Control Engineering for the Processing of Advanced

Functional Materials Final Report for CHEME 5650, Advisor: Detlef Smilgies

Huawei Zhou May 21, 2016

M.Eng. Student

Chemical and Biomolecular Engineering

Cornell University, Ithaca, NY 14850

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Table of Contents Acknowledgement .................................................................................... 2

Abstract ..................................................................................................... 3

Introduction ............................................................................................... 3

Design of Equipment Setup ..................................................................... 4

Overview of Equipment Setup .............................................................. 4

Parts Designed ....................................................................................... 7

Control of Equipment and Experimental Parameters ............................ 7

Control of Equipment ............................................................................ 7

Control of Experimental Parameters .................................................... 8

Coating Procedures and Experiments .................................................... 9

Procedures for Coating ......................................................................... 9

Coating of Materials ............................................................................. 10

Fabrication of Field-Effect Transistors ............................................... 12

Results and Discussions ....................................................................... 13

Conclusion .............................................................................................. 20

Supplemental Information ...................................................................... 21

Detailed Stepping Motor Control Guide ............................................. 21

Detailed Procedure for Coating .......................................................... 24

References .............................................................................................. 30

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Acknowledgement First of all, I would like to thank my principle advisor, Dr. Detlef Smilgies for the

opportunity to be doing this project as my Master of Engineering project. It has been a fun and

educational journey for me as a M.Eng student. I have learned great things from not only project

materials, but on how to design and conduct research experiments as well. Additionally, Dr.

Ruipeng Li has also provided great help and insights on coating experiments and general

procedures in the lab. I want to thank him for his help in the lab and at the beamline.

Also, I would like to address my appreciation to my fellow students and student worker,

Mr. Willy Halim and Miss. Siming Gao. Their help and coordination have made my experience in

the lab a wonderful one. They have always helped me throughout this year. Our team of

students have worked great with each other.

Lastly, I want to thank Mr. Kevin Whitham from Prof. Hanrath’s group for providing the

substrates for me to grow the field-effect transistors, and Mr. Steve Kriske from Cornell Center

for Materials Research on providing and training me on the probe station for testing the devices

I grew.

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Abstract Solution deposition processes are under booming development recently. In this project,

the objective is to build upon the current setup of the equipment to perform slot-die coating.

After designing additional parts to support the coating head, I have learned to control the

coating process and performed coating of water, isopropanol, anthracene/isopropanol, brilliant

yellow dye, indigo carmine dye, and pyrene/toluene solution. During coating, the pumping speed

for the solutions is typically around a few hundred to one thousand microliters per hour, and the

coating head moves at a speed between 0.1 and 10 mm/s for the desired dry film thickness.

The substrates are heated to around 50 °C with a resistive heater, enhancing the evaporation

rate. Coating of these solutions has led to more understanding of the meniscus driven

processes, as well as the morphology and electronic properties (charge carrier transport

mobility) of the small molecules.

Introduction Solution processing technology has been a novel field for the controlled deposition of

functional materials. As a fast developing field, many new technological ideas and findings

appear quickly. In general, solution-based deposition of materials enables coating at relatively

cheaper cost compared to traditional vacuum-based methods. Relying on evaporation of the

solvent to grow well-defined thin films, solution coating processes can generally be operated at

lower temperature (below 100 °C), and at ambient pressure. Although the quality of the coating

layers deposited by solution technologies are intrinsically lower than those deposited in vacuum

because of nucleation conditions, it is nonetheless a promising method for growth of materials

since the price competitiveness and process throughput of this technology is far beyond the

capability of vacuum-based ones. As traditional silicon based, and III-V group crystalline

semiconductors are being developed to their theoretical limits, organic semiconductors have

found their niche in the world of electronics. Using organic material as the active layer for light

emitting diodes (LED), electrode for fuel cells, solar panels, and field effect transistors have

been receiving huge attention.1,2,3

One of the applications of solution deposition process is to deposit organic thin films. As

one of the solution processing technologies, slot-die coating has shown great potentials in its

ability to produce relatively uniform organic film at industrial scale continuously. A schematic of

the slot-die coating process is shown in the figure below:4

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Figure 1. A schematic of a slot-die coater.

As seen in figure 1, this kind of meniscus-driven coating allows uniformity in the thickness of the

solution layer deposited on the substrate. The guiding concept for understanding the slot-die

coating process is that any excess flow into the coater after the coating head is filled equals to

the amount of solution deposited on the substrate. This allows precise control of the deposited

material based on the flow rate into the coating head.

In our lab at Cornell High Energy Synchrotron Source (CHESS), a coating setup based

on a coating head by FOM Technologies is was designed and built by a previous MEng student,

George Guo The objective of my project is to enhance the equipment setup and control the

equipment during coating runs for precise growth of organic electronic materials. Also, coating

of various materials mentioned before in this report has been performed in the lab or at the

CHESS D1 beamline with in-situ Grazing-Incidence Wide-Angle X-ray Scattering (GI-WAXS)

analysis. FET devices have also been made with this coating method; their charge carrier

transport mobility and Ion/Ioff have been tested at the probe station at Cornell’s Center for

Materials Research (CCMR).

