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몇가지 의문사항이 있어 글을 올립니다.
1. acoustic vibration 과 optical vibration이 각각 동일한방향으로의 원자진동과 반대방향으로의 원자진동을 정의하는 단어가 맞는지에 관한 내용
2. Longitudinal mode와 Transverse mode에 관한 정의와
3. raman active와 infrared active 의 정확한 정의를 알고싶습니다.
4. 재료내부의 잔류응력을 평가할때 raman active 인 peak들을 사용하는 이유를 알고 싶습니다.
5. 재료내부의 압축응력이 작용했을 때, peak이 오른쪽으로 이동하는데, 그 이유와 이를 blue shift로 부르는 이유를 알고 싶습니다.
- raman
각 분야 한인연구자와 현업 전문가분들의 답변을 기다립니다.
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답변
신동협님의 답변
2014-10-13- 3
1번 acoustic 과 optical 에 대한 정의
3.번 raman과 infrared active에 대한 정의
를 읽어보시면 알수 있습니다. (볼드체로 강조해놓은 부분입니다.)
추가적으로 이 내용은 아래 웹에서 발췌하였습니다.
p://en.wikipedia.org/wiki/Phonon
than one type of atom – either with different masses or bonding strengths – in the smallest unit cell, exhibit two types of phonons: acoustic phonons and optical phonons.Acoustic phonons are coherent movements of atoms of the lattice out of their equilibrium positions. If the displacement is in the direction of propagation, then in some areas the atoms will be closer, in others farther apart, as in a sound wave in air (hence the name acoustic). Displacement perpendicular to the propagation direction is comparable to waves in water. If the wavelength of acoustic phonons goes to infinity, this corresponds to a simple displacement of the whole crystal, and this costs zero energy. Acoustic phonons exhibit a linear relationship between frequency and phonon wavevector for long wavelengths. The frequencies of acoustic phonons tend to zero with longer wavelength. Longitudinal and transverse acoustic phonons are often abbreviated as LA and TA phonons, respectively.
Optical phonons are out-of-phase movement of the atoms in the lattice, one atom moving to the left, and its neighbour to the right. This occurs if the lattice is made of atoms of different charge or mass. They are called optical because in ionic crystals, such as sodium chloride, they are excited by infrared radiation. The electric field of the light will move every positive sodium ion in the direction of the field, and every negative chloride ion in the other direction, sending the crystal vibrating. Optical phonons have a non-zero frequency at the Brillouin zone center and show no dispersion near that long wavelength limit. This is because they correspond to a mode of vibration where positive and negative ions at adjacent lattice sites swing against each other, creating a time-varying electrical dipole moment. Optical phonons that interact in this way with light are called infrared active. Optical phonons that are Raman active can also interact indirectly with light, through Raman scattering. Optical phonons are often abbreviated as LO and TO phonons, for the longitudinal and transverse modes respectively.
When measuring optical phonon energy by experiment, optical phonon frequencies,
, are often given in units of cm−1, which are the same units as the wavevector. This value corresponds to the inverse of the wavelength of a photon with the same energy as the measured phonon.[9] The cm−1 is a unit of energy used frequently in the dispersion relations of both acoustic and optical phonons, see units of energy for more details and uses. -
답변
신동협님의 답변
2014-10-18- 2
4번과 5번 질문에 참고하시면 도움될 것 같습니다.
In a crystalline material, the frequency of the raman bands is a characteristic inherent to the crystalline structure, and the chemical composition of the material. However, the phonon frequency may be modified by means of introducing an external force able to modify the internal energy of the crystal. When a mechanical stress is applied to a crystal, it results in microscopic atomic displacements, resulting in a net strain. Such strain modifies the interatomic distance, and consequently, the ionic and covalent bonding forces between neighbor atoms. This mechanism is resposible for the vibration of the phonon frequency. In priciple, even though one should take into account the tensor nature of stress and strain magnitudes, a compressive stress results in a reduction in the interatomic distance, increasing the interatomic forces, which leads to a positive (blue) shift of the phonon frequency. When a tensile stress is applied, the phonon frequency is decreased (or red shifted). -
답변
서병일님의 답변
2014-10-19- 2
IR은 분자 진동을 측정하고 라만은 산란을 측정합니다.
IR은 극성분자(dipole 모멘트가 있는 분자)의 진동(신축진동, 회전진동)을 일으키는 것을 측정하며 기능기마다 다르게 나타나며 측정 파장은 200-4000 cm-1 입니다.
라만은 극성이 없으나 순간적인 전자 찌그러짐으로 분자 내 편극(polarizabolity)이 발생하여 빛 투과시 산란이 생기며 이를 탐지하는 것입니다.
예로서 CO2는 분자가 대칭이가 때문에 IR 에는 나타나지 않습니다 그러나 순간적으로 편극이 발생하여 라만산란이 일어나며 이를 탐지하는 것입니다.
200-1000nm 범위의 빛 한가지(예 250nm, 550nm, 1063nm 등)를 조사하면 해당 파장에서 에너지를 흡수 및 방출이 3가지로 구별됩니다.(layleigh 산란, antistokes 산란, stokes 산란) 즉 3가지 peak가 나오는 거죠 그래서 조사 빛과 이동파장(shift)을 측정합니다
이론이 길기 때문에 정확히 관련되는 자료를 첨부합니다
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