Introduction

Since their discovery in 1991 [1], carbon nanotubes (CNTs) have undergone significant advancements in research over the past three decades [2]. The exceptional mechanical, electrical, and thermal properties exhibited by CNTs present huge opportunities for the development of electric devices [3, 4], sensors [5], energy harvesting systems [6], and more. Concurrently, carbon microfibers (CMFs) represent a highly interesting one-dimensional material and serve as a crucial component in carbon microelectromechanical systems (C-MEMS) [7, 8], exhibiting unique transport properties. By adopting a hanging geometry, CMFs can fully utilize their functional potential without compromising performance, unlike fibers attached to substrates [9]. Consequently, the integration of CNTs and suspended CMFs within a unified architecture represents a significant advancement in the integration of micro and nano structures, holding the promise of significantly enhancing the performance and properties of C-MEMS-based devices [10, 11]. On the other hand, carbon fiber mats, known for their exceptional conductivity and surface area, are intentionally investigated for various electronic applications [12, 13]. To generate hierarchical structures of CNTs on carbon fibers (CFs), multistep synthesis strategies have been implemented, involving separate pyrolysis and subsequent chemical vapor deposition (CVD) steps to grow CNTs on CFs using a gaseous carbon precursor [14]. In this study, we streamlined the process by incorporating localized CVD during pyrolysis to facilitate the growth of a CNT forest on the surface of suspended CMFs. Importantly, we are in line with the current trend of utilizing thermosetting resins, such as SU-8, as precursors to fabricate high-quality C-MEMS devices, which exhibit exceptional mechanical and electrical properties [15, 16]. Furthermore, we are actively exploring the utilization of polyacrylonitrile (PAN), a widely recognized non-photoresist resin, as a polymer precursor in our research. By employing PAN instead of SU-8, we can achieve high-quality fibers with low electrical resistance and a high graphitic content. The final carbon structure comprises a supportive pattern made from SU-8 and suspended CMFs made from PAN. Remarkably, we observe a particularly high yield of CNTs grown on a catalyst incorporating cobalt ferrite spinel in conjunction with a carbonaceous precursor (camphor). Our integrated process involves using a highly viscoelastic near-field electrospinning ink that incorporates metal nanoparticles (NPs). To assess the advantages of the integrated process, we conduct approximate economic calculations. Based on an analysis of the corresponding properties, we outline potential applications of hierarchical CNTs on CMFs for future investigations.

Experimental

Fabrication of a single polymeric fiber using near-field electrospinning (NFES) and a nanofiber mat using far-field electrospinning (FFES)

Using the negative photoresist SU-8 as a carbon precursor, a supporting structure comprising two rectangular walls and connecting pads was fabricated through photolithography. Subsequently, a single polymeric fiber was suspended over the two SU-8 walls using NFES (Supplementary Sect. 1, Fig. S1). A detailed description of this process can be found in Salazar et al. [17]. Prior to depositing the fiber, the carbon walls were pyrolyzed. The polymeric fiber deposited in this study was PAN fiber, and the preparation details for the PAN solution can be found in the work of George et al. [18]. Before employing NFES, the PAN-based solutions were prepared by mixing with Fe–Co NPs. The PAN solutions and NPs were mixed at 70 °C for 24 h. The molecular weight of PAN obtained from Sigma Aldrich was determined to be 150000 g mol−1. The loading of NPs in the PAN solution ranged from 0 to 10 wt%.

Far-field electrospinning is employed to produce a carbon nanofiber mat. The PAN solution is prepared with 11 wt% PAN polymer in dimethylformamide, supplemented with 5 wt% NPs. The mixture is stirred extensively at 70 °C for 24 h. The electrospinning process is conducted with an operational voltage set at 25 kV, a pump flow rate of 0.01 mL min−1, and a distance of 30 cm between the syringe tip and collector.

Synthesis of metal NPs

The synthesis of the NPs followed a standardized procedure [19]. Initially, 3.5 g of iron (III) nitrate nonahydrate (Fe(NO3)3·9H2O, ACS reagent, ≥ 98%, Sigma Aldrich) and 1.1 g of cobalt (II) nitrate hexahydrate (Co(NO3)2·6H2O, ACS reagent, ≥ 98%, Sigma Aldrich) were combined with 100 mL of ethanol (ACS grade, ≥ 99%). To achieve complete dissolution of the metal salts, the mixture underwent ultrasonication for 1 h. Subsequently, the resulting solution was subjected to continuous stirring at 90 °C until the complete evaporation of ethanol occurred, leaving behind a solid residue. The residual solid was then subjected to baking at 180 °C until it was entirely dry. Finally, thorough grinding of the resulting solid was performed to obtain a fine powder consisting of Fe–Co NPs.

