레이저 초음파를 이용한 체적종파의 박막 내 전파특성 연구

국문 초록 (Abstract)

본 논문에서는 나노스케일 금속박막 내에서 체적종파가 전파하는 특성을 연구하였다. 실리콘(100) 기판 위에 150 nm 두께의 크로뮴 혹은 알루미늄 박막을 적층하여 시편을 제작하였으며, 펨토초 레이저 시스템으로 구성된 시간영역 열반사율 기법(time-domain theromoreflectance technique)을 이용하여 박막 표면으로부터 여기된 탄성파가 박막과 기판의 계면에서 반향될 때 발생하는 신호를 검출하였다. 체적종파의 거동을 모사하는 열탄성 방정식을 수치해석적으로 풀어 측정값과 곡선맞춤함으로써 박막의 체적종파 속도와 탄성계수를 평가할 수 있었으며, 결과를 문헌값과 비교하여 그 타당성을 검증하였다. 본 연구로부터 확립된 레이저 계측법은 나노재료의 특성평가에 적합함을 보여주며, 이는 기존의 접촉식·파괴식 검사법의 한계를 뛰어넘을 대안을 제시한다.

다국어 초록 (Multilingual Abstract)

This paper presents the investigation of the propagation behavior of bulk longitudinal waves generated by an ultrafast laser system in thin films. A train of femtosecond laser pulses was focused onto the surface of a 150-nm thick metallic (chromium or aluminum) film on a silicon substrate to excite elastic waves, and the change in thermoreflectance at the spot was monitored to detect the arrival of echoes from the film/substrate interface. The experimental results show that the film material characteristics such as the wave velocity and Young’s modulus can be evaluated through curve-fitting in numerical solutions. The material properties of nanoscale thin films are difficult to measure using conventional techniques. Therefore, this research provides an effective method for the nondestructive characterization of nanomaterials.

목차 (Table of Contents)

• 초록
• Abstract
• 1. 서론
• 2. 이론 및 수치해석
• 3. 실험방법
• 4. 결과 및 고찰
• 5. 결론
• References

참고문헌 (Reference)

1 이동진, "유도초음파 분산 특성을 이용한 박판의 탄성계수 측정" 한국비파괴검사학회 32 (32): 41-46, 2012

2 이형일, "마이크로/나노 압입시험에 의한 재료특성평가" 대한기계학회 32 (32): 805-816, 2008

3 C. A. Paddock, "Transient thermoreflectance from thin metal films" 60 (60): 285-290, 1986

4 K. Chang, "The novel stress simulation method for contemporary DRAM capacitor arrays" 424-427, 2013

5 S. G. Nilsson, "Size effect on Young’s modulus of thin chromium cantilevers" 85 (85): 3555-, 2004

6 G. Simmons, "Single Crystal Elastic Constants and Calculated Aggregate Properties: A Handbook" MIT Press 1971

7 Y. H. Kim, "Observation of shear wave modes in the echoes of the longitudinal wave transducer" 15 : 987-994, 1996

8 D. Schneider, "Nondestructive characterization and evaluation of thin films by laser-induced ultrasonic surface waves" 290-291 : 305-311, 1996

9 김윤영, "Non-Destructive Evaluation of Material Properties of Nanoscale Thin-Films Using Ultrafast Optical Pump-Probe Methods" 한국비파괴검사학회 32 (32): 115-121, 2012

10 D. G. Cahill, "Nanoscale thermal transport" 93 (93): 793-818, 2003

11 B. Knight, "Laser-ultrasonic characterization of electrodeposited chromium coatings" 18 : 365-372, 1999

12 Y. Y. Kim, "Influence of radio frequency power on thermal diffusivity of plasma enhanced chemical vapor deposition-grown hydrogenated amorphous carbon thin-films" 109 (109): 113503-, 2011

13 B. Rashidian, "Electrothermal microactuators based on dielectric loss heating" 24-29, 1993

14 Y. Y. Kim, "Effects of deposition time duration on thermal diffusivity of hydrogenated amorphous carbon films" 50 (50): 125602-, 2011

15 M. Chinmulgund, "Effect of Ar gas pressure on growth, structure, and mechanical properties of sputtered Ti, Al, TiAl, and Ti3Al films" 270 (270): 260-263, 1995

16 J. D. Anderson, "Computational Fluid Dynamics" McGraw-Hill 1995

17 G. A. Antonelli, "Characterization of mechanical and thermal properties using ultrafast optical metrology" 31 (31): 607-613, 2016

18 D. E. Gray, "American Institute of Physics Handbook" McGraw-Hill 1982

19 A. Reddy, "A MEMS-based evaluation of the mechanical properties of metallic thin films" 16 (16): 650-658, 2007