CVD Diamond Films Research Articles

Effects of the film microstructures on CVD diamond radiation detectors

The polycrystalline nature of the films has limited the improvement of CVD diamond radiation detectors. In this work, three CVD diamond films with different microstructures were grown by a hot-filament chemical vapor deposition (HFCVD) technique and were fabricated as CVD diamond radiation detectors. The photocurrents and the pulse height distributions (PHDs) obtained by the detectors were measured by using 5.9 keV 55Fe X-rays. The dark-current of 16.0 nA and the photocurrent of 15.9 nA are achieved at a bias voltage of 100 V. The PHD peak is well separated from the noise and a better energy resolution of 21.2% is obtained due to the high ratio of grain size to the film thickness. The time-dependent photocurrent initially increases rapidly and then levels off due to the ‘polarization’ effect.

Combination of CVD Diamond and DLC Film Growth with Pulsed Laser Deposition to Enhance the Corrosive Protection of Diamond Layers

CVD diamond layers are often used as protective layers. One of the most important of these applications requires pinhole-free layers to protect against fluid materials, such as found in chemically aggressive environment. These pinholes are present even in very good quality CVD diamond films. In this work we combined the Pulsed Laser Deposition (PLD) technique with Microwave assisted Chemical Vapor Deposition (MW-CVD). We used CVD diamond films prepared under different conditions and layer thicknesses. Both of these proceses produced inperfect protective layers, but we proved that a PLD DLC film over the diamond layer does reduce the number of pinholes in the coating. We used special chemical alcaline etching to detect the remaining pinholes, and to test the corrosion protective properties of the layers. As a result we were able to prepare samples of 1 x 1cm2 with only 0.2 micron thickness without any pinholes, while in CVD diamond layers a thickness of 2,5 micron was needed for the same level of compactness.

Elastic Constants and Graphitic Grain Boundaries of Nanocrystalline CVD-Diamond Thin Films: Resonant Ultrasound Spectroscopy and Micromechanics Calculation

AbstractUsing resonant-ultrasound spectroscopy coupled with laser-Doppler interferometry, we determine the independent elastic constants of nanocrystalline CVD-diamond thin films with thickness between 2-12 μm. They are deposited on oriented monocrystal silicon substrates by the hot-filament methane/nitrogen CVD method. The diagonal components of the elastic constants are smaller than those of microcrystalline CVD diamond films and bulk diamond. However, the off-diagonal component is larger. We attribute these observations to the presence of sp2-bonded graphitic phase at grain boundaries. A micromechanics model assuming inclusions of thin graphitic plates consistently explains the observations.

Formation and Characterization of Electric Contacts on CVD Diamond Films Prepared by Ion Implantation

Diamond layers have a potential application as the highest band-gap semiconductor for electronic devices. One of the major problems is to form electric contact on the diamond surface useful for an electronic device. This paper shows the properties of the contacts formed by the very promising ion implantation technique. The diamond layers were deposited with Microwave Assisted Chemical Vapor Deposition (MW-CVD) equipped with special extra features like High Voltage Bias and Heated Substrate Holder [1]. Phosphoruos ion implantation and gold deposition were used for the contact formation. This technique resulted graphitization the top of the diamond film and intermixing of gold with the graphite or diamond surface. The properties of the contacts were tested with surface conduction characterization methods, and the properties of the contact to diamond interface was investigated with SIMS (Secondary Ion Mass Spectroscopy ) and XPS (X-ray Photoelectron Spectroscopy).

Study on Polishing of CVD Diamond Film (1st report)

耐摩耗性や潤滑性に優れたCVDダイヤモンド膜をプレス金型にコーティングし, 無潤滑プレスを行うことを検討している. しかし一方でCVDダイヤモンド膜は, 多結晶体構造をしているために表面粗さが大きく, プレス金型のコーティング膜として利用するためにはは研磨が必要になる. そこで, ダイヤモンドとの反応性が高い工具に超音波を印加し, これをダイヤモンド膜に押し当てることによって発生する摩擦熱を利用した, 砥粒を用いない超音波研磨法を提案し, その可能性について検討する.

