In this study, we investigated Cu/Ni nanoparticles synthesized in microcarbon sources during co-deposition by RF sputtering and RF-PECVD, as well as localized surface plasmon resonance for detection of CO gas using Cu/Ni nanoparticles. Morphology of particles. Surface morphology was studied by analyzing 3D atomic force micrographs using image processing and fractal/multifractal analysis techniques. Statistical analysis was performed using MountainsMap® Premium software with two-way analysis of variance (ANOVA) and least significant difference test. Surface nanostructures have local and global specific distribution. The experimental and simulated Rutherford backscattering spectra confirmed the quality of the nanoparticles. The freshly prepared samples were then exposed to a carbon dioxide chimney and their use as a gas sensor was investigated using the method of localized surface plasmon resonance. The addition of a nickel layer on top of the copper layer showed interesting results both in terms of morphology and gas detection. The combination of advanced stereo analysis of thin film surface topography with Rutherford backscattering spectroscopy and spectroscopic analysis is unique in this field.
Rapid air pollution over the past few decades, especially due to rapid industrialization, has prompted researchers to learn more about the importance of detecting gases. Metal nanoparticles (NPs) have been shown to be promising materials for gas sensors1,2,3,4 even when compared to thin metal films capable of localized surface plasmon resonance (LSPR), which is a substance that resonates with strong and strongly limited electromagnetic fields5,6,7,8. As an inexpensive, low-toxic, and versatile transition metal, copper is considered an important element by scientists and industry, especially sensor manufacturers9. On the other hand, nickel transition metal catalysts perform better than other catalysts10. The well-known application of Cu/Ni at the nanoscale makes them even more important, especially because their structural properties do not change after fusion11,12.
While metal nanoparticles and their interfaces with the dielectric medium exhibit significant changes in localized surface plasmon resonances, they have thus been used as building blocks for gas detection13. When the absorption spectrum changes, this means that the three factors of resonant wavelength and/or absorption peak intensity and/or FWHM can change by 1, 2, 3, 4. On nanostructured surfaces, which are directly related to particle size, localized surface plasmon resonance in nanoparticles, rather than in thin films, is an effective factor for identifying molecular absorption14, as also pointed out by Ruiz et al. showed the relationship between fine particles and detection efficiency15.
Regarding the optical detection of CO gas, some composite materials such as AuCo3O416, Au-CuO17 and Au-YSZ18 have been reported in the literature. We can think of gold as a noble metal aggregated with metal oxides to detect gas molecules chemically adsorbed on the surface of the composite, but the main problem with sensors is their reaction at room temperature, making them inaccessible.
Over the past few decades, atomic force microscopy (AFM) has been used as an advanced technique to characterize three-dimensional surface micromorphology at high nanoscale resolution19,20,21,22. In addition, stereo, fractal/multifractal analysis23,24,25,26, power spectral density (PSD)27 and Minkowski28 functionals are state-of-the-art tools for characterizing the surface topography of thin films.
In this study, based on localized surface plasmon resonance (LSPR) absorption, acetylene (C2H2) Cu/Ni NP traces were deposited at room temperature for use as CO gas sensors. Rutherford backscatter spectroscopy (RBS) was used to analyze composition and morphology from AFM images, and 3D topographic maps were processed using MountainsMap® Premium software to study surface isotropy and all additional micromorphological parameters of surface microtextures. On the other hand, new scientific results are demonstrated that can be applied to industrial processes and are of great interest in applications for chemical gas detection (CO). The literature reports for the first time the synthesis, characterization and application of this nanoparticle.
A thin film of Cu/Ni nanoparticles was prepared by RF sputtering and RF-PECVD co-deposition with a 13.56 MHz power supply. The method is based on a reactor with two electrodes of different materials and sizes. The smaller one is metal as an energized electrode, and the larger one is grounded through a stainless steel chamber at a distance of 5 cm from each other. Place the SiO 2 substrate and the Cu target into the chamber, then evacuate the chamber to 103 N/m 2 as the base pressure at room temperature, introduce acetylene gas into the chamber, and then pressurize to ambient pressure. There are two main reasons for using acetylene gas in this step: firstly, it serves as a carrier gas for plasma production, and secondly, for the preparation of nanoparticles in trace amounts of carbon. The deposition process was carried out for 30 min at an initial gas pressure and RF power of 3.5 N/m2 and 80 W, respectively. Then break the vacuum and change the target to Ni. The deposition process was repeated at an initial gas pressure and RF power of 2.5 N/m2 and 150 W, respectively. Finally, copper and nickel nanoparticles deposited in an acetylene atmosphere form copper/nickel nanostructures. See Table 1 for sample preparation and identifiers.
