Selective Area Modification of Silicon Surface Wettability by Pulsed UV Laser Irradiation in Liquid Environment

The overall goal of this experiment is to demonstrate the formation of both hydrophilic and hydrophobic surfaces on silicone by irradiation with krypton fluoride and argonne fluoride lasers from samples immersed in a low concentration of hydrogen peroxide solutions or methanol. This method can help answering some key questions in the laser semiconductor interaction field concerning selective area chemical modification of the semiconductor surface, which may be suitable for biosensing applications. The main advantage of this technique is that they can be applied for in steel control of silicon surface viability without a vacuuming surface.

Morphology of the semiconductor. We first had the idea for this method. We investigating U laser base process for selective area formation of surface defects used in the technology.

Now as quantum mal intermixing, Visual demonstration of this method is critical as the air pocket fleet population of the simple chamber and radiation with the homogenized beam of EXIM laser are relatively difficult steps. To begin, use a diamond scribe to cleave an end type phosphorus obed silicon wafer with one polished side into 12 millimeter by six millimeter samples that are 380 microns thick. Then clean the samples by rinsing them in dine acetone, and then isopropyl alcohol for five minutes each.

Next etch the samples in a 0.9%hydrofluoric acid solution for one minute to remove the initial oxide, then rinse them in deionized water and dry them with a stream of high purity nitrogen. Store the prepared samples in a nitrogen filled bag to curb oxidation when ready to continue place the samples in a 0.74 millimeter tall chamber. Filled the chamber with 0.01 to 0.2%hydrogen peroxide diluted in water or with DGAs methanol, and then sealed the chamber with a fused silica window that has a high transmission UV light.

Make sure no air pockets are left inside the chamber. Irradiate the sample with a homogenized beam at only two sites on each sample by increasing pulse number from 100 to 600 in step of 100 pulses through a circular mask, four millimeters in diameter. Next, irradiate the samples in the same way by using a maple leaf mask.

When finished, rinse the samples with the ionized water and then dry them with a nitrogen flush dilute biotin conjugated and fluorescein stained 40 nanometer diameter nanospheres with PBS to one times 10 to the 12th particles per milliliter at room temperature. Next, immerse the krypton fluoride laser irradiated samples for two hours in this solution at room temperature. Then soak the irradiated samples in PBS for one minute to eliminate any unbound fluorescein stained nanospheres from the surface.

Begin by placing the sample onto a clean flat surface form a drop at the tip of the micro syringe and slowly lower it to the sample surface until it makes contact and transfers to the surface. Using a CCD camera capture and save the water Drop profile images, measure each contact angle independently at each of the laser sites. Then load the images into image J and use the drop analysis plugin drops snake to estimate and average the contact angle values.

Start by turning the images into gray scale images. Next, outline the drop contour from left to right to initialize the snake. Accept the curve connecting these knots and evolve the curve by pressing the snake button.

Repeat this process for each droplet that was imaged. Calculate the average contact angle value from four laser irradiated sites on different samples to perform x-ray photo electron spectroscopy. Start by loading the samples into the vacuum chamber and pulling a vacuum of one times 10 to the negative nine.

Tor then acquire the surface survey data in constant energy modes of a 50 electron volt pass energy. Target an area 220 microns by 220 microns using an ebeam produced aluminum K alpha emission of 150 watt power. Next, acquire high resolution scans from the same analyzed area using a 20 electron volt pass energy.

Finally process the acquired spectra with the appropriate quantification software in accordance with the manufacturer specifications. These contact angle results were acquired after an average 10 minute exposure to hydrogen peroxide solutions. The contact angle decreases with increasing pulse number for all the different peroxide concentrations.

The minimum contact angle of about 15 degrees was obtained using both 0.02 and 0.01%Hydrogen peroxide solutions at 500 pulses x-ray photo electron spectroscopy data show that the quantities of silicon dioxide and silicon hydroxide on the site irradiated by a krypton fluoride laser are greater than those on the non irradiated areas. Since surfaces coated with silicon dioxide have a minimum contact angle of 45 degrees to 50 degrees and silicon hydroxide layers have a minimum contact angle of 13 degrees. The super hydrophilic silicon hydroxide monolayer is most likely responsible for the decreasing contact angle in the irradiated samples.

Since biotin coated fluorescing nanospheres immobilized preferably on hydrophobic non irradiated silicone surfaces, the maple leaf pattern observed on the green background indicates the area of a strongly hydrophilic surface fabricated by the KRF laser. While tapping this procedure, it's important to remember to minimize the oxidation from air exposure and reduce the bubble generation during laser irradiation Following this procedure. Other methods employing, for instance, UV lamps could also be investigated for chemically modified surface with ability of materials.

The potential advantage of this method is in its ability to transform a silicone surface from hydrophobic to hydrophilic and vice versa without removing the wave from a processing chamber. Once master, this technical can be completed in about 30 minutes depending on the complexity of the pattern for selective air modification. So after watching this video, you should have a good understanding of how to use uuv light of an eczema laser to control with ability of silicone surface within selected areas.

Don't forget that working with UV light can be extremely hazardous and UV protective gear should always be wor while performing this procedure. Also working with hydrofluoric acid is dangerous and requires wearing rubber gloves and face shielding equipment.