金刚石薄膜压阻效应及相关问题的研究

P型金刚石薄膜具有压阻效应,是最近五六年才发现的新现象。利用压阻效应,可望将金刚石膜制成高灵敏度的新一类压阻传感器材料和压力微传感器,从而拓宽金刚石膜在电子学领域的应用范围。 对金刚石膜的压阻因子进行了测量,结果表明,P型定向生长的多晶金刚石膜室温压阻因子可达100O以上;金刚石薄膜的压阻效应比硅和金属显著得多;多晶金刚石膜的压阻效应不如单晶金刚石膜。金刚石膜具有显著的压阻效应,其理论原因和机制问题到目前一直不太清楚,本研究工作对此进行了系统和深入的研究。在能带结构和形变势理论的基础上,首次结合价带分裂模型和M-S多晶模型,分别推导出P型单晶和多晶金刚石膜压阻因子的近似计算公式。分析结果认为,金刚石薄膜的压阻效应是应力诱导价带分裂造成的。轻、重空穴有效质量之间的巨大差异,是导致P型金刚石具有显著压阻效应的主要原因之一。P型多晶材料的压阻效应,是应力诱导价带分裂和晶界散射联合作用的结果,晶界有阻碍电阻随应变发生改变的作用。从而,第一次从理论上阐明了导致P型多晶材料压阻效应不如同种的P型单晶材料的原因。 对负偏压热灯丝CVD系统下,金刚石膜核化过程进行了研究,结果认为.负偏压对金刚石膜核化的增强是离子对衬底的轰击与发射电子激发的等离子体联合作用于衬     

金刚石薄膜压阻效应研究现状

对硼掺杂Ｐ型金刚石薄膜压阻效应的国内外研究现状进行了综述，并对Ｐ型金刚石薄膜具有非常显著的压阻效应产生机制进行了初步分析讨论。     

纳米银-聚合物菱形剪纸薄膜应变传感特性的研究

采用银镜制备法和激光切割技术获得了纳米银颗粒/聚二甲基硅氧烷剪纸结构薄膜,并系统地研究了薄膜作为柔性应变传感器的力学及压阻特性。将数值模拟与实验相结合,测量了传感薄膜的应变比γ、压阻滞回特性、线性度及压阻敏感性,重点探讨了薄膜制备工艺、结构参数与上述薄膜传感特性的定量关系。结果表明,在给定结构下,结构薄膜整体与结构单元的应变比γ为常数,反映了结构薄膜的变形特性,是理想的力学性能表征参数。菱形剪纸结构薄膜具有量级可达200的大应变比,即在大应变下,材料的实际应变很小。这一特点极大地提升了薄膜的应变测量范围、压阻稳定性、线性度,并保持了合理的压阻灵敏度。     

热处理对金属薄膜压阻灵敏度的影响

采用磁控溅射法制备锰铜薄膜,溅射和真空蒸发法制备镱薄膜.对热处理前后薄膜的电学性能、微观形貌和结构进行了表征,并采用轻气炮和对顶砧装置对薄膜传感器进行了压阻性能测试,结果表明热处理后薄膜的压阻系数有很大提高.SEM和XRD的分析表明,压阻系数的提高是由于热处理后薄膜晶粒长大、缺陷减少、电阻率下降所致.敏感薄膜的电阻率与传感器的灵敏度直接相关.热处理后,薄膜压阻计的灵敏度已接近箔式传感器的水平,热处理是提高薄膜压阻计灵敏度的有效手段.     

热灯丝CVD金刚石膜的微结构和形貌对其电子性质的影响

利用热灯丝CVD法在硅衬底上合成出了金刚石膜。金刚石膜的质量和电子性质由扫描电子显微镜、拉曼谱、阴极发光及霍尔系数测量来表征。实验结果表明,沉积条件对金刚石膜电子性质和质量有重要影响。载流子迁移率随甲烷浓度增加而减少,但场发射随其增加而增强。压阻效应随微缺陷增多而降低。异质外延金刚石膜压阻因子在室温下100微形变时为1200,但含有大量缺陷的多晶金刚石膜压阻因子低于200,这是由于薄膜中缺陷态密度增加,并依赖于膜结构的变化。     

纳米Si薄膜的压阻效应

纳米Ｓｉ薄膜由大量的超微Ｓｉ晶粒和大量的晶粒间界面区组成。这一特殊的结构造成纳米Ｓｉ薄膜具有较大的压阻效应。本文讨论了薄膜微结构对其压阻效应的作用。认为纳米Ｓｉ薄膜材料是一种优秀的传感器材料。     

