View source for Magnetic self-assembly of three-dimensional surfaces from planar sheets

Original entry: Alexander Lukin, AP 225, Fall 2012

==General information==
'''Authors :'''Mila Boncheva, Stefan A. Andreev, L. Mahadevan, Adam Winkleman, David R. Reichman, Mara G. Prentiss, Sue Whitesides, and George M. Whitesides

'''Publication:'''http://www.pnas.org/content/102/11/3924.full.pdf+html

'''Key words:'''[[Thin film]], [[Self-assembly]], [[Surface Forces]]

== Summary==
[[Image:Unfolding 3D object into plane.png|thumb|right|Fig.1 Scheme illustrating unfolding 3D object into plane and recombining the object by means of self assembly.(magnetic dipols are shown with arrows)]]
Magnetic self-assembly is a powerful  tool to create complex 3D micro- and nano-structures. This technique uses magnetic dipol interaction to fold specially prepared planar surfaces into 3D objects. Nowadays the most complex microelectronic devices are fabricated by stacking and connecting planar layers on top of each other, which is determined by the availability of high developed methods for parallel microfabrication  in 2D but there is no general one in 3D.  Folding of connected 2D plates can yield to 3D microelectromechanical systems and microelectronic devices.

==Explanation==

This method is composed of four steps(Fig. 1): 

*(i) Cutting the 3D surface of interest into connected sections that ‘‘almost’’ unfold into a plane (unpeeling a sphere as one unpeels an orange is an example);
*(ii) Flattening this surface and projecting it onto a plane; 
*(iii) Fabricating the planar projection in the form of an elastomeric membrane patterned with magnetic dipoles; 
*(iv) Allowing this patterned membrane to fold into an ‘‘almost-correct’’ 3D shape by self-assembly

There are three major reasons for using magnetic dipol interactions:

# magnetic interactions are insensitive to the surrounding medium and to the details of surface chemistry 
# the distances over which they act can be engineered to cover a range of sizes (nanometers to meters)
# magnetic dipoles tend to form stable closed loops, and these loops are features easily translated into design rules


==Results==
[[Image:Self assembly of electric circuit.png|thumb|400px|right|Fig 2 Self-assembly of a simple electrical circuit surrounding a spherical cavity.]]
The technique was used to make elementary 3D electrical circuit (Fig. 2). Each section of the sheet was made of PDMS and was designed in such  a way to form a spherical cavity (Fig. 2a). Magnets at the tip and at the middle of the leaf governed self-assembly(Fig 2a,b). Also each leaf contained a photodiode connected to pair of solder pads placed also near the tip to provide electric connectivity(Fig. 2b). After self-assembly was complete, the battery was connected to one top and one bottom contact pad and finally all six LEDs were illuminating, which demonstrates the continuity of an electrical circuit (Fig 2d).

== Reference ==

Mila Boncheva, Stefan A. Andreev, L. Mahadevan, Adam Winkleman, David R. Reichman, Mara G. Prentiss, Sue Whitesides, and George M. Whitesides "Magnetic self-assembly of three-dimensional surfaces from planar sheets" PNAS March 15, 2005 vol. 102 no. 11 3924-3929