Aligned Carbon Nanofibers Research Articles

Electrochemical Activity Assay for Protease Analysis Using Carbon Nanofiber Nanoelectrode Arrays.

There is a strong demand for bioanalytical techniques to rapidly detect protease activities with high sensitivity and high specificity. This study reports an activity-based electrochemical method toward this goal. Nanoelectrode arrays (NEAs) fabricated with embedded vertically aligned carbon nanofibers (VACNFs) are functionalized with specific peptide substrates containing a ferrocene (Fc) tag. The kinetic proteolysis curves are measured with continuously repeated ac voltammetry, from which the catalytic activity is derived as the inverse of the exponential decay time constant based on a heterogeneous Michaelis-Menten model. Comparison of three peptide substrates with different lengths reveals that the hexapeptide H2N-(CH2)4-CO-Pro-Leu-Arg-Phe-Gly-Ala-NH-CH2-Fc is the optimal probe for cathepsin B. The activity strongly depends on temperature and is the highest around the body temperature. With the optimized peptide substrate and measuring conditions, the limit of detection of cathepsin B activity and concentration can reach 2.49 × 10-4 s-1 and 0.32 nM, respectively. The peptide substrates show high specificity to the cognate proteases, with negligible cross-reactions among three cancer-related proteases cathepsin B, ADAM10, and ADAM17. This electrochemical method can be developed into multiplex chips for rapid profiling of protease activities in cancer diagnosis and treatment monitoring.

Effect of Structural Orientation on the Performance of Supercapacitor Electrodes from Electrospun Coal-Derived Carbon Nanofibers (CCNFs)

By incorporating a parallel wire collector in electrospinning process with a hot-drawing treatment, carbon fiber mats with well-aligned coal-derived carbon nanofibers (CCNFs) were successfully fabricated. It was previously reported that the well-aligned fiber orientation could facilitate the mass transfer of electrolyte ion. In this paper, we demonstrate that surface oxygen concentration, pore area/volume and electrical conductivity were also significantly enhanced by the well-aligned carbon fiber, compared the randomly aligned CCNFs. Consequently, the well-aligned CCNFs generated the areal specific capacitance of 1590 mF cm−2 at the current density of 4 mA cm−2 in 6M KOH solution, which outperformed the aligned carbon nanofibers derived from adding carbon nanotubes or graphene as fillers into polymer precursors. Finally, a carbon/carbon supercapacitor cell was assembled with the well-aligned CCNFs mats as electrodes, showing the areal energy density of 15 μWh cm−2 at the power density of 0.3 mW cm−2, as well as gravimetric energy density of 30 Wh kg−1 at the power density of 0.6 kW kg−1 and the volumetric energy density of 18.2 mWh cm−3 at the scan rate of 50 mV s−1. 88.6% specific capacitance of full cell was retained after 5000 cycles of charge-discharge running at current density of 1 A g−1.

Plasma enhanced synthesis of N doped vertically aligned carbon nanofibers on 3D graphene

Graphene and carbon nanotubes/fibers (CNT/CNF) hybrid structures are emerging as frontier materials for high‐efficiency electronics, energy storage, thermoelectric, and sensing applications owing to the utilization of extraordinary electrical and physical properties of both nanocarbon materials. Recent advances show a successful improvement in the structure and surface area of layered graphene by incorporating another dimension and structural form—three‐dimensional graphene (3DG). In this study, vertically aligned CNFs were grown using plasma enhanced chemical vapor deposition on a relatively new form of compressed 3DG. The latter was synthesized using a conventional thermal chemical vapor deposition. The resulting free‐standing hybrid material is in‐situ N doped during synthesis by ammonia plasma and is produced in the form of a hybrid paper. Characterization of this material was done using electrochemical and spectroscopic measurements. The N doped hybrid showed relatively higher surface area and improved areal current density in electrochemical measurements than compressed pristine 3DG, which makes it a potential candidate for use as an electrode material for supercapacitors, sensors, and electrochemical batteries.

