bluuebunny/crossref_metadata_2025 huggingface dataset:
A new loading history for identification of viscoplastic properties by spherical indentation
Authors: Huber N. , Tyulyukovskiy E.
Published: October 2005

In this paper a new loading history for extracting the stress–strain curve as well as the viscosity and creep behavior from indentation experiments is developed. It is based on a simple model describing the viscoplastic spherical indentation with a power-law hardening rule and a velocity-dependent overstress. Using this model, patterns were generated consisting of load-depth data and corresponding material parameters. The loading history for the simulation of the patterns was considered as a variable combination of loading and creep processes. To compare the identification potential of different loading histories, the inverse problem of determining the viscoplastic material parameters was solved by using neural networks. The emerging loading history uses a multiple-creep process with equidistant load steps and allows an identification of material parameters with much higher accuracy than with single creep. It will be used for further work, where the identification method is generalized using more realistic finite element simulations for a finite deformation elastic–viscoplastic material behavior.
Three-dimensional finite element analysis of the effects of anisotropy on bone mechanical properties measured by nanoindentation
Authors: Fan Z. , Rho J.Y. , Swadener J.G.
Published: October 2005

A three-dimensional finite element analysis (FEA) model with elastic–plastic anisotropy was built to investigate the effects of anisotropy on nanoindentation measurements for cortical bone. The FEA model has demonstrated a capability to capture the cortical bone material response under the indentation process. By comparison with the contact area obtained from monitoring the contact profile in FEA simulations, the Oliver–Pharr method was found to underpredict or overpredict the contact area due to the effects of anisotropy. The amount of error (less than 10% for cortical bone) depended on the indentation orientation. The indentation modulus results obtained from FEA simulations at different surface orientations showed a trend similar to experimental results and were also similar to moduli calculated from a mathematical model. The Oliver–Pharr method has been shown to be useful for providing first-order approximations in the analysis of anisotropic mechanical properties of cortical bone, although the indentation modulus is influenced by anisotropy.
Indentation-induced deformation at ultramicroscopic and macroscopic contacts
Authors: Thurn Jeremy , Cook Robert F.
Published: October 2005

Depth-sensing indentation at ultramicroscopic and macroscopic contacts (“nanoindentation” and “macroindentation,” respectively) was performed on four brittle materials (soda-lime glass, alumina titanium carbide, sapphire, and silicon) and the resulting load–displacement traces examined to provide insight to the elastic and plastic deformation scaling with contact size. The load–displacement traces are examined in terms of the unloading stiffness, the energies deposited during loading and recovered on unloading, and the effect of the indenter tip radius on the loading curve. The results of the analyses show that the elastic and plastic deformation during loading and unloading is invariant with the scale of the contact, and the unloading curve is best described by neither a conical tip nor a paraboloid of revolution, but of some compromise.
Polarity-induced changes in the nanoindentation response of GaAs
Authors: Le Bourhis E. , Patriarche G. , Largeau L. , Rivière J.P.
Published: October 2005

We studied the polarity-induced changes in the nanoindentation response of GaAs{111}. The nanoindentations were made under a large range of loads (Fmax between 0.2 mN and 50 mN) at room temperature on {111} faces of A (Ga) or B (As) character. The loading–unloading curves were compared first, with special attention addressed to pop-in events and hardness values (reported previously for microindentation). Transmission electron microscopy was used to observe the nanoindentation structures generated at the two polar surfaces. The size of the dense plastic zone generated around the indent site was found to increase linearly with √Fmax and similarly for both polar surfaces. The indentation rosettes possess a threefold symmetry with arms developed along the <110> directions parallel to the surface. Sizes were found to be very close for both polar surfaces and the entire load range. For an A-polar face, the rosette arms are constituted by two arms: a long arm (LA, α dislocations) and a short arm (β dislocations). At the B surface, only the LA (β dislocations) are formed. Furthermore, microtwinning was observed only for an A-polar face, similar to previous observations of anisotropic microtwinning at GaAs(001) surfaces.
Plasticity size effects in nanoindentation
Authors: Bushby A.J. , Dunstan D.J.
Published: October 2005

In conventional continuum mechanics, the yield behavior of a material is size independent. However, in nanoindentation, plasticity size effects have been observed for many years, where a higher hardness is measured for smaller indentation size. In this paper we show that there was a size effect in the initiation of plasticity, by using spherical indenters with different radii, and that the length scale at which the size effect became significant depended on the mechanism of plastic deformation. For yield by densification (fused silica), there was no size effect in the nanoindentation regime. For phase transition (silicon), the length scale was of the order tens of nanometers. For materials that deform by dislocations (InGaAs/InP), the length scale was of the order a micrometer, to provide the space required for a dislocation to operate. We show that these size effects are the result of yield initiating over a finite volume and predict the length scale over which each mechanism should become significant.
Validated measurement of Young's modulus, Poisson ratio, and thickness for thin coatings by combining instrumented nanoindentation and acoustical measurements
Authors: Jennett N.M. , Aldrich-Smith G. , Maxwell A.S.
Published: October 2005

