Study of the Interface Microstructures of CVD Diamond Films by TEM

 The characteristics of the interface microstructures between a CVD diamond film and the silicon substrate have been studied by transmission electron microscopy and electron energy loss spectroscopy. The investigations are performed on plan-view TEM specimens which were intentionally thinned only from the film surface side allowing the overall microstructural features of the interface to be studied. A prominent interfacial layer with amorphous-like features has been directly observed for CVD diamond films that shows a highly twinned defective diamond surface morphology. Similar interfacial layers have also been observed on films with a <100> growth texture but having the {100} crystal faces randomly oriented on the silicon substrate. These interfacial layers have been unambiguously identified as diamond phase carbon by both electron diffraction and electron energy loss spectroscopy. For the CVD diamond films that exhibit heteroepitaxial growth features, with the {100} crystal faces aligned crystallographically on the silicon substrate, such an interfacial layer was not observed. This is consistent with the expectation that the epitaxial growth of CVD diamond films requires diamond crystals to directly nucleate and grow on the substrate surface or on an epitaxial interface layer that has a small lattice misfit to both the substrate and the thin film material.     

Boron implantation in Si: Channeling effects studied by SIMS and simulation

The axial channeling behaviour of boron implants in <100>, <110> and <111> silicon wafers is investigated by SIMS. Large differences of channeling characteristics such as channeled projected range (the projected range of channeled ions or channeling peak) and the fraction of channeled to implanted ions are observed among the three major crystal orientations. Within the critical angle, the channeling behaviour is very sensitive to the incidence beam angle with respect to crystal orientations. SIMS measurements are performed at different positions along several critical directions over a whole wafer. Well channeled profiles with an incidence beam angle to crystal orientations of 0 ° are obtained for each ion implantation energy and orientation. The results are used to test various models of ion implantation by simulation. A 3-parameter model for electronic stopping power of boron in silicon was proposed.     

Free-standing boron doped CVD diamond films grown on partially stabilized zirconia substrates

Boron doped diamond films have been grown adhered to silicon substrates by chemical vapor deposition using boron containing gases. In this work it was shown that it is possible to grow free-standing boron doped CVD diamond films on partially stabilized zirconia substrates using boron powder as the source for doping. Results from Raman spectroscopy confirmed the boron incorporation with concentration up to ∼10²⁰ cm⁻³. X-ray diffraction and scanning electron microscopy showed that the effect of boron incorporation in the microstructure of the diamond film is negligible. The measurement of the resistivity as a function of temperature confirmed the semiconductor behavior, as expected for p-type diamond.     

The Influence of Doping Levels and Surface Termination on the Electrochemistry of Polycrystalline Diamond

The influence of surface chemistry and boron doping density on the redox chemistry of Fe(CN) at CVD polycrystalline diamond electrodes is considered. It is demonstrated that for this couple both the doping density and the surface chemistry are important in determining the rate of charge transfer at the electrode/electrolyte interface. For hydrogen terminated CVD diamond metallic electrochemical behavior is always observed, even at boron doping densities as low as 7×10¹⁸ cm^?3. In contrast, the electrochemical behavior of oxygen terminated CVD diamond varies with doping density, a metallic response being observed at high doping density and semiconductor behavior at low doping density. It is shown that the results attained may be explained by a surface state mediated charge transfer mechanism, thus demonstrating the importance of controlling surface chemistry in electroanalytical applications of diamond.     

Electroanalysis at Diamond‐Like and Doped‐Diamond Electrodes

Diamond as a high performance material occupies a special place due to its in many ways extreme properties, e.g., hardness, chemical inertness, thermal conductivity, optical properties, and electric characteristics. Work mainly over the last decade has shown that diamond also occupies a special place as an electrode material with interesting applications in electroanalysis. When made sufficiently electrically conducting for example by boron‐doping, ‘thin film' and ‘free–standing' diamond electrodes exhibit remarkable chemical resistance to etching, a wide potential window, low background current responses, mechanical stability towards ultrasound induced interfacial cavitation, a low ‘stickiness' in adsorption processes, and a high degree of ‘tunability' of the surface properties. This review summarizes some of the recent work aimed at applying conductive (boron‐doped) diamond electrodes to improve procedures in electroanalysis.     

