Subsequent Polishing Research Articles

Microstructure grooves with a width of less than 50 μm cut with ground hard metal micro end mills

Mechanical microengineering is an easy and cheap way to fabricate microstructures; for example, molds for injection molding or hot embossing. Restrictions remain in the selection of materials and in the minimum structure size. Especially for cutting microstructures in steel, these limitations included the lack of available small tools and the poor surface quality. We discovered that microstructures can be cut in both brass and stainless steel workpieces by using ground hard metal micro end mills. The minimum groove width achieved is less than 50 μm for cutting brass and about 100 μm for cutting stainless steel. Burrs are removed by a subsequent diamond-cutting step or electrochemical polishing, respectively. Our results represent the first step toward a microstructured, resistant, and cheap mold made of steel, which is then used for mass production of plastic microstructures.

Anisotropic Microstructure of Plasma-Sprayed Deposits

The microstructure of plasma sprayed deposits (PSD) is dominated by two void systems—interlamellar pores and intralamellar cracks—each with a different anisotropy. Anisotropy of these void systems and varying crack-to-pore ratios within PSDs are responsible for the anisotropic properties observed within deposits. While it is difficult to apply standard porosity measurement techniques to the assessment of anisotropic microstructures, novel techniques utilizing different approaches have recently emerged. Image analysis (IA) of impregnated PSD samples is the most direct technique. The structure is stabilized by impregnation and then polished and imaged. The limitations of IA lie in the impregnation process and in the subsequent polishing. Also, the images produced from anisotropic materials can be difficult to interpret quantitatively. The technique of small-angle neutron scattering (SANS) has recently been applied to the study of PSDs. The major advantages of SANS are that it does not require sample preparation and that quantitative information can be obtained concerning the separate crack and pore systems, including their distinctive anisotropies. However, the relationship between the SANS results and the underlying structure is more complex and less intuitive than for IA, and the availability of the SANS technique is limited by the need to have access to a powerful neutron source, such as a reactor. Also, the two techniques present different views of the microstructure because of the different sensitivities in different parts of the size range. This article compares results from IA and SANS for a set of thick plasma-sprayed ceramic deposits possessing a range of crack/pore microstructures and discusses how the two techniques might complement one another.

Direct Bonding of Gallium Arsenide on Silicon

Direct bonding of gallium arsenide on silicon is studied. The technology is expected to enable the easy integration of gallium arsenide optoelectronic devices with silicon very-large-scale integrated circuits. The interface quality of n-GaAs/p-Si can be improved with a thermal annealing process. It is examined by the current-voltage characteristics of the n-GaAs/p-Si diode. The bonding strength was found to be sufficiently high and could “high enough to” withstand the subsequent grinding and polishing procedures of the bonded wafers.

Single point diamond machining of ferroelectric materials

One of the most important ferroelectric ceramic materials used in a wide range of applications is the lead zirconate titanate solid solution series (PZT). The ability to machine ferroelectrics in a ductile manner and by so doing reduce sub-surface damage, could eliminate the need for subsequent lapping and polishing and thus reduce production costs. Fracture mechanics techniques were used to investigate the localised elastic/plastic behaviour in these materials. The possibility of machining brittle materials using single point diamond turning in a 'ductile mode' has been investigated by many researchers in recent years and for this study poled and unpoled PZT ceramics were single point diamond turned under different machining conditions and ductile machining has been achieved. X-ray diffraction (XRD) indicates the degree of domain reorientation caused by machining, and it is suggested that the strain generated by re-orientation accounts for brittle damage. Appropriate poring can have a marked effect on the brittle/ductile machining response.

Single point diamond turning of ferroelectric materials

One of the most important ferroelectric ceramics materials used in a wide range of applications is the lead zirconate titanate solid solution series (PZT). The possibility of machining brittle materials using single point diamond turning in a ‘ductile mode’ has been investigated by many researchers in recent years. The ability to machine ferroelectrics in a ductile manner and by so doing reduce sub-surface damage, could eliminate the need for subsequent lapping and polishing and thus reduce production costs. Fracture mechanics techniques were used to investigate the localised elastic/plastic behaviour. PZT ceramics in the poled and unpoled state were single point diamond turned under different machining conditions and ductile machining has been achieved. X-ray diffraction indicates the degree of domain reorientation caused by machining, and it is suggested that the strain generated by reorientation accounts for brittle damage. Appropriate poling can have a marked effect on the brittle/ductile machining response[1].

