We report about some Chemical Vapor Deposition approaches used

to produce a variety of C-sp2 and C-sp3 crystalline nanostructures. The methodologies

developed in our laboratories provide custom-made solutions for the fabrication

of specific carbon nanomaterials with properties tailored for applications in the field

of nanotechnology

Cianchetta, I

Gay, S

Guglielmotti, V

Orlanducci, S

Rossi, M

Tamburri, E

Terranova Persichelli, M.L

We report about some Chemical Vapor Deposition approaches used
to produce a variety of C-sp2 and C-sp3 crystalline nanostructures. The methodologies
developed in our laboratories provide custom-made solutions for the fabrication
of specific carbon nanomaterials with properties tailored for applications in the field
of nanotechnology

ORLANDUCCI, SILVIA

TAMBURRI, EMANUELA

TERRANOVA PERSICHELLI, MARIA LETIZIA

Rossi, M.

CVD-based techniques for the  synthesis of  nanographites and nanodiamonds

Archivio della Ricerca - Università di Roma Tor vergata

DOI 10.1393/ncc/i2013-11502-x
Colloquia: Nanoforum 2012
IL NUOVO CIMENTO Vol. 36 C, N. 2 Marzo-Aprile 2013
CVD-based techniques for the synthesis of nanographites
and nanodiamonds
V. Guglielmotti(1)(∗), S. Orlanducci(2), E. Tamburri(2), I. Cianchetta(1),
S. Gay(2), T. Lavecchia(1)(2), G. Reina(1)(2), D. Passeri(3), M. Rossi(1)(3)
and M. L. Terranova(1)(2)
(1) NanoShare srl - via G. Peroni, 386, 00131 Rome, Italy
(2) MINIMA Lab and Dipartimento di Scienze e Tecnologie Chimiche, Universita` di Roma
Tor Vergata - Via della Ricerca Scientiﬁca, 00133 Rome, Italy
(3) Dipartimento di Scienze di Base e Applicate per l’Ingegneria, Universita` di Roma Sapienza
via A. Scarpa, 14, 00161, Rome, Italy
ricevuto il 19 Febbraio 2013
Summary. — We report about some Chemical Vapor Deposition approaches used
to produce a variety of C-sp2 and C-sp3 crystalline nanostructures. The methodolo-
gies developed in our laboratories provide custom-made solutions for the fabrication
of speciﬁc carbon nanomaterials with properties tailored for applications in the ﬁeld
of nanotechnology.
PACS 81.05.ug – Diamond.
PACS 61.48.De – Carbon Nanotubes.
PACS 81.15.Gh – Chemical Vapor Deposition.
PACS 81.07.Bc – Nanocrystalline Materials.
1. – Introduction
The recent explosion of novel carbon-based nanomaterials make nowadays the carbon
phase diagram, which traditionally includes only diamond and graphite, by far inade-
quate to describe the richness of the carbon solid-state forms [1]. On the other hand, the
actual and envisaged applications of nanographitic materials and nanodiamonds in many
and diﬀerent technological ﬁelds, stimulated the demand for eﬃcient fabrication routes
with an increasing control of deposition procedures [2]. Tailored C nanostructures are
nowadays designed and obtained mainly using chemical vapour deposition (CVD)-based
apparatuses, where kinetically driven processes promote the creation of novel materials,
allowing at the same time to modulate their size, shape, and structure. It has been exper-
imentally demonstrated that the peculiar conditions occurring in CVD reactors enable to
(∗) E-mail: valeria.guglielmotti@uniroma2.it
c© Societa` Italiana di Fisica 3
4 V. GUGLIELMOTTI, S. ORLANDUCCI, E. TAMBURRI, ETC.
Fig. 1. – Scheme of the MW/RF-PECVD apparatus.
selectively produce in a controlled way C-sp2 nanostructures, such as carbon nanotubes
(CNT), astralenes, graphenes, and a variety of diﬀerently shaped C-sp3 nanomaterials
belonging both to the diamond Fd3m and F-43m space groups [3]. Moreover, from the
theoretical side, many eﬀorts by computer modelling have been performed in order to
relate plasma chemistry to growth processes and nanostructure formation [4].
However, processes carried out under non-equilibrium conditions often reveal sur-
