This work deals with the synthesis, characterization, and application of carbon nanoparticles (CNP) adorned graphene oxide (GO) nanocomposite materials. Here we mainly focus on an emerging topic in modern research field presenting GO-CNP nanocomposite as a infrared (IR) radiation detector device. GO-CNP thin film devices were fabricated from liquid phase at ambient condition where no modifying treatments were necessary. It works with no cooling treatment and also for stationary objects. A sharp response of human body IR radiation was detected with time constants of 3 and 36 sec and radiation responsivity was 3 mAW−1. The current also rises for quite a long time before saturation. This work discusses state-of-the-art material developing technique based on near-infrared photon absorption and their use in field deployable instrument for real-world applications. GO-CNP-based thin solid composite films also offer its potentiality to be utilized as p-type absorber material in thin film solar cell, as well.

In recent years intensive research attention have been paid on the development of cost-effective, flexible, light-weight smart electronics, either by searching for new, naturally available smart materials, processing methods or by structural consideration.1–8 High sensitivity, chemical and thermal stability, non-toxicity, mechanical compliance and bio-compatibility have led to the way for energy-efficient implantable electronic devices.9,10 Advances in electronics have paved the way for the adoption of many different types of photodetectors, sensors by using different materials in individual or with their combination.11–18 Meanwhile, important research reports have been published on the versatile use of graphene and its derivatives and on carbon nanoparticles.19–23 

There are several ways for carbon atoms to bond to form carbon derived materials. Carbon-based nanostructures like fullerenes, nanotubes and nano-onions are being investigated over the past few years owing their outstanding and tunable electronic, mechanical, and electrochemical properties.24–27 The common characteristic of these nanostructures is the presence of graphitic atomic arrangements with in-plane curvature, giving rise to 3-dimensional structure of sp2-coordinated atoms. These 3D units constitute closed cages in the case of spherical fullerene molecules and onion-like carbon.28–30 Generally, CNP based composites consist of primary particles with average particle sizes between a few and approximately 100 nm depending on the mechanism of formation. On the other hand, graphene, which is a single nano-sheet of hexagonally arrayed carbon atoms and its derivative GO obtained by chemical oxidation are drawing immense scientific and technical interest owing to their fascinating optical, electrical, mechanical, properties.18,31–36 The main advantage of GO is that it is well dispersed in aqueous solutions due to the hydrophilic functional groups.37 The high solubility in water makes GO an ideal substrate for catalysts in water phase reactions.38,39 GO serves as a support material to stabilize metal nanoparticles. For example, the synthesis of silver and gold nanoparticles stabilized by GO sheets has been reported by several research groups.20,40 GO is considered as the precursor of graphene but also a promising surfactant for the preparation of graphene based composites due to the functional groups, such as hydroxyl, carboxyl, and epoxy groups, on its surface.18,41 GO is also capable of dispersing insoluble materials such as carbon nanotubes and graphene to form relatively stable aqueous suspensions for subsequent device fabrication.42,43

In this work, GO was prepared via modified synthesis protocol;44 and, whereas, CNP was synthesized from diesel which has been described elsewhere.45 Compared to pure graphene, GO exhibits a significant loss of conductivity. These sheets need to be reduced to restore the sp2 hybrid network and thus reintroduce the conductive property. Incorporation of organic nanoparticles into an individual graphene or graphene oxide with good distribution can provide greater versatility in carrying out selective catalytic or sensing processes. Our recent research efforts have made use of the two-dimensional morphology of graphene oxide solutions to anchor carbon nanoparticles. Thin films were prepared by solution casting of appropriate amount onto glass substrates at ambient condition.

The as-prepared GO is insulating; and can be reduced chemically or by annealing at high temperatures.38,46 Although hydrazine is most widely used as a chemical reductant, its toxicity and explosiveness pose a problem as reported before.47 As thermal reduction has been performed only at high temperatures (400–1100 °C), a cheap processing condition is desirable for making it useful in practical applications. We reported earlier a cost effective practical route to grow device quality thin films on glass at low percolation temperature without using reagent by simply solution casting process.4 However, in order to cover the whole range of physical phenomena that are exploitable for sensors, it is necessary to add a variety of functional materials to the existing base materials.48 Incorporating of CNP into as prepared GO matrix might have enhanced the electrical conductivity of GO-CNP nanocomposite without heating the composite at high temperature or without any chemical treatments.

