Microstructure of c-BN thin films deposited on diamond films

Diamond films were used as substrates for cubic boron nitride (c-BN) thin film deposition. The c-BN films were deposited by ion beam assisted deposition (IBAD) using a mixture of nitrogen and argon ions on diamond films. The diamond films exhibiting different values of surface roughness ranging from 16 to 200 nm (in R_rms) were deposited on Si substrates by plasma enhanced chemical vapor deposition. The microstructure of these c-BN films has been studied using in situ reflexion electron energy loss spectroscopy analyses at different primary energy values, Fourier transform infrared spectroscopy and high resolution transmission microscopy. The fraction of cubic phase in the c-BN films was depending on the roughness of the diamond surface. It was optimized in the case of the smooth surface presenting no particular geometrical effect for the incoming energetic nitrogen and argon ions during the deposition. The films showed a nanocrystalline cubic structure with columnar grains while the near surface region was sp² bonded. The films exhibit the commonly observed layered structure of c-BN films, that is, a well textured c-BN volume lying on a h-BN basal layer with the (00.2) planes perpendicular to the substrate. The formation mechanism of c-BN films by IBAD, still involving a h-BN basal sublayer, does not depend on the substrate nature.     

Synthesis of c-BN films by using a low-pressure inductively coupled BF3–He–N2–H2 plasma

Cubic boron nitride (c-BN) films were synthesized by low-pressure inductively coupled radio-frequency plasma (ICP) chemical vapor deposition (CVD) from a gas mixture of borontrifluoride (BF₃), nitrogen, hydrogen and helium. BN films containing 50–80% cubic phase were obtained under 100 mTorr and at 750–1050 °C of substrate temperature. Substrate bias voltage required to obtain c-BN decreased down to − 20 V with increasing substrate temperature. The adhesion was also improved at high substrate temperatures as compared with those obtained in the B₂H₆–Ar–N₂–H₂ gas system, probably because of the decrease of bombarding energy and chemical effects of fluorine for selective deposition of c-BN.     

Synthesis of nitrogen incorporated diamond-like carbon thin films using microwave surface-wave plasma CVD

Nitrogenated diamond-like (DLC:N) carbon thin films have been deposited by microwave surface wave plasma chemical vapor deposition on silicon and quartz substrates, using argon gas, camphor dissolved in ethyl alcohol composition and nitrogen as plasma source. The deposited DLC:N films were characterized for their chemical, optical, structural and electrical properties through X-ray photoelectron spectroscopy, UV/VIS/NIR spectroscopy, Raman spectroscopy, atomic force microscope and current–voltage characteristics. Optical band gap decreased (2.7 to 2.4 eV) with increasing Ar gas flow rate. The photovoltaic measurements of DLC:N / p-Si structure show that the open-circuit voltage (V_oc) of 168.8 mV and a short-circuit current density (J_sc) of 8.4 μA/cm² under light illumination (AM 1.5 100 mW/cm²). The energy conversion efficiency and fill factor were found to be 3.4 × 10^{− 4}% and 0.238 respectively.     

Depth resolved stress investigations of c-BN thin films

Cubic boron nitride thin films were deposited by ion beam assisted deposition (IBAD) on (100)-oriented silicon cantilever structures prepared by standard micro-machining processes. This enables an accurate determination of the stress-induced bending of the beam by optical microscopy. Depth resolved characterisation of the coatings was achieved by subsequent back-etching and examination of the film stress and the IR data after each sputtering step. Cubic BN containing films exhibit a three layer sequence: non-cubic baselayer/transition h-BN→c-BN/c-BN toplayer. This layered sequence was verified by the evolution of the IR data as well as the stress distribution. These investigations confirm the existence of a transition region between the h-BN baselayer and the c-BN toplayer. Furthermore, the dependence of the depth-resolved c-BN stress σ_c-BN on the main deposition parameters was investigated. A stress reduction can be achieved by reducing the Ar/N₂ ratio and/or by increasing the ion energy. As this stress relief is correlated with an increase of the sp² bonded material within the c-BN toplayer, it can be concluded that stress relaxation occurs at the sp² bonded grain boundary material. Finally, the influence of the stress on the nucleation and the growth of c-BN containing films will be discussed.     

