The orientation effect of silicon grains on diamond deposition

Diamond deposition on mirror-polished polycrystalline silicon substrates which have grains in various orientations has been investigated using electron backscatter diffraction (EBSD) method with scanning electron microscopy (SEM). Diamond was deposited by microwave plasma chemical vapor deposition with application of a negative bias voltage on the substrate. The evidence from systematic SEM observations shows that silicon orientation determined by EBSD has a strong effect on diamond nucleation. In general, the diamond nucleation density on Si grains oriented close to <100> is the highest, while it is the lowest for those grains close to <111>, under the same experimental conditions for deposition. The same phenomena have been observed in the range of methane concentration from 2% to 4% in hydrogen.     

CVD diamond for spintronics

The ability to minimise, control and manipulate defects in CVD diamond has grown rapidly over the last ten years. The application which best illustrates this is probably that of quantum information processing (QIP) or ‘diamond spintronics’. QIP is a rapidly growing area of research, covering diverse activities from computing and code breaking to encrypted communication. All these applications need ‘quantum bits’ or qubits where the quantum information can be maintained and controlled. Controlled defects in an otherwise high perfection diamond lattice are rapidly becoming a leading contender for qubits, and offer many advantages over alternative solutions. The most promising defect is the NV⁻ defect whose unique properties allow the state of its electron spin to be optically written to and read from. Substantial developments in the synthesis of CVD diamond have produced diamond lattices with a high degree of perfection, such that the electron spin of this centre exhibits very long room temperature decoherence times (T₂) in excess of 1 ms. This paper gives a brief review of the advantages and challenges of using CVD diamond as a qubit host. Lastly the various qubit applications being considered for diamond are discussed, highlighting the current state of development including the recent development of high sensitivity magnetometers.     

Synthesis of boron-doped homoepitaxial single crystal diamond by microwave plasma chemical vapor deposition

The deposition of boron-doped homoepitaxial single crystal diamond is investigated using a microwave plasma-assisted chemical vapor deposition system. The objective is to deposit high-quality boron-doped single crystal diamond and establish the relationships between the deposition conditions and the diamond growth rate and quality. Experiments are performed using type Ib HPHT diamond seeds as substrates and growing diamond with varying amounts of diborane in a methane–hydrogen gas mixture. The deposition system utilized is a 2.45 GHz microwave plasma-assisted CVD system operating at 135–160 Torr. Experiments are performed with methane concentrations of 4–6% and diborane concentrations of 5–50 ppm in the feedgas. Diamond is deposited with growth rates of 2 to 11 µm/h in this study. The deposited diamond is measured to determine its electrical conductivity and optical absorption versus wavelength in the UV, visible and IR portions of the spectrum. Data is presented that relates the growth rate and diamond properties to the deposition conditions including substrate temperature and feedgas composition.     

Deposition of thick boron-doped homoepitaxial single crystal diamond by microwave plasma chemical vapor deposition

The deposition of high quality single crystal boron-doped diamond is studied. The experimental conditions for the synthesis of 1–2 mm thick boron-doped diamond are investigated using a high power density microwave plasma-assisted chemical vapor deposition reactor. The boron-doped diamond is deposited at a rate of 8–11.5 μm/h using 1 ppm diborane in the feed gas as the boron source, and the capability to overgrow defects is demonstrated. The experimental study also investigates the deposition of diamond with both 10 ppm diborane and 2.5–500 ppm of nitrogen added to the feedgas. Synthesized material properties are measured including the electrical conductivity using a four-point probe and the substitutional boron content using infrared absorption.     

Extreme UV photodetectors based on CVD single crystal diamond in a p-type/intrinsic/metal configuration

We report on extreme UV (EUV) photodetectors based on CVD single crystal diamond in a p-type/intrinsic/metal configuration fabricated and tested at Roma “Tor Vergata” University laboratory, operating in a sandwich geometry. Particular care has been devoted to the design of the device geometry in order to take advantage of the internal junction electric field and to minimize the signal contribution arising from secondary electron emission, which is known to strongly affect the detection properties in the UV and EUV regions. The device has been characterized in the EUV spectral region by using both He and He–Ne DC gas discharge radiation sources and a toroidal grating vacuum monochromator, with 5 Å wavelength resolution. The reproducibility test has been performed on several photodetectors showing a high uniformity of the device performances. The devices showed negligible undesired effects such as persistent photocurrent and memory effects, resulting in extremely promising stability features of the p-type/intrinsic/metal structured device. The devices have been tested at different bias voltages between 0 and 15 V, showing the best performances at 0 bias voltage. Finally, the external quantum efficiency (EQE), as well as the responsivity have been measured in the range 20 to 100 nm.     

