本論文的目的是透過量測放置在鈮酸鋰基板上的石墨烯薄膜電訊號，以觀察這兩組垂直行進的表面聲波交疊所造成的變化。
表面聲波是固體表面上所傳遞的彈性能量波，量測表面聲波與載子交互作用產生的電訊號來自於聲電效應所產生之聲電流，我們所選用的鈮酸鋰基板具有良好的壓電特性，但不帶有自由電子，而石墨烯能在不影響表面聲波傳遞的狀況下提供載子，故我們在鈮酸鋰基板上放置石墨烯以量測電訊號。
在這篇論文當中，我們利用半導體製程製作基本的表面聲波元件，並透過化學氣相沉積法來成長單層石墨烯，並且另外在石墨烯上塗佈離子液體，透過外加閘極電壓的方式控制石墨烯的費米能階。本論文對此元件通入兩組行進方向垂直的表面聲波訊號，同時量測石墨烯樣品的聲電流訊號，並且改變其中一組表面聲波的行進方向，比較兩組數據不一樣的地方。
實驗數據顯示同時通入兩組垂直的表面聲波訊號時，會使量測到的聲電流訊號變小，而不同的行進方向得到的衰減幅度不同，推測這樣的訊號輸入影響載子傳輸，使得聲電流訊號變小。未來將有機會透過更精密的控制，預計可以更完全的調控載子移動。

We investigate surface acoustic wave (SAW) propagating in a graphene with tuned Fermi-level EF and the modulation of acoustic current by two SAWs generated by a cross interdigitated transducers (IDT). Our device consists of CVD-grown graphene coated with an ion-gel gate on top, and transferred on LiNbO3 substrate. Two IDTs are employed outside graphene area and are placed at a right angle to each other. Interference patterns of SAW are formed at the graphene area by applying a high frequency ac voltage to the IDTs, and EF of graphene is tuned biasing dc voltages on the ion-gel gate. We find the phase shift and SAW attenuations evolved with EF by measuring acoustic currents in graphene. Moreover, as two SAW are launched simultaneously we are able to modulate the acoustoelectronic currents, suggesting the formation of a two-dimensional ‘‘egg-carton’’ density fluctuation in graphene. Our results have a strong implications in the development of novel acoustoelectronic devices, and pave a way to study modulated 2D massless Dirac electrons.

V. Miseikis, "Acoustically induced current flow in graphene," Appl. Phys. Lett. , no. 100, p. 133105, 2012.

Jinjie Shi, Xiaole Mao, Daniel Ahmed, Ashley Colletti, and Tony Jun Huang, "Focusing microparticles in a microfluidic channel with standing surface acoustic waves (SSAW)," Lab Chip, vol. 8, pp. 221-223, 2008.

Jinjie Shi et al., "Acoustic tweezers: patterning cells and microparticles using standing surface acoustic waves (SSAW)," Lab Chip, vol. 9, pp. 2890-2895, 2009.

C. K. Campbell, Surface Acoustic Wave Devices for Mobile and Wireless Communication.: Academic Press, INC., 1998.

A. Wixforth, J. Scriba, M. Wassermeier, and J. P. Kotthaus, "Surface acoustic waves on GaAs/AlxGa1−xAs heterostructures," Phys. Rev. B., no. 40, p. 7874, 1989.

Chun-Chieh Chien, "The design of surface acoustic wave devices and its application in broad oscillator," Institute of Communication, NTCU, 2000.

R. H. Parmenter, "The acousto-electric effect," Physical Review, no. 89, p. 990, 1953.

G. Weinreich, "Acoustodynamic effects in semiconductors," Physical Review, no. 104, p. 321, 1956.

V. I. Fal'ko, S. V. Meshkov, and S. V. Iordanskii, "Acoustoelectric drag effect in the two-dimensional electron gas at strong magnetic field," Physical Review B (Condensed Matter), no. 47, p. 9910, 1993.

A. Esslinger et al., "Acoustoelectric study of localized states in the quantized Hall effct," Solid state communications, vol. 84, p. 939, 1992.

M. Rotter, A. Wixforth, W. Ruile, D. Bernklau, and H. Riechert, "Giant acoustoelectric effect in GaAs/LiNbO3 hybrids," Applied Physics Letters, no. 73, p. 2128, 1998.

J. M. Shilton et al., "Effect of spatial dispersion on acoustoelectric current in a high-mobility two-dimensional electron gas," Physical Review B (Condensed Matter), no. 51, p. 14770, 1995.

P. Wallace, "The Band Theory of Graphite.," Physical Review, no. 79, pp. 622-634, 1947.

P. Avouris, "Graphene: Electronic and Photonic Properties and Devices.," Nano Lett., 2010.

S. Adam, "A self-consistent theory for graphene transport.," Proc Natl Acad Sci USA, no. 104(47), pp. 18392-7, 2007.