The effect of thermal anisotropies during crystallization in phase-change recording media

Belmont, M.R.; Aziz, Mustafa M.; Wright, C. David

doi:10.1063/1.2968447

Cited by 2 publications

(1 citation statement)

References 24 publications

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“…The effects of the release of latent heat during crystallization and thermal anisotropies on the heat flow process are assumed negligible due to the small change in crystalline fraction during each femtosecond laser pulse (and their contribution is small for Ge 2 Sb 2 Te 5 ). 17 The source term, g, represents the transmitted power density of the pump laser beam in the GST layer and is derived using Poynting theorem in the Appendix. The transmission angle of the pump laser beam in the GST layer (incident at 43…”

Section: Heat Flow and Crystallization Modelsmentioning

confidence: 99%

Crystallization of Ge2Sb2Te5 films by amplified femtosecond optical pulses

Liu

Aziz

Shalini

et al. 2012

Journal of Applied Physics

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The phase transition between the amorphous and crystalline states of Ge 2 Sb 2 Te 5 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. V C 2012 American Institute of Physics. [http://dx

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Section: Heat Flow and Crystallization Modelsmentioning

confidence: 99%

Crystallization of Ge2Sb2Te5 films by amplified femtosecond optical pulses

Liu

Aziz

Shalini

et al. 2012

Journal of Applied Physics

Self Cite

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Ultrafast heating and resolution of recorded crystalline marks in phase-change media

Aziz

Belmont

Wright

2008

Journal of Applied Physics

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In situ structure characterization of Pb(Yb1/2Nb1/2)O3-PbTiO3 crystals under high pressure-temperature Appl. Phys. Lett. 101, 062904 (2012) Martensitic transformation and magnetic domains in Mn50Ni40Sn10 studied by in-situ transmission electron microscopy J. Appl. Phys. 112, 033904 (2012) Structural and chemical properties of the nitrogen-rich energetic material triaminoguanidinium 1-methyl-5-nitriminotetrazolate under pressure J. Chem. Phys. 137, 054501 (2012) First-principles theoretical analysis of transition-metal doping of ZnSe quantum dots J. Appl. Phys. 112, 024301 (2012) High-pressure neutron study of the morphotropic lead-zirconate-titanate: Phase transitions in a two-phase system J. Appl. Phys. 112, 014104 (2012) Additional information on J. Appl. Phys. This work presents an analytical study of the thermally activated amorphous-to-crystalline phase-change process when the heating source has a delta function temporal profile. This simulates the case of ultrafast heating where crystallization in the amorphous phase-change medium occurs during cooling. The study produced closed-form expressions that predict the necessary peak temperature, and hence energy density, in the phase-change medium for successful crystallization during ultrafast annealing as functions of the kinetic and thermal parameters of the medium. Closed-form expressions were also derived that provide estimates of the final crystalline mark widths and tail lengths when phase change has ceased. The analysis indicated the need to reduce the activation energy of crystallization and the thermal diffusivity of the medium to reduce the initial peak temperature, produced by the heating source, to avoid melting, to increase the crystallization rate, to achieve sufficient levels of crystalline fractions during cooling, and to reduce the size of recorded crystalline marks. Perturbation analysis was carried out to study the effects of latent heat of crystallization during the fast kinetics phase. The result was reductions in the cooling rate of the phase-change material, thus requiring lower peak temperatures to achieve higher volumes of crystalline fraction. Nevertheless, the effects of heat release during crystallization were found to be modest for the class of current phase-change material used in data storage.

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The effect of thermal anisotropies during crystallization in phase-change recording media

Cited by 2 publications

References 24 publications

Crystallization of Ge2Sb2Te5 films by amplified femtosecond optical pulses

Crystallization of Ge2Sb2Te5 films by amplified femtosecond optical pulses

Ultrafast heating and resolution of recorded crystalline marks in phase-change media

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