纳米Si薄膜的结构及压阻效应

使用ＨＲＥＭ及ＳＴＭ技术检测了纳米Ｓｉ薄膜的微结构，纳米Ｓｉ薄膜由大量的细微Ｓｉ晶粒以及大量的晶粒间界面区组成，这一特殊的结构造成纳米Ｓｉ薄膜具有较大的压阻效应及较高氢含量，本文分析讨论了薄膜微结构对其压阻效应的作用，并认为纳米Ｓｉ薄膜材料将是一种理想的传感器材料。     

金刚石薄膜的研究现状与发展前景

文章介绍了金刚石的性质和应用,总结了金刚石薄膜研究的历史,论述了金刚石薄膜的优良特性和技术发展,指出国内外学术界都在不断地开拓和发展金刚石薄膜的应用领域。     

金刚石膜的磁阻效应和压阻效应

介绍了p型异质外延金刚石膜磁阻效应和压阻效应的特性及应用展望，阐述了目前理论和实验的研究状况，提出了今后有待进一步研究的问题。     

岩石爆破孔壁动态初始压力测试系统研究

本文根据锰钢压阻传感器耐高压,频响特性好和温度系数小等特点,建立了一套以锰铜压阻传感器为主要测试折岩石爆破孔壁动态初始压力测试系统。     

稀土化合物浆料对CVD金刚石厚膜的刻蚀

ＣＶＤ金刚石厚膜具有极高的硬度,使得对其进行表面抛光极为困难．传统的机械抛光方法既不经济又耗费时间,而一些新的抛光技术又由于实验条件限制而难以推广．针对以上情况,我们寻求到一种新的化学刻蚀方法,即利用稀土化合物浆料对金刚石厚膜生长表面进行刻蚀,破坏表面的晶粒使之成为晶骸,降低表面的耐磨性,以提高表面粗糙的金刚石厚膜的抛光效率．     

Materials with extreme properties: Their structuring and applications

This article is a brief review on syntheses of materials with extreme properties and their modification by plasma processes to obtain different morphological structures. First we illustrate general methodologies on preparation of polycrystalline diamond (PD), nanocrystalline diamond (ND), cubic boron nitride (cBN), diamond/cBN multilayer films by low pressure methods. Since cBN synthesis is more challenging, we place more attention to cBN including its growth, structuring and doping. The structural compatibility of cBN and diamond enables the fabrication of multilayer (superlattices); and we describe such an approach to produce composite materials with even more extreme properties. The superior hardness, extreme thermal conductivity and high chemical stability make diamond and cBN well suited for cutting tool and tribological applications. Although doping of these wide bandgap materials for p- and n-type conductivity is difficult, recent works indicate considerable advancement. The combination of high chemical stability and thermal conductivity with attractive electronic properties makes diamond and cBN suitable for construction of high power electronic devices operating in harsh environments. The development of these applications relies on the ability to design patterns and control the film conductivity. We illustrate that despite diamond and cBN are chemically stable and inert against many chemicals, film patterning and device fabrication is possible with the use of plasma processing. Further, we discuss the fundamental issues involved and demonstrate feasibility for the design of practical applications such as deep-ultraviolet (DUV) detectors and surface acoustic wave (SAW) devices. Finally we discuss the existence of other composite materials with extreme properties that have been only barely investigated, and that present promising alternatives for the future commercial applications.     

