Thin Carbon Nitride Research Articles

Thermal properties of carbon nitride toward use as an electrode in phase change memory devices

In phase change memory cells, the majority of heat is lost through the electrodes during the programming process, which leads to significant drops in the performance of the memory device. In this Letter, we report on the thermal properties of thin film carbon nitride with a modest electrical resistivity of 5–10 mΩ cm, a low thermal conductivity of 1.47 ± 0.09 W m−1 K–1, and a low interfacial thermal conductance between carbon nitride and phase change material for length scales below 40 nm. The thermally insulating property of carbon nitride makes it a suitable thermal barrier, allowing for less heat loss during Joule heating within the memory unit. We compare the thermal properties of carbon nitride against the commonly used electrodes and insulators such as tungsten and silicon nitride, respectively, to demonstrate the promise of carbon nitride as a potential material candidate for electrode applications in phase change memory devices.

Molten salt assisted assembly growth of atomically thin boron carbon nitride nanosheets for photocatalytic H2 evolution.

Atomic-level boron carbon nitride nanosheets (BCNNS) have been prepared by a molten salt assisted assembly growth strategy, which effectively promotes the solvation of precursors, minimizes the surface energy and prevents the aggregation of layers. The as-synthesized BCNNS have atomic layered thickness and large lateral size, and show enhanced visible light H2 evolution activity compared to bulk BCN.

Synergy of dopants and defects in ultrathin 2D carbon nitride sheets to significantly boost the photocatalytic hydrogen evolution

Atomically thin 2D carbon nitride sheets (CNs) can improve the photocatalytic performance due to their high specific surface area, exposed active sites, and nano-scaled diffusion path of the charge transferred to surface. However, in practical application, 2D CNs photocatalysts always suffer the low solar absorption. Here, we present a novel approach to achieve the ultrathin 2D CNs photocatalysts with wide spectrum absorption in visible-light range. The new method, i.e. thermal annealing of atomically thin CNs in Se vapor, can dramatically extend the absorption edge of the ultrathin CNs from 418 to 574 nm. Using structural characterization and spin-polarized density functional theory, we identify the loss of the nitrogen atoms at the edges and in situ Se doping into the network of ultrathin CNs, which could change the electronic band structure of the 2D CNs. As a consequence, the ultrathin 2D CNs photocatalyst via Se vapor annealing (Se-CNs) modified by Pt cocatalyst shows a superior photocatalytic hydrogen evolution activity under visible light irradiation. More significantly, the ultrathin Se-CNs photocatalyst also exhibits an impressive photocatalytic hydrogen evolution activity under visible-light irradiation in the absence of Pt cocatalyst. We believe that our study provide a facile and environmentally friendly strategy to realize the utilization of 2D CNs photocatalyst under wide spectrum range of solar radiation to harvest solar energy efficiently, and it can be further applied in various advanced fields, including CO2 photoreduction, organic photosynthesis, and pollutant controls.

Increasing Solar Absorption of Atomically Thin 2D Carbon Nitride Sheets for Enhanced Visible‐Light Photocatalysis

Atomically thin 2D carbon nitride sheets (CNS) are promising materials for photocatalytic applications due to their large surface area and very short charge-carrier diffusion distance from the bulk to the surface. However, compared to their bulk counterpart, CNS' applications always suffer from an enlarged bandgap and thus narrowed solar absorption range. Here, an approach to significantly increase solar absorption of the atomically thin CNS via fluorination followed by thermal defluorination is reported. This approach can greatly increase the visible-light absorption of CNS by extending the absorption edge up to 578 nm. The modulated CNS loaded with Pt cocatalyst as a photocatalyst shows a superior photocatalytic hydrogen production activity under visible-light irradiation to Pt-CNS. Combining experimental characterization with theoretical calculations shows that this approach can introduce cyano groups into the framework of CNS as well as the accompanied nitrogen vacancies at the edges, which leads to both narrowing the bandgap and changing the charge distribution. This study will provide an effective strategy to increase solar absorption of carbon-nitride-based photocatalysts for solar energy conversion applications.

