Patent Publication Number: US-2012031551-A1

Title: Method for transfer printing nanowires

Description:
BACKGROUND 
     1. Technical Field 
     The present disclosure relates to nanowires, and particularly to a method for transfer printing nanowires. 
     2. Description of Related Art 
     Nanowires have a variety of applications such as in sensors and in transistors, because the nanowires show excellent mechanical characteristics, quantum effects, and high surface to volume ratios. 
     Nanowires are usually grown on a substrate. Due to the size of nanowires, it is difficult to allow the nanowires to arrange substantially along a same direction after being collected from the substrate or being transferred from one substrate to another substrate. 
     Dielectrophoresis, micro-fluid channel and blown film extrusion methods have been used to collect or transfer the nanowires. However, these methods each take a substantial amount of time. 
     What is needed, therefore, is a method for transfer printing nanowires which can overcome the above shortcomings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Many aspects of the present method can be better understood with reference to the following drawings. The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating the principles of the present method. Moreover, in the drawings, like reference numerals designate corresponding parts throughout the several views. 
         FIG. 1  is a perspective view of a transfer printing film and a first substrate having nanowires grown thereon in accordance with an exemplary embodiment. 
         FIG. 2  shows a roller apparatus to roll on the combined transfer printing film and the first substrate shown in  FIG. 1 . 
         FIG. 3  is a scanning picture showing the nanowires push over on the first substrate of  FIG. 1 . 
         FIG. 4  shows the transfer printing film of  FIG. 1  has the nanowires transfer printed thereon. 
         FIG. 5  is a scanning picture showing the nanowires on the transfer printing film of  FIG. 4 . 
         FIG. 6  shows a second substrate has the nanowires transfer printed thereon from the transfer printing film of  FIG. 4 . 
         FIG. 7  is a scanning picture showing the nanowires on the second substrate. 
     
    
    
     DETAILED DESCRIPTION 
     Embodiments of the present method will now be described in detail below and with reference to the drawings. 
     Referring to  FIGS. 1 and 2 , an exemplary method for transfer printing nanowires, includes the following steps. 
     First, a first substrate  10  having nanowires  1020  formed on a surface  100  thereof, is provided. The first substrate  10  is Si-based, i.e., the first substrate  10  contains Si element. The first substrate  10  can be made fully by Si. The nanowires  1020  are in a nanowire array  102 . The nanowires  1020  can be Si-based, or are polymer. 
     Second, a transfer printing film  20  is provided. The transfer printing film  20  is hydrophobic and at a soft state during the transfer printing. In the present embodiment, the transfer printing is carried out at room temperature about 25° C., and no heating is needed for softening the transfer printing film  20 . The transfer printing film  20  can be made of a polymer material which has a glass transition temperature below the room temperature, such as polydimethylsiloxane (PDMS), and polybutylacrylate (PBA). 
     The first substrate  10  is Si-based, the transfer printing film  20  is preferably made of PDMS. The PDMS has a molecular formula (CH 3 ) 3 SiO[Si(CH 3 ) 2 O]nSi(CH 3 ) 3 , thus the PDMS is also Si-based, and thus the transfer printing  20  and the first substrate  10  and also the other Si-based substrates have an adhesive property for each other. Also, the PDMS has a hydrophobic characteristic and a low surface energy, thus once the nanowires  1020  are printed on the transfer printing film  20 , the nanowires  1020  can also be taken off the transfer printing film  20  and adhered to other substrates. The transfer printing film  20  is soft, thus preventing for the most extent the nanowires  1020  from being broken into pieces during the transfer printing. 
     Then, the transfer printing film  20  is combined with the first substrate  10  with the nanowires  1020  in contact with a surface  200  of the transfer printing film  20 . 
     Next, a roller apparatus  30  is provided. The roller apparatus  30  includes a first roller  31 , second roller  32  and a delivering belt  33 . The combined first substrate  10  and transfer printing film  20  are disposed on the delivering belt  33 . The first roller  31  rolls under the delivering belt  33 . The second roller  32  rolls on the transfer printing film  20  at the opposite surface of the surface  200  along a straight line direction, thus ensures that nanowires  1020  are push over along a same direction on the first substrate  10  (see  FIG. 3 ). 
     Referring to  FIG. 4 , at a same time the nanowires  1020  are push over, the first substrate  10  and the transfer printing film  20  are compressed, thus the nanowires  1020  can be adhered to the transfer printing film  20 . Then the first substrate  10  can be removed. That is, the nanowires  1020  are transfer printed on the transfer printing film  20  with the nanowires  1020  substantially reoriented along the same direction on the transfer printing film  20  (see  FIG. 5 ). 
     Referring to  FIG. 6 , in a next transfer printing process, a second substrate  40  is first provided. The second substrate  40  can be made of Si, SiO 2  or a polymer material. Then the second substrate  40  is applied to the transfer printing film  20  to allow the nanowires  1020  to make contact with a surface  400  of the second substrate  40 . Next, after a similar rolling step on the transfer printing film  20 , the second substrate  40  and the transfer printing film  20  are compressed. Due to the transfer printing film  20  having the hydrophobic characteristic and the low surface energy, after the transfer printing film  20  is separated from the second substrate  40 , the nanowires  1020  can be transfer printed on the second substrate  40 . 
     Referring to  FIG. 7 , the nanowires  1020  on the second substrate  40  still lie substantially along the same direction. 
     It is understood that the above-described embodiments are intended to illustrate rather than limit the disclosure. Variations may be made to the embodiments and methods without departing from the spirit of the disclosure. Accordingly, it is appropriate that the appended claims be construed broadly and in a manner consistent with the scope of the disclosure.