In the present study, we report synthesis of GO-CNP nanocomposite by solution-phase mixing of the two individuals; and discuss about its applications, like thin film IR detector as well as thin film solar cell absorber. Generally the interaction of light with nanostructures (carbon nanoparticles and graphene) results in considerable absorption of photons in the range 700-1100 nm and consequent heat production due to the generation of phonons owing to the strong sp2 bond in nanostructures.49 GO have nonlinear optical properties its electronic band gap can be changed over a wide range (2.2 to 0.5eV) by altering the amount and type of oxygen-containing groups, which indicates that transitions from insulator to semiconductor and further to semimetal may also be possible.50 

Human bodies are very good infrared sources and wavelength of these infrared sources at room temperature is approximately 780 nm.51,52 Here we show GO-CNP nanocomposite as a future generation of human body radiation detector due to their exact correspondence to the absorption at 780 nm of photon wavelength. This detector enables the acquisition of electrophysiological signals remotely without the necessity for physical or electrical contact with the body.

Commercial grade diesel was collected from oil station in Dhaka City of Bangladesh. Carbon nanomaterials were synthesized form the incomplete combustion of diesel with controlled air oxygen. At first diesel was taken in a clean lamp and was fired. A special type of round bottom flax of glass was placed over the flame of lamp to prevent the excess air oxygen. During the burning of diesel, black colored materials were prepared which was deposited inside the flax. Deposited materials were collected in a dry bottle and stored in a desiccator.

Graphite flakes and KMnO4 were purchased from Alfa Aesar and Kanto Chemical, respectively. PTFE membrane filter with a 0.45 μm pore size was purchased from Millipore. Polyester hollow fiber (Tetoron, 90 dtex, 38 mm) was purchased from Teijin Fibers. Graphene oxide was synthesized with Marcano’s improved method.44 A mixture of concentrated H2SO4/H3PO4 (180 mL/20 mL) was added to a mixture of graphite flakes (1.5 g) and KMnO4 (9.0 g). The mixture was heated with stirring at 50 °C for 14 h, which then was cooled to room temperature and poured onto ice (200 mL), which had been treated with 30% H2O2 (1.5 mL), with further cooling in an ice bath as an exothermic reaction occurred. The mixture was filtered through polyester fiber to yield dark purple solution, which was centrifuged (3750 rpm for 5–15 h), and the supernatant was decanted away. The remaining gray solid was dispersed in water (90 mL) by sonication, and filtered through the polyester fiber. The filtrate was centrifuged and the supernatant decanted away. This washing protocol (dispersion by sonication, filtration, and centrifugation) was repeated with concentrated HCl (90 mL) and ethanol (90 mL) then again with water, concentrated HCl, and ethanol. The new yellow residue was coagulated by treating with diethyl ether, and filtered through a PTFE membrane to yield a yellow solid. The solid obtained on the filter was vacuum-dried overnight at room temperature, affording 0.4–0.6 g of dark-colored product. CNP solution in DMSO (10−9 M/L) was mixed with 0.3 mg/ml concentrated GO solution; and thereby, a homogeneous solution was readily obtained.

In order to study the surface morphology of CNP, certain amounts of CNP (10−9 ML−1) suspension in DMSO was firstly drop casted onto chemically and ultrasonically cleaned SiO2 substrates and spin coated (3000 rpm for 30 seconds). To remove the thermally unstable molecular conformations the sample was heated at 100°C for 5 to 10 minutes. After that, the samples were loaded into the microscope. Atomic force microscopy (AFM) measurements were performed using Peak Force QNM Tapping Mode on the Multimode Atomic Force Microscope (Bruker) with a silicon cantilever (TAP525).

