Hi Fayroz

  What your are observing in your case is quite interesting. But as per my knowledge with decrease in crystallite size the electrical resistance should increase due to the increase in the grain boundary. This is because the electron will suffer more scattering. 

But as it is opposite in your case again you have to recheck with the crystallite size calculation. I also want to mention that please use the proper K value in the Scherrer equation by checking your film morphology as its value varies from 0.62 to 2.08.

Dear Yashabanta, thanks for your answer and interest.

I used K=0.9, and I calculated D by Microsoft office excel so there is no doubt in the result regarding to calculation.

From the other side, small D increased the sensitivity, because small D means high surface-to-volume ratio, that leads to high sensitivity.

1.From the measured resistance of the  thin films (R) and by applying Stuck’s low

                   Sigma=Sigma0 exp(-Ea/KB.T)

  Ea represents the activation energy ( eV ) , T the applied temperature ( oK ) and KB represents Boltzmann constant. By drawing natural of Sigma as function of logarithm of 1/KBT we get a straight line which the activation energy is equal to its sloop.

2.For the relation betweeen cristalline size  and  resistance, i think that you have a linear variation of  size and time deposition in one temperature if we increase temperature the size increases and the linear curve time remaims.

Conclusion:So You must correlate the two answers for obtaining an emperical formula between cristalline size and resistance. 

Dear A. Ouerdane, thank you for the explanation

If I used only one temperature for annealing but different annealing time, how could I use this relation?

What is the material you are talking about? What temperature and ambient are you annealing in? Could it be that there is something else happening (reaction?) besides recrystallisation?

I annealed CuS thin films at 150 oC for 5,15 30 and 45 min. D decreases with time till 30 min (13.4 nm), then it suddenly high increased at 45 min (45.9 nm). And what is making me so confused that at this time (30 min) I got a highest sensitivity which is good for my sensor, but it is not convenient with the principles!!!

Are you annealing in air? Could it be that your material is oxidizing?

Dear colleague Fayroz A Sabah,

Have a nice time and good day,

Peace be up on you.

The relation between crystalline size and the resistance during annealing thin film depends on many factors:

1-The temperature of annealing (below or higher glass transition temperature (Tg), see the attached Fig.

2- The time of annealing (short or long).

3- The nature of the material under consideration, amorphous, poly crystalline or        

       crystalline material. 

4- Type of annealing; fast annealing or slow annealing.

5- The ambient of annealing; air, vacuum, Oxygen, inert gas.

First: You should know the four distinct temperatures from DTA or DSC to get the glass transition, Tg, the onset of crystallization, Tc, Peak of crystallization, Tp and melting point Tm to decide the suitable annealing temperature (between Tc and Tp).

Second if you get the suitable annealing temperature you need to check the suitable annealing time; the increasing of the annealing time may affect the crystallite size positively or negatively.

Three: If the material is amorphous or poly crystalline in nature the crystallite size may be increases due to the structural ordering (in case of suitable annealing temperature and suitable annealing time) otherwise vice versa, If the material is crystalline material the annealing time may has a negative effect on the crystallite size due to the the fact that the bond strength may be broken at high temperatures and produces many defects and localized states. So XRD is needed to be done before and after Tg to identify the existed phase and the ordering effect consequently the crystallite size, strain,…etc.

Four: the type of annealing; fast or slow also may affect the crystallite size positively or negatively, the slow annealing is better than the fast one, the first one gives more time to the atoms to be more order and not stressed so the effect of the strain will be minimum while the fast one may be vice versa.  

Five: The ambient of annealing; air, vacuum, Oxygen, inert gas may affect the crystallite size positively or negatively. The contamination may introduces defects and consequently reduces the crystallite size.

Electrical properties can be improved by improving structural properties and according to the applied temperature the conductivity may be intrinsic or extrinsic.

The lower the density of localized states, the higher the arrangement of material . If the annealing has a positive effect on the material the density of localized states will be annealed out and decreases consequently the order of the material will increases, the resistivity will decreases and vice versa.

Ex. if the intensity if XRD increases and the FWHM decreases with the increasing of annealing, this is a document that the increasing of annealing gives more enhancement of order and the localized states or defects decreases by the increasing of annealing which means the increasing of crystallite size.

To confirm your obtained data you need to process XRD, TEM, AFM and SEM or any.

I wish this is useful and help you.

Yours

A.   El-Denglawey

Dear Pieter, I used close oven for annealing.

Dear A. Eldenglawey

Good day

Thanks a lot for your response and for the excellent explanation, what do you mean by fast annealing or slow annealing? and what is the onset of crystallization?

Replying to the third point, I did XRD for all samples before and after annealing. The result was the same peaks but with different intensity.

Very useful information indeed. Thanks again

Yous;

Fayroz A. Sabah

Dear colleague Fayroz A. Sabah

Thanks for your nice reply, wishing for you all the best.

The fast annealing: the elevating of temperature through a very short time and the other one the vice versa.  The onset of crystallization is starting and the dominating of crystallization.

I wish this is useful and help you.

Yours

A. El-Denglawey

Dear A. Eldenglawey

Thank you for your interest and help. How can you control or decide the type of annealing (fast or slow) since it has the same temperature and time?

Dear colleague Fayroz A. Sabah

Have a nice time and good day,

Peace be up on you.

You can control of annealing (fast or slow) depends on the material type 

and the material structure (amorphous, as amorphous, nano, poly crystalline or crystalline material.

I wish this is useful and help you.

Yours

A. El-Denglawey