Molecular Dynamics Simulations of Growth and Low-Energy Ion Polishing of Thin Molybdenum Films for EUV Multilayer Mirrors

AbstractWe report on the simulation of the growth and subsequent krypton ion polishing of thin molybdenum films, required for extreme ultraviolet multilayer mirror fabrication. We have used a comprehensive Molecular Dynamics (MD) code, principally enabling a simulation of the deposition, ion bombardment and annealing processes. Ion energies used are in the sub-keV range, and the ion angle of incidence is varied between 30 and 60 degrees off-normal.The effects of ion polishing on the surface roughness are discussed, as well as the increase in (surface) atom mobility. We also report data on sputtering yields, ion penetration depths, trapping, energy transfer and krypton implantation and saturation.The results are compared with TRIM results, and the relevance of MD and TRIM simulations for specific purposes is discussed. Also, the effects of short-time, high-temperature annealing of an amorphous film are investigated.

X-ray Topography Study of Surface Damage in Single-Crystal Sapphire

ABSTRACTX-ray diffraction topography was used to investigate the relationship between subsurface damage, near-surface microstructure, and fracture strength in a series of sapphire modulus of rupture (MOR) bars which had been fabricated to proof test fabrication processes. The strength of the bars was determined by failure in four point bending. The tensile surface of the bars was also examined using optical microscopy and non-contacting surface profilometry. Both show that the bars have good surface finish, with a typical RMS roughness of 0.7 nm. No correlation was found between RMS surface finish and fracture strength. Although the bars appeared to be indistinguishable, topographs taken prior to fracture testing revealed that they are of two distinct types. Type 1 has an oriented microstructure consisting of a pattern of linear features running the length of the bars. Type 2 was typical of well-polished sapphire, containing individual dislocations and occasional damage from handling. We attribute the Type 1 microstructure to fabrication damage that was not removed by subsequent processing and/or polishing. Fracture strength data showed that the Type I (damaged) bars had strengths less than 70 % of the bars without damage. Topography is sensitive to near-surface damage that can be correlated to fracture strength. Neither low magnification optical microscopy nor conventional surface finish statistics could be correlated to strength.

Loose abrasive line-contact machining of aspherical optical surfaces of revolution

A new fabrication technique for the generation of optical aspherical surfaces of revolution is presented. This fabrication technique combines the characteristics of conventional loose abrasive machining with features of high-precision machining tools. A prototype of the machine tool based on this fabrication technique is currently being developed. We describe the characteristics of this method. Fabrication of aspherical ultraprecise surfaces using a tube is a line-contact method for the generation of both on- and off-axis, convex and concave, aspherical surfaces of revolution. It employs a self-correcting process and enables the use of loose-abrasive ductile grinding [Appl. Opt. 30, 2761-2777 (1991)] and subsequent bowl-feed polishing [Appl. Opt. 26, 696-703 (1987); Opt. Eng. 31, 1086-1092 (1992); Appl. Opt. 33, 89-95 (1994)] for the generation of aspherical surfaces.

Optical interferometry for surface measurements of CMP pads

Optical interferometry was used to quantitatively characterize the surface of chemical-mechanical polishing (CMP) pads used to polish oxide films. We discuss the optical interferometry technique, including a description of the parameters necessary to compare pad samples. Flat, mesa-like structures formed on the pad during the first 5 min polish when conditioning was not used. The data from the optical interferometer indicated that the surface topography did not change with subsequent polishing, even though the thermal oxide removal rate continued to decrease. We found conditioning roughened the pad surface. Rougher pad surfaces removed more oxide during a single 5 min polish than comparatively smooth pad surfaces. Data indicates that conditioning increases and stabilizes pad surface roughness.

The influence of oriented growth on the surface roughness of CVD diamond films

Experiments and computer simulations were carried out which indicate that very smooth diamond surfaces can be grown without any subsequent polishing of the diamond surface using a two-step deposition technique. The first step is to grow a diamond film under conditions that will establish a (100) textured diamond film. The second step is to decrease the surface roughness by increasing the growth rate of the inclined {111} planes of the (100) textured film.

