J.C. Madaleno

Diamond growth by chemical vapour deposition

This paper reviews the growth of diamond by chemical vapour deposition (CVD). It includes the following seven parts: (1) Properties of diamond: this part briefly introduces the unique properties of diamond and their origin and lists some of the most common diamond applications. (2) Growth of diamond by CVD: this part reviews the history and the methods of growing CVD diamond. (3) Mechanisms of CVD diamond growth: this part discusses the current understanding on the growth of metastable diamond from the vapour phase. (4) Characterization of CVD diamond: we discuss the two most common techniques, Raman and XRD, which have been intensively employed for characterizing CVD diamond. (5) CVD diamond growth characteristics: this part demonstrates the characteristics of diamond nucleation and growth on various types of substrate materials. (6) Nanocrystalline diamond: in this section, we present an introduction to the growth mechanisms of nanocrystalline diamond and discuss their Raman features.This paper provides necessary information for those who are starting to work in the field of CVD diamond, as well as for those who need a relatively complete picture of the growth of CVD diamond.

Surface engineered surgical tools and medical devices

Surface engineered surgical tools and medical devices / , Surface engineered surgical tools and medical devices / , کتابخانه دیجیتال جندی شاپور اهواز

Electron field emission from patterned nanocrystalline diamond coated a-SiO2 micrometer-tip arrays

We report the fabrication of patterned nanocrystalline diamond (NCD) submicrometer-tip arrays. This includes synthesis of silica (a-SiO2) templates by conventional vapor-liquid-solid method and conformal coating of the a-SiO2 nanowires with 5–10nm sized nanodiamond grains by microwave plasma chemical vapor deposition. Detailed structural investigations were carried out by high resolution transmission electron microscopy. Electron field emission of nanodiamond emitter arrays was observed with a threshold field of 5.5V∕μm. A high emission current density of 10mAcm−2 at 11V∕μm has been obtained. This value is comparable to those of high quality NCD films deposited on silicon substrates.We report the fabrication of patterned nanocrystalline diamond (NCD) submicrometer-tip arrays. This includes synthesis of silica (a-SiO2) templates by conventional vapor-liquid-solid method and conformal coating of the a-SiO2 nanowires with 5–10nm sized nanodiamond grains by microwave plasma chemical vapor deposition. Detailed structural investigations were carried out by high resolution transmission electron microscopy. Electron field emission of nanodiamond emitter arrays was observed with a threshold field of 5.5V∕μm. A high emission current density of 10mAcm−2 at 11V∕μm has been obtained. This value is comparable to those of high quality NCD films deposited on silicon substrates.

Use of Electroless Plating Copper Thin Films for Catalysis

Recently, it was demonstrated that copper thin films show good adsorption characteristics for organic polar and non-polar compounds. Also, these films when used in small cavities can favor preconcentration of these organic compounds. It is also known that copper oxide can provide catalysis of organic compounds. Therefore, the aim of this work is the study of copper thin film catalysis when used in small cavities. Copper thin films, 25 nm thick, were deposited on silicon and/or rough silicon. These films do not show oxide on the surface when analyzed by Rutherford backscattering. Also, Raman analysis of these films showed only silicon bands, due to the substrate, however infrared spectroscopy shows oxide bands for films exposed to organic compound aqueous solutions. Cavities with copper films deposited inside were tested with a continuous flow of n-hexane, acetone or 2-propanol admitted in the system. The effluent was analyzed by Quartz Crystal Microbalance. It was shown that n-hexane or acetone can be trapped. The system also shows good reproducibility. Tests of catalysis were carried out using Raman spectroscopy and heating the films up to 300°C during 3 minutes after exposure to n-hexane, 2- propanol and acetophenone – pure or saturated aqueous solution. After the exposure, Raman spectra present intense bands only for 2-propanol, indicating that adsorption easily occurs. However, after heating with all solutions it was not found only silicon bands. Raman microscopy after heating also showed copper oxide cluster formation and, eventually, graphite formation. Although the heating provides oxide copper formation, this reaction does not produce a high amount of residues, which means that catalysis is possible in this condition. Thus, a simple device using copper thin films can be useful as sample pretreatment on microTAS development.

