A Single‐Step Process to Produce Carbon Nanotube‐Zinc Compound Hybrid Materials

An atmospheric‐pressure plasma system is developed and is used to treat carbon nanotube assemblies, producing a hybrid carbon‐zinc structure. This system is integrated into a floating‐catalyst chemical vapor deposition furnace used for the synthesis of macroscopic assemblies of carbon nanotubes to allow for the in‐line, continuous, and single‐step production of nano‐composite materials. Material is deposited from a sacrificial zinc wire in the form of nanoparticles and can coat the surface of the individual carbon nanotubes as they form. Additionally, it is found that the deposited materials penetrate further into the carbon nanotube matrix than a comparable post‐synthesis deposition, improving the uniformity of the material through the thickness. Thus, a single‐step metal‐based coating and carbon nanotube synthesis process which can form the basis of production scale manufacturing of metal‐carbon nanotube composite materials with an atmospheric‐pressure plasma system are demonstrated.


Introduction
New devices and applications increasingly require tailored material properties which necessitate the development of advanced materials and novel nanocomposites to drive corresponding technologies.In addition to the material-specific properties, cost, performance and the environmental impact of the raw materials and associated processes are key features that need to be considered.
Nanoscale carbon and zinc-based materials have been investigated for a wide range of applications including sensors DOI: 10.1002/smtd.202300710such as embeddable mechanical stress [1 ]and strain gauges, [2,3] or electrochemical sensors for both liquid [4] and gas detection. [5]The significant potential is noted for the energy-storage sector, where zinc can provide substantial pseudocapacitance with carbon lending stability and flexibility leading to highquality supercapacitors. [6,7]With the advent of wearable electronic devices, the necessity for flexible, high-performance lithium-ion batteries is pre-eminent.Zn-based compounds such as zinc oxide (ZnO) and zinc sulfide (ZnS) have for instance high theoretical capacities in the application of lithium-ion battery anodes, 978 and 962.3 mAh g −1 respectively, they are relatively abundant, non-toxic, low cost, and environmentally friendly. [8,9]10][11][12] These represent some of the most relevant and industrially relevant applications of these hybrid materials and serve to illustrate the diverse potential of this avenue in the field of materials science.
These carbon-zinc composite materials are typically produced by chemical routes such as solvothermal, [9,10,13] wet chemistry [7,8,14] and sol-gel techniques, [11] or through microwavebased processes. [6]Whilst there are advantages to pre-forming the carbon nanostructures before producing the composite material (e.g., easier selection of the ideal carbon nanomaterials, options for purification of contaminants, and generation of beneficial functional groups), there are some distinct disadvantages.As the process involves a growth stage and a separate assembly step, it results in a longer production time with any further cleaning or purification step exacerbating this further.When combined with the protracted reaction times observed to produce composite material, e.g. up to 37.5 h excluding an overnight drying procedure, [13] it is clear that the up-front investment and manufacturing costs can be relatively high.Handling hazardous chemicals can complicate the implementation of the process on an industrial scale by necessitating greater safety controls and protocols, also ultimately impacting costs, both immediate and those related to a potential accident.Such limitations make the development of other, with faster or single-step processes desirable, especially if these can reduce the use of hazardous chemicals.[17][18][19][20] However to create a composite material with the FC-CVD system as-is, these fibers and mats would have to be post-treated.This will diminish the overall production rate and as such necessitates an "in-line" system for producing the composite material.In this paper, we detail the scaled-up integration of an atmospheric-pressure plasma system [21,22] with an FC-CVD furnace in an attempt to harness the demonstrated impressive carbon-zinc hybrid material properties with the rapid formation mechanical of FC-CVD to provide a first step toward large-scale formation feasibility.This system represents a simple option for "in-line" coating of the aerogel materials, requiring no vacuum and using a relatively cheap zinc rod as the precursor.We successfully obtain a Zn/CNT composite material in a single step, which is compared against an "off-line" configuration, where the plasma system is used to treat a statically positioned, preformed CNT assembly.Scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy are utilized to investigate the integration of the Zn materials with the CNT matrix.

