Free-standing Diamond Research Articles

Structural evolution of Ti destroyable interlayer in large-size diamond film deposition by DC arc plasma jet

The addition of titanium (Ti) interlayer was verified to reduce the residual stress of diamond films by self-fracturing and facilitate the harvest of a crack-free free-standing diamond film prepared by direct current (DC) arc plasma jet. In this study, the evolution of the Ti interlayer between large-area diamond film and substrate was studied and modeled in detail. The evolution of the interlayer was found to be relevant to the distribution of the DC arc plasma, which can be divided into three areas (arc center, arc main, and arc edge). The formation rate of titanium carbide (TiC) in the arc main was faster than in the other two areas and resulted in the preferred generation of crack in the diamond film in the arc main during cooling. Sandwich structures were formed along with the growth of TiC until the complete transformation of the Ti interlayer. The interlayer released stress via self-fracture. Avoiding uneven fragile regions that formed locally in the interlayer and achieving cooperatively released stress are crucial for the preparation of large crack-free diamond films.

Optical, electrical and microstructural properties of nanocomposite Ag/diamond by Ag ion implantation and subsequent annealing

An optical-grade, free-standing diamond (FSD) film is prepared by home-made microwave plasma chemical vapor deposition reactor at a condition of input power 8 kW and gas pressure18 kPa. Then, it is implanted with 80 keV Ag ions up to a fluence of 5.0 × 1016 ions/cm2. After implantation, a subsequent annealing in Ar ambient at 500 °C is carried out to fabricate Ag nanoparticles (NPs). Grazing incidence x-ray diffraction results clearly showed that Ag NPs with a (111) orientation are effectively formed after 500 °C annealing. Results from field emission scanning electron microscope and atomic force microscope observations indicated that Ag NPs could aggregate and grow on the surface of the diamond film during the annealing process. The Hall effects results showed that Ag-implanted FSD film exhibited an enhanced carrier mobility of 34.7 cm2 V−1 S−1 after 500 °C annealing. Moreover, Raman spectroscopy results show that the damages of the Ag-implanted FSD film are essentially a little and the crystallinity is almost recovered by annealing, it is implied that the enhancement in carrier mobility could be attributed to the conductive paths provided by Ag NPs.

Wafer bowing control of free-standing heteroepitaxial diamond (100) films grown on Ir(100) substrates via patterned nucleation growth

The potential of patterned nucleation growth (PNG) technique to control the wafer bowing of free-standing heteroepitaxial diamond films was investigated. The heteroepitaxial diamond (100) films were grown on an Ir(100) substrate via PNG technique with different patterns of nucleation regions (NRs), which were dot-arrays with 8 or 13μm pitch aligned to <100> or <110> direction of the Ir(100) substrate. The wafer bows and the local stress distributions of the free-standing films were measured using a confocal micro-Raman spectrometer. For each NR pattern, the stress evolutions within the early stage of diamond growth were also studied together with a scanning electron microscopic observation of the coalescing diamond particles. These investigations revealed that the NR pattern, in terms of pitch and direction of dot-array, strongly affects the compressive stress on the nucleation side of the diamond film and dominantly contributes to the elastic deformation of the free-standing film. This indicates that the PNG technique with an appropriate NR pattern is a promising solution to fabricate free-standing heteroepitaxial diamond films with extremely small bows.

Diamond-Based Supercapacitors: Realization and Properties.

In this Spotlight on Applications, we describe our recent progress on the fabrication of surface-enlarged boron-doped polycrystalline diamond electrodes, and evaluate their performance in supercapacitor applications. We begin with a discussion of the fabrication methods of porous diamond materials. The diamond surface enlargement starts with a top-down plasma etching method. Although the extra surface area provided by surface roughening or nanostructuring provides good outcome for sensing applications, a capacitance value <1 mF cm-2 or a surface-enlargement factor <100 fail to meet the requirement of a practical supercapacitor. Driven by the need for large surface areas, we recently focused on the tempated-growth method. We worked on both supported and free-standing porous diamond materials to enhance the areal capacitance to the "mF cm-2" range. With our newly developed free-standing diamond paper, areal capacitance can be multiplied by stacking multilayers of the electrode material. Finally, considering the fact that there is no real diamond-based supercapacitor device up to now, we fabricated the first prototype pouch-cell device based on the free-standing diamond paper to evaluate its performance. The results reveal that the diamond paper is suitable for operation in high potential windows (up to 2.5 V) in aqueous electrolyte with a capacitance of 0.688 mF cm-2 per layer of paper (or 0.645 F g-1). Impedance spectroscopy revealed that the operation frequency of the device exceeds 30 Hz. Because of the large potential window and the ability to work at high frequency, the specific power of the device reached 1 × 105 W kg-1. In the end, we made estimations on the future target performance of diamond supercapacitors based on the existing information.

