WO2022169434A1

WO2022169434A1 - Production and characterization of carbon nanowall thin films by pulsed filtered catodic vacuum arc deposition and electron cyclotron resonance microwave plasma tecniques

Info

Publication number: WO2022169434A1
Application number: PCT/TR2021/051343
Authority: WO
Inventors: Birsen KESIK ZEYREK; Hamide KAVAK
Original assignee: Cukurova Universitesi Rektorlugu
Priority date: 2021-02-03
Filing date: 2021-12-03
Publication date: 2022-08-11
Also published as: TR202101621A2

Abstract

The invention relates to the production and characterization method of carbon nanowall thin films by pulsed filtered cathodic vacuum arc deposition and electron cyclotron resonance microwave plasma techniques.

Description

PRODUCTION AND CHARACTERIZATION OF CARBON NANOWALL THIN FILMS BY PULSED FILTERED CATODIC VACUUM ARC DEPOSITION AND ELECTRON CYCLOTRON RESONANCE MICROWAVE PLASMA TECNIQUES

TECHNICAL FIELD

The invention describes to the production and characterization method of carbon nanowall thin films by pulsed filtered cathodic vacuum arc deposition and electron cyclotron resonance microwave plasma techniques.

PRIOR ART

The fact that carbon has different allotropes draws more attention . In the recent years, the number of studies with carbon nanoparticle morphology has been increasing. Great importance is attached to these nanostructures from different starting materials, which are produced in the form of nanowires, nanowalls, nanoflowers, nanoparticles and nanotubes.

Two-dimensional carbon nanowall structures consist of vertically positioned graphene layers on the substrate. The most important features of carbon nanowalls have high aspect ratio, large surface area and sharp edges (Kurita et al., 2005). BRIEF DESCRIPTION OF THE INVENTION

In our invention, the physical properties as depending on the pulse numbers of carbon nanowalls (CNWs) grown by pulsed filtered cathodic vacuum arc deposition technique (PFCVAD) and the CNW structures produced on glass and silicon substrates at different deposition times by electron cyclotron resonance microwave plasma method growth is described. Structural, morphological and optical properties of all produced thin films were investigated. The effects of CNW structures on films produced with different substrates and different methods were investigated. The importance of the substrate and production technique in the growth of carbon nanowall thin films produced with different methods on different substrates has been investigated.

LIST OF FIGURES

Figure 1. Schematic representation of the pulsed filtered cathodic vacuum arc system

Figure 2. Schematic representation of the ECR-MP system Figure 3a. SEM image of the film deposited on Silicon substrate with the PFCVAD system

Figure 3b. SEM image of the film deposited on Silicon substrate with the ECR-MP system

Figure 4a. SEM image of the film deposited on Silicon substrate with the PFCVAD system

Figure 4b. SEM image of the film deposited on Silicon substrate with the ECR-MP system

Figure 5a. Optical reflection plot of the E50 sample deposited on a glass substrate Figure 5b. Optical reflection plot of the E100 sample deposited on a glass substrate

Figure 5c. Optical reflection plot of the E150 sample deposited on the glass substrate

Figure 5d. Optical reflection plot of the E200 sample deposited on the glass substrate

Figure 5e. Optical reflection plot of the E250 sample deposited on the glass substrate

Figure 5f. Optical reflection plot of the E300 sample deposited on a glass substrate

Figure 6a. SEM images of CNW thin films deposited on a glass substrate (E50 x500000 magnification)

Figure 6b. SEM images of CNW thin films deposited on a glass substrate (E100 x25000 magnification)

Figure 6c. SEM images of CNW thin films deposited on a glass substrate (E150 x25000 magnification)

Figure 6d. SEM images of CNW thin films deposited on a glass substrate (E200 x10000 magnification)

Figure 6e. SEM images of CNW thin films deposited on a glass substrate (E250 x 5000 magnification)

Figure 6f. SEM images of CNW thin films deposited on a glass substrate (E300 x 5000 magnification)