Fundamental Carbon Nanotube Ribbon Characterization
The typical physical and chemical properties of standard CNT ribbons are given in (Figure 1).The pristine material takes the form of a tubular sock-like structure with a black coloration (Figure 1a).This sock is made up of entangled CNTs (Figure 1b) with some excess catalyst particles observed on the CNT surfaces.The catalysts that seeded CNT growth can be observed within the base of the CNTs in (Figure 1c).Raman spectroscopy (Figure 1d) shows typical features of CNTs, including the "D-band" peak at ≈ 1330 cm −1 which is due to the in-plane vibration of the sp 2 hybridized carbon atoms in the graphitic lattice and the "G-band" peak at ≈ 1580 cm −1 , attributed to defects in the graphitic lattice edges which affect the ring-breathing mode.In addition to these, two additional peaks can be observed, a small shoulder peak can be assigned to the "D ' -band " at 1610 cm −1 , which is the result of a double-resonance intra-valley process, and the second overtone of the "D-band" referred to as the "2D-band" at ≈ 2650 cm −1 , which arises from a two-phonon lattice vibration process.X-ray photoelectron spectroscopy (XPS) measurements of the surface demonstrate a predominantly carbon surface, with some oxygen as well as iron and sulfur which likely come from catalyst materials that did not nucleate CNTs.

