# Poly(hydridocarbyne) as Highly Processable Insulating Polymer Precursor to Micro/Nanostructures and Graphite Conductors

Authors: Aaron M. Katzenmeyer; Yavuz Bayam; Logeeswaran VJ; Michael W. Pitcher; Yusuf Nur; Semih Seyyidoğlu; Levent K. Toppare; A. Alec Talin; Huilan Han; Cristina E. Davis; M. Saif Islam
Journal: Journal of Nanomaterials
 (2009)

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## Abstract

Carbon-based electronic materials have received much attention since the discovery and elucidation of the properties of the nanotube, fullerene allotropes, and conducting polymers. Amorphous carbon, graphite, graphene, and diamond have also been the topics of intensive research. In accordance with this interest, we herein provide the details of a novel and facile method for synthesis of poly(hydridocarbyne) (PHC), a preceramic carbon polymer reported to undergo a conversion to diamond-like carbon (DLC) upon pyrolysis and also provide electrical characterization after low-temperature processing and pyrolysis of this material. The results indicate that the strongly insulating polymer becomes notably conductive in bulk form upon heating and contains interspersed micro- and nanostructures, which are the subject of ongoing research.


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## Body

## 1. Introduction

Poly(hydridocarbyne) (PHC)
is ansp3 hybridized random network carbon polymer, comprised of a monomeric unit containing one carbon-hydrogen and three carbon-carbon single
bonds not unlike hydrogenated tetrahedral amorphous carbon (ta-C:H).Much interest was generated by the synthesis
of this easily processable polymer and the report of its conversion to diamond and
DLC by means of pyrolysis [1]. Diamond has been reported to
have interesting electrical properties [2, 3]
and applications in MEMS [4] and biology [5].And ta-C:H has also been shown to be relevant
to the electrical and biological communities in the form of protective  coatings
in magnetic disk memories [6] and a hemocompatible material [7], respectively.


## 2. Experimental

We developed a new method for the
synthesis of PHC [8] which enables faster, easier
production and makes this interesting material more accessible for research.
The method of synthesis involves the electropolymerization of chloroform (CHCl3)
which proceeds as shown in Figure 1.UV/visible
data collected during the polymerization are consistent with the production of a
polycarbyne, namely PHC [1, 9, 10]. Transmission infrared spectroscopy shows no
evidence of carbon-carbon double bonds, only carbon-carbon single bond and
carbon-hydrogen stretches.Figure 1
Electrolysis of chloroform (CHCl3) in acetonitrile in the presence of tetrafluoroborate results in the production of PHC.It was found that the polymer could be
annealed at100°C for processing as a liquid, in
addition to the known method of suspending it in tetrahydrofuran (THF) or
toluene, without the loss of its electrically insulating nature after cooling; an
~|8nA| current was measured via probe station at room temperature for |5V|
bias. Semiconductor-like behavior was
observed in the I(V) as the sample was heated.Pyrolysis of the PHC polymer was
performed under constant Ar flow at1000°C for 24 hours in a Thermolyne tube
furnace. A blackened bulk material was
produced which we electrically analyzed and characterized via Raman
spectroscopy. This bulk material was
probed (Figure 2) and found to be much more conductive than the annealed
polymer despite exhibiting a nonlinear I(V) for |V|>0.25. This increase in conductivity is rationalized
by the formation of sp2 hybridized carbon constituents during
pyrolysis (see the following).Figure 2
The I(V) plot for the pyrolyzed bulk shows a significant conductivity increase with respect to the annealed polymer.


## 3. Raman Analysis

A vast body of work has been published
on Raman spectroscopy of carbon-based materials and the techniques used to fit
Raman spectra using their individual constituent peaks, and this remains an
active area of research as certain peak contributions are still debated or are of
unknown origin.Nonetheless, a
literature review revealed well-developed theory, which enabled us to curve fit
our sample to good approximation.Figure3 shows the spectrum of our material plotted against that of known diamond,
the intended product of the pyrolysis.
The two broadened features seen in our spectrum occur in the vicinity of
the well-known D (disordered) and G (graphite) peaks that occur around 1360 cm−1 and 1560 cm−1, respectively, [11] in graphitic carbon materials
and are particularly characteristic of microcrystalline graphite [12].Figure 3
Raman spectra obtained for our pyrolyzed bulk sample and known diamond.To
elucidate this, we followed the convention of curve fitting the spectrum using
a Lorentzian function for the D peak and a Breit-Wigner-Fano (BWF) function for
the contribution near the G peak (Figure4).
The motivation for the use of the BWF function lies in its ability to
represent the merging of the G and D’ peaks, a phenomenon which occurs when the
crystalline domains of a graphitic material are sufficiently small [13, 14].Due to the close fitting of our spectra using
this methodology, we find the majority of the pyrolysis product is small-crystalline
graphite, which explains the notable increase in conductivity after burning the
PHC.Figure 4
The Raman spectrum was fit using a Lorentzian function for the D peak.  The other feature resulting from the combination of the G and D’ peaks can be represented by a BWF function.SEM did however reveal micro
and nanostructures that were clearly morphologically distinct from the majority
product (Figure5). We attempted to account for this material by adding an
additional Lorentzian to the curve-fitting procedure (Figure 6).The added Lorentzian is relatively small in
magnitude is centered at 1513 cm−1,
and improves the curve fitting of the sample’s spectrum.Interestingly, an ~1500 cm−1 peak
in the spectrum of a related polymer precursor, poly(phenylcarbyne) (C6H5C)n,
was observed after laser irradiation [15]. It has been suggested that such a peak could
arise due to either impurity-carbon amorphous networks or amorphous networks of
sp2 and sp3 carbon [16].However, only the latter suggestion is
applicable to our method of pyrolysis.
Therefore, the micro and nanostructures interspersed throughout the bulk
may be comprised of such three- and four-fold coordinated amorphous carbon
networks.SEM micrographs of pyrolyzed PHC reveal micro and nanostructures interspersed in the bulk material.
(a)(b)(c)(d)Figure 6
An improvement to the curve fit shown in Figure4 can be made by adding another Lorentzian function at 1513 cm−1.


## 4. Conclusion

We have developed a novel and facile method for the synthesis of PHC, an easily
processed, insulating polymer. Upon
pyrolysis in inert atmosphere, we note a significant increase in conductivity
of the product with respect to the precursor for the sample we investigated. The majority of the product analyzed was
shown to be consistent with small-crystalline graphite by way of curve fitting
the sample’s Raman spectrum. An improved curve fitting was found through
incorporation of an additional minority constituent contributing to the
spectrum at~1500 cm−1.This
contribution may be the result of micro and nanostructures within the bulk
observed by SEM.



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*Source: 832327-2008-12-24.xml*