Superior wear resistance of diamond and DLC coatings

As the hardest known material, diamond and its coatings continue to generate significant attention for stringent applications involving extreme tribological conditions. Likewise, diamond-like carbon (DLC, especially the tetragonal amorphous carbon, ta-C) coatings have also maintained a high level interest for numerous industrial applications where efficiency, performance, and reliability are of great importance. The strong covalent bonding or sp³-hybridizaiton in diamond and ta-C coatings assures high mechanical hardness, stiffness, chemical and thermal stability that make them well-suited for harsh tribological conditions involving high-speeds, loads, and temperatures. In particular, unique chemical and mechanical nature of diamond and ta-C surfaces plays an important role in their unusual friction and wear behaviors. As with all other tribomaterials, both diamond and ta-C coatings strongly interact with the chemical species in their surroundings during sliding and hence produce a chemically passive top surface layer which ultimately determines the extent of friction and wear. Thick micro-crystalline diamond films are most preferred for tooling applications, while thinner nano/ultranano-crysalline diamond films are well-suited for mechanical devices ranging from nano- (such as NEMS) to micro- (MEMS and AFM tips) as well as macro-scale devices including mechanical pump seals. The ta-C coatings have lately become indispensable for a variety of automotive applications and are used in very large volumes in tappets, piston pins, rings, and a variety of gears and bearings, especially in the Asian market. This paper is intended to provide a comprehensive overview of the recent developments in tribology of super-hard diamond and DLC (ta-C) films with a special emphasis on their friction and wear mechanisms that are key to their extraordinary tribological performance under harsh tribological conditions. Based on the results of recent studies, the paper will also attempt to highlight what lies ahead for these films in tribology and other demanding industrial applications.     

The versatility of hot-filament activated chemical vapor deposition

In the field of activated chemical vapor deposition (CVD) of polycrystalline diamond films, hot-filament activation (HF-CVD) is widely used for applications where large deposition areas are needed or three-dimensional substrates have to be coated. We have developed processes for the deposition of conductive, boron-doped diamond films as well as for tribological crystalline diamond coatings on deposition areas up to 50 cm × 100 cm. Such multi-filament processes are used to produce diamond electrodes for advanced electrochemical processes or large batches of diamond-coated tools and parts, respectively. These processes demonstrate the high degree of uniformity and reproducibility of hot-filament CVD. The usability of hot-filament CVD for diamond deposition on three-dimensional substrates is well known for CVD diamond shaft tools. We also develop interior diamond coatings for drawing dies, nozzles, and thread guides.Hot-filament CVD also enables the deposition of diamond film modifications with tailored properties. In order to adjust the surface topography to specific applications, we apply processes for smooth, fine-grained or textured diamond films for cutting tools and tribological applications. Rough diamond is employed for grinding applications. Multilayers of fine-grained and coarse-grained diamond have been developed, showing increased shock resistance due to reduced crack propagation.Hot-filament CVD is also used for in situ deposition of carbide coatings and diamond-carbide composites, and the deposition of non-diamond, silicon-based films. These coatings are suitable as diffusion barriers and are also applied for adhesion and stress engineering and for semiconductor applications, respectively.     

Pulsed ion beam characterization of CVD diamond surfaces under thin film deposition conditions

Diamond and diamond-like carbon have properties which in principle make them ideally suited to a wide variety of thin-film applications. The widespread use of diamond thin films, however, has been limited for a number of reasons related largely to the lack of understanding and control of the nucleation and growth processes. Real-time, in-situ studies of the surface of the growing diamond film are experimentally difficult because these films are normally grown under a relatively high pressure of hydrogen, and conventional surface analytical methods require an ultrahigh vacuum environment. Pulsed ion beam based analytical methods with differentially pumped ion sources and particle detectors are able to characterize the uppermost atomic layer of a film during growth at ambient pressures in the range 0.7–27 Pa (4–6 orders of magnitude higher than other surface-specific analytical methods). We describe here a system which has been developed for the purpose of determining the hydrogen concentration and bonding sites on diamond surfaces as a function of sample temperature and ambient hydrogen pressure under hot-filament chemical vapor deposition (CVD) growth conditions. It is demonstrated that as the hydrogen partial pressure increases the saturation hydrogen coverage of the surface of a CVD diamond film increases, but that the saturation level depends on the atomic hydrogen concentration and substrate temperature. At the highest temperatures studied (700 °C), it was found that the surface hydrogen concentration did not exceed 1/4 monolayer.     

Protein-modified nanocrystalline diamond thin films for biosensor applications

Diamond exhibits several special properties, for example good biocompatibility and a large electrochemical potential window, that make it particularly suitable for biofunctionalization and biosensing. Here we show that proteins can be attached covalently to nanocrystalline diamond thin films. Moreover, we show that, although the biomolecules are immobilized at the surface, they are still fully functional and active. Hydrogen-terminated nanocrystalline diamond films were modified by using a photochemical process to generate a surface layer of amino groups, to which proteins were covalently attached. We used green fluorescent protein to reveal the successful coupling directly. After functionalization of nanocrystalline diamond electrodes with the enzyme catalase, a direct electron transfer between the enzyme's redox centre and the diamond electrode was detected. Moreover, the modified electrode was found to be sensitive to hydrogen peroxide. Because of its dual role as a substrate for biofunctionalization and as an electrode, nanocrystalline diamond is a very promising candidate for future biosensor applications.     