Production of the Zinc-Carbon Hybrid Material
The scannng electron microscopy (SEM) images in (Figure 2) show that for every condition, deposits of material can be seen on top of the CNT matrix, albeit varying in coverage and morphology.The term "in-line" is used to refer to samples produced with the plasma deposition taking place as the CNT was synthesized from the furnace, while "off-line" refers to samples that were first synthesized and subsequently exposed to the plasma process.For "off-line" treatments the particles on the surface appear to be relatively small with diameters between 50 nm and 100 nm.At both 45 W and 60 W applied power, the coverage of the CNT ribbon by the "off-line" treatment is sparse, with clustering of the particles apparent.By contrast, the "in-line" treatment of the CNT ribbons results in a more complete coverage, with particles attaching along the full lengths of the individual CNTs.Increasing applied power from 45 W to 60 W led to enhanced material deposits and a reduction in diameter from 15-25 nm at 45 W to 5-15 nm at 60 W. It is noteworthy that with the "in-line" treated samples the individual CNTs rather than macroscopic bundles of CNTs appear to have been coated.
Transmission electron microscopy (TEM) further illustrates differences between the "in-line" and "off-line" conditions, although we should note that TEM sample preparation unavoidably has some impact on the analysis, due to sample handling with the tweezers and limited accuracy on sample area selection.Therefore, TEM analysis should be mainly used for assessing the morphology and attachment of the particles on the CNTs, while a quantitative analysis of deposition and coverage will rely on XPS analysis (see further below).The 45 W "off-line" setup leads to particles that form agglomerates (Figure 3a) on the individual CNTs (Figure 3b).By comparison, the 45 W "in-line" procedure yields particles that are much less agglomerated, with superior attachment to the sidewalls of the CNTs (Figure 3c,d), and improved particle size uniformity although some clusters and particle stacking were still observed.
The "G-band" to "D-band" ratio from Raman spectroscopy can be used to compare the graphitization of samples, [23][24][25][26] with a larger ratio corresponding to a less defective and more graphitic sample.From (Figure 4) there is little difference between the pristine (black lines) and "off-line" (red lines) plasma-treated samples in terms of this graphitization ratio for either plasma source power values, all ranging within 0.6-0.7.However, when the CNTs are treated in-line (blue lines), the average graphitization ratio is more than double that of the pristine samples at both 45 W and 60 W applied power.This may be due to cleaning or soft etching of the CNT aerogel surface by interaction with the plasma-generated gas species.This process appears to remove the amorphous carbon on the graphitic lattice surface and may represent an additional benefit of the "in-line" process. [27]-ray diffraction (XRD) measurement of the zinc-carbon nanotube samples illustrates a variety of different crystal structures.A representative XRD spectra ("In-line" at 50 W) is presented in Figure 4c.In addition to the peaks ascribed to CNTs [28][29][30][31] 001 (12.78°), 002 (26.11°), 100 (43.3°), and 101 (44.75°), there are  numerous peaks that can be ascribed to Zn [32] , ZnO [28,31,32] and ZnS.Three peaks are ascribed to Zn, 39.07°43°54.42°linkedto (100), ( 101) and (102) faces.The peaks at 31.87°, 34.62°, 36.39°,47.63°, and 56.74°are ascribed to wurtzite ZnO [33] faces (100), (002), ( 101), (102), and (110).The ZnS can be ascribed to two different structures, wurtzite and cubic ZnS.[34] The wurtzite phase shows peaks at 27.2°29.92°48°belongingto (100) (002) and (110), with the cubic phase having peaks at 28.65°, 48°and 57.42°a scribed to (111), ( 220) and (311).This confirms the crystallinity of the products and suggests that mixed ZnO and ZnS phases are present in the composite; further in-depth analysis below will provide more conclusive details on these aspects.
Energy dispersive X-ray spectroscopy (EDX) measurements show dramatic differences between the conditions explored, with the most significant change between the "off-line" and "in-line" configurations.(Figure 5) shows SEM images used for the EDX analysis with the corresponding sampling locations.The results are summarized in Table 1, where average compositions are reported out of 3-4 locations.Clearly, the "in-line" treatment demonstrates a greater content of zinc over the "off-line" configuration and also Zn is higher for a higher power.Oxygen can be affected by surface contamination and also the oxidation of zinc following sample exposure to air, hence it is difficult to make any reliable conclusion about the oxygen content.However, a significant difference in sulfur content was observed between "off-line" and "in-line".Sulfur from thiophene is used to help the CNT growth process and only traces remain on the CNTs after syn-thesis, while unused sulfur is exhausted with the process gases.This is confirmed by the results for the off-line samples that report close to 0% sulfur.The sulfur content is enhanced in the "inline" sample (10-15%), indicating that Zn has reacted with sulfur in the process gas and subsequently deposited on the CNTs.
XPS depth profiling was undertaken to determine the penetration of the zinc deposits into the CNT bulk and to provide an indication of material uniformity (Figure 6).Specifically, the binding energy of carbon, oxygen, zinc, sulfur, and iron was monitored during sample ion sputtering.For identical sputtering conditions, in only the "off-line 45 W" sample was the underlying silicon detected, a result of complete sputtering through the CNTs, indicating much thinner CNT material.A direct comparison between EDX and XPS results is complicated by the different sample volumes and locations that the two techniques probe.However, the composition ranges are in very good quantitative agreement and confirm the trends previously observed in the EDX analysis.
On the outer surface of the "off-line 45 W" (Figure 6a), 1 at% of zinc was measured, and this drops to 0.5 at% after one sputter step and continues to drop as the sputter cycles increase.A layer of adventitious material coats the surface of the "in-line 45W" sample (Figure 6b), which after one sputter step shows an increase of zinc from 5.1 at% to 8.5 at%.After the first step, the zinc content proceeds to decrease over the first 100 min of sputtering before the rate of decrease tapers off.A layer of zinc is found on the surface of the "off-line 60W" samples (Figure 6c), Table 1.Atomic percentages from the energy-dispersive X-ray spectroscopy measurements for the images presented in (Figure 6).which is significantly reduced after 10 min of sputtering to 1.4 at% zinc.As the depth increases the zinc concentration falls to ≈0.15 at% indicating that the zinc material does not permeate far into the CNT assembly under these conditions, instead forming a surface coating.The "in-line 60W" sample (Figure 6d) shows an adventitious carbon layer that is removed after one sputter cycle, giving an increase in zinc from 19 at% to 34.2 at%.Thereafter, further sputtering time leads to a decrease in the zinc content to ≈1.7 at% after 400 min of total sputtering time.
As a general trend, the oxygen content decreases with the zinc content, with the iron and sulfur contributing more to the collected signal as the zinc layer is sputtered through, exposing the CNT material underneath.It can also be observed that the "inline" conditions show greater contents of sulfur, which mimics the decline of zinc with the increasing sputter time.It is apparent that treating the CNT as it forms, i.e., "in-line" deposition, allows for superior penetration of the deposits into the CNT aerogel (Figure 6e).Whilst after 320 min of total sputtering, the zinc content difference between 45 W and 60 W applied power ("in-line") is negligible, the surface composition at 60 W is dramatically enhanced.
Two components can be deconvoluted from the Zn 2p spectra, one corresponding to a mix of oxide components, zinc hydroxide (ZnOH) and ZnO and the other related to sulfur-based compounds, ZnS and Zinc sulfate (ZnSO 4 ).Obvious differences between the treatment types can be observed when the peak areas of these components are plotted as a function of ion sputtering time, (Figure 7).In general, treating the ribbons "in-line" results in a greater peak area for both oxide and sulfur-based compounds when compared to the "off-line" treatment, and an increase in applied power from 45 W to 60 W also increases the peak area.Oxide-based components have a sharp decrease in peak area over the first 100 min of sputtering, followed by a slower decline after this point.After 100 min it can also be noted that for both "in-line" and "off-line" treatments the 45 W and 60 W samples show roughly similar peak areas, suggesting simply more oxidebased materials at the surface than in the bulk of the material.The sulfur-based compounds again show a substantially higher content at the surface, though the drop-off for the "in-line" samples is a considerably lower rate than in the case of oxides, where one-quarter of the initial peak area is retained after 200 min.This combined information can be used to suggest that the material integrated within the bulk of the material is predominately reacted with the excess sulfur from thiophene during the reaction or via reaction with excess sulfurs retained on the carbon ribbon.As we move toward the sample surface a portion of the zinc-based   compounds are oxidized, due to interaction with the lab environment post-synthesis, as the experiments are performed under a hydrogen atmosphere.
The increased zinc penetration depth with the "in-line" treated samples is ascribed to the time at which the zinc materials meet the CNTs.As the CNTs form after the hot zone of the FC-CVD furnace, they begin to entangle and form a sock-like matrix.As they move further toward the collection zone, aided by the manual extraction on a rod, they condense to form a denser sock-like material, ultimately moving toward a film-like structure.As the zinc material deposited from the plasma is positioned at the end of the furnace work tube, the CNTs have not fully condensed and entangled, therefore allowing for ease of penetration by the zinc material.This is not available in the pre-formed "off-line" samples which have already condensed and are therefore more impervious to zinc inclusion beyond the surface layers.

