New material request: polystyrene microspheres in aqueous suspension

Aaron Hryciw ahryciw at gmail.com
Mon Oct 22 09:12:58 PDT 2007


Hello –

I've been talking with James Conway during Raith training, and he has told
me that unfucntionalised latex microspheres are actually not a new material
for SNF, since they are already used in the e-beam lab, etc.  As such, I
assume that there is no problem with my using the spheres in the lab, so
long as the rest of my process is compatible with SNF procedures.

Cheers!

 – Aaron


On 10/10/07, Aaron Hryciw <ahryciw at gmail.com> wrote:
>
> Dear SpecMat Committee –
>
> Please regard this email as a request for a new material for use at SNF; a
> general MSDS for this class of materials (from the chemical supplier from
> whom the material has been purchased) is attached.
> *
> Contact information*
> Aaron Hryciw
> Coral login:  ahryciw
> Phone:  3-5840 (office); (650) 353-0347 (cell)
> ahryciw at stanford.edu
> PI:  Mark Brongersma (Mat. Sci. Eng.)
>
>
> * Chemical or material name*
> Polystyrene microspheres (diameters between 100 nm and 1 um) suspended in
> DI water, 10% solids by weight, 15 mL vials.
> MSDS from supplier attached.
> Will be diluted with methanol or ethanol before use.
> Common/trade names:  polymer microsphere suspension, polystyrene
> microspheres, polystyrene nanospheres, latex microspheres suspensions.
> Storage group identifier:  *G*. Non-Reactive Materials and Non-Hazardous
> Materials.
> Main hazard class:  11. Non Hazardous.
>
>
> *Vendor/manufacturer info
> *Duke Scientific Corporation
> 2463 Faber Place
> P.O. Box 50005
> Palo Alto, CA
> 94303
>
> Phone: 1-800-334-3883 or 1-650-424-1177
> Fax:  1-650-424-1158
> info at dukesci.com
> www.dukescientific.com (in particular:  http://208.106.133.230/www.dukescientific.com/pages/pagefb6d.html?s=979&ss=984&t=1007
> )
> *
>
> Reason for request
> *My interest in polystyrene microspheres is due to their use as a
> self-assembled monolayer mask, as a means of fabricating large (~cm^2) arrays
> of silicon nanowires (NWs) with controlled size, length, and areal density
> (please refer to Huang et. al, attached).  Nanosphere lithography (NSL)
> comprises a rapid, parallel approach to fabricating well-controlled NWs
> without requiring conventional photolithographic techniques.  The material
> used for the mask (viz., the polystyrene microspheres) is also very benign
> and poses no health or safety hazards when used properly for this technique.
> **
>
> * Process Flow*
> I intend to follow the general process flow detailed in the attached paper
> ( Huang et. al).  if necessary, the entire process flow needn't occur in
> SNF (only use of the RIE tool is strictly required), although, for the sake
> of cleanliness, I would prefer it.
>
> A full process flow in SNF would be as follows:
>
>    1. Clean (100) n-type Si wafers or pieces (ca. 1x1 cm^2) in an
>    ultrasonic cleaner using acetone (10 min), then methanol (5 min).
>    2. Clean in Piranha (4:1 v/v H2SO4:H2O2) and RCA solution (1:1:5
>    v/v/v NH3:H2O2:H2O @ 80 °C) for 1 hr.
>    3. Rinse in DI water.
>    4. Place substrate in a Petri dish (I will have my own dedicated
>    glassware) and cover with DI water.
>    5. Pipette polystyrene microsphere solution (5% solids in 15 mL DI
>    water + 15 mL methanol) onto water surface and gently tilt Petri dish to
>    encourage self-assembly of large single-crystal hcp arrays.
>    6. Allow water to evaporate slowly, depositing microspheres onto
>    substrate. [The foregoing six steps could be performed at wbgeneral,
>    wbmetal, or wbnonmetal, as necessary.]
>    7. RIE microsphere array to desired sphere diameter using O2 plasma
>    etch:  40 sccm, 30 W RF power, 5 Pa pressure. [Performed on one of the
>    drytek tools, consistent with previous material groups.]
>    8. Deposit 40 nm of Ag. [innotec or metallica]
>    9. Etch Si NWs in an etchant consisting of HF (4.6 M) , H2O2 (0.44M), and H2O. [wbgeneral]
>    10. Remove microspheres by soaking in toluene for 2 hr. [wbsolvent]
>    11. Remove Ag film by soaking in nitric acid for 15 min. [wbgeneral]
>
>
> If necessary, steps 1–6 and 7–11 could be performed outside SNF (in our
> lab in McCullough Bldg., for instance).
>
>
> *Amount and form
> *Two or three 30-mL vials containing microspheres (of two or three
> different sizes) suspended in 15 mL DI water + 15 mL methanol.  Once the
> 15-mL DI-water-suspended material (as purchased) has been diluted with
> methanol, no further mixing will be required.
>
>
> *Storage*
> If the entire process flow is approved for use in SNF, I would store the
> vials of microsphere aqueous/methanoic suspensions at SNF.  If only step 7
> is approved for SNF, I would store them in our group's lab.
>
>
> *DIsposal*
>  As per the MSDS, waste materials containing microspheres could be
> disposed of in SNF's hazardous materials bins in a sealed, labeled plastic
> bag, due to their non-hazardous nature.
>
>
> Thank-you for considering this new material for use at SNF.  I would enjoy
> the opportunity to discuss possible amendments to the abovementioned process
> flow if necessary to allow it in the cleanroom.
>
> Best regards,
>
>  – Aaron
>
>
> --
> Aaron Hryciw
> Postdoctoral Scholar
> Geballe Laboratory for Advanced Materials
> Stanford University
> 476 Lomita Mall (04-490)
> McCullough Building, Rm. 325
> Stanford, CA  94305-4045
>
> Tel.:  (650) 723-5840
> Fax.:  (650) 736-1984
>



-- 
Aaron Hryciw
Postdoctoral Scholar
Geballe Laboratory for Advanced Materials
Stanford University
476 Lomita Mall (04-490)
McCullough Building, Rm. 325
Stanford, CA  94305-4045

Tel.:  (650) 723-5840
Fax.:  (650) 736-1984
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