High Quality Diamond Research Articles

Signature of high Tc above 25 K in high quality superconducting diamond.

We have observed zero resistivity above 10 K and an onset of resistivity reduction at 25.2 K in a heavily B-doped diamond film. However, the effective carrier concentration is similar to that of superconducting diamond with a lower Tc. We found that the carrier has a longer mean free path and lifetime than in the previous report, indicating that this highest Tc diamond has better crystallinity compared to that of other superconducting diamond films. In addition, the susceptibility shows a small transition above 20 K in the high quality diamond, suggesting a signature of superconductivity above 20 K. These results strongly suggest that heavier carrier doped defect-free crystalline diamond could give rise to high Tc diamond.

Homoepitaxial growth and stress analysis of (111) diamond film with embedded gold islands

The internal stress in high-quality (111) homoepitaxial diamond film grown on high-pressure high temperature (HPHT) synthesized single crystal diamond substrate by chemical vapor deposition (CVD) can be reduced effectively by embedding Au islands in diamond. Au islands formed from an Au layer deposited on the diamond substrate by electron beam evaporation can be obtained after hydrogen plasma annealing. Transmission electron microscopy and X-ray diffraction results show that the Au islands covered with CVD diamond have a size in a few hundreds of nanometers and are oriented with diamond in the orientation relationship of {111}Au//{111}Dia and <110 > Au//<110 > Dia. The surfaces of the CVD diamond films grown on substrate with and without Au coating exhibit cracks when the film thickness reaches 3.5 μm. As evaluated from the Raman peak shift, it is shown that the internal tensile stress in the film with Au islands is less than in the same thick film on substrate without Au coating. A crack-free (111) homoepitaxial diamond film in the same thickness can be obtained by insertion of multilayers of Au islands in CVD diamond.

Crystal growth and characterization of hydrogen-doped single diamond with Fe(C5H5)2 additive

In this paper, a series of high-quality hydrogen-doped diamonds is successfully synthesized in Ni70Mn25Co5-C system by using Fe(C5H5)2 as hydrogen source at pressures ranging from 5.5 GPa to 6.0 GPa and temperatures of 1280-1400 ℃. We find that both pressure and temperature conditions strengthen with adding the Fe(C5H5)2. Scanning electron microscope micrographs show that the obtained diamonds at low levels of Fe(C5H5)2 additive have smooth surfaces. However, many defects are found and some pores appear on the diamond surface with increasing the Fe(C5H5)2 additive in the system. From the obtained Fourier transform infrared (IR) spectrum, we notice that there is no significant change of nitrogen concentration in the synthesized diamond with the Fe(C5H5)2 additive lower than 0.3 wt%, while the nitrogen concentration gradually decreases with the further increase of Fe(C5H5)2 additive. In the system with 0.5 wt% Fe(C5H5)2 additive, the nitrogen concentration in synthesized diamond is only half that of system without Fe(C5H5)2 additive. Meanwhile, the hydrogen associated IR peaks of 2850 cm-1 and 2920 cm-1 are gradually enhanced with the increase of Fe(C5H5)2 additive in the system, indicating that most of the hydrogen atoms in the synthesized diamond are incorporated into the crystal structure as sp3-CH2-symmetric (2850 cm-1) and sp3 CH2-antisymmetric (2920 cm-1) vibrations. From the obtained Raman spectrum, we find the incorporation of hydrogen impurity leads to a significant shift of the Raman peak towards higher frequencies from 1333.90 cm-1 to 1334.42 cm-1 with increasing the concentration of Fe(C5H5)2 additive from 0.1 wt% to 0.5 wt%, thereby giving rise to some compressive stress in the diamond crystal lattice. This is the first time that the gem-grade hydrogen-doped diamond single crystal, with size up to 3.5 mm has been successfully synthesized by using new hydrogen source Fe(C5H5)2 additive. We believe that our work can provide a new method to study the influence of hydrogen impurity on diamond synthesis and it will help us to further understand the genesis of natural diamond in the future.

