抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

[신간의 별자리x] 우리/미술, 그리고 ‘슬픔의 박물관’

Deposits of clastic carbonate-dominated (calciclastic) sedimentary slope systems in the rock record have been identified mostly as linearly-consistent carbonate apron deposits, even though most ancient clastic carbonate slope deposits fit the submarine fan systems better. Calciclastic submarine fans are consequently rarely described and are poorly understood. Subsequently, very little is known especially in mud-dominated calciclastic submarine fan systems. Presented in this study are a sedimentological core and petrographic characterisation of samples from eleven boreholes from the Lower Carboniferous of Bowland Basin (Northwest England) that reveals a >250 m thick calciturbidite complex deposited in a calciclastic submarine fan setting. Seven facies are recognised from core and thin section characterisation and are grouped into three carbonate turbidite sequences. They include: 1) Calciturbidites, comprising mostly of highto low-density, wavy-laminated bioclast-rich facies; 2) low-density densite mudstones which are characterised by planar laminated and unlaminated muddominated facies; and 3) Calcidebrites which are muddy or hyper-concentrated debrisflow deposits occurring as poorly-sorted, chaotic, mud-supported floatstones. These

Phd by thesis

Diamond-like carbon (DLC) is a metastable form of amorphous carbon with significant sp3 bonding. DLC is a semiconductor with a high mechanical hardness, chemical inertness, and optical transparency. This review will describe the deposition methods, deposition mechanisms, characterisation methods, electronic structure, gap states, defects, doping, luminescence, field emission, mechanical properties and some applications of DLCs. The films have widespread applications as protective coatings in areas, such as magnetic storage disks, optical windows and micro-electromechanical devices (MEMs).

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Diamond-like amorphous carbon

Rapid progress in the synthesis and processing of materials with structure on nanometer length scales has created a demand for greater scientific understanding of thermal transport in nanoscale devices, individual nanostructures, and nanostructured materials. This review emphasizes developments in experiment, theory, and computation that have occurred in the past ten years and summarizes the present status of the field. Interfaces between materials become increasingly important on small length scales. The thermal conductance of many solid–solid interfaces have been studied experimentally but the range of observed interface properties is much smaller than predicted by simple theory. Classical molecular dynamics simulations are emerging as a powerful tool for calculations of thermal conductance and phonon scattering, and may provide for a lively interplay of experiment and theory in the near term. Fundamental issues remain concerning the correct definitions of temperature in nonequilibrium nanoscale systems. Modern Si microelectronics are now firmly in the nanoscale regime—experiments have demonstrated that the close proximity of interfaces and the extremely small volume of heat dissipation strongly modifies thermal transport, thereby aggravating problems of thermal management. Microelectronic devices are too large to yield to atomic-level simulation in the foreseeable future and, therefore, calculations of thermal transport must rely on solutions of the Boltzmann transport equation; microscopic phonon scattering rates needed for predictive models are, even for Si, poorly known. Low-dimensional nanostructures, such as carbon nanotubes, are predicted to have novel transport properties; the first quantitative experiments of the thermal conductivity of nanotubes have recently been achieved using microfabricated measurement systems. Nanoscale porosity decreases the permittivity of amorphous dielectrics but porosity also strongly decreases the thermal conductivity. The promise of improved thermoelectric materials and problems of thermal management of optoelectronic devices have stimulated extensive studies of semiconductor superlattices; agreement between experiment and theory is generally poor. Advances in measurement methods, e.g., the 3ω method, time-domain thermoreflectance, sources of coherent phonons, microfabricated test structures, and the scanning thermal microscope, are enabling new capabilities for nanoscale thermal metrology.

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Nanoscale thermal transport

Electromigration (EM) lifetime and failure mechanisms have been investigated for SnAg Pb-free solder bumps with two types of under bump metallurgy (UBM). The activation energy was determined to be 0.64/spl sim/0.72 eV for Pb-free solders with Cu UBM and 1.03/spl sim/1.11 eV with Ni UBM. EM failure was observed only in solder bumps with electron current flow from UBM to the substrate. SEM and EDX analysis revealed a failure mechanism for solder bumps with Ni UBM caused by the dissolution of UBM as a result of Ni migration and subsequent solder cracking or de-wetting. The failure mechanism of Cu UBM samples showed temperature dependence. At higher temperatures, Cu UBM dissolved continuously while at lower temperatures, open failure was caused by crack formation at the Cu/sub 3/Sn/Cu/sub 6/Sn/sub 5/ interface with little damage to the UBM. This is attributed to a difference of Cu diffusivity in Cu/sub 3/Sn and Cu/sub 6/Sn/sub 5/. The EM lifetime of Pb-free solder was found to be much better than eutectic solders but worse than high-Pb solders at the same temperature.

