Local Tunneling Barrier Height Imaging on Si(111) Surface

Abstract

The present paper describes a three-dimensional (3D) thick-photoresist microstructuring technique that exploits the effect of exposure wavelength on dissolution rate distributions in a thick-film diazonaphthoquinone (DNQ) photoresist. In fabricating 3D microstructure with specific applications, it is important to control the spatial dissolution rate distribution in the photoresist layer, since the lithographic performance for 3D microstructuring is largely determined by the details of the dissolution property. To achieve this goal, the effect of exposure wavelength on dissolution rate distributions was applied for 3D microstructuring. The parametric experimental results demonstrated (1) the advantages of the fabrication technique for 3D microstructuring and (2) the necessity of a dedicated simulation approach based on the measured thick-photoresist property for further verification. Thus, a simple and practical photolithography simulation model that makes use of the Fresnel diffraction theory and an empirically characterized DNQ photoresist property was adopted. Simulations revealed good quantitative agreement between the photoresist development profiles of the standard photolithography and the moving-mask UV lithography process. The simulation and experimental results conclude that the g-line (λ = 436 nm) process can reduce the dimensional limitation or complexity of the photolithography process for the 3D microstructuring which leads to nanoscale microstructuring.

Dependence of the Work Function of TiO2 (Rutile) on Crystal Faces, Studied by a Scanning Auger Microprobe

“…The work function on well-defined single-crystal surfaces has been widely reported for Si, [6][7][8] TiO 2 , 3,4,11,13,15,26,27 Au, 9 Pt, 10,12 and so forth. In general, the crystal face dependence in the work function was explained by the electric double layer formed by the asymmetric distribution of electric charges which depends on the crystal faces.…”

“…The work function of the semiconductor surface has been investigated by using a variety of surface science techniques, including a Kelvin probe force microscope (KPFM), − a scanning tunnel microscope (STM), − and ultraviolet photoelectron spectroscopy (UPS). − Especially the STM and KPFM techniques provide information of the local work function with the spatial resolution of a few nanometers. Sasahara et al investigated the local work function of atomic-level regulated TiO 2 (110) surfaces, prepared by the Ar + ion sputtering and thermal annealing under UHV conditions, with a lateral resolution of several nanometers by using KPFM. , Crystalline islands on an extended terrace exhibited higher work functions than the terrace itself. , The increment of the work function was dependent on the size of the islands; a small island presented an enhanced increment.…”

“…The observed maps for TiO 2 were sensitive to nanoscale topography in a manner different from those for covalent semiconductors. 1,2 The work function of the semiconductor surface has been investigated by using a variety of surface science techniques, including a Kelvin probe force microscope (KPFM), [3][4][5] a scanning tunnel microscope (STM), [6][7][8][9][10][11] and ultraviolet photoelectron spectroscopy (UPS). [12][13][14][15] Especially the STM and KPFM techniques provide information of the local work function with the spatial resolution of a few nanometers.…”

Electronic structures of Au supported on TiO2

“…Local barrier height (LBH) measurement using STM enables us to estimate the local work function of metal [28,29] and semiconductor [30][31][32] surfaces. Several research groups have applied LBH measurement to alkali metals [33][34][35] and oxygen atoms [36,37] deposited on semiconductor surfaces, and found that charge transfer occurred between the adsorbates and substrates.…”

Large modulation-amplitude, local barrier-height, scanning tunneling microscopy

“…φ = 0.952 (d ln I/ds) 2 [4]. A number of authors have presented such "local barrier-height" (LBH) or "local work-function" images of surfaces (that is, local variations of φ) as an alternative to the more commonly shown "topographic images" [5][6][7][8]. In this LBH mode of imaging, the tip-to-sample gap distance is modulated at a frequency above the feedback loop cutoff, such that the mean distance, which is the mean value of the tunneling current, is constant.…”