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SUMMARY:Is equilibrium overrated? Processing of optical materials at finit
 e time scales - Prof. Ursula J. Gibson\, Norwegian University of Science a
 nd Technology
DTSTART:20191120T193000Z
DTEND:20191120T203000Z
UID:TALK129802@talks.cam.ac.uk
CONTACT:Tommy Tai
DESCRIPTION:In materials processing of crystalline materials\, the first 
 “go-to” bit of information is the equilibrium phase diagram –an indi
 cation of the way things might be\, given sufficient time. One can approac
 h that structure by melting\, slow cooling and controlling nucleation\, as
  is\ndone in the semiconductor industry. Molecular Beam Epitaxy (MBE) uses
  high temperatures and the mobility of arriving atoms to make single-cryst
 al thin films of these materials.\n \nThis talk will examine cases where f
 abrication of materials with optical properties of interest occurs far fro
 m equilibrium. Group IV semiconductor-core optical fibres have recently em
 erged as a platform for non-linear optics and mid-to far IR transmission. 
 In processing of these materials\, the atypically large thermal gradient e
 stablished during laser heating has permitted the fabrication of single cr
 ystals with geometrical aspect ratios approaching a million. This works on
 ly at high\nsolidification rates for elemental systems. These rates need t
 o be slower for alloys due to the\nmiscibility gap that hampers the growth
  of bulk material\, but the preferential segregation of\none component all
 ows interesting structuring of the semiconductor core.\nIn depositing semi
 conductor films for electrical devices\, crystal perfection is essential\,
  but if\na large energy-gap material is being used as a host for atomic sp
 ecies that only require local\norder\, the constraints are relaxed. ZnS:Cr
 \, of interest as a mid-IR laser host is just such a\nmaterial\, and the r
 esults of slow vs rapid deposition will be presented.\n\nThese two cases i
 llustrate the value of investigating a wide range of processing conditions
 \, taking into account the requirements for a particular application in ad
 dition to the\nestablished convention for what is deemed “perfect”.\n\
 nThe following article is related to the talk: https://www.nature.com/arti
 cles/ncomms13265.pdf
LOCATION:Wolfson Lecture Theatre\,  Department of Chemistry\, Lensfield Ro
 ad
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