Polishing sample

Polishing sample

We have successfully polished a sample down to 45 micron thickness using template method. Following is a summary.

As shown in the figure, the idea is to create a template using much harder materials (such as glass, rasor blade) than the sample. One advantage of this way is that you can measure the sample thickness using a micrometer (basically sample+glass -glass). Everything is glued using paraffin, which is safe and surprisingly strong for polishing and easy for removing.

The steps are:

1) we can start with as thick as 500 micron

2) polish the template down to 75 micron (150 grit, 400 grit)

3) put on sample, using 800 grit to polish easily down to the same thickness of the template

4) continue polishing with 800 grit until thickness is less than 50 micron

5) continue with 1500 grit, at this time one of the templates may be gone, which is ok.

6) polish until the satisfactory thickness, the lower limit may be 30 micron.

LO-TO splitting

effective charge

Born and ionic effective charge:

Compound	q/e	qB/e
NaCl	1.16	0.80
MgO	1.26	0.77
GaAs	1.48	0.34

The data shown in the upper table is calculated from the data of ε(0), ε(∞), ω_TO found in and Ashcroft[1] and Kittel[2].

The formulas used are:
For Born effective charge
q_B^2=\epsilon_0mV\omega_{TO}^2[\varepsilon(0)-\varepsilon(\infty)]

For ionic effective charge
q^2=\epsilon_0mV\frac{\omega_{TO}^2[\varepsilon(0)-\varepsilon(\infty)]}{\eta^2[\varepsilon(\infty)+1/\eta-1]^2}

I only showed a couple of examples for typical materials, basically, as long as you have the data of ε(0), ε(∞), ωLO, you can calculate ionic and Born effective charge.

Here m is the reduced mass, V is the volume of the oscillator, η is the depolarization factor (for cubic system it is 1/3). The formula is in SI units.

[1] N. W. Ashcroft and N. D. Mermin, Solid state physics (Holt, Rinehart and Winston, New York, 1976).
[2] C. Kittel, Introduction to solid state physics (Wiley, New York, 1966).

Energy conversions

Some useful conversion between energy scales

Let's use jouls as our standard

Unit	Jouls
Jouls	1
eV	1.6e-19
μB	9.27e-24
cm-1	1.98e-23
THz	6.63e-22
Kelvin	1.38e-23