Correlation between photoluminescence, optical and structural properties of amorphous nitrogen-rich carbon nitride films

Amorphous nitrogen-rich carbon nitride (CN_x) films have been prepared by inductively coupled plasma chemical vapour deposition (ICP-CVD) utilizing transport reactions from a solid carbon source. The nitrogen atomic fraction N/(C+N) is about 1 or even higher as detected by various surface and bulk sensitive methods. An investigation of the chemical bonding structure showed that the films are composed of >C=N units with a small fraction of C≡N groups. Based on these findings, several structural units derived from cis- and trans-conjugated carbon–nitrogen chains are proposed. The optical properties of the CN_x films were studied by transmission spectroscopy and spectral ellipsometry; the optical Tauc gap was determined to 2.1±0.05 eV. The photoluminescence characteristics were measured at three different excitation wavelengths (476, 488 and 515 nm) and revealed two individual contributions. These data are interpreted in terms of the different structural units comprising the nitrogen-rich CN_x films. Received: 14 July 2000 / Accepted:17 July 2000 / Published online: 22 November 2000     

Investigations of the sorption behaviour of amorphous nitrogen-rich carbon nitride films as sensitive layers for cantilever-based chemical sensors

We present investigations of the sorption behaviour of amorphous nitrogen-rich carbon nitride films (CN_x) towards water vapour and volatile organic compounds, for example methanol, ethanol, i-propanol and acetone, in order to evaluate their potential as sensitive layers for cantilever-based chemical sensor applications. The CN_x films were deposited by inductively coupled plasma chemical vapour deposition (ICP-CVD) utilizing transport reactions from a solid carbon source. In order to study the influence of the thickness of the sensitive layer on its sensitivity and selectivity, two series of cantilevers coated with 120 nm and 240 nm CN_x films were prepared. We found that the variation of the film thickness affected the sorption process of the CN_x film quantitatively as well as qualitatively. For thin films (120 nm), the sensor dynamic responses (frequency shift) increased with increasing molecular weight of the analytes. The largest responses were observed towards acetone and i-propanol ; here, the cantilever acted as a resonant microbalance. When the film thickness was increased from 120 to 240 nm, the analytes with higher dipole moments caused stronger response signals. In this case we observed, for example, an increase of the sensitivity towards methanol by a factor of more than three. The performance of the cantilever-based sensors functionalised with CN_x coatings was compared to that of organic polymers, and the observed peculiarities were explained by the chemical nature of the sensitive materials. PACS 81.05.-t; 85.85.+j; 07.07.Df     

Improving mechanical properties of a-CNx films by Ti-TiN/CNx gradient multilayer

Amorphous carbon nitride (a-CN_x) films with functional gradient Ti-TiN/CN_x underlayer were deposited by direct current magnetron sputtering. Microstructure and composition of the films were characterized by means of X-ray diffraction (XRD), Raman spectroscopy, atomic force microscope (AFM) and transmission electron microscopy (TEM). Mechanical and tribological properties were investigated by nanoindenter, scratch and ball-on-disk tribometer. The a-CN_x-based films suffer a graphitization process with the increasing deposition temperature, thus the hardness and elastic modulus decrease. With the design of the Ti-TiN/CN_x gradient underlayers, some important advantages of relatively thick CN_x films can be achieved, such as increased hardness, improved adhesion strength, and the wear resistance of the a-CN_x-based films can be also improved significantly.     

高温退火对非晶CNx薄膜场发射特性的影响

采用射频磁控溅射方法在纯N₂气氛中沉积了非晶CN_x薄膜样品，并 在真空中退火至900 ℃.对高温退火引起的CN_x薄膜化学成分、键合结构及其场发射特性方面的变 化进行研究.用傅里叶变换红外光谱和x射线光电子能谱分析样品的内部成分及键合结构的变化，其中sp²键及薄膜中N的含量与薄膜的场发射特性密切相关.退火实验的结果表明 高温退火可以导致CN_x薄膜中N含量大量损失，并在薄膜中形成大量sp^{2< 关键词： x薄膜')" href="#">CN_x薄膜 化学键合 退火温度 场致电子发射}     

Influence of temperature on structure as well as adhesion and friction and wear behavior of hydrogenated carbon nitride films prepared on silicon substrate

