石墨烯喷涂与化学镀镍黑化冷屏性能对比

Performance Comparison of Graphene Spraying and Electroless Nickel Blackening Cold Shield

目的 探索高效的冷屏黑化技术,获得石墨烯环氧胶混合喷涂与化学镀镍黑化后的红外探测器冷屏的光学特性、真空放气特性。方法 采用傅里叶光谱仪对比测试不同粗糙度的基底,以及基底经过化学镀镍、石墨烯喷涂黑化后的样品在2.5~15μm波段内的镜面反射率,利用扫描电子显微镜观察分析黑化表面形貌。采用小孔流导法测试对比不同粗糙度基底250℃除气前后的放气规律,以及除气后基底、化学镀镍、石墨烯喷涂黑化样品的出气率。结果 化学镀镍黑化反射率受基底粗糙度的影响大,若在喷砂面黑化,镜面反射率低于2%。石墨烯喷涂的黑化涂层厚,吸收率不受基底表面粗糙度影响,镜面反射率低于0.4%,但镀层的表面结合力受到基底粗糙度的影响。对放气特性进行分析发现,高温除气可以去除化学吸附气体分子,再次暴露大气吸附的气体多为物理吸附。黑化层对出气率的影响远大于基底粗糙度,石墨烯黑化层的微孔洞结构使初始出气率大于镀黑镍约1个数量级。结论 石墨烯与环氧胶混合喷涂黑化的消杂散光能力显著优于化学镀镍黑化,但总放气量高,采用适当的低出气率处理,改进其真空性能是在红外组件应用中的关键。

In the infrared, radiation from package components near ambient temperature is a source of unwanted photons.Cold shields are used to restrict the field of view of detector. The surfaces of cold shield must be blackened so that photons originating from warm objects are not reflected or scattered into the detector. Absorptive black coatings are used in infrared detectors to trap scattered and stray photons. The vacuum performance of coating is an important characteristic of vacuum packaging infrared detector. The optical and vacuum performance of epoxy resin admixed graphene spraying and electroless nickel blackening coatings are researched. Also, the influence of surface roughness of base material is analyzed.The specular reflectance of substrates with different roughness and the samples after electroless nickel plating and graphene spraying blackening in the 2.5~15 μm wavelength range are compared and tested by Fourier spectrometer. The blackened surface morphology is observed and analyzed by using scanning electron microscope. The outgassing law of substrates with different roughness before and after degassing, the outgassing rate of substrates, electroless nickel plating, and graphene spraying blackened samples after degassing at 250 ℃ is tested and compared by the pinhole conductometric method. The reflectance of thin electroless nickel blackening effected by the roughness of base material. The spectrum reflectance of electroless nickel blackening on sand blasting base material surface are below 2%. In contrary, the spectrum reflectance of thick epoxy resin admixed graphene spraying on different roughness surface are the same and below 0.4%. But the cohesion of thick black graphene coating is affected by the roughness of base material. Scratching tracks and frictional force curves vs applied load are analyzed. The result shows thick black graphene coating have better cohesion on sand blasting base material surface.Two black coatings show band selective property differ from base material. Their morphologies are observed by scanning electron microscope(SEM). The light absorb components are observed in black coatings, while base material mainly shows specular reflectance.The outgassing rates of samples are measured by orifice-conductance method. Outgassing rates and mass spectrums of base material with different roughness surface are measured before and after 250 ℃ gas removing procedure. The outgassing rate rise up along with higher Ra. The compare of outgassing rates and mass spectrums of samples shows high temperature gassing removing procedure which can remove chemisorbed gases. The re-absorbed gases are mostly physically absorbed which can be pumped off in a short time. Also outgassing rates of base material, electroless nickel blackening, and black epoxy resin admixed graphene spraying samples after gas removing procedure are compared. The outgassing rate of samples with black coating is higher than base material. The contribution of black coating on outgassing is more than the rough surface. Because of the micro cavity structure on graphene spraying coating, the initial outgassing rate of epoxy resin admixed graphene spraying sample is higher than electroless nickel blackening sample by one order of magnitude, but degrades faster than black electroless nickel blackening sample. The optical performance of epoxy resin admixed graphene spraying coating is remarkably better than electroless nickel blackening coating when used to trap photons. But the cumulative released gas is more than electroless nickel blackening sample which could decrease the vacuum life of infrared detector. Improving the vacuum performance is the most important thing for the application of black graphene coating on cold shield.