Design of Equipment Setup

Overview of Equipment Setup

The relevant equipment to perform a slot-die coating experiment can be generalized in

the following categories: stepping motor system (controller and motor), slot-die coater, heating

source, vacuum pump, solution feed, and characterization tools. Equipment used for the coating

project is shown in figure 2 below. The polarized microscope, the NE-1000 syringe pump, the

Thor Labs stepping motor, and the coater are labeled. A detailed view of the coating head is

provided in figure 3. Figure 4 shows the temperature controlling unit with a voltage source to

heat or cool the coating platform. The voltage source has been switched out to a direct voltage

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source due to failure of the Peltier layer that controls the temperature of the coating stage.

Figure 5 shows the NE-1000 syringe pump’s user interface. During a normal coating run, the

substrate is often times at an elevated temperature to drive evaporation of the solvent. The

aluminum rod and spring connected to the slider on the coater move the slider and

consequently the coating head. The syringe pump delivers the target solution to the coating

head. After the dead volume within the coating head is filled, the excess solution is deposited

onto the substrate. The substrate is held onto the platform with a vacuum pump. Solvent

evaporation and drying and crystallization of the deposited film can be filmed in-situ with the

cross-polarized microscope.

Figure 2. Photos of the coating system. The respective parts are labeled around the figure.

Microscope

Stepping Motor

Syringe Pump

Coater

Designed

Part 1

6

Figure 3. A detailed view of the coating head and platform.

Figure 4. Photo of the temperature control system. PID controller is on the top and the voltage

source is on the bottom.

Solution Inlet

Moving Slider

Vacuum

Inlet

Designed

Part 2

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Figure 5. NE-1000 Syringe Pump.

Parts Designed

Based on the existing equipment, I have designed additional parts that can support and

enhance the function of the coating head through AutoCAD. The three parts designed are both

aluminum extrusions. The first part, shown in figure 1, is a new holder for the coating platform.

Compared to the previous one, this one allows more room to fit the coater and the microscope.

It also supports the coater better as the thickness of this bracket is larger than the previous one.

The second part was designed after we determined to reverse the alignment of the coating head

and coating direction. It extends the coating heat to be at the center of the coating platform. The

third part was designed during my second semester, which is another moving slider for the

coating head. It allows more room to be available for the coating head to be seen during

experiments. This enables the x-ray beam to be received while doing experiments at the D1

beamline.

Control of Equipment and Experimental Parameters

Control of Equipment

Control of equipment consists of controlling the syringe pump, the temperature controller,

and the stepping motor. The temperature controller was built during a previous MEng project

(George Guo) Tuning the temperature control was done by Dr. Smilgies. The time to reach a

steady state of 50 °C is less than 10 min with less overshooting than in initial tests. However the

Peltier layers that heat the coating stage had been repeatedly failing due to unknown

fluctuations in the PID unit. Hence the voltage source was switched out later on for a direct

source with no built-in PID control. A control-less source cannot automatically reach the set

point and requires manually changing the voltage to reach the desired temperature. A closer

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look should be taken into the PID controller by my successor to fully automate the control for

temperature.

Controlling the syringe pump was first done manually before purchasing a software

package for pump control (SyringePumpPro). After inputs of the diameter of the specific syringe

(B-D 1mL, SGE 250 µL glass, and SGE 1mL glass, all Luer-Lok) are put in, the syringe pump

can pump or withdraw the target solution. The purging option can perform pumping or

withdrawing processes at the maximum rate without having to manually enter the pumping rate.

The calibrated syringe diameters are close to the data provided in SyringePumpPro, which has

built-in feature for selection of specific types of syringes.

Control of the Thor Labs stepping motor and controller is realized through the APT user

software. Through settings, one can control the stepping motor’s speed, stepping distance,

acceleration, deceleration, stopping mode, and target locations. Typically for coating runs, the

speed of the motor is between 0.1 and 10 mm/s. Since the total distance of coating is around 65

mm, a normal coating run takes around 11 min for the slowest speeds of the motor. A detailed

guide for how to control the stepping motor can be found in the supplemental information

section of this report.

Control of Experimental Parameters

For coating organic electronic materials, the desired dry film thickness generally is

around 100 nm. From simple estimation, the required solution flow rate of a specific solution to

grow 100 nm of dry film is shown in equation 1 below.

𝑓 =𝑊𝐺𝑆𝜌

𝐶 (1)

where W is the width of the slot (6.35 mm), G is the desired dry-film thickness (100 nm), S is the

motor speed, ρ is the density of the dry material, and C is the concentration of the solute

electronic material inside the solution. For rubrene, the density of solid bulk material is 1.176

g/cm3. Assuming that the concentration of rubrene solution is 5 mg/mL, and pumping rate is at

1000 µL/hr, which is a reliable pumping rate, the estimated dry-film thickness is shown in table 1

below. If the coating speed is limited to 1 mm/s for morphology concerns, the pumping rate can

be decreased to 537.6 µL/hr for the dry-film thickness to remain at 100 nm.

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Table 1. Estimated Dry-Film Thickness of Rubrene Coated by Slot-Die Coating.

Concentration (mg/mL)

Pumping Rate (µL/hr)

Coating Speed (mm/s)

Dry-Film Thickness (nm)

5 1000 0.1 1859.9

5 1000 1 186.0

5 1000 10 18.6

It is important to note that table 1 only presents a rough estimation of the dry-film

thickness of rubrene. It does not take into the account that the thin film may be more loosely

packed than bulk rubrene crystals. The actual dry-film thickness should be larger than the

estimated value, but should not differ from these values by much.

