Void Features Research Articles

Voiding generation in copper interconnect under room temperature storage in 12 years

We measured the internal residual stress change of ULSI copper interconnects at room temperature for 12 years to confirm the stress migration phenomenon. The residual stress decreased and voids were generated. Furthermore, we investigated the stress change results and void features obtained through physical analyses. The voids had the same features as those in the high-temperature storage. The estimated volume shrinkage agreed with the total volume of the observed voids, suggesting that void generation causes the decrease in stress. From the obtained result, we conclude that the stress migration degradation phenomenon occurs even at room temperature in the long-term storage, and that the void feature is almost identical to that in the high-temperature acceleration test.

Crystalline Hollow Microrods for Site‐Selective Enhancement of Nonlinear Photoluminescence

A class of one-dimensional hollow microstructure is described, which was formed by a kinetically controlled crystal growth process. A hexagonal-phase NaYbF4 microrod comprising isolated holes along the longitudinal axis was synthesized by a one-pot hydrothermal method with the assistance of citrate ligands. The structural void feature modulates light intensity across the microrods as a result of interference arising from light scattering and reflection by the inner walls. A single crystal comprising a structural void was doped with upconverting lanthanide ions. Upon near-infrared excitation of the doped crystal spatially resolvable optical codes were produced.

Crystalline Hollow Microrods for Site‐Selective Enhancement of Nonlinear Photoluminescence

AbstractA class of one‐dimensional hollow microstructure is described, which was formed by a kinetically controlled crystal growth process. A hexagonal‐phase NaYbF4 microrod comprising isolated holes along the longitudinal axis was synthesized by a one‐pot hydrothermal method with the assistance of citrate ligands. The structural void feature modulates light intensity across the microrods as a result of interference arising from light scattering and reflection by the inner walls. A single crystal comprising a structural void was doped with upconverting lanthanide ions. Upon near‐infrared excitation of the doped crystal spatially resolvable optical codes were produced.

Void Formation on PERC Solar Cells and Their Impact on the Electrical Cell Parameters Verified by Luminescence and Scanning Acoustic Microscope Measurements

Ideally formed local Al-contacts of passivated emitter and rear contact solar (PERC) cells feature an eutectic and an uniform local back surface field (LBSF). Under certain conditions the eutectic is missing after the co-firing process, referring to the well-known voids. So far light beam induced current (LBIC) measurements are used to obtain information concerning the passivation quality of the LBSF in local contacts in general. In addition, the destructive technique of scanning electron microscopy (SEM) is established for distinguishing whether a void features a sufficiently thick BSF-layer or a very thin/no BSF-layer. However, both methods are very time consuming.This paper shows a non-destructive and fast characterization of solar cells by applying electroluminescence (EL) and photoluminescence (PL) measurements to investigate the effect on the electrical parameters after locating the voids by scanning acoustic microscopy (SAM). For filled contacts EL and PL measurements correlate well with the resulting values for series resistance (RS) and dark saturation current density (j0): the formed LBSF leads to a good surface passivation (high PL signal intensity, low value for j0) and the eutectic layer ensures a good electrical contact (high EL signal intensity, low value for RS). Voids with a sufficiently thick LBSF show a high PL signal intensity whereas the intensity is significantly reduced for a very thin or completely missing LBSF. Increased values for RS can be explained by the missing eutectic layer. In addition, the electrical connection of the LBSF to the paste can be derived from the value of RS.

Change in the permeability of clastic rock during multi-loading triaxial compressive creep tests

Permeability is a crucial factor for seepage analysis of porous clastic material. This research presents the change in permeability of clastic rock during multi-loading triaxial compressive creep tests. Clastic rock was cored from a critical fault zone of a hydropower station in southwestern China. Based on the physical properties and mineralogical characterisation of the rock material, a series of hydro-mechanical coupling creep tests was designed with three different confining pressures to correlate permeability and material deformation during triaxial compressive creep and reveal the effect of confining pressure on the permeability of the clastic rock. Scanning electron microscopy (SEM) was applied to identify the pore and crack features of the rock material after creep failure and consequently explain the differences in permeability at different confining pressures. The results show that the initial permeability decreased with an increase in confining pressure. During the creep tests, the permeability rapidly decreased during the initial creep and continuously decreased as material deformation increased. Near the accelerating creep, clastic rock permeability began to increase in the low confining pressure creep test but tended to stabilise in the high confining pressure creep test. This finding agrees well with the SEM results of the void features, that is, more connected pores in the sample failed under low confining pressure than under high confining pressure.

