Substitutional phosphorus incorporation in nanocrystalline CVD diamond thin films

Nanocrystalline diamond (NCD) thin films were produced by chemical vapor deposition (CVD) and doped by the addition of phosphine to the gas mixture. The characterization of the films focused on probing the incorporation and distribution of the phosphorus (P) dopants. Electron microscopy evaluated the overall film morphology and revealed the interior structure of the nanosized grains. The homogeneous films with distinct diamond grains featured a notably low sp²:sp³‐ratio as confirmed by Raman spectroscopy. High resolution spectroscopy methods demonstrated a homogeneous P‐incorporation, both in‐depth and in‐plane. The P concentration in the films was determined to be in the order of 10¹⁹ cm^–3 with a significant fraction integrated at substitutional donor sites. (© 2014 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Investigation of properties of Cu containing DLC films produced by PECVD process

Copper containing diamond like carbon (Cu-DLC) thin films were deposited on various substrates at a base pressure of 1×10^?3 Torr using a hybrid system involving DC-sputtering and radio frequency-plasma enhanced chemical vapor deposition (RF-PECVD) techniques. The compressive residual stresses of these films were found to be considerably lower, varying between 0.7 and 0.94 GPa and Cu incorporation in these films improve their conductivity significantly. Their structural properties were studied by Raman spectroscopy, atomic force microscopy, scanning electron microscopy, X-ray photoelectron spectroscopy and X-ray diffraction techniques that clearly revealed the presence of Cu in the DLC structure. Raman analysis yields that Cu incorporation in DLC enhances the graphite-like sp² bonding. However, the sp² bonding was found to continuously reduce with the increasing C₂H₂ gas pressure, this may be due to reduction of Cu nanocrystal at the higher pressure. FTIR results inferred various bonding states of carbon with carbon, hydrogen and oxygen. In addition, hydrogen content and sp³ and sp² fractions in different Cu-DLC films were also estimated by FTIR spectra and were correlated with stress, electrical, optical and nano-mechanical properties of Cu-DLC films. The effect of indentation load (4–10 mN) on nano-mechanical properties of these films was also explored.     

Effects of N2 addition on nanocrystalline diamond films by HFCVD in Ar/CH4 gas mixture

Nanocrystalline diamond (NCD) films were grown on silicon substrates by hot filament chemical vapor deposition in Ar/N₂/CH₄ gas mixtures. The effects of seeding process prior to deposition, the total gas pressure, and concentration of nitrogen on the grain size, morphology and bonding nature in HFCVD technique were investigated. The results indicated that a low total gas pressure is favorable for nanosized diamond crystallites. Films micrograph obtained from scanning electron microscopy showed diamond nanograins elongated with the addition of nitrogen in the plasma. Crystal structure investigations were carried out by X-ray diffraction measurements for deposited films. An increase in the size of crystallite is also observed from XRD measurements in NCD film when nitrogen was added in plasma. From Raman spectra, it was observed that the relative intensity of G peak increases indicating more graphite content after nitrogen added in the plasma. The effects of the nitrogen incorporation in nanocrystalline films in HFCVD are discussed.     

Effect of titanium incorporation on the structural, mechanical and biocompatible properties of DLC thin films prepared by reactive-biased target ion beam deposition method

Amorphous diamond like carbon (DLC) and titanium incorporated diamond like carbon (Ti-DLC) thin films were deposited by using reactive-biased target ion beam deposition method. The effects of Ti incorporation and target bias voltage on the microstructure and mechanical properties of the as-deposited films were investigated by means of X-ray photoelectron spectroscopy, Raman spectroscopy, transmission electron microscopy and nano-indentation. It was found that the Ti content in Ti-DLC films gets increased with increasing target bias voltage. At about 4.2 at.% of Ti, uniform sized well dispersed nanocrystals were seen in the DLC matrix. Using FFT analysis, a facility available in the TEM, it was found that the nanocrystals are in cubic TiC phase. Though at the core, the incorporated Ti atoms react with carbon to form cubic TiC; most of the surface exposed Ti atoms were found to react with the atmospheric oxygen to form weakly bonded Ti-O. The presence of TiC nanocrystals greatly modified the sp³/sp² hybridized bonding ratio and is reflected in mechanical hardness of Ti-DLC films. These films were then tested for their biocompatibility by an invitro cell culturing test. Morphological observation and the cell proliferation test have demonstrated that the human osteoblast cells well attach and proliferate on the surface of Ti incorporated DLC films, suggesting possible applications in bone related implant coatings.     

