Reactive Vapor Deposition of Conjugated Polymer Films on Arbitrary Substrates

This paper presents a protocol for reactive vapor deposition of poly(3,4-ethylenedioxythiophene), poly(3,4-propylenedioxythiophene), and poly(thieno[3,2-b]thiophene) films on glass slides and rough substrates, such as textiles and paper.

Transcript

The overall goal of this experiment is to create conformal coatings of conducting or semi-conducting polymer films on rough and textured substrates using a custom designed reactive vapor deposition chamber. This method allows soft electronic materials to be deposited on unconventional substrates to fabricate unique devices such as textile electronics. The main advantage of our chamber is that a broad section of polymers can be vapor deposited, meaning that structured diverse conjugated polymer films can be created.

To begin the procedure, place 50 milligrams of ProDOT in a quartz martimer ampoule. Connect the ampoule via one fourth inch quick connect couplings and a needle valve. Wrap the ampoule, the metal parts, and the temperature probe with a heating tape.

Connect the ampoule to the tubular chamber, keeping the needle valve open. Then, use long tweezers to place five 1.3 centimeter by 2.5 centimeter substrates of the desired materials adjacent to one another in the substrate heating zone. Place a five milliliter alumina crucible containing 50 milligrams of iron 3 chloride in the oxidant heating zone.

Close the end of the chamber, slowly close the inert gas inlet valve, and start the vacuum pump. Once the chamber pressure is below 525 millitorrs, fill the cold trap dewar with liquid nitrogen. Wrap each of the three heating zones in heating tape.

Connect the tapes to temperature controllers. When the chamber reaches the processing pressure of 52.5 millitorrs, close the martimer ampoule needle valve. Set the oxidant heater to 170 degrees Celsius, and the substrate and martimer heaters to 80 degrees Celsius.

Heat at those temperatures for about ten minutes to fully vaporize the iron 3 chloride from the crucible. Confirm that vaporized iron 3 chloride is depositing as a red solid in the cool region of the tube, between the oxidant and the gas inlet before proceeding. Then, open the needle valve of the martimer ampoule, allow the blue colored thin films to grow to the desired thickness on the substrates.

The needle valve to the martimer ampoules should be opened after iron chloride vapor is formed in the chamber. Otherwise, the martimer vapor will react with oxidant in the crucible to form a polymer layer around the powder surface. Close the martimer ampoule needle valve when the desired film thickness is achieved.

Turn off the heating tapes, and allow the system to cool to room temperature under vacuum. Once the system has cooled, open the inert gas valve, and stop the vacuum pump. Remove the samples from the chamber using long tweezers.

Immerse the samples in methanol for 30 minutes to remove residual unreacted oxidant and martimer. Handle films thicker than 500 nanometers on glass substrates with care, as they may delaminate during rinsing. When the methanol rinsing is complete, carefully dry the samples under a gentle stream of nitrogen gas.

To begin the procedure, place two milliliters of EDOT in a quartz martimer ampoule. Connect the ampoule to the needle valve, and wrap them with the heating tape. Connect the ampoule to the tubular chamber, keeping the needle valve open.

Next, use long tweezers to place 1.3 centimeter by 2.5 centimeter substrates adjacent to one another between the two reagent vapor inlets. Then, close the end of the chamber. In a fume hood, load two milliliters of liquid bromine into a quartz oxidant ampoule.

Equip the ampoule with a closed needle valve. Connect the oxidant ampoule to the chamber via the closed needle valve. Then, start the vacuum pump with the inert gas inlet valve closed.

Once the chamber pressure is below 525 millitorrs, fill the cold trap dewar with liquid nitrogen. Connect the heat tape wrapped martimer heating region to a temperature controller. When the chamber reaches the processing pressure of 52.5 millitorrs, set the martimer heater to 80 degrees Celsius.

Heat at that temperature for about ten minutes to vaporize the martimer. Then, open the oxidant needle valve only slightly as liquid bromine is highly volatile. Monitor the deposition of the blue PE-DOT films so when the flims have reached their desired thickness, close the martimer and oxidant needle valves, turn off the heating tape, and allow the chamber to cool to room temperature under vacuum.

Then, open the inert gas inlet valve, and stop the vacuum pump. When using bromine as the oxidant, rinsing is not needed. The maximum chlorine dubbed polyproDOT film thickness was observed at about two inches from the martimer ampoule inlet.

Atomic force microscophy was used to characterize the morphology. The conductivity of a 100 nanometer thick chlorine dubbed polyproDot film was 106 siemans per centimeter. The removal of residual iron 3 chloride was confirmed with x-ray photo electron spectroscopy indicating that the conductivity is solely from the polymer.

Chlorine dubbed PTT films were deposited on paper, corduroy fabric, and cotton town fabric, ultimately making the pristine white substrates appear dark red. Scanning electron microscopy indicated that the films were uniform in conformal on the three textured surfaces at a micrometer scale. UV vis spectroscopy of the chlorine dubbed polyproDot and bromine dubbed PEDOT films, showed broad featureless absorption bands beyond 600 nanometers, indicating that the films remained P-dubbed after removal of excess oxidant with methanol.

This band was not observed for chlorine dubbed PTT, indicating that it was fully D-dubbed during the methanol rinse. Once mastered, this technique can be done in 2 hours, if it is performed properly. After its development, this technique allowed researchers to transform commercial fabrics and fibers into electronic components, by simply coating them with conducting or semi-conducting polymer films in our chamber.

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Journal (Chemistry)

Journal (Chemistry)

Reactive Vapor Deposition of Conjugated Polymer Films on Arbitrary Substrates

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