调整一些细节
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@@ -34,6 +34,9 @@ These phonons were categorized into two groups according to their electrical pol
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where atoms of the same species vibrate in phase,
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resulting in strong electrical polarization and observable effects in Raman spectra
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(colored lines in @figure-discont).
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The categorized is also illustrated and compared with Raman experiment in @fig-raman.
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#include "figure-raman.typ"
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#include "non-polar/default.typ"
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#include "polar/default.typ"
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@@ -3,6 +3,7 @@
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caption: [
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(a) Phonon dispersion of 4H-SiC along the A–#sym.Gamma–K high-symmetry path.
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(b) Magnified view of the boxed region in (a).
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(c) Magnified view of the boxed region in (b).
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The orange dashed lines mark the phonon wavevectors involved in Raman scattering
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with green laser light under normal and edge incidence configurations.
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],
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@@ -1,27 +1,28 @@
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=== Phonons with Negligible Polarities
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用 gamma 点的声子来近似。
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对弱极性声子的理论分析,首先使用 Gamma 点的声子来近似,然后再讨论不同入射方向导致的差异。
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使用Gamma 点的声子来近似,基于这样的事实:这些声子的色散曲线在 Gamma 点附近连续且非常接近 Gamma 点,并且已经被广泛使用 @_n-sic_2008。
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Gamma 点的声子被用于近似参与拉曼散射的弱极性声子,无论入射配置。
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这个近似是因为这些声子的色散曲线在 Gamma 点附近连续且非常接近 Gamma 点,并且已经被广泛使用。
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Phonons at the #sym.Gamma point were employed to approximate negligible-polar phonons for all incidence configurations.
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Negligible-polar phonons were theoretically analyzed,
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starting with the approximation using phonons at the #sym.Gamma point,
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followed by a discussion of variations arising from non-zero wavevectors
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(e.g. different incidence configurations in Raman experiments).
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This approximation is based on the fact that
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the dispersion of these phonons is continuous and very close to the #sym.Gamma point,
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and has been widely adopted in the literature @_n-sic_2008.
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18 个声子属于 12 个表示。拉曼张量的形状可以确定,大小不能。
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这些声子的拉曼张量的形状可以通过对称性分析来确定。
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使用对称性分析来从理论上研究声子。
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18 个 Gamma 点的弱极性声子包含了 C#sub[6v] 点群的12 个不可约表示(2A#sub[1] + 4B#sub[1] + 2E#sub[1] + 4E#sub[2])。
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通过进一步考虑 C#sub[6v] 中简并表示(E1 和 E2)在 C#sub[2v] 中的表示,所有声子的拉曼张量的非零分量可以确定,如表所示。
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其中,B#sub[1] 模式具有零拉曼张量,不参与拉曼散射;
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其它表示的模式具有非零拉曼张量分量,可能可以在适当的偏振配置下在拉曼实验中观察到。
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然而,模式是否足够强以在实验中可见取决于其拉曼张量分量的大小,而仅通过对称性分析无法确定这些大小。
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The form of the Raman tensors (i.e., which components are non-zero) could be determined by symmetry analysis.
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The 18 negligible-polar phonons at the #sym.Gamma point
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correspond to twelve irreducible representations of the C#sub[6v] point group
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Symmetry analysis was utilized
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to theoretically investigate the properties of 18 negligible-polar phonons at the #sym.Gamma point.
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These phonons correspond to twelve irreducible representations of the C#sub[6v] point group
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(2A#sub[1] + 4B#sub[1] + 2E#sub[1] + 4E#sub[2]).
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By further decomposing the doubly degenerate modes (E#sub[1] and E#sub[2] of C#sub[6v] group)
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in the C#sub[2v] point group,
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@@ -30,7 +31,7 @@ Phonons of the B#sub[1] representation in C#sub[6v] possess zero Raman tensors
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and thus do not contribute to Raman scattering,
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while other phonons have non-zero Raman tensor components,
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making them potentially observable in Raman experiments under appropriate incidence and polarization configurations.