Temperature dependent creation of nitrogen-vacancy centers in single crystal CVD diamond layers

In this work, we explore the ability of plasma assisted chemical vapor deposition (PACVD) operating under high power densities to produce thin high-quality diamond layers with a controlled doping with negatively-charged nitrogen-vacancy (NV−) centers. This luminescent defect possesses specific physical characteristics that make it suitable as an addressable solid-state electron spin for measuring magnetic fields with unprecedented sensitivity. To this aim, a relatively large number of NV− centers (>1012cm−3) should ideally be located in a thin diamond layer (a few tens of nm) close to the surface which is particularly challenging to achieve with the PACVD technique. Here we show that intentional temperature variations can be exploited to tune NV− creation efficiency during growth, allowing engineering complex stacking structures with a variable doping. Because such a temperature variation can be performed quickly and without any change of the gas phase composition, thin layers can be grown. Measurements show that despite the temperature variations, the luminescent centers incorporated using this technique exhibit spin coherence properties similar to those reached in ultra-pure bulk crystals, which suggests that they could be successfully employed in magnetometry applications.

A charge transport study in diamond, surface passivated by high-k dielectric oxides

The recent progress in the growth of high-quality single-crystalline diamond films has sparked interest in the realization of efficient diamond power electronic devices. However, finding a suitable passivation is essential to improve the reliability and electrical performance of devices. In the current work, high-k dielectric materials such as aluminum oxide and hafnium oxide were deposited by atomic layer deposition on intrinsic diamond as a surface passivation layer. The hole transport properties in the diamond films were evaluated and compared to unpassivated films using the lateral time-of-flight technique. An enhancement of the near surface hole mobility in diamond films of up to 27% is observed when using aluminum oxide passivation.

A circumferential antenna ellipsoidal cavity type MPCVD reactor developed for diamond film deposition

In this paper, a new circumferential antenna ellipsoidal cavity type MPCVD reactor possessing advantages of both an ellipsoidal cavity type and a multimode non-cylindrical cavity type MPCVD reactor is described. An ellipsoidal cavity is adopted as its deposition chamber and a circumferential antenna is used in its microwave coupling channel. A ring-shaped quartz window located within the microwave coupling channel has replaced the quartz bell jar that has been used by a conventional ellipsoidal cavity type MPCVD reactor. Therefore, input microwave power of the reactor will be no longer constrained by the quartz bell jar. At the same time, sealing reliability of the microwave window is improved. Using the new reactor, a 2-inch diameter freestanding diamond film has been synthesized at 6kW input power, and Raman spectroscopy analyses indicate that the diamond film prepared using the new reactor is of high quality.Resonant electric field patterns of different sized ellipsoidal cavities were systematically simulated and analyzed. Based on the simulation, a novel circumferential antenna ellipsoid cavity type MPCVD reactor was built. The new MPCVD reactor combines the advantages of an ellipsoidal cavity and a circumferential antenna. Also a ring-shaped quartz window is adopted to replace a conventionally used quartz bell jar as its microwave feeding window. Such a design makes the reactor get rid of the limitation in microwave power levels resulting from usage of the bell jar. Two-inch high quality diamond films have been deposited using the newly built reactor at high input microwave power.

Single-photon emitters based on NIR color centers in diamond coupled with solid immersion lenses

Single-photon sources represent a key enabling technology in quantum optics, and single color centers in diamond are a promising platform to serve this purpose, due to their high quantum efficiency and photostability at room temperature. The widely studied nitrogen-vacancy (NV) centers are characterized by several limitations, thus other defects have recently been considered, with a specific focus of centers emitting in the near-infra red (NIR). In the present work, we report on the coupling of native NIR-emitting centers in high-quality single-crystal diamond with solid immersion lens (SIL) structures fabricated by focused ion beam (FIB) lithography. The reported improvements in terms of light collection efficiency make the proposed system an ideal platform for the development of single-photon emitters with appealing photophysical and spectral properties.

