Micropattern Deposition of Colloidal Semiconductor Nanocrystals by Aerodynamic Focusing

Abstract

We report the use of aerodynamic lenses to deposit micropatterns of colloidal semiconductor nanocrystals (or quantum dots). CdSe and CdSe/ZnS core/shell nanocrystals, with core diameters of 3.5-5 nm, were dispersed in hexane and then nebulized to generate agglomerates a few tens of nm in diameter, consisting of hundreds of nanocrystals. These agglomerates were then focused aerodynamically by a lens system. Microscale towers, lines, and patterns were deposited on thin sapphire plates and silicon wafers. The heights and widths of the deposits were adjustable by varying the experimental parameters. Line widths below 10 µm at fullwidth half-maximum are demonstrated. Upon exposure to near-UV illumination, these deposits exhibited robust fluorescence in the visible, with the color depending on the diameter of the individual nanocrystal cores. A red shift of the photoluminescence peaks from the nanocrystal dispersion to the glassy solid deposits was also observed, which confirmed that the deposits consist of closely packed nanocrystals embedded in the organic matrices. This approach, which is not restricted to semiconductor nanocrystals, provides an alternative means for the deposition of microscale patterns of colloidal nanoparticles.

A Review on Aerosol-Based Direct-Write and Its Applications for Microelectronics

“…The previous techniques worked well for mesoscopic particles but are not designed for nanoparticles. A focusing technique developed by researchers at the University of Minnesota uses a set of aerodynamic lenses under vacuum conditions to focus nanocrystal agglomerates and deposit them on a substrate [12][13][14][15]. Examples of this technique for direct-write applications such as for microelectromechanical systems (MEMS) are minimal, but depositions of traces as small as 35 μm wide were reported.…”

“…A new A-DW system designed for printing nanoparticles which uses aerodynamic lens for focusing was developed by Qi et al [15]. The deposition process of this system, represented schematically in Figure 5, begins with the pneumatic atomization of a suspension of CdSe/ZnS core/shell nanocrystals in hexane.…”

“…The system however will have challenges in commercialization due to the low deposition rate and that printing is required to be performed in an evacuated system. Such evacuated systems are however commonly used in microelectronics fabrication [15].…”

Simple convergent-nozzle aerosol injector for single-particle diffractive imaging with X-ray free-electron lasers

“…Aerodynamic lens stacks are capable of producing collimated streams of protein-sized particles (of the order 5–30 nm in size) with particle beam diameters of a few hundred micrometers (Wang and McMurry, 2006b; Benner et al , 2008). For particles such as large viruses (on the order of 30–500 nm), particle beams can be produced with diameters of just a few tens of micrometers (DiFonzo, 2000; Qi et al , 2010). Formulae and software are available to assist in the design of aerodynamic lens stacks (Wang and McMurry, 2006a).…”

Numerical Simulations on Aerodynamic Focusing of Particles in a Wide Size Range of 30 nm–10 μm

“…First proposed by Liu et al (1995a,b), they have the advantage of being mechanical devices that can be manufactured easily without special electric control units. Submicron particle focusing technology using aerodynamic lenses has diverse applications, including effective aerosol inlets for aerosol mass spectrometers (Schreiner et al 1999;Jayne et al 2000;Zhang et al 2004;Lee et al 2005Lee et al , 2006Lee et al , 2008Liu et al, 2007), micropatterning and material synthesis (Fonzo et al 2000;Dong et al 2004;Qi et al 2010), and inlets for measuring the creation of biomaterials (Harris et al 2006).…”