The observation of photoconduction and nonlinear optical absorption on functionalized multiwall carbon nanotubes decorated with platinum is reported. The samples were prepared by a chemical vapor deposition method. The electrical conductivity of the carbon nanotubes seems to be decreased by the functionalization process; but this property is strongly enhanced after the incorporation of platinum particles. Nonresonant photoconductive experiments at 532 nm and 445 nm wavelengths allow us to detect a selective participation of the platinum to the photoelectrical response. A mechanooptic effect based on Fresnel reflection was obtained through a photoconductive modulation induced by the rotation of a silica substrate where the samples were deposited as a thin film. A two-photon absorption process was identified as the main physical mechanism responsible for the nonlinear optical absorption. We consider that important changes in the nonlinear photon interactions with carbon nanotubes can be related to the population losses derived from phonons and the detuning of the frequency originated by functionalization.
One of the most significant scientific interests related to studying carbon nanostructures comes from their particular advantages for designing nanosystems that can be improved by a number of materials [
Several preparation methods for evaluating the morphological and structural characteristics of CNTs have been carried out [
In many fields of nanotechnology, distinct kinds of CNTs have drawn considerable attention regarding their outstanding optical and electrical parameters [
The research progress of the photoconductive and mechanooptical response of CNTs and other metal elements has originated that different configurations can be considered as ideal candidates for next-generation of flexible transparent conducting films [
With this motivation, in this research an attempt has been made to further investigate the potential applications of the photoconductive and mechanooptic response of multiwall CNTs (MWCNTs). Experimental results associated with functionalization, electrical, photoconductive, and nonlinear optical absorption phenomena that were successfully enhanced by platinum decoration of the studied samples are presented.
MWCNTs were produced by thermal decomposition of Toluene (Fermont, 99.9% purity) and Ferrocene (Sigma-Aldrich, 98% purity) in a tubular reactor at
The f-MWCNTs decorated with platinum particles (Pt/f-MWCNTs) were prepared by an
Afterwards, the resulting samples were suspended in an ethanol solution contained in a quartz cuvette with 1 mm width. The concentration of the solution was heuristically chosen for a better observation of the optical absorption bands that correspond to the plasmonic response of the samples in their linear optical spectra. Then, the obtained liquid solutions were deposited by dripping on different SiO2 substrates, deriving from selected thin film samples with a resulting thickness of approximately 1
Electrical measurements were evaluated using an Autolab/PGSTAT302N high power potentiostat/galvanostat. The impedance spectrum was measured with a 10 mV signal and an integration time of 1 s. The photoconduction on the samples was separately investigated at 445 nm and 532 nm wavelengths with continuous wave (CW) lasers providing 1 W of average power. The incident polarization of the optical beam was aligned to coincide with the path in measurement. The electrodes used for these experiments were in direct contact with the sample; they were located in the neighborhood of the diameter of the incident beam. The conductivity was measured using two metallic electrodes separated by a distance of 5 mm for each studied sample.
The linear absorption spectrum of the samples was acquired with a Perkin Elmer XLS UV-visible spectrophotometer.
The optical transmittance and photoconduction in the thin films were measured by means of a high irradiance single beam transmittance experiment. A 532 nm wavelength with 1 ns pulse duration was monitored using the second harmonic of a Nd-YAG laser source continuum model SL II-10.
Considering the possibility of promoting controlled contributions of light for inducing a photoconduction behavior in the sample, we proposed the optoelectronic system assisted by a mechanical actuator illustrated in Figure
Setup for implementing a mechanooptic modulation of photoconduction.
Figure
Raman spectra of pristine and functionalized nanotubes (f-MWCNTs).
A representative field emission scanning electron microscopy (FE-SEM) image of Pt/f-MWCNTs is shown in Figure
Field emission-SEM image of Pt/f-MWCNTs.
It has been previously reported that the incorporation of Pt will increase the conductivity exhibited by decorated carbon nanotubes [
Electrical response of the studied samples as a function of electrical frequency.
Photoconductive results were obtained in darkness and under 532 nm wavelength of irradiation on the samples. The experimental data are presented in Figure
Photoconductive response under 532 nm irradiation as a function of electrical frequency.
Comparatively, photoconductive explorations carried out in the samples by a 445 nm irradiation seem to activate the photoconductive response in the f-MWCNTs as it can be observed from Figure
Photoconductive response under 445 nm irradiation as a function of electrical frequency.
The fitting of the experimental data shown in Figures
Electrical parameters in the studied samples.
Experiment |
|
|
|
---|---|---|---|
MWCNTs |
260000 | 639594 | 3 |
MWCNTs |
170000 | 659594 | 5 |
MWCNTs |
185000 | 630000 | 5.5 |
f-MWCNTs |
410000 | 809594 | 1.6 |
f-MWCNTs |
899594 | 440000 | 6 |
f-MWCNTs |
385000 | 1000000 | 7 |
Pt/f-MWCNTs |
199000 | 639594 | 6 |
Pt/f-MWCNTs |
220000 | 439594 | 11 |
Pt/f-MWCNTs |
170000 | 500000 | 5 |
Taking into account the data described in Table
On the other hand, the experimental setup illustrated in Figure
Photoconductive response in the studied Pt/f-MWCNTs as a function of the angle of rotation of the supporting substrate.
To better describe the contribution of multiphotonic interactions in the electrical measurements, a quantification of the linear and nonlinear optical response of the samples was undertaken. Similar optical spectra were obtained for studied samples with equivalent amounts of MWCNTs, f-MWCNTs, or Pt/f-MWCNTs. Figure
Linear optical absorption spectrum of Pt/f-MWCNTs.
A high irradiance optical beam at 532 nm wavelength was selected to observe if any involvement of multiphotonic interaction could be discerned during the propagation of a nonresonant optical beam. Figure
Nonlinear optical transmittance exhibited by Pt/f-MWCNTs.
The fit of the nonlinear optical transmittance was performed using the expression for the transmitted irradiance
The best fitting for the linear and nonlinear absorptive coefficients for the samples results in
In order to explain the observed nonlinear optical response, we considered the dipole approximation in a system of
For further investigation of the participation of optical absorption in the physical mechanism responsible for the photoconductivity, we irradiated the samples by employing optical pulses at 532 nm with about 50 MW/cm2 at 1 Hz repetition rate provided by our Nd-YAG system. The data shown in Figure
Photoconductive response dependent on nanosecond irradiation in Pt/f-MWCNTs.
We calculated the heat-transference generated by optical irradiation in propagation through the sample by using [
The possibility of enhancing the nonlinear optical response and the electronic features of CNTs samples by the modification of metastable electronic levels appears to be attractive. What is more, we consider that potential applications for tailoring the optical and the electrical response associated with diverse materials can be also improved by the incorporation of NPs capable of changing electrical and optical interactions. Regarding the contribution of the absorptive nonlinearities to the electrical properties of the studied samples, potential applications for developing optoelectronic nanosystems based on decorated CNTs can be contemplated.
A noticeable enhancement in the electrical and photoconductive response exhibited by f-MWCNTs nanotubes was achieved by platinum decoration. Apparently, the incorporation of platinum NPs into MWCNTs originates a modification in the nonresonant electronic levels that can play an important role in the resulting photoconductive and two-photon absorption effects. A simple mechanooptic effect based on the photoconductive response exhibited by the studied samples was observed.
The authors declare that there is no conflict of interests regarding the publication of this paper.
The authors kindly acknowledge the financial support from the Instituto Politécnico Nacional, Universidad Iberoamericana, and CONACYT. The authors are also thankful to the Centro de Nanociencias y Micro y Nanotecnologías-IPN.