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Fabrication of ultrahigh-density nanowires by electrochemical nanolithography.

Chen F, Jiang H, Kiefer AM, Clausen AM, Ting YH, Wendt AE, Ding B, Lagally MG - Nanoscale Res Lett (2011)

Bottom Line: An approach has been developed to produce silver nanoparticles (AgNPs) rapidly on semiconductor wafers using electrochemical deposition.The closely packed AgNPs have a density of up to 1.4 × 1011 cm-2 with good size uniformity.AgNPs retain their shape and position on the substrate when used as nanomasks for producing ultrahigh-density vertical nanowire arrays with controllable size, making it a one-step nanolithography technique.

View Article: PubMed Central - HTML - PubMed

Affiliation: University of Wisconsin-Madison, Madison, WI 53706, USA. lagally@engr.wisc.edu.

ABSTRACT
An approach has been developed to produce silver nanoparticles (AgNPs) rapidly on semiconductor wafers using electrochemical deposition. The closely packed AgNPs have a density of up to 1.4 × 1011 cm-2 with good size uniformity. AgNPs retain their shape and position on the substrate when used as nanomasks for producing ultrahigh-density vertical nanowire arrays with controllable size, making it a one-step nanolithography technique. We demonstrate this method on Si/SiGe multilayer superlattices using electrochemical nanopatterning and plasma etching to obtain high-density Si/SiGe multilayer superlattice nanowires.

No MeSH data available.


Different ion concentrations cause interparticle interaction transition. (a) Weak interaction at higher concentration (thinner depletion layer), (b) strong interparticle interaction at lower concentration (thicker depletion layer). α is the depletion layer and β is the diffusion layer. The purple lines indicate the interface between diffusion layer and depletion layers.
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Figure 3: Different ion concentrations cause interparticle interaction transition. (a) Weak interaction at higher concentration (thinner depletion layer), (b) strong interparticle interaction at lower concentration (thicker depletion layer). α is the depletion layer and β is the diffusion layer. The purple lines indicate the interface between diffusion layer and depletion layers.

Mentions: Because of the weak chemical interaction between the adatoms and the substrate, nucleation and growth of Ag on Si occurs via a Volmer-Weber mode [31]. For a pulse with long pulse length (such as 0.5 s), the nucleation is an instantaneous process [31], and the growth is diffusion-limited [32]. In the first pulse, the nucleation density reaches its maximum during the first few milliseconds and passes the peak value thereafter, thus nucleus coarsening follows the nucleation in order to reduce the total free energy of the system. At the moment nucleation is completed, the ion-depleted layers (the solution layer near the surface where there are no ions; it is thinner than the diffusion layer) surrounding each nucleus are well separated from each other (Figure 3a). As a result, the growth of a nucleus is not influenced by the growth of neighboring particles. Therefore, in this "weak interparticle interaction" limit, particles grow at equal rates. However, reduction of ions to atoms causes the global ion concentration in the diffusion layer to decrease. The 0.5-s pulse-off time will allow the depleted layer to be repopulated by ions diffusing from far-off electrode regions. This reasoning explains why the particle density decreases with increasing immersion time (t ≤ 40 s) while still remaining quasi-uniform. The particle density decreases from 6.28 × 1010 cm-2 in Figure 2a to 5 × 1010 cm-2 in Figure 2b and stabilizes around 3.5 × 1010 cm-2 in Figure 2c, d. The density reduction rate is slowed at longer immersion time because the solution ion concentration reduction increases the diffusion layer thickness.


Fabrication of ultrahigh-density nanowires by electrochemical nanolithography.

Chen F, Jiang H, Kiefer AM, Clausen AM, Ting YH, Wendt AE, Ding B, Lagally MG - Nanoscale Res Lett (2011)

Different ion concentrations cause interparticle interaction transition. (a) Weak interaction at higher concentration (thinner depletion layer), (b) strong interparticle interaction at lower concentration (thicker depletion layer). α is the depletion layer and β is the diffusion layer. The purple lines indicate the interface between diffusion layer and depletion layers.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3211863&req=5

Figure 3: Different ion concentrations cause interparticle interaction transition. (a) Weak interaction at higher concentration (thinner depletion layer), (b) strong interparticle interaction at lower concentration (thicker depletion layer). α is the depletion layer and β is the diffusion layer. The purple lines indicate the interface between diffusion layer and depletion layers.
Mentions: Because of the weak chemical interaction between the adatoms and the substrate, nucleation and growth of Ag on Si occurs via a Volmer-Weber mode [31]. For a pulse with long pulse length (such as 0.5 s), the nucleation is an instantaneous process [31], and the growth is diffusion-limited [32]. In the first pulse, the nucleation density reaches its maximum during the first few milliseconds and passes the peak value thereafter, thus nucleus coarsening follows the nucleation in order to reduce the total free energy of the system. At the moment nucleation is completed, the ion-depleted layers (the solution layer near the surface where there are no ions; it is thinner than the diffusion layer) surrounding each nucleus are well separated from each other (Figure 3a). As a result, the growth of a nucleus is not influenced by the growth of neighboring particles. Therefore, in this "weak interparticle interaction" limit, particles grow at equal rates. However, reduction of ions to atoms causes the global ion concentration in the diffusion layer to decrease. The 0.5-s pulse-off time will allow the depleted layer to be repopulated by ions diffusing from far-off electrode regions. This reasoning explains why the particle density decreases with increasing immersion time (t ≤ 40 s) while still remaining quasi-uniform. The particle density decreases from 6.28 × 1010 cm-2 in Figure 2a to 5 × 1010 cm-2 in Figure 2b and stabilizes around 3.5 × 1010 cm-2 in Figure 2c, d. The density reduction rate is slowed at longer immersion time because the solution ion concentration reduction increases the diffusion layer thickness.

Bottom Line: An approach has been developed to produce silver nanoparticles (AgNPs) rapidly on semiconductor wafers using electrochemical deposition.The closely packed AgNPs have a density of up to 1.4 × 1011 cm-2 with good size uniformity.AgNPs retain their shape and position on the substrate when used as nanomasks for producing ultrahigh-density vertical nanowire arrays with controllable size, making it a one-step nanolithography technique.

View Article: PubMed Central - HTML - PubMed

Affiliation: University of Wisconsin-Madison, Madison, WI 53706, USA. lagally@engr.wisc.edu.

ABSTRACT
An approach has been developed to produce silver nanoparticles (AgNPs) rapidly on semiconductor wafers using electrochemical deposition. The closely packed AgNPs have a density of up to 1.4 × 1011 cm-2 with good size uniformity. AgNPs retain their shape and position on the substrate when used as nanomasks for producing ultrahigh-density vertical nanowire arrays with controllable size, making it a one-step nanolithography technique. We demonstrate this method on Si/SiGe multilayer superlattices using electrochemical nanopatterning and plasma etching to obtain high-density Si/SiGe multilayer superlattice nanowires.

No MeSH data available.