Low-cost automated spin coater and thermal annealer for additive prototyping of multilayer Bragg reectors Nathan J. Dawson12 Yunli Lu1 Zoe Lowther1 Jacob Abell1 Nicholas D.

2025-05-02 0 0 8.73MB 20 页 10玖币

侵权投诉

Low-cost automated spin coater and thermal annealer for

additive prototyping of multilayer Bragg reﬂectors

Nathan J. Dawson∗1,2, Yunli Lu1, Zoe Lowther1, Jacob Abell1, Nicholas D.

Christianson1, Aaron W. Weiser3, and Gioia Aquino4

1College of Natural and Computational Sciences, Hawaii Paciﬁc University, Kaneohe,

HI 96744, USA

2Department of Physics and Astronomy, Washington State University, Pullman, WA

99164, USA

3Department of Physics and Astronomy, Youngstown State University, Youngstown,

OH 44555, USA

4College of Engineering, University of Hawaii, Honolulu, HI 96822, USA

Abstract

We present and implement a design for an automated system that fabricates multilayer pho-

tonic crystal structures. The device is constructed with low-cost materials. A polystyrene/cellulose

acetate multilayer Bragg reﬂector was fabricated to conﬁrm the device’s capability. A distributed

feedback laser was also fabricated and characterized. The system has also been used to fabricate

microlasers for a Modern Physics laboratory assignment in which students measure ﬂuorescence,

ampliﬁed spontaneous emission, lasing from one-dimensional Bragg reﬂectors, and lasing from scat-

tering media.

1 Introduction

Photonic crystals are an important class of materials because they interact strongly with visible light

through wave interference. [1, 2] They are observed in nature [3–7] and also ﬁnd many uses in science

and technology. [8–10] One-dimensional photonic crystal are used for antireﬂection coatings, [10] vapor

sensors, [9, 11] and other photonic devices such as distributed feedback lasers. [8, 12–14] Inorganic and

hybrid materials are often used to fabricate multilayer photonic crystals, [15–17] but polymers oﬀer an

inexpensive alternative to many costly materials and their morphologies are more easily manipulated

at the nanoscale. Thus, polymers have emerged as a cost-eﬀective option for fabricating photonic

materials. [18]

Spin coating and annealing each individual layer “by hand” can be a serious undertaking where

each prototype ﬁlm can require hours to days of repetitive steps. Thus, automating the process can

greatly decrease the burden on a student or researcher. In this paper, we describe a low-cost, turnkey

system to spin/anneal polymer multilayer ﬁlms that can be created from common consumer electronics

parts and materials found at local hardware stores. Two applications of multilayer photonic crystals

fabricated with the automated system are also presented – a visibly reﬂective Bragg mirror followed by

a distributed feedback (DFB) laser. Implementation of the DFB lasers into a coherent light emission

assignment for a modern physics laboratory course is also discussed.

∗ndawson@hpu.edu

arXiv:2210.13220v1 [physics.ins-det] 18 Oct 2022

Front view

Dispense f luid

Spin sample

Move to annealing position

Heat sample

Cool sample

Move to dispensing position

Anneal?

yes

More layers? yes

End process

Determine f luid type

Begin process

DC motor

+12 V

Relay 2

+12 V

Relay 1

pin 5

pin 8

pin 7

pin 4

pin 2

Y axis

X axis

USB

Raspberry Pi

Arduino

+ CNC

shield

Linear

actuator

Linear

actuator

Arduino

motor

relay DC

motor

relay

Heat

gun

relay

Fan

relay

ESC

(b)

(c)

(d)

(e)

(a)

40 cm

48 cm

10.2 cm

14.9 cm

7.5 cm

26 cm

21 cm

4.5 cm

3.3V relay Linear actuators

Heat gun

Cooling fan

Syringe holders

Power supply

Spin coater

Sample positioner

Figure 1: (Color online) (a) An image of the assembled multilayer spin coater/annealer system and (b)

the frame constructed with aluminum angles. (c) Diagram showing the electronic component connec-

tions and (d) ﬂow chart. (e) The solid-state relay circuit controlling the DC motor used to relocate the

spin coater between dispensing and annealing positions.