Hydrogenated-carbon nitride (CN_x:H) films were synthesized on silicon substrate in a large quantity by the pyrolysis of ethylenediamine in a temperature range of 700-950 °C. The influence of temperature on the morphology, structure, adhesion to substrate, and friction and wear behavior of CN_x:H films was investigated. It has been found that CN_x:H films obtained at 700 °C and 800 °C are amorphous, and those prepared at 900 °C and 950 °C consist of carbon nitride nanocrystal. Besides, CN_x:H film sample obtained at 700 °C has the maximum N content of 9.1 at.% but the poorest adhesion to Si substrate, while the one prepared at 900 °C has the lower N content and the highest adhesion to substrate. As a result, nanocrystalline CN_x:H (nc-CN_x:H) film synthesized at 900 °C possesses the best wear resistance when slides against stainless steel counterpart. N atom is incorporated into the graphitic network in three different bonding forms, and their relative content is closely related to temperature, corresponding to different adhesion as well as friction and wear behavior of the films obtained at different temperatures. Furthermore, the friction coefficient and antiwear life of as-deposited CN_x:H films vary with varying deposition temperature and thickness, and the film with thickness of 1.3 μm, obtained at 900 °C, has the longest antiwear life of over 180,000 s.     

类金刚石和碳氮薄膜的电化学沉积及其场发射性能研究

利用电化学方法在室温下成功地沉积了类金刚石(DLC)薄膜和非晶CN_x薄膜，并 对制备条件进行了讨论.通过扫描电子显微镜、傅里叶变换红外光谱技术，分析了薄膜的表面形貌和化学结合状态.场发射测量结果表明：DLC膜和非晶CN_x的开启场分别为88和 10V/μm；并且在23V/μm的电场下，DLC膜和非晶CN_x膜的发射电流密度分别达到10 和037mA/cm². 关键词： 电化学沉积 类金刚石薄膜 x薄膜')" href="#">CN_x薄膜 场致电子发射     

Structure,transport and field-emission properties of compound nanotubes: CN<Subscript>x</Subscript> vs. BNC<Subscript>x</Subscript> (<Emphasis Type="Italic">x</Emphasis><0.1)

Transport and field-emission properties of as-synthesized CN_x and BNC_x (x<0.1) multi-walled nanotubes were compared in detail. Individual ropes made of these nanotubes and macrofilms of those were tested. Before measurements, the nanotubes were thoroughly characterized using high-resolution and energy-filtered electron microscopy, electron diffraction and electron-energy-loss spectroscopy. Individual ropes composed of dozens of CN_x nanotubes displayed well-defined metallic behavior and low resistivities of ∼10–100 kΩ or less at room temperature, whereas those made of BNC_x nanotubes exhibited semiconducting properties and high resistivities of ∼50–300 MΩ. Both types of ropes revealed good field-emission properties with emitting currents per rope reaching ∼4 μA(CN_x) and ∼2 μA (BNC_x), albeit the latter ropes se- verely deteriorated during the field emission. Macrofilms made of randomly oriented CN_x or BNC_x nanotubes displayed low and similar turn-on fields of ∼2–3 V/μm. 3 mA/cm² (BNC_x) and 5.5 mA/cm² (CN_x) current densities were reached at 5.5 V/μm macroscopic fields. At a current density of 0.2–0.4 mA/cm² both types of compound nanotubes exhibited equally good emission stability over tens of minutes; by contrast, on increasing the current density to 0.2–0.4 A/cm², only CN_x films continued to emit steadily, while the field emission from BNC_x nanotube films was prone to fast degradation within several tens of seconds, likely due to arcing and/or resistive heating. Received: 29 October 2002 / Accepted: 1 November 2002 / Published online: 10 March 2003 RID="*" ID="*"Corresponding author. Fax: +81-298/51-6280, E-mail: golberg.dmitri@nims.go.jp     

Bonding configurations in amorphous carbon and nitrogenated carbon films synthesised by femtosecond laser deposition