Disordered Bilayered V2O5 ⋅ nH2O Shells Deposited on Vertically Aligned Carbon Nanofiber Arrays as Stable High‐Capacity Sodium Ion Battery Cathodes ⋅

AbstractDue to the large radius of Na+ ions, it has been challenging to find suitable host materials for sustainable sodium ion batteries (SIBs). This study investigates sputter‐coated thin V2O5 shells on vertically aligned carbon nanofiber (VACNF) arrays as a novel three‐dimensional (3D) core‐shell material for SIB cathodes. SEM, TEM, XRD and Raman spectroscopy revealed that the as‐deposited V2O5 shell has a highly disordered bilayered V2O5 ⋅ nH2O structure with a large interlayer spacing of 11.0 Å, which can accommodate Na+ ions better than orthorhombic α‐V2O5 crystals. This hydrated metastable structure has been systematically characterized for Na+ storage. A high initial insertion capacity of 277 mAh g−1 can be achieved at a current density of 250 mA g−1 in the potential window of 4.0–1.0 V (vs Na/Na+). Using higher charge‐discharge rate or narrower potential windows, the electrode becomes more reversible, able to reach a coulombic efficiency of ∼99 %. Cyclic voltammetry, galvanostatic charge‐discharge and electrochemical impedance spectroscopy measurements indicate that the Na+ storage is dominated by a large pseudocapacitive contribution due to fast surface reactions, which facilitates the improved stability and high power density. Such highly disordered bilayered V2O5 ⋅ nH2O material in the 3D core‐shell architecture provides new insights for developing future SIB materials.

Enhanced electrochemical properties of hierarchically sheath-core aligned carbon nanofibers coated carbon fiber yarn electrode-based supercapacitor via polyaniline nanowire array modification

Scalable manufacturing of yarn-based supercapacitors with high energy density is highly desired for powering wearable electronics and smart textiles. In this paper, we report a novel type of sheath-core polyaniline nanowire array grown on aligned carbon nanofibers/carbon fiber yarn electrode (CFY@CNFs@PANI NWA) based supercapacitors. The carbon fiber yarn can maintain the yarn electrode with high electrical conductivity and mechanical properties. The introduced PANI NWA can further enlarge the specific surface area of the electrode and introduce pseudo-capacitance. The assembled solid-state supercapacitors show high areal specific capacitance of 234 mF/cm2 at a current density of 0.1 mA/cm2, and corresponded energy density of 21.4 μW h/cm2 at power density of 0.52 mW/cm2 in EMIMBF4/PVDF/DMF gel electrolyte. The supercapacitors also exhibit ultrahigh rate capability (68%) and excellent cycle stability (90% after 8000 cycles). We also demonstrated that a 20-cm long supercapacitor can be readily to power up 36 pieces of red LEDs with a logo of “DHU”. The scalable strategy paves a way towards mass production of wearable energy storage devices for smart textiles.

Microstructures and mechanical properties of aligned electrospun carbon nanofibers from binary composites of polyacrylonitrile and polyamic acid

High mechanical performance carbon nanofibers are highly required for the carbon nanofiber-reinforced composites, and it is necessary to develop novel precursors for the preparation of carbon nanofibers. In this work, blends of poly(acrylonitrile-butyl acrylate mono-butyl itaconate) (co-PAN) and polyamic acid (PAA) were electrospun into aligned nanofibers and the nanofibers were converted to carbon nanofibers by thermal imidization, pre-oxidation and high-temperature carbonization. FT-IR spectroscopy was applied to monitor the chemical structures of the nanofibers before and after pre-oxidation. Tensile tests were used to characterize the mechanical properties of electrospun carbon nanofibers (ECNFs). The microstructures of ECNFs were investigated by high-resolution TEM and Raman spectroscopy. The results indicated that the ECNFs derived from blend of co-PAN/PAA with molar ratio of 6/4 and with carbonization temperature of 1400 °C possessed the highest tensile strength of 1212 MPa, which could be attributed to the ordered graphitic structures in ECNFs.

High Performance Tin-coated Vertically Aligned Carbon Nanofiber Array Anode for Lithium-ion Batteries

ABSTRACTThis study reports a high-performance tin (Sn)-coated vertically aligned carbon nanofiber array anode for lithium-ion batteries. The array electrodes have been prepared by coaxial sputter-coating of tin (Sn) shells on vertically aligned carbon nanofiber (VACNF) cores. The robust brush-like highly conductive VACNFs effectively connect high-capacity Sn shells for lithium-ion storage. A high specific capacity of 815 mAh g-1 of Sn was obtained at C/20 rate, reaching toward the maximum value of Sn. However, the electrode shows poor cycling performance with conventional LiPF6 based organic electrolyte. The addition of fluoroethylene carbonate (FEC) improve the performance significantly and the Sn-coated VACNFs anode shows stable cycling performance. The Sn-coated VACNF array anodes exhibit outstanding capacity retention in the half-cell tests with electrolyte containing 10 wt.% FEC and could deliver a reversible capacity of 480 mAh g-1 after 50 cycles at C/3 rate.