Improving the Per-Reactor Deposition Rates of Zinc
After a successful demonstration of the synthesis of CNT/zincbased composites, efforts were undertaken to enhance the quantity of the Zn component.Rapid plasma etching using H 2 gas is a well-known technique.In our case, this could result in more rapid removal of material from the zinc wire, thus increasing the zinc content found within the CNT ribbon. [35]Using low applied powers (50 W) and adding 0.1 standard liters per minute (sLm) 2% H 2 in argon to the plasma gas mixture (1.3 sLm helium), resulted in an increased brightness of the plasma and increased sputtered material leaving the plasma region.(Figure 8) clearly shows a stripe of zinc materials deposited along the entire length of the CNT.By incorporating multiple plasma jets, full coverage along the walls of the sock-like structure may be possible, thus improving material uniformity.
The micrographs of samples produced with hydrogen added to the plasma (Figure 9a-d) are similar to those for the samples process without H 2 (Figures 3 and 6d).Here, once again, CNTs can be seen to be coated individually with Zn-based nanoparticles, even in layers below the direct surface.
(Figure 10a) shows the composition depth profile for the "inline" deposition with added hydrogen.Despite a small build-up of adventitious carbon on the surface, as evidenced by the drop in carbon after one sputter cycle, the zinc content on the surface of the sample is the dominant element.After this first sputter cycle, the greatest zinc content is measured at 43.7 at%, with oxygen at 25.3 at% and sulfur at 19.95 at% with the remainder of the signal being attributed to carbons.The most rapid decrease in zinc content is observed over the first 100 min of sputtering, falling to 28.5 at%, before the decrease slows over the rest of the sputter profile, finally reaching a minimum of 11.6 at% after 400 min of sputtering.Sulfur is observed to decrease over the first 150 min to 13.3 at%, before also entering a period of slow decrease, dropping to 7.9 at%.Oxygen shows a much more rapid decrease when compared to sulfur and zinc, falling from 25.3 at% after one sputter cycle to ≈5 at% after 320 min of sputtering.
Comparing the zinc contribution to the corresponding samples produced without hydrogen (Figure 10b), it is clear that the addition of hydrogen into the plasma gas has led to the substantial increase of not only the zinc-based surface coating but also the integration of zinc-based materials throughout the sputter depth, presumably a factor of the enhanced deposition rate in the region where the CNT aerogel is forming before condensing.By comparison, after one sputter cycle, the sample produced at 60 W "in-line" without hydrogen has a zinc content ≈10 at% lower than that produced with hydrogen "in-line" and with a lower power (50 W).This 10 at% advantage is maintained as time increases throughout the entire sputter profile, leading to a significant inclusion enhancement of zinc-based compounds.

