High Interfacial Energy Research Articles

The intermixing induced perpendicular magnetic anisotropy in ultrathin Co/Pt multilayers

It has been observed that a perpendicular interface contribution to the magnetic anisotropy can rotate the easy magnetization direction from within the film plane to perpendicular to the film plane when the Co thickness in Co/Pt multilayers is below a critical value that is in the range of (sub)nanometers. In this work, mixed CoPt phases mainly consisting of disordered fcc CoPt were found to be responsible for the perpendicular magnetic anisotropy (PMA) for the film deposition end-Hall voltage equal to 140 V. Estimates of mechanisms that could be responsible for the PMA such as “orange peel” coupling, exchange bias, and magnetostriction indicate that they are too weak. We believe that this PMA is driven by the heat of mixing and relatively higher interfacial energy since the Co layer thickness is about 1 nm.

Polarity effect of electromigration on intermetallic compound formation in SnPb solder joints

The polarity effect of electromigration on the interfacial reactions of micro ball grid array (μBGA) solder joints was studied in terms of microstructural evolution. A dummy μBGA package with the same pair of solder joints was used to obtain reproducible results for a practical application. The μBGA package with Ni(P)/SnPb/Ni(P) structure showed a polarity effect on intermetallic compound (IMC) formation after stress by a current density of 3.0 × 10 3 A cm −2 at 120 °C, compared to the no-current case. Electric current enhanced the growth of Ni 3Sn 4 at the anode and retarded it at the cathode because of the change in Sn diffusion induced by electromigration. The IMC growth at the anode was about one order of magnitude faster than that at cathode. The growth of IMC at the anode had a parabolic dependence on time since the square of thickness of IMC increases linearly with time. The real μBGA package has unique and more complicated geometry compared to ordinary diffusion couples. So not only the polarity growth of IMC but also the fast dissolution of Cu and Ni at specific positions was found with the μBGA package. The unique geometry of μBGA solder joints caused heat generation at the upside interfaces due to Joule heating. Because of the heat generation and the high interfacial energy at the triple point of upside interfaces, the electroless Ni(P) finishes and Cu trace are consumed rapidly in the region where the current is crowded. Thus electromigration induced the rapid dissolution of Ni and Cu into solder and then formed (Cu,Ni) 6Sn 5 at the triple point of the current crowding region at high temperature. This is a rapid failure process because the localized fast dissolution of Ni and Cu accelerated the solid-state reaction between solder and electroless Ni(P) or Cu trace.

A Ni/Surface-Modified Diamond Composite Electroplating Coating on Superelastic NiTi Alloy as Potential Dental Bur Design

Dental diamond bur is now a regular rotary tool, with its head made of diamond particles embedded into nickel coating, and its shank made of stainless steel. There are strong demands from the dentist on prolongation of usage life and avoiding of breakage. To solve this problem, on the one hand, since diamond is hard to be wetted under the condition of normal temperature and pressure due to the high interfacial energy between diamond and general metals and alloys. Diamond particles coated with titanium layer was used for the preparation of composite electroplating with the intention of improving the interfacial adhesion between diamond and metal matrix; on the other hand, superelastic biomedical NiTi alloy was used as the substrate to improve the flexibility and prevent the breakage. In this study, the optimal preparation parameters of Ni/surface-modified diamond electroplating were determined by orthogonal test, and the bonding conditions between the diamond particles and the NiTi alloy substrate were studied by scanning electron microscope. Further performance comparison of Ni/modified and Ni/un-modified diamond composite electroplating was conducted on a pin-on-disc wear machine under the dry sliding condition, and the material removal volume was used as the evaluating criterion of wear resistance. The results showed that the binding strength between diamond particles and NiTi alloy substrate could be enhanced, as well as the wear resistance, which may give direction on the future design of dental bur.

