Amorphisation and Recrystallisation of Nanometre Sized Zones in Silicon

In this paper we present a detailed study in which the formation, by heavy ion impact, and thermal recrystallisation of individual amorphous zones have been studied using in-situ transmission electron microscopy. In agreement with previous work, we observe a reduction in the total volume of amorphous material contained within the amorphous zones following thermal annealing over a wide range of temperatures. When the evolution of the individual amorphous zones is followed, those with similar starting sizes are observed to recrystallise over a range of temperatures from 70 ºC to 500 ºC. The temperature at which an amorphous zone fully recrystallises does not appear to be correlated with initial size. In addition, zones are occasionally observed to increase in size temporarily on some isochronal annealing steps. Furthermore, observations during a ramp anneal show that many zones recrystallise in a stepwise manner separated by periods of stability. These phenomenon are discussed in terms of the I-V pair

Anomalous annealing behavior of isolated amorphous zones in silicon

The formation and annealing of individual amorphous zones in silicon have been studied using in situ transmission electron microscopy. This technique enables us to identify anomalous behavior that cannot be deduced from statistical studies. Zones were formed at room temperature by impacts of single 200 keV Xe+ ions and imaged using structure factor contrast under down-zone conditions. Irradiation to fluences in the range 1011–1012 ions/cm2, results in small zones of black contrast (typically of order 1 nm in radius) which are clearly visible with minimal overlap. In agreement with earlier work, we observe a reduction in the total volume of amorphous material upon annealing over a temperature range from room temperature to 500 °C. Disappearance of individual zones with the same starting radius is observed to occur over a wide range of temperatures and in a small number of cases, zones are observed to increase in size during annealing. A discussion of these effects, based on the bond defect or I–V pair is presented

A key role for Ctf4 in coupling the MCM2-7 helicase to DNA polymerase α within the eukaryotic replisome

The eukaryotic replisome is a crucial determinant of genome stability, but its structure is still poorly understood. We found previously that many regulatory proteins assemble around the MCM2-7 helicase at yeast replication forks to form the replisome progression complex (RPC), which might link MCM2-7 to other replisome components. Here, we show that the RPC associates with DNA polymerase α that primes each Okazaki fragment during lagging strand synthesis. Our data indicate that a complex of the GINS and Ctf4 components of the RPC is crucial to couple MCM2-7 to DNA polymerase α. Others have found recently that the Mrc1 subunit of RPCs binds DNA polymerase epsilon, which synthesises the leading strand at DNA replication forks. We show that cells lacking both Ctf4 and Mrc1 experience chronic activation of the DNA damage checkpoint during chromosome replication and do not complete the cell cycle. These findings indicate that coupling MCM2-7 to replicative polymerases is an important feature of the regulation of chromosome replication in eukaryotes, and highlight a key role for Ctf4 in this process. © 2009 European Molecular Biology Organization | All Rights Reserved