New material request: polystyrene microspheres in aqueous suspension
mtang at stanford.edu
Thu Oct 11 09:55:06 PDT 2007
Hi all --
This sounds good to me. All the chemical work will be done at wbgeneral
or wbsolvent. The nanospheres should be adhered by the time the
substrates reach metal deposition and etch. This, by the way, is
waaaaay cool -- I'd no idea this mechanism existed and am not sure I
entirely believe it...
Aaron Hryciw 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 <mailto: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
> Phone: 1-800-334-3883 or 1-650-424-1177
> Fax: 1-650-424-1158
> info at dukesci.com <mailto:info at dukesci.com>
> www.dukescientific.com <http://www.dukescientific.com> (in
> 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 (0.44
> M), 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.
> 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.
> 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
Mary X. Tang, Ph.D.
Stanford Nanofabrication Facility
CIS Room 136, Mail Code 4070
Stanford, CA 94305
mtang at stanford.edu
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