Vacuum Annealing Research Articles

Ciprofloxacin degradation with a defective TiO2-x nanomaterial under sunlight

TiO2 nanoparticles obtained by microwave-assisted hydrothermal synthesis were subjected to facile post-processing based on vacuum annealing. The resulting defective (TiO2-x) material showed extended light absorption in the visible range, enhancing sunlight compatibility. Structural and optical characterization point to the arising of an Urbach tail as the main reason. TiO2-x was then employed as photocatalyst for the inactivation of ciprofloxacin, an emerging environmental threat and source of antimicrobial resistance, under sunlight. TiO2-x performed significantly better than its parent compound and mechanistic analysis of the degradation pathway indicates that this material is a promising candidate for solar treatment of fluoroquinolones residues in water.Graphical abstract

Annealing effects on the magnetic and magnetotransport properties of iron oxide nanoparticles self-assemblies

In magnetic tunnel junctions based on iron oxide nanoparticles the disorder and the oxidation state of the surface spin as well as the nanoparticles functionalization play a crucial role in the magnetotransport properties. In this work, we report a systematic study of the effects of vacuum annealing on the structural, magnetic and transport properties of self-assembled ∼10 nm Fe3O4 nanoparticles. The high temperature treatment (from 573 to 873 K) decomposes the organic coating into amorphous carbon, reducing the electrical resistivity of the assemblies by 4 orders of magnitude. At the same time, the 3.Fe2+/(Fe3++Fe2+) ratio is reduced from 1.11 to 0.13 when the annealing temperature of the sample increases from 573 to 873 K, indicating an important surface oxidation. Although the 2 nm physical gap remains unchanged with the thermal treatment, a monotonous decrease of tunnel barrier width was obtained from the electron transport measurements when the annealing temperature increases, indicating an increment in the number of defects and hot-spots in the gap between the nanoparticles. This is reflected in the reduction of the spin dependent tunneling, which reduces the interparticle magnetoresistance. This work shows new insights about influence of the nanoparticle interfacial composition, as well their the spatial arrangement, on the tunnel transport of self-assemblies, and evidence the importance of optimizing the nanostructure fabrication for increasing the tunneling current without degrading the spin polarized current.

Structure and electrical conductivity of Ti-Zr-Ni films of quasicrystalline and related crystalline phases

The temperature dependence of electrical resistivity in the temperature range from 4.4 to 300 K for Ti41Zr41Ni18 (at.%) thin coatings of various crystal perfection and phase compositions has been investigated. The films were deposited by the magnetron sputtering method. The following vacuum annealing in various modes provided several combinations of the film phases such as 1/1 and 2/1 crystal-approximant phases, the quasicrystalline icosahedral phase, Laves (Ti,Zr)2Ni phase and α-Ti(Zr) solid solution phase. The structure and composition of the films before and after annealing were studied in detail by X-ray diffractometry and cross-sectional high-resolution transmission electron microscopy. Samples with predominant amorphous, quasi-crystalline, and approximant 2/1 phases have a temperature coefficient of resistance less than zero, while samples dominated by crystalline phases exhibit the characteristic metallic conductivity. For the quasicrystalline Ti41Zr41Ni18 film, the temperature dependence of the electrical resistance turned out to be similar to that of bulk samples with the composition Ti40Zr40Ni20. A significant effect of the presence of phases with metallic conduction on the overall conductivity of the coating is described. The electrical resistance of the 2/1 approximant phase with a low content of the additional Laves phase in the film has an almost constant value over the entire temperature range under study.

Interdiffusion in the formation of thin niobium films on singlecrystal silicon under vacuum annealing conditions