CVDダイヤモンド膜の研磨に関する研究 (第2報)

本研究では, 第1報で提案した砥粒レス超音波研磨法を連続的な研磨に適用できるかについて最初に調べた. さらに超音波振動振幅, 研磨荷重, 工具送り速度, 研磨回数等の研磨条件を変化させたときに, 表面粗さにどのような影響を及ぼすかについて調べた. その結果, 砥粒レス超音波研磨法が連続的な研磨に適用できることを確認した. さらに適当な研磨条件を選ぶことによって, 良好な研磨面が得られることを確認した.

Laser spallation method to measure strength against Mode-I decohesion of CVD diamond films

We have evaluated the absolute adhesive strength against the Mode-I decohesion of 78-μm-thick polycrystalline CVD diamond (CVDD) film deposited on a sintered SiC substrate by pulse laser spallation. Strong tensile stress wave, impinging on the film/substrate interface, was produced by confined silicone grease breakdown to induce the spallation. The spallation was observed at the laser energies above 46 mJ when the laser focusing diameter and grease thickness are 1.0 mm and 20 μm, respectively. The threshold laser energy to cause the spallation changed from 46 to 69 mJ depending on the test position, and interfacial strength was estimated to be larger than 222 MPa by measuring the particle velocity of stress wave at the interface. Next we attempted to determine the spallation initiation utilizing acoustic emission (AE) and laser ultrasonics. An AE sensor detected the high frequency waves of 13–15 MHz besides the component of the main resonant frequency (5 MHz) of the AE sensor. Amplitude of this high frequency component drastically decreased for small spallation of 0.6 mm in diameter. We also observed a distinguishable decrease of 0.42% in the Rayleigh wave velocity through the delaminated part of CVDD/SiC surface.

Effects of the deposition conditions and annealing process on the electric properties of hot-filament CVD diamond films

By using different deposition conditions, four CVD diamond films with different qualities and orientation were grown by the hot-filament CVD technique. The dielectric properties of these films before and after annealing were investigated in detail. A study of the relationship between the different deposition conditions and annealing process with respect to the dielectric properties was carried out. These CVD diamond films were also characterized with Raman spectroscopy, XRD and I – V characteristics. High-quality CVD diamond films were grown on Si substrate mechanically scratched with diamond powder. The annealing process reduces the hydrogen contamination of the films and therefore improves the film quality. CVD diamond films with good electric properties such as a resistivity of 1.2×10 11 Ω cm at a voltage of 50 V, a dielectric constant of 5.73 and a dielectric loss of 0.02 at a frequency of 2 MHz were obtained.

Proceedings of surface and bulk defects in CVD diamond films, IX

The present issue of physica status solidi (a) contains a collection of papers from the 9th International Workshop on Surface and Bulk Defects in CVD Diamond Films (SBDD IX) held in Diepenbeek-Hasselt, Belgium, 18–20 February 2004. The invited lecture by R. Sauer et al., ‘Radiative recombination in phosphorus-doped CVD diamond’ [1] from this workshop is Editor's Choice of this issue. The proceedings of the workshop series are published already for the sixth time in this journal. This year, they are combined with the Proceedings of the international workshop on Defects and Impurities in Crystalline Boron Nitride Compounds, which was also held in Diepenbeek–Hasselt, 20–21 February 2004, as a joint event with SBDD IX. Guest editors of this part are Etienne Goovaerts and Sergiu V. Nistor.