Microstructural characterization of diamond films deposited on c-BN crystals

The morphology and structure of diamond films, deposited on cubic boron nitride (c-BN) crystals by microwave-plasma-enhanced chemical vapor deposition, is studied by high-resolution scanning electron microscopy and micro-Raman spectroscopy. The c-BN crystals, with sizes of 200 to 350 μm and grown by a high-temperature/high-pressure technique, were embedded in a copper holder, and used as substrates in deposition runs of 15 min to 5 h. The nucleation centers for diamond appear as well-shaped cuboctahedral crystallites, having diameters of approximately 100 nm. With increasing deposition time the diamond crystallites grew larger, forming islands on the c-BN faces. In some cases, epitaxial growth was observed on the (111) c-BN faces where coalesced particles gave rise to very smooth regions. A number of diamond crystals with peculiar shapes are observed, such as a pseudo five-fold symmetry due to multiple twinning. Moreover, both randomly distributed carbon tubes, about 100 nm in diameter and 1 μm in length, and spherically shaped features are observed in samples prepared under the typical conditions of diamond deposition, this effect being ascribed to the influence of plasma-sputtered copper contamination. Quite unusual diamond crystals with a deep, pyramidal-shaped hole in the middle grew on the copper substrate between the c-BN crystals.     

Synthesis of carbon nanosheets by inductively coupled radio-frequency plasma enhanced chemical vapor deposition

An ultrathin sheet-like carbon nanostructure, carbon nanosheet, has been effectively synthesized with CH₄ diluted in H₂ by an inductively coupled radio-frequency plasma enhanced chemical vapor deposition. Nanosheets were obtained without catalyst over a wide range of deposition conditions and on a variety of substrates, including metals, semiconductors and insulators. Scanning electron microscopy shows that the sheet-like structures stand on edge on the substrate and have corrugated surfaces. The sheets are 1 nm or less in thickness and have a defective graphite structure. Raman spectra show typical carbon features with D and G peaks at 1350 and 1580 cm⁻¹, respectively. The intensity ratio of these two peaks, I(D)/I(G), increases with methane concentration or substrate temperature, indicating that the crystallinity of the nanosheets decreases. Infrared and thermal desorption spectroscopies reveal hydrogen incorporation into the carbon nanosheets.     

Effects of plasma treatments on the nitrogen incorporated nanocrystalline diamond films

The nitrogen incorporated nanocrystalline diamond (NCD) films were grown on n-silicon (100) substrates by microwave plasma enhanced chemical vapor deposition (MPECVD) using CH₄/Ar/N₂ gas chemistry. The effect of surface passivation on the properties of NCD films was investigated by hydrogen and nitrogen-plasma treatments. The crystallinity of the NCD films reduced due to the damage induced by the plasma treatments. From the crystallographic data, it was observed that the intensity of (111) peak of the diamond lattice reduced after the films were exposed to the nitrogen plasma. From Raman spectra, it was observed that the relative intensity of the features associated with the transpolyacetylene (TPA) states decreased after hydrogen-plasma treatment, while such change was not observed after nitrogen-plasma treatment. The hydrogen-plasma treatment has reduced the sp²/sp³ ratio due to preferential etching of the graphitic carbon, while this ratio remained same in both as-grown and nitrogen-plasma treated films. The electrical contacts of the as-grown films changed from ohmic to near Schottky after the plasma treatment. The electrical conductivity reduced from ~ 84 ohm^– 1 cm^− 1 (as-grown) to ~ 10 ohm^– 1 cm^− 1 after hydrogen-plasma treatment, while the change in the conductivity was insignificant after nitrogen-plasma treatment.     