Kinetic properties of dromedary pancreatic lipase: A comparative study on emulsified and monomolecular substrate

Using the classical emulsified system and the monomolecular film technique, we compared several interfacial properties of dromedary pancreatic lipase (DrPL) with those of a mammal (human) and an avian (turkey) model. Like turkey pancreatic lipase (TPL) and unlike human pancreatic lipase (HPL), in the absence of colipase and bile salts, using tributyrin emulsion or monomolecular films of dicaprin at low surface pressure, DrPL hydrolyses pure tributyrin emulsion, as well as dicaprin films maintained at low surface pressures. DrPL was also able to hydrolyse triolein emulsion in the absence of any additive and despite the accumulation of long-chain free fatty acids at the interface. The difference of behaviours between the two mammal pancreatic lipases (DrPL and HPL) can be explained by the penetration capacity of each enzyme. DrPL presents a critical surface pressure value (21 mN m −1) that is more important than this of HPL. Subsequently, the dromedary pancreatic lipase interacts efficiently with interfaces and it is not denaturated at high interfacial energy. A kinetic study on the surface pressure dependency, stereospecificity and regioselectivity of DrPL was performed using optically pure stereoisomers of either three dicaprin isomers containing a single hydrolysable decanoyl ester bond that were spread as monomolecular films at the air/water interface. Interestingly, in comparison with all the previously studied mammal pancreatic lipases, DrPL presents the highest preference for adjacent ester groups of dicaprin isomers (1,2- sn-dicaprin and 2,3- sn-dicaprin) at high surface pressure. Furthermore, DrPL forms a pancreatic lipase subgroup in which the stereopreference switches from sn-3 position to the sn-1 position when increasing the surface pressure.

Molecular dynamics simulation of defect formation and precipitation in heavily carbon doped silicon

The precipitation process of silicon carbide in heavily carbon doped silicon is not yet fully understood. High resolution transmission electron microscopy observations suggest that in a first step carbon atoms form C Si dumbbells on regular Si lattice sites which agglomerate into large clusters. In a second step, when the cluster size reaches a radius of a few nm, the high interfacial energy due to the SiC/Si lattice misfit of almost 20% is overcome and the precipitation occurs. By simulation, details of the precipitation process can be obtained on the atomic level. A recently proposed parametrization of a Tersoff-like bond order potential is used to model the system appropriately. Preliminary results gained by molecular dynamics simulations using this potential are presented.

Nanocrystallization and interfacial tension of sol-gel derived memory

The formation of the nanocrystals (NCs) by using the sol-gel spin-coating method at various annealing temperatures had been studied. The film started to form the islands at 600°C annealing, and finally transferred into NCs at 900°C. A model was proposed to explain the transformation of thin film. The morphology of sol-gel thin film at 600°C annealing was varied and had higher interfacial energy. The crystallized process at 900°C annealing could minimize the energy. The retention for 900°C annealed sample exhibited less than 30% charge loss after 106s at 125°C measurement.

Nanoscale dynamic wetting and spreading of molten Ti alloy on 6H–SiC

We have investigated nanoscale features at the reactive wetting front of the molten Ag–27.4 wt.% Cu–4.9 wt.% Ti on 6H–SiC using video movies recorded in situ on a high-temperature stage of a high-resolution transmission electron microscope and also proposed a model of a chemical reaction at each tip. One of the features of reactive wetting and spreading at 1073 K in 4 × 10 −5 Pa was the discontinuous motion of the tip, and the halting time depended on the thickness of an amorphous Si–O layer on SiC, which can be explained by the time needed for the decomposition of the layer by Ti atoms to form TiC nanoparticles since Ti atoms in the molten alloy sufficiently rapidly diffuse to the tip on the SiC surface. Molten Ti and TiC nanolayers preceded the Ti 5Si 3 nanolayer at the tip. The reaction required to form the TiC nanolayer is also the rate-determining step for spreading. The contact angle of the tip increased up to 60–80° when the tip halted, whereas the tip decreased down to 10° on the nonbasal plane and 20° on the basal plane of SiC when it traveled rapidly. The high traveling angle of the molten tip on the basal polar plane of SiC indicates a high interfacial energy between Ti and SiC(0 0 0 1).