Microstructure and mechanical properties evaluation of cathodic arc deposited CrCN/ZrCN multilayer coatings

For the development of advanced nanoscale multilayer protective coatings, proper design of microstructure and chemical composition of carbon containing sequential transition metal nitride nanolayers is an important issue. In this work, five different nanostructured CrCN/ZrCN multilayer coatings were deposited periodically by cathodic arc evaporation. The bilayer period of the CrCN/ZrCN multilayer coatings was kept at 20 nm. The C2H2 gas flow ratio was adjusted from 6.3 to 20.0% for achieving CrCN/ZrCN multilayer coatings with 2.3–4.2 at.% carbon content. Nanolaminated CrCN and ZrCN nitride layers and thin amorphous carbon nitride mixed nanolayers ∼5 nm thick were obtained as the carbon content reached 4.2 at.%. It was found that the hardness and adhesion quality were strongly improved by the carbon addition to the CrCN/ZrCN multilayer coatings. An increase of 2.6–4.6 GPa in hardness was found for the CrCN/ZrCN multilayer coatings due to the balance of solution hardening effect of carbon atoms and the softening by the amorphous mixed nanolayer. An optimal combination of high hardness, 28.9 GPa, and good adhesion, 41 N of upper critical load were achieved when the carbon content was 4.2 at.% for the CrCN/ZrCN multilayer coatings.

Se-modified polymeric carbon nitride nanosheets with improved photocatalytic activities

The carbon nitride (CN) with selenide (Se) modification and porous thin nanosheet structure (m-CNNSs) has been successfully presented via an effective two-step continuous thermal treatment method. The as-prepared m-CNNSs show a photocatalytic H2 generation and CO2 reduction performance under visible light, the apparent quantum yield of H2 generation (λ = 420 nm) reached 8.1%. This improved photocatalytic performance originates from the large surface areas and porous nanostructure that accelerated separation of photoexcited charge carriers and promoted mass-transfer process. Particularly, the formation of the Se modified in the thin CN sheets further endow it with reduced band gap, more exposed active edges, and extended visible light absorption range. This work not only presents a simple strategy to enhance the photocatalytic performance for CN, but also opens ups a new pathway for the rational preparation of effective polymeric photocatalysts by harnessing the synergistic effects to simultaneously optimize the electronic and frame structure of polymeric photocatalysts.

Conformal Carbon Nitride Coating as an Efficient Hole Extraction Layer for ZnO Nanowires‐Based Photoelectrochemical Cells

AbstractCharge transfer at the semiconductor–electrolyte junction is one of the main challenges for further improvement of photoelectrochemical (PEC) water splitting cells due to the poor surface catalytic properties of most semiconductors for the water oxidation reaction. Here it is shown, for the first time, that a conformal and thin carbon nitride (CN) layer can efficiently extract holes from ZnO nanowires (NWs), leading to a great enhancement of both PEC performance and stability in alkaline solution. The conformal CN coating is acquired by using a new synthetic method which involves the deposition of small supramolecular assemblies on ZnO‐NWs as a seeding layer for the CN growth. Detailed PEC characterization reveals that the CN facilitates the hole transfer from the ZnO‐NWs to the electrolyte and acts as a protective shell, resulting in 3.5 times higher current densities and high external quantum efficiencies at 1.23 V versus RHE compared to the pristine ZnO‐NWs.

Oxidized carbon nitrides: water-dispersible, atomically thin carbon nitride-based nanodots and their performances as bioimaging probes.

Three-dimensional (3D) carbon nitride (C3 N4 )-based materials show excellent performance in a wide range of applications because of their suitable band structures. To realize the great promise of two-dimensional (2D) allotropes of various 3D materials, it is highly important to develop routes for the production of 2D C3 N4 materials, which are one-atom thick, in order to understand their intrinsic properties and identify their possible applications. In this work, water-dispersible, atomically thin, and small carbon nitride nanodots were produced using the chemical oxidation of graphitic C3 N4 . Various analyses, including X-ray diffraction, X-ray photoelectron, Fourier-transform infrared spectroscopy, and combustion-based elemental analysis, and thermogravimetric analysis, confirmed the production of 3D oxidized C3 N4 materials. The 2D C3 N4 nanodots were successfully exfoliated as individual single layers; their lateral dimension was several tens of nanometers. They showed strong photoluminescence in the visible region as well as excellent performances as cell-imaging probes in an in vitro study using confocal fluorescence microscopy.