Synthesis of nanocrystalline diamond films using microwave plasma CVD

Diamond is one of the most valuable materials for the industrial applications because of its excellent properties including high hardness, with good electrical insulation and thermal conductivity. Mechanical polishing processes of diamond are difficult and very costly. To limit those costs, it is reasonable to think that the surface roughness of the as-grown diamond film should be as small as possible. In this study, a nanocrystalline diamond film was synthesized on a 4-inch Si wafer at 923 K and methane concentration of 10 vol.%, (H₂/CH₄=100/10 sccm) using a microwave plasma CVD system. In order to increase the nucleation density, the substrate was pretreated by dry scratch method with diamond powder of two sizes (250 nm and 5 nm). The nucleation density was approximately 1×10¹¹ cm⁻². The grown diamond films were analyzed by Raman spectroscopy and X-ray diffraction (XRD). The grain size was observed to be approximately 10 nm by FE-SEM observation. Surface roughness was measured as Rms=8.4 nm by atomic force microscope (AFM). The as-grown properties of those nanocrystalline diamond films were almost efficient for tribological and the optical applications.     

Effects of nitrogen plasma treatment of pressure-sensitive adhesive layer surfaces on their peel adhesion behavior

The influence of the surface modification of pressure-sensitive adhesive tapes on their adhesion behavior has been investigated. PBA [poly(butyl acrylate)] and PIB [poly(isobutylene)] adhesives were chosen as pressure-sensitive adhesives and nitrogen plasma was used for the surface modification of the adhesives. The peel force of PBA or PIB adhesive/stainless steel joints was evaluated. The nitrogen plasma treatment showed large effects on the adhesion behavior of both the PBA and the PIB adhesives. The peel force for the PBA adhesive/stainless steel joint decreased by 57 times as a result of the nitrogen plasma treatment and that for the PIB adhesive/stainless steel joint increased by 2.2 times. There are essential differences in the modification reactions caused by the nitrogen plasma between the PBA and PIB adhesives. For the PBA adhesive, cross-linking reactions occurred among the PBA polymer chains and the surface was hardened. For the PIB adhesive, degradation reactions occurred and products with a low molecular weight were formed on the surface. These differences are due to the different responses of the PBA and PIB adhesives towards the nitrogen plasma. The mechanism of the changes in adhesion behavior caused by the nitrogen plasma is discussed.     

PECVD of h-BN and c-BN films from boranedimethylamine as a single source precursor

Boron nitride (BN) thin films have been successfully synthesised via low pressure plasma enhanced chemical vapour deposition (PECVD) by using boranedimethylamine, BH₃NH(CH₃)₂, as a single source precursor in the temperature range 280-550 °C in a nitrogen-argon atmosphere. The plasma power was optimised with the aim of obtaining suitable cubic/hexagonal phase ratios. The annealing of the h-BN films at temperatures up to 1000 °C in a nitrogen atmosphere, at normal pressure, gave rise to a complete transformation into the cubic phase. FTIR measurements provided a suitable method for identifying the structure of BN films. UV-vis spectroscopy was carried out in order to investigate the optical behaviour of the films.     

TiO2 nanopowders via radio-frequency thermal plasma oxidation of organic liquid precursors: Synthesis and characterization

TiO₂ nanopowders have been synthesized via Ar/O₂ thermal plasma oxidation of titanium butoxide (TBO) solutions stabilized with diethanolamine (DEA). Experiments were conducted by varying the O₂ input in the plasma sheath (10–90 L/min) and the DEA/TBO molar ratio (R), while keeping the plasma generation power at 25 kW and the reactor pressure at 500 Torr. The resultant powders are mixtures of the anatase and rutile polymorphs in the studied range, whose anatase content and crystallite size exhibit weak dependence on the O₂ input at a fixed R. Increasing R decreases the anatase content, signifying the role of CO gas, generated via oxidation of the organic precursor, on the phase structure. FE-SEM and TEM analysis show that the resultant powders contain majority of nanoparticles (<50 nm) and some large spheres (>100 nm), whose size and/or number tends to decrease at a higher O₂ input, leading to gradually increased specific surface area. Raman spectroscopy reveals no significant differences in the crystallite size and oxygen-vacancy concentration of the nanocrystals by varying the O₂ input.     