The thickness and surface root mean square (rms) roughness of the GO-CNP nanocomposite film was measured directly by AFM (Agilent). The thickness and surface root mean square (rms) roughness of the GO-CNP nanocomposite film was measured directly by AFM (Agilent) which were approximately 100 nm and 2.26 nm, respectively. In this case AFM measurements were performed by using a Dynamic Force Mode Atomic Force Microscope (SII, SPI3800N-400A) with a silicon cantilever (SI-DF3; spring constant: 1.3 N m−1, resonant frequency: 26 kHz). The frequency of the cantilever was set higher than the resonance frequency. The voltage of 1.0 V was applied to driven the vibration. The amplitude damping factor was determined to a default value of the apparatus. Resolution for topography measurements were 512 × 512 points at 1 Hz frequency. In order to measure the correct thickness of exfoliated GO nanoplatelets mica substrate was used as a support because it is relatively flat and smooth. Mica substrate was purchased from Nisshin EM Corporation and was cleaved before sample preparation. After that a dispersed GO/H2O solution were deposited onto the surface and dried.

X-ray photoelectron spectroscopy (XPS) was performed using a Shimadzu ESCA-3400 spectrometer, where a monochromatized Mg Kα (1253.6 eV) X-ray source was used under the base pressure of <1.5 × 10 –8 Torr. Initially, we had to deposit Pt/Pd metal layer on the samples for the SEM measurements, that’s why the surface was Ar+-etched before the XPS measurements until no Pt/Pd signals were detected.

In order to study the photoresponse property of GO/CNP nanocomposite material (3 × 4) mm2 area thin films were prepared by drop-casting of an appropriate amount of the nanocomposite solution onto the cleaned glass substrate and dried only for 7 minutes at 800 C. To prepare GO-CNP thin films we used glass substrate because it has many properties that make it an ideal substrate for practical applications such as: ultra-high resistivity, low electrical loss, low dielectric constant, adjustable coefficient of thermal expansion, good stiffness, ability to form high quality substrates in a large scale as well as enhanced cost effectiveness. Substrates were purchased from Nisshin EM Corporation, and were cleaned in an ultrasonic bath with DI water, acetone and IPA for 15 minutes, in each case. The obtained thin film was chemically and thermally stable, homogeneous and well-adhered to the substrate as well. A ‘Schimadzu UV-VIS-NIR’ recording spectrophotometer was used to measure the optical transmittance and reflectance spectra.

The resistivity, conductivity, magneto resistance, mobility and average Hall co-efficient were measured by ‘Ecopia Hall-effect measurement system’ by 4-point Van der Pauw approach at ambient condition. Four indium dots were soldered at the four corners of each film.

DC current response due to body irradiation was measured with time by holding one hand at about 1.5 cm proximity of the film. Two indium electrodes were contacted at the two ends of the device and connected to the set-up with copper wiring. In this case for measuring DC current and voltage (at 2 V power supply)due to human body irradiation ‘Keithley’ voltmeters and a dc power supply from ‘Advance Electronics Ltd’ were used.

CNP were synthesized from diesel and their surface morphology was extensively studied by SEM and AFM. Figure 1(a) and 1(b) depict the SEM micrographs of carbon particles at (a) 25,000 and (b) 100,000 magnifications which clearly demonstrated that the particles are not uniform. The spherical particles size is in the range of about 10 to 80 nm in diameter. Figure 1(c) shows the AFM topography of CNP deposited on SiO2 substrate. In this topography image isolated CNP is clearly visible. The shape of the particle is more or less spherical. Figure 1(d) depicts the histogram of height distribution of CNP obtained from Figure 1(c). From this histogram it is seen that the average size (or height) of the CNP is approximately 6 nm. A high resolution AFM image of a single CNP and its 3D representation are presented in Figures 1(e) and 1(f) respectively. The diameter of this single CNP is ∼ 5.5 nm.

FIG. 1.

SEM micrographs of carbon particles synthesized from diesel (a) 25,000×, (b) 100,000×, (c) AFM topography image of CNP deposited on SiO2 (d) Histogram of height distribution of CNP obtained from figure 1(c), (e) A high resolution AFM image of a single CNP and (f) A 3D representation of Figure 1(e).