Nucleation of Intragranular Ferrite on B1-Type Non-Metallic Inclusions

A nucleation of intragranular ferrite grains by B1-type non-metallic inclusions was investigated using electron microscopes. Intragranular ferrite grains surrounding a TiN particle is observed in Ti-containing steel. On the other hand, no intragranular ferrite nucleated on NbN and ZrN. It is deduced that the NbN and the ZrN particle can not promote a nucleation of an intragranular ferrite for their high interfacial energy with ferrite. The TiN particle which has the BN relationship with the intragranular ferrite is an inclusion that effectively promotes an intragranular ferrite nucleation. The acicular ferrite grains formed in the austenite grains were trigged by the intragranular ferrite grain(s) formed around TiN.

A Novel Strategy to Incorporate Carbon Nanotubes into Thermoplastic Matrices

AbstractMultiwalled carbon nanotubes (MWNT) are introduced into thermoplastic matrices (polycarbonate and polyamide) by melt blending using polyethylene (PE) based concentrates with high MWNT loadings (24–44 wt.‐%). MWNT surfaces were treated with a metallocene‐based complex to afford the in‐situ polymerization of ethylene directly from the surface. The resulting concentrates showed excellent MWNT pre‐dispersion. Due to the high interfacial energy between MWNT and PE, the nanotubes migrate into matrix polymers with lower interfacial energies, like polycarbonate and polyamide, and thereby remain in their excellent dispersion state. Thus, electrical percolation is achieved at lower MWNT contents as compared to direct incorporation. For polycarbonate it is shifted from 0.75 to 0.25 wt.‐%.magnified image

Facet formation and lateral overgrowth of selective Ge epitaxy on SiO2-patterned Si(001) substrates

Faceting and lateral overgrowth have been investigated for Ge selectively grown on Si(001) substrates in trench regions bound by SiO2 sidewalls. In wet-etched large trenches with sloped sidewalls, Ge faceting behavior was similar to Si and SixGe1−x faceting: slow-growing {113} facets dominate, with {111} facets expanding as the layer became thicker. However, the {111} facet length for Ge was much smaller than that of Si; this can be explained in terms of mass transport and accumulation, as well as energy minimization and the higher surface diffusivity of Ge. In dry-etched small trenches with vertical sidewalls, minimization of the high-energy interface area between Ge and SiO2 appears to be most critical in determining faceting morphology. Overgrowth of Ge led to void formation at the oxide interface, presumably to avoid the high-energy Ge/SiO2 interface. Upon coalescence of lateral-growth regions, fast-growing (001) forms and dominates subsequent growth. Thus, the total thickness of the overgrown Ge layer was closely related to the width of the SiO2 region between trenches.

Phase-field study of interface energy effect on quantum dot morphology

A multi phase-field model is developed to investigate the effect of interface energy between a film and substrate on the morphological evolution of the film during self-assembled quantum dot (QD) growth in the deposition process. The single- and multi-island growth simulations for the SiGe/Si system are carried out in two-dimensional space with various interface energies. From the numerical results, it is clarified that the island shape and the island morphological transition points dramatic change depending on the magnitude of the interface energy. Here, the transition points, such as that from a pyramid to a dome, occurred in an earlier growth stage with higher interface energy. It is also observed that high interface energy results in large island size fluctuation.

Study of the Wettability between Diamond Abrasive and Vitrified Bond with Low Melting Point and High Strength

The adhesion between diamond grits and the bond strongly influence the properties of diamond tools. Since diamond is covalent crystal, the high interfacial energy leads to the poor interface bonding between diamond grits and the bond. Furthermore, the sintering temperature of traditional vitrified bond is also very high because of the high refractoriness of alkalis containing in the bond, resulting in serious thermal damage to diamond grits. In this paper, a low melting point and high strength vitrified bond has been prepared mainly from borate glass, clay and lead glass. The bond is completely glassy above 850°C and the bending strength of the bond sintered at 850°C for 7 minutes is 125.7MPa with a 6.5:3.5 corundum/bond ratio. Moreover, this bond possesses good wettability with diamond abrasive from 600°C to 850°C.

