 20 .

Open Coordinate Tools Centerand center the structure in all directions.

Click the H-passivator in the left-hand tool bar to passivate the structure.

Defining and running the calculation

In the following you will relax the geometry using DFT-GGA, and calculate the bandstructure of the nanowire with 3 different models, DFT-GGA, DFT-MetaGGA, and theExtended Hckel model.

Note

The Meta-GGA and the Extended Hckel models cannot be used for relaxation.

For this purpose:

Add a New Calculator. Add Optimization/OptimizeGeometry Add Analysis/Bandstructure. Add a New Calculator. Add Analysis/Bandstructure. Add a New Calculator. Add Analysis/Bandstructure. Set the output file to si_100_nanowire.nc

You should now have the following setting.

Open the first New Calculatorblock, and make the following settings:

Set the k-point sampling to: 1, 1, 11. Change the exchange-correlation potential to GGA.

Open the second New Calculatorblock, and make the following settings:

Set the k-point sampling to: 1, 1, 11. Change the exchange-correlation potential to MGGA.

Open the last New Calculatorblock, and make the following settings:

Select the "ATK-SE: Extended Hckel" calculator.


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Uncheck No SCF iteration to make the calculation selfconsistent.

Set the k-point sampling to: 1, 1, 11. Increase the Density mesh cut-off to 20 Hartree.

Electronic structure and optical properties of silicon

Table of Contents

Setting up the calculation Running and analyzing the calculation

o DOS of silicono Optical spectrum

Setting up the calculation

Start VNL, create a new project and give it a name, then select it and click Open. Launch the

Builder by pressing the icon on the toolbar.

In the builder, click Add From Database.... Type silicon in the search field, andselect the silicon standard phase in the list of matches. Information about the lattice, includingits symmetries (e.g. that the selected crystal is face centered cubic), can be seen in the lower

panel.

Double-click the line to add the structure to the Stash, or click the icon in the lower right-hand corner.

Now send the structure to the Script Generatorby clicking the "Send To" icon in thelower right-hand corner of the window, and select Script Generator(the defaultchoice, highlighted in bold) from the pop-up menu.

In the Script Generator,

Add a New Calculator.

Add a Analysis>Bandstructure.

Add a Analysis>DensityOfStates.

Add a Analysis>OpticalSpectrum.

Change the output filename to si.nc

The next step is to adjust the parameters of each block.

Open the New Calculator block by double-clicking it, and

select the ATK-DFT calculator (selected by default), set the k-points to (4,4,4), select the exchange-correlation functional to MGGA, and finally under "Basis set/exchange correlation", select the

DoubleZetaDoublePolarizedbasis set for Si.
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Results and discussions

Si Nanowire

Band Structure Analysis

By noticing the graphs , we can see that when sillicon is not doped by any

Aluminium atoms , then we can clearly observe the that there are no lines

which are crossing the fermilevel . The first curve is at 0.13 above the fermi

level and the lowest curve is at -0.3 below the fermi level. We can observe

the small gap which clearly shows it is semi conductor from fig. a .In fig.b ,

we can see that when sillicon is doped by two Aluminium atoms , then we

can clearly observe the that there is one line which is crossing the fermi

level . The first curve is at 0.03 above the fermi level and the lowest curve is

at -0.01 below the fermi level. We can observe the crossing of line which

clearly shows it is doped.Infig.c , we can see that when sillicon is doped by

four Aluminium atoms , then we can clearly observe the that there is two

line which is crossing the fermi level . The first curve is at 0.02 above the

fermi level and the lowest curve is at -0.06 below the fermi level. We can

observe the crossing of line which clearly shows it is doped. In fig.d, we can

see that when silliconis doped by six Aluminium atoms , then we can clearly

observe the that there is four line which is crossing the fermi level . The first

curve is at 0.01 above the fermi level and the lowest curve is at -0.07 below

the fermi level. We can observe the crossing of lines which clearly shows itis doped.

Density of States

By observing the graph , we can clearly see the pecularity in them . The

peak which is near the fermi level shows downward drift and other peaks

shows near by it shows the upward lift . By seeing the first graph which


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represents the pure sillicon wire which doesnt have doping . The

downward drift of peak which is on the fermi level is at 8 of y axis which is

density of states. The other thing is graph is not much denser from figure

e.In the figure f , when we dope the sillicon nanowire with two Phosphrous

atoms then there is downward shift in the peak which is at middle of fermi

level and the downward drift increaes on increase of doping of atoms . The

downward shift goes 2 which is at density of states in y axis. On comparing

with the other graph , we can see that it is little more denser than other

grpah .In the figure g , when we dope the sillicon nanowire with four

Phosphorus atoms then there is downward shift in the peak which is at

middle of fermi level and the downward drift increase on increase of doping

of atoms . The downward shift goes 1.2 which is at density of states in yaxis. On comparing with the other graph , we can see that it is more denser

than other graph .In the figure h , when we dope the sillicon nanowire with

six Phosphorus atoms then there is downward shift in the peak which is at

middle of fermi level and the downward drift increase on increase of doping

of atoms . The downward shift goes 0.2 which is at density of states in y

axis. On comparing with the other graph , we can see that it is little most

denser than other graph .