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It should be noted, however, that the observability in Raman experiment depends not only on the tensor form,
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It should be noted, however, that the observability in Raman experiment depends not only on the form of Raman tensor,
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but also on the magnitude of its Raman tensor components,
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which cannot be inferred from symmetry considerations alone.
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@@ -43,18 +44,24 @@ It should be noted, however, that the observability in Raman experiment depends
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每个原子对拉曼张量的贡献主要取决于第一近邻原子(它们的贡献记为 $a_i$),更远的原子则归结为小量(记为 $epsilon_i$ $eta_i$ $zeta_i$)。
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此外,我们忽略了同一个振动模式中,同种原子振幅的绝对值的差异,只考虑它们振动方向的不同。
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因此,拉曼张量的大小可以在进一步的第一性原理计算之前给出,结果总结在表中。
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我们的结果表明,756 附近的峰应该比其它峰具有更强的拉曼强度。
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我们的结果表明,756 附近的峰应该比其它峰具有更强的拉曼强度,这与实验一致。
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我们的研究表明,这个峰的高拉曼强度来自于所有键的贡献的相长干涉,这与其他弱极性模式不同(他们的贡献相互抵消)。
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A method to rapidly estimate the magnitudes of the Raman tensors was proposed (see appendix for details).
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This approach is founded on the symmetry analysis and incorporates the assumption
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A method to estimate the magnitudes of the Raman tensors of each mode from their vibration patterns (eigenvectors)
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was proposed (see appendix for details).
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This approach was founded on the symmetry analysis and incorporates the assumption
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that the primary contribution from each atom to the Raman tensor arises from its nearest neighbors (denoted as $a_i$),
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while contributions from more distant atoms are much smaller (denoted as $epsilon_i$, $eta_i$, and $zeta_i$).
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Furthermore, we neglect the absolute amplitude differences among atoms of the same type within a phonon mode,
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considering only their vibrational directions.
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Furthermore, the absolute amplitude differences among atoms of the same type within a phonon mode was neglected,
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and only their vibrational directions were considered.
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This enables a preliminary estimation of the Raman tensor magnitudes prior to detailed first-principles calculations,
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with the results summarized in @table-nopol.
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Our analysis indicates that the E#sub[2] mode at 756.25 cm#super[-1] in simulation (mode 8)
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should possess a much higher Raman intensity than the others.
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Our analysis gave the result that the E#sub[2] mode at 756.25 cm#super[-1] in simulation (mode 8)
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should possess a much higher Raman intensity than the others,
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which is consistent with experimental observations.
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Our result showed that
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the high Raman intensity of this mode arises from the constructive interference of contributions from all bonds,
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in contrast to other negligible-polar modes where contributions tend to cancel each other out.
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#include "table-nopol.typ"
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@@ -117,6 +124,6 @@ Besides, there are small peeks at xxx,
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// 在论文中我们这样来称呼:phonon 对应某一个特征向量,而 modes 对应于一个子空间。
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// 也就是说,简并的里面有两个或者无数个 phonon,但只有一个 mode
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#include "figure-raman.typ"
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// #include "figure-raman.typ"
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// TODO: 解释为什么 E1 可以看到
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@@ -1,11 +0,0 @@
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#figure(
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image("/画图/拉曼整体图/embed.svg"),
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caption: [
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(a) Phonon dispersion of 4H-SiC along the A–#sym.Gamma–K high-symmetry path.
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Gray lines represent negligible-polar phonon modes,
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while colored lines indicate strong-polar phonon modes.
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(b) Magnified view of the boxed region in (a).
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The orange dashed lines mark the phonon wavevectors involved in Raman scattering
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with incident light along the z- and y-directions.
