Free-standing Diamond Research Articles

The Study of Free-Standing Diamond Film SAWF

Surface Acoustic Wave Filter (SAWF) is widely applied in military and civil fields as Radar, Broadcast, Television, etc. The SAWF that the central operating frequency exceeds 1 GHz is one of the key elements in modern high frequency communication system. In this paper, on the free-standing diamond film and silicon wafer substrates, two kinds of SAWF are manufactured. Based on the same IDT structure that the interdigital width is 3μm, the center frequency of ZnO/diamond structures can reach to 1.03 GHz, while the ZnO/Si structures is 120 MHz. The result express that the SAWF on the base of diamond can work in high frequency mode, while the Insertion Loss is high, reach to 23dB.

Effect of Oxygen Partial Pressure on Properties of ZnO Films Deposited on Freestanding Diamond Films

Highly c-axis-oriented ZnO films were deposited successfully on the nucleation sides of freestanding diamond (FSD) films by the direct current (DC) magnetron sputtering method in an oxygen (O2) + argon (Ar) gas mixture. The effect of oxygen partial pressure on properties of ZnO films was investigated by X-ray diffraction (XRD). The results showed that when flux ratio of argon to oxygen was 1, the ZnO films had a better crystalline quality.

Properties of Li-Doped ZnO Films Deposited on Diamond Films

Li-doped zinc oxide (ZnO) films were deposited on nucleation side of freestanding diamond (FSD) films by the radio frequency magnetron sputtering method. The effect of oxygen partial pressure on structural, optical and electrical properties of the ZnO films was investigated by X-ray diffraction (XRD) Raman spectroscopy, semiconductor characterization system and Hall effect measurement system. The results showed that the introduction of oxygen as a reactive gas was helpful to improve the crystalline quality of Li-doped ZnO films.

Thin conductive diamond films as beam intensity monitors for soft x-ray beamlines

Quantitative analysis of X-ray absorption and dichroism data requires knowledge of the beamline photon flux during the measurements. We show that thin conductive (B-doped) diamond thin films can be an alternative to the widely used gold meshes for monitoring the beam intensity of soft X-ray beamlines in situ. Limited by the carbon extended x-ray absorption fine structure oscillations, the diamond films become applicable beginning from about 600 eV photon energy, where the important transition metal edges and the rare-earth edges are found. The 100 nm and 250 nm thick free-standing diamond films were grown and tested against standard gold meshes in real-life dichroism experiments performed at beamline ID08 of the European Synchrotron Radiation Facility, Grenoble, France. Quantitative agreement was found between the two experimental data sets. The films feature an extremely high transmission of about 90% and, at the same time, yield a sufficiently strong and clean reference signal. Furthermore, the thin films do not affect the shape of the transmitted beam. X-rays passing mesh-type monitors are subject to diffraction effects, which widen the beam and become particularly disturbing for small beamsizes in the micrometer range.

Comment s’organiser pour aborder rationnellement la révolution du Catalogue spécifique des actes de rééducation et réadaptation (CSARR) – Expérience de 841 lits et places de SSR pure player