Erosion difference of growth and nucleation sides of free-standing diamond films prepared by DC arc plasma jet CVD

Solid particle erosion behaviors of the nucleation and growth surface of free-standing diamond films as a function of erosion time were studied by a laboratory designed blast type erosion apparatus. The surface roughness and the transmission loss were used to evaluate the extent of erosion performance. Results showed that the erosion damage features generated by impact appeared after erosion for 5s and 30s for nucleation and growth surface of diamond films respectively, and primarily occurred at grain boundaries in the form of micro-cracks. Then the local chipping of small sections on the border of cracks was followed resulting in material removal. The threshold erosion time, to maintain the transmission at 10.6μm still above 60%, was 60s and 300s for nucleation and growth surface of diamond films. The growth surface of diamond films exhibited about 5 times higher erosion resistance for ending up with relatively lower surface roughness and transmission loss compared with the nucleation surface, which was in accordance with the ratio of grain sizes.

Effect of methane concentration in hydrogen plasma on hydrogen impurity incorporation in thick large-grained polycrystalline diamond films

We investigate the impact of methane concentration in hydrogen plasma on the growth of large-grained polycrystalline diamond (PCD) films and its hydrogen impurity incorporation. The diamond samples were produced using high CH4 concentration in H2 plasma and high power up to 4350W and high pressure (either 105 or 110Torr) in a microwave plasma chemical vapor deposition (MPCVD) system. The thickness of the free-standing diamond films varies from 165µm to 430µm. Scanning electron microscopy (SEM), micro-Raman spectroscopy and Fourier-transform infrared (FTIR) spectroscopy were used to characterize the morphology, crystalline and optical quality of the diamond samples, and bonded hydrogen impurity in the diamond films, respectively. Under the conditions employed here, when methane concentration in the gas phase increases from 3.75% to 7.5%, the growth rate of the PCD films rises from around 3.0µm/h up to 8.5µm/h, and the optical active bonded hydrogen impurity content also increases more than one times, especially the two CVD diamond specific H related infrared absorption peaks at 2818 and 2828cm−1 rise strongly; while the crystalline and optical quality of the MCD films decreases significantly, namely structural defects and non-diamond carbon phase content also increases a lot with increasing of methane concentration. Based on the results, the relationship between methane concentration and diamond growth rate and hydrogen impurity incorporation including the form of bonded infrared active hydrogen impurity in CVD diamonds was analyzed and discussed. The effect of substrate temperature on diamond growth was also briefly discussed. The experimental findings indicate that bonded hydrogen impurity in CVD diamond films mainly comes from methane rather than hydrogen in the gas source, and thus can provide experimental evidence for the theoretical study of the standard methyl species dominated growth mechanism of CVD diamonds grown with methane/hydrogen mixtures.

The diamond radiation detector with an Ohmic contact using diamond-like carbon interlayer

A diamond-like carbon thin layer was used as an interlayer between a free-standing diamond substrate grown by microwave plasma enhanced chemical vapour deposition and a Pt/Au layer. The dark-current of about 5·0 pA cm−2 was found for this detector at an electric field of 200 V cm−1. Ohmic contact was achieved by this diamond-like carbon/Pt/Au trilayer structure as evidenced by a linear dark I-V curve. The ratios of photocurrent to dark-current were about 26 and 35 for diamond detectors with Ti/Pt/Au and diamond-like carbon/Pt/Au trilayer electrodes, respectively. The energy resolution for the diamond detector with diamond-like carbon/Pt/Au electrode was about 3·30%, better than 4·56% for the detector with Ti/Pt/Au electrode.

Structure and wettability property of the growth and nucleation surfaces of thermally treated freestanding CVD diamond films

This paper reports the surface features and wettability properties of the (100)-textured freestanding chemical vapor deposited (CVD) diamond films after thermal exposure in air at high temperature. Thermal oxidation at proper conditions eliminates selectively nanodiamonds and non-diamond carbons in the films. The growth side of the films contains (100)-oriented micrometer-sized columns, while its nucleation side is formed of nano-sized tips. The examined wettability properties of the as-treated diamond films reveal a hydrophilicity and superhydrophilicity on the growth surface and nucleation surface, respectively, which is determined by oxygen termination and geometry structure of the surface. When the surface termination is hydrogenated, the wettability of nucleation side converted from superhydrophilicity to high hydrophobicity, while the hydrophilicity of the growth side does not change significantly. The findings open a possibility for realizing freestanding diamond films having not only novel surface structures but also multifunction applications, especially proposed on the selected growth side or nucleation side in one product.

