U.S. patent application number 12/042544 was filed with the patent office on 2009-09-10 for cvd-grown graphite nanoribbons.
Invention is credited to Jessica Campos-Delgado, Mildred S. Dresselhaus, Morinobu Endo, Edgar E. Gracia-Espino, Xiaoting Jia, Jose Manuel Romo-Herrera, Humberto Terrones, Mauricio Terrones.
Application Number | 20090226361 12/042544 |
Document ID | / |
Family ID | 41053796 |
Filed Date | 2009-09-10 |
United States Patent
Application |
20090226361 |
Kind Code |
A1 |
Campos-Delgado; Jessica ; et
al. |
September 10, 2009 |
CVD-GROWN GRAPHITE NANORIBBONS
Abstract
The nanoribbon structure includes a plurality of thin graphite
ribbons having long and highly crystalline structure. A voltage is
applied across the length of the thin graphite ribbons to cause
current flow so as to increase crystallinity as well as
establishing interplanar stacking order and well-defined graphene
edges of the thin graphite ribbons.
Inventors: |
Campos-Delgado; Jessica;
(San Luis Potosi, MX) ; Dresselhaus; Mildred S.;
(Cambridge, MA) ; Endo; Morinobu; (Nagano-shi,
JP) ; Gracia-Espino; Edgar E.; (San Luis Potosi,
MX) ; Jia; Xiaoting; (Cambridge, MA) ;
Romo-Herrera; Jose Manuel; (San Luis Potosi, MX) ;
Terrones; Humberto; (San Luis Potosi, MX) ; Terrones;
Mauricio; (San Luis Potosi, MX) |
Correspondence
Address: |
GAUTHIER & CONNORS, LLP
225 FRANKLIN STREET, SUITE 2300
BOSTON
MA
02110
US
|
Family ID: |
41053796 |
Appl. No.: |
12/042544 |
Filed: |
March 5, 2008 |
Current U.S.
Class: |
423/447.2 ;
423/447.1 |
Current CPC
Class: |
D01F 9/127 20130101;
B82Y 40/00 20130101; C01B 32/15 20170801; B82Y 30/00 20130101 |
Class at
Publication: |
423/447.2 ;
423/447.1 |
International
Class: |
D01F 9/12 20060101
D01F009/12 |
Claims
1. A method of forming bulk nanoribbon structure comprising:
forming a plurality of thin graphite ribbons having long and highly
crystalline nanoribbons; and annealing said thin graphite ribbons
using Joule heating by applying a voltage across the length of the
thin graphite ribbons to cause current flow so as to produce heat
that increases crystallinity as well as establishing interplanar
stacking order and well-defined graphene edges of said thin
graphite ribbons.
2. The method of claim 1, wherein thin graphite ribbons attach to
metal particles and other biological molecules on the surface.
3. The method of claim 1, wherein thin graphite ribbons comprises
N, P, B, Si as dopants.
4. The method of claim 1, wherein thin graphite ribbons comprises
Li-ions as dopants.
5. The method of claim 1, wherein said graphene edges emit
electrons when a voltage is applied
6. The method of claim 1, wherein said thin graphite ribbons are
exfoliated using Li, K, H.sub.2SO.sub.4, FeCl.sub.3, Br.sub.2.
7. The method of claim 1, wherein said highly crystalline
nanoribbons comprise a length less than 30 .mu.m.
8. The method of claim 7, wherein said highly crystalline
nanoribbons comprise a width between 20 nm and 300 nm.
9. The method of claim 1, wherein said interplanar stacking order
comprises an ABAB . . . stacking order.
10. The method of claim 1 further comprising treating said thin
graphite ribbons in an Argon flow at high temperatures up to
2800.degree. C. using a graphite oven.
11. A bulk nanoribbon structure comprising a plurality of thin
graphite ribbons having long and highly crystalline nanoribbons,
wherein a voltage is applied across the length of the thin graphite
ribbons to cause current flow so as to increase crystallinity as
well as establishing interplanar stacking order and well-defined
graphene edges of said thin graphite ribbons.
12. The bulk nanoribbon structure of claim 11, wherein thin
graphite ribbons attach to metal particles and other biological
molecules on the ribbon surface.
13. The bulk nanoribbon structure of claim 11, wherein thin
graphite ribbons comprises N, P, B, Si as dopants.
14. The bulk nanoribbon structure of claim 11, wherein thin
graphite ribbons comprises Li-ions as dopants.
