Frontiers in Materials Science and Engineering 扫二维码继续学习 二维码时效为半小时

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 phase-change materials (Ge Te Sb) 

transformation on (1,0) state--crystallization & amorphization 



Laser- based optical sensors

Laser principle: Absorption, spontaneous emission, and stimulated emission.

Ground state means - lowest possible energy.

When excited with addition of energy through photons the electron goes form ground state to and excited upper state.

BO Approximation

Etot = Eel + Evib + Erot ( treat seperatly)

Eel due to electronic configration of electrons

Evib due to periodic displacment of atoms abt mean positions

Erot due to ratation of atoms abt common axis passing through center of mass

Seperation between  Eel > Evib >  Erot

Allowed transition is by planck's law

Wavlength in UV = Electronic transition occuring


  • 3kind of energies Eel, Evib, Erot
  • QM : energy levels are discrete Quantised and trsnsitions coour between only specific energy levels


1. Scattering

2. Absorption

3 Emission

Lines : Erot        Bands: Evib    System: Eelec

Erot J     

Lines: Single transition 

Molecules with permanent dipole and can interact with microwave termed as microwave active (H2O, HCl )and those who does not have a permanent electric dipole are microwave inactive (N2, H2)

Erot = (1/2) IW2

Evib V

Bands: Vibrations levels asscoiated with rotational levels. 

Evib =( u+ 1/2) hw (h here is hcross=h/2*pi)


System : Transition between 2 electronic levels

Beer Lambert law: Ratio between intial intensity from Laser source to transmitted intensity by photodetector.

Quantitative way of applying absorbtion specta.


B= Rotational Constant = (28* 10^-40) / I

Erot= BJ(J+1)hc

F(J)= BJ(J + 1) cm^-1


1.Power plant emissions (sensing gases)

2. Engine efficiency monitoring

3. Sensing benzene in environment

4. Ammonia sensor







1.Phase Change Materials PCM

  • Group of semiconductors ( Ge, As, Te)
  • Principle: Disordered amorphous phase 0 change to ordered crystalline phase 1

HDD and SSD -retain data for long time

DRAM ans SRAM - loss data when turn off

PCM- Storage class memory- inbetween the above 2

2.Switiching fast

amorphosrous = fast -picoseconds- upon  exciting

Cryatallization- fast- nanoseconds

Upon heating for some nanoseconds amorphous phase can change into crystalline for PCM materials

3. Why GST is fast (GST- Germanium, antimony, Tellurium)

GST crystallises into cubic rocksalt phase

4. Improve writing speed

GST at high tempertsure of around 600K CYRSTALLINE phase fluctuate

  • Higher melting point indicate strong bond strength
  • Ecoh and COHP
  • COHP- to find chemical stability of the system 

From above 3 calculations it was found Sc2Te3 to be best system

 So If Sc2Te3 is in a system with just 10% it could be good for nucleation


GST can withstand more heat upto 1200K  without being changing into disordered state.

6 improve cycling endurance and stabilising

7. Prevent atomic migration.

Thickness of PCM is around several nanometers to 100nm

8 ageging tendency

ageing lead to lower energy

9 SET operations

10 To improve speed power consuption and cycling indurance