Selection of adhesive system for radio-frequency heating of structural sheet molding compound components

A series of laboratory tests and computer simulations of adhesive curing enhanced by radio-frequency heating indicated that not all adhesive systems can be effectively used for RF-based curing because of the danger of thermal runaway. Our investigation of the process mechanism also resulted in several other findings that could lead to further improvement of the processing cycle. Both experimental and theoretical results indicated a high sensitivity of the adhesive exothermal reaction kinetics to the thickness of the bond line, which varies with changes of the thickness of the processed sheet molding compound (SMC) components. Thus, regardless of the type of adhesive system employed, tighter dimensional tolerance would ensure better quality of the bond. Finally, we proved that the initial surface temperature of the SMC members substantially affects the process effectiveness and joint quality, and should be strictly monitored.     

水性聚氨酯胶粘剂在复合薄膜制造上的应用

介绍了聚氨酯胶粘剂在复合薄膜制造上的应用,水性聚氨酯胶粘剂替代溶剂型聚氨酯胶粘剂做复合薄膜用胶的必然性,水性聚氨酯胶粘剂的特性、制备方法以及水性聚氨酯乳液应用于制备复合薄膜的不足之处以及改善方法。     

葡萄糖对苯二酚树脂胶粘剂的合成

以葡萄糖代替甲醛,在碱性条件下合成了葡萄糖对苯二酚树脂胶粘剂。利用红外光谱(IR)及热重分析(TGA)对树脂的结构及热稳定性进行了分析,并通过正交实验获得了该树脂合成的最佳反应条件:pH=13,n(葡萄糖)n∶(对苯二酚)=101,∶反应温度110℃,催化剂用量2.0%,反应时间7h;同时对树脂的固化条件进行了系统研究。     

Influence of nitrogen plasma post-treatment on diamond-like carbon films synthesized by RF plasma enhanced chemical vapor deposition

DLC films were synthesized by RF plasma enhanced chemical vapor deposition and the effects of nitrogen plasma post-treatment at different pressures on the structure and properties of DLC films were investigated. Higher roughness was obtained after plasma post-treatment at higher pressures (0.3 and 0.9 torr) and plasma post-treatment at a lower pressure (0.15 torr) resulted in lower roughness than that of original films. The hardness of DLC films decreased with the decrease of post-treatment pressure, which is consistent with the Raman results of I_D/I_G ratio and G peak position. Compared to the original DLC film, the residual stress after plasma post-treatment decreased slightly due to the relatively thin region involved in the plasma post-treatment.     

空分装置中氮气和氧气采出比研究

通过空气深冷分离装置,同时得到高纯氮气和高纯氧气,以满足化工装置的需要。对于不同的化工装置,高纯氮气和高纯氧气的采出比例要求不同,最终影响着空分装置的工艺流程和能耗水平。文中通过分析空分装置中空气分离上塔及下塔的操作原理,提出以空气分离下塔塔顶的回流比为操作变量,研究空分装置中氮气/氧气的采出比情况;通过工艺计算在不同回流比情况下,同时在下塔和上塔热量耦合的约束下,分别得到下塔和上塔的物流采出情况,并对物流采出情况进行分析,得到了下塔操作回流比的变化对空分装置氮气/氧气采出比的影响。对于氮气/氧气采出比小于1的情况,高纯氮气可全部由下塔采出;对于氮气/氧气采出比大于1的情况,高纯氮气分别由下塔和上塔共同采出。