2 Device Design

We describe an automated spin coater and annealer from materials accessible to most educators and

researchers below.

2.1 Body/Frame

The outer box of the frame is shown in Figure 1(a)(b), where images of the constructed device from

diﬀerent perspectives are shown in Section S1 of the supplementary sections. The frame was constructed

of 1/8” thick aluminum angles with 1” legs. Construction angles are manufactured using a standard

set of imperial dimensions, and they are sold at local hardware stores all over the United States.

Construction angles can be made from a variety of materials and we chose aluminum due to the ease

of cutting and drilling relative to a harder material such as steel. Aluminum angles are usually sold

with standard thicknesses of 1/16” increments. The 1/16” thick aluminum angles can be quite ﬂimsy

and the authors recommend using a minimum angle thickness of 1/8” when using aluminum as the

material. Note that the cost per foot of angles increases with the thickness so ﬁnding the minimum

thickness necessary for your device can save on the ﬁnal cost of your device. Also note that the 1/8”

thickness allowed for some bending away from a 90◦angle with a reasonable amount of torque when

mounting the linear actuators at a shallow angle with respect to the vertical direction. Thus, by

choosing a 1/8” thickness, we were able to use the aluminum angles for both the outer frame and the

structures used to support actuating components. Construction angles can also be sold in a variety of

leg sizes, where 1” legs at 1/8” thickness allowed for rigid frame construction and component mounting

without changing sizes; purchasing 8’ standard lengths and cutting the dimensions shown in Figure 1(b)

resulted in residual pieces that were used for mounting purposes (always cut out your largest pieces

ﬁrst). Standard #4-40 machine screws/nuts were used to fasten the aluminum angles together.

The outward-facing legs at the top of the frame holding the linear actuators were ﬂush (no separation

distance) with the legs of the angles of the outer frame. Small end pieces of aluminum angles were used

to mount the heat gun to the interior support angles that ran from the rear of the frame to the front. A

power strip was mounted on the horizontal angle at the rear of the box. The residual aluminum angle

material was fastened to the back of the frame to secure a switching power supply recycled from an

unwanted/outdated computer.

2.2 Components and actuators

2.2.1 Spin coater

The spin coater was made from a brushless direct-current (BLDC) motor of a hard drive taken from

a retired desktop computer. Any BLDC motor with the ability to reach high revolutions-per-minute

(RPM) can be used for the rotational actuator of the spin coater, but 1) the hard drive frame is large

and can be made into a cart by attaching wheels and 2) there are previously documented procedures

for successfully recycling the BLDC motors from computer hard drives for use as spin coaters. [19–22]

The casing was removed followed by the read/write arm components and platter. Depending on the

institution, protocols can be in place that make it diﬃcult to dispose of outdated university property,

where many units may be in queue for removal over an extended period of time. Thus, it can be

easy for educators/students with limited budgets to take advantage of this local stockpile of outdated

materials/devices held by a university’s Information Technology Services.

A 4.5” diameter, miniature Bundt pan was used as the solvent catch bowl. A 1 1/4” diameter hole

was drilled through the center of the Bundt pan from the rear using a hole-saw drill bit. The drilled

edge of the Bundt pan was ﬁled smooth and mounted on the hard drive frame with the motor viewed

through the center hole. A hollow cylindrical spacer was ﬁxed over the rotor to raise the spin coater

plate above the inner lip of the catch bowl. A circular section on the hard drive casing was placed over

the spacer for use as a spin coater plate and fastened to the rotor with three screws. Various models

of magnetic hard drives are in common use, where this particular model attached the disk with a cap

using three oﬀ-axis screws as opposed to a single centered screw.

Some designs for hard-drive spin coaters require a small hole to be drilled through the rotational axis

of the rotor; these designs can use an external vacuum pump to create a seal with the sample substrate.