Anomalous piezoelectricity in two-dimensional graphene nitride nanosheets.

Piezoelectricity is a unique property of materials that permits the conversion of mechanical stimuli into electrical and vice versa. On the basis of crystal symmetry considerations, pristine carbon nitride (C3N4) in its various forms is non-piezoelectric. Here we find clear evidence via piezoresponse force microscopy and quantum mechanical calculations that both atomically thin and layered graphitic carbon nitride, or graphene nitride, nanosheets exhibit anomalous piezoelectricity. Insights from ab inito calculations indicate that the emergence of piezoelectricity in this material is due to the fact that a stable phase of graphene nitride nanosheet is riddled with regularly spaced triangular holes. These non-centrosymmetric pores, and the universal presence of flexoelectricity in all dielectrics, lead to the manifestation of the apparent and experimentally verified piezoelectric response. Quantitatively, an e11 piezoelectric coefficient of 0.758 C m(-2) is predicted for C3N4 superlattice, significantly larger than that of the commonly compared α-quartz.

Molecular Friction-Induced Electroosmotic Phenomena in Thin Neutral Nanotubes.

We reveal by classical molecular dynamics simulations electroosmotic flows in thin neutral carbon (CNT) and boron nitride (BNT) nanotubes filled with ionic solutions of hydrated monovalent atomic ions. We observe that in (12,12) BNTs filled with single ions in an electric field, the net water velocity increases in the order of Na(+) < K(+) < Cl(-), showing that different ions have different power to drag water in thin nanotubes. However, the effect gradually disappears in wider nanotubes. In (12,12) BNTs containing neutral ionic solutions in electric fields, we observe net water velocities going in the direction of Na(+) for (Na(+), Cl(-)) and in the direction of Cl(-) for (K(+), Cl(-)). We hypothesize that the electroosmotic flows are caused by different strengths of friction between ions with different hydration shells and the nanotube walls.

Deposition of Amorphous Hydrogenated Carbon Nitride Films with a Dielectric Barrier Discharge

AbstractThin amorphous carbon nitride (CNx) films have been deposited by DBD plasma. Deposition experiments have been performed on flat silicon (100) substrates using a C2H6/N2 gas mixture and deposition times of up to 6 h. The C2H6/N2 gas ratio has been varied between 1:1 and 1:5 to observe the influence of the feeding gas mixture on the chemical composition of the deposited films. The experiments were performed at gas pressures of 300 and 500 mbar. The chemical composition and bond structure of the deposited CNx films were evaluated by X‐ray photoelectron spectroscopy and by attenuated total reflectance‐Fourier transform infrared spectrometry. The results show that the chemical composition of amorphous CNx thin films depends on the working gas composition. Films deposited with higher nitrogen gas concentrations show a larger N/C ratio, an increase of C=N and C≡N bonds, and become harder.magnified image

X-Ray Photoelectron Spectroscopy and Raman Spectroscopy Studies on Thin Carbon Nitride Films Deposited by Reactive RF Magnetron Sputtering

Thin carbon nitride (CNx) films were synthesized on silicon substrates by reactive RF magnetron sputtering of a graphite target in mixed N2/Ar discharges and the N2 gas fraction in the discharge gas, F N, varied from 0.5 to 1.0. The atomic bonding configuration and chemical composition in the CNx films were examined using X-ray photoelectron spectroscopy (XPS) and the degree of structural disorder was studied using Raman spectroscopy. An increase in the nitrogen content in the film from 19 to 26 at% was observed at FN = 0.8 and found to influence the film properties; normality tests suggested that the data obtained at FN = 0.8 are not experimental errors. The interpretation of XPS spectra might not be always straightforward and hence the detailed and quantitative comparison of the XPS data with the information acquired by Raman spectroscopy enabled us to interpret the decomposed peaks in the N 1s and C 1s XPS spectra. Two N 1s XPS peaks at 398.3 and 399.8 eV (peaks N1 and N2, respectively) were assigned to a sum of pyridine-like nitrogen and -C≡N bond, and to a sum of pyrrole-like nitrogen and threefold nitrogen, respectively. Further, the peaks N1 and N2 were found to correlate with C 1s XPS peaks at 288.2 and 286.3 eV, respectively; the peak at 288.2 eV might include a contribution of sp3 carbon.

