[3분논문] 제9회 - 안 보이는 광검출기

황용섭의 3분논문 제9회입니다.

오래 기다리셨지요? 개인적으로 바쁜 일이 있어서 한 동안 못 올렸네요. 

총시간은 5분 21초입니다.

재미있게 논문 보면서 들어보세요.

# 방송 바로 듣기

1. 09_3분논문_제9회.mp3

# 방송 mp3 파일 내려받기

(여기를 눌러주세요)

(참고: mp3 파일은 예고 없이 삭제될 수 있습니다.)

# 논문표지

# 간단한 정보

글쓴이: Pengyu Fan, Uday K. Chettiar, Linyou Cao, Farzaneh Afshinmanesh, Nader Engheta and Mark L. Brongersma

제목: An invisible metal–semiconductor photodetector

학술지: Nature Photonics

발행년월: 2012년 5월

이어가기: http://dx.doi.org/10.1038/nphoton.2012.108

# 용어

photodetector: 광검출기. 빛을 측정하는 광검출장치. 광다이오드를 비롯하여 다양한 형태를 포함하는 말이다.

photocurrent: 광전류. 입사된 빛에 의해 발생한 전류. 전류를 측정하면 입사된 빛을 측정할 수 있기 때문에 광전류를 측정하는 방식을 이용한 광검출기를 제작할 수 있다. 

# 발췌

1. 

Figure 2d presents a confocal image of the same region taken under TM-polarized white-light illumination. Compared to Fig. 2a, this image shows a contrast reversal between the metal-coated and bare nanowire regions with the gold-covered regions appearing much dimmer than the bare wire segments. This is in agreement with the predicted cancellation in the scattering due to plasmonic cloaking shown in Fig. 1e.

2. 

As nanotechnology has spurred the development of increasingly complex metallic and semiconductor nanostructures, many new opportunities are emerging for combin-ing these elementary photonic building blocks in hybrid devices that manipulate and actively control the flow of light at the nanoscale.

# 그림

Figure 1: Design and operation of a hybrid gold/silicon nanowire photodetector.

a, Schematic of a silicon nanowire (grey) hooked up by two gold electrodes (yellow). b, SEM image of a 50-nm-diameter silicon nanowire with a 20-nm-thick gold ‘cover’. Scale bar, 100 nm.

Figure 2: Polarization-dependent light-scattering phenomena for a gold-covered silicon nanowire.

d, Images of a 50 nm silicon nanowire captured confocally under  TM illumination with white light (scale bar, 2 µm). The bare and gold-covered regions of the wire are indicated in the images. e, Experimentally determined scattering spectra for the bare and covered regions for TM illumination. The cloaking effect of the gold cover is seen under TM illumination. f, Simulated scattering spectra corresponding to the experimental spectra in  e.

Figure 3: Comparison of the electric field distribution surrounding a bare and a cloaked nanowire on a gold substrate under TM incidence.

A snap shot (in time) of the real part of the electric field amplitude distribution (see colour bar on the right). Scale bar, 500 nm. a, Light scattering from a bare 50-nm-diameter silicon wire distorts the regular interference pattern produced by the incoming and reflected waves from the planar gold substrate. b, At the cloaking wavelength of 650 nm, the placement of a thin gold cover on top of the wire restores the planar wavefronts and the wire effectively become invisible. 

Figure 4: Spectral absorption properties of bare and gold-coated silicon nanowires

a, Spectral photocurrent measurement (normalized) taken under TM illumination for a bare 50 nm silicon nanowire device (black) and for the same device after deposition of a 20-nm-thick gold cover on the wire (red). b, Simulations of the spectral absorption efficiency for the bare (black curves) and gold-covered (red curves) nanowire. Experiments and simulations both show a blueshift of the spectra for the covered wire. Inset to b: side-by-side comparison of scattering (dashed curves) and absorption (solid curves) for the bare (black curves) and covered (red curves) nanowire around 670 nm (plotted on a logarithmic scale). The gold cover causes a dramatic decrease in scattering, as shown by the valley on the red dashed curve, but the variation of absorption as a function of wavelength is much smoother.

# 결론

나노선 광소자를 이용해서 광전류를 측정했는데, 금을 살짝 덮은 것으로 재미를 주었다. 나노선 광소자로 광전류를 측정하는 일은 계속 되어왔던 일인데, 작은 변화로 재미있게 만들어 내었다. 전극을 어차피 연결할 것이라면 그걸 이용해서 플라즈몬 효과를 주어서 광학적으로도 좋은 효과가 나온다면 좋은 일일테니.

끝.

2012년 6월 26일