For the design of technological process for creating device structures based on niobium and single-crystal silicon with thedesired properties, empirical and theoretical knowledge about the solid-phase interaction process in the system of a thin niobium film is required. The purpose of the research was a comprehensive study of the redistribution of components during the formation of thin niobium films on single-crystal silicon obtained by magnetron-assisted sputtering followed by vacuum annealing. The structure and phase composition were studied by X-ray phase analysis, scanning electron microscopy, and atomic force microscopy. Distribution of components along the depth was determined using the Rutherford backscattering spectrometry. The traditional experimental method for studying the process of interdiffusion of components in binary macroscopic systems is the placing of inert marks. However, the use of this method in systems containing thin films is hindered by the comparable thicknesses of the films and marks. This circumstance makes the mathematical modelling the most convenient method for the analysis of the interdiffusion process in thin-film systems. The interdiffusion model during the formation of polycrystalline niobium film – single-crystal silicon systems, developing the Darken’s theory for the limited solubility components was proposed. Grain boundary diffusion of silicon in the intergrain space of a polycrystalline niobium film was proposed. Numerical analysis of the experimental distribution of concentrations within the model established that silicon is the dominant diffusant in the studied system. The temperature dependence of the individual diffusion coefficient of silicon DSi = 3.0 10-12exp(-0.216 eV/(kT)) cm2/s in the temperature range 423–773 K was determined. The model is applicable to the description of the redistribution of components in the thin niobium film – single-crystal silicon system prior to synthesis conditions providing the chemical interaction of the metal with silicon and the formation of silicides. It illustrates the mechanism of the possible formation of silicide phases not by layer-by-layer growth at the Nb/Si grain boundary, but in its vicinity due to deep mutual diffusion of the components

Exploring hafnium oxide's potential for passivating contacts for silicon solar cells

We investigate the potential of ultra-thin HfO2 films grown by atomic layer deposition for passivating contacts to silicon focusing on variations in film thickness and post-deposition annealing temperature. A peak in passivation quality – as assessed by carrier lifetime measurements – is reported for 2.2 nm thick films annealed at 475 °C, for which a surface recombination velocity <1 cm/s is determined. For films <2.2 nm thick, there is a marked decrease in passivation quality. X-ray diffraction highlights a change from crystallised monoclinic to amorphous HfO2 as film thickness decreases from 12 nm to 2.2 nm. Kelvin probe results indicate that as-deposited 2.2–12 nm films have similar effective work functions, although the work function of 1 nm films is considerably lower. Upon post-deposition annealing in vacuum, all films exhibit a reduction in effective work function at temperatures coincident with the onset of passivation in air-annealed samples. An initial investigation into the contact resistivity in a passivating contact structure utilizing HfO2 reveals a strong post-deposition annealing temperature dependence, with the lowest resistance achieved below 375 °C, followed by a decrease in performance as temperature increases towards the optimal temperature for passivation (475 °C). Limitations of the contact structure used are discussed.

Enhancing the NIR shielding ability and controlling the surface wettability of RF magnetron sputter deposited WO3-x thin films by tuning the oxygen vacancies

Enhancement in the near-infrared (NIR) shielding property of tungsten oxide (WO3-x, 0 < x < 1) thin films by the induction of further oxygen vacancies via vacuum annealing is discussed in this work. The property is comprehensively analysed by UV–Vis–NIR spectroscopy and variable angle spectroscopic ellipsometry techniques. From transmittance spectra, an average visible transmittance of ∼48% along with an average NIR transmittance of ∼15% (with Tvis/Tsol ratio of 1.49) is obtained for WO3-x thin films vacuum annealed at 500 °C for 1.5 h. The pronounced NIR absorption is attributed to the enhanced polaron absorption and surface plasmon resonance effects produced by the increased oxygen vacancies in the film. In order to realize their potential as energy saving window coatings, thermal shielding test is performed in which vacuum annealed WO3-x thin films could restraint the indoor temperature of the heat box efficiently. X-ray diffractometry, field emission scanning electron microscopy, Raman spectroscopy and X-ray photoelectron spectroscopy measurements were also performed on the films for elucidating structural, morphological, and compositional characteristics. In addition, contact angle measurements revealed that vacuum annealing could reduce the surface wettability of WO3-x thin films considerably. The present work is significant in the field of development of NIR shielding materials for energy conserving smart window applications, especially for buildings and automobiles.

Synthesis, Ionic, and Phase Compositions of Ferrogarnet Y2.5Ce0.5Fe2.5Ga2.5O12

X-ray powder diffraction, X-ray photoelectron, and Mössbauer spectroscopy are used to study the ionic and phase compositions of samples of powdered ferrogarnet Y2.5Ce0.5Fe2.5Ga2.5O12 obtained by gel combustion followed by crystallization in vacuum and additional annealing in air at 750°С. According to X-ray photoelectron and Mössbauer spectroscopy data, the iron and cerium cations in the homogeneous ferrogarnet structure are stabilized in the formal oxidation state Fe3+. At the same time, along with Ce3+, the surface of Y2.5Ce0.5Fe2.5Ga2.5O12 particles contains Ce4+ ions. The results obtained can be used to create functional materials for a new generation of magnetooptical devices.