Amination of diamond film by ammonia microwave plasma treatment

Functionalization of diamond films is important for various applications, such as electrochemical sensors. In this study, high quality diamond films were prepared by microwave plasma chemical vapor deposition (MPCVD). These surfaces were then functionalized by a surface amination modification (ammonia plasma) using the same system. The characterization results demonstrated that both the surface morphology and microstructure of the diamond films were not altered by the ammonia plasma treatment. The surface nitrogen content was assessed by XPS analyses, which revealed that amine groups (−NH2) were generated on the diamond film surface efficiently. The −NH2 concentration on modified diamond film surface was equal to 6.71% (denoted as −NH2/100C). The contact angle of water was decreased as the hydrophilicity of the aminated diamond film was increased. Based on the optical emission spectrum (OES) study, NH and NH2 radicals were generated in the microwave plasma, and are regarded as the crucial precursors for creating the amine group on diamond surface.

Growth of micro- and nanocrystalline dual layer composite diamond films by microwave plasma CVD: Influence of CO2 concentration on growth of nano-layer

The high quality and smooth micro-and nanocrystalline dual layer composite diamond films were successfully prepared using H2/CH4/Ar/CO2 plasma with a synthesis process of nucleation/MCD growth/nucleation/NCD growth. The carbon dioxide content is demonstrated to be important in controlling the NCD layer grain size and growth rate. The influences of carbon dioxide concentration on the morphology, microstructure and growth rate of the deposited NCD layer are investigated by using scanning electron microscopy (SEM), X-ray diffraction (XRD) and Raman spectroscopy. It is found that the additional carbonaceous sources supplied by CO2 are favourable 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 NCD but also to decrease the growth rate. The appropriate addition of CO2 can increase the high quality and growth rate, decrease the surface roughness. It is demonstrated that adding CO2 strongly affects the contents of various reaction species in plasma, which would determine the growth features of NCD layers. The deposited highly smooth and quality micro-/nano-crystal layered diamond film is also expected to be applicable in surface aroustic wave (SAW) devices and micro-electromechanical systems (MEMS).

Recent Advances on Diamond Surfaces and Devices

Diamond represents a well-known gemstone and traditional industrial material in applications such as cutting and polishing. However, since about 20 years ago, diamond is rising as a new semiconductor material with many unique properties, unrivalled by other materials. Research and development during these years was initially focused on getting high quality, electronic grade diamond materials, possibly without defects and impurities. Nowadays, synthetic high quality diamonds for electronic application are reality and available commercially. Based on this tremendous progress in diamond technology many new fundamental phenomena have been and are being discovered and diamond is studied in diverse fields from nuclear physics and spintronics to biology and medicine. In this respect it is intriguing that originally unwanted defects and impurities have now become one of the key functional elements in diamond research and applications. This makes evident that diamond can bring surprises and shine bright even as a semiconductor. In this special issue of physica status solidi (a) we aim at bringing you refl ection of the most recent activity and advances in diamond science and technology, although without being able to be comprehensive in this already large and quickly developing field. To accomplish this aim, the issue is based on inviting several topical contributions from recognized scientists as well as on selection of papers that were actively contributed by authors worldwide. The articles come from Europe, Asia, and Australia and demonstrate truly intercontinental collaborations. The special issue is organized into fundamental and applied subjects such as growth, impurity and defect control, surface structuring of diamond, surface chemistry, electron emission and excitons in diamond and, of course, diamond devices. Note that while they represent their own research fields these subjects are also obviously interrelated. We would like to attract your attention in particular to the two Feature Articles in this issue. Kane M. O'Donnell and co-workers discuss a new way of generating the highly useful negative electron affinity and facilitate electron emission by merging diamond with lithium 1. Electron emission is indeed a crucial and intensively studied phenomenon in diamond, as shown by the article of I-Nan Lin and coworkers 2. It finds interest from chemistry and biology to power devices, in particular because of its use in applications benefiting our daily lives and contributing to our sustainable future. These and other collected articles show that the research and understanding of diamond and its surfaces is still far from finished and new discoveries may be just behind the corner. Therefore, we strived for an expedite peer-review and editorial process and we hope that you will find the presented works interesting, timely and inspirational. Prague & Hasselt, September 2014 Bohuslav Rezek Miloš Nesládek Ken Haenen