Conclusion
In this paper, we successfully deposited nanoparticles from a sacrificial zinc wire using an atmospheric-pressure plasma system and demonstrated the single-step formation of a Zn/CNT composite material.Zinc deposition during CNT synthesis yields a different Zn-based material compared to the offline treatment.In the former, the excess thiophene/sulfur reaching the plasma deposition zone readily reacts with the Zn to form sulfur-based compounds, whereas, in the latter, predominantly oxide-based zinc is found.The quantity of sputtered material has been enhanced by the addition of a small quantity of hydrogen gas into the plasma.By depositing metal in-line during the synthesis of the CNT ribbon or mat, superior metal coating of the individual CNTs has been achieved along with superior penetration through the ribbon/mat thickness.This is further enhanced by the addition of hydrogen in the plasma gas mixture, where the increased metal removal rate from the sacrificial wire is thought to yield a large concentration of metal species in the region where the CNT aerogel is forming and compacting.
10][11][12] However, the production rate advantages of a continuous single-step process come into play, with it taking seconds to deposit the material in the FC-CVD system compared to 1 h of stirring and 12 h of reaction, followed by an overnight drying process in the hy-drothermal method. [9]Furthermore, this proof of concept work utilized one plasma system to deposit material onto the CNT aerogel as it forms.It can easily be envisioned that an additional plasma system on the opposite side of the gas exchange collar could coat the opposite surface to a high degree.Adding additional jets could enable a ring of deposits to surround and penetrate the aerogel, forming ultra-high maximal loadings of zinc into the CNT, with the quantity controlled by the applied plasma power or the number of jets.As such it is expected that this methodology will become exceptionally competitive with the standard coating methods as it matures.