Nanoindentation is one of the very few techniques that can measure both the elastic and plastic properties of very small volumes of materials. Recently it has been shown that the properties of thin coatings can be determined by nanoindentation, even when the normal indentation response includes a significant component due to the substrate. This paper takes the method a step further and shows how by combining acoustical test methods with nanoindentation, a validated set of values for the thickness, Young's modulus, and Poisson ratio for a coating can be obtained.
An energy-based method for analyzing instrumented spherical indentation experiments
Authors: Ni Wangyang , Cheng Yang-Tse , Cheng Che-Min , Grummon David S.
Published: October 2005

Using dimensional analysis and finite element calculation, we studied spherical indentation in elastic–plastic solids with work hardening. We report two previously unknown relationships between hardness, reduced modulus, indentation depth, indenter radius, and work of indentation. These relationships, together with the relationship between initial unloading stiffness and reduced modulus, provide an energy-based method for determining contact area, reduced modulus, and hardness of materials from instrumented spherical indentation measurements. This method also provides a means for calibrating the effective radius of imperfectly shaped spherical indenters. Finally, the method is applied to the analysis of instrumented spherical indentation experiments on copper, aluminum, tungsten, and fused silica.
Nanoindentation testing for evaluating modulus and hardness of single-walled carbon nanotube–reinforced epoxy composites
Authors: Dutta A.K. , Penumadu D. , Files B.
Published: October 2005

Instrumented indentation testing was used to evaluate the changes in mechanical properties of single-walled carbon nanotube composite specimens with varying weight percentage (0, 0.1, 0.5, and 1.0 wt%) of nanotubes using a low-viscosity liquid epoxy resin. The nanotubes were prepared using laser ablation technique. Reference tensile tests were also performed on the same samples, and relevant comparisons with indentation results were made. The variations in modulus and hardness obtained using nanoindentation (considering time effects) showed quantifiable differences between the various composite specimens, but differed from tensile test data. The small changes in the observed stiffness and breaking strength of carbon nanotube composites was due to the formation of bundles, their curvy morphology, and microporosity in the specimens. Interesting fluctuations obtained from the interpreted values of modulus with depth of indentation is attributed to varying degrees of the local confining effect of nanotube bundles. Creep exponents for these nanocomposites were also evaluated and indicate considerable improvements.
Direct observations of incipient plasticity during nanoindentation of Al
Authors: Minor A.M. , Lilleodden E.T. , Stach E.A. , Morris J.W.
Published: October 2005

The mechanical testing technique for in situ nanoindentation in a transmission electron microscope is described and is shown to provide real-time observations of the mechanisms of plastic deformation that occur during nanoindentation. Here, the importance of this technique was demonstrated on an aluminum thin film deposited on a single-crystalline silicon substrate. Significant results include direct observation of dislocation nucleation, characterization of the dislocation distribution created by indentation, and the observation of indentation-induced grain boundary motion. The observations achieved by this technique provide unique insight into mechanical behavior studied with conventional instrumented nanoindentation techniques and also provide microstructural-level understanding of the mechanics of ultrasmall volumes.
Surface roughness effects on the displacement bursts observed in nanoindentation
Authors: Shibutani Yoji , Koyama Atsuhiro
Published: October 2005

The distinctive finding of unstable displacement bursts of indent depth observed in nanoindentation is thought to be linked to the dislocation emission phenomenon. However, because of a lack of understanding of the surface physics of the contact area, the explanation of the instability mechanism remains vague. In this paper, an effect of the surface roughness on the displacement bursts was experimentally investigated using single-crystalline aluminum. The surface properties of samples with several degrees of roughness of less than 10 nm were measured using atomic force microscopy. The discussion focuses on the relations between critical values of the load at the displacement bursts and the burst width.
Instrumented indentation probing of laser surface-refined cast Al alloy
Authors: Nayak S. , Riester Laura , Dahotre Narendra B.
Published: October 2005

The surface layer of A319 alloy was refined by selective remelting using laser energy. Instrumented indentation technique was used to measure hardness (H) and elastic modulus (E) of the laser-melted layer. Berkovich tip was used to indent the material for 100-nm, 200-nm, 500-nm, and 1000-nm depths. The H and the E were found to be 1.22 GPa and 78.2 GPa, respectively, for 1000-nm indentation depths. The variances associated with H and E were minimal, whereas, the same for substrate possessed significant scattering. Also, H and E increased with decreasing depth of indentation. Closer examination suggested that when the heterogeneity in the material was in the scale of indentation depth, significant scattering took place and the hard phase Si influenced the average hardness. However, the influence of indentation depth on elastic modulus was not statistically significant.
Size effect measurement and characterization in nanoindentation test
Authors: Wei Yueguang , Wang Xuezheng , Zhao Manhong
Published: October 2005