Pyrolysis and local CVD

The functionalization of suspended CMFs with a dense forest of CNTs was conducted using a tube furnace (MTI, mini-CVD tube furnace, OTF-1200X) during the pyrolysis process for carbonizing PAN fiber. Following the established protocol for regular pyrolysis described in [17], the furnace temperature was gradually increased to 900 °C at a rate of 10 °C min−1. Throughout the entire process, a continuous flow of nitrogen gas (N2) at a rate of 40 cm3 min−1 was maintained. At the temperature of 900 °C, camphor was introduced into the reactor via N2 flow for a duration of 1 h. Subsequently, once the combined pyrolysis and CNT growth process were completed, the reactor was passively cooled to ambient temperature. In summary, to attain PAN fiber functionalized with a dense forest of CNTs, the comprehensive process involves the synthesis of NPs, the creation of a polymeric fiber through NFES, and the functionalization of suspended CMF structures with a CNT forest through pyrolysis and local CVD. Each step plays a crucial role in crafting the intricate architecture of the final product. The carbon nanofiber mat, integrated with CNTs, is fabricated using the proposed process. The summary of the work is visually presented in Fig. 1.

Figure 1
figure 1

Visual representation of the synthesis of hierarchical suspended carbon fiber structures decorated with CNTs.

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Characterization

The properties of the NPs and CMFs were investigated using various characterization techniques. The field emission scanning electron microscopy (FESEM) with an EDX detector and X-ray diffraction (XRD) analysis were performed using the ZEISS Supra 40VP (Germany) and Bruker Advance D8 instruments, respectively. To examine the microstructure and morphology of the functional CNTs, transmission electron microscopy (TEM) was employed using the Fei Taitan 80–300 kV instrument. For TEM sample preparation, carbon fibers were grown on a TEM grid (Silicon nitride, 5 nm) at a temperature of 900 °C for 1 h. Raman characterization was carried out using a Renishaw 1000 spectrometer equipped with an 8.5 mW He–Ne laser operating at 633 nm. The spectra were recorded from 1130 to 2760 cm−1 to assess the defects in the CNT structure, while a low wave number scanning range (115–411 cm−1) was used to evaluate the metallic and semiconducting properties.

To emphasize enhanced electrical conductivity, we assessed the resistance of carbon fiber mats integrated with a dense forest of CNTs. The mats, measuring approximately 0.10 cm × 0.02 cm, were affixed to two gold electrodes. Subsequently, the samples were connected to an electrical circuit measurement system via a feedthrough connection and placed within a 3L stainless steel vacuum chamber. To prevent oxidation, it was crucial to purge the chamber with N2 before the experiment. The chamber pressure was maintained at ambient levels. The control and recording of the carbon mat’s resistance were conducted using an electric source meter (Keithley 2636B), applying a voltage of 0.2 V for a duration of 10 s. The Vista One AFM by Molecular Vista was utilized to analyse the topography of the fiber surface in noncontact mode, covering a scan area of 4 mm × 4 mm. During the measurements, a gold-coated silicon tip was employed. The adhesion characteristics of the fiber surface were investigated by varying the vertical movement of the AFM tip from − 40 to 40 nm. The adhesion properties were assessed based on the force–distance relationship between the tip and the sample surface.

Results

Local CVD of CNTs on suspended CMF

In Fig. 2a, a representative SEM image is presented, depicting the surface of a PAN fiber loaded with Fe–Co NPs prior to pyrolysis. Subsequent pyrolysis of the fiber at 900 °C, even in the absence of an intentional gaseous carbon source, results in surface roughening when compared to the polymer fiber pre-pyrolysis (refer to Fig. 2b). Notably, needle-like growths can be observed on the surface of the pyrolyzed fiber. Elemental analysis using SEM–EDX reveals that these needles consist of more than 81 at% carbon (EDX spectra are provided in Supplementary Sect. 2, Fig. S2). The remaining elements detected are Co, Fe, and O.