Coating Procedures and Experiments

Procedures for Coating

Coating of organic electronic materials can generally only be done at low temperature to

preserve the structure and the chemical properties of the target materials. For solution

processes, it is often desired use temperatures slightly above the ambient temperature to

enhance the evaporation of the solvent material. For our processes, we have kept the substrate

temperature at between 50 and 70 °C for enhanced evaporation.

To start a coating run, generally the temperature control has to be activated first due to

the slow response time of this controlling unit. However, since the temperature is kept constant

during coating, the response of the controller does not pose a problem. Then the target solution

of certain concentration (10, 15 mg/mL) is withdrawn into the syringe manually. This has to be

done slowly to avoid excess air bubbles. Air bubbles can be compressed more than the solution,

which not only changes the composition of flow if pumped out, but also changes the flow rate of

the solution. After removing all of the air bubbles inside the syringe, the capillary tubing, about

0.3 mL in volume, can be connected to push the solution to the coating head via the syringe

pump. The purging operation can be used to fill up the tubing faster. Once the entire tubing is

filled and the solution starts to fill the dead volume in the coating head, which is around 4.23 μL,

a smaller pumping speed should be entered manually (~1 mL/hr). After the initial puddle is

dropped onto the substrate, the stepping motor control has to be initiated for coating, and videos

during the experiment can be taken with the microscope through the Debut Video software.

When the stepping motor has moved the coating head to the final position, everything should be

stopped except for the temperature control. A detailed check list for the coating process can be

found in the supplemental information section. For the ease of controlling variables, the coating

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speed vs. pumping rate ratio have been kept constant (1 mm/s : 1 mL/hr) for the same dry-film

thickness for the same film developed.

Coating of Materials

Coating of water was done for preliminary testing purposes on checking if the equipment

system can function properly during coating of other materials as water ischeap. For practicing

purposes, multiple runs of water coating were done to familiarize myself with the coating

processes. I developed the procedures for a normal coating run while practicing with water. Also,

water is non-hazardous and easy to clean up. The water practice runs have returned valuable

information that allowed me to further coat other materials with more knowledge. It was realized

that the pumping speed has to be at least 200 μL/hr for the syringe pump to operate properly for

the B-D 1mL syringe even though its manual states a lower possible flow rate. If using the 250

µL syringes, the pumping speed can be higher. Wetting of the coating head was observed when

water first came out of the coating head, but it was restrained to a relatively small area. Food

coloring was used to make the water film easier to be seen.

After these tests, common organic compounds were coated for seeing if the organic

molecules behave any different from the inorganic ones. Isopropanol (IPA) was coated onto

glass substrates. Interestingly, the IPA wetted the coating blade at a much higher extent

compared to water. Shown in figure 6, the wetting line can be seen on the front side of the

coating head, extending along the blade’s width, covering the width completely up before

forming a connection with the substrate. This has resulted in coating a much wider strip of

material than desired. Also, since the IPA is only pushed out of the coating head from the center,

the meniscus shrinks in length while coating precedes. At the center of the coating head, we

believe that slot-die coating still exists since the meniscus remains constant after a certain

length of coating. On the sides of the substrate, however, the coating performed can be

characterized as knife coating.

Following this, an anthracene solution in isopropanol was coated onto the substrate.

After pumping out the entire syringe, all of the solution remained on the coating head, in the

coating head, or in the tubing. A much higher extent of wetting occurred. The solution wetted the

back side of the coating head as well for anthracene/IPA solution. Change in the coating head

design has to be done in the future to improve the wetting condition.

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Figure 6. Wetting of the coating blade while coating isopropanol on glass substrate.

Coating of brilliant yellow, indigo carmine dyes, and pyrene have been done in the

second semester. Brilliant Yellow is a water-soluable dye that has been used for LED devices1a.

Indigo Carmine is a food color (Blue1) and use in supercapacitors has been explored2. Both

molecules are chemically similar featuring an aromatic ring system and sulfonate groups to

ensure solvability in water. The molecules were primarily studied because of their non-

hazardous character and their ultimate green solvent, water. Pyrene is a more conventional

conjugated molecule with good solvability in toluene.

The meniscus guard has been installed prior to starting these experiments for enhanced

control of the width of the coated film. Brilliant yellow and indigo carmine dyes are dissolved in

water for coating, and pyrene has to be dissolved in toluene. The structures of these chemicals

are shown in figure 7. Coating of brilliant yellow and indigo carmine have resulted in relatively

confined-width films, whereas extensive amount of wetting of the coating head was observed

when coating toluene based solutions. Toluene can also dissolve the B-D plastic syringes,

which have to be replaced by glass syringes for future coating experiments.

Figure 7. Chemical structures of (a) indigo carmine, (b) brilliant yellow, and (c) pyrene.

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Fabrication of Field-Effect Transistors Substrate Measurement

Recently research groups have given thought of more sustainable materials that do not pollute

the environment and are compatible with wearable or even edible electronics7a,8, for instance for

biomedical applications. With the good success in coating brilliant yellow and indigo carmine,

we became interested in the electronic mobility of such films. The mobility can be conveniently

measured in a field-effect transistor (FET) structure.

FET substrates were given by Kevin Whitham, and I have performed measurements on the

dimensions of the channel’s length and width. The FET channel was formed by interdigitating

gold electrodes which creates a large channel length and thus helps to be able to measure even

low mobilities. An image of the FET device channel is presented in figure 8. The bright parts are

the gold electrodes, and the blue region is the uncoated SiO2 gate material (200nm). This

measurement was performed with an imaging microscope at CCMR. The average channel

width is about 5 µm, and the total length of the channel is 0.4771 m. These parameters are

crucial for calculations of the charge carrier transport mobility of the active materials in the FET

we grow, which is discussed further later in this report.

