Computational Design of Chemical Nanosensors: Metal Doped Carbon Nanotubes
J. M. Garc´ıa-Lastra1,2,∗D. J. Mowbray1,2, K. S. Thygesen 2, A. Rubio 1,3, and K. W. Jacobsen 2
1Nano-Bio Spectroscopy group and ETSF Scientiﬁc Development Centre,
Dpto. F ´ısica de Materiales, Universidad del Pa ´ıs Vasco,
Centro de F´ısica de Materiales CSIC-UPV/EHU- MPC and DIPC, Av. Tolosa 72, E-20018 San Sebasti ´an, Spain
2Center for Atomic-scale Materials Design, Department of Physics,
Technical University of Denmark, DK-2800 Kgs. Lyngby, Denmark
3Fritz-Haber-Institut der Max-Planck-Gesellschaft, Berlin, Germany
We use computational screening to systematically investigate the use of transition metal doped carbon nan-
otubes for chemical gas sensing. For a set of relevant target molecules (CO, NH3, H2S) and the main components
of air (N2, O2, H2O), we calculate the binding energy and change in conductance upon adsorption on a metal
atom occupying a vacancy of a (6,6) carbon nanotube. Based on these descriptors, we identify the most promis-
ing dopant candidates for detection of a given target molecule. From the fractional coverage of the metal sites
in thermal equilibrium with air, we estimate the change in the nanotube resistance per doping site as a function
of the target molecule concentration assuming charge transport in the diffusive regime. Our analysis points to
Ni-doped nanotubes as candidates for CO sensors working under typical atmospheric conditions.
PACS numbers: 73.63.–b, 68.43.–h, 73.50.Lw
The ability to detect small concentrations of speciﬁc chem-
ical species is fundamental for a variety of industrial and sci-
entiﬁc processes as well as for medical applications and en-
vironmental monitoring [1]. In general, nanostructured mate-
rials should be well suited for sensor applications because of
their large surface to volume ratio which makes them sensi-
tive to molecular adsorption. Speciﬁcally, carbon nanotubes
(CNT) [2] have been shown to work remarkably well as de-
tectors of small gas molecules. This has been demonstrated
both for individual CNTs [3–8] as well as for CNT networks
[9, 10].
Pristine CNTs are known to be chemically inert – a prop-
erty closely related to their high stability. As a consequence,
only radicals bind strong enough to the CNT to notably affect
its electrical properties [2, 5, 11–13]. To make CNTs attrac-
tive for sensor applications thus requires some kind of func-
tionalization, e.g. through doping or decoration of the CNT
sidewall [13–21]. Ideally, this type of functionalization could
be used to control not only the reactivity of the CNT but also
the selectivity towards speciﬁc chemical species.
In this work we consider the possibility of using CNTs
doped by 3d transition metal atoms for chemical gas sens-
ing. We use computational screening to systematically iden-
tify the most promising dopant candidates for detection of
three different target molecules (CO, NH 3, H2S) under typi-
cal atmospheric conditions. The screening procedure is based
on the calculation of two microscopic descriptors: the bind-
ing energy and scattering resistance of the molecules when
adsorbed on a doped CNT. These two quantities give a good
indication of the gas coverage and impact on the resistance.
For the most promising candidates we then employ a simple
thermodynamic model of the CNT sensor. In this model, the
binding energies are used to obtain the fractional coverage of
the metallic sites as a function of the target molecule concen-
tration under ambient conditions. Under the assumption of
transport in the diffusive rather than localization regime, the
change in CNT resistivity may then be obtained from the cal-
culated coverages and single impurity conductances.
We ﬁnd that oxidation of the active metal site passivates
the sensor in the case of doping by Ti, V , Cr, and Mn un-
der standard conditions (room temperature and 1 bar of pres-
sure). Among the remaining metals, we identify Ni as is the