Figure 7a. SEM images of CNW thin films deposited on a Si substrate (CSi50 x 25000 magnification)

Figure 7b. SEM images of CNW thin films deposited on Si substrate (CSi100 x 25000 magnification)

Figure 7c. SEM images (CSi150 x25000) of CNW thin films deposited on Si substrate Figure 7d. SEM images of CNW thin films deposited on Si substrate (CSi200 x5000 magnification) Figure 8. X-ray diffraction patterns of carbon nanowall films deposited on silicon substrate by ECR-MP method

Figure 9. X-ray diffraction patterns of carbon nanowall films deposited on glass substrate by ECR-MP method

Figure 10. Reflection graphs of CNW thin films deposited on silicon substrate by

ECR-MP method

Figure 11. Transmittance curves of CNW thin films deposited on glass substrate by ECR-MP method

Figure 12. Reflection curves of CNW thin films deposited on glass substrate by ECR- MP method.

Figure 13. SEM image (x 200000 magnification) of SIB4 sample deposited on silicon substrate by ECR-MP method.

Figure 14. SEM image of B4 sample stored on glass substrate by ECR-MP method (x 200000 magnification)

The equivalents of the numbers given in the figures are:

1 . Cathode

2. Anode

3. Arc Plasma

4. Filter Windings

5. Vacuum Output

6. Focusing Coils

7. Cathode Holder

8. Power Supply

9. Trigger

10. Oxygen and Nitrogen Input

11 .Turbo Molecular Pump

12. Substrate

13. Observation window

14. Gas valve

I. Reaction chamber

II. Turbo molecular pump system

III. Atom/lon Hybrid Source

IV. Gas flow - pressure control system V. Mechanical pump

VI. Methane tube

VII. Cooling unit

DETAILED DESCRIPTION OF THE INVENTION

1. Pulsed Filtered Cathodic Vacuum Arc Deposition System

The use of a vacuum arc to produce coatings was first proposed in 1892 by Thomas Edison, who received a patent on arc plasma (3) deposition (Sanders and Anders, 2000). The cathodic vacuum arc deposition system is divided into two groups as DC cathodic vacuum arc and pulsed cathodic vacuum arc, depending on the definition of the power source (8). Since the pulsed cathodic vacuum arcs have high current and high plasma density, they are more stable than DC cathodic vacuum arcs. On the other hand larger surfaces can be coated with the DC cathodic vacuum arc deposition method.

Figure 1 shows the schematic representation of the PFCVAD system. Pulsed Filtered cathodic vacuum arc deposition system consists of the reaction chamber, pulsed plasma arc source (3), turbo molecular pump (11 ), mechanical pump (V) and power supply (8), filter turns for macroparticle control (4), cathode (1), anode (2), trigger (9) and substrates (12).

The reaction chamber, which is made of 304 stainless steel that allows magnetic field entry, consists of a thermo couple gauge, an ion gauge, an observation window (13), a valve and a substrate (12) holder. While in vacuum, the lowest pressure inside is around 1 x 10’⁸ Torr.

The task of the vacuum pump is to evacuate the air of the reaction chamber and create a vacuum environment. Prior to the deposition process, the base pressure can be reduced down to 1 .3 x 10’⁸ Torr.

In our invention, glass and silicon substrates (12) are cleaned in an ultrasonic bath with acetone for 20 minutes. It is then washed using deionized water at room temperature, immersed in a beaker filled with methanol, and finally dried by blowing compressed nitrogen gas tube. The cleaned substrate (12) is placed in the vacuum chamber, and a 3mm diameter graphite rod is placed in an alumina ceramic tube. The surface temperature is kept at room temperature and deposited at a working pressure of 10’³ Torr. An arc voltage of 500V is applied between the anode (2) and the cathode (1 ) to pass the arc to a workable trigger (9). To initiate an arc between the anode (2) and the cathode (1 ), the starting plasma is created by setting the trigger voltage to 12kV. Plasma is formed by an arc discharge from the cathode (1 ) with the applied high voltage and this plasma is directed to the substrate via the anode- magnetic filter (90°) then (12) deposition is performed. When the applied voltage is below 12 kV, plasma formation cannot be achieved because of the graphite rod cannot be triggered. The production parameters of CNW thin films deposited on glass and silicon substrates (12) with the PFCVAD system are listed in Table 1.