Chemical vapour deposition of microdrill cutting edges for micro- and nanotechnology applications

Conventional cemented tungsten carbide-cobalt (WC-Co) microdrills generally have a low cutting efficiency and short lifetime mainly because they operate at very high cutting speeds. Since it is relatively expensive to make microtools it is highly desirable to improve their lifetime and in-service performance. Microtools used to make microelectronic and mechanical systems (M.E.M.S) devices with sharp cutting edges, such as milling or drilling tools need protective coating in order to extend life and improve performance. One method of achieving this objective is to use a suitable surface engineering technology to deposit a hard wear resistant coating, such as diamond. Diamond has excellent mechanical properties, such as ultra-high hardness and a low friction coefficient. One of the most promising surface treatment technologies for depositing diamond onto complex shaped components is chemical vapour deposition (CVD). However, CVD of diamond coatings onto the cemented WC-Co tool has proved to be problematic. Binder materials such as cobalt can suppress diamond nucleation resulting in poor adhesion between the coating and substrate. In this paper the effects of pre-treated substrate material on the coating structure are reported. The morphology and the crystallinity of the as-grown films was characterised by using scanning electron microscopy (SEM). Raman spectroscopy was used to assess the carbon-phase purity and give an indication of the stress levels in the as-grown polycrystalline diamond films. The diamond coated tools have potential applications in micro- and nanomachining of micro- and nano-sized components used in M.E.MS.     

Growth behavior of CVD diamond films with enhanced electron field emission properties over a wide range of experimental parameters

In this study, diamond films were synthesized on silicon substrates by microwave plasma enhanced chemical vapor deposition (CVD) over a wide range of experimental parameters. The effects of the microwave power, CH₄/H₂ ratio and gas pressure on the morphology, growth rate, composition, and quality of diamond films were investigated by means of scanning electron microscope (SEM), X-ray diffraction (XRD), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). A rise of microwave power can lead to an increasing pyrolysis of hydrogen and methane, so that the microcrystalline diamond film could be synthesized at low CH₄/H₂ levels. Gas pressure has similar effect in changing the morphology of diamond films, and high gas pressure also results in dramatically increased grain size. However, diamond film is deteriorated at high CH₄/H₂ ratio due to the abundant graphite content including in the films. Under an extreme condition of high microwave power of 10 kW and high CH₄ concentration, a hybrid film composed of diamond/graphite was successfully formed in the absence of N₂ or Ar, which is different from other reports. This composite structure has an excellent measured sheet resistance of 10–100 Ω/Sqr. which allows it to be utilized as field electron emitter. The diamond/graphite hybrid nanostructure displays excellent electron field emission (EFE) properties with a low turn-on field of 2.17 V/μm and β = 3160, therefore it could be a promising alternative in field emission applications.     

系统压强对微波等离子体化学气相沉积金刚石成核的影响

为了在氧化铝上制备（100）定向织构的金刚石薄膜,必须先提高金刚石的成核密度,在微波等离子体化学气相沉积（MPCVD）系统中,采用低压成核的方法,在氧化铝陶瓷上沉积出高成核密度的金刚石薄膜,扫描电镜显示其成核密度可达10^8cm^-2。在此基础上,沉积出（100）织构的金刚石薄膜。     

探索人工干预诱导二次形核技术制备纳米金刚石膜

围绕纳米金刚石膜生长的二次形核理论,利用直流热阴极PCVD技术,在微晶金刚石膜连续生长模式常用的一些生长条件下,通过改变工作气压,改变生长温度,同时采取人工干预间歇生长模式进行金刚石膜生长实验,探索纳米级金刚石膜制备的新途径.实验表明:在金刚石膜生成的过程中,降低工作气压或生长温度,可使等离子体激励能量减弱,导致二次形核基团比例增加,成为人工干预二次形核的内在诱因;通过调节激励电压,使等离子体能量状况改变,有利于二次形核行为的引导,成为人工干预二次形核的外在诱因,在此内外因素共同作用下,可以实现二次形核现象的有效诱导,制备出纳米金刚石膜.人工干预诱导二次形核技术制备纳米金刚石膜的实现,使纳米金刚石膜制作方法得到了扩展,也拓宽了直流热阴极PCVD技术的应用范围.