Homoepitaxial single crystal diamond grown on natural diamond seeds (type IIa) with boron-implanted layer demonstrating the highest mobility of 1150 cm/V s at 300 K for ion-implanted diamond

The homoepitaxial single crystal diamond growth by microwave plasma assisted CVD at high microwave power density 200 W/cm³ in a 2.45 GHz MPACVD reactor using natural diamond seeds (type IIa) was investigated. The semiconductor CVD diamond of p-type was obtained by doping technique of ion implantation. Boron ions were implanted at the acceleration energy of 80 keV with two cases of dose: 5 · 10¹⁴ and 3 · 10¹⁵ cm^− 2. To recover the damage layer and activate dopants in CVD diamond the rapid annealing at nitrogen atmosphere at 1380° C was used. B-implanted diamond layer showing the mobility of 1150 cm²/V s at 300 K which is the highest for ion-implanted diamond was obtained.     

Simulation of morphological instabilities during diamond chemical vapor deposition

The diamond chemical vapor deposition (CVD) process has been investigated theoretically and the morphological instabilities associated with the growth of diamond films have been examined with a model based on the continuum species conservation equation coupled to surface reaction kinetics. A linear stability analysis and numerical calculations have been carried out to determine critical parameters affecting the diamond deposition layer morphology. A two-dimensional model describes the evolution of the gas-solid interface. The dynamic behavior of the interface depends on the reactants' diffusivity and surface kinetics. These factors depend upon the reactant material properties and film growth conditions such as the reactor temperature and pressure. From the analyses, it has been found that the ratio ( /k) of gas phase diffusivity ( ) to the surface reaction rate constant (k) plays the critical role in promoting diamond morphological instabilities because the film morphology stabilizing processes of surface diffusion and re-evaporation are absent or negligible during diamond CVD. It is found that the film nonuniformity increases as the ratio ( /k) decreases. Increasing growth rates also result in increasing morphological instability, leading to rough surfaces. It is shown that increasing reactor pressure and decreasing gas-phase temperature and/or substrate temperature promote deposition layer nonuniformity. An approach to avoiding these instabilities is proposed.     

以丙烯为碳源气的化学气相沉积模型

以丙烯为碳源气,考察了热解炭在化学气相沉积中的生长过程:包括丙烯裂解后的脱氢、断链、歧化以及加成等复杂的化学过程,还包括裂解产物在气相中通过在自由活化点上(基体表面或聚合芳香烃网平面边缘处)的加成反应以及在基体表面通过物理吸附进行堆积的过程。不同结构热解炭的生成,主要取决于丙烯裂解后的中间产物在基准面进行加成反应后的产物。     

Extreme UV single crystal diamond Schottky photodiode in planar and transverse configuration

We report on the study of the performances of two extreme ultraviolet (EUV) photovoltaic single crystal diamond Schottky diodes based on metal/intrinsic/p-type diamond junction developed at the University of Rome “Tor Vergata” and having different contact geometries. One detector operates in transverse configuration with a semitransparent metallic contact evaporated on the intrinsic diamond surface, while the second one operates in planar configuration with an interdigitated contact structure on the growth surface of the intrinsic diamond layer. Both devices can work in an unbiased mode by using the built-in potential arising from the electrode–diamond interface and show excellent rectifying properties with a rectification ratio of about 10⁸.The devices have been characterized in the EUV spectral region by using He–Ne DC gas discharge radiation source and a toroidal grating vacuum monochromator, with a 5 Å wavelength resolution. The extremely good signal-to-noise ratio, the reproducibility of the device response, the absence of persistent photoconductivity and undesirable pumping effects suggest the high quality of our CVD diamond for UV applications. The external quantum efficiency (EQE) as well as the responsivity have been measured in the spectral range from 20 to 120 nm and opposite behaviours for the two different geometries proposed have been observed.     

Boron-doped hydrogenated amorphous carbon films grown by surface-wave mode microwave plasma chemical vapor deposition

We report the effects of boron (B) doping on optical and structural properties of the hydrogenated amorphous carbon thin films grown by surface-wave mode microwave plasma (SW-MWP) chemical vapor deposition (CVD) on n-type silicon and quartz substrates at room temperature. Argon and acetylene were used as a carrier and carbon source gases respectively. Analytical methods such as X-ray photoelectron spectroscopy (XPS), Nanopics 2100/NPX200 surface profiler, JASCO V-570 UV/VIS/NIR spectroscopy, Fourier transform infrared spectroscopy (FT-IR) and Raman spectroscopy were employed to investigate the properties of the films. Low atomic concentration of B (0.08 at.%) was found in the doped film. The optical band gap of the undoped film was 2.6 eV and it decreased to 1.9 eV for the B-doped film. Structural property shows the crystalline structure of the film and it has changed after incorporating B as a dopant. The structural modifications of the films leading to being more graphite in nature were confirmed by the Raman and FT-IR characterization.     