3D images of freshly prepared samples were recorded in a 1 μm × 1 μm square scan area using a nanometer multimode atomic force microscope (Digital Instruments, Santa Barbara, CA) in non-contact mode at a scanning speed of 10–20 μm/min. With. MountainsMap® Premium software was used to process the 3D AFM topographic maps. According to ISO 25178-2:2012 29,30,31, several morphological parameters are documented and discussed, height, core, volume, character, function, space and combination are defined.
The thickness and composition of freshly prepared samples were estimated on the order of MeV using high-energy Rutherford backscattering spectroscopy (RBS). In the case of gas probing, LSPR spectroscopy was used using a UV-Vis spectrometer in the wavelength range from 350 to 850 nm, while a representative sample was in a closed stainless steel cuvette with a diameter of 5.2 cm and a height of 13.8 cm at a purity of 99.9 % CO gas flow rate (according to Arian Gas Co. IRSQ standard, 1.6 to 16 l/h for 180 seconds and 600 seconds). This step was carried out at room temperature, ambient humidity 19% and fume hood.
Rutherford backscattering spectroscopy as an ion scattering technique will be used to analyze the composition of thin films. This unique method allows quantification without the use of a reference standard. RBS analysis measures high energies (He2+ ions, ie alpha particles) on the order of MeV on the sample and He2+ ions backscattered at a given angle. The SIMNRA code is useful in modeling straight lines and curves, and its correspondence to the experimental RBS spectra shows the quality of the prepared samples. The RBS spectrum of the Cu/Ni NP sample is shown in Figure 1, where the red line is the experimental RBS spectrum, and the blue line is the simulation of the SIMNRA program, it can be seen that the two spectral lines are in good agreement. An incident beam with an energy of 1985 keV was used to identify the elements in the sample. The thickness of the upper layer is about 40 1E15Atom/cm2 containing 86% Ni, 0.10% O2, 0.02% C and 0.02% Fe. Fe is associated with impurities in the Ni target during sputtering. Peaks of underlying Cu and Ni are visible at 1500 keV, respectively, and peaks of C and O2 at 426 keV and 582 keV, respectively. The Na, Si, and Fe steps are 870 keV, 983 keV, 1340 keV, and 1823 keV, respectively.
Square 3D topographic AFM images of Cu and Cu/Ni NP film surfaces are shown in Figs. 2. In addition, the 2D topography presented in each figure shows that the NPs observed on the film surface coalesce into spherical shapes, and this morphology is similar to that described by Godselahi and Armand32 and Armand et al.33. However, our Cu NPs were not agglomerated, and the sample containing only Cu showed a significantly smoother surface with finer peaks than the rougher ones (Fig. 2a). On the contrary, the open peaks on the CuNi15 and CuNi20 samples have an obvious spherical shape and higher intensity, as shown by the height ratio in Fig. 2a and b. The apparent change in film morphology indicates that the surface has different topographical spatial structures, which are affected by nickel deposition time.
AFM images of Cu (a), CuNi15 (b), and CuNi20 (c) thin films. Appropriate 2D maps, elevation distributions and Abbott Firestone curves are embedded in each image.
The average grain size of the nanoparticles was estimated from the diameter distribution histogram obtained by measuring 100 nanoparticles using a Gaussian fit as shown in FIG. It can be seen that Cu and CuNi15 have the same average grain sizes (27.7 and 28.8 nm), while CuNi20 has smaller grains (23.2 nm), which is close to the value reported by Godselahi et al. 34 (about 24 nm). In bimetallic systems, the peaks of the localized surface plasmon resonance can shift with a change in the grain size35. In this regard, we can conclude that a long Ni deposition time affects the surface plasmonic properties of Cu/Ni thin films of our system.