(Invited) Dielectrophoretic Capture and Detection of Microbial Pathogens Using Nanoelectrode Arrays

Rapid and highly sensitive detection of pathogenic microbes is critical for food safety and environmental protection. To achieve this, it requires combining novel sample preparation techniques and extremely sensitive detection methods. In this presentation, I summarize a series of studies in my lab on developing a nanoscale dielectrophoresis (DEP) device for effective capturing and concentrating pathogenic particles such as viral and bacterial particles in a fluidic chip. This technique was then integrated with various detection methods such as fluorescence imaging, surface enhanced Raman spectroscopy (SERS) and real-time impedance measurements for quantitative assessment of the pathogen concentration. Due to the small size (~1 micron for bacterial cells and ~100 nm for viral particles), it is challenging to capture and concentrating these pathogenic particles from dilute solutions. Here we demonstrate that the highly focused electric field at the tip of an embedded nanoelectrode array can be utilized to generate a large DEP force to effectively manipulate pathogenic particles. The nanoelectrode array was made of vertically aligned carbon nanofibers (VACNFs), about 5 micron in length and 100 nm in diameter, and embedded in a SiO2 film. It was placed at the bottom of a microfluidic channel against a macroscopic indium tin oxide (ITO) top electrode, forming a DEP device in “points-and-lid” configuration. We have shown that E. coli DHα5 cells flowing through the channel can be effectively captured and concentrated at the desired microscale areas inside the channel using a small AC voltage (~6-10 Vpp). This device is particularly effective in capturing viral particles (such as bacteriophage T4r) due to the comparable size between the viral particles and the exposed VACNF tip. To achieve specific detection, the DEP chip has been integrated with a Raman probe for SERS measurements of nanotag-labelled E. coli DHα5 cells. The SERS nanotags are based on iron oxide-gold (IO-Au) core-shell nanoovals (NOVs) of ~50 nm in size, which are coated with QSY21 Raman reporters and attached to E. coli cells through specific antibodies. The combination of the greatly enhanced Raman signal by the SERS nanotags and the effective DEP concentration significantly improves the detection limit and speed. The SERS signal has been fully validated with fluorescence microscopy measurements under all DEP conditions. A concentration detection limit as low as 210 cfu/mL using a portable Raman system has been obtained with a DEP capture time of only ~50 s. The detection has been validated in purified solutions as well as complex samples including chicken broth, soil solution and apple juice. Real-time impedance measurements has also been demonstrated as a feedback during DEP capture of vaccinia viral particles. By controlling the proper AC voltage, the nucleic acid contents in the viral particles can be released by opening the envelope with electroporation under the high electric field at the VACNF tips. These results demonstrate the potential to develop a compact portable system for rapid and highly sensitive detection of specific pathogens. Furthermore, this technique is based on physical method and the pathogenic particles are fully released after the AC voltage is turned off, making it a robust device that can be repeatedly used.

Multiplexed Electrochemical Immunosensor for Label-Free Detection of Cardiac Markers Using Carbon Nanofiber Array Device

A sensor platform based on vertically aligned carbon nanofiber (CNF) electrode arrays was developed. CNF’s inherent nanometer scale, high conductivity, wide potential window, good biocompatibility and well-defined surface chemistry make them ideal candidates as biosensor electrodes. Here we present a 3x3 electrode device, with each electrode containing 40,000 carbon nanofiber nanoelectrodes. The device was demonstrated as a multiplexed immunosensor for simultaneous, label-free detection of cardiac troponin-I, C-reactive protein and myoglobin. A hydrophobic photoresist layer was used to generate wells for discretely printing antibody probes on each electrode pad. Antibodies specific to cardiac troponin-I, C-reactive protein and myoglobin were covalently bound to the CNF surface and non-specific binding is controlled through a milk protein backfill. Antibody probe immobilization and subsequent protein binding were characterized using electrochemical impedance spectroscopy and differential pulse voltammetry. Each step of the modification process resulted in changes in resistance to charge transfer due to the changes at the electrode surface upon antibody immobilization and binding to the specific cardiac protein. The real-time label free detection of the three cardiac markers from pure components and mixtures was demonstrated with high sensitivity, down to 0.2 ng/mL, and good selectivity. Detection in human blood serum did not present false positives from non-specific protein adsorption. The results demonstrate that the present sensor can serve a miniaturized, low cost device for detection of proteins in complex mixtures making this platform a good candidate for early stage diagnosis of myocardial infarction.

