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dc.contributor.authorLiu, Y.
dc.contributor.authorAziz, Mustafa M.
dc.contributor.authorShalini, Ashawaraya
dc.contributor.authorWright, C. David
dc.contributor.authorHicken, R.J.
dc.date.accessioned2012-11-29T15:55:31Zen_GB
dc.date.accessioned2013-03-20T12:19:22Z
dc.date.accessioned2013-05-17T08:30:37Z
dc.date.issued2012
dc.description.abstractThe phase transition between the amorphous and crystalline states of Ge2Sb2Te5 has been studied by exposure of thin films to series of 60 femtosecond (fs) amplified laser pulses. The analysis of microscope images of marks of tens of microns in size provide an opportunity to examine the effect of a continuous range of optical fluence. For a fixed number of pulses, the dependence of the area of the crystalline mark upon the fluence is well described by simple algebraic results that provide strong evidence that thermal transport within the sample is one-dimensional (vertical). The crystalline mark area was thus defined by the incident fs laser beam profile rather than by lateral heat diffusion, with a sharp transition between the crystalline and amorphous materials as confirmed from line scans of the microscope images. A simplified, one-dimensional model that accounts for optical absorption, thermal transport and thermally activated crystallization provides values of the optical reflectivity and mark area that are in very good quantitative agreement with the experimental data, further justifying the one-dimensional heat flow assumption. Typically, for fluences below the damage threshold, the crystalline mark has annular shape, with the fluence at the centre of the irradiated mark being sufficient to induce melting. The fluence at the centre of the mark was correlated with the melt depth from the thermal model to correctly predict the observed melt fluence thresholds and to explain the closure and persistence of the annular crystalline marks as functions of laser fluence and pulse number. A solid elliptical mark may be obtained for smaller fluences. The analysis of marks made by amplified fs pulses present a new and effective means of observing the crystallization dynamics of phase-change material at elevated temperatures near the melting point, which provided estimates of the growth velocity in the range 7-9 m/s. Furthermore, finer control over the crystallization process in phase-change media can be obtained by controlling the number of pulses which, along with the laser fluence, can be tailored to any medium stack with relaxed restrictions on the thermal properties of the layers in the stack.en_GB
dc.identifier.citationVol. 112 (12), article 123526en_GB
dc.identifier.doi10.1063/1.4770359
dc.identifier.urihttp://hdl.handle.net/10871/9441
dc.language.isoenen_GB
dc.publisherAmerican Institute of Physicsen_GB
dc.relation.replaceshttp://hdl.handle.net/10036/4024
dc.relation.replaces10036/4024
dc.relation.urlhttp://dx.doi.org/10.1063/1.4770359en_GB
dc.subjectamorphous semiconductorsen_GB
dc.subjectantimony compoundsen_GB
dc.subjectcrystallisationen_GB
dc.subjectgermanium compoundsen_GB
dc.subjectheat transferen_GB
dc.subjecthigh-speed optical techniquesen_GB
dc.subjectlaser beam effectsen_GB
dc.subjectlight absorptionen_GB
dc.subjectmeltingen_GB
dc.subjectmelting pointen_GB
dc.subjectoptical microscopyen_GB
dc.subjectorder-disorder transformationsen_GB
dc.subjectphase change materialsen_GB
dc.subjectreflectivityen_GB
dc.subjectsemiconductor thin filmsen_GB
dc.subjectspecific heaten_GB
dc.subjectthermal conductivityen_GB
dc.titleCrystallization of Ge2Sb2Te5 films by amplified femtosecond optical pulsesen_GB
dc.typeArticleen_GB
dc.date.available2012-11-29T15:55:31Zen_GB
dc.date.available2013-03-20T12:19:22Z
dc.date.available2013-05-17T08:30:37Z
dc.identifier.issn0021-8979
dc.descriptionCopyright © 2012 American Institute of Physicsen_GB
dc.identifier.eissn1089-7550
dc.identifier.journalJournal of Applied Physicsen_GB


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