# 3.14 Sspd_chapter1_part 8continued_electron in an infinite potential  (Page 3/3)

The abrupt change in the refractive index or the dielectric constant is referred to as step index change. In the same way abrupt voltage change is referred to as step voltage change.

Matter wave behaves in an analogous fashion at a step voltage change as a light wave behaves at step index change.

Fig(1.26) Reflection and Transmission of electron matter wave across step voltage change from V 1 to V 2 .

For matter wave,

wave vector k=2π/λ = 2πp/h = [√{2m(E-V)}]/ћ;

Therefore the two wave vectors are:

k 1 = [√{2m(E-V 1 )}]/ћ and k 2 = [√{2m(E-V 2 )}]/ћ;

The incident forward electron matter wave:

ψ(z,t) incident = ψ 0incident Exp[j(ωt- k z1 .z)]

The reflected backward electron wave:

ψ(z,t) reflected = ψ 0reflected Exp[j(ωt+ k z1 .z)] 1.55

The transmitted forward electron wave:

ψ(z,t) transmitted = ψ 0transmitted Exp[j(ωt- k z2 .z)] 1.56

At the interface or at the step,

ψ 0incident - ψ 0reflected = ψ 0transmitted 1.57

Eq.(1.57) is the interface boundary condition.

Inside the potential well we have both the wave vectors ±i[√{2mE}]/ћ]hence we have both forward and backward traveling wave components.

Outside the well Schrodinger Equation is of the form:

2 ψ /∂x 2 + (2m(E-V)/ћ 2 )ψ = 0

But outside the well, V = ∞ therefore the wave equation reduces to:

2 ψ /∂x 2 - (2m∞/ћ 2 )ψ = 0

The characteristic equation has real roots hence the solution is hyperbolic.

Therefore ψ(z,t) = [AExp(-k 2 .z) + BExp(+k 2 .z)]Exp(iωt) 1.58

Where k 2 = [√{2m∞}]/ћ]

In Eq(1.58), the term Exp(+k 2 .z) is not admissible as it is exponentially growing function. Hence B=0 and the solution outside the well is:

ψ(z,t) = [AExp(-k 2 .z)]Exp(iωt) 1.59

But since k 2 = infinity implies the wave function does not exist outside the well. The transmitted wave outside the well almost instantaneously attenuates to zero since k 2 is the attenuation coefficient of the exponentially decaying wave and this coefficient is infinite.

Inside the potential well there are two waves one forward and the second backward and both have equal amplitude but opposite sign so that at the two boundaries of the potential well the sum of the two produce nodes.

ψ 0incident - ψ 0reflected = 0 at the boundaries 1.60

Therefore

ψ(z,t) incident = A Exp[j(ωt- k z1 .z)]

ψ(z,t) reflected = -AExp[j(ωt+ k z1 .z)] 1.61

The superposition of the two waves is:

ψ(z,t) = AExp[j(ωt)] [ Exp(- k z1 .z)- Exp(+ k z1 .z)]

ψ(z,t) = AExp[j(ωt)][Cos(k z1 .z)-iSin(k z1 .z) -Cos(k z1 .z)-iSin(k z1 .z)]

ψ(z,t) = -2iAExp[j(ωt)][Sin(k z1 .z)]

or ψ(z,t) = BExp[j(ωt)][Sin(k z1 .z)] 1.62

Eq.(1.62) is the mathematical formulation of the standing wave.

According to boundary conditions, this standing wave is suppose to have two nodes :

ψ(0,t)= ψ(W,t) =0

therefore k z1 .W = (2π/λ n )W = n π where n = 1, 2, 3,………….

Therefore W=n. λ n /2 1.63

This is the same restriction as was imposed in Eq.(1.51). This Eq(1.63) sheds a very important light on the quantization of energy levels permitted for an electron in an infinite potential well.

Inside the potential well there is the superposition of incident and reflected wave. There are only certain cases for which constructive interference takes place for the remaining cases there is destructive interference.

The cases for which the superposition leads to node formation at the boundaries z = 0 and W, only for those cases electron has an existence. For all the remaining cases electron goes out of existence by destructive interference.

Therefore we assert that in an infinite potential well , the electron can be in existence only for the energy levels:

E= E 0 , 4 E 0 , 9 E 0 , 16 E 0 ………

Where E 0 = h 2 /(8mW 2 )

The above result comes from Eq.(1.50) and its previous line.

An identical situation prevails in a hydrogen atom. The orbits which allow constructive interference to take place only those orbits are permitted. Remaining are forbidden. The orbital radii which support constructive interference are the radii where electron can exist as standing wave.

These are the radii exactly predicted by Bohr’s Law:

Orbital Angular Momentum = Integral Multiple of (h/(2π)) as already seen in Chapter 1_part 6.

Fig(1.27) An electron in 3 quantum states n=1,2,3 in an infinite potential well.

An electron in first three permissible quantum states in an infinite potential well are shown in Fig.(1.27

Is there any normative that regulates the use of silver nanoparticles?
what king of growth are you checking .?
Renato
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
why we need to study biomolecules, molecular biology in nanotechnology?
?
Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
why?
what school?
Kyle
biomolecules are e building blocks of every organics and inorganic materials.
Joe
anyone know any internet site where one can find nanotechnology papers?
research.net
kanaga
sciencedirect big data base
Ernesto
Introduction about quantum dots in nanotechnology
what does nano mean?
nano basically means 10^(-9). nanometer is a unit to measure length.
Bharti
do you think it's worthwhile in the long term to study the effects and possibilities of nanotechnology on viral treatment?
absolutely yes
Daniel
how to know photocatalytic properties of tio2 nanoparticles...what to do now
it is a goid question and i want to know the answer as well
Maciej
Abigail
for teaching engĺish at school how nano technology help us
Anassong
Do somebody tell me a best nano engineering book for beginners?
there is no specific books for beginners but there is book called principle of nanotechnology
NANO
what is fullerene does it is used to make bukky balls
are you nano engineer ?
s.
fullerene is a bucky ball aka Carbon 60 molecule. It was name by the architect Fuller. He design the geodesic dome. it resembles a soccer ball.
Tarell
what is the actual application of fullerenes nowadays?
Damian
That is a great question Damian. best way to answer that question is to Google it. there are hundreds of applications for buck minister fullerenes, from medical to aerospace. you can also find plenty of research papers that will give you great detail on the potential applications of fullerenes.
Tarell
what is the Synthesis, properties,and applications of carbon nano chemistry
Mostly, they use nano carbon for electronics and for materials to be strengthened.
Virgil
is Bucky paper clear?
CYNTHIA
carbon nanotubes has various application in fuel cells membrane, current research on cancer drug,and in electronics MEMS and NEMS etc
NANO
so some one know about replacing silicon atom with phosphorous in semiconductors device?
Yeah, it is a pain to say the least. You basically have to heat the substarte up to around 1000 degrees celcius then pass phosphene gas over top of it, which is explosive and toxic by the way, under very low pressure.
Harper
Do you know which machine is used to that process?
s.
how to fabricate graphene ink ?
for screen printed electrodes ?
SUYASH
What is lattice structure?
of graphene you mean?
Ebrahim
or in general
Ebrahim
in general
s.
Graphene has a hexagonal structure
tahir
On having this app for quite a bit time, Haven't realised there's a chat room in it.
Cied
what is biological synthesis of nanoparticles
how did you get the value of 2000N.What calculations are needed to arrive at it
Privacy Information Security Software Version 1.1a
Good
Got questions? Join the online conversation and get instant answers!