The effect of nitrogen addition and laser fluence on the atomic structure of amorphous carbon films (a-C) synthesized by femtosecond pulsed laser deposition has been studied. The chemical bonding in the films was investigated by means of X-ray photoelectron (XPS) and Raman spectroscopies. XPS studies revealed a decrease in the sp³ bonded carbon sites and an associated increase in the N-sp²C bonding sites with increasing nitrogen content in the CN_x films. An increase in laser fluence from 0.36 to 1.7 J/cm² led to a rise in sp³C sites. These results were further confirmed by Raman spectroscopy. The I_D/I_G ratio increased monotonically and G line-width decreased with the increase of nitrogen content in the films indicating a rise in either the number or the size of the sp² clusters. Furthermore a visible excitation wavelength dependence study established the resonant Raman process in a-C and CN_x films. PACS 81.05.Uw; 81.15.Fg; 82.80     

Growth of Y-junction bamboo-shaped CNx nanotubes on GaAs substrate using single feedstock

Nitrogen-doped Y-junction bamboo-shaped carbon nanotubes were synthesized by chemical vapor deposition of monoethanolamine/ferrocene mixture on GaAs substrate at 950 °C. The use of monoethanolamine as the C/N feedstock simplifies the experimental arrangement by producing ammonia during the growth process. The structure, morphology and graphitization of as-grown nitrogen-doped carbon nanotubes (CN_x) were examined by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Raman spectroscopy analysis. TEM analysis indicates that nanotubes have a bamboo-like structure. The nitrogen concentration on as-grown CN_x nanotube was found to be 7.8 at.% by X-ray photoelectron spectroscopy (XPS) analysis. XPS analysis also indicated that there are two different types of nitrogen atoms (pyridinic and graphitic) in these materials. The possible growth mechanism of formation of Y-junction CN_x nanotubes was briefly discussed. Field emission measurement suggested that as-grown CN_x nanotubes are excellent emitters with turn-on and threshold fields of 1.6 and 2.63 V/μm, respectively. The result indicated that monoethanolamine proves to be an advantageous precursor to synthesize Y-junction nitrogen-doped carbon nanotubes and such nanotubes might be an effective material to fabricate various field emission devices.     

Structural and tribological properties of cluster-assembled CNx films

We report the structural and tribological characterization of nanostructured CN_x thin films produced by the deposition of a supersonic carbon cluster beam assisted by nitrogen ion bombardment. The influence of the deposition parameters on the chemical composition and structure of the films has been systematically studied by X-ray photoelectron spectroscopy, elastic recoil detection analysis, transmission electron microscopy and atomic force microscopy. Depending on the deposition parameters, the films show a structure ranging from amorphous to disordered graphitic with interlinked planes. Nitrogen content depends on the nitrogen ion kinetic energy. The films have a very low density with a high surface roughness. Friction measurements at the nanoscale show a correlation between nitrogen content and mechanical properties of the system. PACS 61.46-w     

Photoelectron spectroscopic characterization of titanium-containing amorphous hydrogenated silicon–carbon films (aSi1-xCx:H/Ti)

Titanium-containing amorphous hydrogenated silicon–carbon films (aSi_1-xC_x:H/Ti) have been deposited by reactive magnetron cosputtering. Core-level photoelectron spectroscopy (XPS) and valence-band photoelectron spectroscopy (UPS) have served as means for the characterization of these films. The spectroscopic data are interpreted by a structural model on the basis of a nanocomposite containing clusters of a Ti-C-Si alloy being embedded in an amorphous hydrogenated silicon–carbon matrix (aSi_1-xC_x:H). The Ti-C-Si compound is of metallic character and most likely a substitutional solid solution. This novel nanocomposite material is a promising candidate for applications, especially as optical selective absorber coating for solar collectors. Received: 10 July 2000 / Accepted: 15 September 2000 / Published online: 21 March 2001     

Deposition of carbon nitride films for space application

Carbon nitride thin films were prepared by electron-beam evaporation assisted with nitrogen ion bombardment and TiN/CN_x composite films were by unbalanced dc magnetron sputtering, respectively. It was found that the sputtered films were better than the evaporated films in hardness and adhesion. The experiments of atomic oxygen action, cold welding, friction and wearing were emphasized, and the results proved that the sputtered TiN/CN_x composite films were suitable for space application.     