The effect of CO2 on the high-rate homoepitaxial growth of CVD single crystal diamonds

In this paper, we report the effect of gaseous carbon dioxide (CO₂) introduced in the typical reaction atmosphere of CH₄/H₂/N₂ (60/500/1.8 in sccm) on the growth rate, morphology and optical properties of homoepitaxy single crystal diamonds (SCDs) by microwave plasma chemical vapor deposition. The additional carbonaceous sources supplied by CO₂ are favorable to increase the growth rate, and meanwhile, the oxygen related species generated would enhance the etching effect not only to eliminate the non-diamond phase of SCD but also to decrease the growth rate. The appropriate addition of CO₂ can increase the high growth rate, decrease the surface roughness, and reduce the concentration of N-incorporation. It is demonstrated that adding CO₂ strongly affects the contents of various reaction species in plasma, which would determine the growth features of CVD SCDs.     

Corrosion resistance and chemical stability of super-hydrophobic film deposited on magnesium alloy AZ31 by microwave plasma-enhanced chemical vapor deposition

A super-hydrophobic film was successfully deposited on magnesium alloy AZ31 by the microwave plasma-enhanced chemical vapor deposition (MPECVD) process. The film surface showed a static water contact angle of more than 150°. The hydrophobicity and root mean square roughness of the film surface increased with an increase in deposition time. The anticorrosion resistance of the deposited film was estimated by electrochemical impedance spectroscopy (EIS) measurements. The EIS measurements and appropriate equivalent circuit models revealed that the super-hydrophobic film considerably improved the anticorrosion resistant performance of magnesium alloy AZ31. The anticorrosion mechanism of the super-hydrophobic film was also considered. Moreover, the chemical stability of the super-hydrophobic film in acidic, neutral, and alkaline aqueous solutions was investigated. The super-hydrophobic film showed high chemical stability in acidic and neutral aqueous solutions.     

Arrowhead-like diamond crystals formed by hot-filament chemical vapor deposition

Arrowhead-like diamond crystals have been formed by using a simple method of hot-filament-assisted chemical vapor deposition. These are contact twins with {111} as the twin plane, of which each individual is composed of {100}, {110} and {111} faces. These twins flatten along {110} face and elongate parallel to {111} contact plane. The flattened {110} face consists of many {110} terraces sided by 〈110〉 and 〈112〉 steps. So the twinned crystal looks like an arrowhead. These twins are formed just underneath the uppermost substrate temperature for diamond growth.     

Mechanical properties of nanocrystalline diamond/amorphous carbon composite films prepared by microwave plasma chemical vapour deposition

Nanocrystalline diamond films (NCD) have been deposited by microwave plasma chemical vapour deposition from CH₄/N₂ mixtures with varying methane content. They consist of diamond nanocrystallites with sizes of 3–5 nm embedded in an amorphous matrix with grain boundary widths of 1–1.5 nm. The CH₄ content in the gas phase has almost no influence on the microscopic structure but a strong effect on the macroscopic structure and morphology. The mechanical and tribological properties of these films have been investigated by nanoindentation, nano tribo tests, and nano scratch tests. The hardness of a 4-μm-thick film deposited with 17% methane was about 40 GPa, the indentation modulus 387 GPa, and the elastic recovery 75%. Ball-on-disk tests against an Al₂O₃ ball revealed, after initially higher values, a friction coefficient of ≤0.1. Tribo tests and scratch tests proved a strong adhesion and a protective effect on silicon substrates. Finally, the correlations between the macroscopic structure of the films and their mechanical and tribological properties are discussed.     

Structure of copolymer films created by plasma enhanced chemical vapor deposition

The interface structure in copolymer films made using plasma enhanced chemical vapor deposition (PECVD) has been probed for the first time using X-ray reflectivity. Copolymer films made from comonomers benzene (B), octafluorocyclobutane (OFCB), and hexamethyldisiloxane (HMDS) show extremely sharp interfaces and scattering length density depth profiles that are uniform with depth, making them useful for optical applications. The polymer/air interface has an rms roughness (∼5 Å) that is only slightly larger than that of the supporting substrate (∼3 Å). Addition of either benzene or HMDS as a comonomer in the deposition of OFCB alters a transient deposition behavior at the silicon oxide interface that occurs when using only OFCB. For the B-OFCB copolymer films, a facile control of refractive index with monomer feed composition is achieved. A nonlinear variation in the X-ray scattering length density with composition for the HMDS-OFCB copolymer films is consistent with the nonlinear visible light refractive index (632.8 nm) variation reported earlier.     