Preface: phys. stat. sol. (a) 201/11

We are glad to introduce in this issue of physica status solidi (a) a series of papers which were presented at the international workshop on Defects and Impurities in Crystalline Boron Nitride Compounds, held in Diepenbeek-Hasselt, Belgium, on 20–21 February 2004. Because of the strong scientific connections, this workshop was jointly organised with the 9th International Workshop on Surface and Bulk Defects in CVD Diamond Films (18–20 February 2004) and this led to the joint publication of the contributions in the present issue. For several years boron nitride, and in particular cubic boron nitride, is back in the centre of materials research activities because of new potential applications as a wide band gap semiconductor for electronics and opto-electronics in extreme conditions. However, important efforts are needed to understand the role of defects and impurities in controlling its semiconducting properties and growth processes in order to realise these promises. An international group of researchers (30 participants from 12 countries: Belarus, Belgium, Czech Republic, Germany, Italy, Japan, Latvia, Romania, Russia, Sweden, Ukraine, USA; among which 8 invited) has gathered to discuss the present status of research on the following topics: Impurities and morphology, Synthesis and microstructure, Optical and electrical properties, and Point defects characterisation. Contributions were presented on boron nitride single crystals, on p–n junctions formed with this material, but also on crystalline powders, thin films and B–C–N nanotubes. Among the characterisation methods which have been discussed, we mention optical spectroscopy (absorption, luminescence, Raman), multifrequency electron spin resonance, high resolution and analytical electron microscopy and analytical micro ion beam techniques. This workshop was organised as a final activity of the Flemish–Romanian scientific and technological cooperation project “Defects in diamond-like materials of the B/C/N system”, involving from the Flemish side both the Experimental Condensed Matter Physics Laboratory at the Physics Department of the University of Antwerp and the Materials Physics Division at the Institute for Materials Research of the Limburgs Universitair Centrum, and from the Romanian side the Microstructure of Defects in Solids Laboratory of the National Institute for Materials Physics in Magurele–Bucuresti. We gratefully acknowledge the financial support of the Flemish and Romanian governments through the above mentioned international bilateral project, as well as the organisational support of all three home institutions along the duration of the whole project. We also wish to personally thank Miloš Nesládek and Ken Haenen for the invaluable and continuous assistance in the practical organisation of this workshop.

Preface: phys. stat. sol. (a) 201/11

The present issue of physica status solidi (a) contains a collection of 24 papers presented at the 9th International Workshop on Surface and Bulk Defects in CVD Diamond Films held in Diepen- beek–Hasselt, Belgium, 18–20 February 2004. The concept of this workshop originated in 1996 with the idea of bringing together scientists who are active and innovative in the field of electronic and optical properties of thin film diamond. Since then, this meeting have grown up to a regular conference devoted to new issues in CVD diamond research and related to diamond as a material for electronics and nanobioelectronics. This year the programme was spread over two and a half days, including 8 invited lectures from a total of 39 talks, and a poster session featuring 15 posters. In addition we were able to connect this meeting with a workshop on Defects and Impurities in Crystalline Boron Nitride Compounds, scientifically organized from the University of Antwerp and leading finally to a joint meeting lasting four days. The papers from the BN workshop are joining this proceeding issue on pages 2559–2598. At SBDD IX, topics ranged from homo- and heteroepitaxial growth, doping, hydrogen induced surface conductivity, defects and their characterization, to devices including bio-sensing applications. As usual, very intense and lively discussions took place among participants, from young students to established scientists, after talks, during breaks and in the evenings while enjoying the hospitality of the Limburgs Universitair Centrum and especially the city of Hasselt. The number of participants reached a record breaking 96 this year, with participants coming from fifteen different countries (Australia, Austria, Belgium, Czech Republic, France, Germany, Israel, Italy, Japan, Mexico, Romania, Russia, Sweden, UK, USA). This yearly increasing number indicates that this workshop is continuing to be very attractive to a large scientific community, as it summarizes the up-to-date research on diamond as a wide band gap semiconductor. The workshop would have not been possible without the support of many people and institutions. For financial aid we are especially indebted to the Scientific Research Community “Surface Modification of Materials” of the F. W. O.-Vlaanderen (Belgium) and its continuous support since starting this workshop 9 years ago. We also thank the Limburgs Universitair Centrum for offering the lecture hall and infrastructure facilities. Finally we highly appreciate the active approach of the editorial staff of physica status solidi in this conference and would like to thank most notably Stefan Hildebrandt and Katharina Fröhlich, for their excellent and patient work, making this already the sixth successfully published proceedings of SBDD in pss (a). To finish, we would all like to invite you for the 10th anniversary of the SBDD series in February 2005 in Diepenbeek-Hasselt and we look forward to seeing you at: Surface and Bulk Defects in CVD Diamond Films, X 23–25 February 2005 Limburgs Universitair Centrum, Diepenbeek – Hasselt, Belgium http://www.imo.luc.ac.be/SBDD2005