掺杂CVD金刚石薄膜的应力分析

在不同实验条件下，用微波等离子体化学气相沉积(MPCVD)技术在Si基体上制备了S掺杂和B-S共掺杂CVD金刚石薄膜，利用X射线衍射仪和拉曼光谱仪研究掺杂对CVD金刚石薄膜的应力影响.研究结果发现，随着S掺杂浓度的增加，薄膜中sp²杂化碳含量和缺陷增多，CVD金刚石薄膜压应力增加；小尺寸的B原子与大尺寸的S原子共掺杂时，微量B的加入改变了CVD金刚石薄膜的应力状态，共掺杂形成B-S复合体进入金刚石晶体后降低金刚石晶体的晶格畸变程度，减少S原子在晶界上偏聚数量和晶体中非金刚石结构相含量，降低由于杂质、缺陷及sp²杂化碳含量产生的晶格畸变和薄膜压应力，提高晶格完整性. 关键词： 金刚石薄膜 掺杂 应力     

Effect of oxygen on regulation of properties of moderately boron-doped diamond films

Regulation of oxygen on properties of moderately boron-doped diamond films is fully investigated. Results show that, with adding a small amount of oxygen (oxygen-to-carbon ratio < 5.0%), the crystal quality of diamond is improved, and a suppression effect of residual nitrogen is observed. With increasing ratio of O/C from 2.5% to 20.0%, the hole concentration is firstly increased then reduced. This change of hole concentration is also explained. Moreover, the results of Hall effect measurement with temperatures from 300 K to 825 K show that, with adding a small amount of oxygen, boron and oxygen complex structures (especially B₃O and B₄O) are formed and exhibit as shallow donor in diamond, which results in increase of donor concentration. With further increase of ratio of O/C, the inhibitory behaviors of oxygen on boron leads to decrease of acceptor concentration (the optical emission spectroscopy has shown that it is decreased with ratio of O/C more than 10.0%). This work demonstrates that oxygen-doping induced increasement of the crystalline and surface quality could be restored by the co-doping with oxygen. The technique could achieve boron-doped diamond films with both high quality and acceptable hole concentration, which is applicable to electronic level of usage.     

Incorporation of nitrogen into amorphous-hydrogenated carbon (diamond-like) films

Nitrogen-doped amorphous hydrogenated carbon films (a-C:H) were prepared by mixing nitrogen gas and benzene during dc plasma discharge deposition. The growth rate of the film decreases strongly with increasing nitrogen content in the mixture. The nitrogen concentration in the films was determined by nuclear reaction analysis (NRA) and Auger electron spectroscopy (AES) using suitable calibration samples. The results of AES measurements are generally consistent with NRA values. Nitrogen incorporation in the a-C:H films shows pronounced doping effects as reflected in their optical and electrical properties.Dedicated to Professor J. P. F. Sellschop for his 60^th birthday     

Impact of nitrogen doping on growth and hydrogen impurity incorporation of thick nanocrystalline diamond films

A much larger amount of bonded hydrogen was found in thick nanocrystalline diamond(NCD) films produced by only adding 0.24% N2 into 4% CH4 /H2 plasma,as compared to the high quality transparent microcrystalline diamond(MCD) films,grown using the same growth parameters except for nitrogen.These experimental results clearly evidence that defect formation and impurity incorporation(for example,N and H) impeding diamond grain growth is the main formation mechanism of NCD upon nitrogen doping and strongly support the model proposed in the literature that nitrogen competes with CH x(x=1,2,3) growth species for adsorption sites.     