Optical Spectrum

By observing the graphs , we can say that in the first graph which shows

pure sillicon without doping , the red line is at 3 , blue line at 2 and

green line at 1.7 which is for real part and all these lines coincide with

each other an the end and seems to be like one line but on the other

hand by looking at the imaginary part we can observe that initial point of

the three peaks formed by red,blue and green are at o but the peaks are

raising to 2 , 1.5 and 1 and then at end these three lines coincide each

other and merge with each other at the end in the figure I . When the

sillicon nanowire is doped with two aluminium atoms then we can see

that red line forms a peak and shows a rise but other two lines are at 1.5

and 1.3 and doesnt show a merge at end as usual in the real part . In the

case of imaginary part , the red line shows a peak whose initial point is 0and touches the 1.5 and other lines and doesnt show any merge at end.


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When the sillicon nanowire is doped with four aluminium atoms then we

can see that red line forms a peak and shows a rise at 2 and green line is

at 0.3 and the blue line became invisibleand doesnt show a merge at

end as usual in the real part . In the case of imaginary part , the red line

shows a peak whose initial point is 0 and touches the 1.2 and other lines

and doesnt show any merge at end. When the sillicon nanowire is

doped with six aluminium atoms then we can see that red line forms a

peak and shows a rise at 5 and green line is at 3 and the blue line at 1.8

doesnt show a merge at end as usual in the real part . In the case of

imaginary part , the red line shows a peak whose initial point is 0 and

touches the 4 and other lines and doesnt show any merge at end. It

shows multi peaks may be becoz of increasing metallic nature .Byobserving the above graphs , we can say that in the first graph which

shows pure sillicon without doping , the red line is at 3 , blue line at 2

and green line at 1.7 which is for real part and all these lines coincide

with each other an the end and seems to be like one line but on the

other hand by looking at the imaginary part we can observe that initial

point of the three peaks formed by red,blue and green are at o but the

peaks are raising to 2 , 1.5 and 1 and then at end these three lines

coincide each other and merge with each other at the end .By observing

the above graphs , we can say that in the first graph which shows pure

sillicon nanowire doping it with two aluminium atoms , the red line is

at 2.5 , blue line at 0.3 and green line at 0.2 which is for real part and all

these lines coincide with each other an the end and seems to be like one

line but on the other hand by looking at the imaginary part we can

observe that initial point of the three peaks formed by red,blue and

green are at o but the peaks are raising to 1.5 , 0.5 and 0.2 and then atend these three lines coincide each other and merge with each other at

the end .By observing the above graphs , we can say that in the first

graph which shows pure sillicon nanowire by doping it with four

aluminium atoms , the red line is at 10 , blue line at 4and green line at 2

which is for real part and all these lines coincide with each other an the

end and seems to be like one line but on the other hand by looking at

the imaginary part we can observe that initial point of the three peaks

formed by red,blue and green are at o but the peaks are raising to 3 , 1.5


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and 0.2 and then at end these three lines coincide each other and merge

with each other at the end .By observing the above graphs , we can say

that in the first graph which shows pure sillicon nanowire by doping it

with six aluminium atoms , the red line is at 2.2 , blue line at 1.2 and

green line at 0.7 which is for real part and all these lines coincide with

each other an the end and seems to be like one line but on the other

hand by looking at the imaginary part we can observe that initial point of

the three peaks formed by red,blue and green are at o but the peaks are

raising to 1.2 , 0.4 and 0.1 and then at end these three lines coincide

each other and merge with each other at the end .

Absortpiton Coefficient

By observing the figure , when the sillicon nanowire was not doped by

aluminum atoms then we can see the red line touching the 0.003 and we

can observe the simple plain line .By observing the graph , when the sillicon

nanowire was doped by 2 aluminum atoms then we can see the red line

touching the 0.003 and we can observe the little peak becoz of doping.By

observing the graph , when the sillicon nanowire was doped by 4 aluminumatoms then we can see the red line raising upwards and touching the 0.003

and we can observe the little peaks becoz of increase in doping .When the

sillicon nanowire was doped 6 aluminum atoms , the line starts at 0.004

and shows a rise in the peak till 0.006 and 0.008 and end line touches at

0.002 .By observing the graph , when the sillicon nanowire was not doped

by aluminum atoms then we can see the red line touching the 0.003 and

we can observe the simple plain line .By observing the graph , when the

sillicon nanowire was doped by 2 aluminum atoms then we can see the red

line touching the 0.003 and we can observe the little peak becoz of

doping.By observing the graph , when the sillicon nanowire was doped by 4

aluminum atoms then we can see the red line raising upwards and touching

the 0.003 and we can observe the little peaks becoz of increase in

doping.When the silliconnanowire was doped 6 aluminum atoms , the line

starts at 0.004 and shows a rise in the peak till 0.006 and 0.008 and end line

touches at 0.002 .


