Highly oriented diamond (HOD) films were grown at a high growth rate on (100) silicon substrates by microwave plasma chemical vapor deposition (MPCVD), following the standard bias-enhanced nucleation (BEN) process. The growth rate and diamond quality were investigated as a function of methane concentration in hydrogen (2-6%), and N2/CH4 ratio (0 to 0.12). A four-fold increase in the growth rate of HOD films and a three times faster expansion and coalescence of (100) facets was observed within the above process window. The films with the best quality were grown under an N2/CH4 ratio of 0.08 at methane concentration of 3.5%. The ratio of x-ray intensity between the first order twins and {111} poles was only 1%. A detailed study of the crystalline quality and phase purity as a function of methane concentration and nitrogen addition is presented.

Diamond is valued mainly as a symbol of power and value (the girl's best friend) and as a solution to many materials processing problems (the engineer's best friend). The 1950s saw both striking developments in diamond synthesis and the beginnings of the rise of silicon as the semiconductor of choice. Since then, silicon has transformed the world. Diamond has reinforced its known roles, and found niches that exploit its special qualities. It is also one of the carbon materials that, in combination, have a variety of superb properties. Could there be bigger opportunities for diamond, more than mere niches, arising from the major social needs: the life sciences, the information technologies, energy, and perhaps others. I attempt to identify areas that might develop formidably.

Severe environmental tolerability is the prime factor in the development of novel space materials exhibiting excellent physical properties accompanied by lightweight, reusability, and multifunctional capabilities. Diamond is known for its reputation being radiation hard besides a range of outstanding properties (electronic, optical, mechanical, and chemical) and hence it is preferable in harsh environments. Carbon nanotubes are also of great interest because of several unsurpassable physical properties and it needs to be shown that they are physically stable and structurally unaltered when subjected to irradiation. Therefore, a family of novel nanocarbons (nanodiamond and nanotubes) films deposited by microwave plasma-assisted chemical vapor deposition (MWCVD) technique was subjected to gamma radiation (1, 5, and 20 Mrads) and to medium energy electron-beam irradiation to study their effects on the microscopic structure and corresponding physical properties to establish property-structure correlation. Microstructural and physical properties characterizations prior to and post-irradiation include scanning electron microscopy (SEM), atomic force microscopy (AFM), Raman spectroscopy (RS), X-ray diffraction (XRD), field emission (FE), and high-resolution transmission electron microscopy (HRTEM). Dramatic improvement in the field emission properties for microcrystalline diamond and relatively small but systematic behavior for nanocrystalline diamond with increasing radiation dose is discussed in terms of the critical role of defects which tends to form clusters. The results also indicate that nanocrystalline carbon tends to reach a state of damage saturation they are discussed in terms of sp3, sp2+δ ←→ sp2 C inter-conversion. The effects of electron beam irradiation on the carbon nanotube show that multi¡Vwalled nanotubes tend to be relatively more robust than those of single–walled. This is because increased exposure on an individual bundle of single-walled nanotubes promoted graphitization, pinching, and cross-linking similar to polymers forming intra-molecular junction (IMJ) within the area of electron beam focus, possibly through aggregates of amorphous carbon. Formation of novel nanostructures (nano– ring and helix– V like) due to irradiation is also observed. These studies gleam on the dynamics of nano-manufacturing and a regime of possible relevance to these materials for a) short-term space missions; b) radiation hard programmable logic circuits; and c) radiation pressure sensors.

Transient photocurrent measurements in the Time-of-Flight (TOF) configuration were used to study the electrical transport in single crystalline diamond layers using a Nd:YAG - pumped OPO (2.7 nsec) laser pulse excitation source working at a wavelength of ∼ 218 nm. The amount of collected charge was measured and the hole and electron drift mobilities were determined at room temperature for natural IIa diamond and intrinsic single crystalline CVD diamond samples. A variation of the laser intensity over several orders of magnitude enabled switching between the so called “small signal TOF” and “space charge limited current” (SCLC) modes. Experiments were done using electrical fields in the range of 0.05-1.2 V/μm.

