Micro-sized Specimens Research Articles

Precise quantification of the adhesion between metallic thin films and silicon wafer

The performance and reliability of integrated circuits depend on the mechanical and electrical properties of the interfaces between thin films and the silicon wafer. One of the essential properties of the interface is its adhesion energy. However, conventional adhesion characterization methods could be further improved, especially in providing repeatable and reliable measurements. In this paper, we measured the adhesive strength of the interface between tungsten thin films and silicon wafers in micro-sized specimens using a direct push-to-pull device built into a nano-indenter. A scratch method with a transparent theoretical model was applied to quantify the same interfaces' adhesive strength, adhesion energy, and fracture resistance. Microscopic and mechanical analysis clarified the physical origin of thin film delamination. The current method precisely quantified the interfaces' adhesive strength and fracture resistance. This method is promising for sub-micron thin film designs in the semiconductor industry with its superior repeatability, reliability, and ease of operation.

Physical Properties of Sintered Stainless Steel 17-4PH Micro-Part Processed by MicroPowder Injection Molding

Micro-powder injection molding (μPIM) is a modification of powder injection molding (PIM) process and a globally recognized manufacturing process route that can be used largely to produce sophisticated micro-sized components using a wide range of metals and ceramics. The demand of μPIM process is currently increasing in various applications in telecommunication, electronics, aerospace, biomedical, and automotive industries. In this research work, sintering at three different temperatures between 1250 °C and 1350 °C at a heating rate of 10 °C/min with a dwelling period of 3 h on micro-injection molded and debound (solvent and thermal) micro-sized components of stainless steel 17-4PH (SS 17-4PH) was carried out. After the sintering operation, defect-free SS 17-4PH micro-specimens were achieved. The relative density, which is referred to as an important physical property of SS 17-4PH micro-parts, increased substantially from 95.3% to 97.5% when the sintering temperature was enhanced from 1250 °C to 1350 °C. The maximum shrinkage of 12.9% was observed in micro-sized specimens at the sintering temperature of 1350 °C. After the completion of sintering process, the findings revealed that SS 17-4PH micro-parts can be produced successfully on the grounds of μPIM process employing the SS 17-4PH feedstock with powder loading of 69 vol.%.

High fracture toughness in van der Waals-layered MoTe2: Disappearance of stress singularity

In this study, we demonstrated that van der Waals-layered MoTe2, where two-dimensional atomic layers are closely laminated by weak interactions, has higher fracture toughness in out-of-plane cracks than that in in-plane cracks owing to structural anisotropy. In situ electron microscopy fracture toughness tests were performed on micro-sized specimens. The apparent fracture toughness of the out-of-plane crack based on the continuum assumption was approximately twice that of the in-plane crack. In the out-of-plane crack specimen, as the loading progressed, interlaminar slip occurred between layers, and this discrete nature caused the stress singularity to disappear, leading to high fracture toughness.

Long-term behaviour of welded polypropylene liners for pit thermal energy storages

This paper deals with the global ageing behaviour of a polypropylene random copolymer (PP-R) liner material with tailor-made primary structure, morphology and stabilization package. Specific focus was given to the long-term behaviour of the liner material in the welding zones. Conventional weld line testing was not feasible due to plastic deformation of the peel arms. Hence, a novel testing approach based on micro-sized specimen was implemented and used. The PP-R liner was welded varying the hot wedge temperatures ranging from 320 to 410 °C. For accelerated ageing, welded micro-specimens with a thickness of 100 μm were manufactured and exposed to hot air at 95, 115 and 135 °C. The investigated ageing indicators included phenol index and oxidation temperature which are highly sensitive to stabilizer degradation. Moreover, the carbonyl index and strain-at-break values were monitored reflecting primarily polymer degradation. To evaluate potential effects of welding, welded and unwelded micro-specimens were compared. By assessment of phenol index and oxidation temperature a critical temperature dependent consumption of stabilizer was ascertained. Nevertheless, the rate of stabilizer degradation was comparable for unwelded and welded PP-R. The investigated hot wedge temperatures had no significant impact on further stabilizer depletion or polymer degradation. So far, failure of the PP-R material was obtained for an exposure temperature of 135 °C after 3750 h. The long-term behaviour and the embrittlement time of the polymer material was not affected by welding.

Micro versus Macro Shear Bond Strength Testing of Dentin-Composite Interface Using Chisel and Wireloop Loading Techniques.