Coating of carbon nanotubes with amorphous carbon nitride thin films and characterization of long-term emission stability

The effects of amorphous carbon nitride (CN) thin films that were coated on carbon nanotubes (CNTs) and their thermal treatment were investigated, in terms of the chemical bonding and morphologies of the CNTs and their field emission properties. CNTs were directly grown on conical tip-type tungsten substrates via the inductively coupled plasma-chemical vapor deposition (ICP-CVD) system, and the CNTs were coated with CN films using the RF magnetron sputtering system. The CN-coated CNTs were thermally treated using the rapid thermal annealing (RTA) system by varying the temperature (300–700 °C). The morphologies, microstructures, and chemical compositions of the CN-coated CNTs were analyzed as a function of the thickness of the CN layers and the RTA temperatures. The field emission properties of the CN/CNT hetero-structured emitters, and the fluctuation and long-term stability of the emission currents were measured and compared with those of the conventional non-coated CNT-emitter. The results showed that the electron emission capability of CNT was noticeably improved by coating a thin CN layer on the surface of the CNT. This was attributed to the low work function and negative electron affinity nature of the CN film. The CN-coated CNT-emitter had a more stable emission characteristic than that of the non-coated one. In addition, the long-term emission stability of the CN-coated emitter was further enhanced by thermal treatment, which was verified by x-ray photoelectron spectroscopy (XPS) analysis.

Electron Emission Properties of Hetero-Junction Structured Carbon Nanotube Microtips Coated With BN And CN Thin Films

Boron nitride (BN) and carbon nitride (CN) films, which have relatively low work functions and commonly exhibit negative electron affinity behaviors, were coated on carbon nanotubes (CNTs) by magnetron sputtering. The CNTs were directly grown on metal-tip (tungsten, approximately 500nm in diameter at the summit part) substrates by inductively coupled plasma-chemical vapor deposition (ICP-CVD). The variations in the morphology and microstructure of CNTs due to coating of the BN and CN films were analyzed by field-emission scanning electron microscopy (FE-SEM). The energy dispersive x-ray (EDX) spectroscopy and Raman spectroscopy were used to identify the existence of the coated layers (CN and BN) on CNTs. The electron-emission properties of the BN-coated and CN-coated CNT-emitters were characterized using a high-vacuum field emission measurement system, in terms of their maximum emission currents (Imax) at 1kV and turn-on voltage (Von) for approaching 1µA. The results showed that the Imax current was significantly increased and the Von voltage were remarkably reduced by the coating of CN or BN films. The measured values of Imax-Von were as follows; 176µA-500V for the 5nm CN-coated emitter and 289µA-540V for the 2nm BN-coated emitter, respectively, while the Imax-Von of the as-grown (i.e., uncoated) emitter was 134µA-620V. In addition, the CNT emitters coated with thin CN or BN films also showed much better long-term (up to 25h) stability behaviors in electron emission, as compared with the conventional CNT emitter.

Ion-beam assisted deposited C–N coating on magnesium alloys

In this study, thin carbon nitride (CN) coating was made on magnesium (Mg) alloy (AZ31) substrate by ion beam assisted deposition. The morphology, composition and phase structure of the coating were investigated by scanning electron microscopy with an energy dispersive spectroscopy, X-ray diffraction and Raman spectroscopy. Atomic force microscopy and contact angle test were used to analyze surface properties. In addition, mechanical properties were investigated by nanoindentation technique. The results of the properties of CN coating on the Mg alloy substrate provide useful information for the biological applications in the future.