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Sillicon Nanowire doped with 0,2,4,6 Al atoms


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Sillicon Nanowire doped with 0,2,4,6 P atoms


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Band Structure analysis while doping with phosphorous atoms


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Optical Spectrum while doping of silicon atoms


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Optical Spectrum while doping of P atoms


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Density of States while doping of Al atoms


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Density of states while doping of P atoms


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Absorption Coefficient while doping of Al atoms


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Absorption Coefficeint while doping of P atoms


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Titanium Nanowire

Bandstructure Analysis

By observing the figure , we can clearly say that when titanium is not

doped with any atoms still it shows metallic nature . Thats why the fermi

level is crossed by many lines. The last curve above the fermi level is at 0.01

and the last curve below the fermi level is -1.0 . There is no band gap which

shows it is metal .When titanium is doped by two aluminium atoms , then

metallic nature increases . The curve which is above the fermi level at 0.03and the curve which is below the fermi level is -0.013 . As usual there is no

band gap , still there crossing of lines in fermi level . This clearly shows the

doping nature .When titanium is doped by four aluminium atoms , then

metallic nature increases . The curve which is above the fermi level at 0.05

and the curve which is below the fermi level is -0.013 . As usual there is no


doping nature .When titanium is doped by six aluminium atoms , then

metallic nature increases . The curve which is above the fermi level at 0.01

and the curve which is below the fermi level is -0.012 . As usual there is no


doping nature .By observing the above graphs , we can clearly say that

when titanium is not doped with any atoms still it shows metallic nature .

Thats why the fermi level is crossed by many lines. The last curve above the

fermi level is at 0.01 and the last curve below the fermi level is -1.0 . There

is no band gap which shows it is metal .When titanium is doped by twophosphorous atoms , then metallic nature increases . The curve which is

above the fermi level at 0.03 and the curve which is below the fermi level is

-0.013 . As usual there is no band gap , still there crossing of lines in fermi

level . This clearly shows the doping nature .When titanium is doped by four

phosphorous atoms , then metallic nature increases . The curve which is



level . This clearly shows the doping nature .When titanium is doped by six


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phosphorous atoms , then metallic nature increases . The curve which is



level . This clearly shows the doping nature . This graph clearly has lot of

dense lines crossing each other which shows it has maximum metallic

nature.

Density of states

By observing the figure , we can clearly say that when titanium is not

doped then , the graph which is at the middle of fermi level is 50 in the

density of states on y axis and there are around 2-3 little peaks near it .But

after doping the titanium nanowire with two aluminium atoms , then wecan see a decrease in the level of peak which turns out to be 45 on the

middle of fermilevel at density of states and peaks near it increase .But

after doping the titanium nanowire with four aluminium atoms , then we

can see a decrease in the level of peak which turns out to be 40 on the

middle of fermilevel at density of states and peaks near it increase .But

after doping the titanium nanowire with six aluminium atoms , then we can

see a decrease in the level of peak which turns out to be 35 on the middle

of fermilevel at density of states and peaks near it increase and becomes 5 .

We can clearly observe the decline by 5 times of fall is every doping .By

observing the figure , we can clearly say that when titanium is not doped

then , the graph which is at the middle of fermi level is 43 in the density of

states on y axis and there are around 2-3 little peaks near it .But after

doping the titanium nanowire with two phosphorous atoms , then we can


of fermilevel at density of states and peaks near it increase .But afterdoping the titanium nanowire with four phosphorous atoms , then we can


of fermilevel at density of states and peaks near it increase .But after

doping the titanium nanowire with six phosphorous atoms , then we can


of fermilevel at density of states and peaks near it increase and becomes 5 .

We can clearly observe the decline by 5 times of fall is every doping .


