利用掃描探針顯微鏡研究類鑽碳薄膜

Abstract

類鑽碳(Diamond-Like Carbon, DLC)薄膜由石墨鍵結(sp^2)及鑽石鍵結(sp^3)所構成的非晶質結構，sp^2鍵結及sp^3鍵結含量會影像到類鑽碳薄膜的性質，本實驗利用掃描探針顯微鏡研究電沉積薄膜隨沉積時間的成長及電性。 利用原子力顯微鏡(Atomic Force Microscopy, AFM)掃描到的影像觀察DLC薄膜隨沉積時間的顆粒大小及厚度，接著利用STM的掃描穿隧能譜模式得知DLC薄膜的穿隧能譜，為了得到個別沉積時間的平均能隙(band gap)，我們將電流影像穿隧能譜分成25等分並分別計算出能隙大小，再使用數張圖統計做成能隙分布圖，利用高斯擬合得出峰值，此峰值即代表固定某沉積時間下的平均能隙，我們可以發現隨沉積時間變長，能隙會越來大，但沉積時間長達1600秒以後，能隙變大的現象會逐漸趨緩，其結果與X光電子能譜(X-ray Photoelectron Spectroscopy, XPS)量測到的結果相同。 此外，我們在電流影像穿隧能譜中發現，在沉積時間1600秒到2400秒的DLC薄膜，會出現大面積且主要為sp^3鍵結的區域，但在1600秒以下我們沒有發現此現象，我們計算沉積時間1600秒到2400秒的DLC薄膜的中〖sp〗^3鍵結區域的面積，發現此面積大小約為3000 - 4000 〖nm〗^2。

Diamond-like carbon (DLC) thin films consist of sp^2 and sp^3 bonding and they reveal an amorphous structure. The ratio and concentration of sp^2 and sp^3 bonds shall influence the physical properties of DLC thin films. In this work, by using scanning probe microscopy, we show electronic properties and growth behaviors of DLC thin films with regard to the thin-film deposition time. Particle size and thickness of DLC thin films were observed by images of atomic force microscope (AFM), and current-image tunneling spectra (CITS) were obtained by scanning tunneling microscopy (STM) measurements. To obtain the band gap information of the DLC thin films, we derived it from the calculation of CITS curves on STM images and we divided one image into 25 portions for comparison. By fitted with Gaussian function, the peak can be obtained from the statistical distribution of the band gap on each portion of the STM images. The peak represents average band gap at the specific deposition time. We found out that, with an increase of the deposition time, the average energy gap becomes larger. This result is in agreement with that measured by X-ray photoelectron spectroscopy (XPS). On the other hand, for the DLC thin films with deposition time of 1600 - 2400 seconds, we discovered some large areas on which the CITS spectra show mainly sp^3 bonding. The area size is about 3000 - 4000 〖nm〗^2.