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A free-standing high boron-doped diamond nanosheet (BDDNS) has been fabricated for the development of a flexible BDDNS strain senor. High boron-doped diamond was initially grown on a tantalum substrate in a microwave plasma-assisted chemical vapor deposition method, and was then transferred to a Kapton polymer substrate to fabricate the flexible BDDNS/Kapton device. Before performing the transfer process, the thin BDDNS’s morphology and bonding structure on the top and bottom surfaces were investigated using scanning electron microscopy and Raman spectroscopy. The contact potential difference and work function values of the BDDNS top and bottom surfaces were measured using a Kelvin probe atomic force microscope. Significant electrical conducting properties were observed from the resistance mapping of the BDDNS foil, and the average resistance value of 31 Ω attained from the top surface of the BDDNS foil. The electrical response of the BDDNS/Kapton device was investigated using a custom-made measurement system and a positive residual resistance change with strain was observed. The developed BDDNS/Kapton device was able to sustain for measuring up to 0.55% of strain, which indicates it may have great potential to be utilized in low-strain sensor applications.

The reaction of three types of carbon with oxygen (1 atm) at different temperatures was investigated. The precursors for the carbons studied were Kapton (polyimide), cellulose and cellulose that was carbonized with ammonium chloride. Two consecutive processes are confirmed to occur during the reaction with oxygen. The build up of oxygenated surface complexes by chemisorption of oxygen and the well-known gasification of these surface groups. The carbons originating from Kapton or cellulose carbonized in the presence of NH 4 Cl contain nitrogen. As the nitrogen content in the carbon is higher, the uptake of oxygen at the carbon surface by chemisorption is more pronounced. Hall effect measurements demonstrate that electrons are the major charge carrier in nitrogen containing carbons, while holes are the charge carriers in the nitrogen-free carbons. The determination of the type of charge carrier explains the observation that the nitrogen-containing carbons chemisorb oxygen more readily than the nitrogen-free carbons. Electronic conductivity demonstrates the affect of the sign of the charge carrier on the chemisorption of the carbons during chemisorption of oxygen. While in the case of n-type carbon a decrease in the conductivity was observed, p-type carbons exhibit a slight increase followed by a decrease in the conductivity.

Carbon membranes were prepared by carbonisation of Kapton ® polyimide at different temperatures under vacuum and nitrogen flow. Pore structure development of the membranes during carbonisation was studied. Carbonisation temperature was critical in the modification of membrane structure. At the same temperature, the carbon membranes fabricated under nitrogen atmosphere had higher gas permeances than those fabricated under vacuum. During heat treatment, the value of d -spacing for the carbon membranes decreased with increasing temperature, however, vacuum and nitrogen atmosphere had different influences on the changes in the d -spacing. CO 2 adsorption showed that the carbon membranes prepared at 1273 K under vacuum had the highest micropore volume whilst the membranes prepared at 1073 K under vacuum had the highest characteristic adsorption energy. N 2 adsorption showed that the samples obtained at 873 K under vacuum had the highest nitrogen uptake. Mesopores were deemed to be connected through micropores and narrow channels between meso- and/or micropores were supposedly present. The micropores predominantly controlled the transport properties of the carbon membranes. The membrane samples obtained at 1173 K under vacuum yielded ideal separation factors of 558.27, 60.87, 19.69 and 138.53 for He/N 2 , CO 2 /N 2 , O 2 /N 2 and CO 2 /CH 4 , respectively, with permeances of 7.26, 0.79, 0.26, 0.13 and 0.006 mol/(m 2 s Pa) for He, CO 2 , O 2 , N 2 and CH 4 , respectively.

Two kinds of shavings with different degrees of defect concentration were filed away from Kapton with 50 μm in thickness using two sheets of diamond paper with different diamond particle size. Kapton is known as a starting material for preparation of well-crystallized graphite film. The shavings were carbonized and their graphitization behaviors were investigated by X-ray diffraction and Raman microprobe measurements. The carbonized shavings heat-treated at 3000 °C show lower graphitizability than that of the carbonized Kapton film heat-treated at 3000 °C. Existence of turbostratic structure in the 3000 °C-treated shavings was verified by X-ray diffraction. The results of the Raman microprobe on the 3000 °C-treated shavings indicated inhomogeneous graphitization proceeded during heat treatment. The graphitization degree of the 3000 °C-treated shavings has been found to depend on the average size of the diamond particles of the diamond paper used.

