Chii-Ruey Lin

Origins of the residual stress in CVD diamond films

Abstract Diamond films were deposited on (100) Si wafer, WC (5%Co) and quartz substrate materials by a microwave plasma chemical vapor deposition (CVD) system. The effects of deposition and substrate conditions on residual stress of the films were systematically investigated. The films were characterized by scanning electron microscopy, X-ray diffraction, Raman and indentation adhesion testing. The film structure including its non-diamond carbon content, crystal size, texture coefficient, film thickness and surface roughness were examined. The results show that the residual stress of the films is a function of the surface pretreatment, in addition to the substrate material and deposition conditions. The origins of the residual stress are mainly the thermal stress and the intrinsic stress. The intrinsic stress is mainly from the effect of the non-diamond carbon content in the diamond crystals, not at the crystal boundaries. A greater non-diamond carbon content in diamond crystals results in a greater residual stress. The texture of the films has no significant effect on the residual stress. A low compressive residual stress on Si wafer is beneficial to the adhesion of the film.

High-gain photoconductivity in semiconducting InN nanowires

We report on the photoconductivity study of the individual infrared-absorbing indium nitride (InN) nanowires. Temperature-dependent dark conductivity measurement indicates the semiconducting transport behavior of these InN nanowires. An enhanced photosensitivity from 0.3 to 14 is observed by lowering the temperature from 300to10K. A calculated ultrahigh photoconductive gain at around 8×107 at room temperature is obtained from the low-bandgap nitride nanowire under 808nm excitation.

Improvement in adhesion of diamond films on cemented WC substrate with Ti-Si interlayers

Abstract Diamond films were deposited on the cemented WC+(3–5)% Co substrates by a microwave plasma chemical vapor deposition system. The substrates were pretreated with various processing steps before diamond deposition, including: polishing, etching for Co removal, Ti coating by DC sputter, and amorphous Si coating by E-gun. The residual stress of the films was determined by both Raman shift and low incident beam angle X-ray diffraction (LIBAD) methods. The adhesion of the films was evaluated by indentation adhesion testing. The film morphology and film–substrate interface structure were examined by SEM and Auger electron spectroscopy, respectively. The results show that Ti–Si can be a good interlayer to improve film adhesion and inhibit diffusion of Co to the substrate surface on diamond nucleation. This is due to the formation of strong TiC and SiC bonding to enhance film adhesion; Si acts as a promoter for diamond nucleation, and the residual stress with application of interlayer is much lower than that interlayer-free. The results also show the existence of an optimum Ti thickness for the best film adhesion.

High adhesion and quality diamond films on steel substrate

Abstract A process to deposit a diamond coating on steel substrates has been successfully developed. It includes the electroplating of nickel by using an electrolyte dispersed with micro-diamonds, and then a diamond deposition through a microwave plasma chemical vapor deposition system. The diamond films were characterized by Raman and CL spectroscopy, XRD, SEM and SEM line scanning. The results show a high diamond crystal quality, low residual stress (about 0.67 GPa) and high nucleation density. The adhesion of the films was evaluated by a cutting test and an interface examination. The results show that the retentivity of the diamond grits in the films after the cutting test is much better than that in the commercial electroformed diamond tools. The advantages of the process are: (1) the formation of nickel-carbon-hydrogen alloys to enhance diamond nucleation and growth, (2) the micro-diamonds acting as the seeds for diamond nucleation and growth, and forming effective mechanical interlocking with the nickel interlayer, and (3) the formation of good diffusion bonding of the nickel interlayer with the steel substrate.

A Wireless Sensor Enabled by Wireless Power

Through harvesting energy by wireless charging and delivering data by wireless communication, this study proposes the concept of a wireless sensor enabled by wireless power (WPWS) and reports the fabrication of a prototype for functional tests. One WPWS node consists of wireless power module and sensor module with different chip-type sensors. Its main feature is the dual antenna structure. Following RFID system architecture, a power harvesting antenna was designed to gather power from a standard reader working in the 915 MHz band. Referring to the Modbus protocol, the other wireless communication antenna was integrated on a node to send sensor data in parallel. The dual antenna structure integrates both the advantages of an RFID system and a wireless sensor. Using a standard UHF RFID reader, WPWS can be enabled in a distributed area with a diameter up to 4 m. Working status is similar to that of a passive tag, except that a tag can only be queried statically, while the WPWS can send dynamic data from the sensors. The function is the same as a wireless sensor node. Different WPWSs equipped with temperature and humidity, optical and airflow velocity sensors are tested in this study. All sensors can send back detection data within 8 s. The accuracy is within 8% deviation compared with laboratory equipment. A wireless sensor network enabled by wireless power should be a totally wireless sensor network using WPWS. However, distributed WPWSs only can form a star topology, the simplest topology for constructing a sensor network. Because of shielding effects, it is difficult to apply other complex topologies. Despite this limitation, WPWS still can be used to extend sensor network applications in hazardous environments. Further research is needed to improve WPWS to realize a totally wireless sensor network.