Experimental Study on Relationships among Composition, Microscopic Void Features, and Performance of Porous Asphalt Concrete

AbstractThe performance of porous asphalt concrete (PAC) is dependent on its microscopic void features, which may refer to content and distribution of its constituents. In other words, PAC mixtures with identical air voids may have significantly different performances under given loading and environmental conditions. Air voids and their distributions are determined by aggregate gradation, nominal maximum aggregate size (NMAS), and binder content. Therefore, it is necessary to investigate the correlation among material composition, microscopic void features, and material performance. In this study, X-ray computed tomography (CT) images were obtained and analyzed to study microscopic void features of different PAC mixtures. Experimental tests were performed to study permeability, acoustic absorption coefficients, clogging, shear strengths, wheel tracking, and Cantabro loss of those PAC mixtures. The following findings were observed: (1) microscopic void features were significantly affected by gradation and ...

세라믹 방열 복합체의 열전도도 분석 및 Wetting Process를 이용한 SiC/에폭시 복합체

세라믹 방열 복합체의 특성 비교를 위해 casting method로 제작하였으며, 이들의 광학적 이미지와 단면 FE-SEM 분석을 실시하였다. 각각의 복합체의 열전도성 특성을 비교 분석하였으며, silicon carbide(SiC)의 분산도 문제를 해결하기 위해 wetting process를 도입하여 SiC/epoxy 복합체를 제작하였다. 기존의 방법에서 발견된 복합체 내공극과 분산도 문제가 wetting process를 통해 향상되었으며, 충전제 함량에 따른 열전도성 특성을 분석하였다. SiC 복합체의 함량에 따른 공극률 해석을 통해 70 wt% SiC 복합체에서 가장 높은 열전도도 값을 보였으며, 이들의 단면 FE-SEM 분석을 통해 복합체 내의 충전제 분산도를 확인하였다. Various kinds of thermal conductive ceramic/polymer composites (aluminum nitride, aluminum oxide, boron nitride, and silicon carbide/epoxy) were prepared by a casting method and their optical images were observed by FE-SEM. Among these, SiC/epoxy composite shows inhomogeneous dispersion features of SiC and air voids in the epoxy matrix layer, resulting in undesirable thermal conductive properties. To enhance the thermal conductivities of SiC/epoxy composites, the epoxy wetting method which can directly infiltrate the epoxy droplet onto filtrated SiC cake was employed to fabricate the homogeneously dispersed SiC/epoxy composite for ideal thermal conductive behavior, with maximum thermal conductivity of 3.85W/mK at 70 wt% of SiC filler contents.

20-nanogold Au20(Td) cluster and its hollow cage isomers: structural and energetic properties

The present work discusses the capability of 20-nanogold low-energy clusters to encage atomic and molecular species and investigates hollow cages of Au20, their structures and stability, and their void reactivity. We begin with performing a systematic computational search of hollow cages on the potential energy surface of doubly anionic Au20 which, according to the experimental abundance spectra of Au202−, has an approximately degenerate ground state. Since the computed second electron affinity of the neutral tetrahedral ground-state cluster Au20(Td) agrees well with the experimental value EA2expt(Au20), this ground state is thus partly occupied by [Au20(Td)]2− whose original neutral Td−symmetry is broken. Determining the other, yet unknown isomer and applying 'reverse' charge state mappings Z = −2 ⇒ Z = 0, ±1, we identify stable and low-energy Au20 hollow cages which are further studied from different angles and compared with Au20Z(Td). The void reactivity of these 20-nanogold hollow cages is the key theme - it is suggested that, together with the global characteristics, such as the ionization potential and electron affinity, the molecular electrostatic potential and HOMO-LUMO patterns are actually tools that may shed a light on the general features of voids of these golden fullerenes and their capability to encage H and Li. The confinement character of the studied golden fullerenes is compared with the classical examples, C60 in particular.