Shear bond strength (SBS) testing is a commonly used method for evaluating different dental adhesive systems. Failure mode analysis provides valuable information for better interpretation of bond strength results. The aim of this study was to evaluate the influence of specimen dimension and loading technique on shear bond strength and failure mode results. Eighty macro and micro flowable composite cylindrical specimens of 1.8 and 0.8 mm diameter, respectively, and 1.5 mm length were bonded to dentinal substrate. Four study groups were created (n = 20): Macroshear wireloop, Gp1; Microshear wireloop, Gp2; Macroshear chisel, Gp3; and Microshear chisel, Gp4. They were tested for SBS using chisel and wireloop loading devices followed by failure mode analysis using digital microscopy and SEM. Two- and one-way ANOVA were used to compare stress at failure values of different groups while the Kruskal–Wallis test was used to compare between failure modes of the tested groups. Gp4 recorded the highest mean stress at failure 54.1 ± 14.1 MPa, and the highest percentage of adhesive failure in relation to the other groups. Specimen dimension and loading technique are important parameters influencing the results of shear bond strength. Micro-sized specimens and chisel loading are recommended for shear testing.

Effect of Small Amount of Ni Addition on Microstructure and Fatigue Properties of Sn-Sb-Ag Lead-Free Solder.

The effect of the addition volume of Ni on the microstructures and tensile and fatigue properties of Sn-6.4Sb-3.9Ag (mass%) was investigated using micro-size specimens. The addition of Ni into Sn-6.4Sb-3.9Ag tends to increase the number of grains formed in the solidification process and produce a high-angle grain boundary. An amount of 0.1% proof stress of Sn-6.4Sb-3.9Ag decreases with an increase in the Ni addition volume at a strain rate of 2.0 × 10−1 s−1. The effect of the addition of Ni into Sn-6.4Sb-3.9Ag on tensile strength is negligible at both 25 °C and 175 °C. The elongation of Sn-6.4Sb-3.9Ag decreases with an increase in the Ni addition volume at 25 °C according to the fracture mode change from ductile chisel point fracture to shear fracture. The effect of the addition of Ni into Sn-6.4Sb-3.9Ag on the elongation is negligible at 175 °C. The low cycle fatigue test result shows that the fatigue life does not degrade even at 175 °C in all alloys investigated. The fatigue life of Sn-6.4Sb-3.9Ag-0.4Ni (mass%) is superior to those of Sn-6.4Sb-3.9Ag and Sn-6.4Sb-3.9Ag-0.03Ni (mass%) in the high cycle fatigue area. The electron back scattering diffraction (EBSD) analysis result shows that fine recrystallized grains are generated at the cracked area in Sn-6.4Sb-3.9Ag-0.4Ni in the fatigue test at 175 °C, and the crack progresses in a complex manner at the grain boundaries.

Effects of moisture content on mechanical properties of micro-size oak wood

Effects of moisture content (MC) were investigated for the mechanical properties of oak wood (Quercus petraea Liebl.) using micro-size test specimens. The micro-size specimens for bending, tensile, and compression tests were prepared and divided into five groups. Each group was conditioned at a different relative humidity and temperature to achieve MC values of 8%, 12%, 16%, 20%, and above-fiber-saturation-point MCs. After conditioning, the bending strength, modulus of elasticity (MOE) in bending, tensile strength, and compression strength values were determined. The results showed that MC had statistically significant effects on all the measured mechanical properties in the micro-size oak wood samples. The greatest decrease was observed for the compression strength, while the lowest decrease was observed for the tensile strength, when MC increased. The changing rates induced by 1% MC were calculated as 3% for bending strength, 2.5% for the MOE, 2.0% for the tensile strength, and 3.1% for the compression strength.

Global and Local Aging in Differently Stabilized Polypropylenes Exposed to Hot Chlorinated Water with and without Superimposed Mechanical-Environmental Loads.

The influence of chlorinated water on the global and local aging behavior of polypropylene (PP) was investigated for three differently stabilized PP grades consisting of the same PP base polymer. While one of the PP grades contained only a processing stabilizer (PP-S0), the other two were modified with a primary phenolic antioxidant (PP-S1) and a combination of a primary phenolic antioxidant and a hindered amine stabilizer (PP-S3). To study global aging effects, micro-sized specimens were pre-exposed to chlorinated water (5 mg/L free chlorine) at 60 °C for up to 750 h. Over the entire exposure period, significant material aging was detected by monitoring a continuous decrease in stabilizer content, oxidation induction temperature, mean molar mass, and mechanical strain at break. In terms of aging resistance and ultimate mechanical performance, PP-S1 was found to outperform the other two material formulations under these test conditions. Moreover, superimposed mechanical-environmental fatigue tests with cracked round bar specimens were carried out with the three PP grades in non-chlorinated (0 mg/L free chlorine) and chlorinated (5 mg/L free chlorine) water at 80 °C and 95 °C to study local crack tip aging effects. While the fatigue crack growth resistance substantially deteriorated for all three materials in chlorinated water, a significantly stronger effect was found for the higher temperature, with crack growth rates at a given stress intensity factor range in chlorinated water being ca. 30 to 50 times faster than in non-chlorinated water, depending on the material. Molar mass measurements of material samples taken from various positions of the tested CRB specimens provided clear evidence of enhanced local crack tip aging due to the chlorinated water environment.

Chlorinated Water Induced Aging of Pipe Grade Polypropylene Random Copolymers.

Polypropylene random copolymers (PP-R) are common materials for pressurized hot water pipes. In many pipe systems, potable water is disinfected by chlorine to prevent waterborne diseases. This paper deals with hot chlorinated water induced aging of two PP-R grades with varying morphology. One material had a conventional monoclinic α crystal form (PP-Rα), whereas the other was explicitly beta-nucleated resulting in a trigonal β crystal form with a fine spherulite structure (PP-Rβ). Micro-sized specimens with a thickness of 100 µm were used for aging experiments at 60 °C in chlorinated water with 5 mg/L free chlorine, and aging indicators were monitored for exposure times of up to 2000 h. On the other hand, superimposed mechanical-environmental tests were carried out by using cracked round bar specimens with a diameter of 14 mm to determine the fatigue crack growth (FCG) resistance of both PP-R grades at 60 °C in non-chlorinated and chlorinated water. PP-Rβ was found to outperform PP-Rα with an about 30% higher time-to-embrittlement value of 2000 h. Furthermore, PP-Rβ exhibited an enhanced FCG resistance in both non-chlorinated and chlorinated water. The effect of chlorine content on the deterioration of the FCG resistances was significantly more pronounced for PP-Rα.

Aging behavior and lifetime assessment of polyolefin liner materials for seasonal heat storage using micro-specimen

The paper deals with the lifetime assessment of polyethylene (PE) and polypropylene (PP) liner materials for seasonal heat storages. Temperature loading profile was estimated for a storage type with maximum temperatures of 85 °C in September and minimum temperatures of 50 °C in March. Aging experiments in hot air or water at elevated temperatures were carried out using micro-sized specimen. The aging indicator strain-at-break was monitored. From experimental data at elevated temperatures endurance times at service-relevant temperatures were extrapolated using an Arrhenius approach. By weighting the endurance times with the loading profiles and assuming cumulative damages, lifetime values were deduced. The investigated PP random copolymer liner material exhibited a significant better long-term performance than the well-established PE liner material.

Effect of thickness and temperature on the global aging behavior of polypropylene random copolymers for seasonal thermal energy storages

This paper deals with the global aging behaviour of a polypropylene random copolymer liner material for seasonal thermal energy storages. Hot air aging experiments at elevated temperatures of 95 °C, 115 °C and 135 °C were carried out using micro-sized specimens with thicknesses ranging from 50 to 2000 µm. The aging indicator strain-at-break was monitored for an exposure of up to 1500 days. Potential and Arrhenius equations were used to fit the experimental hot air aging data referring to thickness and temperature dependency. A semi-empirical model was established and used to assess the lifetimes of polypropylene based thermal energy storage liners. The high quality of the thickness/temperature-model was approved by low divergence of the lifetime values between experimental and modelled failure data. Depending on the temperature loading profile of the seasonal thermal energy storage lifetime values ranging from 20 to 47 years were deduced for a PP liner with a thickness of 2 mm.

Effect of carbon nanotubes on the global aging behavior of β-nucleated polypropylene random copolymers for absorbers of solar-thermal collectors

This paper deals with the effect of carbon nanotubes (CNT) on the basic characteristics and the global aging behaviour of β-nucleated polypropylene random copolymer absorber material for overheating protected solar thermal collectors. Hot air aging experiments at an elevated temperature of 135 °C were carried out using micro-sized specimens with a thickness of 100 µm. The unaged specimens were characterized as to the antioxidant content and the mechanical and thermal properties. The CNT pigment affected the semi-crystalline morphology (less β-content) and increased the stiffness significantly. The aging indicators strain-at-break, average molar mass, primary antioxidant content and oxidation temperature were monitored for up to 4000 h. A more pronounced degradation was deduced for the compounds with CNT. Compared to carbon black modified grades a higher deterioration rate was ascertained for the CNT compounds. The amount of CNT should be kept at low levels (<0.1 wt%) just needed to achieve sufficient solar absorbance (>90%) of the absorber sheet.

Mechanical properties evaluation of micro-sized specimens made of Ti alloy for Tough MEMS

Mechanical properties evaluation of micro-sized specimens made of Ti alloy for Tough MEMS

Micro-mechanical properties of Oak wood and comparison with standard-sized samples

The aim of this study was to investigate micro-mechanical properties of Oak (Quercus petraea) wood and to compare with standard-size test specimens values. Bending strength, modulus of elasticity in bending, compression strength and tensile strength were determined using micro- and standard-size mechanical test samples. In the micro- and standard size samples, bending strengths were evaluated as 71,2 MPa and 99,4 MPa, modulus of elasticity in bending as 2741,3 MPa and 11394,1 MPa tensile strengths as 98,7 MPa and 93,8 MPa and compression strengths as 45,4 MPa and 46,6 MPa respectively. The results showed that the bending strength, modulus of elasticity and compression strength of the micro-size samples were lower compared to the standard-size samples, while the tensile strength was higher in the micro-size samples. The compression strength values of micro- and standard-size samples were not significantly different. The regression analyses indicated a positive linear regression between the mechanical properties of micro- and standard-size samples. Micro-size specimens can be used to estimate the mechanical properties of Oak wood when obtaining standard-size specimens is not possible.

Hydrogen embrittlement revealed via novel in situ fracture experiments using notched micro-cantilever specimens

The susceptibility of the FeAl intermetallic alloy to hydrogen-assisted cracking was investigated by in situ fracture experiments using notched micrometre-sized specimens using an Environmental Scanning Electron Microscope (ESEM). The notched beams were loaded under two different environmental conditions: one in high vacuum (5 × 10−4 Pa) to avoid hydrogen effects and one under a certain water vapor pressure (450 Pa) to promote hydrogen uptake. The fracture behaviour on a non-ASTM-standard micro-sized specimen was successfully studied by the experimental approach, and the microstructure of the whole crack area was analysed by Transmission Kikuchi Diffraction (TKD) and Transmission Electron Microscopy (TEM) techniques. Three crack growth stages were observed in all the specimens: i) elastic regime, ii) notch blunting and micro-crack formation; and iii) stable crack growth. We observed an accelerated crack propagation rate in specimens under hydrogen exposure. The hydrogen embrittlement phenomenon was found to occur because of the strong hydrogen-dislocation interactions. The combined effect of hydrogen-enhanced dislocation nucleation and hydrogen-restricted dislocation mobility is responsible for the hydrogen-enhanced cracking behaviour.

In-situ Elastic Strain Mapping via EBSD of Micro-Sized Specimens

In-situ Elastic Strain Mapping via EBSD of Micro-Sized Specimens

Fracture Toughness of Granite Measured Using Micro to Macro Scale Specimens

The objective of this study is to examine any variation from micro to macro scale mode-I fracture toughness of granite using micro-sized specimen and semi-circular specimen. The rock used in the tests is Iksan granite (Korea) which is composed of minerals, such as plagioclase and alkali feldspar, quartz. In order to investigate micro scale fracture toughness, a mechanical testing machine was used. This machine is an original one and developed by ourselves. In the test, a micro-sized cantilever beam type specimen was used. Its dimension is 10 × 10 × 50μm. On the other hand, in order to examine macro scale fracture toughness, Semi-Circular Bend (SCB) test is adopted. This is one of ISRM-suggested methods for estimation of the mode-I fracture toughness of rocks. The semi-circular specimens are prepared with a radius of 12.5mm to 50mm. Based on the fracture toughness obtained from both tests, the size effect of granite is discussed in the range from micro to macroscale.

Tensile tests of micro-specimens composed of electroplated gold

Tensile tests were conducted using micro-sized specimens fabricated from constant current and pulse current electroplated Au. The micro-specimens were fabricated by a focused ion beam system and tested by a specially designed micro-mechanical testing machine. Fine-grained electroplated Au was achieved by the pulse current electroplating. Average grain size of the pulse current electroplated Au film was 0.77±0.33μm. Strengthening by grain refinement was observed from the micro-tensile test of the pulse current electroplated Au. The yield stress reached 387MPa. The results obtained in this study followed the Hall-Petch relationship well.

Comparison of Micro- and Standard-Size Specimens in Evaluating the Flexural Properties of Scots Pine Wood

The aim of this study was to investigate the flexural properties (bending strength and modulus of elasticity) of Scots pine wood (Pinus sylvestris L.) using micro- and standard-size test specimens. In the standard- and micro-size specimens, the average bending strengths were evaluated as 72.8 and 62.4 MPa, and the bending modulus of elasticity was 9917 and 2884 MPa, respectively. These results showed that the bending strength and modulus of elasticity values of the micro-size specimens were lower than those of the standard-size specimens. The statistically significant effects included the specimen size, individual trees, and the interactions of the specimen size and trees on the bending strength and modulus of elasticity. Furthermore, regression analyses indicated a positive linear regression between the flexural properties of the micro- and standard-size specimens. The results indicated that micro-size specimens can be used to estimate the flexural properties of Scots pine wood when obtaining standard-size specimens is not possible.

Fine Grained Au Films with Controllable Mechanical Strength By Pulse Plating for Micro-Electrical-Mechanical System Accelerometer

Au materials fabricated by electroplating are commonly used as contact materials for high reliability circuit boards, electrical connectors, relays, and micro- and nano-scale electronic components for many decades because of their high electrical conductivity, chemical stability, corrosion resistance, and ductility. In recent years, Au has become a promising material to be used as the movable structures and proof mass in micro-electrical-mechanical system (MEMS) accelerometer devices, mostly because of the high density (19.3×103 kg/m3 at 298 K), which is about 10 times higher than that of silicon (2.33×103 kg/m3at 298 K) [1]. However, Au is known to be a soft material. The mechanical strength becomes a concern in miniaturization of the MEMS device. Yield stress of bulk Au is reported to be 55~200 MPa [2]. Decreasing grain size of the Au materials is expected to further enhance the mechanical properties according to the Hall-Petch relationship [3]. Pulse electroplating (PE) has been reported to be effective in fabricating Au materials with fine grains, high uniformity, and low porosity [4]. Also, it is possible to control the composition and the film thickness by regulating the pulse amplitude and width. Most importantly, an increase in the nuclei density could be achieved to obtain electroplated films with finer grains. On the other hand, for evaluating mechanical properties of the electroplated films, Vickers micro-hardness test is the most popular method. However, the hardness results are often affected by the substrate. It cannot show the real strength of the electroplated materials, especially for films in mico-/nano-scale. Therefore, it is necessary to evaluate micro-mechanical strength of the Au electroplated films for the practical applications in the miniaturized devices. Au electrolyte used in this study was a commercially available sulfite-based electrolyte provided by Matex Japan (Matex Gold NCA). The electrolyte contains 50 g/L of Na2SO3, 50 g/L of (NH4)2SO3, and 21.63 g/L of Na3[Au(SO3)2] with pH of 8.0 and 5% sodium gluconate. Cu plates and Pt plates were used as the cathode and anode, respectively. For the PE, the pulse current (Ion) was 10 mA/cm2, and the off-time current (Ioff) was 0 mA/cm2. The on-time (Ton) of the PE varied from 1 to 100 ms, and the off-time (Toff) was 10 ms. The reaction temperature was 40 ºC for the gold electroplating. The Au films prepared by the PE showed less defect, lower surface roughness, finer grain size, and denser texture when compared with the Au films prepared by the conventional constant-current electroplating (CE). Micro-mechanical properties of Au micro-pillars fabricated from the Au films were evaluated by micro-compression test. Dimensions of the fabricated pillars were 10 μm×10 μm×20 μm. The compression tests were carried out using a test machine specially designed for micro-sized specimens equipped with a flat-ended diamond indenter at a constant displacement of 0.1μm/s. The Au micro-pillars prepared by the PE showed controllable high strength ranged from 500 to 800 MPa, where the grain size was adjusted by the PE parameters. Finest grain size was estimated to be 10.4 nm, and the highest compressive strength was 800 MPa [5]. The compressive strength obtained is much higher than the values reported in other studies [6,7]. The high strength is suggested to be due to the grain-boundary strengthening mechanism. The results demonstrated that the PE method and the sulfite-based electrolyte are promising for applications in miniaturization of the MEMS devices. To the best of our knowledge, this is the also first report on micro-mechanical strength of pure Au materials fabricated by the PE.