Modification of magnetic properties of metal nanoparticles using nanotemplate approach

We demonstrate a nanotemplate approach by which different metal magnetic nanoparticles (Ni–Co, Ni–Fe and Co–Pt alloy particles) can be fabricated on a polyimide (PI) film. The process relies on the high interfacial energy between deposited metal and the PI film which forces the deposited metal film to preferentially nucleate on the pre-existing Ni seed particles. During subsequent thermal annealing, the deposited metal film coalesced onto the Ni seed particles to form a monolayer of magnetic nanoparticles on the PI film. Furthermore, the deposition/annealing can be repeated to change both size and constituent of the nanoparticles by introducing a different metal film during deposition. Potentially, any metal film can be deposited onto the Ni seed particles provided that the metal does not react with the Ni seed particles to create a monolayer of metal nanoisland structures with desire magnetic properties.

The Anomalous Electrical Performance of Bonded n-GaAs Wafers

Electrical performance was found to be closely related to the variation of nanosized interface morphology. This work investigated in detail the microstructural development of in- and anti-phase bonded interfaces for n-type (100) GaAs wafers treated at 500, 600, 700 and 850 oC. The interfacial energy of anti-phase bonding is higher than that of in-phase bonding based on the first-principles calculations. The higher interface energy tends to stabilize the interfacial oxide layer. The continuous interfacial oxide layer observed below 700 oC behaves to deteriorate the electrical property due to its insulating property. However, the existence of nanoscaled oxide at anti-phase bonded interfaces can improve the electrical conductivity at 700 oC. The reason will be discussed based on the analysis of autocorrelation function from HRTEM (high-resolution transmission electron microscope) and energy dispersive x-ray spectroscopy.

Mesoporous Poly(benzimidazole) Networks via Solvent Mediated Templating of Hard Spheres

Mesoporous Poly(benzimidazole) with well-defined porosity and pore diameter of 11 nm was synthesized via a hard templating approach using silica nanoparticles as template. The effect of the template concentration as well as the influence of the cross-linking density on the resulting pore structure was investigated. The samples were characterized by small-angle X-ray scattering and nitrogen sorption, revealing a linear increase of the porosity and surface area with increasing content of the template up to a critical concentration. Exceeding this concentration leads to a breakdown of some pores due to the emerging high interfacial energy. The effect of the cross-linking density was shown to be nonlinear. Samples with more than 20 mol % cross-linker revealed perfect replication of the template, while a lower cross-linking density leads to a breakdown of some pores.

Anomalous electrical performance of nanoscaled interfacial oxides for bonded n-GaAs wafers

Electrical performance was found to be closely related to the variation of nanosized interface morphology in previous studies. This work investigated in detail the microstructural development of in- and anti-phase bonded interfaces for n-type (100) GaAs wafers treated at 500, 600, 700 and 850°C. The interfacial energy of anti-phase bonding is higher than that of in-phase bonding based on the first-principles calculations. The higher interface energy tends to stabilize the interfacial oxide layer. The continuous interfacial oxide layer observed below 700°C can deteriorate the electrical property due to its insulating property. However, the existence of nanoscaled oxide at anti-phase bonded interfaces can improve the electrical conductivity at 700°C. This is due to the suppression of the evaporation of As atom by the interfacial nanoscaled oxides based on the analysis of autocorrelation function and energy dispersive x-ray spectroscopy.

Implementation of high interfacial energy anisotropy in phase field simulations

Abstract We show changes of equilibrium shape and artifacts of enhanced particle coalescence and numerical pinning, introduced by boundary thickness variation associated with anisotropy in interfacial energy in phase field simulations. Methods to implement high anisotropy in interfacial energy without altering boundary thickness are presented.