prises, due to the dynamic competition between concomitant reaction routes. The ex-
perimental evidence suggests that many less considered details of already settled synthesis
methodologies could be just as important in determining the nature and nanostructure of
the ﬁnal products as the main deposition conditions usually taken into consideration [5].
Previously we have reported the successful growth of a series of interesting nanostructured
carbon materials [6-16]. To obtain guidelines for the selective and reproducible genera-
tion of carbon nanostructures, our current focus is to analyse the conditions that develop
during the processes occurring in CVD reactors and to set-up speciﬁc methodologies.
For the production of nanographites and nanodiamonds, in our labs various CVD-based
apparatuses have been designed and custom engineered. We brieﬂy report the results
obtained by using the following CVD reactors, and will illustrate the advantages that
they can provide:
– Micro-Waves/Radio-Frequency-Plasma Enhanced CVD (MW/RF-PECVD);
– Hot-Filament CVD (HF-CVD);
– Thermal-CVD (T-CVD).
2. – Experimental
2.1. MW/RF-PECVD . – In the MW/RF-PECVD reactor (ﬁg. 1) the gas phase is
excited by MWs (frequency: 2.46GHz, power: 500W) coupled to RF (work frequency:
CVD-BASED TECHNIQUES FOR THE SYNTHESIS OF NANOGRAPHITES ETC. 5
Fig. 2. – SEM images of diamond nanocones arrays.
13.56MHz, power: 600W). The gaseous reactants are introduced by a multi-channel
ﬂowmeter system. The MW/RF-PECVD works in the pressure range 1–100mbar and
in temperature range 500–1000 ◦C. The coupling of MW and RF makes it possible to
modulate at the best the rates of the growth/etching processes. This technique couples
indeed the typical and well-known advantages of MW discharge, such as homogeneity of
plasma and high concentration of active chemical species, with the ability to control ion
energy by proper biasing of the substrate [17,18].
The use of such apparatus allows the production of nanosized diamonds, of diamond
nanocones arrays [14], of hybrid systems such as CNT on Si nanocones (see ﬁg. 2 and
ﬁg. 3) [15,16].
In this case, the key parameter is the capacitive coupling of MW and RF plasmas
along the lines of the electric ﬁeld and the kinetic energy of the H ions impinging on the
growing nanostructures [16].
2.2. HF-CVD . – In the HF-CVD (ﬁg. 4) apparatus a Joule-heated Ta ﬁlament
(T = 2200 ◦C) provides activation of the reactants, that are gaseous hydrocarbons and
hydrogen. Atomic hydrogen is produced at a distance ranging from 2 to 8mm from
the substrate surface. Substrate holder is heated in a temperature range of 600–900 ◦C.
Fig. 3. – SEM image of Si nanocones covered by CNT bundles (a) and a detail of the deposit in
(b).
6 V. GUGLIELMOTTI, S. ORLANDUCCI, E. TAMBURRI, ETC.
Fig. 4. – Scheme of HF-CVD apparatus.
The peculiarity of the chamber consists in a powder-ﬂowing system, specially designed
for powder storage and delivering, that enables the combined use of gases and powders
as reactants and the controlled doping of the growing structures.
As reported in [6-12], this reactor has being used to produce continuous or pat-
terned deposits of oriented CNT bundles (both SWCNT and MWCNT), nanodiamond
ﬁlms and coatings (also characterized by pre-determined metal-like or semiconductive
charge transport properties), interesting deposits of nanodiamond on nanotube arrays,
carbon nanoﬁbers, tree-like and onion-like carbons. The conductive or semiconductive
diamond ﬁlms are obtained by inserting metal and semiconductor powders (W, Nd, Si)
or organometallic compounds driven by inert gas carriers during the growing of the di-
amond phase. The nanodiamond-coated nanotubes are produced using as reactants H2
(ﬂow rate: 200 sccm) and carbon nanopowders (mean diameter 40 nm) carried by Ar
