Lingjun Guo

Studies on diamondlike carbon films for antireflection coatings of infrared optical materials

Diamondlike carbon (DLC) films were directly deposited onto germanium (Ge) and zinc sulphide (ZnS) slices by a capacitively coupled 13.56 MHz rf glow discharge plasma with Ar‐C2H2 gas mixtures. The IR transmittance was measured using a Fourier‐transform infrared spectrometer. The maximum values of the IR transmission of Ge and ZnS with DLC films on both sides are 99% and 95.8%, respectively, which come up to the theoretical values. A nonuniform DLC film, of which the refractive index gradually changes along the thickness, has been successfully deposited onto a Ge slice for the first time and the IR transmission of a nonuniform DLC film coated onto both sides of a Ge substrate at the wider wave band of 2.5–15 μm is over 85%.

Influence of deposition parameters on the refractive index and growth rate of diamond-like carbon films

Abstract In order to use diamond-like carbon (DLC) films as protective and antireflection coatings for IR optical materials exposed to hostile environments, an investigation has been systematically conducted on the influence of the deposition parameters on the refractive index and growth rate of DLC films, which are two of the most important parameters in evaluating optical characteristics of antireflection coatings. The experimental results show that both the refractive index and growth rate of DLC films depend strongly on the negative d.c. bias voltage. The refractive index increases with increasing bias voltage and decreases with increasing partial pressure of the hydrocarbon gas and total flow rate of the mixture. The growth rate increases greatly when the bias voltage is larger than a threshold value. The various parameters which influence the structure and properties of DLC films are interrelated. Fourier transform IR spectroscopy results show that the strength of the C−H stretching absorption band in the range 3300–2850 cm−1 is gradually weakened with increasing negative bias voltage and argon concentration. High energy bombardment of the growing film plays an important role in the structure and hence the properties of DLC films.

Study on the Microstructures and Mechanical Properties of 2D C/C Composites: Study on the Microstructures and Mechanical Properties of 2D C/C Composites

采用等温化学气相渗透方法,通过调整沉积工艺,制备了具有不同微观组织结构的2D C/C复合材料.利用偏光显微镜（PLM）、扫描电子显微镜（SEM）、透射电子显微镜（TEM）结合选区电子衍射（SAED）,研究了热解炭基体微观组织结构,借助万能试验机测试了材料的三点弯曲性能.结果表明：层状高织构（HT）热解炭基体占优时C/C复合材料表现为假塑性断裂;扁平片状中织构（MT）热解炭与颗粒状各向同性层热解炭（ISO）有利于提高材料的弯曲强度;HT基体与炭纤维界面结合良好,界面处不存在非HT织构,但取向角（OA）略有增大.

Micro- and Nano-structure Characterization of Isotropic Pyrocarbon Obtained via Chemical Vapor Deposition in Hot Wall Reactor

The hot wall reactor was used to deposit isotropic pyrocarbon. The density of the product was measured by Archimedes method. The fracture morphology and texture of the product were investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Raman spectroscopy was also applied to characterizing the structure of the product. The results show that the density of the product is about 1.31 g/cm 3 . The pyrocarbon consists of granular particles with the size of about 1.5 „m under SEM images. Under TEM images, the pyrocarbon is composed of irregular grains and onion-like particles are also detected. The orientation angle (180 deg.) of pyrocarbon reveals its isotropic character. The ID/IG ratio in Raman spectrum is about 1.2, indicating the isotropic feature of the product qualitatively.

Effect of chemical vapor infiltration treatment on the wave-absorbing performance of carbon fiber/cement composites

Abstract Short carbon fibers were treated at high temperatures around 1100°C through chemical vapor infiltration technology. A thinner layer of pyrocarbon was deposited on the fiber surface. The dispersion of carbon fibers in a cement matrix and the mechanical properties of carbon fiber/cement composites were investigated by scanning electron microscopy (SEM) and other tests. The reflectivity of electromagnetic waves by the composites was measured in the frequency range of 8.0–18 GHz for different carbon fiber contents of 0.2wt%, 0.4wt%, 0.6wt%, and 1.0wt%. The results show that the reflectivity tends to increase with the increase of fiber content above 0.4wt%. The minimum reflectivity is −19.3 dB and the composites exhibit wave-absorbing performances. After pyrocarbon is deposited on the fiber, all the reflectivity data are far greater. They are all above −10 dB and display mainly wave-reflecting performances.

X-ray diffraction and raman spectroscopy characterization of isotropic pyrocarbon obtained by hot wall chemical vapor deposition

Varying the flow rate of natural gas from 50 to 80 to 120 l/h, isotropic pyrocarbon produced by hot wall chemical vapor deposition at 1000 °C were examined by X-ray diffraction and Raman spectroscopy. The X-ray data were evaluated by Scherrer equation, and the intensity ratio of D to G band derived from Raman data was used to evaluate the lateral extension of isotropic pyrocarbon. The experimental results show that the d002-spacing of isotropic pyrocarbon decreases from 0.3499 nm to 0.3451 nm, while the stack height increases from 6.5 to 8.4 nm with the increase of flow rate of natural gas. The intensity ratio of D to G band and lateral extension of isotropic pyrocarbon increases with natural gas flow rate increasing. After heat treatment, all the crystallite parameters (stack height, lateral extension, and d002-spacing) decrease, indicating the improvement of the arrangement of the basic structural units of isotropic pyrocarbon.

Effects of carbon nanotubes by electrophoretic deposition on interlaminar properties of two dimensional carbon/carbon composites

Carbon nanotubes (CNTs) were deposited uniformly on carbon cloth by electrophoretic deposition (EPD). Thereafter, CNT-doped clothes were stacked and densified by pyrocarbon via chemical vapor infiltration to fabricate two-dimensional (2D) carbon/carbon (C/C) composites. Effects of EPD CNTs on interlaminar shear performance and mode II interlaminar fracture toughness (GIIc) of 2D C/C composites were investigated. Results showed that EPD CNTs were uniformly covered on carbon fibers, acting as a porous coating. Such a CNT coating can obviously enhance the interlaminar shear strength and GIIc of 2D C/C composites. With increaing EPD CNTs, the interlaminar shear strength and GIIc of 2D C/C composites increase greatly and then decrease, both of which run up to their maximum values, i e, 13.6 MPa and 436.0 J·m−2, when the content of EPD CNTs is 0.54 wt%, 2.27 and 1.45 times of the baseline. Such improvements in interlaminar performance of 2D C/C composites are mainly beneficial from their increased cohesion of interlaminar matrix, which is caused not only by the direct reinforcing effect of EPD CNT network but also by the capacity of EPD CNTs to refine pyrocarbon matrix and induce multilayered microstructures that greatly increase the crack propagation resistance through “crack-blocking and -deflecting mechanisms”.