**3. Results and discussion**

Using spin coating, P3GC solutions were deposited onto glass substrates which were coated by two silver planar electrode arrays with a length of 4 mm and separated from each other by a distance of 2 mm, which is similar to the image in **Figure 1**. The following parameters were used for spin coating: a delay time of 100 s, a rest time of 45 s, a spin speed of 1500–1800 rpm, an acceleration of 500 rpm, and finally a drying time of 300 s. To dry the composite films, a flow of dried gaseous nitrogen was used for 10 h. For a solidification avoiding the use of solvents, the film samples were annealed at 120°C for 2 h in a "SPT-200" vacuum drier. To compare the performance efficiency of P3HT + rGO + CNT with the one for PEDOT:PSS + rGO + CNTbased sensors, PEDOT:PSS + rGO + CNT composites (shortly called PEGC) were prepared by

the abovementioned procedure with replacement of P3HT by PEDOT:PSS polymer.

For humidity sensing measurements, the samples were put in a 10 dm3

The thickness of the films was measured on a "Veeco Dektak 6M" stylus profilometer. The size of GQDs and the surface morphology of the films were characterized by using "Hitachi" Transmission Electron Microscopy (TEM), Emission Scanning Electron Microscopy (FE-SEM), and NT-MDT atomic force microscope operating in a tunnel current mode. Crystalline structures were investigated by X-ray diffraction (XRD) with a Philips D-5005 diffractometer using

humidity value could be fixed in a range from 20 to 80% by the use of an "EPA-2TH" moisture profilometer (USA). The adsorption process is controlled by insertion of water vapor, while desorption process was done by extraction of the vapor followed by insertion of dry gaseous Ar. The measurement system that was described in [30] consisting of an Ar gas tank, gas/ vapor hoses and solenoids system, two flow meters, a bubbler with vapor solution, and an airtight test chamber connected with collect-store data DAQ component. The Ar gas played a

For each sample, the number of measuring cycles was chosen to be at least 10 cycles. The humidity flow taken for measurements was of ~60 sccm ml/min. The sheet resistance of the samples were measured on a "KEITHLEY 2602" system source meter. To characterize humidity sensitivity of the composite samples, the devices were placed in a test chamber and device

For monitoring gases, the prepared sensing samples were put in a testing chamber of 10 dm3 in volume. The gases value can be fixed in a rage from 10 to 1000 ppm by use of an "EPA-2TH" profilometer (USA). To characterize the gas sensitivity of the samples, the devices were placed in a test chamber at the room temperature (namely 300 K) and the Ar gas pressure of 101.325 kPa (or 1 Atm); the device electrodes were connected to electrical feedthroughs. The measurements that were carried out included two processes: adsorption and desorption. In the adsorption process, the gas (or vapor) flow consisting of Ar carrier and measuring vapor from a bubbler was introduced into the test chamber for an interval of time, following which the change in resistance of the sensors was recorded. In the desorption process, a dried Ar gas flow was inserted in the chamber in order to recover the initial resistance of the sensors. Through the recovering time dependence of the resistance, one can obtain information on the

radiation (λ = 0.15406 nm). The ultraviolet–visible absorption spectra were car-


**2.2. Characterization techniques**

86 Nanocomposites - Recent Evolutions

ried out on a Jasco UV–VIS–NIR V570.

role as carrier gas, dilution gas, and purge gas.

electrodes were connected to electrical feedthroughs.

desorption ability of the sensor in the desorption process.

filtered Cu-K<sup>α</sup>