Figure 8. Image of a part of the FET device channel.

Coating

Indigo carmine and brilliant yellow dyes were coated onto the FET substrates. Out of the

three sample devices that were grown for each of the material, two of them were coated at a

pumping rate of 1 mL/hr and a coating speed of 1 mm/s. The other one was coated at 0.75

mL/hr and 0.75 mm/s. The gap between the meniscus guard and the substrate was kept at 200

nm for all coating experiments mentioned. The coated FETs are shown in the results section.

I-V Test

Multi-sweep I-V measurements were carried out for the FET structures grown. The

probe station at CCMR can provide vacuum down to 10-3 mbar in roughly 15 mins. For testing

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the mobility of indigo carmine and brilliant yellow films, gate-source voltage (Vgs) and source-

drain voltage (Vds) are set to multiple constant values (0-50 V in increments of 5V) and

sweeping (0-50 V in increments of 1 or 0.1 V) respectively, and source-drain current (Ids) is

measured with respect to the voltage bias from the gate and source. It is okay to test with

constant Vds and sweeping Vgs, but the results are the same. Also, due to the unknown

characteristics on these two materials on whether they are p- or n-type semiconductors, both

positive and negative polarities in the voltage sources were tested.

Mobility Calculations

Calculation for the charge carrier transport mobility (µ) can be done with I-V

measurements on the FET devices. Equation 2 and 3 below present the way to determine the

mobility.5 The negative signs in these equations assumes that that the semiconducting material

is p-type, which is common for most of the organic semiconducting materials. For n-type

materials, the negative signs should be eliminated. Cox is the capacitance of the gate oxide (200

nm SiO2). The dielectric constant of SiO2 is 3.8, through which the actual permittivity of SiO2 can

be calculated by multiplying the vacuum permittivity of 8.854*10-2 F/m, which equals 0.3365

F/m.6 Cox can then be calculated by dividing the actual permittivity by the thickness of the oxide,

which equals 168.25 F/cm2. W and L are width and length of the device channel, which have

been specified earlier.

𝐼𝐷𝑆 = −𝜇𝐶𝑜𝑥𝑊

𝐿𝑉𝐷𝑆(𝑉𝐺𝑠−𝑉𝑇) (2)

𝐼𝐷𝑆 = −𝜇𝐶𝑜𝑥𝑊

2𝐿(𝑉𝐺𝑠−𝑉𝑇)2 (3)

Matlab was used to analyze the data of the I-V curve and calculate mobilities. The

developed Matlab code is included in the supporting information section. Smoothened trends

were used to estimate the start of the saturation region, in which Vds=Vgs-VT at the beginning.

Results and Discussions Control

Based on the experimental findings stated above, the coating process control still needs to be

developed further to perform coating of rubrene or other semiconducting materials. As of now, it

is realized that coating from the current slot-die coater would result in serious wetting of the

coating head. This can not only increase the volume needed for the solution to reach the

substrate, but also changes the mechanism of coating on the sides of the substrate. Finally, for

resolution reasons the coated strip should have a width of 0.25” (6.35 mm) for the planned in-

situ x-ray scattering studies. To better control the flow of solution, a meniscus guard is most

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likely needed in future coating experiments.7 Secondly, the mechanism of flow between the

coating head and the substrate has to be better understood before a more precise estimation of

the deposited layer thickness can be obtained.

Pyrene Coating

Pyrene was dissolved in toluene to be coated onto cleaned glass substrates at a

concentration of 10 mg/mL. This coating experiment was performed at the beamline. Coating

speed of 1-10 mm/s were used. The resulted pumping rate were 1-10 mL/hr. Smaller pumping

rates were not used because of the extreme level of wetting between toluene and the coating

head. The solution had to be pumped out at a higher rate to avoid crystallization on the coating

head. Also, since we only had plastic syringes, and toluene can dissolve the syringe, solution

had to be withdrawn into the capillary without reaching the syringe. This provided difficulties

sometimes as pumping out the entire volume of 0.3 mL in the capillary tube does not trigger a

puddle formed on the substrate. Thus only the higher pumping rates were used to ensure

growth on the glass substrate. Furthermore, due to the high affinity between toluene and the

glass substrate, solution wetted the entire width of the substrate. This induces a non-uniform

pyrene film. Alternative solvents were researched, but since pyrene has only aromatic rings, it is

hard for other types of solvents to dissolve it at the concentration we desired.

The cross-polarized microscope has provided direct images on the morphology of the

pyrene film in the real space. Figure 9 below presents the some of the films grown on glass

substrate. From this figure it can be seen that the direction of the coating head/meniscus guard

plays an important role in the growth direction of the pyrene film. The crystallized pyrene

molecules tend to form “feather-like” structure in which the molecules stick together around a

center wire of molecules. Comparing the figure 9 (a) and (c), the morphology does not differ

much from each other. The direction of coating still has an important effect in the film deposited.

This can be due to fast evaporation of toluene in air at 50 °C. The deposited films looked more

like powders than a continuous film from eye observation. The directional alignment can be

seen as well when observing the film by eye.

