Phonon anharmonicity in silicon from 100 to 1500 K

Kim, Dennis; Smith, Harold L.; Niedziela, Jennifer L.; Li, Chen W.; Abernathy, D. L.; Fultz, B.

doi:10.1103/physrevb.91.014307

Cited by 61 publications

(60 citation statements)

References 47 publications

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“…In another study describing felodipine-loaded PCL microspheres, PCL (80 kDa) had the most viscous organic phase, so the encapsulation efficiency was the highest. 37 In our study, this trend was more pronounced for high Mw PCL microspheres in which gelatine was also used.…”

Section: Loading and Encapsulation Efficiencymentioning

confidence: 46%

“…41 It was indicated that the viscosity of the organic phase of high Mw PCL was higher than that of low Mw PCL. 37 Microspheres prepared with PVA-gelatin were smoother and more homogeneous than those prepared with PVA (4%). Similar positive effects of gelatin use have been reported in other studies.…”

Section: Resultsmentioning

confidence: 88%

“…14,35,36 Smaller microspheres have been previously reported with the use of surfactant during the preparation of microspheres due to the amphiphilic behavior of the surfactant (PVA). [37][38][39][40] Further optimization involved use of gelatin in the preparation of microspheres, from 1 to 3% (w/v) and at different temperatures (37 and 45 C) for preventing gellation. SEM images of PCL microspheres at different evaporation temperatures (data not shown) showed that evaporation at 37 C resulted in a more homogeneous shape and size distribution than at 45 C. Uniform and spherical microspheres were obtained with 1% gelatin concentration but increasing the concentration resulted in more roughness and caused the formation of aggregates.…”

Section: Resultsmentioning

confidence: 99%

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Study on physiochemical structure and in vitro release behaviors of doxycycline‐loaded PCL microspheres

Aydın

Tezcaner

et al. 2014

J of Applied Polymer Sci

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This study aimed to develop drug delivery system of doxycycline-loaded polycaprolactone (PCL) microspheres. The investigated microsphere formulation can be considered for local application in bone infections and degenerative joint diseases, which generally require long-term treatments via systemic drugs. PCL-14 kDa and 65 kDa were used in microsphere preparation. Before release, the microspheres were characterized by scanning electron microscopy, differential scanning calorimetry, and X-ray photoelectron spectroscopy. The mean particle size of microspheres was in the range of 74-122 mm and their drug loadings ranged between 10 and 30%. In vitro release profiles were described using the Higuchi and the Korsmeyer-Peppas equations. Diffusion model was applied to experimental data for estimating diffusion coefficients of microspheres; calculated as between 4.5 3 10 210 and 9.5 3 10 210 cm 2 /s.Although long-term release from microspheres of PCL-14 kDa obeyed diffusion model, PCL-65 kDa microspheres showed this tendency only for some period. Modeling studies showed that the drug release mechanism was mainly dependent on loading and molecular weight differences. Release behavior of PCL-65 kDa microspheres, however, might be better represented by derivation of a different equation to model for the total release period.

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Section: Loading and Encapsulation Efficiencymentioning

confidence: 46%

Section: Resultsmentioning

confidence: 88%

Section: Resultsmentioning

confidence: 99%

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Study on physiochemical structure and in vitro release behaviors of doxycycline‐loaded PCL microspheres

Aydın

Tezcaner

et al. 2014

J of Applied Polymer Sci

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“…A comparison is interesting. Diamond cubic Si has a large pure anharmonicity at ambient pressure, several times larger than quasiharmonic effects from thermal expansion 13 . At ambient pressure, the average thermal shift of the phonon modes of Si 24 (red line in Fig.…”

Section: Discussionmentioning

confidence: 99%

Phonons inSi24at simultaneously elevated temperature and pressure

Tong

Fultz

et al. 2017

Phys. Rev. B

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Raman spectroscopy was used to measure the frequencies of phonons in Si24 with an open clathrate structure at temperatures from 80 K to 400 K, with simultaneous pressures of 0 to 8 GPa. The frequency shifts of the different phonons were substantially different under either temperature or pressure. The quasiharmonic behavior was isolated by varying pressure at low temperature, and the anharmonic behavior was isolated by varying temperature at low pressure. Phonon modes dominated by bond bending were anomalous, showing stiffening with temperature and softening with pressure. Both the quasiharmonic behavior and the anharmonic behavior changed markedly with simultaneous changes in temperature, ∆T , and pressure, ∆P . With ∆T =320 K and ∆P =8 GPa, some frequency shifts that scaled with the product ∆T ∆P were as large as the shifts from ∆T and ∆P alone. The thermodynamic entropy of this material likely has a dependence on ∆T and ∆P that cannot be obtained by adding effects from quasiharmonicity and phonon-phonon anharmonicity.

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“…where γ is the thermal Gruneïsen parameter and v Si is the equilibrium atomic volume, which would yield a correction of 1.2 k B /atom (with the correction restricted to core atom) if one were to consider v rel = −20Å 3 and γ from [56]. The relaxation volume v rel defined in equations (3) and (4) may differ from the relaxation volume derived from the thermodynamical formation volume…”

Section: Vibrational Formation Entropymentioning

confidence: 99%

On the ab initio calculation of vibrational formation entropy of point defect: the case of the silicon vacancy

Seeberger

Vidal

2017

EPJ Photovolt.

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Formation entropy of point defects is one of the last crucial elements required to fully describe the temperature dependence of point defect formation. However, while many attempts have been made to compute them for very complicated systems, very few works have been carried out such as to assess the different effects of finite size effects and precision on such quantity. Large discrepancies can be found in the literature for a system as primitive as the silicon vacancy. In this work, we have proposed a systematic study of formation entropy for silicon vacancy in its 3 stable charge states: neutral, +2 and -2 for supercells with size not below 432 atoms. Rationalization of the formation entropy is presented, highlighting importance of finite size error and the difficulty to compute such quantities due to high numerical requirement. It is proposed that the direct calculation of formation entropy of VSi using first principles methods will be plagued by very high computational workload (or large numerical errors) and finite size dependent results.

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Phonon anharmonicity in silicon from 100 to 1500 K

Cited by 61 publications

References 47 publications

Study on physiochemical structure and in vitro release behaviors of doxycycline‐loaded PCL microspheres

Study on physiochemical structure and in vitro release behaviors of doxycycline‐loaded PCL microspheres

Phonons inSi24at simultaneously elevated temperature and pressure

On the ab initio calculation of vibrational formation entropy of point defect: the case of the silicon vacancy

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