Effects of Annealing on Surface Residual Impurities and Intrinsic Defects of β-Ga2O3

In this study, the effects of annealing on the surface residual impurities and intrinsic defects of unintentionally doped (UID) β-Ga2O3 are investigated by adopting high-temperature thermal treatments at 1000 °C for 1 h under vacuum and O2 ambience. It is found that the recovery between the divacancies VGa+VO and interstitials (Oi) occurs during annealing, and the residual impurities are identified as Si and Cr, which are repelled toward the surface during annealing. Interestingly, these impurities occupy the formation of Ga vacancies (VGa) near the surface formed by oxygen annealing, consequently weakening the relevant impurity scattering and improving carrier mobility. Moreover, the carrier density of the samples is explored using temperature-dependent Hall measurements, which show a slight reduction in both vacuum and oxygen annealing. This reduction might be a result of the VGa pushing the Fermi level away from the conduction band. In addition, the activation energy of Si ions occupying VGa(I) is lower than that of the interstitial Si ions.

Tailoring Structural, Chemical, and Photocatalytic Properties of ZnO@β-SiC Composites: The Effect of Annealing Temperature and Environment.

For achieving unified functionalities of rare-earth free materials, the development of innovative zinc oxide and β-silicon carbide (ZnO@β-SiC) composites by a solid-state reaction method is presented. The evolution of zinc silicate (Zn2SiO4) is evidenced by X-ray diffraction when annealed in air beyond 700 °C. Detailed X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy analyses reveal the involvement of silicon dioxide in forming Zn2SiO4. Transmission electron microscopy and the associated energy-dispersive X-ray spectroscopy elucidate the evolution of the zinc silicate phase at the ZnO/β-SiC interface, though it can be averted by vacuum annealing. These results manifest the importance of air in oxidizing SiC before a chemical reaction with ZnO from 700 °C. Finally, ZnO@β-SiC composites are found to be promising for methylene blue dye degradation under ultraviolet radiation, but the annealing above 700 °C is detrimental due to the evolution of a potential barrier in the presence of Zn2SiO4 at the ZnO/β-SiC interface.

The effect of the redox potential of annealing environment on the mechanical properties of Al2O3-YAG:Ce eutectics

Mechanical characteristics of the eutectics Al2O3-Y3Al5O12:Ce grown by the method of horizontal directional crystallization were established. The influence of the redox potential of the annealing environments on the microhardness and fracture toughness of Al2O3-Y3Al5O12:Ce eutectics has been investigated. Three kinds of environments that differed by the redox potentials have been applied: oxidizing (in the air), in a vacuum, and reducing (Ar. CO, H2).The obtained results showed that doping with Ce ions deteriorates the mechanical properties of the Al2O3-YAG eutectic, both microhardness and fracture toughness. Annealing improves the mechanical properties of the eutectic for all concentrations of Ce ions, but the value of the redox potential of the annealing environment does not affect the degree of the enhancement of these mechanical properties. Only vacuum annealing has a stronger effect on the fracture toughness of eutectics. The increase in microhardness in samples with Ce after annealing is more noticeable compared to samples without Ce.Despite the anisotropy of the eutectic morphology and crystalline texture of the constitutional phases, the mechanical properties of the eutectics didn’t depend noticeably on the direction in the ingot.

A reversal of positive to negative magnetoresistance in Fe3O4-based heterostructures at room temperature by annealing

In this paper, a transition of magnetoresistance (MR) from positive to negative was obtained at room temperature by vacuum annealing of Fe3O4 (128 nm) / Si (with natural SiO2) heterostructures at 780 °C. Considering the wire-like nanograins with varying length and the effect of interface, the sign of MR is decided by the contribution of two Fe3O4 layers. One is the layer at the Fe3O4/SiO2 interface where the scattering of conducting electrons in the natural SiO2 layer on the top of Si can lead to spin polarization reversal of Fe3O4 and the other is the Fe3O4 far away from the absorbing interface. The reversal sign of MR indicates the dominant contrition of Fe3O4 far away from the absorbing interface as the stabilized SiO2 phase on top of the Si substrate with fewer ion defects by annealing the Fe3O4 film on natural Si at 780 °C. For the Fe3O4 film prepared on the substrate of corroded Si (chemically etching the natural SiO2 layer), positive MR is maintained even vacuum annealed at 780 °C, while for the Fe3O4 film on SiO2, an additional α-Fe2O3 phase is obtained even negative MR for films both as deposited and annealed at 780 °C. It can be concluded that the SiO2 layer on top of the substrate plays an important role in the interface and then the magnetotransport properties of the Fe3O4 heterostructures. Well property and negative spin polarization of Fe3O4 film can be obtained by vacuum annealing the Fe3O4 film on Si substrate with a proper thickness of natural SiO2 layer at 780 °C.