Figure 2
figure 2

a SEM image showing a PAN fiber embedded with NPs before pyrolysis. b SEM image illustrating a pyrolyzed PAN fiber embedded with Fe–Co NPs. Notably, the formation of CNTs via CVD is observed even in the absence of a gaseous carbon source during pyrolysis. c SEM image displaying a single suspended PAN fiber functionalized with a dense forest of CNTs. The local CVD process is significantly enhanced by intentionally introducing a carbon source (camphor in the current case) during pyrolysis. d A TEM image showing CNT grown on Fe–Co NPs. e SEM image showing that CNTs were exclusively grown on the CMF without contaminating the Si substrate, achieved through variations in NFES conditions.

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The growth of these new carbon structures necessitates a carbon source, and during the pyrolysis of the PAN fiber depicted in Fig. 2b, no additional carbon source was introduced into the reactor. Consequently, the feasible carbon precursors in this scenario are derived from the pyrolyzing PAN fiber itself. The PAN polymer, composed of interconnected polyethylene chains via nitrile groups (—CN), undergoes fragmentation when exposed to high temperatures. This fragmentation releases carbon gases like methane, carbon dioxide (CO2), and carbon monoxide (CO), which are vital for the localized CVD process [20,21,22]. The CVD process, facilitated by these carbon gases, leads to the formation of carbon nanostructures.

Furthermore, SEM images of the PAN fibers post-pyrolysis reveal a significant reduction in fiber volume, ranging from 21 to 55 vol% (Supplementary Sect. 3, Fig. S3). This observed shrinkage in fiber volume can be attributed to the release of gaseous components, such as water, hydrogen, carbon monoxide (CO), carbon dioxide (CO2), etc., at elevated temperatures. The emission of these volatile substances from the PAN fibers during pyrolysis serves as a crucial source of precursors for the localized CVD, leading to the formation of small needle-like structures on the fiber surface. The term “Local CVD” refers to the localized deposition of this forest of CNTs solely on the CMF, without contaminating the entire carbon chip. To facilitate the expansion of carbon nanostructures, experiments were undertaken to introduce camphor vapor as an additional carbon source. The outcomes revealed a substantial growth of CNTs on the CMF, as illustrated in Fig. 2c. The microstructure and morphology of the CNT functional material were analyzed using TEM characterization. Figure 2d displays a representative TEM micrograph of the CNTs, revealing an entangled mesh of CNTs with a significant size distribution. Examination of numerous TEM images indicates that the CNT diameters range from 16 to 245 nm, while the lengths can extend up to 40 µm, resulting in aspect ratios reaching up to 800. To prevent contamination on the carbon electrodes, we reduced the amount of dimethylformamide solvent from 89 to 85 wt%, while also increasing the applied voltage during electrospinning from 110 to 300 V. A small-size syringe needle with a 30G needle was used. Figure 2e illustrates that the CNTs were exclusively grown on the CMF without contaminating the silicon substrate.

The XRD profiles of the PAN fiber pyrolyzed without camphor and the PAN fiber laden with Fe–Co NPs pyrolyzed in the presence of an external carbon source are presented in Fig. 3a. The introduction of camphor, as observed, induces abundant CVD of CNTs. The XRD pattern of the carbonized PAN fiber, as depicted in Fig. 3a, exhibits diffraction peaks at 20.96° and 25.04°, corresponding to the (010) and (002) crystallographic planes of the graphite structure [23]. Notably, with the substantial growth of CNTs, two prominent additional diffraction peaks emerge at 2θ = 9.13° and 28.96°, corresponding to the (110) and (002) planes of CNTs, respectively [24, 25]. The sharpness of these peaks indicates the high crystallinity of the deposited CNTs.

Figure 3
figure 3

a XRD pattern of pyrolyzed PAN fiber and PAN fiber functionalized with a forest of CNTs. b Powder XRD pattern of Fe–Co NPs displaying the presence of three main phases in the catalyst powder: CoFe2O4, β-Fe2O3 and Co(OH)2.

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The powder XRD pattern of Fe–Co NPs is presented in Fig. 3b, revealing the presence of three primary phases in the catalyst powder: spinel ferrite (CoFe2O4), β-Fe2O3 and Co hydroxide (Co(OH)2). The XRD peaks obtained at 2θ values of 18.6°, 30.5°, 35.6°, and 37.5° correspond to the (111), (022), (113), and (222) crystallographic planes of pure CoFe2O4 spinel (JCPDS card no. 22-1086). The reflections observed at 2θ values of 13.2°, 20.0°, and 28.5° are attributed to the (002), (010), and (013) planes, respectively, of the pristine β-Fe2O3 phase (No.1214964). Furthermore, the peaks observed at 19.1°, 32.6°, and 38.0° correspond to the (001), (010), and (011) planes, respectively, of the standard Co(OH)2 phase (No.1713580). It is highly believable that the nature of the original catalyst powder significantly influences the properties of CNTs during the pyrolysis/CVD process.