Nanoindentation test at scale of hundreds of nanometers has shown that measured hardness increases strongly with decreasing indent depth, which is frequently referred to as the size effect. Usually, the size effect is displayed in the hardness-depth curves. In this study, the size effect is characterized in both the load–displacement curves and the hardness–depth curves. The experimental measurements were performed for single-crystal copper specimen and for surface-nanocrystallized Al-alloy specimen. Moreover, the size effect was characterized using the dislocation density theory. To investigate effects of some environmental factors, such as the effect of surface roughness and the effect of indenter tip curvature, the specimen surface profile and the indentation imprint profile for single-crystal copper specimen were scanned and measured using the atomic force microscopy technique. Furthermore, the size effect was characterized and analyzed when the effect of the specimen surface roughness was considered.
Hall–Petch relationship in pulsed-laser deposited nickel films
Authors: Knapp J.A. , Follstaedt D.M.
Published: October 2005

Thin-film mechanical properties can be measured using nanoindentation combined with detailed finite element modeling. This technique was used for a study of very fine grained Ni films, formed using pulsed-laser deposition on fused silica, sapphire, and Ni substrates. The grain sizes in the films were characterized by electron microscopy, and the mechanical properties were determined by ultra-low load indentation, analyzed using finite element modeling to separate the mechanical properties of the thin layers from those of the substrates. Some Ni films were deposited at high temperature or annealed after deposition to enlarge the grain sizes. The observed hardnesses and grain sizes in these thin Ni films are consistent with the empirical Hall–Petch relationship for grain sizes ranging from a few micrometers to as small as 10 nm, suggesting that deformation occurs preferentially by dislocation movement even in such nanometer-size grains.
Instrumented pyramidal and spherical indentation of polycrystalline graphite
Authors: Sakai M. , Nakano Y.
Published: October 2005

The elastoplastic surface deformation of a polycrystalline graphite was studied by examining the indenter’s geometry dependence of load P versus penetration depth h relation (P–h relation) in instrumented pyramidal/spherical indentation tests. The tetrahedral pyramid indenters included inclined face angles β of 10.0°, 22.0° (Vickers pyramid), and 40.0°. The tip radius of spherical indenters used were 32 μm, 200 μm, 794 μm, 1.59 mm, and 6.35 mm. The true hardness H as a measure for plasticity was singled out of the elastoplastic loading parameter k1 in the quadratic expression of P = k1h2 and then quantitatively related to the yield stress Y that was determined from the mean contact pressure for spherical indentation at the onset of plastic yielding. The size effect of Y, decreasing with the increase in the tip radius of spherical indenter, is discussed using the model of geometrically necessary dislocations in terms of the material length scales for a plastic field with strain gradient.
Nanoindentation of bone: Comparison of specimens tested in liquid and embedded in polymethylmethacrylate
Authors: Bushby A.J. , Ferguson V.L. , Boyde A.
Published: October 2005

Elastic modulus of bone was investigated by nanoindentation using common methods of sample preparation, data collection, and analysis, and compared to dynamic mechanical analysis (DMA: three-point bending) for the same samples. Nanoindentation (Berkovich, 5 μm and 21 μm radii spherical indenters) and DMA were performed on eight wet and dehydrated (100% ethanol), machined equine cortical bone beams. Samples were embedded in polymethylmethacrylate (PMMA) and mechanical tests repeated. Indentation direction was transverse to the bone long axis while DMA tested longitudinally, giving approximately 12% greater modulus in DMA. For wet samples, nanoindentation with spherical indenters revealed a low modulus surface layer. Estimates of the volume of material contributing to elastic modulus measurement showed that the surface layer influences the measured modulus at low loads. Consistent results were obtained for embedded tissue regardless of indenter geometry, provided appropriate methods and analysis were used. Modulus increased for nanoindentation (21 μm radius indenter) from 11.7 GPa ± 1.7 to 15.0 GPa ± 2.2 to 19.4 GPa ± 2.1, for wet, dehydrated in ethanol, and embedded conditions, respectively. The large increases in elastic modulus caused by replacing water with ethanol and ethanol with PMMA demonstrate that the role of water in fine pore space and its interaction with collagen strongly influence the mechanical behavior of the tissue.
Depth-sensing indentation response of ordered silica foam
Authors: Toivola Yvete , Stein Andreas , Cook Robert F.
Published: October 2005

Depth-sensing indentation was applied to three-dimensionally ordered silica foams of two different pore diameters—500 nm and 850 nm—formed by colloidal crystal templating. The contact responses of indentations with Berkovich and hemispherical indentation tips are presented over a load range of 1 mN to 100 mN. Scanning electron microscopy images of residual indentation impressions showed homogeneous deformation for small loads in which the peak displacement was shallow relative to the film–substrate interface. The characteristics of the load–displacement responses changed from periodic discontinuities, associated with cell wall fracture and pore collapse, to smooth and increased stiffness, as a result of densification due to the accumulation of material under the indentation tip and proximity (and contact) of the substrate. Load–displacement responses were translated into pressure–volume space, in which the average pressure during indentation is a measure of the crushing pressure of the cell walls.
A nanoindentation technique for functional evaluation of cartilage repair tissue
Authors: Ebenstein Donna M. , Kuo Alfred , Rodrigo Juan J. , Reddi A. Hari , Ries Michael , Pruitt Lisa
Published: October 2005