Supercapacitors: Battery‐like Supercapacitors from Vertically Aligned Carbon Nanofiber Coated Diamond: Design and Demonstrator (Adv. Energy Mater. 12/2018)

Supercapacitors: Battery‐like Supercapacitors from Vertically Aligned Carbon Nanofiber Coated Diamond: Design and Demonstrator (Adv. Energy Mater. 12/2018)

Magnetic field induced tunability on the thermal conductivity of ferrofluids loaded with carbon nanofibers

In this paper, it is shown that the thermal conductivity of magnetic fluids, formed by a ferrofluid loaded with carbon nanofibers, can be tuned by applying a moderate intensity magnetic field. The tuning is generated by orienting the nanoparticles in the ferrofluid, which in turn partially align the carbon nanofibers, favoring or hindering heat flow along a given direction. Thermal diffusivity at several volume concentrations of nanofibers (0, 0.25, 0.50, 1, 2 and 5%) was measured using the thermal wave resonant cavity technique, located inside a uniform moderate intensity magnetic field. Measurements were performed for random and aligned carbon nanofibers, oriented in the parallel and perpendicular directions with respect to the heat flux. The experimental results show that for 5% volume concentration of carbon nanofibers in the ferrofluid, in random configuration, i.e. without external magnetic field applied, the effective thermal conductivity increased 3 times compared to that of the ferrofluid matrix. Moreover, for parallel alignment of the carbon nanofibers with respect to the heat flux direction, the effective thermal conductivity increased 5 times. However, for perpendicular alignment of the carbon nanofibers with respect to the heat flux direction only a 2 times increment in the effective thermal conductivity is obtained. A 750 G intensity magnetic field is used for both alignment configurations. Additionally, the effect of the concentration of carbon nanofibers on the thermal time-response of the magnetic fluids was studied by switching on/off the magnetic field. The Lewis–Nielsen model was used to interpret the dependence of the thermal conductivity results as a function the concentration and orientation of the carbon nanofibers.

Battery‐like Supercapacitors from Vertically Aligned Carbon Nanofiber Coated Diamond: Design and Demonstrator

AbstractTo fabricate battery‐like supercapacitors with high power and energy densities, big capacitances, as well as long‐term capacitance retention, vertically aligned carbon nanofibers (CNFs) grown on boron doped diamond (BDD) films are employed as the capacitor electrodes. They possess large surface areas, high conductivity, high stability, and importantly are free of binder. The large surface areas result from their porous structures. The containment of graphene layers and copper metal catalysts inside CNFs leads to their high conductivity. Both electrical double layer capacitors (EDLCs) in inert solutions and pseudocapacitors (PCs) using Fe(CN)63−/4− redox‐active electrolytes are constructed with three‐ and two‐electrode systems. The assembled two‐electrode symmetrical supercapacitor devices exhibit capacitances of 30 and 48 mF cm−2 at 10 mV s−1 for EDLC and PC devices, respectively. They remain constant even after 10 000 charging/discharging cycles. The power densities are 27.3 and 25.3 kW kg−1 for EDLC and PC devices, together with their energy densities of 22.9 and 44.1 W h kg−1, respectively. The performance of these devices is superior to most of the reported supercapacitors and batteries. Vertically aligned CNF/BDD hybrid films are thus useful to construct high‐performance battery‐like and industry‐orientated supercapacitors for future power devices.

Integrated on-chip solid state capacitor based on vertically aligned carbon nanofibers, grown using a CMOS temperature compatible process

Complete miniaturized on-chip integrated solid-state capacitors have been fabricated based on conformal coating of vertically aligned carbon nanofibers (VACNFs), using a CMOS temperature compatible microfabrication processes. The 5 µm long VACNFs, operating as electrode, are grown on a silicon substrate and conformally coated by aluminum oxide dielectric using atomic layer deposition (ALD) technique. The areal (footprint) capacitance density value of 11–15 nF/mm2 is realized with high reproducibility. The CMOS temperature compatible microfabrication, ultra-low profile (less than 7 µm thickness) and high capacitance density would enables direct integration of micro energy storage devices on the active CMOS chip, multi-chip package and passives on silicon or glass interposer. A model is developed to calculate the surface area of VACNFs and the effective capacitance from the devices. It is thereby shown that 71% of surface area of the VACNFs has contributed to the measured capacitance, and by using the entire area the capacitance can potentially be increased.