Table 1. CNW thin films deposited on silicon and glass substrate at different pulse rates with the PFCVAD system

2. Electron Cyclotron Resonance Microwave Plasma (ECR-MP) System

Figure 2 schematically shows the ECR-MP system used in the production of carbon nanowall thin films.

Glass and silicon substrates (12) are placed on the substrate (12) holder inside the reaction chamber (I) which has been previously cleaned with methanol. The substrate (12) holder is placed in front of the plasma source so that the ion beams to fall on the substrates. After all these processes are completed, the lid of the reaction chamber (1 ) is closed and the vacuum pump is started until the base pressure reaches 2.1x1 O’³ Torr. Methane gas is introduced into the reaction chamber after the system reaches base pressure. Initially, a gas flow rate of around 4-6.5 seem is given and the pressure is adjusted to the 3.5x1 O’³ Torr. The power, current and voltage values of the system can be adjusted by the atom/ion hybrid source (III). The atom/ion hybrid source (III) consists of power indicators that can vary between 25-150 Watts, adjustable accelerating voltage of 0-2keV and ion current indicators that can vary between 0-1 mA.

As the plasma power is gradually increased, the ion energy is also increased and the ion current is set to the maximum value so that the plasma is ignited. After the plasma ignites, it is waited for about 5 minutes for the source temperature to reach equilibrium (the pressure should not be higher than 3.5x1 O’³ Torr during the formation of the plasma). After the system reaches equilibrium, the power is set to 70W and thin film is deposited. In our invention, glass and silicon substrates (12) are placed in the sample holder at the same time and bias is applied to the silicon substrate (12). The surface adhesion of the coating was increased by applying a bias voltage to the silicon substrate.

The production parameters of CNW thin films deposited with the ECR-MP system are given in Table 2.

Table 2: Production conditions of CNW thin films deposited on a silicon and glass substrates.

Carbon nanowall films were produced with PFCVAD and ECR-MP systems and the results were compared as below.

SEM images of CNW thin films produced with PFCVAD and ECR-MP systems on silicon substrates (12) are given in Figures 3a and 3b. In Figures 4a and 4b, SEM images of CNW thin films produced with PFCVAD and ECR-MP systems on glass substrates are given. When SEM images are examined, the substrate (12) and technique have different effects on CNWs. The analysis results given below also confirm this.

When the X-ray diffraction (XRD) analysis of the films deposited on the silicon and glass substrate (12) at different pulse numbers with the PFCVAD system was examined, it was observed that the films produced on the silicon substrate (12) were polycrystalline, while the films deposited on the glass substrate (12) were amorphous. The XRD analysis results of the films deposited on the silicon substrate (12) are given in Table 3.

Table 3. XRD values of CNW thin films deposited on silicon substrate When Table 3 is examined; The change in the location and intensity of the substrate peaks observed in the diffraction pattern of the CSi50, CSi100, CSi150 and CSi200 samples was due to the recrystallization of the structure. It was understood that the peak values around 22.5 in CSi100 and CSi150 samples belong to CNW. (Kumari et al., 2016). From SEM analyzes, nanowall structures are clearly observed in CSi100 and CSi150 samples (Figures 7b and 7c).

