Evidence Against a Reduced Melting Temperature in Amorphous Silicon

1981 ◽  
Vol 4 ◽  
Author(s):  
S.A. Kokorowski ◽  
G.L. Olson ◽  
J.A. Roth ◽  
L.D. Hess
Keyword(s):  
Melting Point ◽  
Amorphous Silicon ◽  
Melting Temperature ◽  
Laser Heating ◽  
Crystalline Silicon ◽  
Phase Changes ◽  
Experimental Results ◽  
Melting Point Depression ◽  
Time Resolved ◽  
Cw Laser

ABSTRACTExperimental results are presented which indicate that amorphous silicon does not melt at a temperature significantly lower than the melting point of crystalline silicon (1693°K), contrary to recent reports which suggest a 300 to 500°K melting point depression. Time-resolved optical reflectivity measurements are used to determine the temperature and to investigate phase changes which occur in silicon during cw laser heating. It is shown that amorphous silicon films produced by arsenic implantation into Si(100) do not melt when heated to temperatures in excess of 1600°K. An alternate interpretation of previous work that is consistent with the present findings is proposed.

Effects of Impurities on the Competition between Solid Phase Epitaxy and Random Crystallization In Ion-Implanted Silicon

1984 ◽  
Vol 35 ◽  
Author(s):  
G.L. Olson ◽  
J.A. Roth ◽  
Y. Rytz-Froidevaux ◽  
J. Narayan
Keyword(s):  
Laser Heating ◽  
Crystallization Process ◽  
Solid Phase ◽  
Crystallization Rate ◽  
Solid Phase Epitaxy ◽  
Temperature Dependent ◽  
Kinetics Parameters ◽  
Time Resolved ◽  
Cw Laser ◽  
Ion Implanted

ABSTRACTThe temperature dependent competition between solid phase epitaxy and random crystallization in ion-implanted (As+, B+, F+, and BF2+) silicon films is investigated. Measurements of time-resolved reflectivity during cw laser heating show that in the As+, F+, and BF2+-implanted layers (conc 4×1020cm-3) epitaxial growth is disrupted at temperatures 1000°C. This effect is not observed in intrinsic films or in the B+-implanted layers. Correlation with results of microstructural analyses and computer simulation of the reflectivity experiment indicates that disruption of epitaxy is caused by enhancement of the random crystallization rate by arsenic and fluorine. Kinetics parameters for the enhanced crystallization process are determined; results are interpreted in terms of impurity-catalyzed nucleation during the random crystallization process.

Time-Resolved Optical Reflectivity and Transmission During Laser-Induced Oxidation of Cadmium Films

1983 ◽  
Vol 29 ◽  
Author(s):  
L. Baufay ◽  
M. Wautelet ◽  
A. Pigeolet ◽  
R. Andrew
Keyword(s):  
Melting Point ◽  
Laser Irradiation ◽  
Oxide Layer ◽  
Probe Beam ◽  
Laser Power ◽  
Time Resolved ◽  
Optical Reflectivity ◽  
Glass Substrates ◽  
Cw Laser

ABSTRACTThe laser-induced oxidation of 2000 Å thick cadmium films on glass substrates is studied by measuring the time-resolved reflectivity and transmission of a probe beam. Under CW laser irradiation, the thickness of the oxide layer is shown to increase linearly with time. Also, the velocity, v, of the CdO-Cd interface increases with increasing laser power, with a step when the melting point of Cd is attained. At the highest powers studied in this work, v varies as v = voexp(−a/P), with vo = 6100 Ås−1 and a=4.8 W.

In Situ Fast Temperature Measurement of Silicon Thin Films during the Excimer Laser Annealing

2006 ◽  
Vol 326-328 ◽  
pp. 195-198
Author(s):  
Seung Jae Moon
Keyword(s):  
Thin Films ◽  
Optical Properties ◽  
Melting Point ◽  
Temperature Measurement ◽  
Amorphous Silicon ◽  
Laser Annealing ◽  
Crystalline Silicon ◽  
Excimer Laser Annealing ◽  
Silicon Thin Films

The formation and growth mechanism of polysilicon grains in thin films via laser annealing of amorphous silicon thin films are studied. The complete understanding of the mechanism is crucial to improve the thin film transistors used as switches in the active matrix liquid crystal displays. To understand the recrystallization mechanism, the temperature history and liquidsolid interface motion during the excimer laser annealing of 50-nm thick amorphous and polysilicon films on fused quartz substrates are intensively investigated via in-situ time-resolved thermal emission measurements, optical reflectance and transmittance measurements at near infrared wavelengths. The front transmissivity and reflectivity are measured to obtain the emissivity at the 1.52 μm wavelength of the probe IRHeNe laser to improve the accuracy of the temperature measurement. The melting point of amorphous silicon is higher than that of crystalline silicon of 1685 K by 100-150 K. This is the first direct measurement of the melting temperature of amorphous silicon thin films. It is found that melting of polysilicon occurs close to the melting point of crystalline silicon. Also the optical properties such as reflectance and transmittance are used to determine the melt duration by the detecting the difference of the optical properties of liquid silicon and solid silicon.

