This protocol details the fabrication of silver structures inside a polymer matrix in three dimensions using a femtosecond laser begin by mixing PVP and silver nitrate in water to yield silver ions in inside a polymer matrix coated glass Slide with the solution and bake to create a thick polymer layer doped with silver ions then irradiate the polymer layer with femtosecond laser pulses in order to grow silver structures inside the polymer. Analytical results from optical microscopy and scanning electron microscopy show the silver structure growth in laser irradiated volumes of the sample. The primary advantage of this technique over other methods, such as UV photolithography, is that femtosecond laser direct writing can create middle structures in one step, and it can do so in 3D.
The key to this process is a combination of chemical reagents in the sample because it limits the silver growth to the laser rated volume. An application of this method includes the 3D fabrication of isotropic metal, dielectric meta materials for infrared and optical wavelengths. Measure eight milliliters of water in a beaker.
Add 206 milligrams of polyvinyl perine and mix until the solution is clear. Then add 210 milligrams of silver nitrate and dissolve by mixing. Now using drop casting coat, a glass slide with the silver solution, bake the glass slides in a 100 degree Celsius oven for 30 minutes.
Remove and cool the treated slides for 30 minutes. The optical setup includes a titanium sapphire laser, a faraday isolator, a pulse compressor, an kuo optic modulator, an indie filter, a home-built microscope with the CCD camera and a three axis translation stage. Align the laser beam all the way through the microscope.
Objective to the sample mount. The entire setup should be on an optical table with vibration isolators. Adjust the compressor to obtain 50 femtosecond pulses after the microscope objective.
Also adjust the neutral density filters to obtain three nano dual pulses. After the objective, now ensure the laser spot size is larger than the back aperture of the microscope objective. Next, set the al optic modulator to produce 10 microsecond exposure windows during which the sample is irradiated.
Set the repetition rate to 25 hertz. Block the laser beam before it reaches the microscope. Place the sample onto a three axis translation stage.
The beam path of the femtosecond laser pulses should pass through the imaging microscope objective and focus into the sample. Switch the microscope illumination source to observe the sample in C two. Using the CCD camera, translate the Z axis of the stage to find the interface between the glass substrate and the polymer film.
Then refocus the microscope to the desired depth inside the polymer. For patterning the bottommost layer unblock the laser beam. Set the motion controller software to translate the sample in x, Y, and Z directions with a speed of 100 microns per second.
Z translation during patterning must be in the direction away from the glass polymer interface to avoid interference with fabricated structures. The darkened laser exposed foxholes contain silver. The pulse energy and exposure time.
Determine the size of the silver dots and the custo optic modulator frequency and the sample translation speed. Determine the spacing. The current settings produce large dots with a four micrometer period for clear.
In C two imaging, the AO optic modulator and neutral density filters permit fine control of the amount of energy deposited into the sample. For example, silver structures are readily visible through the NC two optical microscope using an exposure of 110 pulses for voxel and three nano joules per pulse with the stage translating at 100 microns per second. In this 3D rendering of optical microscopy images, the fabricated sample consists of an array of silver dots on top of another of array of silver dots.
They're held in place by the polymer matrix. The data can also be visualized as sequential optical microscopy images that are animated as the samples are translated away from the microscope objective, different features come in and out of sharp focus. This video shows the previously 3D rendered sample.
This video shows two dot patterns that spiral in the Z direction. High resolution images of fabricated silver structures can also be obtained using a scanning electron microscope. This sample consists of a 2D array of dots that are fabricated directly on the glass substrate.
Note, the silver features are sub micrometer in size. After watching this video, you should have a good understanding of how to make three dimensional silver structures in a polymer matrix using a femtosecond laser. Don't forget that working with lasers and chemicals can be extremely hazardous and you should always wear the appropriate protective equipment when performing this procedure.
This technique makes it possible to explore new designs and metamaterials and fabricate devices that cannot be made using other techniques.