氮气氛下(100)织构金刚石薄膜的成核与生长研究

利用热丝化学气相沉积法研究了氮气浓度对金刚石薄膜成核和生长的影响.实验发现氮气的 加入对金刚石成核密度影响不大,但促进了已形成的金刚石核的长大.适量的氮气不仅使金 刚石生长速率得到很大的提高,而且稳定了金刚石薄膜(100)面的生长,使金刚石薄膜具有 更好的(100)织构.利用原位光发射谱对衬底附近的化学基团进行了研究.研究表明,氮气的 引入使得金刚石生长的气相化学和表面化学性质发生了很大变化.含氮基团的萃取作用提高 了金刚石表面氢原子的脱附速率,从而提高了金刚石膜的生长速率.而含氮基团的选择吸附 使金刚石 关键词： 氮气 金刚石薄膜 织构 原位光发射谱     

Hydrogen gas-sensing properties of Pt/WO<Subscript>3</Subscript> thin film in various measurement conditions

A well-known gasochromic material is Pt particle-dispersed tungsten trioxide (Pt/WO₃). Its optical properties could make it effective as a hydrogen gas sensor. In this study, Pt nanoparticle-dispersed WO₃ thin films were prepared using the sol–gel process, and their optical and electrical properties dependent on the working environment (i.e., temperature, hydrogen gas concentration, oxygen partial pressure, etc.) were investigated. The Pt/WO₃ thin films prepared at 400 °C showed the largest change in optical transmittance and electrical conductivity when exposed to hydrogen gas compared with the films prepared at other temperatures. The optical absorbance and electrical conductivity were found to be dependent on the hydrogen and oxygen gas concentration in the atmosphere because generation and disappearance of W⁵⁺ in the thin films depend on the equilibrium reaction between injection and rejection of H⁺ into and from the thin films. In addition, the equilibrium reaction depends on the hydrogen and oxygen gas concentrations.     

High quality CVD diamond: a Raman scattering and photoluminescence study

High quality synthetic diamonds were grown on single-crystal silicon by microwave plasma enhanced chemical vapour deposition (CVD). A careful optimisation of both the experimental setup and the growth parameters was necessary before that the achievement of the best results was made possible. The films were deposited using a CH₄-H₂ gas mixture at methane concentrations variable in the range 0.6-2.2%, while the substrate temperature was fixed at 750 ^°C. Raman spectroscopy and photoluminescence (PL) were utilised to monitor the quality of the deposited films and to study the spatial distribution of defects, respectively. Micro-Raman analysis shows that linewidths of the diamond peak lower than 2.4 cm^-1 can be easily measured at the growth surface, indicating that the crystalline quality of individual grains is comparable to that of the best natural diamonds. The excellent phase purity of the diamond microcrystals at the growth surface is witnessed by the complete absence of any non-diamond carbon feature and by a very weak luminescence background in the 1.6-2.4 eV spectral range. A worsening of the quality of the diamond particles is found moving from the growth surface towards the film-substrate interface. A photoluminescence feature at about 1.68 eV, commonly associated to Si impurities, is distinctly observed as the exciting laser beam is focused close to the interface. A progressive degradation of the global quality of the films is found with increasing methane concentration in the gas mixture, as witnessed by an increased PL background in the films grown at higher methane concentrations. Received 24 November 2000     

金刚石薄膜的结构特征对薄膜附着性能的影响

在不同实验条件下，用微波等离子体化学气相沉积设备在硬质合金(WC+6%Co)衬底上沉积了 具有不同结构特征的金刚石薄膜.用Raman谱表征薄膜的品质和应力，用压痕实验表征薄膜的 附着性能，考察了薄膜中sp²杂化碳含量、形核密度、薄膜厚度对薄膜附着性能 的影响.结 果表明：sp²杂化碳的缓冲作用使薄膜中sp²杂化碳的含量对薄膜中 残余应力有较大的影 响，从而使薄膜压痕开裂直径统计性地随sp²杂化碳含量的增加而减小；仅仅依 靠超声遗 留的金刚石晶籽提高形核密度并不能有效改变薄膜与硬质合金基体之间的化学结合状况，从 而不能有效提高薄膜在衬底上的附着性能；在薄膜较薄时，晶粒之间没有压应力的存在，开 裂直径并不明显随厚度增加而增加，只有当薄膜厚度增加到一定值，晶粒之间才有较强压应 力存在，开裂直径随厚度的增加而较为迅速地增加. 关键词： 金刚石薄膜 附着性能 2杂化碳')" href="#">sp²杂化碳 成核密度 薄膜厚度     