15. The bulk nanoribbon structure of claim 11, wherein said
graphene edges emit electrons when a voltage is applied
16. The bulk nanoribbon structure of claim 11, wherein said thin
graphite ribbons are exfoliated using Li, K, H.sub.2SO.sub.4,
FeCl.sub.3, Br.sub.2.
17. The bulk nanoribbon structure of claim 11, wherein said highly
crystalline ribbons comprise a length less then 30 .mu.m.
18. The bulk nanoribbon structure of claim 17, wherein said highly
crystalline nanoribbons comprise a width between 20 nm and 300
nm.
19. The bulk nanoribbon structure of claim 11, wherein said
interplanar stacking order comprises an ABAB . . . stacking
order.
20. The bulk nanoribbon structure of claim 17, said thin graphite
ribbons are treated in an Argon flow at high temperatures up to
2800.degree. C. using a graphite oven to modify original
properties.
Description
BACKGROUND OF THE INVENTION
[0001] The invention relates to the field of nanoribbons, and in
particular to the possibility of synthesizing bulk amounts of
graphene nanoribbons.
[0002] Following the discovery of C.sub.60 and its bulk production,
nanoscale carbon science emerged, and other fullerene-like carbons,
such as nanotubes, started to attract the attention of numerous
researchers due to their fascinating physico-chemical properties.
Subsequently, new experimental approaches have led to the synthesis
of graphitic nanocones and nanodiscs, as well as nanohoms and
toroidal structures. These results have also motivated theoretical
studies on novel forms of carbon such as Schwartzites, toroids,
fullerenes, nanotubes and graphene nanoribbons. In particular,
graphene nanoribbons have been predicted to be metallic if their
edges exhibit a zigzag morphology, whereas armchair edges can give
rise to either semiconducting or metallic transport. This
theoretical work has motivated the synthesis of individual graphene
sheets and nanoribbons.
SUMMARY OF THE INVENTION
[0003] According to one aspect of the invention, there is provided
a bulk nanoribbon structure. The bulk nanoribbon structure includes
a plurality of thin graphite ribbons having long and highly
crystalline ribbons. A voltage is applied across the length of the
thin graphite ribbons to cause current flow so as to increase
crystallinity as well as establishing interplanar stacking order
and well-defined graphene edges of the thin graphite ribbons.
[0004] According to another aspect of the invention, there is
provided a method of forming bulk nanoribbon structures. The method
includes forming a plurality of thin graphite ribbons having long
and highly crystalline ribbons. In addition, the method includes
annealing the thin graphite ribbons using Joule heating by applying
a voltage across the length of the thin graphite ribbons to cause
current flow so as to produce heat that increases crystallinity as
well as establishing interplanar stacking order and well-defined
graphene edges of the thin graphite ribbons. Finally thermal
(static) heat treatments could also be applied to the nanoribbons
up to 2800.degree. C. in order to modify the structure and
properties of the ribbons.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] FIGS. 1A-1C are SEM images illustrating graphene nanoribbons
formed in accordance with the invention;
[0006] FIGS. 2A-2C are TEM and HRTEM images illustrating graphene
nanoribbons formed in accordance with the invention;
[0007] FIG. 3A-3B are graphs illustrating X-ray powder diffraction
patterns and Raman spectra of the nanoribbons formed in accordance
with the invention;
[0008] FIGS. 4A-4D are HRTEM images, diagrams and graphical results
of a nanoribbon before and after Joule heating; and
[0009] FIG. 5 is a graph illustrating the three regimes observed
when graphene nanoribbons are heat treated using Joule heating
under vacuum.
DETAILED DESCRIPTION OF THE INVENTION
[0010] The invention provides a technique using chemical vapor
deposition (CVD) for the bulk production (grams per day) of thin
graphite ribbons consisting of long and highly crystalline
nanoribbons (<20-30 .mu.m in length) exhibiting widths of 20-300
nm, and small thicknesses (2-40 layers). These layers usually
exhibit ABAB . . . stacking as in highly crystalline graphite. The
structure of the novel material has been carefully characterized by
several techniques as well as their electronic transport and gas
adsorption properties. With this material available to researchers,
it is now possible to discover new applications and
physico-chemical phenomena associated with layered graphene.
[0011] It has been shown experimentally that zigzag and armchair
graphene ribbon edges result in different Raman spectra and
electronic properties. For example, armchair edges result in a
large intensity Raman D-band, whereas the D-band signal from zigzag
edges is substantially reduced. In addition, the zigzag edges
appear to have a high density of electronic states at the Fermi
level.
[0012] Individual graphene sheets are synthesized in order to
characterize Raman modes as well as physico-chemical properties.
