We present electromigration experiments on single-crystalline silver nanowires. The wires were grown on 4° vicinal silicon (100) substrates by self-organization and were contacted by electron beam lithography. The electromigration experiments were performed in situ in a scanning electron microscope at room temperature with constant dc conditions. In contrast to other experiments we observe void formation at the anode side of the wires. If the current is reversed, the electromigration behavior is also reversed.

Electromigration in self-organized single-crystalline silver nanowires

We present the results of an ultrahigh vacuum (UHV) scanning‐tunneling‐microscopy study of large scale mass transport in current carrying metal films. Scans were taken in situ on a current carrying 2100‐A‐thick Ag film with current densities ranging from 5.0×104 A/cm2 up to 3.2×105 A/cm2, at which point the sample failed due to a runaway thermal fusing mechanism. Axial UHV inchworms allowed us to obtain data from the same 2‐μm‐square region of the sample throughout the experiment in spite of large temperature‐induced drifts. Calculations of the driving forces demonstrate that the electromigration driving force was dominant for this current range. Significant topographical changes were observed including current aligned grain growth, current induced faceting, and complex mass flow divergences. A model that explains the observed divergences is presented. It is based upon diffusion in the presence of local inhomogeneities of the electric field.

In situ scanning‐tunneling‐microscopy studies of current driven mass transport in Ag

This article reviews efforts to structurally characterize metallic nanocontacts. While the electronic characterization of such junctions is relatively straight forward, usually it is technically challenging to study the nanocontact's structure at small length scales. However, knowing that the structure is the basis for understanding the electronic properties of the nanocontact, for example, it is necessary to explain the electronic properties by calculations based on structural models. Besides using a gate electrode, controlling the structure is an important way of understanding how the electronic transport properties can be influenced. A key to make structural information directly accessible is to choose a fabrication method that is adapted to the structural characterization method. Special emphasis is given to transmission electron microscopy fabrication and to thermally assisted electromigration methods due to their potential for obtaining information on both electrodes of the forming nanocontact. Controlled electromigration aims at studying the contact at constant temperature of the contact during electromigration compared to studies at constant temperature of the environment as done previously. We review efforts to calculate electromigration forces. We describe how hot spots are formed during electromigration. We summarize implications for the structure obtained from studies of the ballistic transport regime, tunneling, and Coulomb-blockade. We review the structure of the nanocontacts known from direct structural characterization. Single-crystalline wires allow suppressing grain boundary electromigration. In thin films, the substrate plays an important role in influencing the defect and temperature distribution. Hot-spot formation and recrystallization are observed. We add information on the local temperature and current density and on alloys important for microelectronic interconnects.

/pdf/electromigration-and-the-structure-of-metallic-nanocontacts-481k493pbt.pdf

Electromigration and the structure of metallic nanocontacts

A new compound Ca2PdWO6 has been synthesized by solid state sintering. The phase transition of this compound was investigated by means of differential thermal analysis (DTA), X-ray phase analysis, precise measurement of lattice parameters and other methods. It is discovered that the compound has a displacive phase transition of the first order at (806 +/- 5)degrees C. The low temperature phase, alpha-Ca(2)dWO(6), belongs to orthorhombic system with space group Pmm2. Its lattice parameters at room temperature are: a = 0.799 46 nm, b = 0.554 04 nm and c = 0.580 08 nm. The measured density is D-m = 6.26 g/cm(3), and each unit cell contains two formula weights. The high temperature phase, beta-Ca2PdWO6, belongs to the cubic system, with space group Fm3m and the lattice parameter is a = 0.810 3 nm at 860 degrees C; Z = 4. The calculated density is D-x = 5.821 g/cm(3). The crystal structure of alpha-Ca2PdWO6 and beta-Ca2PdWO6 was also determined by means of the X-ray polycrystal diffraction method. The factors influencing phase transition temperature are discussed in detail.