Exfoliation and blistering of Cd0.96Zn0.04Te substrates by ion implantation

As part of a series of wafer bonding experiments, the exfoliation/blistering of ion-implanted Cd0.96Zn0.04Te substrates was investigated as a function of postimplantation annealing conditions. (211) Cd0.96Zn0.04Te samples were implanted either with hydrogen (5×1016 cm−2; 40–200 keV) or co-implanted with boron (1×1015 cm−2; 147 keV) and hydrogen (1–5×1016 cm−2; 40 keV) at intended implant temperatures of 253 K or 77 K. Silicon reference samples were simultaneously co-implanted. The change in the implant profile after annealing at low temperatures (<300°C) was monitored using high-resolution x-ray diffraction, atomic force microscopy (AFM), and optical microscopy. The samples implanted at the higher temperature did not show any evidence of blistering after annealing, although there was evidence of sample heating above 253 K during the implant. The samples implanted at 77 K blistered at temperatures ranging from 150°C to 300°C, depending on the hydrogen implant dose and the presence of the boron co-implant. The production of blisters under different implant and annealing conditions is consistent with nucleation of subsurface defects at lower temperature, followed by blistering/exfoliation at higher temperature. The surface roughness remained comparable to that of the as-implanted sample after the lower temperature anneal sequence, so this defect nucleation step is consistent with a wafer bond annealing step prior to exfoliation. Higher temperature anneals lead to exfoliation of all samples implanted at 77 K, although the blistering temperature (150–300°C) was a strong function of the implant conditions. The exfoliated layer thickness was 330 nm, in good agreement with the projected range. The “optimum” conditions based on our experimental data showed that implanting CdZnTe with H+ at 77 K and a dose of 5×1016/cm2 is compatible with developing high interfacial energy at the bonded interface during a low-temperature (150°C) anneal followed by layer exfoliation at higher (300°C) temperature.

Epitaxial growth of celestite on barite (0 0 1) face at a molecular scale

In situ AFM experiments have been conducted in order to obtain information about kinetics of celestite epitaxial growth on barite. Growth has been promoted by passing aqueous solutions supersaturated with respect to celestite over freshly cleaved barite (0 0 1) surfaces. Solution supersaturation, β celestite, was varied from 1 to 45.7 ( β celestite = a ( Sr 2 + ) · a ( SO 4 2 - ) / K sp , cel ) . At supersaturations below 10 neither two-dimensional nucleation neither step advancement are observed on barite (0 0 1) surfaces. However, once the two-dimensional nucleation barrier is overcome ( β celestite > 10), nuclei preferentially form on cleavage steps parallel to [1 0 0], [1 1 0] and [1 2 0] directions and more scarcely on terraces. The subsequent growth of two-dimensional nuclei leads to the development of celestite “islands”. Their morphology is defined by (0 0 1) face and {2 1 0} and {1 0 0} forms and can be explained on the basis of PBC theory. The coalescence of such islands results in the formation of a homogeneous SrSO 4 layer. Growth rates along [0 0 1] direction have been measured for the whole supersaturation range. The growth rate equation for “Birth and Spread” crystal growth mechanism has been successfully fitted to our experimental data. The fitting process has provided basic growth parameters in a good agreement with theoretical ones. Both the high transitional supersaturation required for two-dimensional nucleation and the high interfacial energy value obtained from the fitting of the “Birth and Spread” equation ( σ 001 cel – bar = 0.137 J / m 2 ) indicate low affinity of SrSO 4 growth units for barite (0 0 1) faces. This is consistent with the relative high mismatch between celestite and barite structure. The behaviour of the epitaxial growth described in this work can help to interpret the oscillatory zoning frequently occurring in both natural and synthetic crystals of the Ba x Sr 1− x SO 4 solid solution.

Interfacial Reaction Phenomena of Sn−Pb Solder with Au/Ni/Cu Metallization

The utilization of a very thin Ni metallization in the Au/Ni/Cu facilitates faster diffusion of Cu to the solder interface. The out-diffusion of Cu during an aging period changes the chemistry and morphology of the Au-containing intermetallic compounds (IMCs) at the interface. This study suggests that (Au,Ni)Sn4 has a lower interfacial energy with Ni3Sn4, whereas AuSn4 has a higher interfacial energy with (Cu,Ni)6Sn5. However, both (Au,Ni)Sn4 and AuSn4 have lower interfacial energies with Pb.