High-quality polycrystalline diamond film has been extremely attractive to many researchers, since the maximum transition frequency (fT) and the maximum frequency of oscillation (fmax) of polycrystalline diamond electronic devices are comparable to those of single crystalline diamond devices. Besides large deposition area, DC arc jet CVD diamond films with high deposition rate and high quality are one choice for electronic device industrialization. Four inch free-standing diamond films were obtained by DC arc jet CVD using gas recycling mode with deposition rate of 14 μm/h. After treatment in hydrogen plasma under the same conditions for both the nucleation and growth sides, the conductivity difference between them was analyzed and clarified by characterizing the grain size, surface profile, crystalline quality and impurity content. The roughness of growth surface with the grain size about 400 nm increased from 0.869 nm to 8.406 nm after hydrogen plasma etching. As for the nucleation surface, the grain size was about 100 nm and the roughness increased from 0.31 nm to 3.739 nm. The XPS results showed that H-termination had been formed and energy band bent upwards. The nucleation and growth surfaces displayed the same magnitude of square resistance (Rs). The mobility and the sheet carrier concentration of the nucleation surface were 0.898 cm/V s and 1013/cm2 order of magnitude, respectively; while for growth surface, they were 20.2 cm/V s and 9.97 × 1011/cm2, respectively. The small grain size and much non-diamond carbon at grain boundary resulted in lower carrier mobility on the nucleation surface. The high concentration of impurity nitrogen may explain the low sheet carrier concentration on the growth surface. The maximum drain current density and the maximum transconductance (gm) for MESFET with gate length LG of 2 μm on H-terminated diamond growth surface was 22.5 mA/mm and 4 mS/mm, respectively. The device performance can be further improved by using diamond films with larger grains and optimizing device fabrication techniques.

Structural and Electrical Properties of High C-Orientation GaN Films on Diamond Substrates

Preferred orientation GaN films are deposited on freestanding thick diamond films by electron cyclotron resonance plasma enhanced metal organic chemical vapor deposition (ECR-PEMOCVD). The TMGa and N2 are applied as precursors and different N2 flux is used to achieve high quality GaN films. The influence of N2 flux on the properties of GaN films is systematically investigated by x-ray diffraction analysis (XRD), atomic force microscopy (AFM), electron probe microanalysis (EPMA) and Hall Effect Measurement (HL). The results show that the high quality GaN films deposited at the proper N2 flux display a fine structural and electrical property and the Ga/N atomic ratio plays an important role in the electrical property of GaN films.

Factors Affecting the Fracture Strength of Freestanding Diamond Films

As an emerging brand new type of engineering material for a variety of important high technology applications, the deep understanding of the mechanical behavior of freestanding diamond films has become an emergent task of vital importance. Unfortunately the mechanical behavior of this brand new material is not fully understood. Effects that affect the fracture strength are still not very clear except that the fracture strength of freestanding diamond films is only depended on the grain size (film thickness), and is insensitive to the microscopic defects, and the strength is considerably higher when the nucleation side is in tension than that when the growth side is in tension. However, this is not the full story. Based on the experimental date accumulated in USTB (University of Science and Technology Beijing) for high power dc arcjet diamond films, other factors that may affect the fracture strength of freestanding diamond films are discussed in detail. Effects of the quality of the diamond films, impurities (nitrogen, hydrogen, non-diamond carbon etc.), film morphology and texture, on fracture strength are discussed. Effects of the deposition parameters are explained. Advantages for small amount of nitrogen addition, and for the use of higher substrate temperatures in the increase in fracture strength are demonstrated, which have already been applied in the mass production of tool grade freestanding diamond films. It is hoped that the present paper will be helpful for those who wish to understand and use this brand new type of engineering material

Nucleation and growth surface conductivity of H-terminated diamond films prepared by DC arc jet CVD

High-quality polycrystalline diamond film has been extremely attractive to many researchers, since the maximum transition frequency (fT) and the maximum frequency of oscillation (fmax) of polycrystalline diamond electronic devices are comparable to those of single crystalline diamond devices. Besides large deposition area, DC arc jet CVD diamond films with high deposition rate and high quality are one choice for electronic device industrialization. Four inch free-standing diamond films were obtained by DC arc jet CVD using gas recycling mode with deposition rate of 14μm/h. After treatment in hydrogen plasma under the same conditions for both the nucleation and growth sides, the conductivity difference between them was analyzed and clarified by characterizing the grain size, surface profile, crystalline quality and impurity content. The roughness of growth surface with the grain size about 400nm increased from 0.869nm to 8.406nm after hydrogen plasma etching. As for the nucleation surface, the grain size was about 100nm and the roughness increased from 0.31nm to 3.739nm. The XPS results showed that H-termination had been formed and energy band bent upwards. The nucleation and growth surfaces displayed the same magnitude of square resistance (Rs). The mobility and the sheet carrier concentration of the nucleation surface were 0.898cm/Vs and 1013/cm2 order of magnitude, respectively; while for growth surface, they were 20.2cm/Vs and 9.97×1011/cm2, respectively. The small grain size and much non-diamond carbon at grain boundary resulted in lower carrier mobility on the nucleation surface. The high concentration of impurity nitrogen may explain the low sheet carrier concentration on the growth surface. The maximum drain current density and the maximum transconductance (gm) for MESFET with gate length LG of 2μm on H-terminated diamond growth surface was 22.5mA/mm and 4mS/mm, respectively. The device performance can be further improved by using diamond films with larger grains and optimizing device fabrication techniques.