FIG. 1.

SEM micrographs of carbon particles synthesized from diesel (a) 25,000×, (b) 100,000×, (c) AFM topography image of CNP deposited on SiO2 (d) Histogram of height distribution of CNP obtained from figure 1(c), (e) A high resolution AFM image of a single CNP and (f) A 3D representation of Figure 1(e).

Close modal

Figure 2(a) & 2(b) show the SEM images of exfoliated GO flakes used in GO-CNP nanocomposite device and an AFM image of same GO flakes are presented in Figure 2(c). The exfoliations to achieve GO sheets were confirmed by thickness measurements of a single sheet using AFM. A two-dimensional line profile recorded along the dashed line of Figure 2(c) is presented in Figure 2(d). The line profile in Figure 2(d) of approximately 1 nm height on mica substrate confirms the detection of a single GO sheet.44 Since we used very low concentration of GO/H2O suspension, single and multiple GO sheets are clearly discernible in the SEM and AFM images.

FIG. 2.

(a) and (b) SEM image of exfoliated GO on glass substrate at different magnifications, (c) A typical AFM image of exfoliated GO sheets deposited on a mica substrate and (d) A line profile recorded along the dotted line on the GO sheets in Figure 2(c), the sheet is ∼ 1 nm thick.

FIG. 2.

(a) and (b) SEM image of exfoliated GO on glass substrate at different magnifications, (c) A typical AFM image of exfoliated GO sheets deposited on a mica substrate and (d) A line profile recorded along the dotted line on the GO sheets in Figure 2(c), the sheet is ∼ 1 nm thick.

Close modal

SEM and AFM surface morphology study of GO-CNP film is presented in Figure 3. Figures 3(a) and 3(c) display the surface morphology of GO thin film used in the present study. These images were recorded by SEM (Fig. 3a) and AFM (Fig. 3c) respectively. The SEM micrograph in Figure 3(b) and the AFM topography in Figure 3(d) show the role of GO solution in producing well-dispersed CNP. These measurements show a simple synthetic strategy for anchoring single-nanoparticle system on GO.

FIG. 3.

(a) SEM image of GO thin film on a glass substrate, (b) SEM image of GO-CNP nanocomposite film on a glass substrate, (c) An AFM topography image of GO film on a glass substrate and (d) An AFM topography image of GO-CNP nanocomposite.

FIG. 3.

(a) SEM image of GO thin film on a glass substrate, (b) SEM image of GO-CNP nanocomposite film on a glass substrate, (c) An AFM topography image of GO film on a glass substrate and (d) An AFM topography image of GO-CNP nanocomposite.

Close modal

Figure 4(a, b) shows the x-ray photoelectron spectroscopic (XPS) spectra for the CNP sample on silicon substrate. The wide range scan, which is shown in 4(a), exhibits peaks derived from carbon in addition to silicon and oxygen as well as the peaks from Au, which we used for calibration. The high-resolution spectrum in the C 1s region is shown in 4(b). The deconvolution revealed three peaks at 282.8 eV, 284.4 eV (which is most prominent) and 286.8 eV. We attributed the main peak at 284.4 eV as sp2 carbons because the peak position is close to that of graphite, which appears at 284.5 eV. The higher energy peaks are assigned to sp3 carbons or carbons bonded to oxygen. If these higher-energy peaks arise from carbons bonded to oxygen-containing species, the major 286.8 peak is likely due to carbons adjacent to hydroxy or ether groups, while even higher energy peaks likely arise from carboxyl carbons. XPS study was also performed on GO and presented in Figures 4(c, d).

FIG. 4.

(a) and (b) XPS spectra for CNP, (c) and (d) XPS spectra for GO, (e) and (f) XPS spectra of GO-CNP nanocomposite.

FIG. 4.

(a) and (b) XPS spectra for CNP, (c) and (d) XPS spectra for GO, (e) and (f) XPS spectra of GO-CNP nanocomposite.