Structural properties of TiN films grown on stainless steel substrates by a reactive radio-frequency sputtering technique at low temperature

TiN thin films were grown on stainless steel substrates by using the reactive radio-frequency magnetron-sputtering technique at relatively low temperature (200°C) using Ti and N₂. The deposition rate of the TiN film increased linearly with increasing applied radio-frequency power, and it decreased with increasing partial-pressure ratio of the N₂ gas to the Ar gas. Scanning electron microscopy (SEM) showed that the surfaces of the TiN films had very smooth morphologies. The TiN thin film had good stoichiometry for a partial-pressure ratio of 0.05. The stoichiometry of the TiN films and the interface qualities of the TiN/stainless steel heterostructures were investigated by Auger electron spectroscopy (AES) measurements. Auger depth profiles indicated that the compositions of the as-grown films consisted of titanium and nitrogen uniformly distributed throughout the films and that the films exhibited smooth interfaces. The interface quality of the TiN films to the stainless steel substrates were improved by annealing. These results indicate that annealed TiN thin films grown on stainless steel substrates hold promise for potential applications in advanced ceramic devices.     

Hydrogen induced voids in hydrogenated amorphous silicon carbon (a-SiC:H): Results of effusion and diffusion studies

The void formation in Si-rich a-SiC:H films deposited with dc magnetron sputtering is studied by effusion measurements of hydrogen and of implanted rare gases and secondary ion mass spectrometry (SIMS). Rare gas atoms were incorporated into the material by ion implantation. The results suggest a widening of the network openings with increasing alloy concentration. However, the void formation is mainly attributed not to an increase in carbon concentration but to an increase in hydrogen incorporation.     

Effect of hydrogen doping in ZnO thin films by pulsed DC magnetron sputtering

This study examined the role of hydrogen impurities in highly oriented ZnO thin films. Hydrogen intentionally incorporated was found to play an important role as a donor in n-type conduction, improving the free carrier concentration. The increase in the conductivity of ZnO thin films was attributed to the two centers assigned to isolated hydrogen atoms in the anti-bonding sites as well as bond-centered interstitial hydrogen located between the Zn–O bonds and Zn vacancy passivated by one or two hydrogen atoms. Micro Raman spectroscopy showed two additional modes at approximately 501 and 573 cm⁻¹. These two peaks were attributed to damage to the crystal lattice, which could be explained by the optical-phonon branch at the zone boundary and host lattice defects, such as vacancy clusters, respectively.     

Effects of hydrogen flow on properties of hydrogen doped ZnO thin films prepared by RF magnetron sputtering

The hydrogen doped ZnO (ZnO:H) thin films were deposited on quartz glass substrates by radio frequency magnetron sputtering. The doping characteristics of ZnO:H thin films with varied hydrogen flow ratio were investigated. At low hydrogen flow ratio (H₂/(H₂+Ar)≤0.02), the ZnO:H thin films exhibited dominant (002) peaks from X-ray diffraction and the lattice constants became smaller. The particles were mainly a columnar structure. The particles’ size became smaller, and the island-like structure appeared on the thin films surface. In addition, the low resistivity properties of ZnO:H thin films was ascribed to the increase of the carriers concentration and carriers mobility; When the hydrogen flow ratio was more than 0.02 (M≥0.02), two absorption bands at 1400–1800 cm^?1 and 3200–3900 cm^?1 were observed from the FT-IR spectra, which indicated that the ZnO:H thin films had typical Zn–H bonding, O–H bonding (hydroxyl), and Zn–H–O bonding (like-hydroxyl). The scanning electron microscope (SEM) results show that a large number of hydroxyl agglomeration formed an island-like structure on the thin films surface. The absorption peak at about 575 cm^?1 in the Raman spectra indicated that oxygen vacancies (V_O) defects were produced in the process of high hydrogen doping. In this condition, the low resistivity properties of ZnO:H thin films were mainly due to the increasing electron concentration resulted from V_O. Meanwhile, the Raman absorption peaks at approximately 98 cm^?1 and 436 cm^?1 became weaker, and the (002) XRD diffraction peak quenched and the lattice constants increased, which shows that the ZnO:H thin films no longer presented a typical ZnO hexagonal wurtzite structure. With the increasing of hydrogen flow ratio, the optical transmittance of ZnO:H thin films in the ultraviolet band show a clear Burstein–Moss shift effect, which further explained that electron concentration was increased due to the increasing V_O with high hydrogen doping concentration. Moreover, the optical reflectance of the thin films decreased, indicating the higher roughness of the films surface. It was noteworthy that etching effect of H plasma was obvious in the process of heavy hydrogen doping.     