Tribological properties of extremely thin protective carbon nitride films deposited on magnetic discs by complex treatment

Extremely thin nitrogen-containing carbon (C-N) films with thicknesses of 3, 6, and 9 nm were prepared as a protective overcoat on CoCrTa magnetic discs by complex treatment, including plasma irradiation and C-N reactive sputtering in an atmosphere of nitrogen (N2) and nitrogen and helium (N2 + He) gaseous mixture. Films of various thicknesses were obtained by controlling deposition time. The bonding structure and composition of the film were studied by X-ray photoelectron spectroscopy. A radio frequency power of 25 W was experimentally confirmed to be the optimum plasma irradiation power at which a ratio of magnetic loss is &lt;5 per cent. Nanohardness and elastic modulus of the films were measured by nanoindentation. Wear and oscillation scratch tests were carried out to investigate the wear-resistance property of the films. The improved performance of C-N films is attributed to the high indentation hardness, good wear-resistant property, and corrosion resistance of the coatings due to complex treatment and He addition.

Analysis of nano-indentation measurements on carbon nitride films

Analysis of nano-indentation experiments on thin carbon nitride films is complicated by the high elastic recovery and high unloading curvature observed with these materials. Methods of data analysis are compared, and a recent model by Cheng and Cheng [Surf. Coat. Technol. 133–134 (2000) 417], which uses the work done during indentation, is applied to carbon nitride films for the first time. This is found to give better estimates of hardness and modulus than the other methods.

Cryogenic deposition of carbon nitride films using a neutralized atomic nitrogen beam

Thin carbon nitride CN x films were successfully prepared by co-deposition at cryogenic temperatures, ranging from 20 to 80 K, of fullerene C 60 or cyanogen with energetic neutralized atomic nitrogen fluxes under initial ion beam energies varied from 200 to 700 eV. Film growth rates in excess of 1 μm h −1 and stoichiometries ranging from almost pure C to above 40 at.% N were formed. Film hardness and adherence were good for films with approximately 20 at.% nitrogen while higher nitrogen concentrations yield cyano-rich, soft films. The Fourier transform infrared, Raman and X-ray photoelectron spectra showed the predominantly sp 2 character of the chemical bonding between nitrogen and carbon in the films containing 29–37 at.% N, and suggest an amorphous graphite-like structure for the carbon nitride C 3N 4 phase present along with graphitic carbon as a by-product in the films prepared by cryodeposition onto Si substrates. X-Ray diffraction and scanning electron microscopy studies did not indicate the presence of any crystalline carbon nitride polymorphs in the film.

Optical, electrical and mechanical properties of nitrogen-rich carbon nitride films deposited by inductively coupled plasma chemical vapor deposition

An inductively coupled plasma utilizing chemical transport reactions has been used to deposit thin carbon nitride films with a high nitrogen content [N/(C+N) of approximately 0.5 or higher]. We report on the characterization of the application relevant properties of these films, especially the optical (refractive index, transmission), electrical (dielectric constant, resistivity) and mechanical characteristics (stress, hardness, wear resistance). The refractive index is in the order of 1.5–1.8 depending on the deposition conditions; furthermore, the films are highly transmitting for wavelengths above 600 nm. C– V curves indicate the insulating character of the CN x films which was confirmed by I– V measurements yielding resistivities up to 10 11 Ω cm at room temperature. The layers possess marginal stress as measured by the bending method on silicon cantilevers. The hardness is in the range of 1 GPa, and a friction coefficient of 0.6 was determined by ball-on-disc tests against stainless steel balls. The investigations showed that these films may be suited especially for optical and electrical applications. Finally, we correlate the films characteristics with the composition and structure of the coatings.

Characterization of elastic properties of hard carbon and boron nitride films using the Brillouin light scattering technique

The elastic properties of thin graphitic carbon and hexagonal boron nitride films have been determined by Brillouin light scattering from thermally excited surface acoustic phonons. The carbon films have been grown by plasma beam deposition at 420°C. The BN films have been deposited by r.f.-magnetron sputtering and simultaneous ion plating. In the case of amorphous carbon a layered substructure has been found with a rather compliant intermediate layer at the interface. The stiffness of the films increases with increasing ion energy. As for carbon the BN coatings exhibit a pronounced elastic anisotropy indicating a preferred orientation of the hexagonal planes perpendicularly to the surface. The comparison of the Young's moduli determined by load indentation and by Brillouin light scattering allows the conclusion that the material is composed of two or more components of different stiffness.