Fabrication and characterizations of large homoepitaxial single crystal diamond grown by DC arc plasma jet CVD

Homoepitaxial diamond layers have been grown on HPHT synthetic type Ib (100) single crystal diamond plates brazed on a Φ65mm Mo holder using a commercial type 30kW dc arc plasma jet CVD with rotating arc root and operating at gas recycling mode with gas mixture of Ar/H2/CH4. The effects of substrate temperature and CH4/H2 ratio on the surface morphology, the growth rate and the quality of the synthesized diamond have been studied using optical microscopy and Raman spectroscopy. The growth rate up to 17.4μm/h has been obtained in the single crystal diamond sample deposited at 1000°C with CH4/H2=0.813%, exhibiting relatively smooth surface morphology with the typical feature of step-flow growth, without any non-epitaxial diamond crystallites. Under the optimum synthesis conditions, large size (7.5mm×7.5mm) polished freestanding single crystal diamond plate up to 1.03mm thickness has been produced and characterized by UV–vis–IR absorption, photoluminescence and Raman spectroscopy, as well as high-resolution X-ray diffraction. It was demonstrated that the quality of the as-grown CVD single crystal diamond was close to that of the natural type IIa single crystal diamond. It was shown that the epitaxial growth of high quality CVD single crystal diamonds could be achieved over the entire Φ65mm Mo holder on which a large quantity of CVD single crystal diamonds could be grown simultaneously. This is of economical importance in the development of high power DC arc plasma jet CVD systems for fabricating large size, high quality CVD single crystal diamond.

Growth of carbon nanotubes on spontaneously detached free standing diamond films and their field emission properties

Carbon nanotubes (CNTs) have been fabricated on free-standing microcrystalline diamond (FSD) films by hot filament chemical vapor deposition using Ni as catalyst. Micro Raman spectroscopy has been used as a primary technique to characterize the hybrid material, while electron microscopy and electron energy loss spectroscopy served as complementary characterization techniques. The fabricated material shows the presence of multiwall carbon nanotubes of diameters in the range of 10–15nm with a wall thickness of 5–6nm protruding from the free-standing microcrystalline diamond films of crystallite sizes ranging from 0.5 to 2.0μm. The CNT-FSD films show good field emission properties with low turn-on field, large field enhancement factor, and an excellent current stability over a period of 10days.