Experimental Section
CNT Synthesis: The carbon nanotube assemblies in this work were produced in a floating-catalyst chemical vapor deposition system that had been previously reported. [36]Hydrogen gas carries ferrocene powder (130 sccm) and liquid thiophene vapor (90 sccm) from bubbling systems into the furnace where they thermally decompose to form the catalyst particles.The hydrogen carrier gas (1350 sccm) also helped maintain the iron particles' catalytic activity by etching amorphous carbon coatings.Methane (160 sccm) was flown into the furnace as the carbon source.After the hot zone of the furnace (1290 °C) the material cools and condenses to form a CNT aerogel in the center of the work tube.This aerogel was mechanically strong enough to be drawn out of the work tube using a rod.
Plasma Treatments: A non-equilibrium atmospheric-pressure plasma was utilized to deposit nanomaterials from a sacrificial Zn wire onto the CNT assemblies.This metal-wire plasma system had evolved from the previous experience in ZnO nanoparticle synthesis [21,22] leading to a new design and geometry configuration (Figure 11a-c); here the plasma system consists of a 1 mm diameter metal wire electrode, which was enclosed in the center of a borosilicate capillary tube (2 mm inner diameter and 3 mm outer diameter) and with a concentric electrode positioned near the outlet of the capillary.A radio-frequency (MKS instruments, Elite 300HD-01) plasma was generated between the two electrodes with the helium gas flowing along the capillary tube sustaining the plasma.A matching network comprised of a 1.8 μH inductor and two variable capacitors, 25-840 and 75-1075 pF, was used to reduce the reflected power to near-zero.Initially, plasma coating was investigated post-synthesis.The aerogel was collected and secured on a piece of silicon wafer and the plasma ignited immediately above the CNTs to assess the range of deposition rates and coverage which might be obtained.Thereafter, the plasma system was discharged during the furnace operation to deposit material into the aerogel region as the CNTs were collected, (Figure 11d).
Materials Characterization: A Schottky field emission Hitachi SU5000 instrument with an X-MaxN 80 silicon drift detector from Oxford Instruments was used in this work for scanning electron microscopy (SEM).Double-sided copper tape was used to both attach and ground the sample to the SEM sample stub for measurements.
The Zn/CNT nanoparticles (NPs) composites were examined by transmission electron microscopy (TEM) and high-resolution TEM using a JEOL JEM-2100F electron microscope operated at 400 and 600 keV.Zn/CNT samples for TEM were prepared by using tweezers to remove a small cluster of CNTs from a section of the ribbon.Ethanol drops were added to CNT/Zn-NPs placed above a holey carbon mesh (300)/Au TEM grids and dried overnight in ambient conditions.
A Horiba LabRAM 300 spectrometer with a 632.81 nm helium-neon fixed wavelength laser was used to obtain Raman spectra.Measurements were taken 0.5 cm apart for a total of five measurements per sample to assess the variance of the graphitization within the sample.An 8th-order polynomial baseline subtraction was performed using the system software.Automatic fitting of a Gaussian peak to the different bands was performed by setting peak parameters within the Origin software.The Dband was considered with a peak center at 1330 cm −1 with the G-band at 1580 cm −1 .The third peak centered at 1610-1620 cm −1 was considered as the D'-band and was fitted to exclude it from the G-band area.The area enclosed by each of these components was calculated by integrating the peaks with OriginPro 2020b software, where a peak was defined as having a minimum height of 15% of the data and a width between 5% and 15% of the data.Finally, the area ratio of G:D was calculated by dividing the two peak areas.
X-ray photoelectron spectroscopy (XPS) was used to determine the elemental composition and chemical bonding with an ESCALAB XI + spectrometer (ThermoFisher).The base pressure during spectra acquisition was better than 8 × 10 −10 mbar achieved by an Edwards E2M28 rotary vane pump, dropping to better than 5 × 10 −7 mbar when the sources are all active.The main background gas in the analysis chamber was argon at all points during the loading, pumping, and measurements.The excitation source was a monochromated aluminum anode with an excitation energy of 1486.68 eV operated at ≈15 kV and 15 mA, giving a source power of 225 W. The work function of the spectrometer was determined to be 4.68 eV.The recorded spectra include survey spectra, C 1s, O 1s, Zn 2p, Zn LMM Auger peak, Si 2p S 2p, and Fe 2p which were acquired sequentially with a total acquisition time of 374.2 s per depth level.The calibration and linearity of the binding energy scale were confirmed with three reference standards which were sputter-cleaned with the ion gun before measurement, Au 4f 7/2 (83.96 eV), Ag 3d 5/2 (368.21eV) and Cu 2p 3/2 (932.62 eV).The latest linearity calibration to the time of measurement (measured every 6 months) returned values of 83.92 eV for the Au 4f 7/2 peak, 368.22 eV for the Ag 3d 5/2 peak, and 932.59 eV for the Cu 2p 3/2 peak.With the selected scan parameters, the energy resolution was 0.1 eV for high-resolution spectra and 1 eV for survey spectra.The size of the analyzed sample area was 650 μm and takes the form of an elongated circle.The samples were prepared by securing the CNTs directly to the sample stage via double-sided copper tape.These samples were stored overnight in standard lab conditions before loading into the spectrometer.The transfer procedure within the fast entry lock of the spectrometer includes exposure to 2 × 10 −6 mbar achieved with an Edwards RV5 rotary vane pump in <10 min before XPS analysis.Charge compensation utilizing an electron beam was applied via a flood gun operated at 100 μA.The charge referencing method was performed by shifting the asymmetric Pt 4f 7/2 peak of freshly sputter-cleaned Pt foil to 71.2 eV.This foil was pressed onto the surface of the CNTs by a copper clip to ensure good electrical contact with both the sample and the sample bar.The sputter cleaning was performed with a monoatomic argon ion gun held at 4000 eV and 15 mA at an angle of 30°to the sample over a 1.5 mm wide square.This was expected to give a sputter rate of 0.97 nm s −1 for Tantalum (V) oxide.XPS depth profiling was performed with a monoatomic argon source with an accelerating voltage of 4000 eV and a current of 15 mA at an angle of 30°to the sample over a 1.5 mm wide square.Each level was formed by sputtering for 240 s, after which the ion beam was blanked, followed by a 10-second delay to allow for charge compensation before the spectra were taken.