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Figure 9. Image of (a) PY1 (1 mm/s, 1 mL/hr, 50 °C), (b) PY3 (3 mm/s, 3 mL/hr, 50 °C), and (c)

PY6 (10 mm/s, 10 mL/hr, 50 °C) taken from the cross-polarized microscope.

Results from GI-WAXS images basically coincides with the observations under the

microscope. Figure 10 below presents the GI-WAXS images taken in-situ at the beamline during

coating. For figure 10 (a) and (b), it can be observed that although strong signals are seen at

positions directly above the beam, and to the right of the beam, the images have extensive

amount of bright spots that forms rings around the beam. This can indicate a powder-like

material since directional alignment is almost nonexistent. Counterintuitively, the film grown by

the fastest coating speed (10 mm/s) had the best image, and the strong signals can be

interpreted into strong directional alignment without much power-like material.

(a) (b) (c)

Figure 10. GI-WAXS images of (a) PY1, (b) PY3, and (c) PY6.

Indigo Carmine Coating

Indigo carmine dye was dissolved in water with two different concentrations: 10 and 15

mg/mL. To clarify, the samples grown with in-situ GI-WAXS are from 10 mg/mL solution; the

FET samples were from 15 mg/mL solution. In terms of the range for coating speed and

pumping rate, coating speeds between 0.5 mL/hr and 20 mL/hr have been tried. The pumping

rate varies accordingly to the coating speed stated previously in this report. Although slower

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speed (~1mm/s) is desired for maximizing the directional impact from the meniscus guard, the

ones grown at higher speed has shown better results in terms of crystallization. Figure 11 below

presents the images from coating at 0.5 mm/s, 1 mm/s, 2 mm/s, 15 mm/s. It can be seen that

the crystalline structure can be better seen starting at 2 mm/s. Although this can be due to the

fact that switching to a bigger sample incident angle (0.15 to 0.2) helps strengthening the image

intensity, sample IC 15 definitely had better crystalline structure as all of the five spots (1 right

above the beam stop, 3 further above the beam stop, and 1 to the right of the beam stop) have

strong signals. Strong ring-like signal in figure 11(e) and (f) indicates that there is still water

present by the end of the image shooting (30s). Focusing on IC15, as the coating head passes

by the beam stop, solution started to be deposited onto the substrate. 5.4 seconds after the

head passes by, crystals were observed by the beam receiver. By the end of the 30 s run, water

had not been completely evaporated. This may suggest that crystallization without impact from

the meniscus guard yields better crystal structure, which was not expected. This reasoning is

still not confirmed valid.

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(a) (b) (c)

(d) (e) (f)

Figure 11. GI-WAXS images of (a) IC11 (0.5 mm/s, 0.5 mL/hr, 70 °C), (b) IC22 (1mm/s, 1mL/hr,

70 °C), (c) IC13 (2 mm/s, 2 mL/hr, 70 °C), and (d)-(f) IC15 (15 mm/s, 15 mL/hr, 70 °C) samples.

(d)-(f) are time-elapsed images of the coating process of coating IC15. (d) is the moment when

the coating head passes right through the beam. (e) is 5.4 seconds after the coating head

passes, which is when crystallization was first observed. (f) is the end image of the image series.

Three FET devices were fabricated with slot-die coating of indigo carmine. Shown in

figure 12, the coating parameters used to deposit indigo carmine have been listed in the figure

caption. The concentration of indigo carmine/water solution is 15 mg/mL. From eye observation,

the three samples all have indigo carmine covering the entire channels.

(a) (b) (c)

Figure 12. Indigo carmine based FET samples. (a) sample 1: 1 mm/s, 1 mL/hr, 50 °C, (b)

sample 2: 1 mm/s, 1 mL/hr, 50 °C, different direction, (c) sample 3: 0.75 mm/s, 0.75 mL/hr,

50 °C.

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Mobility of both holes and electrons were tested for samples 1 to 3 due to previous

literature on indigo being an ambipolar semiconductor, meaning that it has both donating part

and accepting part for electrons.8 The I-V curve of the 3 samples as an n-type semiconductor

are shown below in figure 13 a)-c). Sample 1 was tested for hole mobility, while the other two

had failed after a week of storage. The p-type I-V curve of sample 1 is also shown in figure 13.

A peculiar thing is that in figure 13 d), even though the gate-source voltage is 0, the current

across the device changes with respect to source-drain current. The exact mobility of indigo

carmine could not be determined since no constant threshold voltage could have been found.

a) b)

c) d)

Figure 13. I-V characteristics of a) sample 1, Vds=0-50V, stepping increment: 1V, Vgs=2-10V,

stepping increment=2V, b) sample 2, Vds=0-15V, stepping increment: 0.1V, Vgs=2-10V, stepping

increment=2V, c) sample 3, Vds=0-50V, stepping increment: 1V, Vgs=2-10V, stepping

increment=2V, d) sample 1, Vds=0-(-50)V, stepping increment: -1V, Vgs=0-(-50)V, stepping

increment=-5V.

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Brilliant Yellow Coating

Brilliant yellow dye was deposited on glass substrates and analyzed by GI-WAXS at the

beamline. Although the films looked nice by eye, there was no sign from GI-WAXS that it

crystallized under the growth. We have proceeded the research on brilliant yellow dye on its

charge carrier transport mobility.