Characterization of crystal faces of polycrystalline HFCVD diamond films by STM/STS

Among the numerous techniques available for the characterization of diamond films scanning tunnelling microscopy (STM) in combination with spectroscopy (STS) provides information about the morphology and electronic surface properties down to the atomic scale. Here results of STM/STS obtained on diamond films are reported. 0.5 to 1.25 μm thick films have been grown on silicon substrates by hot filament chemical vapour deposition (HFCVD) by variable CH₄/H₂ mixtures in the range of 0.5% to 3% CH₄. Morphological features of diamond crystallites were studied in detail by STM. A distinct increase of the surface roughness of (111) crystal faces with increasing CH₄ concentration (from 0.5% to 3%) was found. For a CH₄ concentration of 3% (100) faces were smoother than (111) faces. STS revealed significant differences in the tunneling current/voltage (I/V)-characteristics between (111) and (100) crystal surfaces. For (111) surfaces distinct changes in the I/V-characteristics depending on the CH₄ concentration were observed: The I/V-characteristics change and the conductivity increases raising the CH₄ concentration from 0.5% to 3%. This effect is explained with increasing formation of non-diamond carbon (NDC) on (111) surfaces for higher CH₄ concentrations. Thus NDC is also responsible for the enhanced surface roughness observed on (111) surfaces with increasing CH₄ concentrations.     

Hydrogenated polycrystalline diamond films: Elastic and inelastic electron reflectivity

The microstructure and properties of carbon-based thin films depend on the deposition process and conditions used, including pressure, gas phase composition, and substrate temperature, as well as the energy of the reactive species (atoms or ions). For instance concerning diamond films, each method results in different type of films which may differ in terms of diamond grain size (from nano to micro), grain boundary nature, hydrogen content, defect density, amorphous or graphitic components, morphological properties and different chemical and physical properties. Among them, the well-known negative electron affinity, very attractive for the detection and emission of electrons, and high conductivity of diamond surfaces are properties of fully hydrogenated diamond surfaces. Similarly, diamond grain size may influence the electronic and optical properties of the films. More generally the chemical and physical characterization of the uppermost surface atomic layer of diamond films presents a great challenge.In this review we present results on hydrogen bonding configuration in hydrogenated polycrystalline diamond films of varying size (few nanometers up to micrometers) obtained by high resolution electron energy loss spectroscopy (HREELS). More precisely we will present energy loss spectra extended up to 800 meV, as well as elastic and inelastic reflectivity curves (associated to different vibrational modes of hydrogenated diamond surfaces), measured over the 3–18 eV electron energy range. We will show in particular that due to the specific features of diamond bulk electronic band structure, which is maintained up to the surface in the case of fully hydrogenated diamond, it is possible to extract from these data valuable information about the surface properties and composition such as diamond or graphitic like nature of the films, surface versus lattice nature of the vibrational modes.     

Interfacial study of cubic boron nitride films deposited on diamond

We have studied the nucleation and growth of cubic boron nitride (cBN) films deposited on silicon and diamond-coated silicon substrates using fluorine-assisted chemical vapor deposition (CVD). These comparative studies substantiate that the incubation amorphous/turbostratic BN layers, essential for the cBN nucleation on silicon, are not vital precursors for cBN nucleation on diamond, and they are inherently eliminated. At vastly reduced critical bias voltage, down to -10 V, cBN growth is still maintained on diamond surfaces, and cBN and underlying diamond crystallites exhibit an epitaxial relationship. However, the epitaxial growth is associated with stress in the cBN-diamond interfacial region. In addition, some twinning of crystallites and small-angle grain boundaries are observed between the cBN and diamond crystallites because of the slight lattice mismatch of 1.36%. The small-angle grain boundaries could be eliminated by imposing a little higher bias voltage during the initial growth stage. The heteroepitaxial growth of cBN films on different substrate materials are discussed in the view of lattice matching, surface-energy compatibility, and stability of the substrate against ion irradiation.     

