Local metal deposition

FIGURE 36.1 Schematic illustration of some electrochemical techniques employed for surface nanostructuring (a) tip-induced local metal deposition (b) defect nanostructuring (c) localized electrochemical nucleation and growth d) electronic contact nanostructuring. 

A shadow-mask technique has been applied for the local metal deposition to exclude metal residues on other designs processed on the same wafer (Fig. 4.2b). Such metal residues may be caused by imperfections in the patterned resist due to topographical features on the processed CMOS wafers or dust particles. The metal film is only deposited in those areas on the wafer, where it is needed for electrode coverage on the microhotplates. This also renders the lift-off process easier since no closed metal film is formed on the wafer, so that the acetone has a large surface to attack the photoresist. Another advantage of the local metal lift-off process is its full compatibility with the fabrication sequence of chemical sensors based on other transducer principles [20]. 

A so-called tip-induced local metal deposition" was recently achieved in systems k i hkt)/C and Ag(/i /)/Cu with hkt) - (100), (111) using the in situ STM technique by Kolb et al. [6.187, 6.188]. First, a certain amount of metallic copper is cathodically deposited on the tip. Copper is then transferred fi-om the tip to the substrate by bringing the tip closer to the substrate surface. Originally, this was achieved by pulse polarization changing the sign of the tunneling voltage, f/r. The... 

The results obtained in the system C xQikt)/C x clearly correspond to 3D Me phase formation on the native substrate involving spiral growth and/or 2D nucleation and multilayer growth. It is evident that experiments in such systems are solely carried out to demonstrate local metal deposition, but not for surface heterostructuring and modification. 

Figure 6.28 Local metal deposition of copper on Au(lOO) in the system Au(100)/5 x 10 M CU2SO4 + 10 M H2SO4 at r= 298 K 16.190]. (a) Bare substrate at AE = 10 mV (b) alter cantilever-induced local metal deposition at 7 = - 10 mV.

An analysis of potentiostatic current density transients indicates progressive nucleation and a cluster growth controlled by hemispherical diffusion (cf. Section 6.2), as shown in Fig. 6.37. From the initial part of the transients, the nucleation rate, /, as a function of rj was determined. The number of atoms forming the critical nuclei, Afcrit -2, was determined from the slope of the log/vs. t] plot in the overpotential range - 210 mV < T <- 100 mV. These results show that localized metal deposition under electrochemical conditions using in situ local probe techniques and appropriate poiarization routines seems to be realistic. 

Early experiments aimed at localized metal deposition on semiconductor surfaces were carried out by Hartnagel et al. in the system n-GaAs/commercial KAu(CN)2 solution using a simple two-probe technique without potentiostatic control [6.199], At very... 

In addition to analytical applications for monitoring surftice structures and dynamics STM can also be used as a tool for the deliberate modification of electrode surfaces on the mesoscopic scale. By applying appropriate signals to an STM tip, local metal-deposition reactions can be induced from metal-ion-containing solutions [12, 15, 16]. As an example. Fig. 8 shows a platinum particle on an HOPG surface, which was... 

Yatziv Y, Turyan I, Mandler D (2002) A new approach to micropatteming application of potential-assisted ion transfer at the liquid-liquid interface for the local metal deposition. J Am Chem Soc 124 (20) 5618-5619.doi 10.1021/ja0257826... 

Turyan, I., M. Etienne, D. Mandler, and W. Schuhmann. 2005. Improved resolution of local metal deposition by means of constant distance mode scanning electrochemical microscopy. Electroanalysis 17 538-542. 

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