Microgravimetric and ground penetrating radar geophysical methods to map the shallow karstic cavities network in a coastal area (Marina Di Capilungo, Lecce, Italy)

The coastal area Marina di Capilungo located ~50 km south-west of Lecce (Italy) is one of the sites at greatest geological risk in the Salento peninsula. In the past few decades, Marina di Capilungo has been affected by a series of subsidence events, which have led in some cases to the partial collapse of buildings and road surfaces. These events had both social repercussions, causing alarm and emergency situations, and economic ones in terms of the funds for restoration.With the aim of mapping the subsurface karstic features, and so to assess the dimensions of the phenomena in order to prevent and/or limit the ground subsidence events, integrated geophysical surveys were undertaken in an area of ~70 000 m2 at Marina di Capilungo. Large volume voids such as karstic cavities are excellent targets for microgravity surveys. The absent mass of the void creates a quantifiable disturbance in the earth’s gravitational field, with the magnitude of the disturbance directly proportional to the volume of the void. Smaller shallow voids can be detected using ground-penetrating radar (GPR). Microgravimetric and GPR geophysical methods were therefore used. An accurate interpretation was obtained using small station spacing and accurate geophysical data processing. The interpretation was facilitated by combining the modelling of the data with the geological and topographic information for explored caves. The GPR method can complement the microgravimetric technique in determining cavity depths and in verifying the presence of off-line features and numerous areas of small cavities, which may be difficult to be resolved with only microgravimetric data. However, the microgravimetric can complement GPR in delineating with accuracy the shallow cavities in a wide area where GPR measurements are difficult. Furthermore, microgravity surveys in an urban environment require effective and accurate consideration of the effects given by infrastructures, such as buildings, as well as those given by topography, near a gravity station. The acquired negative anomaly in the residual Bouguer anomalies field suggested the presence of possible void features. GPR and modelling data were used to estimate the depth and shape of the anomalous source.

Coupled heat and fluid flow model and experimental verification of aluminium plate die casting

The present work aims to forecast mould filling, void shape, location and size as well as columnar to equiaxed transition (CET) in commercial pure aluminium casting. A model coupling the momentum equations of the fluid flow and heat transfer equations is presented, in which metallostatic pressure, air gap and oxide layer are considered. Different casting parameters were investigated such as casting configuration by varying the plate thickness from 5 to 20 mm, melt superheat from 40 to 120°C, mould preheat up to 200°C and different pouring heads ranging from 0·3 to 0·6 m. Regarding the microstructure and void formation, the approach based on the Niyama criterion, was considered. The experimental verification of the model was achieved by gravity die casting in the form of a rectangular cavity. Voids inside aluminium plate were investigated by X-ray imaging. Microstructure and CET was investigated microscopically. The supposed model proves its validity for mould filling and in detecting the void features and CET.

The use of microgravity technique in archaeology: A case study from the St. Nicolas Church in Pukanec, Slovakia

The use of microgravity technique in archaeology: A case study from the St. Nicolas Church in Pukanec, SlovakiaThe detection of subsurface cavities, such as crypts, cellars and tunnels, in churches and castles belongs to successful applications of the employment of surface gravity measurement techniques in archaeo-prospecting. The old historic building exploration requires using of non-invasive methods, and hence the microgravity technique is a proper candidate for this task. On a case study from the Roman-Catholic Church of St. Nicolas in the town Pukanec the results of using microgravity for detection and delineation of local density variations caused by a near-surface void are shown. The acquired negative anomaly in the residual Bouguer anomalies field suggested the presence of a possible void feature. Euler deconvolution and 3D modelling were used to estimate the depth and shape of the anomalous source. Additionally, measurements of the vertical gravity gradient on several stations were performed. We tested how the use of a downward continuation of gravity, utilizing the real vertical gravity gradient, influences the shape and amplitude of the final Bouguer anomaly map.