ZrN, ZrxAlyN and ZrxGayN thin films – novel materials for hard coatings grown using pulsed laser deposition

High-quality thin films of ZrN, Zr_xAl_yN and Zr_xGa_yN have been grown by pulsed reactive crossed-beam laser ablation using Zr, Zr-Al and Zr-Ga ablation targets, respectively, and a N₂ gas pulse. The films were characterized for their chemical, crystallographic and tribological properties. All the films had very low impurity levels and a cubic rock salt crystal structure over the entire investigated temperature range between room temperature and 600 °C. High-quality epitaxial films could be grown on Si (001) at 400 °C, though the crystallinity was disrupted at 525 °C by Si diffusion into the film bulk and the formation of ZrSi₂ crystallites. Films grown on stainless steel were polycrystalline. The ratios of the metals in the alloy targets were in general not equal to those in the films: the Al content in the Zr_xAl_yN films was lower than the target value, which we attribute to differential scattering in the ablation plume. The Ga content in the Zr_xGa_yN films fell with increasing substrate temperature, indicative of re-evaporation of Ga from the substrate surface. Those Zr_xGa_yN films with the highest Ga content, grown at the lowest temperatures, were particularly nitrogen-deficient, which we attribute to the low reactivity of Ga with N₂. The Zr_xAl_yN films had an exceptionally low coefficient of friction (0.20) versus steel and the greatest nanohardness of 28 GPa. Received: 9 November 2000 / Accepted: 14 November 2000 / Published online: 28 February 2001     

不同氮源制备CNx纳米管薄膜及其低场致电子发射性能

采用高温热解法，分别以氯化铵(NH₄Cl)和乙二胺(C₂H₈N₂)为氮源在洁净的硅片上沉积生长CN_x纳米管薄膜.利用扫描电子显微镜、高分辨率透射电子显微镜和拉曼光谱对CN_x纳米管进行形貌观察和表征.结果显示不同氮源制备出的CN_x纳米管薄膜的洁净度、有序度以及纳米管的结构明显不同.热解乙二胺(C₂H₈N₂)/二茂铁(C₁₀H₁₀Fe)制备出的结晶度较低的“竹节状” 结构CN_x纳米管平行基底表面有序生长，而且低场致电子发射性能优越,开启电场1.0V/μm，外加电场达到2.89V/μm时发射电流密度为860μA/cm². 关键词： x纳米管')" href="#">CN_x纳米管 高温热解 “竹节状”结构 场致发射     

脉冲偏压电弧离子镀CNx薄膜研究

用脉冲偏压电弧离子镀通过控制不同的氮流量在(100)单晶Si基片上制备了不同成分的CN_x薄膜.用光学显微镜,XPS,XRD,激光Raman和Nanoindenter等方法研究了薄膜的形貌、成分、结构和性能.结果表明,薄膜表面平整致密、氮含量随着氮流量的降低而降低、结构为非晶且为类金刚石薄膜;随着氮含量从18.9%降低到5.3%(摩尔百分比,全文同),薄膜的硬度和弹性模量单调增加而且增幅较大,其中硬度从15.0 GPa成倍增加到30.0 GPa;通过氮流量的调整能够敏感地改变薄膜中的sp³键的含量,是CN_x薄膜的硬度和弹性模量获得大幅度调整的本质原因. 关键词： x薄膜')" href="#">CN_x薄膜 脉冲偏压 电弧离子镀 硬度     

碳、碳氮和硼碳氮纳米管场发射性能的比较研究

采用高温热解法在860℃分别制备出了碳、碳氮和硼碳氮纳米管，提纯后利用丝网印刷工艺分别将它们制备成薄膜，并测试了它们的场发射性能.结果表明：碳纳米管、碳氮纳米管和硼碳氮纳米管薄膜的开启电场分别为2.22，1.1和4.4V/μm，当电场增加到5.7V/μm时，它们的电流密度分别达到1400，3000μA/cm²和小于50μA/cm².碳和碳氮纳米管薄膜的场增强因子分别为10062和11521.可见，碳氮纳米管的场发射性能优于碳纳米管，而硼碳氮纳米管的场发射性能比前两者要差.解释了这三种纳米管场发射性能差别的原因. 关键词： 碳纳米管 碳氮纳米管 硼碳氮纳米管 场发射     

Growth and characterization of silicon nitride films on various underlying materials