Nucleation and growth microstructural study of ti films on 304 SS substrates

Coating of steel surfaces with titanium films has been studied with the objective to protect them against corrosion, and to create an intermediate film for CVD diamond and TiN film deposition. In this work, the nucleation, growth mechanisms and microstructural formation of the titanium films deposited on 304 stainless steel (304 SS) substrate are presented and discussed. The titanium films of variable thickness were obtained by vapour phase deposition produced by electron beam. The surfaces of these samples were observed by scanning electron microscopy. The cross sections of these samples were observed by using an atomic force microscope. The Ti film-304 SS interfaces were analyzed by X-ray diffraction. The results showed that titanium films have a columnar growth. The Ti film-304 SS interface had a residual compression stress at room temperature due to the interdiffusion process.

Optically stimulated luminescence dosimetry on CVD diamond films

Diamond thin films chemically vapor deposited containing different B/C concentration in the range of 2000-20000 ppm were exposed to a p-ray dose of 0.8-3000 Gy. The optically stimulated luminescence (OSL) response of previously irradiated samples was excited with light of 470 nm at room temperature. The OSL decay curves were measured and found them to be a function of the dose exposure. The remaining thermoluminescence (TL) glow curve after optical stimulation indicates the existence of main charge carriers trapped in traps located at 323-523 K, meaning that the OSL emission appears to originate from charge trapped mainly at those traps related to the low temperature TL glow peaks. The results indicate that CVD diamond films perform well as OSL dosimeter for ionizing radiation.

Properties of Diamond Film/Alumina Composites for IntegratedCircuits with Ultra-High Speed and High Power

We report the properties of the diamond film/alumina composites whichwere thought of as promising substrate materials for integratedcircuits with ultra-high speed and high power. The measurement resultsof dielectric properties of diamond film/alumina composites show thatthe coating of CVD diamond films could effectively reduce thedielectric constant of the composite. Carbon ion implantation intoalumina substrates prior to the diamond deposition can reduce thedielectric loss of the composite from 5×10−3 to 2×10−3,and can give the composite better frequency stability. The thermalconductivity of composites could be obviously increased by coating CVDdiamond film. The composite has a dielectric constant of 6.5 and athermal conductivity of 3.98 W/(cmK) when the thickness of diamond filmis up to 100 μm.

Development of Ultra Fine Crystalline Diamond Film and Some Applications

We would like to report on the development of our new ultra fine crystalline CVD diamond film and some applications. CVD Diamond films have good wear resistance, but the crystal size is too large. Therefore, in case of application of diamond films for cutting tools, we cannot get fine surface finish on work materials. Recently we succeed in production ultra fine crystalline CVD diamond film and various cutting tools as taps, drills and end mills. Aluminum alloys have lately been consumed more than ever in airplanes and automobiles for the purpose of decreasing the weight of structural materials.Copper alloys are used for the electrode of electric discharge machines (EDM) recently. EDM electrodes are required fine surface finish because the surface quality of mold depends on accuracy of EDM electrodes. Soft materials such as aluminum and copper alloys have high viscosity and additionally activity. So during cutting aluminum and copper alloys we have sometimes adhesion between cutting tools and work pieces. Diamond film on tools is able to improve the reactivity to aluminum and copper alloys. But up to now the diamond film has a lot of course crystal and tend to supply rough surface finish on work pieces. We developed ultra fine crystalline diamond film on end mills by plasma chemical vapor deposition (CVD) method. Now our aircraft, automotive and molding customers can get smooth surface finish of work pieces.Keeping ISO14001, we recommend oil free cutting with ultra fine crystalline diamond coated cutting tools. Here I introduce background of the development and cutting examples with new fine diamond coated end mills.

