Laser Micrometers

How do you expect a hand held device to have the ability to measure 1 nm? Almost everything around you during a day expands and contracts at least 10 -100 times that!

Also, 1nm to 1cm is an awfully large range! I've used actuators from Newport that have a resolution of 40 nm and that was impressive. You could manually move the spindle about 10 mm, then the fine adjusting was done by a device driver box that allowed me to manipulate the spindle in the nm range.

What exactly are you trying to measure?

Hi,

we are using micro interferometers with a maximum range of 250mm and a resolution of 10nanometer.

These will be available with 1 nm resolution next spring.

But your test fixture shall be made of Zerodur or quartz-glass or be temperature controlled to miilidegrees.

1 cm length of steel is expanding (12ppm/K) by 120 nanometer per degree.

Next:

Curvature is equivalent to bending stress and this can be removed by tension that is giving plastic deformation. Do you look at this?

RHABE

Yes, thats what Im looking for. Specifically, I am researching curvature of thin films after plastic deformation. 1 nm is probably unfeasible, but 10 nm is probably easier. I will check micro interferometers and see if they have cheap benchtop or handheld versions.

Hi,

which type of thin film, which is the thickness?

You will never get a handheld interferometer, measurement down to below micrometer is really complicated and requiring the utmost stable measurement setup.

We had the necessity to insulate the compartment thermally and against floor vibrations.

And have a separate stabilised power supply and and and...

I think you may need a measurement device that is directly indicating curvature.

RHABE

Uh, yeah I'm on the outside looking in. And, well, uhh, I gotta break it to ya, What you are looking for aint gonna come cheap.

Oh. I see. well, well. yes sir. Right away, one in red and another in black. yessir I see, his and hers. yes sir Mr Rockefeller.

Just givin' the rub.

But it's still not gonna be cheap.

When I was at uni we set up our own Michealsons Interferometer using a laser and a prism. Can't remember exactly how we did it but I have the report somewhere. As a previous person said, when we were using it we had to lock the lab door because the effect of someone entering the room disturbed the accuracy of the readings. Even at 10nm you are going to find you have quite a high degree of error.

Yes, you have to remember that the visible light spectrum is from about 350nm to 800nm (ROUGHLY!). So you're talking measurements of about 10 times smaller than a visible light wave.

So is there any other option to measure thin film curvature other than interferometry?

Hi,

the interferometer with lowest price I know cost around 10K$. You need 3 to make curvature measurement.

Another approach is capacitive distance measurement: make 3 conductive areas (thin flim or ordinary metalising or thick film), surround these with conducting rings and surround these with a second set of conducting rings.

Make these using ceramics or quartz glass and connect the second rings to individual shields at the sides and at the back: this is the guard structure that is eliminating stray capacitance and make the structure for the second ring similar but bigger.

Connect the conducting areas to three capacitive measurement electronics (1-2K$ each) connect the guard connections of the electronics to the second rings and the second ring structure to the zero voltage pin of the electronics.

The distance between the sensor structure and the electronics should be as small as possible, preferrably not longer than 4" but in good lownoise environments may be up to 1m.

Making these structures as metal-epoxi composites or printed circuit boards will be possible but will not give sufficient quality and stability below 100nm.

Take the three measurement x1, x2, x3 to a computer and calculate x1-2x2+x3.

That divided by the square of the distance between the centers of the sensors is your curvature.

RHABE

Wow, I feel so dumb. Im actually doing research on capacitive pressure sensing, and I didnt think of using that to measure curvature. Thanks for jarring my mind back into thinking.

Good for you, mecharine!!! Sounds like you're on your way!

Just curious, did you really need 1 nm resolution, and if it isn't telling, why so small?

Regards,

vermin

BTW, the shields are made of ceramic, correct? And the ring structures are singular, as in 2 rings per sensing area?

Hi,

we make a cylindrical part from ceramic (typically 0.5 to 2 cm diameter and length to 0.5 to 2 times the diameter) grind a small groove alomg the length overcoat totally with metal, regrind the outer diameter so that only a fine conducting line will be left.

This is giving the measurement capacitance.

A second part : a hollow cylinder of inner diameter matching the outer diameter of the inner part and coated on the front side and circumference as the first one also with the small groove.

The third part made in the same manner but without the groove and the metalising on the outside remaining .

These three parts glued together with high temperature epoxi will give one capacitive sensor.

We tried many different approaches, this is only one example.

The outermost shields (the electrical common) should be tied together also mechanically.

There are so many differnt possibilities that I cannot judge which solution will be really good for you without any knowledge about your environment and solutions.

Which type of electronics do you have?

Is this to be operated during coating or later?

Which size has your part to be measured.?

How do you shied electrically and mechanically?

Which type of pressure sensor are you talking about?

Have success

RHABE