Cartilage repair is an ongoing challenge in orthopaedic research. Both biological and mechanical properties are needed for full functional characterization of a tissue replacement. However, assessment of cartilage repair tissue has relied primarily on histological markers because mechanical properties are difficult to measure in small tissue regions. Nanoindentation is a technique that is specialized for measuring local mechanical properties in small specimens. In this study, nanoindentation was used to measure the mechanical properties of cartilage repair tissue following microfracture treatment of chondral defects in three rabbit knees. The mechanical properties were then correlated with histology findings from the same tissue samples. Nanoindentation provided complementary information to histology. In particular, the nanoindentation results showed that the mechanical properties of the repair tissue were inferior to the control tissue properties, even though some tissue regions were histologically similar to the control tissue.
Measuring the strain rate sensitivity by instrumented indentation. Application to an ultrafine grain (equal channel angular–pressed) eutectic Sn–Bi alloy
Authors: Alkorta J. , Sevillano J. Gil
Published: October 2005

The ability of using nanoindentation raw data for characterizing the strain rate sensitivity of the flow stress of elastic–plastic materials has been assessed by finite element calculations. Correction factors for deducing the true strain rate sensitivity from the hardness sensitivity to the hardness penetration rate have been obtained for situations where the elastic contribution to the penetration is not negligible. The results of the analysis are applied to the experimental measurement by nanoindentation of the strain rate sensitivity of an ultrafine grain Sn–Bi eutectic processed by equal channel angular pressing. The flow stress of this material displays bilinear power-law strain-rate dependence. It is also shown that at very low indentation depths, discontinuities of the hardness–penetration curve of the fine-grain Sn–Bi can be correlated with local grain or interphase boundary slip events near the indentation.
Nanoindentation and nanoscratch of a thermal oxide layer on a FeAl alloy
Authors: Xia J. , Li C.X. , Dong H. , Bell T.
Published: October 2005

An iron aluminide (Fe–40 at.% Al) was thermal oxidation (TO)-treated at 1000 °C for 30 to 150 h. The mechanical properties (e.g., hardness and elastic modulus), the scratch resistance, the deformation and damage behaviors of the TO-treated surface layers were evaluated using nanoindentation and nanoscratch techniques. It has been found that the TO treatment produced an oxide layer containing α–Al2O3 on the iron aluminide surface, which increased the surface hardness (H) and elastic modulus (Er) but reduced the ratio of Er/H. This has significantly improved the scratch resistance of the iron aluminide. Longer treatment resulted in a thicker oxide layer and led to further reduced scratch rate and an increased critical load to failure. The scratch resistance has been correlated with the scratch load, the hardness, and the Er/H ratio of the surface oxide layer.
Measurement of hardness and elastic modulus by instrumented indentation: Advances in understanding and refinements to methodology
Authors: Oliver W.C. , Pharr G.M.
Published: October 2005

The method we introduced in 1992 for measuring hardness and elastic modulus by instrumented indentation techniques has widely been adopted and used in the characterization of small-scale mechanical behavior. Since its original development, the method has undergone numerous refinements and changes brought about by improvements to testing equipment and techniques as well as from advances in our understanding of the mechanics of elastic–plastic contact. Here, we review our current understanding of the mechanics governing elastic–plastic indentation as they pertain to load and depth-sensing indentation testing of monolithic materials and provide an update of how we now implement the method to make the most accurate mechanical property measurements. The limitations of the method are also discussed.
Young's modulus measurements on ultra-thin coatings
Authors: Chudoba T. , Griepentrog M. , Dück A. , Schneider D. , Richter F.
Published: October 2005

The determination of the mechanical properties of ultra-thin coatings has become more and more important because of the increasing number of applications using such films. However, an accurate mechanical testing of coatings with a thickness down to some nanometers is still a challenge, despite the improvements of existing measurement techniques. Nanoindentation is an often used mechanical nanoprobe. Using the conventional test method with a sharp Berkovich indenter, the problem of the influence of the substrate on the results arises with decreasing film thickness. Therefore, it is nearly impossible to measure the modulus of films with a thickness less than 100–200 nm. The problem can be overcome by using spherical indenters in combination with an analytical solution for the Hertzian contact of coated systems. It allows a separation of film and substrate properties from the load–displacement curve of the compound. Indentation measurements were done at a 44 nm TiN film and at diamondlike carbon coatings in the thickness range between 4.3 nm and 125 nm on Si substrates. Several corrections were applied to obtain wholly elastic force–displacement curves with high accuracy. It is shown in more detail how zero point and thermal drift corrections are used to obtain statistical depth errors below 0.2 nm. Laser-acoustic measurements based on ultrasonic surface waves were chosen as a second method, which also measures the Young’s modulus in this thickness range. Although the indentation technique is a local probe and the laser-acoustic technique gives an integrated value for a surface range of some millimeters, the results agree well for the investigated samples. In contrast, it was impossible to get the correct Young’s modulus results by conventional indentation measurements with Berkovich indenter, even for ultra-low loads.
Depth-sensing indentation tests in studying plastic instabilities
Authors: Chinh N.Q. , Gubicza J. , Kovács Zs. , Lendvai J.
Published: October 2005