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Optical Spectrum

By observing the figure , here without doping the titanium ,we can clealry

see that blue line is missing and there is only presence of green and red line

. Green line is at 80 and red line is at 38 after that they coincide with eachother and merge themselves in the real part then in the imaginary part

there are two lines which are red and green that shows peak whose initial

point starts at zero and at end conincide each other and merge.By

observing the graph , after doping it with two aluminium atoms we can

clealry see that blue line is missing and there is only presence of green and

red line . Green line is at 50 and red line is at 40 after that they coincide

with each other and merge themselves in the real part then in the

imaginary part there are two lines which are red at 33 and green at 25 that

shows peak whose initial point starts at zero and at end conincide each

other and merge.By observing the graph , after doping with four aluminum

atoms ,we can clealry see that blue line is present and there is also

presence of green and red line . Red line is at 66 ,Green line is at 63and red

line is at 61 after that they coincide with each other and merge themselves

in the real part then in the imaginary part there are two lines which are red

, blue and green that shows peak at 40, 35 and 30 whose initial point startsat zero and at end conincide each other and merge.By observing the graph ,

after doping with six aluminum atoms we can clealry see that blue line is

present and there is only presence of green and red line . Green line is at 30

and red line is at 60 after that they coincide with each other and merge

themselves in the real part then in the imaginary part there are two lines

which are red and green that shows peak whose initial point starts at zero

and at end conincide each other and merge.By observing the above graphs ,

when titanium is not doped by any phosphorous atoms then red line is on

40 and green line is on 80 but on the case but on the other hand we can see

the imaginary part which has green line and red line whose initial point

starts with 0 and the peaks of the green line on 50 and red line on 20 . At

the other end , those lines coincide each other .By observing the above

graphs , when titanium is not doped by any phosphorous atoms then red

line is on 75 and green line is on 80 but on the case but on the other hand

we can see the imaginary part which has green line and red line whoseinitial point starts with 0 and the peaks of the green line on 35 and red line


30/43

on 10 . At the other end , those lines coincide each other .By observing the

above graphs , when titanium is not doped by any phosphorous atoms then

red line is on 50 and green line is on 25 but on the case but on the other

hand we can see the imaginary part which has green line and red line

whose initial point starts with 0 and the peaks of the green line on 50 and

red line on 10 . At the other end , those lines coincide each other .By

observing the above graphs , when titanium is not doped by any

phosphorous atoms then red line is on 45 , green line is on 89 and blue line

is on 25 but on the case but on the other hand we can see the imaginary

part which has green line and red line whose initial point starts with 0 and

the peaks of the green line on 60 , red line on 20 and blue line 10 . At the

other end , those lines coincide each other .

Absorption Coefficient

By observing the figure , we can say that ,When titanium isnot doped by

aluminium atoms , then we can see sharp curve in the graph which shows it

is not doped and there is no peak formation, the curve starts from 0 and

goes upwards.By observing the above graphs , we can say that ,When

titanium is doped by two aluminium atoms , then we can see some

distortion in sharp curve of graph and there is little peak formation, the

curve starts from 0 and goes upwards. This graph clearly shows variations

when it is doped little.By observing the above graphs , we can say that

,When titanium is doped by four aluminium atoms , then we can see many

distortion in sharp curve of graph and there is high peak formation, thecurve starts from 0 and goes upwards. This graph clearly shows variations

when it is doped .By observing the above graphs , we can say that ,When

titanium is doped by six aluminium atoms , then we can see distortions in

sharp curve of graph and there is no peak formation. But because of

extreme doping , it shows peculiar charecterstic , the intial and end point

changes and even peaks are depressed .By observing the above graphs , we

can say that ,When titanium isnot doped by phosphrous atoms , then we

can see sharp curve in the graph which shows it is not doped and there is


31/43

no peak formation, the curve starts from 0 and goes upwards.By observing

the above graphs , we can say that ,When titanium is doped by two

phosphrous atoms , then we can see some distortion in sharp curve of

graph and there is little peak formation, the curve starts from 0.005 and

goes downwards. This graph clearly shows variations when it is doped

little.By observing the above graphs , we can say that ,When titanium is

doped by four phosphorous atoms , we can see the peculiar charecterstics

like the curve starts by 0 and totally sticking to the x axis and from 500 it

rises above .By observing the above graphs , we can say that ,When

titanium is doped by six phosphorous atoms , then we can see distortions

in sharp curve of graph and there is no peak formation. But because of

extreme doping , it shows peculiar characteristic , the intial and end pointchanges and even peaks are depressed. This also resembles the extreme

doping of aluminium too.


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Titanium Nanowire doped by 0,2,4,6 Al atoms


33/43

Titanium Nanowire doped by 0,2,4,6 p atoms


34/43

Band structure analysis while doping of Al atoms


35/43

Band structure analysis while doping of P atoms


36/43

Optical Spectrum while doped by Al atoms


37/43

Optical Spectrum doped by P atoms


38/43

Density of states while doping with Al atoms


39/43

Density of states while doped with P atoms


40/43

Absorption Coefficient while doped with Al atoms

.


41/43

Absorption Coefficient while doped with P atoms


42/43

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Electronic and Optical Properties of Sillicon and Titanium Nanowires

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