Raman analysis of CMFs

In order to assess the potential applications of the hierarchical material consisting of CNTs on CMF platforms, Raman spectra were collected to analyse the nanostructures, relative mechanical strengths, and electronic properties. Figure 4a illustrates the distinct D-band and G-band Raman characteristics of carbon structures at approximately ⁓1331 and ⁓1576 cm−1, respectively, observed in both pristine CMFs and CMFs with CNTs. However, the G-peak of pristine CMFs appears broader and less intense, while the G-peak of hierarchical CMFs is sharper and higher. The shape of the G-peaks has changed due to the presence of graphene sheets in the carbon material mixture [26]. The original CMFs exhibit an ID/IG ratio of 1.09 (Fig. 4a), indicating a high degree of disorder in the hexagonal carbon lattice and the presence of numerous defects such as heptagons, pentagons, and vacancies [27]. Conversely, the Raman data of CNTs grown using Fe–Co NPs embedded in PAN fiber show an ID/IG ratio closer to 1 (around 1.01), indicating the formation of higher quality CNTs with a high degree of symmetry. The presence of CNTs contributes to an 8% reduction in the original ID/IG ratio. To further investigate the nature of the CNTs, the RBM spectra of CNTs grown using Fe–Co NPs embedded in CMFs were examined and are presented in Fig. 4b. The RBM spectrum reveals two distinct peaks at 217 cm−1 and 282 cm−1.

Figure 4
figure 4

a Raman spectra comparing the pristine CMFs and the hierarchical structure with CNTs on CMFs. b Radial breathing mode (RBM) profile indicating the metallic nature of CNTs grown on suspended PAN fiber. c Raman spectra illustrating the effect of Fe–Co NP loading on the hierarchical structure of CNTs on CMFs.

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The mechanical strength of CMFs is closely associated with their nanostructures. We examined the structural improvement of CMFs by varying the content of embedded Fe–Co NPs within the host fiber. Figure 4c displays two shifts in the adsorption wavelength as the concentration of Fe–Co NPs in CMFs changes from 0 to 3 wt%. The D-peak undergoes a red shift from 1349 to 1331 cm−1, while the G-peak experiences a blue shift from 1560 to 1588 cm−1.

Examination of electrical conductivity and surface properties

To underscore the potential applications of hierarchical carbon fiber structures in various scenarios, we conducted an investigation into the resistance of a carbon fiber mat subjected to a 0.2 V application for 10 s. As shown in Fig. 5a, the standard carbon fiber mat is attached to gold electrodes and connected to the circuit system. Figure 5b illustrates the enhanced electrical properties of hierarchical carbon fiber mat structures compared to pristine carbon fiber mat, with resistance significantly reduced from 536 kΩ to 58 Ω.

Figure 5
figure 5

a Illustration of the feedthrough connection to connect a typical carbon fiber mat sample to the circuit system. b Column chart comparing the resistance of pristine carbon fiber mat with that of the hierarchical structure incorporating CNTs on carbon fiber mat. Error bars represent ± 2σ.

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The improvement of surface properties was investigated by examining adhesion properties during AFM tip scanning on fiber surfaces. Figure 6a and b illustrates the surface topography of pristine CMFs and PAN fibers functionalized with a dense forest of CNTs. Figure 6c presents the adhesion force between the AFM tip and the surface of pristine CMFs. The X-axis represents the force converted to an electrical signal in millivolts (mV), while the Y-axis indicates the vertical movement of the AFM tip during surface scanning. Figure 6d displays the adhesion force between the AFM tip and the PAN fiber functionalized with a dense forest of CNTs.

Figure 6
figure 6

AFM images illustrating the topography of: a pristine CMFs, and b the hierarchical structure incorporating CNTs on CMFs. The inserted images in a and b display SEM images of pristine CMFs and the hierarchical structure incorporating CNTs on CMFs, respectively. The force–distance relationship between the AFM tip and the sample surface during variations in the vertical position of the AFM tip: c for the pristine CMFs sample, and d for the hierarchical structure incorporating CNTs on CMFs. The blue line and the red dotted line represent the approach and retract interactions of the AFM tip and sample surface, respectively. The inserted animation in c illustrates the contacting procedure during the AFM scan.