Characteristics of the Fine Grained CVD Diamond Film and its Industrial Applications

Characteristics of the Fine Grained CVD Diamond Film and its Industrial Applications

Damage processes and substrate surface design for CVD diamond films

Experimental results on the development of damage processes for CVD diamond (hereafter referred to as CVDD) films and substrate surface design are presented with the purpose of application to cutting tools. The initial stage of damage was investigated with a mechanically scanned acoustic microscope. It is shown that the damage is formed by development of cracks, which extends to the top surface. Delaminations around the cracks finally result in peeling off from the substrate. These facts suggest that interface structures inhibiting the extension of cracks and delamination around the cracks are advantageous for adhesion enhancement of CVDD films. Accordingly, the phase transformation of cemented carbide was investigated. As a result, it is demonstrated that by a specific surface treatment under H 2 plasma atmosphere, a surface structure, which is best suitable for the synthesis of CVDD films, can be obtained.

Field emission enhancement by graphitic nano-scale channels through ta-C layers

A key issue in field emission (FE) from CVD diamond and other carbon films is to understand the role that non-diamond inclusions and conduction pathways in the material have on the FE process. FE is significantly enhanced, apart from geometric enhancements due to rough surface morphologies, by the presence of non-diamond phases embedded in the diamond matrix. These phases appear in the form of grain-boundaries, graphitic inclusions, graphite nano-particles and others. It is, however, not clear in most reports, what the relative contribution of surface morphology and the presence of conductive channels to improved emission is. To investigate the possibility of FE originating from graphitic regions in a perfectly smooth material, we performed ion-irradiation to selectively transform diamond-like carbon (sp 3 bonding) into graphite like (sp 2 bonding) material. Single ion tracks were formed by implanting high-energy single ions at extremely low doses through a thin smooth amorphous tetrahedral–amorphous–carbon (ta-C) layer. The layers were thin enough for the ions to penetrate through them and stop in the substrate. N-doped conductive and un-doped ta-C films were used and the FE results were compared. Four ion-implantation schemes were used: (a) 1 GeV U ions at a low dose; (b) sub MeV Xe ions at a low dose; both were meant to form well separated single ion tracks through the material; (c) sub MeV C ions at a high dose, for complete material transformation; and (d) un-implanted sample as a control. Field emission turn-on conditions were carefully studied for these, employing a very slow voltage ramp-up, to avoid undesired vacuum electric discharges, known to result in a ‘conditioning’ affect on FE. Field emission seems to initiate at the lowest applied field for samples that include nano-scale graphitized channels threading all the way through the layer, as realized by single ion implantations. A 40% reduction in the field required for emission onset is found for all samples with single ion tracks compared to the un-implanted sample. However, the sample implanted for full coverage transformation shows no emission up to at least 100 V/μm. The observed improvement in FE is shown to be consistent with field enhancement calculations due to conductive pathways in the material.

An ellipsometric analysis of CVD-diamond films at infrared wavelengths

The ellipsometric measurements of diamond films, which were deposited onto polished [100]-oriented silicon and rough alumina ceramic substrates by hot filament chemical vapor deposition (HFCVD) technique, have been performed over the spectral range from 3 to 12 μm. The parameters of the films, namely, film thickness and volume fraction for each constituent have been calculated from the ellipsometric data by the best fitting procedure using the optimized model. A two-layer stack with about 870-nm thick surface rough layer on top of diamond basis can be perfectly used to simulate the films on silicon substrates. However, the films on alumina substrates cannot be well described by the two-layer model. For the sake of good fit, a three-component interface layer, which consists of 64.13±4% alumina, 23.34±3% diamond and 12.53±1% void, must be appended to the model by Bruggeman effective medium approximation.

Proceedings of the 7th International Workshop on Surface and Bulk Defects in CVD Diamond Films (SBDD 2002)

The cover picture on this issue of physica status solidi (a) symbolizes a diamond crystal, representing the logo of the 7th International Workshop on Surface and Bulk Defects in CVD Diamond Films, held in Diepenbeek-Hasselt, Belgium, March 13–15, 2002. This high successful series of topical workshops originated in 1996. Its proceedings are published in this journal for the fourth time. They have continously met high interest and generated remarkable citation rates (up to an impact of 5) among our readers. Topics of this year's meeting concentrated on diamond as a wide band gap semiconductor and covered surface and growth related phenomen a, doping, hydrogen, defects and their characterization as well as device applications and carbon nanotubes.