Diffusion on semiconductor surfaces

Semiconductor devices continue to get ever smaller, which means that individual defects play an increasingly important role in their performance. In the process of fabricating more innovative, better performing devices, crystal growers have developed an amazing intuition about how atoms and molecules behave on crystal surfaces. Their intuition, formed from knowledge of fundamental atomic-scale processes and honed through experience, concerns such questions as where atoms and molecules stick, how they interact with each other and the substrate, and how they diffus

Tuning of defects in ZnO nanorod arrays used in bulk heterojunction solar cells.

With particular focus on bulk heterojunction solar cells incorporating ZnO nanorods, we study how different annealing environments (air or Zn environment) and temperatures impact on the photoluminescence response. Our work gives new insight into the complex defect landscape in ZnO, and it also shows how the different defect types can be manipulated. We have determined the emission wavelengths for the two main defects which make up the visible band, the oxygen vacancy emission wavelength at approximately 530 nm and the zinc vacancy emission wavelength at approximately 630 nm. The precise nature of the defect landscape in the bulk of the nanorods is found to be unimportant to photovoltaic cell performance although the surface structure is more critical. Annealing of the nanorods is optimum at 300°C as this is a sufficiently high temperature to decompose Zn(OH)2 formed at the surface of the nanorods during electrodeposition and sufficiently low to prevent ITO degradation.RIGHTS : This article is licensed under the BioMed Central licence at http://www.biomedcentral.com/about/license which is similar to the 'Creative Commons Attribution Licence'. In brief you may : copy, distribute, and display the work; make derivative works; or make commercial use of the work - under the following conditions: the original author must be given credit; for any reuse or distribution, it must be made clear to others what the license terms of this work are

Highly Effective GeNi Alloy Contact Diffusion Barrier for BiSbTe Long-Term Thermal Exposure

A GeNi alloy diffusion barrier for contacts on bismuth antimony telluride is proposed. Multiple gold contact diffusion barriers were tested at different thermal aging conditions in air and reducing atmospheres. Among all diffusion barriers, the GeNi alloy barrier shows the best performance for bulk samples with no substantial degradation of the contact resistance, no contact color change, and no change of thermoelectric properties. We observed DAu−GeNi = (9.8 ± 2.7) × 10−20 m2/s within the GeNi alloy barrier, which is 4 times smaller than DAu−BiSbTe. The presence of the initial Ge layer also proves to be effective in reducing nickel diffusion yielding DNi−BiSbTe = (8.57 ± 0.49) × 10−19 m2/s. During GeNi alloy formation, Ge diffusion into BiSbTe produces GeTe, which apparently blocks the van der Waals gaps eliminating Au and Ni fast diffusion pathways. Thermal aging of BiSbTe nanowires shows that Au and Ni diffusion degrades the thermoelectric power factor, whereas the GeNi alloy barrier sample is mostly preserved. The GeNi alloy barrier is a reliable solution to long-term thermal applications of BiTe-based materials

Molecular-scale studies of single-channel membrane pores : final report.

We present our research results on membrane pores. The study was divided into two primary sections. The first involved the formation of protein pores in free-standing lipid bilayer membranes. The second involved the fabrication via surface micromachining techniques and subsequent testing of solid-state nanopores using the same characterization apparatus and procedures as that used for the protein pores. We were successful in our ability to form leak-free lipid bilayers, to detect the formation of single protein pores, and to monitor the translocation dynamics of individual homogeneous 100 base strands of DNA. Differences in translocation dynamics were observed when the base was switched from adenine to cytosine. The solid state pores (2-5 nm estimated) were fabricated in thin silicon nitride membranes. Testing of the solid sate pores indicated comparable currents for the same size protein pore with excellent noise and sensitivity. However, there were no conditions under which DNA translocation was observed. After considerable effort, we reached the unproven conclusion that multiple (<1 nm) pores were formed in the nitride membrane, thus explaining both the current sensitivity and the lack of DNA translocation blockages

Diffusion Kinetics in the Pd/Cu(001) Surface Alloy

We use atom-tracking scanning tunneling microscopy to study the diffusion of Pd in the Pd/Cu(001) surface alloy. By following the motion of individual Pd atoms incorporated in the surface, we show that Pd diffuses by a vacancy-exchange, mechanism. We measure an effective activation energy for the diffusion of incorporated Pd atoms of 0.88 eV, which is consistent with an ab initio calculated barrier of 0.94 eV

"Bottom-up" meets "top-down" : self-assembly to direct manipulation of nanostructures on length scales from atoms to microns.

This document is the final SAND Report for the LDRD Project 102660 - 'Bottomup' meets 'top-down': Self-assembly to direct manipulation of nanostructures on length scales from atoms to microns - funded through the Strategic Partnerships investment area as part of the National Institute for Nano-Engineering (NINE) project

Diffusional kinetics of SiGe Dimers on Si(100) using atom-tracking scanning tunneling microscopy

Quantitative measurements of the diffusion of adsorbed mixed Ge-Si dimers on the Si(100) surface have been made as a function of temperature using atom-tracking scanning tunneling microscopy. These mixed dimers are distinguishable from pure Si-Si dimers by their characteristic kinetics--a 180-degree rotation between two highly buckled configurations. At temperatures at which the mixed dimers diffuse, atomic-exchange events occur, in which the Ge atom in the adsorbed dimer exchanges with a substrate Si atom. Re-exchange can also occur when the diffusing Si-Si dimer revisits the original site of exchange

Atomic-scale identification of Ge/Si intermixing on Si(100) at submonolayer Ge coverages

The positions of Ge atoms intermixed in the Si(100) surface at very low concentration are identified using empty-state imaging in scanning tunneling microscopy. A measurable degree of place exchange occurs at temperatures as low as 330 K. Contrary to earlier conclusions, good differentiation between Si atoms and Ge atoms can be achieved by proper imaging conditions