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Discussions

In a previous study [28], we observed the local deposition of carbon nanomaterials on pyrolyzing SU-8 pillars, even in the absence of intentionally introduced gaseous carbon sources. We observed significant carbon nano growth beyond the small amount of initially embedded CNTs. In this research, we validate our hypothesis that the local emission of gaseous carbon vapors during the pyrolysis of SU-8 and CFs is responsible for the additional growth of carbon nanostructures.

Raman characterization of our samples indicates that their quality, as measured by the ID/IG ratio, is comparatively superior to CNTs synthesized using alternative ferrite spinel catalysts such as cobalt ferrite and iron nanoparticles, which exhibit ID/IG ratios of approximately 1.9 [29] and 1.89 [30], respectively. For nickel ferrite catalysts, this ratio is reported to be around 0.94 [31]. Importantly, the red shift of the D-peak can be attributed to the development of covalent crosslinking between the graphite planes, which prevents the slipping of carbon planes under shearing forces during tensile experiments. The increased amount of crosslinking implies enhanced tensile strength of the host CMFs [32]. Additionally, the blue shift of the G-peak and the narrower peaks indicate a higher ordered structure, suggesting a higher tensile modulus [32]. Although we have not measured the mechanical properties in this study, the reinforcing effect of Fe–Co NPs on CMFs provides strong evidence of the quality of our samples in terms of mechanical properties. The existence of features in the RBM region of Raman spectra suggests that the CNTs exhibit metallic and conductive characteristics [33]. Moreover, the reported Young’s modulus and electrical conductivity of the host CFs fall within the ranges of 100–400 GPa and 103–107 S m−1, respectively [15, 34]. Therefore, we anticipate that the addition of CNT material will enhance the performance of existing CMFs. By comparing the Raman characteristics of the current hierarchical CMFs with other previously studied CFs, we can gain initial insights into their potential applications. The suspended hierarchical CMFs hold promise for sensor applications [35, 36] due to their ultra-sensitivity and fast response times [37]. With an ID/IG ratio around 1 and CNT diameters ranging from 16 to 245 nm, this material is suitable for fabricating lithium-ion electrodes [38]. Furthermore, the high aspect ratio CNTs, reaching up to 800, provides a large surface area that meets the demands of microfabrication in the C-MEMS system [39, 40].

The electrical improvement is attributed to the presence of CNTs, which enhance conductivity and reduce defects [41]. This outcome is further supported by the Raman results. Additionally, the electrical enhancement can be ascribed to the expanded surface area, facilitating more contact points between conductive carbon fibers [42]. In comparison to the force–distance curve in Fig. 6c, the force–distance relationship in Fig. 6d exhibits more peaks in both the approach and retract curves. These peaks seem to correlate with the surface roughness of the hierarchical structure observed in Fig. 6b. The variation in the shape of the force–distance curve reflects interactions between the tip and different regions of the sample surface [43]. Additionally, the additional peaks could be attributed to the unique conductivity properties of CNTs, leading to distinct electrostatic interactions between the AFM tip and the CNTs [44]. The diverse improvements observed in hierarchical carbon fiber structures, such as enhanced conductivity, reduced resistance, and unique surface properties, position them as versatile materials with applications in various electronic devices. The enhanced conductivity and reduced defects in the hierarchical structures address challenges related to conductivity and charge transport for electric applications [45]. Additionally, the expanded surface area and improved electrical characteristics can serve as components in microdevices and electronic circuits, contributing to the development of efficient and high-performance electronic systems [46]. The CMF structure significantly influences the growth and properties of the CNTs. Detailed investigations are described in Supplementary Sect. 4. This study primarily focuses on the preparation and characterization technique of an integrated micro/nano carbon structure using a novel method that combines subtractive (pyrolysis) and additive (deposition) processes. Based on these findings, a detailed investigation of the applications of the CNT forest on CMF platforms warrants a separate investigation in the future.