ﬂowing at 30 sccm. For the growth of CNTs and onion-like carbons the feeding gas is
CH4, the diﬀerent forms of C-sp2 are generated by selecting pressure values (in the range
20–80Torr) and modulating the temperature ramps (see ﬁgs. 5 and 6).
Fig. 5. – SEM images of a SWCNT macroscopic ﬁber covered by nanodiamond crystals (a); a
detail of the nanodiamond crystal is depicted in (b).
CVD-BASED TECHNIQUES FOR THE SYNTHESIS OF NANOGRAPHITES ETC. 7
Fig. 6. – TEM image of an onion-like structure (a) and a tree-like one in (b).
Fig. 7. – Scheme of T-CVD apparatus.
Fig. 8. – SEM images of CNT bundles grown onto diﬀerently patterned Si substrates.
2.3. T-CVD . – The T-CVD (ﬁg. 7) system uses a ﬂow reactor quartz tube inserted
in a furnace. The reactor is kept under atmospheric pressure, the operating temperature
is in the range 200–1100 ◦C. The apparatus is connected to a gas inlet and mass ﬂow
controller, and is equipped with a system for separated injection of gases and liquids,
that are subsequently vaporized.
This technique demonstrated the ability to grow highly homogeneous deposits of
oriented nanotubes on rather large areas. The structural order of the CNT arrays makes
them good candidates for the building of more complex architectures. Moreover the
nanomaterials are produced in absence of atomic hydrogen, and this makes it possible
the direct integration of CNT also inside series of electronic components (see ﬁg. 8).
8 V. GUGLIELMOTTI, S. ORLANDUCCI, E. TAMBURRI, ETC.
3. – Conclusions
Activation of carbon-containing chemical species and reactions with atomic hydrogen
using various CVD apparatuses and diversifying the methodologies allowed us to generate
a large number of nanocrystalline carbon materials in a tailored and controlled way.
The CVD apparatuses are suitable for the production of carbon nanotubes and curled
nanoﬁlaments, onions-like and cages, tree-like and dendritic carbons, nanodiamond ﬁlms
and nanocones.
An exciting new class of materials is represented by the hybrid systems, such as
nanotubes ensembles on elongated 1D Si structures, or nanodiamonds supported on
nanotube bundles. The obtained microstructures depend upon the kinetics, in which the
balance between the relative rates of competing mechanisms drives the reactions along
speciﬁc chemical routes.
In such kinetically controlled processes the selective production of a variety of C-sp2
and C-sp3 crystalline nanostructures is promoted by the diﬀerent reaction pathways that
open up under conditions far from thermodynamic equilibrium. Moreover, we would
also like to outline the feasibility to use the same CVD apparatuses for post-synthesis
treatments of other carbon nanomaterials. An example is the use of the MW/RF-CVD
apparatus for the etching of diamond ﬁlms produced by HF-CVD or of deposits obtained
by self-assembling of detonation nanodiamonds [13,19]. In these last cases packed arrays
of diamond nanowhiskers can be fabricated.
The possibility of shaping in a predeﬁned way low-dimensional structures either by
direct synthesis or by post-synthesis treatments opens new scenarios in the preparation
of diamond-based systems for electronic and optoelectronic applications. A deep inves-
tigation of the processes occurring in diﬀerent CVD systems is being carried out in our
laboratories in order to deﬁne the methodologies for the production of selected carbon
forms under conditions far from the thermodynamic equilibrium. The know-how ac-
quired during the research stage represents a boost for the scaling of processes and the
industrial production of innovative crystalline carbon nanomaterials.
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CVD-based techniques for the synthesis of nanographites and nanodiamonds

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