With these techniques, substrates, highly oriented pyrolytic
graphite-HOPG, are used as a source of individual sheets.
Unfortunately, present synthesis methods make difficult the
manipulation of the nanoribbons and the amounts of sheet material
is very limited. Chemical vapor deposition (CVD) is used here for
producing bulk quantities of thin graphite ribbons. This material
has been carefully characterized by several techniques that
include: high resolution transmission electron microscopy (HRTEM),
scanning electron microscopy (SEM), X-ray powder diffraction (XRD),
electron diffraction (ED), X-ray photoelectron spectroscopy (XPS),
thermogravimetric analyses (TGA), Raman spectroscopy, adsorption
characterization, and electronic transport.
[0013] It is important to emphasize that a single-step and simple
CVD process was used to synthesize the nanoribbons under
atmospheric pressure conditions, at relatively high temperature
(950.degree. C.). Furthermore, the physico-chemical properties of
these ribbons are novel when compared with other forms of carbon.
The new graphite nanoribbons material should advance the
understanding of few layer graphenes, and could well be used in the
fabrication of novel composites, gas storage devices, nanosensors,
field emission sources, catalysts, electronic conductors,
batteries, or the like.
[0014] The synthesis of these graphite nanoribbons was carried out
using the aerosol pyrolysis process. Solutions containing 2.80 mg
of ferrocene (FeCp.sub.2), 2.66 ml of thiophene (C.sub.4H.sub.4S)
in 280 ml of ethanol (CH.sub.3CH.sub.2OH) were used. An aerosol was
generated ultrasonically and then carried by an argon flow (0.8
lt/min) into a quartz tube located inside a two-furnace system
heated to 950.degree. C. (both furnaces were operated at the same
temperature). After 30 minutes of operation, the ultrasonic sprayer
was turned off, the Ar flow was decreased to 0.2-0.3 lt/min, and
the furnaces were allowed to cool to room temperature. Once the
system had cooled down, the quartz tube was removed and a black
powder material was scraped from the walls of the tube located in
the first furnace area.
[0015] The reproducibility of the experiments has been confirmed.
Nevertheless, some variables were found to be critical. One of them
was the storage time of the solution. It was found that 3 weeks
after its preparation, the quality of the resulting thin graphene
ribbon material deteriorates relative to that obtained with a fresh
solution, and more by-products were produced (short nanotubes in
addition to iron particles). As described above, the solution is
ultrasonically vaporized, generating a dense cloud that remained
constant during the 30 min synthesis period.
[0016] Transport measurements are carried out on individual
nanoribbons inside the HRTEM and Joule heating experiments were
performed that resulted in the generation of highly crystalline
graphite nanoribbons. This was achieved using a HRTEM (JEOL 2010F
operated at 200 keV) equipped with a scanning tunneling microscopy
(STM) probe, which is further attached to a piezoelectric
stage.
[0017] The morphology of the initial black powder consisted of
ribbon-like structures exhibiting lengths of several microns,
widths ranging from 100-1000 nm and thicknesses of <15 nm, as
shown in FIG. 1A. It is interesting to note that the ribbons 2
revealed both flat regions as well as rippled areas, as shown in
FIG. 1B. The edges of the as-prepared ribbons also displayed
relatively sharp junctions that could be related to the presence of
either zigzag or armchair edges, as show in FIG. 1C. Since the
ribbons were extremely thin, SEM images almost suggested
transparency when observed at 10-15 keV; note the schematic of the
hexagonal structure of armchair and zigzag edges underneath the
HRTEM image of the ribbons depicted in FIG. 1C.
[0018] High-angle annular-dark-field (HAADF) images using scanning
transmission electron microscopy (STEM), and dark field TEM images
of the ribbons were also used to analyze the nanoribbons,
respectively. The ribbons displayed only one type of contrast and
Fe catalyst particles were never observed in these structures; note
carbon nanotubes containing metal catalyst particles at the
nanotube tips were usually produced in the second furnace while the
graphene nanoribbon material was extracted from the first furnace.
By performing detailed elemental energy dispersive X-ray (EDX)
spectroscopy line-scans along the ribbons, it was found that the
nanoribbons consisted of C, while S was notably absent. Even
surface-sensitive XPS could not detect any trace of S. Although
graphene nanoribbons consist of only carbon, S appears to be
crucial to grow the ribbons and could well act as a catalyst.
