Measuring the thickness of a film of unknown density and porosity by weight method is never accurate. You need to do optical measurement by means of Michelson interferometer you can build in your lab. Mask some of the glass during the deposition and measure the step at the bare glass and the deposited thin film. Simple and fast measurement. Progress in Physics edition on Thin films ~1975 describes in detail how to build your own cheap and yet very powerful interferometer.

extreme: much high or much low?

You might have coating at the both side of the substrate

Real density might be completely differnt than bulk

I see two general sources if error: i) the measuring accuracy of the substrate weight before and after deposition of the film (try to use substrate that is as thin as possible) and ii) the density used for calculation. I absolutely agree with D.K.Sarkar that the film density may differ substantially from the bulk density

i also agree with both D. K. Sarkar  and Tsvetanka Babeva

there is many parameter make the weight method not accurate

1- the difficult in measure the difference in the mass of substrate before and after deposition

specially when u use thick substrate , for deposition some nm of film

(try to use corning glass)

2- non homogenize of the thin film also  give u error in measure the area of the thin thin film ( chose a small area)

3 - as they mention above ( there is different between the density of the film and bulk )

can  u show us how u calculated it ? can u put numbers?

in this file i measure the thickness of the ZnS thinfilm and compare with sawnepoal method 

with full respect to the previous answers from respected colleagues , you Raghad should describe in details how did you estimate the thickness using weight method. Before knowing that it will be just conceptual answers.

Measuring the thickness of a film of unknown density and porosity by weight method is never accurate. You need to do optical measurement by means of Michelson interferometer you can build in your lab. Mask some of the glass during the deposition and measure the step at the bare glass and the deposited thin film. Simple and fast measurement. Progress in Physics edition on Thin films ~1975 describes in detail how to build your own cheap and yet very powerful interferometer.

Determining the density by measuring the weight of the crystal will lead you nowhere. Measuring the thickness by optical means as I suggested will lead you to better understanding of the density of the film. With the thickness and density you can calculate the index of refraction, etc.

Dear 

Use the technique above for Kiril (deposited your material as  steps) and use Mickelson interferometric Method to measure the thickness as in the attached publication that (Superficies y Vacío 9, 283-285, Diciembre 1999)

Hope will help you 

Dear Raghad Al-Bayatti,

Extreme sound like it is far off. I would suggest that you are sure that your film is properly rinsed and dried. Then run some XPS or TOF-SIMS analysis, perhaps X-ray if the film is thick enough and SEM/EDX to see if your film is pure ZnS. To answer the question it would also be good to have a description of your procedure. Gravimetric methods work best if the difference your measuring is in the multi-mg regimes and the dw/w is significant (ie many > 100 ppm). Give more info.

best wishes

Frederik C. Krebs

Optical Measurement is the best way as  mentioned by Kiril A. P.

Hello, why don't you mask one small area of your sample by Kaplan tape or any other tapes that can withstand high temperature. Then measure the thickness using the profiler. I think profiler is the basic equipment that you must have in order to measure thickness of thin film.

It would be easier to answer the question if you gave specific numbers related to what you were doing. There are a lot of ways to go wrong here.

After you determine the thickness as suggested in my previous comment, using the same method you can determine the index of refraction and density of the layer. Total cost to construct your in house Michelson interferometer is less than $50.

Optical measurements is recomended, However I use a contact perfilometer, which allows to measure up to 100nm. By CBD I got a 100 nm thick films in one hour

Dear Raghad Al-Bayatti

Please, open the attach files. It contains a Swanepoel's method for calculating the thickness with high precision. If you unable to calculate, you can send me your data for calculations.

what you have done is not an exact method, you can use optical   methods

can you calculate the thickness by Scanning Electron Microscope( as cross- section)

What about measuring the film thickness by X-ray reflectivity which you could easily do. It is like coplanar symmetrical XRD  (theta - 2theta) but at very low angles. The film thickness one can get from the fringes distance D as 2Pi/D. Best regards.

If you have F20 filmitric system, then you can calculate thickness of your thin film

As optical method maybe spectroscopic ellipsometry is a good optical methode to characetrize your film.

Even on transparent material we work with an Imaging Ellipsometer using a knife edge illumination to avoid backside reflection.

Best regards

Christian

You can use SEM.

Dear Raghad Al-Bayatti

you can identify the thickness with high precision if you have spectroscopic ellipsometry apparatus. If you haven't, please measure transmission and reflection and use exact equations (in terms of Neuton-Raphson method) to identify it. It means that you need a numerical solution to identify the thickness with high precision.