Particle size distribution of (a) Cu, (b) CuNi15, and (c) CuNi20 thin films obtained from AFM topography.
Bulk morphology also plays an important role in the spatial configuration of topographic structures in thin films. Table 2 lists the height-based topographic parameters associated with the AFM map, which can be described by time values of mean roughness (Sa), skewness (Ssk), and kurtosis (Sku). The Sa values are 1.12 (Cu), 3.17 (CuNi15) and 5.34 nm (CuNi20), respectively, confirming that the films become rougher with increasing Ni deposition time. These values are comparable to those previously reported by Arman et al.33 (1–4 nm), Godselahi et al.34 (1–1.05 nm) and Zelu et al.36 (1.91–6.32 nm ), where a similar sputtering was performed using these methods to deposit films of Cu/Ni NPs. However, Ghosh et al.37 deposited Cu/Ni multilayers by electrodeposition and reported higher roughness values, apparently in the range of 13.8 to 36 nm. It should be noted that differences in the kinetics of surface formation by different deposition methods can lead to the formation of surfaces with different spatial patterns. Nevertheless, it can be seen that the RF-PECVD method is effective for obtaining films of Cu/Ni NPs with a roughness of no more than 6.32 nm.
As for the height profile, the higher-order statistical moments Ssk and Sku are related to the asymmetry and normality of the height distribution, respectively. All Ssk values are positive (Ssk > 0), indicating a longer right tail38, which can be confirmed by the height distribution plot in inset 2. In addition, all height profiles were dominated by a sharp peak 39 (Sku > 3), demonstrating that the curve The height distribution is less flat than the Gaussian bell curve. The red line in the height distribution plot is the Abbott-Firestone 40 curve, a suitable statistical method for evaluating the normal distribution of data. This line is obtained from the cumulative sum over the height histogram, where the highest peak and deepest trough are related to their minimum (0%) and maximum (100%) values. These Abbott-Firestone curves have a smooth S-shape on the y-axis and in all cases show a progressive increase in the percentage of material crossed over area covered, starting from the roughest and most intense peak. This confirms the spatial structure of the surface, which is mainly affected by the nickel deposition time.
Table 3 lists the specific ISO morphology parameters associated with each surface obtained from the AFM images. It is well known that the area to material ratio (Smr) and the counter area to material ratio (Smc) are surface functional parameters29. For example, our results show that the region above the median plane of the surface is completely peaked in all films (Smr = 100%). However, the values of Smr are obtained from different heights of the bearing area coefficient of the terrain41, since the parameter Smc is known. The behavior of Smc is explained by the increase in roughness from Cu → CuNi20, where it can be seen that the highest roughness value obtained for CuNi20 gives Smc ~ 13 nm, while the value for Cu is about 8 nm.
Blending parameters RMS gradient (Sdq) and developed interface area ratio (Sdr) are parameters related to texture flatness and complexity. From Cu → CuNi20, the Sdq values range from 7 to 21, indicating that the topographic irregularities in the films increase when the Ni layer is deposited for 20 min. It should be noted that the surface of CuNi20 is not as flat as that of Cu. In addition, it was found that the value of the parameter Sdr, associated with the complexity of the surface microtexture, increases from Cu → CuNi20. According to a study by Kamble et al.42, the complexity of the surface microtexture increases with increasing Sdr, indicating that CuNi20 (Sdr = 945%) has a more complex surface microstructure compared to Cu films (Sdr = 229%). . In fact, the change in the microscopic complexity of the texture plays a key role in the distribution and shape of rough peaks, which can be observed from the characteristic parameters of the peak density (Spd) and the arithmetic mean peak curvature (Spc). In this regard, Spd increases from Cu → CuNi20, indicating that the peaks are more densely organized with increasing Ni layer thickness. In addition, Spc also increases from Cu→CuNi20, indicating that the peak shape of the surface of the Cu sample is more rounded (Spc = 612), while that of CuNi20 is sharper (Spc = 925).