Effect of martensite content on the sliding behaviour of boron-ion-implanted 304 stainless steel

We have investigated the effects of boron ion implantation on the wear behaviour of 304 stainless steel. The initial phase composition of the specimens was varied by using two different kinds of polishing technique. Electropolishing resulted in purely f.c.c. (austenitic) specimens. Subsequent mechanical polishing resulted in a phase transformation that introduced a b.c.c. (martensite) phase. The specimens studied were either electropolished or fully polished (electropolished and mechanically polished). In general, we observed that boron implantation improves the wear performance of the steel. The result of boron implantation is to inhibit hardening of the surface during wear, as was seen from measurements of the microhardness inside the wear tracks. (Such hardening has previously been shown to occur in studies on unimplanted material, through martensitic transformation, and leads to the formation of a brittle surface sheet that is prone to cracking.) Interestingly, the improvement on implantation and the associated inhibition of hardening in the wear tracks were seen to be much more pronounced when full polishing was employed rather than just electropolishing, i.e. when the specimen contained a small amount of martensite prior to implantation. The measurement of the microhardness inside the wear tracks provided a quick method of assessing the transformation during the wear process, which we then correlated with the friction and wear behaviour in each case. Measurements of the microhardness on as-implanted surfaces showed that a fully polished surface strengthens to a greater extent than an electropolished surface. This appears to result in reduced plastic deformation, leading to the observed reduction in transformation during wear and, thus, could explain the greatly improved behaviour.

Increase in forming limit of sheet metals by removal of surface roughening with plastic strain (Balanced biaxial stretching of aluminium sheets and foils)

When forming a sheet metal, the free surface of the sheet becomes rough with increasing plastic strain. This is well known as orange peel phenomena and has a great effect not only on the surface quality of a product but also on the forming limit. In an attempt to increase the forming limit of thin sheet metals, in the present paper, a new forming technique is proposed in which surface asperities generated during the forming process are polished to eliminate the weak portions of the sheet which lead to the onset of a localized necking. Balanced biaxial stretching of aluminium sheets and foils is carried out in this manner, and how the forming limit can be increased is examined. It is shown that the forming limit of sheet metal can be appreciably improved by a simple method of polishing the surface roughness during the stretching process. The polishing of surface roughness at the strain somewhat before the onset of localized necking is recommended to efficiently increase the forming limit. The effect of polishing surface roughness on the forming limit becomes large as the thickness of sheet decreases. For aluminium sheets with 0.1 and 0.2 mm in thickness, for example, the forming limit strains achieved have been about 1.4 times as large as those for the ordinary balanced biaxial stretching without the interstage polishing. When such processes of stretching and subsequent polishing are repeated in turn 2 or 3 times, further increase in the forming limit can be achieved.

Enamel surfaces after orthodontic bracket debonding.

The enamel surfaces of extracted teeth were studied clinically and with a scanning electron microscope following debonding of orthodontic attachments and subsequent polishing. Excess orthodontic resin was removed with tungsten carbide burs and abrasive discs. Several combinations of polishing agents were evaluated. The no. 30 fluted tungsten carbide bur appeared to be the most efficient method of removing highly filled resin, and it produced the least amount of scarring. A polishing sequence was developed which used resin points and cups followed by a water slurry of fine pumice and brown and green cups. This procedure was tested clinically and appeared to return the enamel to an acceptable condition. This procedure is fast, efficient, and comfortable for the patient.

Effect of the kind of thermal cutting on the fractographic features of steel 14KhGNMDAFBRT in low-cycle circular bending

On the basis of fractographic and microfractographic analysis of fractures of steel 14KHGNMDAFBRT subjected to low-cycle circular bending tests, qualitative and quantitative traits of the physical influence of three kinds of thermal (plasma-arc in air and in air-hydrocarbon atmosphere, and oxyacetylene) and mechanical (milling with subsequent polishing) cutting on the nature of failure and on the durability of the material were detected and compared with each other. Against the background of a general tendency to enhanced durability of specimens after thermal cutting compared with mechanical treatment, the greatest positive effect on the investigated steel was found with plasma cutting in a hydrocarbon mixture ensuring a strengthened subsurface zone with maximal thickness which attained 160–200 μm.

Fast heterogeneous electron transfer rates for glassy carbon electrodes without polishing or activation procedures

Glassy carbon (CG) is an attractive choice for an electrode material because it has a wide potential range, is inexpensive, readily available, and chemically inert in most electrolytes. The typical preparation of a GC electrode includes the removal of gross surface features by abrasion with silicon carbide paper and subsequent polishing with alumina. The electrochemistry of many redox systems such as ascorbic acid (AA), ferri/ferrocyanide, and dopamine on GC are very sensitive to the polishing procedure, with variations in the heterogeneous electron transfer rate constant K(o), for the Fe(CN){sub 6} (3-/4-) redox system covering at least three orders of magnitude. This variation has been attributed primarily to superficial impurities and polishing debris.