Hydrogen incorporation in ultrananocrystalline diamond/amorphous carbon films

The incorporation of hydrogen within ultrananocrystalline diamond/amorphous carbon composite films has been investigated by nuclear reaction analysis (NRA) and Fourier transform infrared spectroscopy (FTIR). The film bulk contains ca. 7.5–8% H (for a deposition temperature of 600 °C), while the H concentration in the surface region is considerably higher. FTIR measurements show that the hydrogen‐rich surface is formed right at the beginning of the deposition process and grows outward as the film thickness increases. It can thus be concluded that surface hydrogen species play an active role in the formation of ultrananocrystalline diamond/amorphous carbon films. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Formation of CNx thin films by reactive pulsed laser deposition assisted by electron cyclotron resonance microwave discharge

Amorphous carbon nitride thin films were synthesized by pulsed laser deposition combined with electron cyclotron resonance (ECR) microwave discharge in nitrogen gas. The ECR discharge supplies active nitrogen species in the deposition environment and to the growing film surface, enhancing the film growth in complex processes accompanied by chemical reaction. The synthesized films were characterized by Rutherford backscattering spectroscopy (RBS), X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared spectroscopy (FTIR), and Raman spectroscopy. The films were determined to consist purely of carbon and nitrogen with a nitrogen concentration of 42%, and have a thickness of 550 nm over which carbon and nitrogen are well distributed. Structural characterizations based on XPS, FTIR and Raman analysis showed that these films appear to contain several bonding configurations between carbon and nitrogen with a small amount of C≡N bonds compared with other bonding states. Received: 31 August 2000 / Accepted: 12 December 2000 / Published online: 23 May 2001     

Microstructural characterization of Ti-C-N thin films prepared by reactive crossed beam pulsed laser deposition

In this work, Raman spectroscopy has been used to characterize Ti-C-N thin films in order to obtain information about the microstructure of the deposited materials, and in particular to study the effects due to the carbon incorporation into the TiN lattice. Ti-C-N thin films were prepared using a crossed plasma configuration in which the ablation of two different targets, titanium and carbon, in a reactive atmosphere was performed. With this configuration, the carbon content in the films was varied in an easy way from 5.0 at% to 40.0 at%. Thin film composition was determined from Non-Rutherford Backscattering Spectroscopy (NRBS) measurements. X-ray photoelectron spectroscopy and X-Ray diffraction measurements were also carried out in order to characterize the films in more detail, with this being used to give support to the interpretation of the Raman spectra. The Raman results revealed that at lower carbon concentrations a solid solution Ti(C, N) is formed, whilst at higher carbon concentrations a nanocomposite, consisting of nanocrystalline TiCN and TiC immersed in an amorphous carbon matrix is obtained.     

Electrochemical properties of undoped CVD diamond films

The electrochemical properties of undoped diamond polycrystalline films grown on tungsten wire substrates using methanol as a precursor are described. The diamond film quality was changed by introducing sp²-bonded non-diamond carbon impurity through adjustment of the methanol-to-hydrogen (C/H) source gas ratio used for diamond growth.The electrodes were characterized by Raman spectroscopy, scanning electronic microscopy (SEM) and cyclic voltammetry (CV).Diamond coated tungsten wires were then used as a working electrode to ascertain their electrochemical behavior in electrolytic medium. Electrochemical windows of these films were found to be suitable in the potential range of [−2.5 V, +2.2 V] vs. Ag/AgCl in acid medium (0.1 M KCl).The electrochemical behavior was evaluated also using the Fe(CN)₆^3−/4−redox couple.The results demonstrate that the grain boundaries and sp²-hybridized carbon impurity can have a significant influence on electrochemical window of undoped diamond electrodes. It was observed that with increasing sp² carbon impurity concentration the electrochemical window decreases.