(a) (b) (c)

Figure 14. Brilliant yellow based FET samples. (a) sample 4: 1 mm/s, 1 mL/hr, 50 °C, (b) sample

5: 1 mm/s, 1 mL/hr, 50 °C, different direction, (c) sample 6: 0.75 mm/s, 0.75 mL/hr, 50 °C.

The charge carrier transport mobility of brilliant yellow is also calculated through their I-V

characteristics. The I-V curves are presented in figure 15. Sample 6 was not successfully made

so the I-V curve is not displayed here. After a week of storage, sample 4 and 5 have failed so

there is no data available to calculate the hole mobility. Electron mobility can be determined by

the Matlab code developed as well.

The threshold voltage, which is supposed to be independent of the test conditions, have

yielded unexpected results. In general, the threshold voltage Vt is found in graphs of Ids vs. Vg,

with different constant Ids. The gate voltage required for the current to be non-zero is the

threshold voltage. As seen now in figure 15 c) and d), it appears to be abnormal since at a

constant Vds, Ids decreases as Vg increases. This behavior is addressed by Sirringhaus, et al.9 It

may be necessary to test the devices at a higher Vg for mobility measurements. Graphing Ids vs.

Vg has shown that at Vd=0V, Ids is always negative as the second-order polynomial fit indicates

that the curve never hits the x-axis; at Vd=20V, Ids is always positive. This has presented great

difficulty in trying to determine a constant threshold voltage for mobility calculations.

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a) b)

c) d)

Figure 15. I-V characteristics of a) sample 4, Vds=0-20V, stepping increment: 1V, Vgs=2-10V,

stepping increment=2V, b) sample 5, Vds=0-35V, stepping increment: 1V, Vgs=2-10V, stepping

increment=2V, c) Ids vs. Vg characteristics of a), d) Ids vs. Vg characteristics of b).

Conclusion After spending two semesters on this project, the slot-die coating setup has been

completed, with various materials coated in the lab and beamline at CHESS. Realization of fully

computerized control on station temperature, fluid pumping and coating head movement have

been achieved. In terms of coating experiments, we have found out that indigo carmine and

pyrene crystallize well on glass substrates at 50 °C, but brilliant yellow does not seem to

crystallize. GI-WAXS on these molecules was performed at the beamline to determine the

crystallinity of the coated materials. In general, a fast coating speed generates a more free-

crystallizing film, which does not essentially give the worst results in terms of crystallinity. The

effect of the meniscus guard can still be seen even at these faster coating speeds.

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During experiments, an excessive amount of wetting from toluene solutions on both the

coating head and the glass substrate was observed. This can be mainly attributed to the wetting

between toluene and the coating head. This issue can be looked further in the next step. If the

surface of the coating head can be treated with toluene-phobic materials, nice and confined

films can be coated with toluene as the solvent.

My preliminary mobility measurements for coated films of indigo carmine and brilliant

yellow showed some problems. Mobility values, if possible to obtain, should not be considered

final. In the future, further analysis on charge carrier transport mobility of edible and wearable

organic small molecules can be carried out. The FET devices have to be grown in a more

controlled environment, with an appropriate storage place before tested at the probe station at

CCMR. The charge carrier transport mobility can be determined with confidence if the I-V

characteristics is nice.

Supplemental Information

Detailed Stepping Motor Control Guide The motor controller connects the stepping motor and the PC together. The APT User

application is used to control the controller. Before starting the program on the PC, make sure

that the controller is off. The User Interface of the APT user software is shown in figure 16 below.

Figure 16. Interface of the APT user software

Possible Operations

Pressing the “Home” button moves the motor to the homed position (towards the right)

The “Stop” button stops the moving operation at any time during the operation.

Pressing the “Jog” button incurs a step move of the stepping motor. The upper button moves

the motor in the positive position (to the left), and the lower button moves the motor in the

negative direction (to the right).

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Pressing and holding the “Jog” button incurs constant moving of the motor, either at “single step”

mode, or “continuous mode”, which can be set in the settings.

By entering values in the numbered windows, the motor can change positions on the absolute

scale.

Settings can be viewed and changed by pressing the “setting” button. The settings

interface is shown in figure 17 below.

Figure 17. Settings interface of the APT user software.

Velocities are entered in units of mm/s; accelerations are entered with mm/s^2 units.

Stepping distance is in mm. Stopping mode indicates the current stopping mode when the

moving process is terminated. While set to “Immediate”, the motor stops quickly when moving is

stopped. The “profiled” stopping mode indicates stopping at a deceleration rate defined in the

“acce/dec” entries.

Sequencing of movements

The move commands on the motor can be piled via the move sequencing function by

clicking into the second tab on the top of the GUI interface. Right click in the chart of the move

sequencing interface allows programming the moves desired to be performed by the stepping

motor. The move sequence interface is shown in figure 18 below. The detailed move sequence

programming interface is shown in figure 19 below.

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Figure 18. Move sequencing interface.

Figure 19. Detailed move editor for programming move sequences.

The move editor can deal with relative and absolute positions while selected. The dwell

time option allows the time interval to be put in for the step. The return function calls the return

of motor to the previous position after moving the motor to the designated one. Compiling the

move sequences allows more complicated moves performed by the motor.

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Detailed Procedure for Coating IMPORTANT: Do not move the Aluminum rod connected to the stepping motor. Calibration of

motion limits is needed every time the position of the rod is adjusted, so that the coating stage is

not damaged!

The execution of movement of the stepping motor is simultaneous with the syringe pump and

the microscope.

Cleaning Glass Substrates

1. Rinse with water.

2. Sonicate in acetone for 10 min.

3. Sonicate in isopropanol for 10 min.

4. Sonicate in ethanol for 10 min.

5. Rinse with water.

6. Dry with nitrogen gas.

7. Oven at 105 °C for 10 min.

8. UV/Ozone for 0.5 hr

9. Oven at 105 °C for 10 min.

Making Solutions

1. Calculate the amount of chemicals needed for the amount of solutions.

2. Weight the solute and add solvent to a beaker or vail.

3. Sonicate for 10 min to dissolve.

4. Store in vent hood if needed.

Filling the syringe

1. Disconnect the capillary tube head on the syringe and coating head.

2. Release the syringe from the pump, pump out all possible air in the syringe, and draw

solution into the syringe.

3. Screw the tube to the syringe, put the other end of the tube into the solution, and pump

out all the air in the tubing. Retract the syringe to full volume and install everything back

to the experimental setup.

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Syringe Pump Control

1. Turn on the syringe pump.

2. Open SyringePumpPro software (screenshot of interface shown in figure 20), and

choose the appropriate type of syringe for its diameter value. The interface is shown in

the figure below. When pump is recognized by the software, it shows up in the table.

3. Enter the pumping rate and the to-be-pumped volume, then hit “Set” to update the

settings. Change the direction of flow by selecting “INF” for infusion and “WDR” for

withdrawal.

4. Click “Run All”. When coating has completed, click “Pause/Stop” twice to stop the pump.

Update settings if needed between coating runs.

Figure 20. Software interface of SyringePumpPro for the control of the NE-1000 syringe pump.

Stepping Motor Control (Refer to the “Motor Controller Guide” file for more detailed

information.)

1. Start the Motor Control software.

2. In settings, put in the desired coating speed and proper acceleration.

3. Move the motor to the position at 100mm.

4. Only move the motor between 35mm and 100mm during coating.

5. Coating direction is from 100mm to 35mm (left to right).

6. Initiate movements to 35mm from 100mm after pumping the syringe and observing the

collection of the solution at the tip of the coater.

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Temperature Control

1. Make sure the thermal couple is connected to the heating plate.

2. Turn on the temperature controller and the voltage source.

3. Set the desired temperature on the temperature controller with manual entry, press the

arrow button to confirm the set point.

4. Press the “Out” button on the voltage source to start heating of the coating platform.

Microscope Movie Shooting

1. Start the “Debut Video Capture Software”

2. Turn on the coaxial lighting of the microscope and adjust the brightness with the

controller.

3. Press the “Record” or the “Snapshot” button to capture a movie or a single shot,

respectively.

Coating

1. Put the substrate on the coating platform.

2. Start the temperature control. Set the appropriate coating temperature (~50°C).

3. Turn the micrometer screw on the back of the coater to just touching the substrate.

4. Level the coating head with the two screws located at the top of the coating head.

5. Raise the coating head with the screw on the back of the coater. One full turn would

raise the head by 100 microns. Typical gap is 100 microns.

6. Withdraw solution to the syringe pump. (Refer to the “Filling the Syringe” section above.)

7. Using the syringe pump, pump the solution out to fill all of the dead volume in the coating

head. Stop when starting to see solution at the coating head. Remove extra solution at

the coating head with Kimtech wipes. (Refer to the “Syringe Pump Control” section

above.)

8. Adjust the position of the microscope to ensure good video taken during coating

process. Adjust the lighting if needed. (Refer to the “Microscope Movie Shooting”

section.)

9. Start pumping of the solution with proper parameters (pumping speed, diameter, and

volume to be dispensed).

10. Start the stepping motor with the “Motor Control” software and appropriate parameters

(Motor speed, acceleration/deceleration, and stopping mode). (Refer to the “Stepping

Motor Control” section above.)

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11. Start the movie-taking with the video capture software. (Refer to the “Microscope Movie

Shooting” section.)

12. Stop the syringe pump and video capturing when the stepping motor has reached its

final destination.

Matlab Code for Plotting and Calculation of Charge Carrier Transport

Mobility

Main Code % FET I-V Curve Graphing % Huawei Zhou, 5/16/2016

clear all; close all; clc; filename='sample 1 ds-50_1 gs-50_5 3.txt'; test=importdata(filename); %Access data data=test.data;

% Getting the number of sweeps in the data file a=max(abs(data(:,1))); for i=1:length(data(:,1)) if a==abs(data(i,1)) L=i; break end end

% Extract current profile Vd1=data(1:L,1); Id1=data(1:L,2); Vg1=data(1,3); Vd2=data(L+1:2*L,1); Id2=data(L+1:2*L,2); Vg2=data(1+L,3); Vd3=data(2*L+1:3*L,1); Id3=data(2*L+1:3*L,2); Vg3=data(1+2*L,3); Vd4=data(3*L+1:4*L,1); Id4=data(3*L+1:4*L,2); Vg4=data(1+3*L,3); Vd5=data(4*L+1:5*L,1); Id5=data(4*L+1:5*L,2); Vg5=data(1+4*L,3); Vd6=data(5*L+1:6*L,1); Id6=data(5*L+1:6*L,2); Vg6=data(1+5*L,3); Vd7=data(6*L+1:7*L,1); Id7=data(6*L+1:7*L,2); Vg7=data(1+6*L,3); Vd8=data(7*L+1:8*L,1); Id8=data(7*L+1:8*L,2); Vg8=data(7*+L,3); Vd9=data(8*L+1:9*L,1); Id9=data(8*L+1:9*L,2);