Figure 1 .
Figure 1.Pristine carbon nanotube ribbon morphology and chemical information.a) Photograph of the as-prepared ribbon with b) scanning electron and c) transmission electron micrographs.d) Raman spectroscopy and e) X-ray photoelectron spectroscopy survey spectrum and atomic percentages give information on the chemical makeup of the ribbon.

Figure 2 .
Figure 2. Scanning electron micrographs of the carbon nanotube-zinc material composite for applied plasma powers of 45 and 60 W for both "off-line" and "in-line" treatments.

Figure 3 .
Figure 3. TEM micrographs of the Zn/CNT connections for the different plasma conditions.a,b) 45 W off-line, c,d) 45 W in-line, e,f) 60 W off-line, and g,h) 60 W in-line.

Figure 4 .
Figure 4. Representative Raman spectra for samples with a) "Off-line" and b) "In-line" plasma treatment compared to the pristine material for applied powers of 45 and 60 W. c) X-ray diffraction patterns for the produced materials.

Figure 5 .
Figure 5. Scanning electron microscopy images marked with the spots used for energy-dispersive x-ray spectroscopy.a) 45 W off-line, b) 45 W in-line, c) 60 W off-line, and d) 60 W in-line.

Figure 6 .
Figure 6.A comparison of the atomic percentage composition of samples treated at 45W for both a) "off-line" and b) "in-line" as well as 60W of applied power for both c) "off-line" and d) "in-line".An isolated comparison of the atomic percentage of Zinc at each step of the depth profile is presented for comparison of the deposition for each condition in (e).

Figure 7 .
Figure 7.A comparison of the peak area attributed to either oxygen-components or sulfur-components of zinc comparing through the thickness of ribbons treated at 45 and 60 W for both "in-line" and "off-line" procedures.

Figure 8 .
Figure 8.A photograph of the areas where zinc materials (white-silver) have been deposited along the length of the CNT ribbon (black) as it forms.

Figure 9 .
Figure 9. SEM micrographs of the material from a zinc wire with hydrogen mixed into the plasma (50 W) gas deposited onto the carbon nanotube ribbon as it formed.Representative areas along the length of the materials at a,b) ×10 000 and c,d) ×1000 magnification.

Figure 10 .
Figure 10.a) XPS depth profile measurement of the materials deposited onto CNT aerogel by "in-line" deposition at 50 W with hydrogen in the plasma gas.b) A comparison of the atomic percentage of zinc across the different plasma conditions.

Figure 11 .
Figure 11.a-c) Photographs of the plasma system positioned in the brass gas exchange collar section are ready for use.The other gas lines seen are the nitrogen dilution and exhaust lines.d) Schematic diagrams of the in-line plasma treatment of the CNT materials.