Mechanical properties of micro- and nanocrystalline diamond foils.

Diamond coating of suitable template materials and subsequent delamination allows for the manufacturing of free-standing diamond foil. The evolution of the microstructure can be influenced by secondary nucleation via control of process conditions in the hot-filament chemical vapour deposition process. Bending tests show extraordinarily high strength (more than 8 GPa), especially for diamond foils with nanocrystalline structure. A detailed fractographic analysis is conducted in order to correlate measured strength values with crack-initiating defects. The size of the failure causing flaw can vary from tens of micrometres to tens of nanometres, depending on the diamond foil microstructure as well as the loading conditions.

Nanostructured Diamond Device for Biomedical Applications.

Diamond is increasingly used in biomedical applications because of its unique properties such as the highest thermal conductivity, good optical properties, high electrical breakdown voltage as well as excellent biocompatibility and chemical resistance. Diamond has also been introduced as an excellent substrate to make the functional microchip structures for electrophoresis, which is the most popular separation technique for the determination of analytes. In this investigation, a diamond electrophoretic chip was manufactured by a replica method using a silicon mold. A polycrystalline 300 micron-thick diamond layer was grown by the microwave plasma-assisted CVD (MPCVD) technique onto a patterned silicon substrate followed by the removal of the substrate. The geometry of microstructure, chemical composition, thermal and optical properties of the resulting free-standing diamond electrophoretic microchip structure were examined by CLSM, SFE, UV-Vis, Raman, XRD and X-ray Photoelectron Spectroscopy, and by a modified laser flash method for thermal property measurements.

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.

Enhancing electrical conductivity and electron field emission property of free standing diamond films by employing embedded Ag nanoparticles

Abstract Ag nanoparticles (NPs) were introduced into free-standing diamond (FSD) film by ion implantation to improve its electrical conductivity and electron field emission (EFE) property. Ag-implanted FSD film exhibits improved conductivity with the carrier mobility of 16.2 cm 2 V −1 s −1 , owing to the conductive paths provided by Ag NPs. The EFE behavior of Ag -implanted FSD film can be turned on at E 0 =18 V/μm, attaining a current density of 89.6 μA/cm 2 at an applied field of 30 V/μm. The origin of improving the EFE was discussed based on F-N equation. The present study shows the interest of using embedded conductive NPs to improve the EFE of diamond.

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.

Diamonds are a spectroscopist's best friend: thin-film diamond mid-infrared waveguides for advanced chemical sensors/biosensors.

The first combination of mid-infrared (MIR) tunable quantum cascade lasers (tQCLs) with thin-film diamond strip waveguides (DSWGs) suitable for advanced chemical sensing/biosensing is demonstrated. The sensing system is composed of thin diamond films grown on surface-passivated Si wafers via chemical vapor deposition (CVD) and microstructured using inductively coupled plasma (ICP) etching, serving as photonic waveguides for radiation emitted by a broadly tunable quantum cascade laser (tQCL) in the spectral regime of 5.78-6.35 μm (1570-1730 cm(-1)). The characterization of the free-standing diamond waveguides reveals excellent transmission properties across a broad MIR band. As a proof of concept, the detection of acetone in D2O via evanescent field absorption is demonstrated achieving a limit of detection (LOD) as low as 200 pL, which indicates a significant sensitivity improvement compared to conventional MIR slab/strip waveguides reported to date. Providing characteristic absorption features within the tuning range of the tQCL, studies using anisaldehyde as an analyte further corroborate the potential of tQCL-DSWG-based chemical sensors/biosensors.