A diamond based insulated gate bipolar transistor is incorporated into a two-dimensional device simulator (MEDICI) to examine the current gain (β) and potential distribution across the device. Initially, work has focused on an important component of IGBT structure, the PNP bipolar transistor, which has been simulated and is reported upon in this paper. Empirical parameters for emitter and collector regions were used. Various carrier concentrations for base region were used to optimize the simulation. It was found that decreasing the thickness of base region leads to an increase in current gain. A buffer layer is needed to prevent the punch-through at low carrier concentration in the base region. Various approaches of increasing the current gain are also discussed in this paper.

The methane effects on nucleation and growth of diamond during bias enhanced nucleation treatment have been studied on 3C-SiC (100) surfaces. At low methane concentration of 1%, no diamond nucleation was observed, whether at 3 %, nucleation density values as high as 4×1010/cm2 were reached. A further increase of the methane concentration up to 5% induces a significant enhancement of the diamond nucleation density that was observed only slightly higher at 7×1010/cm2. Moreover, the Field Emission Gun Scanning Electron Microscopy (FEG-SEM) pictures well emphasized that the methane content affects both the nucleation and growth mechanisms.

DNA sensitive field-effect transistors (DNA-FET) have been realized using single crystalline diamond grown by plasma-enhanced chemical vapor deposition (CVD). To bond DNA to diamond, amine linker-molecules are covalently attached by photochemical means to H-terminated diamond surfaces. Using hetero-bifunctional cross-linker and thiol-modified single-strand (ss) marker DNA, the gate of diamond FETs is modified to sense hybridization of DNA, forming double-strand (ds) DNA molecules on the gate. The density of DNA bonded to diamond is varied between 1012 and 1013 cm−2 to explore sensitivity enhancements by reduction of the DNA molecule density. DNA-FET characterization in 1M NaCl buffer solution (pH 7.2) reveal gate-potential threshold shifts by hybridization in the range 30 mV to 100 mV with decreasing DNA density. The variation is discussed based on the transfer doping model which predicts with decreasing pH increasing hole-densities in the surface conductive layer of diamond.

Boron-doped diamond film coated titanium (Ti/BDD) becomes increasingly attractive because of the combined properties of these two unique materials. The challenge for the composite material is the stability especially when it is used as an electrode. In order to meet this challenge, two temperature (2-temp) staged hot filament chemical vapor deposition method was employed in this study. The accelerated working life time was significantly increased to 804 hours for the 2-temp electrode, compared with 244 hours for the diamond film electrode fabricated under one temperature (1-temp) stage method. With the characterization of micro-Raman, XRD, and cross-sectional SEM, a multilayer of Ti/TiC/(Diamond+Amorphous Carbon)/Diamond can be found in the 2-temp sample and the structure of Ti/TiC/Diamond in the 1-temp sample. There was less void space observed in the interlayer of 2-temp sample. The multi-layered compact structure plays an important role in improving the adhesion of diamond film to the titanium substrate which in turn increases the electrode working life time by over 3 times.

Electric field of less than 5 V/μm is enough to extract electrons from diamond, whereas field of one to two orders of magnitude higher is needed to extract electrons from metal emitter tips. Despite such low-threshold field, the difficulty in clarification of electron emission mechanism is the factor preventing diamond from being used in a practical use. Quite a few numbers of possible mechanisms were proposed to better understand the origin and properties of the observed emission. Most of these mechanisms were, however, based on the conventional I (Emission current)-V (Anode voltage) characteristics. Energy distribution of the field-emitted electrons is essential in direct clarification of the mechanism. In this study, combined XPS/UPS/FES system was used to characterize the electron emission mechanism of doped chemical vapor deposited (CVD) diamond. The results indicated successful observation of the origin of field-emitted electrons from doped CVD diamond comparison with natural diamond, used as a reference.

Diamond like carbon (DLC) films were deposited on Si and then patterned to form 40 nm features as nanoimprint templates. A plasma enhanced chemical vapor deposition (PECVD) system with CH4 precursor was used to deposit DLC films on Si and quartz substrates. Then these films were characterized using Raman spectroscopy, atomic force microscopy (AFM), nanoindentation, and contact angle measurement. By varying the RF power and pressure of the PECVD, DLC films with good uniformity, smooth surfaces (<0.2 nm RMS), low surface energy (∼40 mJ/m2), and high hardness (∼22 GPa) were achieved. Nanoimprint lithography and liftoff process were used to pattern Cr mask on DLC films. An inductively coupled plasma (ICP) etching process was performed with CF4 to transfer the patterns into the DLC films to form nanostructured template for nanoimprint. Water contact angles on the patterned DLC templates were measured and it was stable at about 70° under thermal annealing at 180 °C for more than 12 hours. With these DLC templates, UV and reversal UV nanoimprint lithography were carried out on SU-8 at typical imprint conditions and then the fidelity of pattern-transfer was investigated. These experimental results indicate that DLC is an excellent material for nanoimprint templates because of its high wear resistance, robust low surface energy, UV transparency, and ease of patterning.