Raman Scattering with Nanosecond Resolution During Pulsed Laser Heating of Silicon

1982 ◽  
Vol 13 ◽  
Author(s):  
D. Von Der Linde ◽  
G. Wartmann ◽  
A. Ozols
Keyword(s):  
Phase Transition ◽  
Raman Scattering ◽  
Laser Heating ◽  
Crystalline Silicon ◽  
Silicon Crystal ◽  
Pulsed Laser ◽  
Lattice Temperature ◽  
Time Resolved ◽  
Pulsed Laser Heating ◽  
Anti Stokes

ABSTRACTWe present time-resolved measurements of spontaneous anti-Stokes and Stokes Raman scattering during pulsed laser heating of crystalline silicon. The time-evolution of the lattice temperature is determined from the measured anti-Stokes/Stokes intensity ratio. In a separate calibration experiment we measure the temperature dependence of the anti-Stokes/Stokes ratio of an oven-heated silicon crystal from 300 K up to 900 K. The phase transition occuring during laser heating is detected by monitoring the changes of the optical reflectivity during laser irradiation. Our data suggest that the phase transition occurs at a lattice temperature of ∼600 K.

Comparison of different models for melting point change of metallic nanocrystals

2001 ◽  
Vol 16 (11) ◽  
pp. 3304-3308 ◽  
Author(s):  
M. Zhao ◽  
X. H. Zhou ◽  
Q. Jiang
Keyword(s):  
Melting Point ◽  
Phenomenological Model ◽  
Size Dependence ◽  
Size Range ◽  
Experimental Results ◽  
Melting Point Depression ◽  
Thermodynamic Models ◽  
Point Change ◽  
The Difference ◽  
Theoretical Considerations

Our phenomenological model without adjustable parameters for the size dependence and dimension dependence of melting point depression and enhancement of nanocrystals is introduced. The predictions of our models are consistent with both of experimental results and other thermodynamic models for metallic nanocrystals while the difference between our model and other theoretical considerations in mesoscopic size range is discussed.

scholarly journals Comparison of the observed size-dependent melting point of CdSe nanocrystals to theoretical predictions

2018 ◽  
Vol 9 (1) ◽  
pp. 39-43
Author(s):  
Albert Demaine Dukes III ◽  
Christopher Dylan Pitts ◽  
Anyway Brenda Kapingidza ◽  
David Eric Gardner ◽  
Ralph Charles Layland
Keyword(s):  
Melting Point ◽  
Surface Area ◽  
Melting Temperature ◽  
Volume Ratio ◽  
Melting Point Depression ◽  
Cdse Nanocrystals ◽  
Size Dependent ◽  
Theoretical Predictions

Cadmium selenide nanocrystals were observed to have a size-dependent melting point which was depressed relative to the bulk melting temperature. The observed size-dependent melting point ranged from 500-1478 K, while a model based on the surface area to volume ratio predicted that is should range between 774-1250 K. The nanocrystals were heated in situ in the electron microscope, and the melting point was almost immediately followed by the vaporization of the CdSe nanocrystals, allowing for straightforward determination of the melting temperature. The differences between the observed melting point of CdSe nanocrystals and the values predicted by the surface area to volume ratio model indicates that additional factors are involved in the melting point depression of nanocrystals.

Time Resolved Spectra of Raman and Thermal Emission During Pulsed Laser Heating of Silicon

1983 ◽  
Vol 23 ◽  
Author(s):  
D. Von Der Linde ◽  
G. Wartmann ◽  
M. Kemmler ◽  
Zhen-He Zhu
Keyword(s):  
Laser Heating ◽  
Thermal Emission ◽  
Crystalline Silicon ◽  
Laser Pulses ◽  
Low Frequencies ◽  
Time Resolved ◽  
Emission Time ◽  
Pulsed Laser Heating ◽  
Anti Stokes ◽  
532 Nm

ABSTRACTLaser heating of crystalline silicon is investigated with 10 ns laser pulses at 532 nm Raman spectra below the transition threshold show distinct shifts to low frequencies. The absence of line shifts at higher energy is due to a time resolution artifact. Temperatures evaluated from frequency resolved anti-Stokes/Stokes ratios are in agreement with the temperature estimated from line shifts, and provide clear evidence that the surface reaches the melting point. These conclusions are confirmed by independent measurements of the thermal emission. Time-resolved pyrometry also provides the temperature evolution of the liquid phase.

Variable strain energy in amorphous silicon

1988 ◽  
Vol 3 (6) ◽  
pp. 1201-1207 ◽  
Author(s):  
W. C. Sinke ◽  
S. Roorda ◽  
F. W. Saris
Keyword(s):  
Raman Spectroscopy ◽  
Free Energy ◽  
Amorphous Silicon ◽  
Melting Temperature ◽  
Structural Relaxation ◽  
Laser Heating ◽  
Strain Energy ◽  
Preparation Conditions ◽  
Calorimetric Measurements ◽  
Initial States

Different Raman experiments on structural relaxation of a-Si and a-Ge are reviewed and discussed in relation to calorimetric measurements on a-Ge. On the basis of the correlation found between results from Raman spectroscopy and results from calorimetry in the case of a-Ge and of the strong similarity between a-Si and a-Ge in terms of their Raman spectra, it is suggested that the strain energy in a-Si may vary considerably with preparation conditions and subsequent treatments. Under this assumption the a-Si Gibbs free energy versus temperature has been constructed for material in different initial states of relaxation. It is shown that the melting temperature of amorphous silicon should increase when relaxation occurs during the heating phase prior to melting. Thus differences in apparent melting temperature, as observed under different laser heating conditions, may be explained.

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