The rough profile of each film also shows distinct spatial patterns in the peak, core, and trough regions of the surface. The height of the core (Sk), decreasing peak (Spk) (above the core), and trough (Svk) (below the core)31,43 are parameters measured perpendicular to the surface plane30 and increase from Cu → CuNi20 due to the surface roughness Significant increase . Similarly, peak material (Vmp), core material (Vmc), trough void (Vvv), and core void volume (Vvc)31 show the same trend as all values increase from Cu → CuNi20. This behavior indicates that the CuNi20 surface can hold more liquid than other samples, which is positive, suggesting that this surface is easier to smear44. Therefore, it should be noted that as the thickness of the nickel layer increases from CuNi15 → CuNi20, the changes in the topographic profile lag behind the changes in higher-order morphological parameters, affecting the surface microtexture and the spatial pattern of the film.
A qualitative assessment of the microscopic texture of the film surface was obtained by constructing an AFM topographic map using the commercial MountainsMap45 software. The rendering is shown in Figure 4, which shows a representative groove and a polar plot with respect to the surface. Table 4 lists the slot and space options. The images of the grooves show that the sample is dominated by a similar system of channels with a pronounced homogeneity of the grooves. However, the parameters for both maximum groove depth (MDF) and average groove depth (MDEF) increase from Cu to CuNi20, confirming previous observations about the lubricity potential of CuNi20. It should be noted that the Cu (Fig. 4a) and CuNi15 (Fig. 4b) samples have practically the same color scales, which indicates that the microtexture of the Cu film surface did not undergo significant changes after the Ni film was deposited for 15 min. In contrast, the CuNi20 sample (Fig. 4c) exhibits wrinkles with different color scales, which is related to its higher MDF and MDEF values.
Grooves and surface isotropy of microtextures of Cu (a), CuNi15 (b), and CuNi20 (c) films.
The polar diagram in fig. 4 also shows that the surface microtexture is different. It is noteworthy that the deposition of a Ni layer significantly changes the spatial pattern. The calculated microtextural isotropy of the samples was 48% (Cu), 80% (CuNi15), and 81% (CuNi20). It can be seen that the deposition of the Ni layer contributes to the formation of a more isotropic microtexture, while the single layer Cu film has a more anisotropic surface microtexture. In addition, the dominant spatial frequencies of CuNi15 and CuNi20 are lower due to their large autocorrelation lengths (Sal)44 compared to Cu samples. This is also combined with the similar grain orientation exhibited by these samples (Std = 2.5° and Std = 3.5°), while a very large value was recorded for the Cu sample (Std = 121°). Based on these results, all films exhibit long-range spatial variations due to different morphology, topographic profiles, and roughness. Thus, these results demonstrate that the Ni layer deposition time plays an important role in the formation of CuNi bimetallic sputtered surfaces.
To study the LSPR behavior of Cu/Ni NPs in air at room temperature and at different CO gas fluxes, UV-Vis absorption spectra were applied in the wavelength range of 350–800 nm, as shown in Figure 5 for CuNi15 and CuNi20. By introducing different CO gas flow densities, the effective LSPR CuNi15 peak will become broader, the absorption will be stronger, and the peak will shift (redshift) to higher wavelengths, from 597.5 nm in airflow to 16 L/h 606.0 nm. CO flow for 180 seconds, 606.5 nm, CO flow 16 l/h for 600 seconds. On the other hand, CuNi20 exhibits a different behavior, so an increase in CO gas flow results in a decrease in the LSPR peak wavelength position (blueshift) from 600.0 nm at air flow to 589.5 nm at 16 l/h CO flow for 180 s . 16 l/h CO flow for 600 seconds at 589.1 nm. As with CuNi15, we can see a wider peak and increased absorption intensity for CuNi20. It can be estimated that with an increase in the thickness of the Ni layer on Cu, as well as with an increase in the size and number of CuNi20 nanoparticles instead of CuNi15, Cu and Ni particles approach each other, the amplitude of electronic oscillations increases, and, consequently, the frequency increases. which means: the wavelength decreases, a blue shift occurs.
Post time: Aug-16-2023