Low temperature time of flight mobility measurements on synthetic single crystal diamond

We study the temperature dependence of low charge injection drift mobility in single crystal (SC) diamond using an alpha particle source. We present time of flight (ToF) mobility measurements to investigate the charge carrier scattering mechanisms in SC synthetic diamond in the temperature range 200 K–300 K. We have used a gold contacted pad detector, with a “sandwich” contact structure, fabricated using a SC chemical vapour deposition (CVD) diamond synthesised by Element Six Ltd. ToF analysis of alpha particle induced current pulses shows a strong increase in hole mobility at reduced temperatures, consistent with acoustic phonon scattering processes dominating the charge carrier transport. On the other hand, electron mobility values appear to remain relatively constant with lower temperatures suggesting different mechanisms than optical or acoustic phonon scattering limiting the charge transport.     

Anisotropic dry etching of boron doped single crystal CVD diamond

Semiconducting boron doped single-crystal CVD diamond has been patterned using aluminum masks and an inductively coupled plasma (ICP) etch system. For comparison insulating HPHT diamond samples were also patterned using the same process. Diamond etch rates above 200 nm/min were obtained with an O₂/Ar discharge for a gas pressure of 2.5 mTorr using 600 W RF power. We have accomplished the fabrication of structures with a minimum feature size of 1 μm with vertical sidewalls in both CVD and HPHT diamond. The ICP etching produced smooth surfaces with a typical root-mean-square surface roughness of 3 nm. The dependence of etch rate on bias voltage was somewhat different for the two types of diamond. However, for all samples both the etch rate and anisotropy were found to improve with increasing bias voltage.     

Spinose carbon nanotubes grown on graphitized DLC film by low frequency r.f. plasma-enhanced chemical vapor deposition

Spinose carbon nanotubes (SCNTs) are grown on silicon substrates covered with diamond-like carbon film and iron catalyst film (Fe/DLC/Si structure) by low frequency r.f. plasma-enhanced chemical vapor deposition (LFRF-PECVD). During the pre-treatment of the Fe/DLC/Si substrate, there are three processes happened, namely, iron film spalled to small islands, the DLC film graphitized, and the iron island reacted partially with the graphitized DLC (GDLC), which can be deduced from the Raman spectroscopy and SEM pictures. SCNTs film grew from C₂H₂---H₂ mixture under low plasma density. The good contact of carbon nanotube with GDLC film was acquired by the accumulation of the graphite sheets and the reaction between the iron particles and GDLC film. The homogeneous spines with the length of approximately 15 nm and the thickness of <5 nm burgeoned from the defects at the wall of carbon nanotube and distributed uniformly, which were in fact thin bent or rolled-up graphite sheets.     

Nitrogen-doped diamond films selected-area deposition by the plasma-enhanced chemical vapor deposition process

The nitrogen-doped diamond films have been successfully synthesized by using urea as the nitrogen source. Selected-area deposition of diamond nuclei was formed by using a SiO₂ layer as the masking material. Diamond pads, around 9 μm in diameter, were obtained when the N-doped diamond films were deposited on these patterned diamond nuclei using the chemical vapor deposition process. An emission current density as high as 200 μA/cm², with a turn-on field of around 8 V/μm, was obtained. However, the diamond emitters broke down easily, which is ascribed to the localized melting of the substrate materials surrounding the diamond pads.     

Comparative study of homoepitaxial single crystal diamond growth at continuous and pulsed mode of MPACVD reactor operation

Homoepitaxial growth of single crystal diamond by microwave plasma chemical vapor deposition in pulsed regime of a 2.45 GHz MPACVD reactor operation at pulse repetition rates of 150 and 250 Hz was investigated. The high quality CVD diamond layers were deposited in the H₂-CH₄ gas mixture containing 4% and 8% of methane, gas pressures of 250 and 260 Torr and substrate temperature of 900 °C without any nitrogen addition. The (100) HPHT single crystal diamond seeds 2.5 × 2.5 × 0.3 mm (type Ib) were used as substrates. At pulse repetition rate 150 Hz the high quality single crystal diamond was grown with growth rate of 22 μm/h. The comparison of the single crystal diamond growth rates in CW and pulsed wave regimes of MPACVD reactor operation at microwave power density 200 W/cm³ was made. It was found that at equal power density, the growth rate in pulsed wave regime was higher than in CW regime. Differences in single crystal diamond growth for two sets of experiments (with continuous and pulsed wave regimes) were explained.