This review surveys the phenomenon of plastic instabilities occurring in depth-sensing indentation measurements. Investigations presented focus on the characterization of Portevin–Le Châtelier type instabilities observed in different metal alloys during indentation. The effect of some important factors such as solute concentration, the formation of Guinier–Preston zones, and grain size and orientation are described and discussed. The phenomenon of plastic instabilities as serrated flow recently observed in bulk metallic glasses is also briefly reviewed.
Analyzing the mechanical behavior of thin films using nanoindentation, cantilever microbeam deflection, and finite element modeling
Authors: Schwaiger R. , Kraft O.
Published: October 2005

A comprehensive study was undertaken to identify the extent to which the mechanical properties of thin metal films on substrates could be determined quantitatively from instrumented sharp indentation. The mechanical behavior of thin Cu films on substrates was investigated using three different methods: nanoindentation, cantilever microbeam deflection, and microtensile testing. Finite element calculations of the nanoindentation and microbeam deflection experiments were conducted to extract yield strength and hardening modulus. Systematic experiments were performed to investigate the consistency of the different experimental techniques. The mechanical behavior of the Cu films was observed to depend on the film thickness. However, the results from finite element modeling of nanoindentation and microbeam deflection are quite different. In both cases, unique solutions for yield strength and hardening modulus were found. This is particularly noteworthy for the nanoindentation experiments; it is argued that the substrate destroys the self-similarity that is present during indentation of bulk material using a Berkovich tip. Microbeam deflection experiments seem to be more sensitive to the elastic–plastic transition, whereas the nanoindentation results describe the mechanical behavior at larger plastic strains. This is corroborated by microtensile tests.
The R8–BC8 phases and crystal growth in monocrystalline silicon under microindentation with a spherical indenter
Authors: Zarudi I. , Zhang L.C. , Zou J. , Vodenitcharova T.
Published: October 2005

The morphology and distribution of high-pressure metastable phases BC8 and R8, formed in monocrystalline silicon under microindentation, were identified and assessed using transmission electron microscopy nanodiffraction analysis. It was discovered that the crystal growth inside the transformation zone was stress-dependent with large crystals in its central region. The crystal size could also be increased using higher maximum indentation loads. The BC8 and R8 phases distributed unevenly across the transformation zone, with BC8 crystals mainly in the center of the zone and smaller R8 fragments in the peripheral regions. Such phase distribution was in agreement with the theoretical residual stress analysis.
Measurement of the loss tangent of a thin polymeric film using the atomic force microscope
Authors: McGuiggan P.M. , Yarusso D.J.
Published: October 2005

An atomic force microscope was used to measure the loss tangent, tan δ, of a pressure-sensitive adhesive transfer tape as a function of frequency (0.01 to 10 Hz). For the measurement, the sample was oscillated normal to the surface and the response of the cantilever resting on the polymer surface (as measured via the photodiode) was monitored. Both oscillation amplitude and phase were recorded as a function of frequency. The atomic force microscopy measurement gave the same frequency dependence of tan δ as that measured by a dynamic shear rheometer on a film 20 times thicker. The results demonstrate that the atomic force microscope technique can quantitatively measure rheological properties of soft thin polymeric films.
A survey of instrumented indentation studies on metallic glasses
Authors: Schuh C.A. , Nieh T.G.
Published: October 2005

The development of instrumented nanoindentation equipment has occurred concurrently with the discovery of many new families of bulk metallic glass during the past decade. While indentation testing has long been used to assess the mechanical properties of metallic glasses, depth-sensing capabilities offer a new approach to study the fundamental physics behind glass deformation. This article is a succinct review of the research to date on the indentation of metallic glasses. In addition to standard hardness measurements, the onset of plasticity in metallic glasses is reviewed as well as the role of shear banding in indentation, structural changes beneath the indenter, and rate-dependent effects measured by nanoindentation. The article concludes with perspectives about the future directions for nanocontact studies on metallic glasses.
Using multidimensional contact mechanics experiments to measure Poisson's ratio
Authors: Lucas B.N. , Hay J.C. , Oliver W.C.
Published: October 2005

Using a new multidimensional contact mechanics system, the normal and tangential elastic contact stiffnesses of six bulk materials with Poisson’s ratios ranging from 0.17 to 0.42 were measured. It is shown that the experimentally measured tangential to normal stiffness ratio can be described as a function of the bulk Poisson’s ratio of the material as predicted by Mindlin. The technique shows a high sensitivity to variations in Poisson’s ratio, suggesting that the technique is a viable means for measuring the Poisson’s ratio of new novel materials. The technique was subsequently applied to two metal film–glass substrate systems. Experimental observations indicate that even when Poisson’s ratio mismatch between the film and the substrate is large, the technique yields appropriate bulk values for the Poisson’s ratio of the film. The experimental details and apparatus are introduced and described.
A numerical study of indentation using indenters of different geometry
Authors: Min Li , Wei-min Chen , Nai-gang Liang , Ling-Dong Wang
Published: October 2005