Kapton-type polyimide film having boron-bearing functional groups in the molecule was synthesized and its carbonization/graphitization behavior was investigated by XPS, SEM, XRD, Raman spectrometry, and the measurements of electronic properties. It was found that >B–N

Two types of boron containing polyimide (Kapton type) film were prepared either by adding dihydroxyphenylborane (DPB) to polyamic acid [mixing method] or by using diaminodiphenyl ether having a boron containing functional group (DDE–B) to prepare polyamic acid [substitution method]. Formed polyimide films containing boron were carbonized at 600–1200°C. By doping boron into the precursor polyimide, preferential formation of B–N bonds in carbonized films was observed and appreciable amounts of nitrogen were chemically trapped in the carbon film even after carbonization at 1200°C. The polyimide prepared by the substitution method gave uniform carbon films in composition and structure, though DDE–B is not simply synthesized and didn't polymerize to high degree. The polyimide prepared by the mixing method gave non-uniform carbon films, but the process was very simple and possible to increase boron content by using different boron compounds.

The chemical bonding state of the nitrogen which remains in the carbon films derived from a polyimide Kapton film was studied by X-ray photoelectron spectroscope and related to the changes in structure and transport properties. The nitrogen remaining after heat treatment up to 2200 °C was in a tertiary bonding state, replacing carbon atoms in hexagonal layers, which was supported by theoretical calculation based on ab-initio molecular orbital theory. The departure of substituted nitrogen atoms from hexagonal layers showed a good correspondence with structure development and changes in transport properties, the presence of nitrogen depressing the developments in structure and transport properties. After the departure of nitrogen above 2300 °C graphitization of the films was very remarkable.

Polyamide acid was prepared from pyromellitic dianhydride (PMDA) and oxydianiline (ODA), and was then reacted with NaH and various kinds of alkyl halides for transformation into alkyl ester. The cast films were imidized as fixed on glass substrate to give Kapton-type polyimide films, and were then carbonized by heating to 900 °C. It was shown that the electrical conductivity of the carbonized films decreased with the increase of the size of the leaving group at the imidization. The carbonized films were further heated to 2800 °C for graphitization. Their degrees of graphitization and orientation of the graphite crystallites as a function of weight loss at imidization were studied by X-ray diffraction measurements at room temperature and magnetoresistance measurements at liquid nitrogen temperature. Both measurements clearly indicate that the graphitized films prepared from polyamide acid alkyl ester starting from PMDA and ODA have high degrees of graphitization. It was also made clear that, in the case of polyimide having flexible ether linkage, the orientation of the graphitized films did not depend on the size of the leaving group at imidization.

Graphitization behavior of the carbonized film of commercially available aromatic polyimide film Kapton 25 μm in thickness was studied by X-ray diffractometry, measurements of the transport properties such as the electrical resistivity, Hall coefficient and magnetoresistance, and scanning electron microscopy. The specimens were films carbonized at 900 °C and heat-treated at temperatures between 1000 and 3000 °C with a step of 100 °C. For the specimens carbonized and heat-treated below 2000 °C, the average lattice constant a0 was measured to be lower than that of the single crystal of graphite. Changes related to the transformation from the turbostratic structure to the graphitic occurred at a heat treatment temperature around 2200 °C in the microtexture on the fracture surface and the resistivity at liquid nitrogen temperature. The changes also appeared in the ratio of the resistivity at room temperature to that at liquid nitrogen temperature, and the Hall coefficient and magnetoresistance at liquid nitrogen temperature. The dependences of the resistivity ratio and also the Hall coefficient on HTT for the specimens with turbostratic structure can be related to the average crystallite size L0(110) along the a-axis. The results of the resistivity, Hall coefficient and magnetoresistance were analyzed by a simple model.

The carbon films prepared from polyimide Kapton were investigated by XPS and elemental analysis. The chemical states of carbon and nitrogen gradually changed with carbonization temperature and the changes in the peak intensity ratio of I[ N1s ] I[ C1s ] by XPS were consistent with N C mole ratios by elemental analysis. The N1s peak around 401 eV which was a main component at 1200 °C was considered to correspond to quaternary species such as a pyrrole type nitrogen. This species may exist in the carbon films prepared at 2000 °C and affect their properties.

Highly crystallized graphite films were prepared by successive heat treatments at 3100 °C for 40 minutes and then 3200 °C for 23 minutes under atmospheric pressure of pure argon gas from thin carbonized polyimide films. The starting polyimide films were a commercially available Kapton and a laboratory prepared high-modulus-polyimide film formed via polyamic acid gel. The crystallinity of the graphite films obtained was examined by the measurements of interlayer spacing d002, mosaic spread MS, electrical conductivity σ at 300 and 77 K, residual resistivity ratio RRR, and maximum transverse magnetoresistance ( AΔϱ ϱ ) max , mean magnetoresistance anisotropy ratio r , and Hall coefficient R H at 77 K. The present graphite films exhibit the highest crystallinity as graphite films obtained from polyimide films (i.e., the values of d002, MS, σ at 300 K, RRR, and ( AΔϱ ϱ ) max and r in the field of 1 T at 77 K were 0.3354 nm, 1.7–2.3 °, 1.80–2.14 × 106 S/m, 13.49–17.26 and 0.0040–0.0086, respectively, and small positive values of R H in fields around 0.2 T at 77 K were observed).