Thermal evolutions of residual stress and strain hardening of GH4169 Ni-based superalloy treated by laser shock peening

Residual stresses and strain hardening in GH4169 Ni-based superalloy treated by four different laser shock peening (LSP) configurations and their thermal evolution behaviors under two vacuum annealing conditions were investigated with X-ray diffraction (XRD) and two uniaxial progressive loading tests with two loading rates. Results showed that the thermal relaxations of residual stress under the two vacuum annealing conditions are quite limited, which can be attributed to the fairly low strain hardening levels (<3 %) produced by the current LSP configurations. Besides, an abnormal elevation of strain hardening under vacuum annealing condition VA2 (650 °C, 12 h) was observed, which is caused by the precipitation and growth of plate-like δ-phase particles at the grain boundaries (GBs) and the twin boundaries (TBs). Last but not least, the characteristic relationship between strain hardening and XRD peak width calibrated in this study can also be used to quantitatively study strain hardening of GH4169 Ni-based superalloy in the same heat treatment state treated by other cold working processes below 650 °C.

Effects of intrinsic mechanical properties on the dynamic bonding strength of GLC films undergoing ball bearing contact fatigues

Wear-resistant films, which are widely applied to extend the service life of the gears and bearings, usually surfer from dynamic bonding fatigue failure induced by the Hertz-like contact. However, there is still lack of research on the influence of the main mechanical parameters of films on the dynamic bonding fatigue failure mechanism. In this work, graphite-like carbon (GLC) films with a low friction coefficient and different Ti doping ratios were deposited on the surface of stainless steel via direct current magnetron sputtering (DCMS) technology. The microstructure and mechanical properties of the films before and after vacuum annealing were investigated by SEM, Raman, and nanoindentation, and the dynamic bonding failure life of the films were evaluated by the ball-bearing-disc method with dynamic contact fatigue loads. The results revealed that the critical dynamic bonding strength exhibited a significant function dependence on the values of hardness-to-elastic modulus (H3/E2) parameters of the GLC films. The film failure mechanism showed a transition from the film/substrate interface spalling mode to the near-surface cohesion shear spalling mode with the increase of H3/E2.

Relation Between Tensile Strength and Annealing Temperature for High Purity Niobium

Herein, the relationship between the annealing temperature and the tensile strength of high-purity fine-grain niobium is systematically examined. The superconducting radio frequency (SRF) cavity is housed in a helium tank to be cooled by liquid helium; therefore, it is subject to the High-Pressure Gas Safety Act, and its strength must be guaranteed; for example, whether its wall possesses sufficient strength to endure the outer pressure. It is essential that the strength of the processed material is investigated according to the actual treatment protocol of the SRF cavity. The specimens for tensile testing, residual resistivity ratio (RRR) measurement, and microscopy are cut from the same niobium sheet and annealed simultaneously. This study is significant to specify seven properties (annealing temperature, RRR, tensile strength, 0.2% proof stress, elongation, hardness, and grain size) altogether. When vacuum annealing is performed in the range of 800–1100°C, the RRR is slightly changed. As the annealing temperature increases, the tensile strength decreases. The 0.2% proof strength, elongation, and hardness are almost constant. As the annealing temperature increases, the recrystallization of niobium is promoted, thereby resulting in coarsening of the crystal grains. Evidently, the relationship between the average grain size and tensile strength depends on the Hall–Petch relationship.