Fundamentals and Applications of Diamond

Dear colleagues, We are pleased to introduce you to this Special Issue of physica status solidi (a), focussed on fundamental and applied science and technology of diamond and nanodiamond materials. This special issue aims at providing a brief but hopefully broad overview of those topics that are today at the centre of the diamond community's current interests, such as diamond growth and doping, colour centres, nanophotonics, devices and electronics, bioapplications of diamond and nanodiamonds, surface properties, etc. The Feature Article by Dean Ho and Han Man 1 reviews the use of diamond materials in various nanomedicine applications, with a particular focus on therapeutics and drug delivery. They demonstrate that, in addition to their well-known properties such as biocompatibility and outstanding imaging capability, diamond nanoparticles are promising vehicles for drug delivery resulting in enhanced therapeutic efficacy and reduced premature drug release. This exciting field of applications is expected to grow rapidly with the full understating and control over the surface functionality of diamond nanomaterials. A relatively recent field of excitement for the diamond community is nanophotonics, an area of research that has rapidly evolved from the study of colour centres in bulk diamond to a plethora of phenomena and applications enabled by a precise nanostructuring of diamond single crystals. In their Feature Article, Birgit Hausmann and colleagues 2 from Harvard University review some of their recent contributions, such as the use of diamond nanowires to increase single photo collection from nitrogen-vacancy (NV) centres embedded in these nanostructures, or the coupling of single NV centres to planar resonators on-chip. This article highlights the outstanding challenges that still need to be addressed both in terms of fabrication nanotechnology, implantation of colour centres, and device design. The third Feature Article in this special issue, by Markus Dankerl and colleagues 3 of the Walter Schottky Institute, reviews solution-gated field effect transistors (SGFETs) based on surface-conductive single crystalline diamond with a focus on bioelectronic applications, in particular for the development of cell-transistor electronic interfaces. The article covers technology aspects, fundamental issues of the diamond/electrolyte interface, and finally reports on the successful recording of cell's action potentials using arrays of diamond SGFETs. In a special issue related to diamond, the most demanding challenge for the community, i.e. the growth of high quality diamond films and their doping, cannot be missing. In the Editor's Choice article, André Sartori and co-workers 4 provide a detailed study of in-situ boron doping during heteroepitaxial growth of diamond, a promising path towards the preparation of doped, high-quality, large area diamond thin films, which is a step that seems mandatory for the success of any of the potential applications of diamond in electronics. In another contribution, Jocelyn Achard et al. 5 explore the suitability of boron-doped freestanding diamond single crystals for vertical power electronic devices. In contrast to the most standard co-planar structures, the vertical configuration offers several advantages, at the expense of requiring high quality, heavily doped, thick films. The electrical characterization of diamond films as well as of diamond devices is still a very active topic in the diamond community, and is well represented in this special issue of physica status solidi (a). For instance, the contribution by Yuto Hoshino and colleagues 6 reports on the electrical properties of a novel lateral p–n junction diode fabricated by selective growth of phosphorous n+ diamond, aiming at avoiding some of the drawbacks of vertical p–n junctions. Two studies report on fundamental aspects of the electronic properties of charge carriers in diamond films. J. Barjon et al. 7 characterize homoepitaxial boron-doped diamond, grown with a very residual donor impurity concentration which results in low compensation and thus films exhibiting high conductivities. In their contribution, P. Ščajev et al. 8, provide an extensive study on the effect of the crystalline structure of diamond films on the carrier recombination and diffusivity. With this special issue of physica status solidi (a) we do not only aim at providing you with a selection of the currently most active fields of research related to the science, technology, and applications of diamond. In addition, we also hope that the contributions included in this issue can help to point out the challenges ahead while at the same time provide inspiration for your future work. Garching & Hasselt, September 10, 2012 Jose A. Garrido Miloš Nesládek Ken Haenen

Freestanding diamond films phototransistor

High quality freestanding diamond (FSD) films with smooth nucleation surfaces were grown by microwave plasma chemical vapor deposition (MPCVD) method. A p-type hydrogenated surface conductivity of FSD film was obtained by using hydrogen plasma treatment. The annealing process in vacuum on the p-type behavior of FSD nucleation surfaces was investigated by Hall effect measurement. H-terminated diamond phototransistors were fabricated and the results suggest that they may be ideally suited for ultraviolet (UV) switching applications.