Finite element simulation of the Berkovich, Vickers, Knoop, and cone indenters was carried out for the indentation of elastic–plastic material. To fix the semiapex angle of the cone, several rules of equivalence were used and examined. Despite the asymmetry and differences in the stress and strain fields, it was established that for the Berkovich and Vickers indenters, the load–displacement relation can closely be simulated by a single cone indenter having a semiapex angle equal to 70.3° in accordance with the rule of the volume equivalence. On the other hand, none of the rules is applicable to the Knoop indenter owing to its great asymmetry. The finite element method developed here is also applicable to layered or gradient materials with slight modifications.
Mechanical characterization of secondary-hardening martensitic steel using nanoindentation
Authors: Ohmura T. , Hara T. , Tsuzaki K. , Nakatsu H. , Tamura Y.
Published: October 2005

Mechanical characterizations using nanoindentation technique were performed for the martensitic steel used as practical dies steel containing carbide-former elements of Cr, Mo, W, and V, which are responsible for secondary hardening by tempering. The nanohardnessHncorresponding to the matrix strength shows obvious secondary hardening, and the hardening-peak temperature coincides with that of the macroscale hardnessHv. By comparing the temper-softening behavior of the high-purity Fe–C binary martensite, the ratio of the nanohardnessHnof the dies steel to that of the Fe–C binary steel is approximately a factor of two, whereas the same ratio of the macroscopic hardnessHvis three at the secondary-hardening peak. These results suggest that the secondary hardening of the dies steel during tempering is attributed not only to the nanoscale strengthening factors such as precipitation hardening by the alloy carbides, but also to some other factors in larger scale. One of the strengthening factors in larger scale is a decomposition of 9% retained austenite to much harder phases, such as martensite and/or ferrite–cementite constituent.
Finite element study for nanoindentation measurements on two-phase materials
Authors: Durst Karsten , Göken Mathias , Vehoff Horst
Published: October 2005

Finite element simulations of conical indentations in two-phase elastic–plastic materials were used to investigate the influence of the shape and the aspect ratio of particles embedded in a matrix material on the deformation behavior and hardness during depth-sensing indentation. Starting with single-phase materials, pile-up behavior and its influence on the contact area was studied. Particle–matrix systems were simulated for elastic–perfectly plastic particles embedded in a matrix, with a yield-strength ratio of 2 or 0.5, respectively. The simulations were motivated by indentation experiments in precipitation hardened nickel-base superalloy with a nanoindenting atomic force microscope. In the studied alloys, the matrix formed channels with a thickness of about 100 nm around the precipitates with diameters of about 500 nm. The simulations explained an experimentally observed transition from particle to matrix deformation behavior during indentation. Depth limits in hardness testing in particle–matrix systems were evaluated. Depending on the aspect ratio, soft and hard particles were tested reliably up to a normalized contact radius of about 70% particle diameter.
Semi-insulating cadmium telluride at low impurity concentrations
Authors: Fiederle M. , Babentsov V. , Fauler A. , Witte W. , Benz K.W. , James R.B.
Published: October 2005

We report a substantial reduction in the impurity concentration of semi-insulating CdTe:Ge grown by the vertical Bridgman method by using sublimation of the feed material. Specific resistivity (ρdark) values of up to 3 × 109 Ω cm were obtained for samples with a relatively high photosensitivity (PS) value and optimal compensation. Concentrations of impurities in the feed and as-grown crystals were determined by the glow discharge mass spectroscopy (GDMS) method. The energy levels in the band-gap were studied by photoluminescence (PL), and the data were correlated with the GDMS measurements. The highest values of ρdark and PS were observed in the regions where the PL bands via the deep levels of Ge and Te antisite were present.
The reaction sequence and microstructure evolution of an MgB2 layer during ex situ annealing of amorphous boron film
Authors: Kim Hyun-Mi , Yim Sung-Soo , Kim Ki-Bum , Kang Dae-Hwan , Moon Seung-Hyun , Kim Young-Woon , Lee Ho-Nyun
Published: October 2005

The reaction sequence and microstructure evolution of a crystalline MgB2 layer were examined during ex situ annealing of evaporated amorphous boron (a-B) with Mg vapor. Mg was found to migrate rapidly into the a-B layer in the initial stage of reaction with a uniform concentration of about 12 at.%. A thin layer of crystalline MgO was observed at the interface between a-B and the Al2O3 substrate. It was identified that an MgB2 layer started to form at the surface by the nucleation and growth process in polycrystalline form. It appears that there exists two distinct growth fronts in the MgB2 layer: one lying at the surface and the other lying at the interface between the MgB2 layer and the a-B. The microstructural evolution of this layer showed significant differences depending on the location of these two growth fronts.
A study on the growth and structure of titania nanotubes
Authors: Wang Wenzhong , Varghese Oomman K. , Paulose Maggie , Grimes Craig A. , Wang Qinglei , Dickey Elizabeth C.
Published: October 2005

Titania nanotubes synthesized by a soft chemical process are described, having diameters of 8 nm to 10 nm and lengths ranging from approximately 0.1 μm to 1 μm. X-ray diffraction studies show the structure of the as-prepared nanotubes is the same as that of the starting anatase TiO2nanoparticles. Energy-dispersive x-ray analysis and electron energy loss spectroscopy studies further indicate that the as-prepared nanotubes are composed of titania. Studies using transmission electron microscopy verified that the nanotubes are formed during alkali treatment, with subsequent acidic treatments having no effect on nanotube structure and shape.
Synthesis and characterization of single-crystal indium nitride nanowires
Authors: Tang Tao , Han Song , Jin Wu , Liu Xiaolei , Li Chao , Zhang Daihua , Zhou Chongwu , Chen Bin , Han Jie , Meyyapan M.
Published: October 2005