When the optical properties of the films deposited on the silicon and glass substrate by the PFCVAD system at different pulse numbers were examined, it was observed that the transmittance of all samples was around 80%. When the reflection graphics of CNW thin films deposited on the glass substrate (12) are examined; The reason why the E50 sample does not create the reflection minimum that we observed in the nanowalls is the absence of wall structures. SEM images of the E50 sample showed that wall structures were not formed. E100 and E150 samples gave a reflection minimum (nanowall distance) of around 750 nm, and it is observed from the AFM and SEM results that the nanowall distances are around 750 nm. The reflection minimums of E200, E250, E300 samples are around 1500 nm, 1250 nm and 1000 nm, respectively (Figures 5a-5f). As can be understood from this, it can be concluded that the thickness does not increase linearly as the number of pulse increases. When the Eg values are examined, it is expected that the film thickness will increase and the Eg values will decrease as the number of pulse increases. However, it has been concluded that the Eg value is higher than expected due to the decrease in the effective thickness of the film when the number of pulses to disrupt the structure is produced. Eg values of CNW thin films produced on glass substrate are given in Table 4. In the E300 sample, the separation of the film layer-by-layer from the surface was also clearly seen in the SEM images. (Fig. 6a-6f)

Table 4. Optical properties of CNW thin films deposited on a glass substrate. In the Raman spectra of all samples, there is a wide peak in the range of about 1000 cm’¹ and 2000 cm’¹. By fitting these peaks with the Gaussian curve, the D and G peak positions, half-maximum width and intensity ratios (ID/IG) were determined. These values are listed in Table 5.

It was observed from the SEM images that the wall heights of the nanowall structures increased as the number of pulses increased. Accordingly, it was observed that there was an increase in the ID/IG values. It is understood from the films produced on the glass substrate (12) that the best wall structure is in the E150 example. It is clearly observed that the height of the wall and the gaps in the walls are clear. Since the ratio of the wall inner void to the film volume is the highest in this example, it provides a suitable environment for the absorption of various gases on the surface. By using this feature, it allows the use of nanowall structures in other applications. It can be said to form a substrate (12) for various gas absorption applications and catalyst.

It is understood from the results of X-ray diffraction analysis of the films deposited on the silicon and glass substrate (12) with the ECR-MP system at different gas flows and times that the differences in the substrate (12) have very distinct effects on the samples (Figures 8 and 9). When Figure 9 is examined; It was understood that the peaks around 13.5 and 16.4 observed in the B3 sample belong to CNW structures (Kumari et al., 2016).

When the optical properties are examined; It was observed that the reflection increased as the deposition time of the thin films deposited on the silicon substrate (12) increased (Figure 10).

The fact that the reflection gives a minimum at 1250 and 750 nm in the SiB2 sample shows that the effective wall distances of the nanowall are agglomerated at two different wall distances. Since the inter-wall filling is observed in SiB3, the effective wall distance is around 600 nm, but it is not a good nanowall example. On the other hand, the SiB4 sample displays a more regular reflection minimum (nanowall gap) of around 780 nm compared to the others.

It has been observed that the transmittance of the films deposited on the glass substrate (12) is above 80% (Figure 11). When the reflection graphs were examined, it was seen that the nanowalls gave two reflection minimums. It has been observed that there is a two-fold difference between the first reflection minimum and the second reflection minimum. This means that there is a two-fold between the first nanowall and the second nanowall gap. In other words, it turns out that this may have harmonic reflectance, the main nanowalls are the larger ones, and the others are its harmonic (Figure 12). As can be seen here, glass and Si substrates (12) have distinctly different effects on the samples.

In the Raman spectrum, if the peak value of the 2D band observed in both graphite and graphene structures is less than the peak value of the G band, it resembles graphite, but if it is greater than the peak value of the G band, it resembles graphene. (Kim et al., 2014). Accordingly, it was determined that the samples deposited on the Si substrate (12) showed graphitic properties. As the G and 2D peak intensity increases, the film layer thickness increases (Table 6). At the same time, the broadening of the absorption band indicates that the layer thickness increases. The ID/IG ratio increases with time in thin films deposited on silicon and glass substrates (12). For this reason, it is concluded that as the time increases, the defect density increases with the increase of the film thickness.

Table 6. D and G peak positions, G peak half maximum widths and ID/IG ratios found as a result of Raman measurement of CNW thin films deposited on silicon and glass substrate with the ECR-MP system.