A remarkable host effect on the intercalation of CuCl2 in a molten salt system of CuCl2-KCl was observed. Even after 12 days in the molten salt at 380°C, no graphite intercalation compounds (GICs) were obtained from the graphite films prepared from a polyimide Kapton, while from highly oriented pyrolytic graphite and kish graphite with similar physical sizes, GICs were obtained within one day and from natural graphite flakes with the size of 400 μm, within two hours. The graphite film containing more defects (H-film) was transformed to the stage-2 GIC at 500° by applying Cl2 pressure, but the more perfect film (O-film) did not under the same condition.

Graphitizability of various carbonized polyimide films heat treated at 2950°C was studied by X-ray and magnetoresistance measurements and SEM observation. The films used were commercially available polyimide films, Kapton and Upilex, and two kinds of laboratory-prepared polyimide films. Results obtained show experimental evidence that there are three conditions involved in obtaining highly graphitizable carbon films; 1. (1) flatness of original organic molecules, 2. (2) high degree of their orientation and 3. (3) simple release of non-carbon atoms during carbonization.

The effect of heating rate during carbonization on graphitization was studied on the carbon films derived from commercially available aromatic polyimide films, Kapton and Novax. The carbon film from Kapton gave the higher value of ( Δρ ρ ) max with the longer residence time between the glass transition and decomposition temperatures, that is, the slower heating rate, but that from Novax showed a maximum at a residence time of around 120 min. The results were discussed on the basis of intramolecular vibration above the glass transition temperature.

In this letter magnetoresistance measurements and scanning electron microscopy observations on the same specimen show that the low degree of preferred orientation in the film is due to the formation of pores during the graphitisation process

Carbon film has been prepared by pulse-YAG laser (λ=1064nm, pulse width; 8ns) irradiation to the Kapton-type polyimide film under N2 and air atmosphere, and the structure has been characterized by Raman spectroscopy bycomparing with those obtained through ordinary heat treatment under Ar atmosphere using graphite resistance furnace.Carbon films from Kapton film are prepared as a function of laser irradiation time. They have a characteristic of pebble-like texture caused by rapid carbonization. The carbon films obtained have been evaluated to be the same crystallographicstructural level as 2000°C heat-treated Kapton film by Raman profile. Carbon film by laser-irradiation has the potentialof the applications for such as conducting circuit.

Polyimide film “Kapton” C22H10O5N2 has been known to give well-oriented graphite film by high temperature heat treatment. Its carbonization behavior was followed as a function of carbonization temperature up to 1000°C. Carbon films without any appreciable deformation and cracks were obtained by carbonization up to 1000°C in between two alumina plates, though it showed large weight loss up to 40 wt% and also large shrinkage up to 23%. Carbonization proceeded in two steps; in the first step, an abrupt release of oxygen associated with remarkable weight loss and shrinkage occurred over a rather narrow temperature range of 550–650°C and in the second, nitrogen and the remaining oxygen were released gradually above 700°C. In the second carbonization step, a rapid increase of electrical conductivity, reaching about 65 S/cm after 1000°C and growth of carbon layers were observed.

In this work, we first screen print thin GO laminates on Kapton film and then chemically reduce to rGO with desired sheet resistance by controlling printing cycles and reduction time. The thin rGO laminates have a wide range of conductivity from 2.8 S m −1 up to 1.3×10 4 S m −1, exhibiting excellent consistency of electric performance even after 50000 times bending. Commonly used rGO reduction level characterization methods have been compared with the proposed sheet resistance method. It is revealed that the later has higher variation with reduction time, providing a new method for reduction monitoring of rGO. Benefiting from the tunability of its sheet resistance, the rGO laminate not only can be used in flexible electronic circuits as conductors or resistors, but also highly efficient to absorb microwave radiations with proper design. Therefore, a printed, three-layer, Jaumann structured microwave absorber has been designed, fabricated and characterised. The maximum microwave absorption rate is up to 99.9997% where the −10 dB fractional bandwidth is over 153%, which covers L, S and C bands. Moreover, the fabricated absorber can absorb efficiently even when the incident angle is as low as 20°. Full design procedure, simulation and measurement results are presented.

ESR spectra of N2+-irradiated polyimide (Kapton) films have been investigated as a function of the irradiation dose. Two narrow single lines with slightly different g-values close to 2.003 have been detected in the highly irradiated Kapton films, and they have tentatively been assigned to giant aromatic radicals being in the areas of different carbonization stages. The Kr+ -irratiation has given ESR spectra similar to those by the N2+-irradiation. Some different features of the ESR spectra between the carbonaceous substances produced by ion-irradiation and those by pyrolysis have been discussed.