To assess the economic benefits of our integrated process combining CVD with pyrolysis, we conducted a preliminary comparison with the current technique used for decorating CNTs using embedded catalyst NPs within the CF matrix. The conventional CNT growing procedure, commonly found in literature [47, 48], involves multiple high-temperature thermal treatment stages in an inert or reductive atmosphere to reduce metallic sites and create particles. In the final step, CVD is performed to promote CNT growth on the CFs. The stringent treatment conditions can significantly diminish the mechanical and electrical performance of the resulting hierarchical fibers. Moreover, the catalyst precursors used in most cases are noble metals or high-cost materials such as Palladium (II) acetate (Pd(CH3CO2)2·xH2O) [49] or Nickel (II) acetate (Ni(CH3CO2)2·xH2O) [50]. Through screening calculations, our integrated process has been shown to reduce the operation time by 81% to 90%. The energy consumption and carrier gas usage are less than 3% and 1%, respectively. Further details of this calculation can be found in Supplementary Sect. 5. Thanks to the high activity of Fe–Co NPs, we eliminate the need for a reduction gas such as hydrogen, which requires stringent safety conditions. Additionally, our chemical compound cost is 1.7 USD/1 g, while other processes range from 1.2 to 7 USD/1 g (Supplementary Sect. 6). The preparation of Fe–Co NPs can be scaled up for industrial manufacturing using conventional equipment such as precipitation, stirring, and grinding devices. The raw materials, Fe and Co, are readily available as nitrate salts, and ethanol serves as the solvent. These chemicals are abundant and commonly used in the industry [51, 52]. The operating temperature range is not severe, typically between 70 and 200 °C at atmospheric pressure. Furthermore, we avoid the use of base or acid solutions, which can cause corrosion, thereby eliminating the need for resistance materials in the equipment. Importantly, our process does not generate harmful waste residues, and ethanol vapor can be easily recycled through a simple condensation process.

The characterization results suggest potential applications for hierarchical CMF structures with CNTs in sensors and lithium-ion electrodes, offering advantages such as ultra-sensitivity and fast response times. The hierarchical CMF structures also demonstrate suitability for microfabrication in C-MEMS systems. The enhanced electrical conductivity, reduced resistance, and distinctive surface properties position hierarchical carbon fiber structures favorably for a range of electronic applications. Adhesion force measurements, reflecting surface roughness and electrostatic interactions, further underscore these advantages. The integrated process, combining CVD with pyrolysis, demonstrates economic benefits over traditional multi-step processes, highlighting its potential for large-scale, cost-effective industrial manufacturing.

Conclusion

In conclusion, this study successfully demonstrates the fabrication of hierarchical CMF structures decorated with CNTs by simultaneously conducting pyrolysis and CVD. The local CVD of CNTs on suspended CMFs was achieved by utilizing Fe–Co NPs embedded in PAN fibers as catalysts. The SEM and elemental analysis revealed the formation of needle-like carbon structures on the pyrolyzed fiber surface, with carbon gases released from the pyrolyzing PAN fiber serving as the carbon source for localized CVD. The presence of an additional carbon source, such as camphor vapor, significantly enhanced the growth and density of CNTs on the CMF. XRD analysis confirmed the crystalline nature of the deposited CNTs and identified the phases of the catalyst powder. TEM characterization revealed entangled CNT mesh structures with varying diameters and lengths, indicating the successful growth of CNTs on CMFs. Raman analysis provided insights into the nanostructures and mechanical strengths of the hierarchical CMFs. The presence of CNTs resulted in sharper and higher G-band peaks, indicating an enhancement in structural order. The ID/IG ratio of the CNTs suggested higher-quality CNTs compared to other catalysts. The mechanical strength of CMFs improved with the addition of Fe–Co NPs, as evidenced by shifts in the D-peak and G-peak wavelengths and narrower peak widths. The RBM spectra of CNTs indicated metallic and conductive characteristics. The characterization results indicate potential applications in sensors and lithium-ion electrodes. The suspended configuration of the hierarchical CMFs provided advantages for ultra-sensitivity, fast response times, and microfabrication in C-MEMS systems. Additional enhancements, including improvements in conductivity, resistance reduction, and distinctive surface properties, have been thoroughly investigated to elucidate the advantages of hierarchical carbon fiber structures. Adhesion force measurements, revealing additional peaks in the force–distance relationship, indicate correlations with surface roughness and distinct electrostatic interactions. The significant reduction from 536 kΩ to 58 Ω upon incorporating CNTs underscores their positive impact on electrical conductivity and defect reduction. Collectively, the enhanced electrical conductivity and surface properties position hierarchical carbon fiber structures as promising candidates for a wide array of electronic applications. Furthermore, optimizing the process by integrating CVD with pyrolysis demonstrated economic benefits compared to traditional processes involving multiple intermediate steps. The reduction in operation time, energy consumption, and carrier gas usage, along with the elimination of costly catalyst precursors and the need for reduction gases, presented significant advantages. Overall, this study provides a promising approach for the efficient fabrication of hierarchical CMFs decorated with CNTs. The presented integrated process shows great potential for industrial manufacturing with its simplified and cost-effective methodology, making it a viable option for large-scale production.