Aligning carbon nanofibres in glass-fibre/epoxy composites to improve interlaminar toughness and crack-detection capability

An electric field is used to align carbon nanofibres (CNFs) in the matrix of a glass-fibre reinforced-polymer (GFRP) composite to simultaneously improve the (a) delamination toughness, (b) electrical conductivity, and (c) damage-sensing capability. The CNFs are added to the epoxy resin prior to the manufacture of the GFRP composites. To align the CNFs, an alternating current (AC) electric field of 30 V/mm at 10 kHz is applied across the GFRP sheet throughout the matrix-curing process. The electromechanical force induced by the electric field, applied in the through-thickness direction of the composite sheet, rotates and aligns the CNFs in the direction of the applied electric field prior to the gelation of the epoxy matrix. After curing, the resultant aligned, ‘chain-like’, microstructure of the CNFs in the epoxy matrix significantly enhances both the interlaminar fracture toughness and the through-thickness electrical conductivity of the GFRP composite. Specifically, the addition of 0.7 vol% of randomly-orientated CNFs in the GFRP composite yielded an ∼50% and 25% increase in the values of the mode I fracture toughness pertinent to the initiation, GIci, and steady-state growth, GIcss, of delamination crack, respectively, compared to the control GFRP composite. The alignment of the CNFs, in the transverse direction to the direction of the crack growth, increases the mode I toughness values of GIci and GIcss by ∼100% and ∼80%, respectively, compared to the control GFRP composite. These significant increases are attributable to multiple toughening mechanisms, including debonding of the CNFs from the matrix, void growth of the epoxy matrix, pull-out and rupture of the CNFs. Further, the electric-field induced alignment of the CNFs, in the through-thickness direction, increases the out-of-plane electrical conductivity of the GFRP by about twenty-six times, compared to the GFRP composite containing randomly-orientated CNFs. Of particular interest, the damage-sensing capacity is enhanced for the GFRP composite with aligned CNFs in the epoxy matrix, which stems from the greatly increased out-of-plane electrical conductivity, as confirmed by a modelling study. Therefore, this present work has identified a new strategy to develop GFRP composites with greatly improved delamination toughness, electrical conductivity, and higher crack-detection sensitivity.

Carbon nanospikes for biosensing applications.

In this paper, we discuss the structure and characteristics of carbon nanospikes. We also compare carbon nanospikes with previously grown carbon nanostructures known as vertically aligned carbon nanofibers (VACNF). Plasma enhanced chemical vapor deposition (PECVD) is used to fabricate both the nanospikes and VACNF. However, carbon nanospikes do not require a catalyst for the growth process, whereas VACNF requires a catalyst in the growth process. This facilitates batch fabrication with greater reproducibility. Scanning electron microscope images and Raman spectroscopy show that carbon nanospikes fabricated on silver wires will show superior performance.

Coin-cell Supercapacitors Based on CVD Grown and Vertically Aligned Carbon Nanofibers (VACNFs)

Complete supercapacitors (SCs) comprising vertically aligned carbon nanofibers (VACNFs) as electrode materials have been assembled as coin-cells. The VACNFs were grown directly onto the current collector by direct current plasma enhanced chemical vapor deposition (DC-PECVD), thereby providing excellent contact with the current collector, but also eliminating the need of any binder. The vertical alignment facilitates fast ion transport and the electrolyte to access the entire surface of the CNFs. The morphology of the VACNFs was evaluated by scanning electron microscopy (SEM), while the performance was assessed by several methods: cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and device related cycling by galvanostatic charge/discharge. The capacitance, 3.64 mF/cm2 , is >15 times higher than the capacitance of a coin-cell without CNFs and the cyclic performance shows these proof-of-concept SCs to retain >80% of the capacitance after 2000 full charge/discharge cycles. The direct growth of VACNFs as electrodes at the current collector opens pathways for SC production using existing coin-cell battery production technology.