Close modal

Since the GO was produced from graphite by means of Marcano’s improved method,44 so we got similar results i.e. four peaks in the XPS spectrum that corresponds to the following functional groups: carbon sp2 (C=C, 284. 2 eV), epoxy/hydroxyls (C-O, 286.3 eV), carbonyl (C=O, 287.9 eV), and carboxylates (O-C=O, 290.1 eV) as reported in the article.44 It is found that the GO produced by using this method contains approximately 69% oxidized carbon and 31% graphitic carbon,44 i.e. Marcano’s method gives us the highly oxidized materials.

The XPS was performed to investigate the electronic structure of carbon and oxygen atoms in the prepared GO-CNP. The binding energy scale was calibrated to the C sp2 (C=C) peak at 284.5 eV for charging correction. The C1s and O1s XPS spectra are shown in Figures 4(e) and 4(f), respectively. The XPS spectra of composite showed significant shifting of C and O signals corresponding to the binding energy of graphene oxide: binding energy 285.0 and 532.1 eV, respectively.53 The binding energies of 284.5 eV, 285–285.2 eV, 286.5 eV, 288.2 eV and 289.7 eV were attributed to C sp2 (C=C), C sp3 (C-C and C-H), C-OH, C=O and O=C-OH, respectively.54,55 C sp2 (C=C) and C sp3 (C-C and C-H) are overlapped. Figure 4(e) (C1s) showed the significant peak of C signal with a binding energy of 284.5 eV, which can be attributed to the C=C species. In addition two peaks with binding energy 293.3 eV and 296.2 eV appears as satellite peaks indicating the presence of extended delocalized (π − π) electrons in the prepared composite. Again, the significant peaks with a binding energy of 530.6 eV, 531.6 eV and 533.2 eV in Figure 4(f) for O1s spectrum are attributed to the C-O-H, C=O and H-O-CO, respectively. A satellite peak with binding energy of 536.4 eV is attributed to the extent of delocalized (π − π) electrons in the composite. Such observations of XPS spectra for C1s and O1s, lowering of binding energy of main peak and appearing of satellite peaks at higher binding energy, suggested that the prepared composite contains large numbers sp2-carbon and delocalized (π − π) electrons, ready to enhance the conductivity of composite, which was supported by the electrical Hall-effect measurements (Table I). One additional peak in Figure 4(e) at 292.4 eV and two additional peaks in Figure 4(f) were also observed at 534.8 eV and 537.7 eV respectively but the assignment of these peaks is not straightforward according to the literature. We tentatively assign the peaks at binding energies 292.4 eV to carbon atoms and 534.8 eV and 537.7 eV to oxygen atoms bonded to the residual metals (used for electrodes) present on the sample.

TABLE I.

Electrical parameters of GO, CNP, and GO-CNP nanocomposite thin film.

Parameters GO CNP GO-CNP
Bulk concentration (/cm3 1.34×1018  9.03×104  1.07×1019 
Sheet concentration (/cm2 2.94×1013  4.52×1016  1.07×1016 
Resistivity (Ohm-cm)  5.24×10−2  4.29×10−7  3.64×10−2 
Conductivity (Ohm-cm)−1  1.90×101  2.33×106  2.75×101 
Magneto resistance (Ohm)  4.7×101  3.64×10−2  3.53×101 
Mobility (cm2/V.s)  1.33×10−1  1.61×103  1.61×101 
Hall co-efficient (cm3/C)  4.68×10−3  6.91×10−4  5.85×10−1 
Parameters GO CNP GO-CNP
Bulk concentration (/cm3 1.34×1018  9.03×104  1.07×1019 
Sheet concentration (/cm2 2.94×1013  4.52×1016  1.07×1016 
Resistivity (Ohm-cm)  5.24×10−2  4.29×10−7  3.64×10−2 
Conductivity (Ohm-cm)−1  1.90×101  2.33×106  2.75×101 
Magneto resistance (Ohm)  4.7×101  3.64×10−2  3.53×101 
Mobility (cm2/V.s)  1.33×10−1  1.61×103  1.61×101 
Hall co-efficient (cm3/C)  4.68×10−3  6.91×10−4  5.85×10−1 