Evaluation of freestanding boron-doped diamond grown by chemical vapour deposition as substrates for vertical power electronic devices

In this study, 4 × 4 mm2 freestanding boron-doped diamond single crystals with thickness up to 260 μm have been fabricated by plasma assisted chemical vapour deposition. The boron concentrations measured by secondary ion mass spectroscopy were 1018 to 1020 cm−3 which is in a good agreement with the values calculated from Fourier transform infrared spectroscopy analysis, thus indicating that almost all incorporated boron is electrically active. The dependence of lattice parameters and crystal mosaicity on boron concentrations have also been extracted from high resolution x-ray diffraction experiments on (004) planes. The widths of x-ray rocking curves have globally shown the high quality of the material despite a substantial broadening of the peak, indicating a decrease of structural quality with increasing boron doping levels. Finally, the suitability of these crystals for the development of vertical power electronic devices has been confirmed by four-point probe measurements from which electrical resistivities as low as 0.26 Ω cm have been obtained.

A study of high-quality freestanding diamond films grown by MPCVD

The fabrication process of high-quality freestanding diamond films grown by Microwave Plasma Chemical Vapor Deposition (MPCVD) was studied. Under the optimal condition, freestanding diamond films 55mm in diameter with a thickness up to 1mm were fabricated, showing an excellent crystalline structure as examined from Raman and X-Ray Diffraction (XRD) spectra. For most processing conditions, including substrate temperatures varied from 800 to 1050°C, the films were found in a [111] preferential texture, whereas [220] and [001] film textures occurred in some special cases. Optical measurements of one side polished diamond films showed a cutoff wavelength 225nm, and a transmission ≥70% at λ≥2.5μm.

A Review on Mechanical Properties of Freestanding Diamond Films

As an emerging brand new type of engineering material for a variety of important high technology applications, the deep understanding of the mechanical behavior of freestanding diamond films has become an emergent task of vital importance. Of the many deposition methods dc arc plasma jet has been regarded as the most promising technique for large area high quality and low cost production of freestanding diamond films. In the present paper, recent progress in mechanical properties of freestanding diamond films mainly by high power dc arc plasma jet with rotating arc root and gas recycling is reviewed. Testing methods for fracture strength and fracture toughness are discussed. Experimental data are presented and compared to that by MWCVD. Dc arcjet diamond films start to oxidize at about 700°C, however, oxidation up to 800°C for 10 min does not affect the fracture strength. Fracture mechanism is discussed. The strange mechanical behavior of freestanding diamond films is explained. It is surprising that CVD diamond film is such a kind of material which is strong, but full of different size of defects. It is hoped that the present paper will be helpful for those who wish to understand and use this brand new type of engineering material.

Growth of High Quality Znmgo Films on Diamond Substrates

Abstract ZnMgO films were prepared at room temperature on freestanding diamond (FSD) substrates by co-sputtering. The Mg content was controlled by varying RF sputtering power of MgO and the effects of Mg contents on the properties of ZnMgO films were investigated. The results showed that the (0002) peak of ZnMgO shifted from 34.5° to 35.6° with the increasing sputtering power of MgO target. The UV-visible and PL spetra of ZnMgO films revealed that the bandgap of ZnMgO was approximately linear related to the sputtering power of MgO target.

Freestanding single crystal chemical vapor deposited diamond films produced using a lift-off method: Response to α-particles from 241Am and crystallinity