[0019] In order to carry out TEM and HRTEM studies, the ribbon
material (2-5 mg) was dispersed ultrasonically in methanol (10 mL)
and deposited on holey carbon grids. FIG. 2A-2C depicts ribbons
under TEM and HRTEM image conditions. At low magnification, the
material consisted only of carbon ribbons 4 as shown in FIG. 2A.
HRTEM images of the ribbons 4 are shown in FIG. 2B, which reveals
the presence of hexagonal patterns 8, that are confirmed after
obtaining the fast Fourier transform (FFT) using the inset 6. In
order to confirm the graphitic structure and the layer stacking
order, and to identify the edge structure, electron diffraction
patterns were recorded from different ribbons as show in FIG. 2C.
Interestingly, all the ribbons we analyzed consisted of AB . . .
stacked graphite, since all reflections from 3D graphite are seen
in FIG. 2C, and the edges exhibited clear armchair and zigzag (or
close to zigzag) morphologies after Joule heating, as shown in FIG.
1C. Heat treatment of the nanoribbons to 2800.degree. C. increased
the average Lc size as shown in the inset to FIG. 3A where the
narrowing of the (002) reflection is seen.
[0020] The average bulk structure of the ribbon materials was
further studied by XRD, and it was found that the nanoribbons
exhibited a highly crystalline graphite-like structure, with the
presence of strong (002), (100), (101), (004) and (110) reflections
as shown in FIG. 3A. It is important to note that the linewidth of
the (002) diffraction line gave an average L.sub.c crystallite size
of ca. 10-14 nm, in good agreement with SEM observations.
[0021] Raman spectroscopy measurements on the ribbons revealed the
presence of the D and G bands, located at 1355 and 1584 cm.sup.-1
respectively, as shown in FIG. 3B. In general, it was found that
the D-band for the pristine ribbons exhibited the highest
intensity, probably due to the high proportion of edges and ripples
within the ribbons. Other defect sensitive Raman features were also
intense. In particular, it was noted that when Raman spectra from
individual ribbon edges were recorded, the presence of the D'
feature at 1620 cm.sup.-1, was especially pronounced and well
defined, and identified with the large number of ribbon edge
structures. The disorder induced combination mode (D+G) at about
2940 cm.sup.-1 is also exceptionally strong. Significant D-band
intensity remained after heat treatment to 2800.degree. C., which
is identified with ribbon edges.
[0022] Experiments showed that the nanoribbons were highly
crystalline, as suggested by TGA studies. It was found that the
decomposition temperature of the ribbons in air corresponded to
702.degree. C. for ribbons heat treated to 1000.degree. C. in argon
gas. This value is almost the same as that observed in highly
crystalline carbon nanotubes produced by arc discharge
techniques.
[0023] XPS studies revealed the nature of the carbon bonds present
in the sample. The material contained sp.sup.2 and sp.sup.3
hybridized carbon atoms (39% sp.sup.2 and 39% sp.sup.3), and the
rest of the carbonaceous material was bonded to O and consisted of
carbonyl groups (C.dbd.O) and carboxylic groups (COO); note that 85
at % corresponded to C and 15 at % to O. It is understood that the
large number of sp.sup.3 hybridized carbon atoms was caused by the
exposed edges and the rippled (highly curved) regions within the
nanoribbons. The 1:1 ratio of sp.sup.3:sp.sup.2 carbon atoms could
also explain the large intensity of the D-band observed in Raman
spectroscopy, because the material was indeed highly crystalline
and showing an AB . . . stacking of the graphene layers.
[0024] N.sub.2 adsorption measurements on the carbon nanoribbons
revealed a BET surface area of 59 m.sup.2/g, which was similar to
the surface area of acetylene black (86 m.sup.2/g). The adsorption
data indicated that the nanoribbon material corresponds to a flat
surface, which was not porous to N.sub.2 molecules. The interaction
of an N.sub.2 molecule with the surface of the nanoribbon is weaker
than that with well-crystalline carbon black, which is in agreement
with the presence of predominant edge-like surfaces. However,
H.sub.2 adsorption at 77 K indicated the presence of rather strong
sites for supercritical H.sub.2 adsorption corresponding to ca. 15
% of the monolayer capacity of N.sub.2. Consequently, the
nanoribbon should have a unique nanostructural fit for the
adsorption of supercritical H.sub.2.
[0025] In order to study electron transport along these
nanoribbons, in-situ transport measurements using a piezo stage
inside a HRTEM were carried out. Two electrodes 12, 14 were
attached to a piece of an individual ribbon 10, and a voltage
started to be applied across the ribbon, as shown in FIG. 4A.