Ion implantation doping and electrical properties of high-temperature ladder polymers

We report the first ion implantation doping studies on high-temperature ladder polymers and show that insulting films of the benzimidazobenzophenanthroline-type ladder polymer (BBL) can be doped by boron, argon, and krypton implantation to conductivities as high as 224 S/cm at a dose of 4.0 × 10¹⁶/cm² while retaining the excellent mechanical properties of the pristine films. Effects of dose (ions/cm²) and beam current density (microamps/cm²) on electrical conductivity at fixed ion energies are reported. The temperature dependence of the conductivity indicates that the implanted ladder polymer films are semiconductors. Spatially selective implantation, creating regions of conducting lines in an insulating matrix, which suggests microelectronic device applications of the ladder polymers, is demonstrated.     

CdO as the archetypical transparent conducting oxide. Systematics of dopant ionic radius and electronic structure effects on charge transport and band structure

A series of yttrium-doped CdO (CYO) thin films have been grown on both amorphous glass and single-crystal MgO(100) substrates at 410 degrees C by metal-organic chemical vapor deposition (MOCVD), and their phase structure, microstructure, electrical, and optical properties have been investigated. XRD data reveal that all as-deposited CYO thin films are phase-pure and polycrystalline, with features assignable to a cubic CdO-type crystal structure. Epitaxial films grown on single-crystal MgO(100) exhibit biaxial, highly textured microstructures. These as-deposited CYO thin films exhibit excellent optical transparency, with an average transmittance of >80% in the visible range. Y doping widens the optical band gap from 2.86 to 3.27 eV via a Burstein-Moss shift. Room temperature thin film conductivities of 8,540 and 17,800 S/cm on glass and MgO(100), respectively, are obtained at an optimum Y doping level of 1.2-1.3%. Finally, electronic band structure calculations are carried out to systematically compare the structural, electronic, and optical properties of the In-, Sc-, and Y-doped CdO systems. Both experimental and theoretical results reveal that dopant ionic radius and electronic structure have a significant influence on the CdO-based TCO crystal and band structure: (1) lattice parameters contract as a function of dopant ionic radii in the order Y (1.09 A) < In (0.94 A) < Sc (0.89 A); (2) the carrier mobilities and doping efficiencies decrease in the order In > Y > Sc; (3) the dopant d state has substantial influence on the position and width of the s-based conduction band, which ultimately determines the intrinsic charge transport characteristics.     

Nanomolar hydrogen peroxide detection using horseradish peroxidase covalently linked to undoped nanocrystalline diamond surfaces

In this article, we report on the low-level detection of hydrogen peroxide, a key player in the redox signaling pathway and a toxic product in the cellular system, using a colorimetric solution assay. Amine-terminated undoped nanocrystalline diamond thin films were grown on glass using a linear-antenna microwave plasma CVD process. The diamond surface consists mainly of -NH(2) termination. The aminated diamond surface was decorated with horseradish peroxidase (HRP) enzyme using carbodiimide coupling chemistry. The success of the HRP immobilization was confirmed by X-ray photoelectron spectroscopy (XPS). The enzymatic activity of immobilized HRP was determined with a colorimetric test based on the HRP-catalyzed oxidation of 2,2'-azino-bis(3-ethylbenzothiazoline-6-sufonic acid (ABTS) in the presence of hydrogen peroxide. The surface coverage of active HRP was estimated to be Γ = 7.3 × 10(13) molecules cm(-2). The use of the functionalized diamond surface as an optical sensor for the detection of hydrogen peroxide with a detection limit of 35 nM was demonstrated.     