A study of electromigration failure in Pb-free solder joints

Plastic deformation in submicron wide Al-1 wt %Cu interconnects was studied in situ using a straining device in the transmission electron microscope. Dislocation motion occurred readily in unpassivated lines but was nonexistent in passivated lines due to the presence of stiff oxide sidewalls. Instead heterogeneous void nucleation occurred on straining to a critical limit. The void morphology was always near hemispherical and the nucleation always took place at the line edges. Further stretching of the lines led to a rupture of the sidewalls away from the lines, resulting in immediate dislocation motion. Void nucleation, cross slip, and operation of dislocation sources at line edges were all recorded on video. It was noted that dislocations almost parallel to the plane of the lines are rarely observed and furthermore, their movement is sluggish. Based on the dislocation configuration observed in these lines, a generalized geometrical model was arrived at in order to determine the significance of grain orientation on yield stress of passivated lines with columnar, bamboo grains. Frequent occurrence of twinning within the grains indicated that plastic deformation was indeed restricted in confined metal lines.

In situ transmission electron microscopy study of plastic deformation and stress-induced voiding in Al–Cu interconnects

The electromigration drift velocity of Al in Al(3wt.% Si), Al(2wt.%Cu), and Al(2wt.%Cu,3wt.%Si) was measured in a temperature range 133 to 220 °C with current densities of 1.0 to 1.5×106A/cm2. In Al(3wt.% Si), a significant Al depletion at the cathode end and accumulation at the anode end of stripe were observed within a few hours at 1.5×106A/cm2 and 200°C. In addition, local hillocks and voids along the metal lines were observed. For Al(Cu,Si), the Al drift velocity was slowed down by Cu addition. The majority of hillocks started to grow at a distance about 6 μm away from the cathode end with current density of 1.5×106 A/cm2. The drift velocity of Al in Al(Cu,Si) was found to be a function of time starting with an initial low value and increasing to a an final steady-state value. The behavior was attributed to the migration of Cu and dissolution of Al2Cu precipitates. The activation energies of the depletion 3 Aμm of Al(2%,Cu, 3%Si) was determined to be 0.90±02 eV. The dissolution and growth of A12Cu in the tested samples of Ti/Al(2%Cu)/Ti/TiN were observed using the scanning electron microscope and an electron microprobe.

Electromigration in Al/W and Al(Cu)/W Interconnect Structures

The impact of chip-package interaction (CPI) on the mechanical reliability of Cu low-k interconnects was investigated using a 3D multi-level sub-modeling method. The analysis was focused on the die attach process for Pb-free solder where a high thermal load will occur during solder reflow before underfilling to maximize the packaging effect. We compared first the CPI for a CVD-OSG (k=3.0) with MSQ (k=2.7) and spin-on polymer (k=2.7) to investigate how better material properties can improve interconnect reliability. Then the study was extended to porous MSQ (k=2.3) to examine CPI for the 65nm node and beyond. Finally, requirements of the mechanical properties of low-k ILD for improving interconnect reliability are discussed

Effects of Chip-Package Interaction on Mechanical Reliability of Cu Interconnects for 65nm Technology Node and Beyond

Electromigration (EM) reliability of Cu/low-k interconnects with a conventional preclean-first process, and an advanced barrier-first process has been investigated. Compared with the preclean-first process, extrinsic early failures were not observed for the barrier-first process. This suggests that process-induced defects, which are the most probable cause for early failures, are significantly reduced for the barrier-first process. Transmission electron microscopy observation demonstrated a more uniform and thicker Ta barrier for the barrier-first process than the preclean-first process. This led to a higher (jL)c product, and prolonged the EM lifetime accordingly. In addition, a predeposited Ta barrier during the barrier-first process protected the mechanically weak low-k dielectrics from plasma etch damage, and a uniform via profile resulted. In contrast, the via opening at the top was found to be larger than that of at the via bottom for the preclean process. The uniform via profile is another advantag...

Paul S. Ho

Papers

A study of electromigration failure in Pb-free solder joints

In situ transmission electron microscopy study of plastic deformation and stress-induced voiding in Al–Cu interconnects

Electromigration in Al/W and Al(Cu)/W Interconnect Structures

Effects of Chip-Package Interaction on Mechanical Reliability of Cu Interconnects for 65nm Technology Node and Beyond

Effect of barrier process on electromigration reliability of Cu/porous low-k interconnects