Ultrananocrystalline diamond (UNCD) films have been deposited using hot filament chemical vapour deposition using Ar/CH4/H2 gas mixtures plus additions of B2H6 in an attempt to make p-type semiconducting films. With increasing additions of B2H6 from 0 to 40,000 ppm with respect to C, the film growth rate was found to decrease substantially, whilst the individual grain sizes increased from nm to μm. With 40,000 ppm of B2H6, crystals of boric oxide were found on the substrate surface, which slowly hydrolysed to boric acid on exposure to air. These results are rationalised using a model for UNCD growth based on competition for surface radical sites between CH3 and C atoms.

Electrochemical deposition of amorphous carbon (a-C) film is performed by applying a direct-current potential to substrates immersed in methanol. Both scanning electron microscopy and Raman results indicate that smooth and homogeneous a-C films are grown on specific substrate materials such as Si, Ti, and Al. Field emission measurements demonstrate excellent emission properties such as threshold fields lower than 5 V/μm. Field enhancement factors are estimated to be 1300–1500; these are attributed to local field enhancements around sp2 carbon clusters that are embedded in the a-C films. Emission properties of a-C films grown on Si exhibit a current saturation under higher applied fields. These saturation behaviors are explained by an effect of a potential barrier formed at the interface between a-C films and substrates. Since the interface barrier is reduced by formation of the Ti interfacial layer, an approach to use carbide formation at the interface is verified as useful to improve the emission properties of a-C films.

Diamond-like carbon (DLC) films were synthesized using pulsed plasma sputtering deposition techniques. Microscope and Raman scattering techniques were used to study the effects of bias voltages on the properties of diamond-like carbon films. With d.c. bias voltage up to 1000V, the smooth and thick DLC films together with a few nanoparticles were obtained. An increase of the d.c. bias voltage up to 2000V yielded thicker DLC films but its surface became slightly rough and size of particles became large. The crystalline properties of these particles were studied. A tiny diamond peak from Raman spectrum was also observed.

We study electronic and geometrical properties of B-doped diamond in the framework of the density functional theory. The systems studied are simple-cubic (sc) BC7 and face-centered-cubic (fcc) BC15 and B2C14. In the case of BC7, we also study the effect of the tetragonal and rhombohedral distortions of the unit cell to be introduced to the B-doped diamond grown homoepitaxially on the diamond (100) and (111) films, respectively. In the case of fcc B2C14, on the other hand, the inhomogeneous doping effects are discussed from the viewpoint of the energetics. It is confirmed that in the homogeneous doping case, B doping gives rise to hole doping into the valence band, which should be responsible for the metallic and superconducting transport properties of the material. In the case of the inhomogeneous doping, two B atoms on the first-nearest neighbor sites as well as on the second-nearest neighbor sites are found to lower the Fermi-level density of states, which is unfavorable for superconductivity. Although tetragonal and rhombohedral distortions are found to give a sizable change to the electronic states near the Fermi level, the value of the Fermi-level density of states itself is found to remain almost unchanged. Finally, in order to study the fundamental-gap value of the heavily B-doped diamond, we study the electronic structure of the sc BC7 and fcc BC15 in the GW approximation. A large reduction of the gap value upon doping is confirmed.