Figure 5(a) reveals the optical transmittance (%T) and reflectance (%R) spectra in the photon wavelength ranging between 300 and 2500 nm. The GO-CNP nanocomposite film shows a horizontal transmittance regime starting from 2500 down to 1800 nm of photon wavelength showing a transmittance from 79 to 88%. At around 780 nm, a sharp absorption takes place where transmittance reaches down to zero, and this corresponds to the wavelength of the IR radiation emitted by human body at room temperature. The material gives very negligible amount of reflectance which is ideal for a better detector. Absorption co-efficient (α) plotted as a function of photon energy in Figure 5(b) shows a high value of 6 × 105 (cm−1). Tauc’s plot is represented in Figure 5(c). Band gap is determined by extrapolating the linear part to the x-axis, and thus giving the value of direct allowed band gap as 2.0 eV. High absorption co-efficient is beneficial as a useful candidate as an thin film absorber in tandem solar cell, where different layers of having varying optical band gap is required for matching with the entire solar spectrum. The variation of extinction co-efficient of GO-CNP nanocomposite thin film as a function of photon wavelength is shown in Figure 5(d). The extinction coefficient (k) is the imaginary part of the complex index of refraction (n1 = n + ik), where n1, n, and k are the complex refractive index, refractive index, and extinction coefficient respectively. The extinction coefficient also relates to light absorption. It determines the light absorption capability of the materials. When light passes through a medium, some part of it will always be absorbed. The k indicates the amount of absorption loss when the light propagates through the materials. In most circumstances k > 0 (light is absorbed) or k=0 (light travels without loss). The extinction coefficient can be calculated by using the relation, k = αλ/4π where λ is the wavelength of light. It is observed from the Figure 5(d) that the extinction coefficient sharply decreases with increasing wavelength up to 1250 nm and then it becomes almost constant for up to 2250 nm. This non-zero extinction coefficient of GO-CNP nanocomposite for different wavelength demonstrates that this material is a good light absorber, which is in agreement with Figure 5(b). This is to mention here that there is no effect of glass substrate on the optical properties of GO-CNP thin film because its effect automatically subtracted during measurements by spectrophotometer as it is programmed in the software.

FIG. 5.

(a) Optical transmittance, reflectance as a function of photon wavelength, (b) Absorption co-efficient as a function of photon energy, (c) Tauc’s plot and (d) Extinction co-efficient as a function of photon wavelength.

FIG. 5.

(a) Optical transmittance, reflectance as a function of photon wavelength, (b) Absorption co-efficient as a function of photon energy, (c) Tauc’s plot and (d) Extinction co-efficient as a function of photon wavelength.

Close modal

Electrical Hall-effect measurements were conducted in lateral direction of the GO, CNP, and GO-CNP nanocomposite film using ‘Ecopia Hall-effect measurement system’ by 4-point Van der Pauw approach at ambient condition. The electrical parameters obtained from this measurement are presented in Table I. As prepared GO is an insulator but after amalgamation carbon nanoparticles in GO, the prepared GO-CNP nanocomposite contains a large numbers sp2-carbon and delocalized (π − π) electrons, which enhance the conductivity of nanocomposite significantly; and this is in agreement with the XPS study.

The room temperature DC transport measurements were carried out using a standard two-probe technique. The cartoon of a final device for electrical transport measurement setup is depicted in Figure 6(a) and the current-voltage characteristic of this device in dark is presented in Figure 6(b).

FIG. 6.

(a) Cartoon of the DC electrical measurements setup and (b) Current-Voltage characteristic curve of the GO-CNP nanocomposite thin film detector device.

FIG. 6.

(a) Cartoon of the DC electrical measurements setup and (b) Current-Voltage characteristic curve of the GO-CNP nanocomposite thin film detector device.

Close modal

The continuous growth and decay current curve of IR response for GO-CNP radiation detector device before saturation are shown in Figure 7(a), where radiation current is drawn as a function of time with and without body radiation on the device. The source of radiation (hand) was kept at a distance of about 1 cm away from the detector. When the hand of a human body is place to the proximity of the device, current starts rising immediately. As soon as the hand is put away from the device, the current rapidly falls to zero. It means the radiation-current retention time (RRT) is very poor. The RRT is defined as the time, a radiation current can sustain in the sample after the IR is switched OFF (hand away from the detector). The rapid rise and fall of the body current due to hand in repeated proximity and removal is presented in Figure 7(b).