Low cost microstructures for preconcentration of polar and non-polar organic compounds

Films produced by plasma polymerization of ethyl ether and methyl or ethyl acetate show good adsorption characteristic for polar and non-polar organic compounds. These films when used in microchannels machined in a 3D-structure present some preconcentration of organic compounds. Therefore, the aim of this work is to investigate the physical-chemical preconcentration mechanisms on this structure. The test molecules used were n-hexane and 2-propanol. Quartz crystal microbalance and mass spectrometry were used to measure preconcentration. Two different procedures for reactant injection on the structure were used: a continuous flow during several minutes or a small amount injected on a single pulse and in a few seconds. The microchannels were also modified by the introduction of small ceramic particles for enhancement of the flow dispersion. It was possible to notice for all films a similar kinetic of retention. The main removal mechanism is adsorption. Although all films can provide the removal of the adsorbents molecules, the most important characteristic for the adsorption and/or retention is the surface condition. Thus, the retention of polar compound can be troubled if a non-polar compound was used previously. The most promising films for retention are ethyl ether and ethyl acetate when n-hexane and 2-propanol are used as test molecules. The results using n-hexane or 2-propanol point out the use of low-cost microchannels for preconcentration development.

Impact of surface roughness of diamond coatings on the cutting performance when dry machining of graphite

Time Modulated Chemical Vapour Deposition (TMCVD) process regime has been used to deposit diamond coatings onto commercially available tungsten carbide tool inserts. The TMCVD process was developed in our laboratories so that diamond films with fine grains could be deposited. It accomplishes this by promoting secondary nucleation during larger methane flow modulations. The average surface roughness of the diamond coatings were correlated with the cutting performance of the coatings when dry machining of graphite. Inserts coated were characterised by Scanning Electron Microscopy (SEM) and Raman spectroscopy and were tested for turning performance using graphite as the workpiece material. The cutting forces were measured by the DynoWareT™ data acquisition system. Polycrystalline Diamond (PCD) inserts were also used for comparison. Repeated turning tests showed that the surface roughness of the coatings is a limiting factor when achieving better chip flow during machining.

Electrical Imaging Map on Polycrystalline Diamond Films and Diodes and Structural Relationship Obtained by Micro-Raman

In this work we present an equipotential surface map with a resolution higher than 100 nm, resulting from conductive atomic force microscopy (AFM). The images, obtained in polycrystalline MPCVD (Microwave Plasma Assisted Chemical Vapor Deposition) diamond devices, are clearly structure dependent. Diamond and non-diamond phases were identified by micro-Raman spectroscopy and correlated with the electrical conduction map. The application of the non-homogeneous contact theory lead to the extraction of two Schottky Barrier Heights (SBH), one close to 0.6 V with dispersion ~ 0.1 V, attributed to the diamond / metal interface, and the other close to 0.4 V with dispersion ~ 0.04 V, due to the non-diamond phases / metal interface. The diamond / non-diamond phase ratio is about 85:15, taken from the micro-Raman spectra. Combining these results with the electrical conduction map, a general model to predict the macroscopic electrical behavior of polycrystalline diamond based devices is proposed.

Carrier Transport Investigation on Organic Semiconductor by Electrical DC and AC Measurements: the Case of Alq3

In the present work, the nature of the electrical mechanism for carrier transport in Alq3 is studied by current-voltage measurements and broadband dielectric spectroscopy. The d.c. currentvoltage characteristics at low applied electrical field exhibits a classical “N” shape due to interfacial states located at metal-organic interface, but tend to disappear when successive higher forward bias is applied. Using dielectric spectroscopy it is possible to observe that the main relaxation peak shifts to a higher frequency with the increase of the applied d.c. voltage (from approximately 100 Hz with 0 V d.c. bias to approximately 400 Hz with 6 V d.c. bias) indicating a semiconductor structure change. The logarithmic Z’’ vs. Z’ plot has a slope about 0.7 that decreases to 0.5 with the increasing applied d.c. voltage, reaching a classic Debye relaxation. An attempt to correlate with some structural changes is made.

Surface Engineering of Artificial Heart Valves to Using Modified Diamond-like Coatings

There are two types of artificial heart valves, namely, (i) biological valves and (ii) mechanical valves. biological heart valves are made from tissue taken from animals or human cadavers. They are treated with preservatives and sterilized for human implantation. On the other hand, mechanical heart valves are made of man-made materials. The advantage of mechanical valves over biological valves is that they normally last for a comparatively longer lifetime. The biological valves exhibit a shorter lifetime and tend to wear out with time in service. This chapter discusses mechanical heart valves and highlights the underlying problems faced with biomaterials used in the manufacture of such valves.

Biomaterial-cell tissue interactions in surface engineered carbon-based biomedical implants and devices

Implantable prosthesis and medical devices are subjected to several interacting forces whenever they come in contact with the physiologic systems (blood, immune, musculoskeletal, nervous, digestive, respiratory, reproductive and urinary) and organs of the human body. These interactions include the effects of core body temperature (and/or variable temperatures in the oral cavity), the body physiologic fluids containing several ions and biomolecules, proteins and cells of various progeny and functions. This chapter focuses on cell tissue–implant interactions and how carbon-based implants are being developed for next-generation implantable devices.