Effect of Methane Concentration on the Performance of Diamond Films Prepared by MPCVD

Diamond films were deposited by using methane and hydrogen as the gas source and utilizing the approach of chemical vapor deposition of microwave plasmas on the monocrystalline silicon piece. An analysis was also conducted to investigate the influence of methane concentration on the diamond film. When the methane concentration was set at 0.5%, the experiment turned out to have the high quality diamond film which was dense with homogeneous sizes. In condition that the methane concentration was 2.44%, the film obtained was much denser but with larger proportion of non-diamond components. In case that the methane concentration was about 0.25%, the purity of diamond film was declined while the film was inconsistent.

Simulation of Temperature Distribution in HFCVD Diamond Films Growth on the End Surfaces of Seals

The uniform temperature flied of substrates is a key factor to deposit high-quality diamond films on milling tools by the hot filament chemical vapor deposition (HFCVD). In this study, a 3-D computational model is established to simulate the temperature distribution on the substrates. Thereafter, the influence of the rotational speed of worktable n and the water flux of water-cooled worktable Q are investigated. The simulation results show that the increasing of the rotational speed of worktable is suitable to grow homogeneous diamond films and gently decrease the even temperature of seals. What’s more, the deceasing of the water flux will significantly increase the overall temperature of seals.

High temperature thermal conductivity of free-standing diamond films prepared by DC arc plasma jet CVD

Free-standing diamond films with 1.68mm in polished thickness have been prepared by DC arc plasma jet CVD. By means of simply changing the placing orientation of diamond films along the laser transmission direction while testing, the through-thickness thermal conductivity (κ⊥) together with the in-plane (κ//) thermal conductivity of free-standing diamond films were measured by laser flash technique over a wide temperature range. Results show that the thermal conductivity κ⊥ and κ// of free-standing diamond films are up to 1916 and 1739Wm−1K−1 at room temperature, respectively, showing small anisotropy (9%), and following the relationship κ~T−n as temperature rises. The conductivity exhibits similar value compared to that of high-quality single crystal diamond above 500K for both through-thickness and in-plane directions of CVD diamond films. The effects of impurities and grain boundaries on thermal conductivity of diamond films with increasing temperature were discussed.

Effects of copper interlayer on deposition and flexibility improvement of diamond microelectrode

Tungsten with sputtered copper layer (W/Cu) and bare tungsten (W) substrates were investigated for boron doped diamond microelectrode (BDDME). Traditional tungsten substrate becomes brittle after diamond film deposition and is prone to fracture when BDDME confronts slight bending force in practice because of formation of carbide on the surface of tungsten. To improve the flexibility of the microelectrode, a 100nm sputtered copper layer has been chosen as a barrier interlayer to hinder diffusion of carbon into tungsten, as copper does not form compounds with carbon and tungsten. We have found that the copper layer greatly curbs the formation of tungsten carbide, making the W/Cu substrates more flexible than W substrates after deposition and the bending angle was up to 40°, which was 4 times higher than that of bare tungsten substrates. Besides, the sputtered copper layer made it easier for diamond nanoparticles to adsorb on the surface, which has improved nucleation and growth of diamond film. High-quality and well-adhesive diamond film without crack and holes has been deposited on the W/Cu substrate.

Focused-ion-beam overlay-patterning of three-dimensional diamond structures for advanced single-photon properties