FIG. 7.

(a) The continuous growth and decay current upon radiation due to body radiation and (b) Rapid growth and decay current curve due to body radiation.

FIG. 7.

(a) The continuous growth and decay current upon radiation due to body radiation and (b) Rapid growth and decay current curve due to body radiation.

Close modal

The continuous increase of current due to body radiation detected by the composite thin film as a function of time is plotted in Figure 8(a). Exponential fit to the experimental data point is presented in Figure 8(b). In first 5 secs the current increased 2 times which is twice as much higher as compared to the performance obtained from only reduced graphene oxide detector as reported before.56,57 In 10 seconds the current increases 12 times of the first count and increases linearly for the first 60 seconds. After that, the current increases gradually for another 10 minutes. The rise of current due to body irradiation with time fits with the equation of exponential growth I(t) = I0 + C(1 - exp(-t/τC) +D(1 - exp(-t/τD)); where t is the time when hand was taken to proximity of the film, τ is the time constant, I0 is the current before irradiation by the body (dark current),56,57 C, D are scaling constants. The ‘τ’ is defined as the amount of time required for holes inflowing the electrode. In the growing curve two regimes are found corresponding to two time constants τC and τD which are 3 sec and 36 sec, respectively. The GO-CNP detector responses within 2 sec after bringing the hand to proximity of the device and then the current increases in about 36 sec before saturating.

FIG. 8.

(a) Current due to continuous exposure with hand and (b) Exponential fit to the experimental data curve (a).

FIG. 8.

(a) Current due to continuous exposure with hand and (b) Exponential fit to the experimental data curve (a).

Close modal

To characterize the detector two important parameters; irradiation responsivity (Rλ) and external quantum efficiency (EQE) were calculated. The Rλ is defined as the ratio of current generated at the thin film under IR irradiation by the body to the intensity of the incident irradiation on the effective area of a detector58 whereas the EQE is defined as the number electrons perceived per incident photon. The high responsivity depends on the values of Rλ and EQE. The two parameters were determined by using the following two equations Rλ = Iλ /(Pλ S)58,59 and external quantum efficiency as EQE =hcRλ /(eλ), where, Iλ is the photocurrent(Iirradiation – I dark), Pλ the light intensity, S the effective illuminated area, h Planck’s constant, c the velocity of light, e the electronic charge, and λ the exciting wavelength.60,61 According to our experimental results, Rλ and EQE of GO-CNP devices are 3 mA W−1 and 0.48%, respectively. The obtained results were very much reproducible with no degradation of the device performance. It was also observed that the detector did not respond to other source having wavelength other than 780 nm; and this specific wavelength detection capability is crucial for optimum device working performance. Typical thermal sensors utilize the Seebeck effect in which thermoelectric force is generated due to the temperature difference at the contact points between two different kinds of metal. In the present study recombination/generation of electron-hole pairs when exposed to human body radiation is the plausible phenomena to detect radiation emitted by the body.56,57 Figures (1,2,3) were produced using the program WSxM.62 

The synthesis of GO-CNP nanocomposite from naturally available and abundant sources is reported; and its structural, morphological, size distribution and electrical properties of such material in thin film form are studied. The AFM study confirms the spherical formation of carbon nanoparticles. The XPS measurement suggested that after incorporation of CNP in GO, the conductivity of GO-CNP composite enhanced significantly as conformed by the electrical Hall-effect measurements. This study offers the possibility of using GO-CNP nanocomposite as a IR radiation detector without any chemical and annealing treatment of composite. Due to the availability of CNP source in nature, improved method of synthesis of GO, and the cheap and mass production technique of this nanocomposite make this attempt economically feasible. Moreover, such extraordinary properties of the composite presented here encourage us to contemplate on this protocol for next generation device engineering of human body IR detector.

This work is supported by ISP, Sweden.

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