SEM images of films of SiB4 and B4 samples are displayed in Figures 13 and 14. SiB4 and B4 samples are produced on different substrates (12) at the same time. The voids between the walls are seen, and it was also obtained from the reflection graphs that the distance between the gaps is greater in the CNW film deposited on the glass substrate (Figure 10 and Figure 12).

When the morphological properties of the films produced by the ECR-MP system were examined, it was observed that the formation of nanowalls growing on the silicon substrate (12) was completed compared to the nanowalls growing on the glass substrate (12). The reason for this is explained by the application of bias to the silicon in the samples deposited on the Si substrate (12). In addition, due to the smooth crystal structure of the silicon substrate, the film formed on it is expected to be more homogeneous. When the surface roughness values of the films deposited on the glass substrate are examined, it is not concluded that the surface roughness is related to the effect of time as in the thin films deposited on the Si substrate (12). From this point of view, it is understood that the substrate (12) difference has an important effect. Surface roughness values are given in Table 7.

able 7. AFM surface roughness values of CNW thin films deposited on silicon and glass substrates. The importance of the substrate in the growth of nanowall structures emerges in films produced at the same time with the same production system under the same conditions.

PFCVAD method;

1 ) Excellent control over thin film morphology

2) Ability to produce films with low substrate temperatures and high film density

3) Easy to adhere to the film

4) Having perfect coating smoothness on all surfaces

5) Easy controllability of control parameters such as temperature, pressure, current-voltage to obtain films under different deposition

6) Due to its magnetic field and filter feature, it provides a privilege in film production due to its features such as the elimination of macro particles that disrupt the morphology of the film conditions.

The ECR-MP method is;

1 ) high stability

2) high ionization efficiency

3) high plasma density

4) It provides advantages due to its properties such as high degree of dissociation of molecules at low temperatures. However, it also has some disadvantages such as high power consumption, having a cooling unit (VII) and high cost and complex technology due to microwave components.

Claims

CLAIMS ) It is a method of producing carbon nanowall thin films with electron cyclotron resonance microwave plasma (ECR-MP) system, and its characterized by;

- Placing glass and silicon substrates (12) on the substrate (12) holder in the reaction chamber (I) , the interior of which was previously cleaned with methanol,

- The substrate (12) holder is placed in front of the plasma source such that the ion beams fall on the substrates (12)

- After closing the lid of the reaction chamber (I), operating the vacuum pump until the base pressure reaches 2.1x1 O’³ Torr,

- After the system reaches the base pressure, the methane gas is started to be given to the deposition chamber,

- Adjusting the pressure to be around 3.5x1 O’³ Torr by initially giving a gas flow of around 4-6.5 seem,

- The ion energy is brought to the maximum mode and the magnetron voltage is slowly increased,

- Adjusting the power to 70 W and gradually increasing the gas flow to ignite the plasma,

- Waiting for 2-5 minutes for the source temperature to stabilize when the plasma is obtained,

- It is characterized by the processes of film production at 2.1x10’ 3Torr base pressure and 3.5x1 O’³ Torr operating pressure and 70 Watt power values. ) It is a method of producing carbon nanowall thin film with a pulsed filtered cathodic vacuum arc deposition system, and its characterized by;

- cleaning the glass and silicon substrates (12) in an ultrasonic bath with acetone for 20 minutes,

- washing using deionized water at room temperature,

- immersing in a beaker filled with methanol and drying by spraying compressed air with a nitrogen cylinder, - The cleaned substrate (12) is placed in the vacuum chamber. Placing a 3mm diameter graphite rod into an alumina ceramic tube,

- Maintaining the surface temperature at room temperature and deposited at a working pressure of 10’³ Torr,

- Application of an arc voltage of 500V between anode (2) and cathode (1 ) to switch the arc to a reliable trigger (9),

- To start an arc between the anode (2) and the cathode (1), the trigger voltage is set to 12kV to form the starting plasma

- It is characterized by the stages of depositing the plasma, which is formed by an arc discharge from the cathode (1 ) by applying high voltage, to the substrate (12) by directing it through the anode- magnetic filter.