Diamond turning of mirrors and infrared optical components

The authors describe an experimental study of single-point diamond-machining techniques with a view to producing a low-cost production machine for the manufacture of infrared optical components such as aluminium mirrors, germanium lenses and zinc sulphide domes. These components may be machined to a high form accuracy and surface finish such that they require no subsequent polishing. Of the three possible machine configurations, X-Y, R- theta and spherical generation, the last two are considered the most efficient and cost effective for the present requirement. They have been extended to produce aspheric components with departures up to +or-2 mm from a best-fit sphere.

Use Of Aspheric Surfaces In Infrared Optical Designs

The cost effectiveness of using aspheric surfaces in infrared systems is reviewed. In particular, two design studies are described, the first of a Maksutov-type objective and the second of a high numerical aperture pyroelectric vidicon objective. In the first case, the use of first one and then two aspheric surfaces results in an increasing ability to satisfy all of the aberration and dimension requirements of its specification. In addition, a size versus raw material trade-off becomes possible. In the second case, a four-element spherical design is compared with a two-element aspheric design over a large range of numerical apertures. The analysis demonstrates that the improved transmission and reduced materials costs that result from the use of aspheric surfaces outweigh the cost of aspheric manufacture. The paper concludes that in the cases examined, aspherics are highly cost effective, provided that a facility for diamond machining to an optical finish, without subsequent polishing, is available.

POROSITY DEVELOPMENT DURING HEAT TREATMENT OF ALUMINUM-LITHIUM ALLOYS

The development of a sub-surface layer of porosity during heat treatment has been studied in a variety of Al-Li alloys. Pure binary Al-Li alloys and three commercial materials were heat treated in air, vacuum and hydrogen for various lengths of time. Subsequent metallographic sectioning and polishing revealed the presence of a band of pores in the near-surface region extending approximately 300 µm into the sample after a 16 h heat treatment. This band of porosity is thought to arise from a Kirkendall effect due to the loss of lithium during heat treatment of the sample. The evolution of the spatial distribution of these pores was characterized with a quantitative image analyzer. The effects of prior surface preparation were also determined. The results showed that structural defects influenced pore nucleation and that environmental factors were also significant. A simultaneous pore healing process also occurred immediately adjacent to the external surface.

Formation of planar n+pockets in GaAs for mixer diode fabrication

A novel technique has been developed to produce n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> "pockets" in semi-insulating GaAs bulk material. This technique has produced thick pockets of highly conducting epitaxial material on the substrate surface. The pockets were formed by the growth of a liquid-phase epitaxial (LPE) layer into holes which had been etched into the substrate. Surface uniformity was obtained by chemo-mechanically polishing the substrate surface under tightly controlled conditions. Polishing rates as low as 0.2 µm/min have been obtained. Photographs taken of the pocket cross-sectional area have revealed that growth occurred throughout the entire pocket region. Growth was even found to have occurred along the irregularly shape walls of the pockets. The continuous growth throughout the pockets coupled with the subsequent polishing of the substrate have produced exceptionally smooth and planar surfaces. Thicknesses as great as 10 µm have been obtained for the n <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> pockets using this technique. Mixer diodes have been fabricated onto these layers and tested. Preliminary dc measurements taken on these devices have yielded a zero-biased cutoff frequency (F <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">co</inf> ) of 800 GHz with a series resistance (R <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</inf> ) of 6 Ω and a zero-biased capacitance (C <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0</inf> ) of 30 fF.

Restoration of Primary Teeth with Amalgam

Dental amalgam used by the dentist as a restorative material should meet the following criteria: (1) a reduced risk of marginal failure with a minimal risk of recurrent caries, (2) resistance to creep and corrosion, and (3) the characteristics for mixing, inserting, and polishing that are optimally duplicated. To achieve these criteria, the optimal amalgam technique includes the use of the following: Rubber dam whenever possible Conservative cavity preparations to offset the amalgam's inherent weak physical properties A high copper alloy combined with the appropriate amount of mercury for optimal plasticity and to reduce susceptibility to creep and corrosion Trituration, precondensation, and condensation methods that are consistently practiced by the dental assistant and dentist A burnishing scheme combined with a subsequent polishing method to complete the final amalgam restoration.