Yoshiaki Mokuno

Fabrication of 1 Inch Mosaic Crystal Diamond Wafers

We fabricated so-called mosaic single-crystal-diamond (SCD) wafers that consist of SCD sub-crystals with identical characteristics. These sub-crystal clones were obtained from a SCD seed crystal by repeating the lift-off process using ion implantation. We found that the junctions between the cloned sub-crystals were smoothly covered and no abnormal crystal growth occurred along the junctions. Therefore, the lift-off process can be applied to the production of freestanding SCD wafers with the same size. Based on these findings, we have succeeded in synthesizing 1 in. mosaic diamond wafers.

A 2-in. mosaic wafer made of a single-crystal diamond

We synthesized a mosaic diamond wafer 2 in. in size (40 × 60 mm2), which consisted of 24 single-crystal diamond (SCD) plates 10 × 10 mm2 in area, by using microwave plasma chemical vapor deposition. Even by using a cloning technique, cracking frequently occurred and the non-uniformity was remarkable for wafers that were larger than 1 in. in size. This has not been observed in smaller samples before. Appropriate crystallographic directions could avoid the cracking and is one of the predominant factors in fabricating large area SCD wafers. Comparison with numerical simulations highlighted the importance of uniformity of the substrate temperature distribution on the uniformity of the growth.

Preliminary experimental results on mapping of the elemental distribution of the organic tissues surrounding titanium-alloy implants

Abstract Titanium alloy (Ti 6Al 4V) is one of the most common materials which are used as orthopaedic and dental implants. In this paper, preliminary experimental results are presented on the measurement of distribution (mapping of X-ray intensities) of the constituent elements of the tissues as well as the released impurity elements in the organic tissues around a Ti-alloy implant. Micro-beam PIXE was carried out for the case of a Ti 6Al 4V implant which was inserted in tibial metaphysis of a rabbit for 12 weeks, using a Nissin high voltage accelerator. Maps of Ca and P clearly show the situation of bone formation and Ca concentration with respect to implant surface. The maps of Kα intensities of Ti and Al are also obtained to investigate the possible release of these elements. In conclusion, application of micro-beam PIXE to mapping of the constituent and impurity elements around implants can be used as a powerful tool in clarifying the mechamism of osseo-integration, and release of impurity ions from the implants.

Formation of Crystalline SiC Buried Layer by High-Dose Implantation of MeV Carbon Ions at High Temperature

A buried layer of crystalline SiC in silicon wafer is synthesized by 1.5 MeV C+ implantation at a dose of 1.5×1018 ions/cm2 at a high temperature of 880°C. The infrared absorption spectrum and the X-ray diffraction pattern of this sample show formation of 3C-type SiC crystal. The pole figures of X-ray diffraction show that crystallographic orientation of the SiC buried layer is aligned along the lattice of the Si substrate, that is, topotaxial internal growth of crystalline SiC occurs in a single crystal of Si during the high-temperature ion implantation.

Simplified description of microwave plasma discharge for chemical vapor deposition of diamond

A fluid model to prescribe microwave plasma is proposed. The conservation equations for electron are reduced to only one differential equation. Therefore, the computational cost is also reduced as small as possible. One may extend functions of existing program for vacuum field analysis to microwave plasma simulator by coupling this differential equation with Maxwell equations. While the model is quite simple, this model can prescribe distributions of electron temperature as well as the number density, whereas effects of inelastic collisions with ions and neutrals are taken into account. Test calculation is carried out in three dimensional system and well reproduces experimental observation and prediction obtained by other model.

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.

High energy resolution PIXE with high efficiency using the heavy ion microbeam

Abstract An X-ray crystal spectrometer using a position sensitive proportional counter combined with tandem microbeam line at Osaka National Research Institute have been developed. This system realizes high energy resolution PIXE analysis using a heavy ion microbeam (E

MICROPROBE PIXE ANALYSIS OF ALUMINIUM IN THE BRAINS OF PATIENTS WITH ALZHEIMER'S DISEASE

To investigate the cause of Alzheimers disease (senile dementia), we examined aluminium (Al) in the rat liver, and in the brains (hippocampus) of Alzheimers disease patients using heavy ion (5 MeV Si3+) microprobe and proton (2 MeV) microprobe PIXE analysis. Heavy ion microprobes (3 MeV Si2+) have several times higher sensitivity for Al detection than 2 MeV proton microprobes. (1) In the rat liver, Al was detected in the cell nuclei, where phosphorus (P) was most densely distributed. (2) We also demonstrated Al in the cell nuclei isolated from Alzheimers disease brains using heavy ion (5 MeV Si3+) microprobes. Al spectra were detected using 2 MeV proton microprobes in the isolated brain cell nuclei. Al could not be observed in areas where P was present in relatively small amounts, or was absent. Our results indicate that Alzheimers disease is caused by irreversible accumulation of Al in the nuclei of brain cells.

Large Single Crystal Diamond Plates Produced by Microwave Plasma CVD

Recent developments in producing large single crystal CVD diamond plates are reviewed. The developments consist of synthesis of large single crystal diamond and production of single crystal diamond plates from the bulk diamond by the lift-off process. Combining these developments, half-inch single crystal CVD diamond plates have been successfully produced.

Formation of hydrogenated amorphous carbon films by plasma based ion implantation system applying RF and negative high voltage pulses through single feedthrough

Abstract A plasma-based ion implantation system that can apply both radio frequency wave (RF) and negative high voltage pulses through single feedthrough has been developed. The system was successfully applied to the formation of hydrogenated amorphous carbon (a-C:H) thin films. The a-C:H films were deposited by capacitively coupled continuous wave (CW) RF discharge of pure methane (CH 4 ) or mixture of CH 4 and Ar. Ion implantation by negative high voltage pulse bias was also demonstrated under the pulsed RF discharge of CH 4 . Mechanical properties of the deposited a-C:H films were measured by nano indentation. Maximum hardness and elastic modulus of the film was 23 and 220 GPa, respectively.