[19] Pumps can be costly and not all recycled hard drives can support this capability. Therefore, we

used three ∼0.5 cm pieces of Scotch brand mounting tape instead of a vacuum seal. When a rotor

speed above 6000 rev/min was required, we replaced one of the pieces of Scotch brand mounting tape

with a piece of Gorilla Glue Heavy Duty mounting tape. Note that glass substrates were easily removed

from the spin coater plate when only Scotch brand mounting tape was used or when only one piece of

the heavy duty mounting tape was used, but glass substrates would often break from the stress applied

to remove them when all three pieces of mounting tape were heavy duty.

A line of lead-based solder was ironed onto the bottom of the spin coater plate’s outer edge to form

a lip. The dense lead-based lip served two purposes; 1) residual solvent after spinning dripped from

the lip into the solvent catch bowl instead of ﬂowing into the motor, and 2) the heavy lip increased the

plate’s moment-of-inertia to reduce angular jerk when accelerating/decelerating.

2.2.2 Solvent deposition

Spin coating layers of polymeric materials requires the polymers to ﬁrst be dissolved in solvents. The

polymers in spin coated multilayers are limited to pairs soluble in orthogonal solvents, [18] where an

orthogonal solvent only dissolves only one of the two polymers used during processing. During the spin

cycle, the radial acceleration of the rigid substrate allows the viscous ﬂow of material to coat the ﬂat

surface. [23] The coated ﬁlm can be made with relatively uniform thickness across much of the substrate

over a broad range of spin parameters. [24]

In addition to multilayer reﬂectors with quarter-wavelength layer thicknesses, constructive inter-

ference in the reﬂected light can also occur at greater layer thickness intervals. [25] For multilayers

composed of high/low refractive index bilayers, the optimal thickness tfor a layer to reﬂect light at

a wavelength λfollows as t= (m+ 1/2) λ/2n, where nis the refractive index of a single layer and

m= 0,1,2, . . .. A multilayer Bragg grating typically consists of tens to hundreds of individual layers.

The polymer/solvent solutions were deposited on the substrate by actuated syringes above the spin

plate. The syringes were mounted using spare aluminum angle material and 3/4” split ring hangers

as shown in Figure 1(a). The syringes were surrounded by pipe insulation foam before being clamped

tightly into position by the split ring hangers. The heavy duty linear actuators were the most expensive

components used in the automated system. Optical mounts were connected to the actuator and two

washers were tightened around the syringe plunger to hold it in place. Other designs for multilayer

spin coaters employ dispensers fed through tubes. [26] Our system was designed to use 12 ml disposable

syringes which reduces the amount of cleaning required after operation; however, the chosen length of

the linear actuators (20 cm travel length) allows for much larger syringes, if required.

2.2.3 Annealing

In addition to macroscopic mechanical parameters such as angular speed, duration of radial acceleration,

and higher-order time derivatives of the rigid substrate’s angular position (e.g., jerk), open-system

interactions of the polymer/solvent solution with the local environment are also of great importance.

The solvent in the polymer/solvent solution must be allowed to evaporate prior to subsequent layers

being deposited. Therefore, adequate time during the spin process, annealing time, and cooling time

must be allowed for the solvent in each layer to evaporate. Ambient conditions such as temperature and

relative humidity can directly aﬀect the time required to evaporate the solvent in each layer. [27, 28]

Thermal annealing can signiﬁcantly raise the temperature of the sample and surrounding environ-

ment. Therefore, the annealing steps were performed away from the dispensing needles by moving the

spin coater to the rear of the device. To make the spin coater assembly mobile, sets of wheels were

fastened to the front and rear of the spin coater which rolled along the legs of aluminum angles at

the base of the apparatus. A belt-fed linear actuator driven by a DC motor, recycled from a Canon