The properties of BCN films formed by ion beam assisted deposition

A study has been made on the formation and the properties of boron carbonnitride (BCN) thin films. The BCN films were produced by ion beam assisted deposition, in which boron and carbon were deposited by electron beam heating and nitrogen was supplied by ion implantation simultaneously. The mechanical properties of BCN films were measured using a ultra micro hardness tester and a friction tester. The atomic ratio and the structure of BCN thin films were estimated by means of X-ray photoelectron spectroscopy, laser Raman spectroscopy and Fourier transform infrared spectroscopy. As preliminary results, it was found that the BCN films are higher in hardness and lower in friction coefficient than diamond-like carbon (DLC) films. The mechanical properties are discussed with the relation of surface composition and structure.     

Surface chemical modifications and surface reactivity of nanodiamonds hydrogenated by CVD plasma

The present study focuses on the interaction of hydrogen microwave CVD plasma with nanodiamonds (NDs). Hydrogen treated NDs (H-NDs) were characterized using electron spectroscopies (XPS, AES) without air exposure. A surface temperature higher than 700 °C is needed to remove the oxygen present on raw NDs. The kinetics of oxygen removal were investigated. Moreover, UHV annealings of H-NDs after ageing in ambient air clearly underline that 75% of the oxygen is related to physisorbed species. Finally, H-NDs were efficiently grafted using photochemical reaction with alkenes and a spontaneous coupling of aryldiazonium salts. These results confirm similar electronic surface properties between bulk and nano diamond materials.     

氢终止金刚石表面的形成机理

为考察金刚石形成氢终止表面的反应机制,采用微波氢等离子体处理以及电阻丝氢气气氛加热处理进行对比研究.利用光发射谱(OES)和漫反射傅里叶变换红外光谱(DRIFTS)分别表征了微波氢等离子体中的活性基团和金刚石表面氢终止浓度.结果表明,微波氢等离子体环境下,随着衬底温度、等离子体密度和能量的增加,温度至700 ℃ (800 W/3 kPa)时,等离子体中出现了明显的CH基团;相应地,金刚石表面氢终止浓度随温度、等离子体密度和能量的增加而增加.采用氢气气氛下电阻丝加热的方法同样形成了氢终止金刚石表面,表明微波等离子体处理金刚石表面形成氢终止主要源于由温度控制的表面化学反应,而非等离子体的物理刻蚀作用.氧终止金刚石表面形成氢终止的机制是表面C=O键在高于500 ℃时分解为CO,相应的悬挂键由氢原子或氢分子占据.     

Sulfur-Doped n-Type Diamond: Preparation and Electrochemical Properties

Films of sulfur-doped synthetic diamond are chemical-vapor-deposited using codoping with sulfur and boron. The sulfur in diamond is detected with particle-induced x-ray emission (PIXE), x-ray photoelectron spectroscopy (XPS), and secondary ion mass spectroscopy (SIMS). Electrochemical and thermoelectric measurements show that the sulfur-containing diamond films grown in gas phase lean in boron are n-type, whereas those grown with higher boron content are overcompensated, hence, p-type. Electrochemical properties of the n-type diamond films are studied for the first time using methods of electrochemical impedance, open-circuit photopotential, and voltammetric curves in Fe(CN)₆ ^3-/4- solutions. A mechanism of boron-stimulated sulfur incorporation into diamond and the nature of donors thus formed is discussed.     