Orientation variation along growth direction of millimeter free-standing CVD diamond thinned by mechanical grinding

A free-standing diamond film with millimeter thickness prepared by DC arc plasma jet was thinned successively by mechanical grinding. The orientation and quality of the diamond films with different thicknesses were characterized by X-ray diffraction and Raman spectroscopy, respectively. The results show a random grain-orientation distribution during the initial growth stage. As the film thickness increases, the preferred orientation of the diamond film changes from (111) to (220), due to the competitive growth mechanism. Twinning generated during the nucleation stage appears to stabilize the preferential growth along the 〈110〉 direction. The interplanar spacing of the (220) plane is enlarged as the film thickness increases, which is caused by the increase of non-diamond-phase carbon and impurities under the cyclic gas. In addition, the quality of the diamond film is barely degraded during the growth process. Furthermore, the peak shift demonstrates a significant inhomogeneity of stress along the film growth direction, which results from competitive growth.

A nitrogen doped low-dislocation density free-standing single crystal diamond plate fabricated by a lift-off process

A nitrogen-doped single crystal diamond plate with a low dislocation density is fabricated by chemical vapor deposition (CVD) from a high pressure high temperature synthetic type IIa seed substrate by ion implantation and lift-off processes. To avoid sub-surface damage, the seed surface was subjected to deep ion beam etching. In addition, we introduced a nitrogen flow during the CVD step to grow low-strain diamond at a relatively high growth rate. This resulted in a plate with low birefringence and a dislocation density as low as 400 cm−2, which is the lowest reported value for a lift-off plate. Reproducing this lift-off process may allow mass-production of single crystal CVD diamond plates with low dislocation density and consistent quality.

Characterization of free-standing single-crystal diamond prepared by hot-filament chemical vapor deposition

Hot filament chemical vapor deposition (HFCVD) possesses a large potential to scale-up for the growth of single-crystal diamond (SCD). This study investigates the crystalline qualities of SCD fabricated by HFCVD. A tungsten impurity level of 1018cm−3 was detected with secondary ion mass spectroscopy. The full-width at half maximum (FWHM) of the rocking curve (004) was 39.5arcsec, where that of seed substrates was 42.8arcsec. A clear free-exciton recombination radiation was observed in cathodoluminescence spectra. The Raman spectra presented a single peak centered at 1333.2cm−1 with a FWHM value of 1.9cm−1. These results indicate that the HFCVD-grown SCD has good crystalline quality comparable to the seed substrates.

Design of a new TM021 mode cavity type MPCVD reactor for diamond film deposition

Abstract A new TM021 mode cavity type microwave plasma chemical vapor deposition (MPCVD) reactor for diamond film deposition was derived by analyzing the TM021 resonant pattern of microwave electric field in an idealized TM021 mode reactor. Important characteristics of the reactor, including microwave electric field, electron density, gas temperature as well as absorbed microwave power density were obtained by using a phenomenological model of hydrogen plasma. On the basis of the simulation, a new TM021 mode cavity type MPCVD reactor was built and 2-inch diameter freestanding diamond films were synthesized at 6 kW input microwave power. Raman and optical transmission spectroscopy analyses indicate that the diamond films prepared by using the new TM021 mode cavity type reactor are of high quality.

Rapid deposition of polycrystalline diamond film by DC arc plasma jet technique and its RF MESFETs

Diamond is a promising semiconductor material for high power, high frequency and high temperature electronic devices. High-purity polycrystalline diamond with large grain size has showed prominent RF properties. In this work, polycrystalline free-standing diamond film with grain size of 150 μm was grown by DC arc plasma jet technique with a growth speed as high as 20 μm/h. The prepared diamond sample showed high-purity with a (220) preferred orientation by the XRD and Raman spectra measurements. By a self-aligned process, hydrogen terminated p -type diamond MESFETs with gate length of 100 nm were fabricated on the 15 mm × 15 mm diamond film and showed good DC and RF performances with drain saturation current 225.7 mA/mm and maximum oscillation frequency ( f max ) 46.8 GHz. • 15 × 15 mm 2 diamond film is prepared by dc arc plasma jet method. • I DS of 225.7 mA/mm and f max of 46.8 GHz are reached.

Effect of Temperature on GaN Films Deposited on Diamond Substrate Using an ECR-PEMOCVD

Highly-quality GaN films were deposited on diamond substrate using an electron cyclotron resonance plasma enhanced metal organic chemical vapor deposition system (ECR-PEMOCVD) at the proper temperature. The source of gallium is Trimethyl gallium (TMGa) and N2, and the influence of temperature on the properties of GaN films was investigated systematically by X-ray diffraction analysis (XRD), atomic force microscopy (AFM), room temperature photoluminescence (PL), respectively. The dense and uniformed GaN films with highly c-axis preferred orientation were successfully achieved on free-standing diamond substrates under optimized deposition temperature of 400 °C.