InN nanowires were synthesized and characterized using a variety of techniques. A two-zone chemical vapor deposition technique was used to operate the vapor generation and the nanowire growth at differential temperatures, leading to high-quality single-crystalline nanowires and growth rates as high as 4–10 μm/h. Precise diameter control was achieved by using monodispersed gold clusters as the catalyst. Photoluminescence and Raman studies have been carried out for the InN nanowires at room temperature. Devices consisting of single nanowires have been fabricated to explore their electronic transport properties. The temperature dependence of the conductance revealed thermal emission as the dominating transport mechanism.
Comments on “Fabrication of ternary Mg–Cu–Gd bulk metallic glass with high glass-forming ability under air atmosphere” [H. Men and D.H. Kim, J. Mater. Res. 18, 1502 (2003)]
Authors: Lu Z.P. , Liu C.T.
Published: October 2005

A new Mg-based bulk amorphous alloy (i.e., Mg65Cu25Gd10) has successfully been developed by Men and Kim [H. Men and D.H. Kim, J. Mater. Res. 18, 1502 (2003)]. They showed that this alloy exhibits significantly improved glass-forming ability (GFA) in comparison with Mg65Cu25Y10 alloy. However, this improved GFA cannot be indicated by the supercooled liquid region ΔT and the reduced glass-transition temperature Trg. As shown in the current comment, the new parameter γ, Tx/(Tg + Tl) defined in our recent papers [Z.P. Lu and C.T. Liu, Acta Mater. 50, 3501 (2002); Z.P. Lu and C.T. Liu, Phys. Rev. Lett. 91, 115505 (2003)] can well gauge GFA for bulk metallic glasses, including the current Mg-based alloys.
Elucidation of the electrodeposition mechanism of molybdenum oxide from iso- and peroxo-polymolybdate solutions
Authors: McEvoy Todd M. , Stevenson Keith J.
Published: October 2005

The cathodic electrodeposition of molybdenum oxide thin films prepared from aqueous solutions containing iso-polymolybdates and peroxo-polymolybdates is described. Chronocoulometry, x-ray photoelectron spectroscopy, spectroelectrochemistry, and electrochemical quartz crystal microgravimetry were used to establish corresponding reaction mechanisms for films grown at different deposition potentials. Electrodeposition from acidified iso-polymolybdate solutions proceeds by the reduction of molybdic acid, whereas deposition from aqueous peroxo-based solutions involves the graded reduction of several solution components, primarily comprising molybdic acid and peroxo-polymolybdates. Careful regulation of the deposition potential allows for controlled growth of distinct molybdenum oxide compositions producing films with varied water content and valency.
Electrochemical behavior of bimetallic Ni–Ti surface generated by ion implantation
Authors: Pham M.T. , Maitz M.F. , Reuther H. , Richter E. , Matz W. , Muecklich A. , Prokert F.
Published: October 2005

Thin films Ni−Ti (<100 nm) having surface Ni content below 5 at.% were prepared by ion-implanting Ni into Ti surfaces. The Ni-containing phase exposed or buried within the Ti matrix was amorphous. Following an anodic oxidation in NaOH, the material was shown to be redox active and to promote the electrocatalytic oxidation of glucose depending on the surface Ni–Ti composition. Compared to the Ni–Ti bulk alloy (55.9:44.08), the Ni-implanted Ti displayed a more efficient catalytic activity and improved corrosion resistance.
Microstructural characterization of sputter-deposited Pt thin film electrode
Authors: Lim Ji-Eun , Jeong Jae Kyeong , Ahn Kun Ho , Kim Hyeong Joon , Hwang Cheol Seong , Park Dong-Yeon , Lee Dong-Su
Published: October 2005

Pt thin films of various thicknesses (30 nm ∼ 200 nm) were deposited on Si wafers with SiO2, Ti, TiO2, or IrO2 buffer layers at various temperatures (room temperature ∼200 °C) by a direct current magnetron sputtering process. The Pt films showed a strong (111)-preferred texture irrespective of the thickness, under-layer, and growth temperature. The authors previously reported [J-E. Lim, D-Y. Park, J.K. Jeong, G. Darlinski, H.J. Kim, and C.S. Hwang, Appl. Phys. Lett. 81, 3224 (2002)] that the films were composed of three kinds of grains with slightly different (111) lattice parameters (bulklike, 1.0% and 2.1% larger). This study details the microstructural variations of the Pt films according to the variations of experimental parameters. The different deposition conditions produced slightly different crystalline structures, but the three different (111) lattice parameters were always found. Epitaxial (200) Pt films on a (200) MgO substrate and a highly (111) textured Au thin film on a SiO2/Si did not show the same splitting in the lattice parameter. The grains with 1.0% and 2.1% larger (111) lattice parameter almost disappeared after postannealing at 1000 °C. However, surface chemical binding of the Pt film before and after annealing was unchanged. Therefore, it is believed that the lattice parameter splitting in the (111) textured Pt film originated from the interfacial grains with the distorted crystal structure due probably to growth stress.
Combustion synthesis of nanocrystalline yttria-doped ceria
Authors: Chavan S.V. , Tyagi A.K.
Published: October 2005