聚乙炔的离子注入法掺杂

<正> 离子注入是一种物理摻杂方法,在半导体器件的制备中已得到广泛的应用,它与常规的化学、电化学或热扩散掺杂相比具有一些特点:可以通过质量分析器选取单一的注入离子,故掺杂杂质的纯度高;根据注入离子的剂量和能量,精确控制到掺人杂质的数量和深度等等。近年来,采用离子注入技术进行掺杂,改变聚合物或其它绝缘材料表面性质的研究已逐步引起重视真视。     

Effect of Nb,Ti, and W ion implantation on surface properties and cell compatibility of silicon carbide

Silicon carbide is considered as a bio-inert semiconductor material; consequently, it has been proposed for potential applications in human body implantation. In this study, we study the effect of implanting different metal ions on the surface properties of silicon carbide single crystal. The valence states of the elements and the surface roughness of implanted SiC were studied using X-ray photoelectron spectroscopy and atomic force microscope, respectively. Osteoblastic MG-63 cells were utilized to characterize the cytocompatibility of ion implanted SiC. The results show that after Nb ion implantation on the SiC surface, it mainly exists in the form of Nb–C bond, Nb–O bond, and a small amount of metallic niobium. The titanium implanted on SiC primarily forms Ti-C bond and Ti-O bond. The tungsten implanted on SiC mostly presents as metallic tungsten and W–O bond. The roughness of silicon carbide single crystal is improved by ion implantation of all three metal ions. Ion implantation of titanium and niobium can improve the cell compatibility and hydrophilicity of silicon carbide, whereas ion implantation of tungsten reduces the cell compatibility and hydrophilicity of silicon carbide.     

Effect of pressure on the growth of boron and nitrogen doped HFCVD diamond films on WC–Co substrate

Boron and nitrogen compounds are added in the acetone/hydrogen gas mixture to deposit hot filament chemical vapor deposition (HFCVD) diamond films on the cobalt cemented tungsten carbide (WC–Co) substrate under the pressure of 1–4 kPa. The as‐deposited diamond films are characterized by field emission scanning electron microscope (FESEM), atomic force microscopy (AFM), X‐ray diffraction (XRD) spectroscopy and Raman spectroscopy. The results reveal that the surface morphology, growth rate, structure and quality of the diamond films vary with the pressure and the type of the impurity addition. The diamond grains tend to develop into the nanometer scale with the decrease of the pressure. However, adding of boron or nitrogen impurities in the gas mixture will weaken the nanocrystallization effect by reducing the carbon supersaturation. Density functional theory (DFT) calculations indicate that co‐adsorption of B and N containing radicals can favor the adsorption of CH₃ on diamond (100) surface. Thus, at low pressure of 1 kPa, large grained cubic (100) facet diamond rather than typical nanometer diamond is produced for B–N co‐addition gas mixture. The present results appear to be useful to efficiently synthesize high quality doped diamonds with desirable properties for mechanical application. Copyright © 2015 John Wiley & Sons, Ltd.     

Quantitative investigation of boron incorporation in polycrystalline CVD diamond films by SIMS

Polycrystalline diamond films have been produced on pre-treated silicon substrate by CVD hot filament method, with B(C₂H₅)₃ added to the gas phase. However, under identical surface conditions, boron incorporation is not homogeneous. In {111} growth sectors, the boron concentration is found to be about 5 times higher than in {100} growth sectors. Moreover, a marked increase in contaminating elements such as aluminium and sodium in regions with higher boron concentrations is detected. Under SIMS fine focus conditions it can be shown that the interface between these two different facet regions is smaller than 0.5 μm. With 3D-depth profile images it can also be shown that the carbon distribution in the diamond layer is not totally homogeneous.     

Quantitative investigation of boron incorporation in polycrystalline CVD diamond films by SIMS

Polycrystalline diamond films have been produced on pre-treated silicon substrate by CVD hot filament method, with B(C₂H₅)₃ added to the gas phase. However, under identical surface conditions, boron incorporation is not homogeneous. In {111} growth sectors, the boron concentration is found to be about 5 times higher than in {100} growth sectors. Moreover, a marked increase in contaminating elements such as aluminium and sodium in regions with higher boron concentrations is detected. Under SIMS fine focus conditions it can be shown that the interface between these two different facet regions is smaller than 0.5?μm. With 3D-depth profile images it can also be shown that the carbon distribution in the diamond layer is not totally homogeneous.