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]
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)<raman>
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@@ -12,7 +12,7 @@
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[Simulation (cm#super[-1])],
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// E2 E2 E1 A1 E1 E2 E2 A1
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[190.51], [197.84], [257.35], m2[591.90], [746.91], [756.25], [764.33], m2[812.87],
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[Experiment (cm#super[-1])],
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[Experiment (cm#super[-1], averaged)],
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// E2 E2 E1 A1 E1 E2 E2 A1
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[195.5], [203.3], [269.7], m2[609.5], [Invisible], [776], [Invisible], m2[839],
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// E2 E2 E1 A1 E1 E2 E2 A1
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@@ -33,10 +33,12 @@
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// TODO: 改正正负号
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// E2 E2 E1 A1 E1 E2 E2 A1
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[0.17], [1.13], [2.43], [2.83], [1.79], [0.09], [88.54], [0.50], [0.01], [1.78],
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[Experiment result (a.u.)],
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[Experiment result #linebreak() (a.u., averaged)],
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// TODO: 填充
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// E2 E2 E1 A1 E1 E2 E2 A1
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[], [], [], [], [], [Invisible], [], [Invisible], [Invisible], [],
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)},
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caption: [Negaligible-polarized Phonons at $Gamma$ Point.],
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)<table-nopol>]
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// TODO: 从多个方向的实验中取得平均值。
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@@ -12,14 +12,10 @@
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table.cell(rowspan: 2)[*Representation*],
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[C#sub[6v]], A1, B1, m2(E1), m2(E2),
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[C#sub[2v]], A1, B1, B2, B1, A2, A1,
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table.cell(rowspan: 2, colspan: 2)[*Vibration Direction*],
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[out-of-plane], [out-of-plane], m2[in-plane], m2[in-plane],
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[z], [z], [x], [y], [x], [y],
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m2[*Vibration Direction*], [z], [z], [x], [y], [x], [y],
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m2[*Raman Tensor*],
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[$mat(a,,;,a,;,,b)$], [$0$], [$mat(,,a;,,;a,,;)$], [$mat(,,;,,a;,a,;)$], [$mat(,a,;a,,;,,;)$], [$mat(a,,;,-a,;,,;)$],
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m2[*Raman visibility*],
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[xx/yy: $a^2$ #linebreak() zz: $b^2$ #linebreak() others: 0], [0],
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m2[xz/yz: $a^2$ #linebreak() others: 0], m2[xx/xy/yy: $a^2$ #linebreak() others: 0],
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[$mat(a,,;,a,;,,b)$], [$0$],
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[$mat(,,a;,,;a,,;)$], [$mat(,,;,,a;,a,;)$], [$mat(,a,;a,,;,,;)$], [$mat(a,,;,-a,;,,;)$],
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)},
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caption: [
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Irreducible representations and raman tensors of phonons in 4H-SiC.
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@@ -168,3 +168,19 @@
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- 在不同入射方向下,极性模式最多会呈现出三个峰。
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// TODO: 拟合时不考虑fano共振,结果有些不好。是否将它考虑进去再拟合?
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= 其他
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== 缺陷
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- 比对各个峰的结果,得到:(我们只看 E2 模式的 yy 和 xy,以及 A1 的 yy)
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- 半高宽/高度/积分来看,似乎富C的样品缺陷更多(更宽、更矮)。这是一个合理的现象。
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- 富C的E1 xy有非常明显的蓝移,但因为暂时不知道来源,所以暂时不分析(需要其它方向的实验)。
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- 细节来说,富C的E2 xy有明显红移,A1几乎没有移动,E2 yy有红移但很少。
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- 主E2,yy和xy不同。xy的高度几乎只受到生长环境的影响,xx的高度则还会受到掺杂浓度的影响。xy的宽度会明显受到生长环境的影响,yy的宽度则不变。次高的E2也有类似的规律。
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- 以上规律中,积分主要受到高度的影响,所以不单独分析(或者使用积分来分析,或许更合适)。
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== 拟合 LOPC
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有很多可调的参数。我们首先固定一些参数,以便于拟合。
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