Sources of single photons are of fundamental importance in many applications as to provide quantum states for quantum communication and quantum information processing. Color centers in diamond are prominent candidates to generate and manipulate quantum states of light, even at room temperature. However, the efficiency of photon collection of the color centers in bulk diamond is greatly reduced by refraction at the diamond/air interface. To address this issue, diamond structuring has been investigated by various methods. Among them, focused-ion-beam (FIB) direct patterning has been recognized as the most favorable technique. But it has been noted that diamond tends to present significant challenges in FIB milling, e.g., the susceptibility of forming charging related artifacts and topographical features. In this work, periodically-positioned-rings and overlay patterning with stagger-superimposed-rings were proposed to alleviate some problems encountered in FIB milling of diamond, for improved surface morphology and shape control. Cross-scale network and uniform nanostructure arrays have been achieved in single crystalline diamond substrates. High quality diamond solid immersion lens and nanopillars were sculptured with a nitrogen-vacancy center buried at the desired position. Compared with the film counterpart, an enhancement of about ten folds in single photon collection efficiency was achieved with greatly improved signal to noise ratio. All these results indicate that FIB milling through over-lay patterning could be an effective approach to fabricate diamond structures, potentially for quantum information studies.

Rocking curve measurements revisited

In order to correctly analyse high-resolution rocking curves of high-quality crystals, a special effort is needed to estimate the systematic contributions coming from the experimental setup. This article highlights the main areas that require special analytical treatment and presents results obtained using different approaches to the problem, as well as some typical results for high-quality silicon and diamond crystals.

Large Area Single-Crystal Diamond Synthesis by 915 MHz Microwave Plasma-Assisted Chemical Vapor Deposition

A 75 kW, 915 MHz microwave plasma-assisted chemical vapor deposition system was adapted and utilized to scale up production of high-quality single-crystal diamonds at high growth rates. A 300 mm diameter plasma discharge was achieved with uniform temperature distributions of ±250 °C on up to 300 single-crystal diamond substrates. Diamond single crystals were synthesized from H2/CH4/N2 gas mixtures at pressures between 90 and 180 Torr, with recorded growth rates from 10 to 30 μm/h. The source of N2 was from vacuum chamber leakage, and it greatly affected synthesis chemistry. Optical emission spectroscopy was used to probe the localized plasma chemistry and plasma uniformity at different gas pressures. Production rates of up to 100 g/day of single-crystal diamonds were demonstrated, with 25% of the material categorized as colorless. Crystals up to 3.5 mm in thickness could be produced during a single deposition run. The quality of the crystals produced was assessed by photoluminescence and UV–visible absorp...

Large-area high-quality single crystal diamond

Abstract

Development of a templated approach to fabricate diamond patterns on various substrates.

We demonstrate a robust templated approach to pattern thin films of chemical vapor deposited nanocrystalline diamond grown from monodispersed nanodiamond (mdND) seeds. The method works on a range of substrates, and we herein demonstrate the method using silicon, aluminum nitride (AlN), and sapphire substrates. Patterns are defined using photo- and e-beam lithography, which are seeded with mdND colloids and subsequently introduced into microwave assisted chemical vapor deposition reactor to grow patterned nanocrystalline diamond films. In this study, we investigate various factors that affect the selective seeding of different substrates to create high quality diamond thin films, including mdND surface termination, zeta potential, surface treatment, and plasma cleaning. Although the electrostatic interaction between mdND colloids and substrates is the main process driving adherence, we found that chemical reaction (esterification) or hydrogen bonding can potentially dominate the seeding process. Leveraging the knowledge on these different interactions, we optimize fabrication protocols to eliminate unwanted diamond nucleation outside the patterned areas. Furthermore, we have achieved the deposition of patterned diamond films and arrays over a range of feature sizes. This study contributes to a comprehensive understanding of the mdND-substrate interaction that will enable the fabrication of integrated nanocrystalline diamond thin films for microelectronics, sensors, and tissue culturing applications.

X-Ray Topographic Study of a Homoepitaxial Diamond Layer on an Ultraviolet-Irradiated Precision Polished Substrate

Suitable techniques for the growth of high-quality single-crystal diamond are needed in order to use single-crystal diamond in power devices. Because the ion plantation technique cannot be used for diamond doping, a drift layer and a conduction layer for a diamond power device were grown by chemical vapor deposition. An important challenge in this eld is to reduce the dislocation density in the epitaxial layer. The dislocation density was found to increase during the chemical vapor deposition process. Because a defective surface is one cause of increased dislocation density, the use of a UV-polished substrate having no scratches due to mechanical polishing was investigated.