Correspondence of fracture surface features with mechanical properties in 304LN stainless steel

Ductile fracture behaviour of 304LN stainless steel at various strain rates has been studied through the examination of void morphologies (i.e. void size, void density and void size distribution) on the tensile fracture surface. An image-processing technique has been employed to quantify the metrices of voids on the fracture surface formed through the coalescence of microvoids. It is noted that at lower strain rates, when the void number density was higher and the average circular diameter of void was lower, the strength was higher and ductility was lower. At high strain rates, a reverse correlation between void features and mechanical properties was obtained. Deformation-induced martensite (DIM) was noted to be responsible for the high void number density at low strain rates. At high strain rates, DIM formation was suppressed due to adiabatic heating and hence a low void number density resulted.

A comparison of optical and X-ray CT technique for void analysis in soil thin section

The application of X-ray computed tomography (CT) in soil micromorphology has motivated researchers to quantify soil structure, particularly void space, for three dimensional analysis. The objective of this study was comparison of optical and a proposed CT method for void space determination, using a set of four thin section samples. The thin section samples were imaged for optical data using plain polarized, cross polarized and oblique incidental light. CT imaging used a 3D reconstruction to attain the average X-ray attenuation value of the thin section. After registering the two imagery types, an identical region of optical and CT imagery was extracted for analysis. Optical and CT imagery was classified as void or solid, from which simple characteristics of soil-voids were obtained. The characterization of voids indicated that the optical method was proficient in identifying continuous and linear void features, whereas CT readily identified a greater number of voids with higher circularity. The data also suggested that the CT method identified a greater degree of void space in thin section than was evident to the optical classification. The results of binary comparison imply that CT identified a category of void often overlooked by optical imagery classification and therefore would make an excellent complementary technique to the soil micromorphology tool set.

Study of Kirkendall Effect in Ni/Ni<sub>3</sub>Al Welded Joint after the High Temperature Annealing

The study of composition and microstructure of welded joints was performed before and after the diffusion annealing at elevated temperatures for different annealing time. The Kirkendall effect in the Ni/Ni3Al diffusion couples was observed by means of different methods, e.g. using light, scanning electron and atomic force microscopies. The study suitably completes and specifies the morphology features of Kirkendall voids at different evolution stages, i.e. at nucleation, growing and coalescence. Kirkendall voids occurred in the region between the Matano and γ/γ´interface planes. The location of the γ/γ´ interface that moved in the direction of Ni3Al phase during the annealing resulted from the Al concentration profile measured by EDAX. The Matano plane location was determined by means of Boltzmann-Matano’s method using concentration profile data. It was observed that the void size was increasing in the direction from the Matano plane to the γ/γ´ interface. The obtained results were completed by surface topography of Kirkendall voids of slightly etched specimens by atomic force microscopy (AFM).

Estimation of structural element sizes in sand and compacted blocks of ground calcium carbonate using a void network model

An algorithm has been developed for the calculation of the size of the effective structural or skeletal elements which make up the solid phase of an unconsolidated or consolidated porous block. It is based on a previously presented algorithm, but it has now been validated on unconsolidated samples and tested on consolidated samples. It also includes a virtual reality representation of the structures. First, a network model named Pore-Cor is made to reproduce the percolation behaviour of the experimental sample, by matching its simulated percolation characteristics to an experimental mercury intrusion curve. The algorithm then grows skeletal elements between the cubic pores and cylindrical throats of the void network model until they touch up to four of the adjacent void features. The size distributions of the simulated solid elements are compared with each other and with experimentally determined particle size distributions, using a Mann–Whitney test. The algorithm was shown to simulate skeletal elements with the correct trends in size distribution for two different sand samples, provided the sand packed itself optimally under the applied mercury pressure. It was also applied to two samples of variously compressed calcium carbonate powder, having fine and coarse particle size distributions respectively. The simulation demonstrated that on compressing the powder at the minimum force, the skeletal elements differed from the constituent particle sizes, as expected. The average size of the skeletal elements increased as the compression force was increased on the calcium carbonate powders. The results suggest that the method could be useful as a tool for probing the effect of compaction on aggregation or sintering, and for studying other effects such as cementation in geological samples, where other more direct techniques cannot be applied.