Nanocrystalline yttria-doped ceria powder, with the composition Ce0.55Y0.45O1.775, was synthesized by a combustion technique using citric acid as the fuel and the corresponding metal nitrates as oxidants. This process involves mild conditions as the external temperature required to initiate the combustion is only approximately 250 °C. The product was characterized by x-ray diffraction (XRD) to ascertain the phase purity. The crystallite size of these calcined samples, as seen by transmission electron microscopy, was found to be in the range 6 nm to 50 nm. The surface area of the fine powder, as obtained from the Brunauer–Emmett–Teller technique, was about 140 m2/g. The agglomeration behavior as a function of temperature and the lattice thermal expansion studies were carried out using high-temperature XRD. This nanocrystalline powder resulted in nearly theoretical bulk density at a relatively lower temperature, which is attributed to the superior powder properties. The sintered microstructure, as studied by scanning electron microscopy, revealed the presence of fine grains.
Characteristics of thin film transistors fabricated employing various sequential lateral solidification poly-Si microstructures
Authors: Park Ji-Yong , Park Hye-Hyang , Lee Ki-Yong , Chung Ho-Kyoon
Published: October 2005

Sequential lateral solidification (SLS) is known to be a promising method to make low-temperature poly-Si thin film transistors (LTPS TFTs) with superior performance for fabrication of highly circuit-integrated flat panel displays such as TFT liquid crystal display and TFT organic light-emitting diode. The dependence of TFT characteristics on the details of the SLS poly-Si microstructures was studied by varying the size, direction, and shape of the grains by applying different SLS crystallization mask patterns and processing details. The TFTs results demonstrated that various device properties and characteristics are obtained depending on the specifics of the microstructures. Nearly direction-insensitive TFTs of mobility about 300 cm2/V·s (within 5% variation of average value) were successfully fabricated by controlling the microstructures. Such a characteristic is recognized as being desirable for an optimal integration of the peripheral circuits.
Size effects of nanoindentation creep
Authors: Li H. , Ngan A.H.W.
Published: October 2005

The size effects on indentation creep were studied on single-crystal Ni3Al, polycrystalline pure Al, and fused quartz samples at room temperature. The stress exponents were measured by monitoring the displacement during constant indentation loads after correction for thermal drift effects. The stress exponents were found to exhibit a very strong size effect. In the two metals Al and Ni3Al, the stress exponent for very small indents is very small, and for Al, this even approaches unity, suggesting that linear diffusional flow may be the controlling mechanism. The stress exponents in these two metals rise rapidly to over 100 as the indent size gets larger, indicating a rapid change of the dominating mechanism to climb-controlled to eventually glide-controlled events. In fused quartz, the stress exponent also exhibits a sharply rising trend as the indent size increases. The stress exponent is also close to unity at the smallest indents studied, and it rises rapidly to a few tens as the indent size gets larger.
Effect of silicon addition on surface morphology and structural properties of titanium nitride films grown by reactive unbalanced direct current-magnetron sputtering
Authors: Shen Y.G. , Liu Z-J. , Jiang N. , Zhang H.S. , Chan K.H. , Xu Z.K.
Published: October 2005

Thin films of Ti1–x–y Six Ny were produced on unheated Si(100) substrates by reactive unbalanced dc-magnetron sputtering of titanium and silicon in an Ar–N2 gas mixture. The effects of silicon incorporation on surface morphology and structural properties of these films as well as the influence of postdeposition annealing have been studied. These films were characterized ex situ in terms of their core-level electron bonding configuration by x-ray photoelectron spectroscopy, their microstructure by cross-sectional transmission electron microscopy and x-ray diffraction, their hardness by nanoindentation measurements, and their roughening kinetics by atomic force microscopy (AFM) with the scaling analysis. It was found that a linear increase in the Si concentration of the films was observed with increasing Si target current up to 2 A whereas the reverse trend was seen for the Ti concentration. The films consisted of 15–20-nm-sized TiN crystallites embedded in an amorphous SiNx matrix. They had a hardness of about 32.8 GPa with silicon concentration x = 0.1. The improved mechanical properties of Ti1–x–y Six Ny films with the addition of Si into TiN were attributed to their densified microstructure with development of fine grain size and reduced surface roughness. The reduction in grain size has been supported by means of a Monte Carlo simulation that reveals that the average size of TiN grains decreases with the volume fraction of amorphous SiNx approximately according to a power law, showing a reasonable agreement with the experimental results. By applying the height–height correlation functions to the measured AFM images, a steady growth roughness exponent α = 0.89 ± 0.05 was determined for all the films with different Si additions. It was also found that the nanocomposite films were thermodynamically stable up to 800 °C. The effect of thin SiNx layer in stabilizing nanocrystalline TiN structure is also elucidated and explained on the basis of structural and thermodynamic stability.