Characteristics of silicon nitride (SiN_x:H) films, grown by plasma enhanced chemical vapor deposition (PECVD) on various metals such as Ta, IrMn, NiFe, Cu, and CoFe at various temperatures down to 100 °C, were studied using measurements of BHF etch rate, surface roughness and Auger electron spectroscopy (AES). The results were compared with those obtained for SiN_x:H films on Si. The deposition rate of SiN_x:H films increased slightly as deposition temperature decreased, and showed a weak dependence on the underlying materials. The surface of the nitride films deposited on all underlying materials at lower temperatures (below 150 °C) became rougher. In particular, a bubble-like surface was observed on the nitride film deposited on NiFe at 100 °C. At higher deposition temperatures (above 200 °C), SiN_x:H films on all the above metals had small RMS values, except for films on Cu which cracked at 250 °C. BHF (10:1) etch rate increased dramatically for nitride films deposited below 150 °C. For different underlying films, the BHF etch rate was quite different, but exhibited the same trend with decrease in deposition temperature. AES measurements showed that Si and N concentrations in the SiN_x:H films were only slightly different for the various deposition temperatures and underlying materials. AES depth profile of nitride films indicated that both surface O content and the depth of oxygen penetrating into SiN_x:H increased for low temperature-deposited films. However, there was no observed oxygen signal from within the films, even for films deposited at 100 °C, and both Si and N concentrations were uniform throughout the film. Received: 26 October 2001 / Accepted: 2 March 2001 / Published online: 20 June 2001     

Defect reduction and surface passivation of SiO2/Si by heat treatment with high-pressure H2O vapor

Heat treatment with high-pressure H₂O vapor was applied to improve interface properties of SiO₂/Si and passivate the silicon surface. Heat treatment at 180–420 °C with high-pressure H₂O vapor changed SiO_x films, 150 nm thick formed at room temperature by thermal evaporation in vacuum, into SiO₂ films with a Si-O-Si bonding network similar to that of thermally grown SiO₂ films. Heat treatment at 130 °C with 2.8×10⁵ Pa H₂O for 3 h reduced the recombination velocity for the electron minority carriers from 405 cm/s (as-fabricated 150-nm-thick SiO_x/Si) to 5 cm/s. Field-effect passivation was demonstrated by an additional deposition of defective SiO_x films on the SiO₂ films formed by heat treatment at 340 °C with high-pressure H₂O vapor. The SiO_x deposition reduced the recombination velocity from 100 cm/s to 48 cm/s. Received: 1 March 1999 / Accepted: 28 March 1999 / Published online: 24 June 1999     

Oxygen-segregation-controlled epitaxy of Y2O3 films on Nb(110)

We demonstrate a very simple and reliable method of manufacturing clean, single-crystalline Y₂O₃ films on Nb(110) substrates in situ. The method exploits the oxygen bulk contamination of Nb as a source of clean oxygen. For substrate temperatures above 800 K oxygen segregation to the Nb surface is so efficient, that yttrium becomes oxidized during deposition without any background oxygen pressure required in the ultrahigh vacuum system. The crystallinity and stoichiometry of these films can be tuned by the deposition temperature. For Y deposition at 1300 K the formation of well-ordered (111)-oriented Y₂O₃ films is achieved. Received: 19 April 2000 / Accepted: 20 April 2000 / Published online: 23 August 2000     

The relationship between the macroscopic properties of PECVD silicon nitride and oxynitride layers and the characteristics of their networks

Silicon nitride and oxynitride films have been deposited on silicon wafers using plasma-enhanced chemical vapour deposition. Various amounts of ammonia, silane and nitrous oxide gases were applied at fixed total gas flow and at the same deposition temperature. The dependence of the macroscopic properties of the layers such as refractive index, internal stress and etch rate on the reaction atmosphere during deposition has been demonstrated. The chemical structure of amorphous layers was studied using infrared spectroscopy. The network was found to be characterised by SiN_xO_yH_z tetrahedra, joined to each other by common corners. The characteristic vibrational bands due to species that join tetrahedral units (N(-Si≡)₃, ≡Si-N-Si≡, ≡Si-O-Si≡) and species that stop this interconnection (Si-H, N-H) were determined and discussed with reference to the corresponding species available during deposition. The analysis resulted in the determination of the relationship between the chemical structure of the network and the layer’s refractive index, internal stress and etch rate. Received: 24 July 2000 / Accepted: 30 May 2001 / Published online: 30 August 2001