Normal incident infrared absorption from InGaAs/GaAs quantum dot superlattice

Tremendous efforts have been made in the search for a cure or effective treatment of Alzheimer's disease (AD) to develop therapies aimed at halting or reversing amyloid plaque deposition in the brain. This necessitates in vivo detection and quantification of amyloid plaques in the brain for efficacy evaluation of anti‐amyloid therapies. For this purpose, a wide array of amyloid‐imaging probes has been developed, mainly for in vivo studies based on positron emission tomography and single photon emission computed tomography. This review provides a full account of the development of amyloid‐imaging agents. The in vitro binding properties and in vivo pharmacokinetic profiles of all amyloid‐imaging agents so far reported are comprehensively and uniquely surveyed. Emphasis is placed on the development of small‐molecule probes based on amyloid dyes, such as Congo red and thioflavin T. Compared to large biomolecules, these small‐molecule probes have been systematically investigated through extensive structure activity relationship studies. Many of the probes show favorable properties for in vivo studies. As a result, three lead compounds, termed PIB (Pittsburgh‐Compound B, [11C]6‐OH‐BTA‐1), FDDNP (2‐(1‐[6‐[(2‐[18F]fluoroethyl)(methyl)amino]‐2‐naphthyl]ethylidene)malononitrile), and SB‐13 (4‐N‐methylamino‐4′‐hydroxystilbene), have been identified and evaluated in human subjects. Preliminary studies have indicated that these lead compounds exhibit a characteristic retention in AD subjects that is consistent with the AD pathology, thus proving the concept that amyloid deposits in the brain can be readily detected and quantified in vivo. The progress to date paves the way for further investigation in various aspects of AD research. Once developed, these amyloid‐imaging agents could be used as biomarkers to aid in early and definitive diagnosis of AD, facilitate drug discovery and development, and allow pathophysiological studies of the disease mechanism. Furthermore, the success in the development of amyloid‐imaging agents helps with the development of imaging agents for in vivo studies of other AD pathologies in particular and of neurodegenerative disorders in general.

Amyloid imaging: from benchtop to bedside.

The mass-transport mechanisms that are responsible for the early stages (resistance change 1%) of electromigration damage in metals are poorly understood. A deeper understanding of these processes is important both for the direct application to metal lines in electronic devices and for expanding our basic knowledge of these complex phenomena. A major reason for our lack of understanding is that the structural changes that must take place during early-stage electromigration occur at extremely small length scales that are beyond the resolution capabilities of conventional electromigration experiments. We report in situ studies of early-stage electromigration using scanning tunneling microscopy. A single 2-\ensuremath{\mu}m square region of a 2100-\AA{} Ag film was studied under UHV conditions for over 200 h with current densities up to 4.5\ifmmode\times\else\texttimes\fi{}${10}^{4}$ A/${\mathrm{cm}}^{2}$. Although the temperature and resistivity of the sample remained nearly constant throughout this period, significant small-scale morphology changes occurred that were a result of the applied current.

/pdf/in-situ-scanning-tunneling-microscopy-studies-of-early-stage-340y4rrj6i.pdf

In situ scanning-tunneling-microscopy studies of early-stage electromigration in Ag.

High resolution in situ imaging of metal surfaces during annealing and/or current transport is of great interest both for the application of metal lines in electronic devices and for extending our basic knowledge of the related complex physical phenomena. Due to its high resolution, the scanning tunneling microscope (STM) is a promising tool for in situ investigations of the structural changes of metals with respect to temperature (annealing) and current transport (electromigration). In this article, the instrumental modifications necessary for in situ scanning tunneling microscopy of heated and/or current carrying thin films under ultrahigh vacuum conditions are discussed. Using results obtained on Ag films, the ability of our STM to image the surface dynamically is demonstrated, while structural changes induced by the current transport are taking place.

/pdf/ultrahigh-vacuum-scanning-tunneling-microscope-for-in-situ-1zjb928epa.pdf

Ultrahigh vacuum scanning‐tunneling microscope for in situ studies of annealing and electromigration behavior of thin films

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In situ scanning‐tunneling‐microscopy studies of current driven mass transport in Ag

In situ scanning-tunneling-microscopy studies of early-stage electromigration in Ag.

Ultrahigh vacuum scanning‐tunneling microscope for in situ studies of annealing and electromigration behavior of thin films