Concentration anomalies of galvanomagnetic properties of (Bi1-хSbх)2Te3 solid solutions based on Sb2Te3 in the (Bi1-хSbх)2Te3 system

Today, solid solutions based on antimony and bismuth tellurides are among the most widely used materials for the p-legs of thermoelectric converters used at room temperature and below. This paper presents the results of a study of galvanomagnetic properties (electrical conductivity σ, Hall coefficient RH, Hall mobility of charge carriers μH) of thermoelectric solid solutions (Bi1-хSbх)2Te3 in the range of compositions close to pure antimony telluride (x = 1 – 0.96) at temperatures T = 80 K and T = 300 K. The study was carried out on cast polycrystalline samples obtained by the method of crystallization from the melt followed by long-term annealing in vacuum at a temperature of T = 650 K. Galvanomagnetic properties were measured by the standard dc-method, the experimental cell was cooled with liquid nitrogen. The measurement error of RH and σ did not exceed ± 5%. It is shown that the introduction of the first portions of Bi2Te3 leads to a sharp decrease in σ, which is associated with a high degree of disorder of the crystal lattice. In the range of compositions x = 0.99 – 0.9825, the concentration dependences of σ(x) and μH(x) revealed anomalous growth of σ and μH. The presence of concentration anomalies is associated with the transition from dilute to concentrated solid solutions. An assumption is made about the percolation nature of the phase transition. Within the framework of the problem of spheres of percolation theory, within the framework of the task of spheres of the theory of percolation the radius of the deformation sphere of an impurity atom (Bi) is estimated. The obtained value is consistent with the short-range potential of the impurity. It is shown that the position of the anomalies in the σ(x) and μH(x) dependences does not change with the decrease in temperature down to 80K. Thus, the observation of concentration anomalies of the properties for the solid solution (Bi1-xSbx)2Te3 is another confirmation of the hypothesis about the universal nature of the behavior of solid solutions at a low impurity concentration. The detected anomalies must be taken into account when developing methods for increasing the thermoelectric performance of materials by creating solid solutions and doping.

Fe ion valence states and oxygen vacancies in the La0.5Sr0.5FeO3-γ ferrite under vacuum annealing

The changes in the substituted La0.5Sr0.5FeO3−γ orthoferrite under vacuum annealing in the temperature range of 200–650 °C have been studied by X-ray diffraction analysis, as well as Mössbauer and Raman spectroscopy. Annealing of the as–prepared ferrite with the rhombohedral structure (R3‾c) resulted in its transition to the cubic one (Pm3‾m) at 650 °C. In the as–prepared ferrite being paramagnetic at room temperature, Fe ions were detected in an averaged–valence state between Fe3+ and Fe4+, which was not revealed with a decrease in the temperature down to 85 K. Gradual oxygen loss and an increase in the number of oxygen vacancies took place with an increase in the vacuum annealing temperature. Only Fe3+ ions were present in the ferrite at a vacuum annealing temperature above 500 °C. Several Zeeman sextets in the Mössbauer spectra associated with Fe3+ ions were resulted from the presence of oxygen vacancies and Fe4+ ions in the local environment of Fe3+ ions. The variations in the ratio of the valence states of Fe ions obtained from Mössbauer data depending on a vacuum annealing temperature allowed determining the content of oxygen in all the investigated samples. The contribution of Fe3+ ions that did not have Fe4+ ions and oxygen vacancies in their local environment was shown to increase with a vacuum annealing temperature from 12% (for the as–prepared sample) to 60% (for the sample annealed at 650 °C). On a whole, the process taking place under vacuum annealing can be characterized as a variation of the local environment of Fe3+ ions towards a decrease in its distortion. It was found that the width of the peaks of the Raman spectra decreased and their amplitude increased with an increase in the vacuum annealing temperature, which also demonstrated the improvement of the structural perfection of the samples.

A fabrication of low diffused PtHf co-doped Ni-Al coating on Ni-based superalloy

Two PtHf co-doped Ni-Al coatings were fabricated by the following steps: first, NiHf layer and Pt layer were electroplated on the substrate, then vacuum annealed at 800 ℃ for 5 h; Second, Al layer was deposited via arc ion plating (AIP); Finally, vacuum annealing was proceeded at 1050 ℃ for 2 h. The Al contents in PtHf co-doped γʹ coating and PtHf co-doped γʹ+β coating were about 24 at.% and 42 at.%, respectively. In addition, no topologically close-packed (TCP) phases were precipitated in the diffusion affected zone (DAZ) in the PtHf co-doped γʹ coating, while many TCP phases were precipitated in the DAZ in the PtHf co-doped γʹ+β coating. The interdiffusion coefficient of Al gradually decreased with the reduction of Al content and the increase of Pt content in coating, consequently suppressing the precipitation of TCP phases.