A recent experiment performed by S. S. Afshar [reviewed in M. Chown, New Scientist183, 30 (2004)] has been interpreted as a possible violation of the complementarity principle of quantum mechanics. Starting from a single-photon wavefront-splitting interference experiment, we propose a new scheme for Afshar's experiment, and we show that Afshar's interpretation is incorrect. Furthermore, this design is well suited to illustrate the complementarity inequality in the interesting intermediate regimes with partial fringe visibility and partial which-path information.

n-Type doping of diamond is one of the most important issues for electronic application of diamond. Phosphorus is the best candidate as an n-type dopant at this moment. We have succeeded to grow high quality phosphorus doped diamond thin films on {111} diamond substrates. Although the ionization energy of phosphorus donor is large (0.57 eV), the n-type conductivity is clearly observed by Hall measurements. The Hall mobility is as high as 660 cm2/V-sec at room temperature. In this paper, current status of n-type diamond research are mentioned mainly focused on the growth of high mobility n-type diamond and its electrical properties. The Hall measurements performed in a wide temperature range gives detailed information about the n-type conductivity nature of phosphorus doped diamond.

In the continuing thrust to extend Moore's law, silicon is beginning to confront several issues that require innovative materials solutions to increase transistor and interconnect speeds while dealing with the increasing thermal loads of advanced microprocessors. The unsurpassed thermal and mechanical properties of diamond can be profitably exploited to enhance the performance characteristics of silicon based circuits. The discussion focuses primarily on the integration of diamond with silicon for the manufacture of silicon on diamond (SOD) wafers for spreading heat from hot spots in microprocessors. Other interesting property combinations are also presented as food for thought regarding other possible enhancements to silicon device performance. Recent data and prognosis for the future will be presented.

The near-frictionless carbon (NFC) thin films grown at Argonne National Lab are excellent candidates for mitigating friction and wear issues in rotating and sliding MEMS applications. In this study, NFC films with Si/Si3N4 substrates were tested with static and CSM (continuous stiffness measurement) nanoindentation methods. Furthermore, the same NFC films with 900 nm thickness were fabricated into freestanding structures for the membrane deflection experiment (MDE). The Young's modulus obtained from these three methods were compared and contrasted. The E values obtained from the nanoindentation methods were nearly constant when the indent depth was less than 100 nm (1/10 of the film thickness). Both the static and CSM indentation data indicated a clear increasing trend of the Young's modulus with the indent depth until the elastic response from the substrate started to dominate the values (depth larger than 800 nm). The average modulus obtained from static and CSM nanoindentations were 49.5 ± 4.3 GPa and 50.2 ± 1.8 GPa for as-deposited films, respectively. The values changed to 46.9 ± 5.4 GPa and 46.8 ± 2.9 GPa after microfabrication processing. The larger standard deviation values indicated the affect of the increased surface roughness to the indentation tests. The E value determined from MDE tests was 35.1 ± 2.3 GPa, which was measurably smaller those from the indentation tests. As the AFM analysis showed little/no pile-up during indentation, the difference might come from the residual stress relief, which influences the measurement, when the NFC membranes were released from the substrate.

Freestanding and suspended single crystal diamond devices, micro disks and beam structures, have been fabricated on single crystal diamond substrates using a lift-off process employing ion implantation followed by electrochemical etching. The ion implantation created subsurface damage in the diamond while the top surface was sufficiently undamaged that a subsequent homo-epitaxial diamond layer could be grown by chemical vapor deposition (CVD). After the CVD growth and patterning by lithography and reactive ion etching, the underlying damage layer was etched/removed by an electrochemical etch. Different implant ions and energies were simulated and tested to optimize the process. The electrochemical etching process was monitored by an optical video technique. The electrochemical etching process used both ac and dc applied electrical potentials. Photoluminescence (PL), Raman spectra, and polarized light transmission microscopy have been used to characterize the implanted substrate and lift-off films. AFM has been used to monitor the surface changes after mechanical polishing, ion implantation, CVD growth and the lift-off process. This research has revealed that the parameters of ion implantation (implant species, dose and energy) dramatically affect the lift-off process. The etching mechanism and critical parameters are discussed in this work. PL spectroscopy indicated differences between the uppermost layers of the homo-epitaxial film and the lift-off interface. Three principal classes of defects have been observed: growth defects inherent in the diamond substrates (type Ib, HPHT), defects induced by the polishing process and associated stress, and point defects.

Nanocrystalline diamond films have generated substantial interest in recent years due to their low cost, extreme properties and wide application arena. Diamond is chemically inert, has a wide electrochemical window and is stable in numerous harsh environments. Nanocrystalline diamond has the advantage of being readily grown on a variety of substrates at very low thickness, resulting in smooth conformal coatings with high transparency. These films can be doped from highly insulating to metallically conductive and at very high concentrations become superconducting.