Synthesis of vertically aligned carbon nanofibers using inductively coupled plasma-enhanced chemical vapor deposition

This journal paper reports a highly reliable and efficient method for the growth of vertically aligned carbon nanofibers. The inductively coupled plasma-enhanced chemical vapor deposition method utilizes a low substrate temperature (approx. 650 $${^{\circ }}$$ C) for the growth purpose using toluene as carbon source. Carbon nanofibers are characterized using SEM (scanning electron microscopy), EDX (energy-dispersive X-ray) and Raman spectroscopy. Uniform carbon nanofibers are grown on different substrates. The results further show that the use of catalyst is not mandatory to grow the carbon nanofibers.

The electrochemical enhancement due to the aligned structural effect of carbon nanofibers in a supercapacitor electrode

Aligned carbon nanofibers (ACNFs) were fabricated by electrospinning using a high speed of rotary collector (2000rpm). To achieve a synergy effect of the electron double layer and redox faradaic reaction, NiCo2O4 was deposited on the surface of the ACNFs using an electrodeposition method. The improved electrochemical performance of the electrodes was investigated by cyclic voltammetry, galvanostatic charge-discharge testing, and electrochemical impedance analysis. Among the prepared electrodes, which were deposited for different times (5, 10, 20, and 30s), the sample deposited by NiCo2O4 for 10s had the highest specific capacitance (90.1Fg−1 at 5mVs−1), good rate capability (64.7%), and cycle stability (85.2% after 1000 cycles). In addition, to examine the effects of the alignment and redox faradaic reaction of NiCo2O4, the ACNFs covered with NiCo2O4 for 10s (NC-ACNFs) were compared with the ACNFs deposited by Co3O4 (C-ACNFs) and randomly oriented carbon nanofibers covered with NiCo2O4 (NC-RCNFs). The NC-ACNFs had a 15.8% and 11.3% higher specific capacitance than that of the C-ACNFs and NC-RCNFs, respectively. These results suggested that the electrochemical properties of carbon nanofibers could be improved through the structural effects of aligned nanofibers and a redox faradaic reaction of NiCo2O4.

AC dielectrophoretic manipulation and electroporation of vaccinia virus using carbon nanoelectrode arrays.

This paper reports the capture and detection of vaccinia virus particles based on AC dielectrophoresis (DEP) and electrochemical impedance measurements employing an embedded vertically aligned carbon nanofiber (VACNF) nanoelectrode array (NEA) versus a macroscopic indium-tin-oxide (ITO) transparent electrode in a "points-and-lid" configuration. The nano-DEP device was fabricated by bonding two SU-8 covered electrodes patterned using photolithography. The bottom electrode contains a 200 × 200 μm2 active region on a randomly distributed NEA and the top electrode contains a microfluidic channel in SU-8 spin-coated on ITO to guide the flow of the virus solution. The real-time impedance change was measured during DEP capture and validated with fluorescence microscopy measurements. The NEA was able to capture virus particles with a rather low AC voltage (∼8.0 V peak-to-peak) at 1.0 kHz frequency as the particles were passed through the fluidic channel at high flow velocities (up to 8.0 mm/s). A concentration detection limit as low as ∼2.58 × 103 particles/mL was obtained via impedance measurements after only 54 sec of DEP capture. At the low AC frequencies (50.0 Hz or less), the high electric field at the exposed VACNF tips induced electroporation of the DEP-captured virus particles, which was validated by fluorescence emission from the dyes staining lipophilic membrane and internal nucleic acid, respectively. This study suggests the possibility of integration of a fully functional electronic device for rapid, reversible and label-free capture and detection of pathogenic viruses, with a potential of generating electroporation to the captured the virus particles for further biochemical study.

On the image formation in x-ray radiography using aligned carbon nanofibers

Evidence is presented that field electrons emitted from vertically-aligned carbon nanofibers (CNFs) yield clearer x-ray images than do thermionic electrons, under the identical electron-optical condition. Specifically, the same sample, an LSI circuit, mounted on the same x-ray chamber could be imaged far more sharply with a CNF emitter than with a thermionic one. It is hypothesized that electrons discharged from CNF tips hit the target to form “discrete focal points” thereon, thereby generating multiple x-ray beams that interplay to form a brilliant, sharply-delineated x-ray image. This hypothesis may stimulate open discussion on how to define the “focal point” for the x-ray imaging using nano-structured electron sources. Also, the improved resolution attained with CNFs might indicate that the heat generation originating in electron-target interactions is not so serious in the present field-emission mode.