Adhesion of cold sprayed soft coatings: Effect of substrate roughness and hardness

When depositing a soft material (e.g. pure Cu) onto a harder substrate (e.g. stainless steel) by cold spraying, the attainable coating adhesion depends on both the hardness and the roughness of the substrate. To decouple their respective influences, the present work focuses on a model system of cold sprayed copper onto AISI 304 steel surfaces with differently adjusted hardness and roughness values. AISI 304 stainless steel plates were either polished or grit-blasted to different roughness, and then employed as substrates either as-is, i.e. in the “hardened” condition, or in the “softened” vacuum-annealed state. SEM analyses and nano-indentation tests showed that grit-blasting causes severe plastic deformation of the surface, where any visible austenite grain structure is lost up to a depth of some tens of microns. The corresponding microstructures are work-hardened, reaching a hardness of about 350–400 HV0.001. Vacuum annealing induced recrystallization and restored the original, lower hardness (≈200 HV0.001) of AISI 304, without changing the surface roughness, as obtained by the grit-blasting. Through cavitation tests on single-particle deposition experiments, it was found that cold sprayed Cu particles' adhesion was lower on roughened and hardened substrates than on polished surfaces. In contrast, the situation was reversed for roughened and annealed (“softened”) substrates, showing an increase in adhesion of cold-sprayed Cu particles with increasing roughness up to a maximum at Rz of about 34 μm. The latter trend was confirmed by bond strength testing of complete Cu coatings onto “softened” substrates, while the maximum adhesion on hardened substrates was attained with Rz = 18 μm. The underlying mechanisms are discussed with respect to particle deformation and the substrate surface topographies needed to trap areas of mutual shear instabilities of the particles and the substrate. Identifying the conditions that ensure metallurgical bonding then should help to provide a more general understanding of deposit adhesion in cold spraying.

Thermal Annealing Driven Enhancement of Perpendicular Magnetic Anisotropy and the Interfacial Dzyaloshinskii–Moriya Interaction in Ultrathin Ru/Co/W/Ru Films

Spin-related effects discovered in ultrathin magnetic films generally have an interfacial nature. The quality of interfaces between a heavy metal and a ferromagnet is the main driver of surface anisotropy, antisymmetric exchange, chiral damping, spin Hall effect, and spin–orbit torques. To understand the physics and usage of these phenomena for future atomic-scale devices, one has to study systems with disordered interfaces and search there for novel practically desirable effects, which lie beyond the atomic order and surface flatness. Here, we report the interface-related effects in Ru/Co/W/Ru ultrathin films treated by thermal annealing in vacuum. The surface roughness and degree of atomic intermixing at Ru/Co and Co/W interfaces change with increasing annealing temperature up to 240 °C, promoting an enhancement of perpendicular magnetic anisotropy and the interfacial Dzyaloshinskii–Moriya interaction (i-DMI). Further annealing at higher temperatures brings the interface deterioration and, consequently, a drastic degradation of the magnetic properties. Our first-principles calculations qualitatively support the experimental findings, providing an understanding of the i-DMI enhancement nature.

Nanoscale morphology tailoring in plasma deposited CN x layers

Magnetron discharge plasma was applied for the synthesis of CN x thin layers using methane and nitrogen gas precursors. The incorporation of nitrogen in the carbon network resulted in the dramatic evolution of growth morphology: from a ‘buried’ porous layer observed at low nitrogen incorporation to aligned bundles of nanorods grown perpendicular to the substrate surface at maximum discharge power and nitrogen flow. The films deposited at the low discharge power and high nitrogen incorporation exhibited a mesoporous sponge-like morphology after vacuum annealing. Relevant physical mechanisms responsible for the formation of nano- and mesoshaped morphology are discussed in terms of the effects of internal mechanical stresses and plasma etching. In addition, the sensing properties of the sponge-like layer were preliminarily examined in water vapor and ammonia ambients. The CN x films showed enhanced sensitivity to ammonia and reverse electrical response to moisture in comparison with a nitrogen-free nanoporous carbon film, which were assigned to modification of the electronic properties of the nitridated surface.