Subsequently, I-V curves for different ribbons, before and after
annealing by Joule heating, are shown in FIGS. 4B. For all ribbons
studied, the material behaved like a metal that followed Ohm's law.
For the ribbon shown in FIG. 4A, a 20 k.OMEGA. resistance value was
measured when a low voltage was applied. Interestingly, after a
voltage of 1.6 V was applied for more than 15 minutes, the
resistance value dropped to 10.5 k.OMEGA., corresponding to the
structure 20 shown in FIG. 4C, suggesting that crystallization of
the material due to Joule heating had taken place.
[0026] These results shown in FIG. 4B confirm that the ribbons
behave like metals. Specifically, FIG. 4D reveals the exceptional
clarity of the many long zigzag and armchair edges that are usually
observed after the Joule heating is applied. Here, one can clearly
see that the ribbon edge could be commensurate with armchair and
zigzag orientations. In addition, the FFT from FIG. 4D (shown in
the inset to FIG. 4C) confirms the AB layer stacking of the
graphene ribbon.
[0027] Due to the large proportion of edges, it is possible that
the edges could emit electrons when a voltage is applied. In
particular, anodes containing graphene nanoribbons could be used as
electron field emission sources.
[0028] These ribbons could also be exfoliated (detachment of the
layers into individual layers) and cut into shorter pieces and into
narrow ribbons. The exfoliation process usually consists in
intercalating atoms or molecules (e.g. Li, K, H.sub.2SO.sub.4,
FeCl.sub.3, Br.sub.2, etc) between layers, followed by rapid
reactions in liquids or by subjecting the material to abrupt
temperature changes. It is therefore clear that the exfoliated form
of these ribbons (containing several exposed edges) could be used
as gas storage devices, electronic wires, sensors, catalytic
substrates, etc. By using this material, it is now possible to
unveil new applications and novel physico-chemical properties
associated with layered sp.sup.2 hybridized carbon.
[0029] It is also possible to dope these ribbons with N, P, B, Si
and other elements. By doping, the physicochemical properties of
these ribbons are modified. For example, the presence of
substitutional atoms in the hexagonal carbon lattice could make
more reactive sites that will also modify the electronic properties
as well as the electrical and thermal conductivity of the
nanoribbons.
[0030] The structures produced using the invention could also be
heat treated under an inert gas like argon (FIGS. 3A and 3B) and
then further modified under vacuum using Joule heating by applying
a voltage across the length of the nanoribbon to cause current
flow. Heating by this dynamic process dramatically increases the
crystallinity and establishes interplanar AB stacking order and
well-defined graphene edges, principally along the zigzag edges.
The new material thus formed has its own distinct properties
depending on both the static heat treatment conditions (FIG. 3) and
the Joule heating conditions (FIG. 4). Further control of these
structures can be achieved by combining the heat treatment
procedure with Joule heating described herein in varying
proportions.
[0031] FIG. 5 shows three regimes of behavior used in Joule
heating: low Joule heating (Regime 1), where the current follows
the applied voltage linearly. In Regime 2, annealing by Joule
heating results in a dramatic improvement in crystallinity. The
mechanism responsible for the observed increase in crystallinity is
identified with an electro-migration process which serves to anneal
defects was discussed herein. Beyond some value of the applied
voltage, the temperature of the ribbon gets too high and the
breakdown of graphene layers starts, defining the onset of Regime
3. In this regime, layers of graphene continue to vaporize and
eventually some weak link along the ribbon fractures causing an
open circuit.
[0032] The invention allows for the first time to synthesize bulk
amounts of a novel form of nanocarbon (graphene nanoribbons). This
material was characterized using diverse techniques and the results
have confirmed that graphene nanoribbons are indeed a promising
novel nanocarbon form of carbon which could be interesting for both
scientific studies of graphene edges and for practical
applications. It is possible that in the future, these ribbons
could be exfoliated into individual graphene sheets providing new
possibilities for detailed studies of the structure and properties
of clean graphene edges, not previously available. The ribbons
could also be used to attach metal particles and other biological
molecules on the surface and at the edges, and therefore they could
be used as sensors, and protein immobilizers. The ribbon material
could also be used to incorporate Li-ions in between the graphene
layers so as to store the Li ions. This behavior is important in
the fabrication of Li-ion batteries, in which the anodes would
contain graphene nanoribbons.
[0033] Although the present invention has been shown and described
with respect to several preferred embodiments thereof, various
changes, omissions and additions to the form and detail thereof,
may be made therein, without departing from the spirit and scope of
the invention.
* * * * *