Automated Detection of Micro Void in Solder Bump

In the flip chip junction, void in the solder bump has serious influences on reliability and electric characteristic. In this paper, we propose an automated detection technique of micro voids in solder bump. The void makes hollow on the bump shape in X-ray image. We developed subtraction-based method by means of combination of morphology filter and image subtraction to detect the voids. Furthermore, we introduced noise elimination method using some void feature values and discriminant analysis. We evaluated this technique using simulation model and real bump. As a result, a correct rate reached 99.2%, which demonstrates this technique has very high detection ability.

Estimation of the effective particle sizes within a paper coating layer using a void network model

A range of calcium carbonate-based tablets and paper coating layers, with latex or starch as binder, were prepared. Their dry porous structures were analysed by mercury porosimetry. Some of these samples were also examined by electron microscopy. The porous space of these structures has been simulated using a network model named Pore-Cor, which creates network structures with percolation behaviour and porosity matching those of the experimental sample. Representative particles were grown between the cubic pores and cylindrical throats of the void network model until they touched up to four of the adjacent void features. The sizes of these representative particles, or skeletal elements, have been previously shown to be realistic for the case of unconsolidated sand and glass beads. The size distributions of these skeletal elements were compared with each other and with experiment using a Mann–Whitney test. The sizes of the skeletal elements were found to increase with the particle size of the calcium carbonate powder. The properties of the binders, used in the paper coating formulations, were found to have a major influence on the sizes of the skeletal elements, whose sizes also increased with coating thickness. These findings give insights into the wet structure and the drying process of paper coatings.

Influence of anisotropy on the dynamic wetting and permeation of paper coatings

A void network model, named Pore-Cor, has been used to study the permeation of an ink solvent into paper coating formulations coated onto a synthetic substrate. The network model generated anisotropic void networks of rectangular cross-sectional pores connected by elliptical cross-sectional throats. These structures had porosities and mercury intrusion properties which closely matched those of the experimental samples. The permeation of hexadecane, used as an analogue for the experimental test oil, was then simulated through these void structures. The simulations were compared to measurements of the permeation of mineral oil into four types of paper coating formulation. The simulations showed that the inertia of the fluid as it enters void features causes a considerable change in wetting over a few milliseconds, a timescale relevant to printing in a modern press. They also showed that in the more anisotropic samples, fast advance wetting occurred through narrow void features. It was found that the match between experimental and simulated wetting could be improved by correcting the simulation for the number of surface throats. The simulations showed a more realistic experimental trend, and much greater preferential flow, than the traditional Lucas–Washburn and effective hydraulic radius approaches.

A transmission electron microscopy investigation of sulfide nanocrystals formed by ion implantation

Ion implantation was used to form compound semiconductor nanocrystal precipitates of ZnS, CdS, and PbS in both glass and crystalline matrices. The precipitate microstructures and size distributions were investigated by cross-sectional transmission electron microscopy techniques. Several unusual features were observed, including strongly depth-dependent size variations of the ZnS precipitates and central void features in the CdS nanocrystals. The morphology and crystal structure of the nanocrystal precipitates could be controlled by selection of the host material. The size distribution and microstructural complexity were significantly reduced by implanting a low concentration of ions into a noncrystalline host, and by using multi-energy implants to give a flat concentration profile of the implanted elements.

GEOPHYSICAL SURVEY AT BODEN VEAN, CORNWALL, INCLUDING AN ASSESSMENT OF THE MICROGRAVITY TECHNIQUE FOR THE LOCATION OF SUSPECTED ARCHAEOLOGICAL VOID FEATURES*

A geophysical survey was conducted at Boden Vean, St. Anthony Meneage, Cornwall, over the site of a buried chamber thought to be the remains of a souterrain or fogou. A combination of geophysical techniques was successfully applied including an experimental microgravity survey over the location of the buried chamber itself. Magnetometer survey revealed a complex palimpsest of archaeological activity extending throughout the surrounding landscape, centred on a rectangular ditched enclosure containing the fogou. A series of gravity anomalies were recorded in the vicinity of the latter which were consistent with the collapsed section of the feature recorded by the Cornish Archaeological Unit. Further gravity anomalies suggested the presence of additional void features, possibly related to the extended passages of the fogou.