Synthesis of highly transparent ultrananocrystalline diamond films from a low- pressure, low-temperature focused microwave plasma jet

This paper describes a new low-temperature process underlying the synthesis of highly transparent ultrananocrystalline diamond [UNCD] films by low-pressure and unheated microwave plasma jet-enhanced chemical vapor deposition with Ar-1%CH4-10%H2 gas chemistry. The unique low-pressure/low-temperature [LPLT] plasma jet-enhanced growth even with added H2 and unheated substrates yields UNCD films similar to those prepared by plasma-enhanced growth without addition of H2 and heating procedure. This is due to the focused plasma jet which effectively compensated for the sluggish kinetics associated with LPLT growth. The effects of pressure on UNCD film synthesis from the microwave plasma jet were systematically investigated. The results indicated that the substrate temperature, grain size, surface roughness, and sp3 carbon content in the films decreased with decreasing pressure. The reason is due to the great reduction of Hα emission to lower the etching of sp2 carbon phase, resulting from the increase of mean free path with decreasing pressure. We have demonstrated that the transition from nanocrystalline (80 nm) to ultrananocrystalline (3 to 5 nm) diamond films grown via microwave Ar-1%CH4-10%H2 plasma jets could be controlled by changing the pressure from 100 to 30 Torr. The 250-nm-thick UNCD film was synthesized on glass substrates (glass transition temperature [Tg] 557°C) using the unique LPLT (30 Torr/460°C) microwave plasma jet, which produced UNCD films with a high sp3 carbon content (95.65%) and offered high optical transmittance (approximately 86% at 700 nm).

Improvement of mechanical properties of electroplated diamond tools by microwave plasma CVD diamond process

The growth and surface modification of irregular diamond grains of electroplated diamond tools have been developed successfully. Results show that the adherence, cutting ability, and wear resistance of diamond grains are improved by this process. In this study, the crystallization and quality of diamond grains were determined by SEM (SE and BSE), Raman spectroscopy, and XRD determination. Tests using a block-on-ring tribotester were also carried out to examine the adherence, cutting ability, and wearing resistance of the electroplated diamond tools. The adherence of diamond grains was also observed on a SEM microphotograph of the cross-section view of specimens. SEM line scanning was performed to determine whether the alloy elements are effectual in promoting the diffusion bonding strength among diamonds, the interlayer and substrate.

Application of heat treatment and dispersive strengthening concept in interlayer deposition to enhance diamond film adherence

Abstract Two different deposition processes were carried out to enhance adherence of diamond films on WC+3~5%Co substrate with Ti-Si as the interlayer. One process can be called two-step diamond deposition process. Another process can be called interlayer heat treatment process. Diamond films were deposited by a microwave plasma chemical vapor deposition system. Ti and Si interlayer are deposited by DC sputter and an E-gun, respectively. Film morphologies, interface structure and film quality were examined by SEM, XRD, Auger electron spectroscopy and Raman spectroscopy. The residual stresses and adhesion strengths of the films were determined by Raman spectroscopy and indentation adhesion testing, respectively. Comparing the regular one-step diamond deposition process with the present two different new processes, the average dP/dX values, which are a measure of the adherence of the film, are 354 kgf/mm, 494 kgf/mm and 787 kgf/mm, respectively. In other words, the interlayer heat treatment process gives the best film adherence on average. For the two-step diamond deposition process, the interlayer thickness and the percent diamond surface coverage of the first diamond deposition step are the main parameters, and there exists an optimum Ti thickness and percent diamond coverage for the best film adherence. The main contribution to better film adherence is not a large difference in residual stress, but is due to the following reasons. The interlayer heat treatment can transform amorphous Si to polycrystalline Si, and may form strong TiC and SiC bonding. The polycrystalline Si and the diamond particles from the first diamond deposition step can be an effective seeds to enhance diamond nucleation.

Nano-tip diamond-like carbon fabrication utilizing plasma sheath potential drop technique

Microwave plasma chemical vapor deposition (MPCVD) system with microwave frequency 2.45 GHz was used for exciting mixed reaction gases of methane and hydrogen to produce plasma. The p-type (100) silicon substrate surface was put to contact with plasma to induce plasma sheath potential drop. It introduces an electric field to accelerate positive and lighter hydrogen ions (H + ) to etch out sp 2 clusters and amorphous carbons anisotropically. Besides, high-energy ions, hydrocarbon species and hydrogen atoms (H) are diffused to etch out sp 2 clusters and amorphous carbons isotropically. Without externally applying negative bias, nano-tip diamond-like carbon (DLC) film with a few nano-size diamonds and many sp 3 bonding was successfully deposited under the competition of etching and deposition. SEM study shows that the density of DLC nano-tips is up to 20 x 10 8 cm -2 . Its length, bottom diameter and top diameter are about 1.5-2 μm, 300-400 nm, and 20-30 nm, respectively. The deposited film was analyzed by energy dispersion spectrometer (EDX). The result shows that there is no transition metal incorporated in the film. This suggests that the DLC nano-tip growing mechanism is not similar to general growing mechanism of carbon nanotubes. X-ray diffraction spectrometer (XRD) was applied to confirm that a few nano-size diamonds are contained in the film. Finally, Raman spectrometer and Auger electron spectrometer (AES) were used to confirm that a larger amount of sp 3 bonding is incorporated in the film.

Concurrent improvement in biocompatibility and bioinertness of diamond-like carbon films with nitrogen doping

The surfaces of implantable biomaterials improving biocompatibility and bioinertness are critical for new application of bioimplantable devices. Diamond-like carbon (DLC) film is a promising biomaterial with use for coating bioimplantable devices because of its good biocompatibility, bioinertness, and mechanical properties. In this study, concurrent improvement in biocompatibility and bioinertness of DLC films has been achieved using N-incorporation technique. The N doping degree was found to play an important role in affecting the biocompatibility and bioinertness of N-doped DLC films. The results indicated that the N-doped DLC films deposited at N(2) concentration of 5% could help to create suitable condition of surface/structure/adhesion combination of DLC films in the both affinity of the L929 mouse fibroblasts and electrochemical inertness in the Hanks balanced salt solutions (simulating human body fluids). N doping supports the attachment and proliferation of cells and prevents the permeation of electrolyte solutions, thereby simultaneity improved the biocompatibility and bioinertness of DLC films. This finding is useful for the fabrication and encapsulation of in vivo devices without induced immune response in the human body.