Fabrication of 3D Carbon Microelectromechanical Systems (C-MEMS)

Summary

Long and hollow glassy carbon microfibers were fabricated based on the pyrolysis of a natural product, human hair. The two fabrication steps of carbon microelectromechanical and carbon nanoelectromechanical systems, or C-MEMS and C-NEMS, are: (i) photolithography of a carbon-rich polymer precursor and (ii) pyrolysis of the patterned polymer precursor.

Abstract

A wide range of carbon sources are available in nature, with a variety of micro-/nanostructure configurations. Here, a novel technique to fabricate long and hollow glassy carbon microfibers derived from human hairs is introduced. The long and hollow carbon structures were made by the pyrolysis of human hair at 900 °C in a N₂ atmosphere. The morphology and chemical composition of natural and pyrolyzed human hairs were investigated using scanning electron microscopy (SEM) and electron-dispersive X-ray spectroscopy (EDX), respectively, to estimate the physical and chemical changes due to pyrolysis. Raman spectroscopy was used to confirm the glassy nature of the carbon microstructures. Pyrolyzed hair carbon was introduced to modify screen-printed carbon electrodes ; the modified electrodes were then applied to the electrochemical sensing of dopamine and ascorbic acid. Sensing performance of the modified sensors was improved as compared to the unmodified sensors. To obtain the desired carbon structure design, carbon micro-/nanoelectromechanical system (C-MEMS/C-NEMS) technology was developed. The most common C-MEMS/C-NEMS fabrication process consists of two steps: (i) the patterning of a carbon-rich base material, such as a photosensitive polymer, using photolithography; and (ii) carbonization through the pyrolysis of the patterned polymer in an oxygen-free environment. The C-MEMS/NEMS process has been widely used to develop microelectronic devices for various applications, including in micro-batteries, supercapacitors, glucose sensors, gas sensors, fuel cells, and triboelectric nanogenerators. Here, recent developments of a high-aspect ratio solid and hollow carbon microstructures with SU8 photoresists are discussed. The structural shrinkage during pyrolysis was investigated using confocal microscopy and SEM. Raman spectroscopy was used to confirm the crystallinity of the structure, and the atomic percentage of the elements present in the material before and after pyrolysis was measured using EDX.

Introduction

Carbon has many allotropes and, depending on the particular application, one of the following allotropes can be chosen: carbon nanotubes (CNTs), graphite, diamond, amorphous carbon, lonsdaleite, buckminsterfullerene (C₆₀), fullerite (C₅₄₀), fullerene (C₇₀), and glassy carbon^1,2,3,4. Glassy carbon is one of the most widely used allotropes because of its physical properties, including high isotropy. It also has the following properties: good electrical conductivity, low thermal expansion coefficient, and gas im....

Protocol

1. 3D Human Hair-derived Carbon Structure Fabrication

NOTE: Use personal protective equipment. Follow laboratory instructions to use the instruments and to work inside the laboratory.

1. Prepare collected human hair by washing it with DI water and drying it with N₂ gas.
2. Arrange the hairs as desired, such as in parallel strands, cross over, with two hairs wound together, etc.
3. Attach the hairs to a silicon substrate using SU8 or keep them directly in a ceramic boat.
4. Place the hair-attached silicon substrate or boat into a furnace.
5. Turn on the furnace and open the valve of an....

Results

A schematic of the fabrication process for human hair-derived hollow carbon microfibers is shown in Figure 1. The carbonized human hair was characterized using SEM to estimate the shrinkage. The hair diameter shrank from 82.88 ± 0.003 µm to 31.42 ± 0.003 µm due to the pyrolysis. Scanning electron microscopic (SEM) images of various patterns made using hair-derived carbon microfibers are shown in Figure 2. The atomic percentages o.......

Discussion

In this paper the methods for manufacturing a variety of carbon microstructures based on the pyrolysis of natural precursor materials or photo-patterned polymer structures were reported. The carbon materials resulting from both the traditional and non-conventional C-MEMS/C-NEMS processes are typically found to be glassy carbons. Glassy carbon is a widely used electrode material for electrochemistry and also for high-temperature applications. The microstructure of glassy carbon is composed of both crystalline and amorphou.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
SU8-2100	Microchem	Product number-Y1110750500L
Spinner	Laurell Technologies Corporation	Model-WS650HZB-23NPP/UD3
Hotplate	Torrey Pines Scientific	HS61
UV-exposer	Mercury Lamp, SYLVANIA	H44GS-100M, P/N-34-0054-01
Photomask	CAD/Art		No number
Developer	Microchem	Y020100 4000L
DI water system	Milli Q	ZOOQOVOTO
IPA	CTR Sientific	CTR 01244
N2 gas	AOC Mexico		No number
Furnace	PEO 601, ATV Technologie GMBH	Model-PEO 601, Serial no.-195
Si/SiO2	Noel Technologies