MG2500 series printer, was attached to the hard disk’s frame and oriented to move towards and away

from the front of the multilayer spin coater system. The use of a belt-driven linear actuator was due to

availability only, where most linear actuators found in computer parts (e.g., optical disk tray or laser

positioner from a CD/DVD drive) would work well for the task of translating the spin coater assembly

between the dispensing and annealing positions. In the back-most position, a 300 W heat gun was di-

rected straight down and ﬁxed to aluminum angle supports. The placement of the aluminum mounting

angles used to hang the heat gun are shown in Figure 1(b). The heat gun was mounted in the optimal

position and orientation to heat the sample based on the distance that the spin coater was able to move

away from the deposition position. A 12 V cooling fan was aﬃxed to vertical rail and oriented towards

the annealing position, where the fan was used to cool the sample following thermal annealing.

2.2.4 Controls and automation

An Arduino with a ZYLTech CNC shield was loaded with the GRBL library and fastened to an interior

aluminum angle. The Xand Yaxes controllers on the CNC shield were connected to the stepper motors

that drove the linear actuators used for depositing the polymer/solvent solutions on the substrate. A

second Arduino was loaded with the code given in Section S2 of the supplementary sections. The pulse

width modulation (PWM), pin 5, acted as a virtual DC signal to an electronic speed controller (ESC)

which controlled the spin coater’s rotor. The ESC did not require a motor with Hall sensors, but instead,

it determined the rotor speed by sensing the induced emf of the stator winding as the magnetic ﬂux

changed during rotation of the motor’s permanent magnets. This type of ESC is colloquially referred

to as “sensorless.” The remaining logic pins were connected to 3.3 V relays with optocouplers. The

relays connected to pin 2 controlled the heat gun by closing a circuit with a 120 V AC source, and the

relay connected to pin 8 closed a circuit with a 12 V source in series with a computer cooling fan. The

relays connected to pins 4 and 7 controlled the tray movement by closing a ±12 V sourced circuit with

the DC motor. Both Arduinos were connected to the USB ports of a Raspberry Pi 3B with a 5” touch

screen which was fastened to the apparatus frame.

2.3 Polymers and solvents

Low-cost, commercially available polymers and solvents were chosen for this study. Polystyrene (PS)

was recycled from an expanded polystyrene cooler used to ship frozen goods. Klean Strip®toluene

was used to dissolve the PS. Cellulose acetate (CA) was taken from graﬁxTM acetate overlay sheets.

文档加载中……请稍候！
如果长时间未打开，您也可以点击刷新试试。

下载文档到电脑，查找使用更方便

10 玖币 0人已下载

立即下载

摘要：

Low-costautomatedspincoaterandthermalannealerforadditiveprototypingofmultilayerBraggreectorsNathanJ.Dawson*1,2,YunliLu1,ZoeLowther1,JacobAbell1,NicholasD.Christianson1,AaronW.Weiser3,andGioiaAquino41CollegeofNaturalandComputationalSciences,HawaiiPacicUniversity,Kaneohe,HI96744,USA2DepartmentofPhysi...

展开>> 收起<<

Low-cost automated spin coater and thermal annealer for additive prototyping of multilayer Bragg reectors Nathan J. Dawson12 Yunli Lu1 Zoe Lowther1 Jacob Abell1 Nicholas D..pdf

共20页,预览4页

还剩页未读，继续阅读

声明：本站为文档C2C交易模式，即用户上传的文档直接被用户下载，本站只是中间服务平台，本站所有文档下载所得的收益归上传人(含作者)所有。玖贝云文库仅提供信息存储空间，仅对用户上传内容的表现方式做保护处理，对上载内容本身不做任何修改或编辑。若文档所含内容侵犯了您的版权或隐私，请立即通知玖贝云文库，我们立即给予删除！

Low-cost automated spin coater and thermal annealer for additive prototyping of multilayer Bragg reectors Nathan J. Dawson12 Yunli Lu1 Zoe Lowther1 Jacob Abell1 Nicholas D.

相关推荐

开通VIP享超值会员特权

作者详情

相关内容

热门标签

举报选择: