Novel Differential Surface Stress Sensor for Detection of Chemical and Biological Species

A miniature sensor consisting of two adjacent micromachined cantilevers (a sensing/reference pair) is developed for detection of chemical and biological species. A novel interferometric technique is utilized to measure the differential bending of sensing cantilever with respect to reference. Presence of species is detected by measuring the differential surface stress associated with adsorption/absorption of chemical species on sensing cantilever. Surface stress associated with formation of alkanethiol self-assembled monolayers (SAMs) on the sensing cantilever is measured to characterize the sensor performance

Ultrahard Polycrystalline Cubic Boron Nitride Composite through Hybrid Laser/Waterjet Heat (LWH) Treatment

Ultra-hard materials that are chemically inert and thermally stable at high temperatures are desirable for enhancing machining and wear performance in demanding chemical and thermal environments. Single and polycrystalline diamonds are the hardest tool materials; however, at high temperatures, diamond reacts with ferrous alloys, losing its chemical inertness and thermal stability. In contrast, cubic boron nitride (cBN) has exceptional chemical and thermal stability but has much lower hardness (35-45 GPa). Increasing the hardness of BN is expected to fill the property gap in state-of-the-art tool materials as shown and to generate huge industrial interest for meeting the stringent design requirements such as machining optical surfaces and reducing the cost and time for machining ferrous materials. A novel laser/waterjet heat treatment (LWH) process is investigated to enhance the surface hardness of a dual phase boron nitride (BN) material composed of 50% cubic and 50% wurtzite phases. Results indicate that experimentally measured hardness increase is dependent on the processing parameter such as laser fluence and overlap between heat treatment passes. Statistical analysis is carried out to identify the processing parameter that result in maximum hardness increase

Improved Method of CO2 Laser Cutting of Aluminum Nitride

The traditional “evaporation∕melt and blow” mechanism of CO2 laser cutting of aluminum nitride (AlN) chip carriers and heat sinks suffers from energy losses due to its high thermal conductivity, formation of dross, decomposition to aluminum, and uncontrolled thermal cracking. In order to overcome these limitations, a thermochemical method that uses a defocused laser beam to melt a thin layer of AlN surface in oxygen environment was utilized. Subsequent solidification of the melt layer generated shrinkage and thermal gradient stresses that, in turn, created a crack along the middle path of laser beam and caused material separation through unstable crack propagation. The benefits associated with thermal stress fracture method over the traditional method are improved cut quality, higher cutting speed, and lower energy losses

Obtaining a Relationship Between Process Parameters and Fracture Characteristics for Hybrid CO2 Laser∕Waterjet Machining of Ceramics

A combined experimental and analytical approach is undertaken to identify the relationship between process parameters and fracture behavior in the cutting of a 1mm thick alumina samples by a hybrid CO2 laser∕waterjet (LWJ) manufacturing process. In LWJ machining, a 200W power laser was used for local heating followed by waterjet quenching of the sample surface leading to thermal shock fracture in the heated zone. Experimental results indicate three characteristic fracture responses: scribing, controlled separation, and uncontrolled fracture. A Green’s function based approach is used to develop an analytical solution for temperatures and stress fields generated in the workpiece during laser heating and subsequent waterjet quenching along the machining path. Temperature distribution was experimentally measured using thermocouples and compared with analytical predictions in order to validate the model assumptions. Computed thermal stress fields are utilized to determine the stress intensity factor and energy release rate for different configurations of cracks that caused scribing or separation of the workpiece. Calculated crack driving forces are compared with fracture toughness and critical energy release rates to predict the equilibrium crack length for scribed samples and the process parameters associated with transition from scribing to separation. Both of these predictions are in good agreement with experimental observations. An empirical parameter is developed to identify the transition from controlled separation to uncontrolled cracking because the equilibrium crack length based analysis is unable to predict this transition. Finally, the analytical model and empirical parameter are utilized to create a map that relates the process parameters to the fracture behavior of alumina samples

Fracture Modeling of Lithium-Silicon Battery Based on Variable Elastic Moduli

Mechanical stresses which develops during lithiation of crystalline silicon particles in lithium silicon battery causes fracture and limits the life of silicon based lithium batteries. We formulated an elasto-plastic stress formulation for a two-phase silicon model and investigated the influence of different mechanical properties of lithiated silicon on the fracture of nanoparticles during first cycle charging. A chemo-mechanical model was developed to determine lithium distribution and associated stress states during first cycle lithiation. The concentration gradient of lithium and an elastic perfectly plastic material behavior for silicon were considered to evaluate stress distribution formulation and determine stress field in the particle. The stress profile was used to perform a crack growth analysis. The stress distribution formulation was validated by evaluating stress field for different elastic modulus value for lithiated silicon and comparing our inference against observations from prior experiments. The results showed lower modulus of lithiated silicon yielded results like experimental observations for nanoparticles. The size dependent fracture behavior was also observed in lower elastic modulus of lithiated silicon. We conclude that accurate mechanical characterization of lithiated silicon nanoparticle is necessary to model the failure of silicon particle and improving the mechanical properties may suppress crack growth in silicon nanoparticles during charging

Microcantilever deflection induced to hybridization of monomolecular DNA films: lower immobilization densities lead to larger deflections?

Experimental results show that specific binding between a ligand and surface immobilized receptor such as hybridization of single-stranded DNA (ssDNA) immobilized on a microcantilever surface leads to cantilever deflection. The binding induced deflection may be used as a method for detection of biomolecules, such as pathogens and biohazards. Mechanical deformation induced because of hybridization of surface immobilized DNA strands is a commonly used system to demonstrate the efficacy of microcantilever sensors; therefore, hybridization induced cantilever deflection has been reported for range of parameters that chain distributions – ssDNA immobilization densities, hybridization efficiencies, and ssDNA conformation [1–7]. However, it has been hard to draw general conclusions on the DNA hybridization induced deflections because a large range of deflections has been reported for similar density of hybridized DNA strands on the cantilever. To understand the mechanism underlying the cantilever deflections, a theoretical model that incorporates the influence of ligand/receptor complex surface distribution, conformation, configuration, and empirical interchain potential is developed to predict the binding induced deflections. The cantilever bending induced because of hybridization of DNA strands is predicted for different receptor immobilization densities, hybridization efficiencies, receptor configuration, and spatial arrangements. Predicted deflections are compared with experimental reports to validate the modeling assumptions and identify the influence of various components on mechanical deformation. Comparison of numerical predictions and experimental results suggest that initial immobilization density of receptors is a primary factor that determines the conformation and distribution of hybridized DNA strands and in turn, the cantilever deflection associated with DNA hybridization. Contrary to our expectations, the cantilever deflections are found to be larger for smaller receptor immobilization densities. For high immobilization densities, hybridization-induced mechanical deformation is determined primarily by immobilization density and hybridization efficiency as the hybridized DNA strands are restricted to be in standing-up conformation, whereas at lower immobilization densities, different conformations and spatial arrangement of hybridized chains need to be considered in determining the cantilever deflection. In addition, for similar immobilization densities, changing the immobilized receptor configuration from one end-tethered to both end-tethered leads to larger cantilever deflection on hybridization. Comparison of numerical predictions and experimental results highlights the importance of immobilized receptor configurations, immobilization density, and spatial disorder imposed during immobilization and hybridization on the hybridization induced cantilever bending

Load Assisted Dissolution AND Damage of Copper Surface under Single Asperity Contact: Influence of Contact Loads and Surface Environment

Copper has become a widely used material in advanced submicron multilevel technologies due to its low resistivity and high electromigration resistance. Copper based devices are manufactured using additive patterning and subsequently undergo chemical mechanical planarization (CMP) to ensure good interconnection. During CMP, material is removed through synergistic combination of chemical reactions and mechanical stimulations. Empirical models such as Preston’s equation are used to explain the material removal rate during CMP but a mechanism based understanding of the synergistic interactions between chemical environment and mechanical loading is still lacking

Picosecond Laser based Additive Manufacturing of Hydroxyapatite Coatings on Cobalt Chromium Surfaces

We report high repetition rate picosecond laser based additive manufacturing process to coat nanoscale rough hydroxyapatite (HA) on cobalt chromium plates (CoCr). Nanoscale rough coatings of hydroxyapatite are desirable as they mimic the naturally formed hydroxyapatite and in addition provide very high surface area and surface roughness, which leads to better cell adhesion and cell-matrix interaction. Nanoscale HA powders are synthesized using sol-gel procedure and ball milling. Ball-milled powders are suspended in volatile solvents and coated on the CoCr surface using picosecond laser irradiation. The chemical composition and morphology of the coated material was characterized using electron microscopy. The laser-assisted fusion process results in HA coatings that have hierarchical surface roughness down to nanometer scale which may enhance the biocompatibility of the CoCr implants

Cantilever deflection associated with hybridization of monomolecular DNA film

Recent experiments show that specific binding between a ligand and surface immobilized receptor, such as hybridization of single stranded DNA immobilized on a microcantilever surface, leads to cantilever deflection. The binding-induced deflection may be used as a method for detection of biomolecules, such as pathogens and biohazards. Mechanical deformation induced due to hybridization of surface-immobilized DNA strands is a commonly used system to demonstrate the efficacy of microcantilever sensors. To understand the mechanism underlying the cantilever deflections, a theoretical model that incorporates the influence of ligand/receptor complex surface distribution and empirical interchain potential is developed to predict the binding-induced deflections. The cantilever bending induced due to hybridization of DNA strands is predicted for different receptor immobilization densities, hybridization efficiencies, and spatial arrangements. Predicted deflections are compared with experimental reports to validate the modeling assumptions and identify the influence of various components on mechanical deformation. Comparison of numerical predictions and experimental results suggest that, at high immobilization densities, hybridization-induced mechanical deformation is determined, primarily by immobilization density and hybridization efficiency, whereas, at lower immobilization densities, spatial arrangement of hybridized chains need to be considered in determining the cantilever deflection

Study the Effect of Changing the Surface Roughness and the Laser Focus Distance to the Aluminum Appearance using Picosecond Laser

Picosecond laser device is used to treat Aluminum samples, the appearance of the treated samples is affected by the variation of laser focus distance and the samples surface roughness. Samples with smoother surface before laser treatments show dark colors and high increase in surface roughness after laser treatments, while samples with rougher surfaces before laser treatments show brighter colors with slightly change in surface roughness after the laser treatments. The surface texture, topography, and roughness of the treated samples is characterized to identify the mechanism driving appearance change. The characterization results indicate that size and shape of laser processing induced microscale cavities on the surface may account for the differences in samples appearance