Thick (∼100μm) undoped diamond films were grown homoepitaxially on single crystal (SC) diamond substrates by microwave plasma chemical vapor deposition (CVD). To form a freestanding SC diamond film (plate), the substrate was pre-ion-implanted with high-energy ion beams before the film growth, and after the thick-film deposition, the substrate was eliminated using a lift-off method, resulting in fabrication of a SC CVD diamond plate. Two samples were prepared; sample 1 was grown on a (001) oriented, nitrogen doped CVD SC diamond at ∼900°C with the input microwave power of 1.7kW, while sample 2 was grown on a (001) oriented, high-pressure high-temperature synthesized type-Ib SC diamond at ∼900°C with the input microwave power of 1.25kW. The formed SC plates have high optical transparencies, indicating no remarkable optical absorptions seen in the wavelength from ultraviolet to near infrared. The photoluminescence (PL) spectra of both samples show strong free exciton FE peaks, while in sample 2 relatively strong optical emissions corresponding to nitrogen related centers were observed in the visible region. After the metal electrodes were formed on both faces of the SC diamond plate to fabricate a sandwich-type diamond particle detector, the energy spectra of 5.486MeV α-particles from 241Am were measured. The charge collection efficiencies (CCEs) of sample 1 were CCE=98% for a hole transport and CCE=89% for an electron transport, respectively, while CCEs of sample 2 were CCE=80% for a hole transport and CCE=78% for an electron transport, respectively. These results indicate that both holes and electrons in sample 2 were trapped much more than those in sample 1. Possible candidates of carrier capture centers are nitrogen and/or nitrogen-vacancy centers observed in PL, nonradiative defect (complex) centers, extended defects such as threading dislocations observed in micrographs taken with polarizers. The different growth conditions most likely affected crystallinity and responses to α-particles of the samples.

Effect of buffer layer on the structural and morphological properties of GaN films grown with ECR-PEMOCVD

Prefer-oriented GaN films are deposited on freestanding thick diamond films by electron cyclotron resonance plasma enhanced metal organic chemical vapor deposition (ECR-PEMOCVD) at various buffer layers. Trimethyl gallium (TMGa) and N 2 are applied as precursors and various buffer layers are used to achieve high quality GaN films. The influence of buffer layers process on the properties of GaN films is systematically investigated by reflection high energy electron diffraction (RHEED), X-ray diffraction analysis (XRD) and atomic force microscopy (AFM). The results show that the high quality GaN films deposited at proper buffer layer process display the fine structural and morphological properties.

Freestanding Ultrananocrystalline Diamond Films with Homojunction Insulating Layer on Conducting Layer and Their High Electron Field Emission Properties

Freestanding ultrananocrystalline diamond (UNCD) films with homojunction insulating layer in situ grown on a conducting layer showed superior electron field emission (EFE) properties. The insulating layer of the films contains large dendrite type grains (400-600 nm in size), whereas the conducting layer contains nanosize equi-axed grains (5-20 nm in size) separated by grain boundaries of about 0.5-1 nm in width. The conducting layer possesses n-type (or semimetallic) conductivity of about 5.6 × 10(-3) (Ω cm)(-1), with sheet carrier concentration of about 1.4 × 10(12) cm(-2), which is ascribed to in situ doping of Li-species from LiNbO(3) substrates during growth of the films. The conducting layer intimately contacts the bottom electrodes (Cu-foil) by without forming the Schottky barrier, form homojunction with the insulating layer that facilitates injection of electrons into conduction band of diamond, and readily field emitted at low applied field. The EFE of freestanding UNCD films could be turned on at a low field of E(0) = 10.0 V/μm, attaining EFE current density of 0.2 mA/cm(2) at an applied field of 18.0 V/μm, which is superior to the EFE properties of UNCD films grown on Si substrates with the same chemical vapor deposition (CVD) process. Such an observation reveals the importance in the formation of homojunction on enhancing the EFE properties of materials. The large grain granular structure of the freestanding UNCD films is more robust against harsh environment and shows high potential toward diamond based electronic applications.

Effects of Annealing Treatment and Buffer Layer on Properties of ZnMgO Films Prepared on Diamond Substrates

ZnMgO films were prepared at room temperature on freestanding diamond (FSD) substrates with and without ZnO buffer layers by radio-frequency (RF) reactive magnetron sputtering method. The effects of annealing treatment and ZnO buffer layers on the structural, optical, and electrical properties of the ZnMgO films were studied by X-ray diffraction (XRD), UV-visible spectrophotometer, and electrical measurements. The experimental results suggested that the annealing treatment and buffer layer were helpful to improve the crystalline quality of ZnMgO/diamond heteroepitaxial films.