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Vg9=data(1+8*L,3); Vd10=data(9*L+1:10*L,1); Id10=data(9*L+1:10*L,2); Vg10=data(1+9*L,3); Vd11=data(10*L+1:11*L,1); Id11=data(10*L+1:11*L,2); Vg11=data(1+10*L,3);

% Graphing subplot (1,2,1) % plot(Vd1, Id1, 'b', Vd2, Id2, 'k', Vd3, Id3, 'c', Vd4, Id4, 'r', Vd5, Id5,

'g',Vd6, Id6, 'y','linewidth',2) plot(Vd1, Id1, 'b', Vd2, Id2, 'k', Vd3, Id3, 'c', Vd4, Id4, 'r', Vd5, Id5,

'g',Vd6, Id6, 'y',Vd7, Id7,

'm',Vd8,Id8,Vd9,Id9,Vd10,Id10,Vd11,Id11,'linewidth',2) title('sample 1 ds-50V_1 gs-50_5 3') xlabel('Drain Voltage (V)') ylabel('Drain Current (A)') legend('Vg=0V','Vg=-5V', 'Vg=-10V', 'Vg=-15V', 'Vg=-20V', 'Vg=-25V','Vg=-

30V','Vg=-35V','Vg=-40V','Vg=-45V','Vg=-50V','location','northwest')

% Curve Smoothening sm1=smooth(Id1, 0.1, 'rloess'); sm2=smooth(Id2, 0.1, 'rloess'); sm3=smooth(Id3, 0.1, 'rloess'); sm4=smooth(Id4, 0.1, 'rloess'); sm5=smooth(Id5, 0.1, 'rloess'); sm6=smooth(Id6, 0.1, 'rloess'); sm7=smooth(Id7, 0.1, 'rloess'); sm8=smooth(Id8, 0.1, 'rloess'); sm9=smooth(Id9, 0.1, 'rloess'); sm10=smooth(Id10, 0.1, 'rloess'); sm11=smooth(Id11, 0.1, 'rloess');

% Plot smoothened curves subplot (1,2,2) plot(Vd1, sm1, 'b', Vd2, sm2, 'k', Vd3, sm3, 'c', Vd4, sm4, 'r', Vd5, sm5,

'g',... Vd6, sm6, 'y', Vd7,sm7, 'm', Vd8, sm8, Vd9, sm9, Vd10, sm10, Vd11, sm11,

'linewidth', 2) % p-type has 11 voltage sweeps % Plot(Vd1, sm1, 'b', Vd2, % sm2,'k',Vd3,sm3,'c',Vd4,sm4,'r',Vd5,sm5,'g',Vd6,sm6,'y','linewidth',2) % % n-type has 5 voltage sweeps title('Smoothened Curve') xlabel('Drain Voltage (V)') ylabel('Drain Current (A)') legend('Vg=0V','Vg=-5V', 'Vg=-10V', 'Vg=-15V', 'Vg=-20V', 'Vg=-25V','Vg=-

30V','Vg=-35V','Vg=-40V','Vg=-45V','Vg=-50V','location','northwest') saveas( gcf, 'sample 1 ds-50_1 gs-50_5 3.jpg'); % Saves graph

% Calculation of Mobility Mo(1,:)=Mobility(Id1, sm1, Vd1, Vg1); Mo(2,:)=Mobility(Id2, sm2, Vd2, Vg2); Mo(3,:)=Mobility(Id3, sm3, Vd3, Vg3); Mo(4,:)=Mobility(Id4, sm4, Vd4, Vg4); Mo(5,:)=Mobility(Id5, sm5, Vd5, Vg5);

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Mo(6,:)=Mobility(Id6, sm6, Vd6, Vg6); Mo(7,:)=Mobility(Id7, sm7, Vd7, Vg7); Mo(8,:)=Mobility(Id8, sm8, Vd8, Vg8); Mo(9,:)=Mobility(Id9, sm9, Vd9, Vg9); Mo(10,:)=Mobility(Id10, sm10, Vd10, Vg10); Mo(11,:)=Mobility(Id11, sm11, Vd11, Vg11); avmobility=mean(Mo(:,4))

Mobility Calculation Function function [ Mo ] = Mobility( Id, sm, Vd, Vg) % Calculation of Charge Carrier Transport Mobility % Use Capacitance, Width and Length of Channel to Calculate Mobility and % Threshold voltage % Huawei Zhou % 5/18/2016 C=1.68*10^(-6); %200 nm SiO2 capacitance, cm2V-1s-1 W=5*10^(-6); L=0.4771; dsm=diff(sm); dVd=diff(Vd); l=length(Id); for i=1:l; if Id(i)<0 break end end Vth=Vd(i); for b=1:l-1; dId(b)=dsm(b)/dVd(b); end ddsm=diff(dsm); for b=1:l-2; ddId(b)=ddsm(b)/dVd(b); end for i=1:l-2; if ddId(i)<0 && Vd(i)<Vth break end end Mo(1)=Id(i); Mo(2)=Vd(i); Mo(3)=Vth; for c=1:i slope(c)=Vd(i)/Id(i); end aslope=mean(slope); Miu=(Vg-Vth(1))*C*aslope*W/L; Mo(4)=abs(Miu);

end

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