Limits...
Shrinking of Solid-state Nanopores by Direct Thermal Heating.

Asghar W, Ilyas A, Billo JA, Iqbal SM - Nanoscale Res Lett (2011)

Bottom Line: Direct heating results in shrinking of the silicon dioxide nanopores.The inbuilt stress in the oxide film is also reduced due to annealing.The surface composition of the pore walls remains the same during the shrinking process.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Electrical Engineering, University of Texas at Arlington, Arlington, TX 76019, USA. smiqbal@uta.edu.

ABSTRACT
Solid-state nanopores have emerged as useful single-molecule sensors for DNA and proteins. A novel and simple technique for solid-state nanopore fabrication is reported here. The process involves direct thermal heating of 100 to 300 nm nanopores, made by focused ion beam (FIB) milling in free-standing membranes. Direct heating results in shrinking of the silicon dioxide nanopores. The free-standing silicon dioxide membrane is softened and adatoms diffuse to a lower surface free energy. The model predicts the dynamics of the shrinking process as validated by experiments. The method described herein, can process many samples at one time. The inbuilt stress in the oxide film is also reduced due to annealing. The surface composition of the pore walls remains the same during the shrinking process. The linear shrinkage rate gives a reproducible way to control the diameter of a pore with nanometer precision.

No MeSH data available.


Pore fabrication process and EDS analysis of membrane. (a) The schematic showing a cross-section view of the device. It consists of 250 nm thick free-standing SiO2 membrane, in 200 μm thick wafer. The small circle on the top of the membrane depicts a nanopore drilled using FIB. (b) EDS spectrum from SiO2 membrane confirming the presence of only Si and O. TEM micrograph (inset) shows the nanopore in free-standing membrane drilled with FIB.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC3211463&req=5

Figure 1: Pore fabrication process and EDS analysis of membrane. (a) The schematic showing a cross-section view of the device. It consists of 250 nm thick free-standing SiO2 membrane, in 200 μm thick wafer. The small circle on the top of the membrane depicts a nanopore drilled using FIB. (b) EDS spectrum from SiO2 membrane confirming the presence of only Si and O. TEM micrograph (inset) shows the nanopore in free-standing membrane drilled with FIB.

Mentions: A boron-doped double-side-polished Si (100) wafer was thermally oxidized to a thickness of 400 nm. Square etch-start windows were opened in the SiO2 using standard photolithography. Free-standing SiO2 membranes (30 × 30 μm2) were achieved using wet tetramethylammonium hydroxide (TMAH) anisotropic etching through the whole wafer thickness. The schematic in Figure 1(a) depicts the membrane formed after anisotropic etching. Bulk membrane composition was determined by energy dispersive X-ray spectroscopy (EDS). The EDS analysis showed that the membranes contained only Si and O, as shown in Figure 1(b). The EDS analysis revealed 31% Si and 69% O. This was in good agreement with the expected stoichiometric film ratio of 33.33% Si and 66.66% O in SiO2. A FIB was then employed to drill nanopores in free-standing SiO2 membranes operated at a 30 kV acceleration voltage [23]. A larger portion of the drilled nanopores were in the diameter range of 100 to 300 nm. The high-resolution transmission electron microscope operating at 300 kV was used to image the nanopores after FIB drilling as shown in the inset of Figure 1(b). The nanopore dyes were kept in heating furnace at specific temperature for pore shrinking. The nitrogen flow rate of 20 sccm was maintained during this process.


Shrinking of Solid-state Nanopores by Direct Thermal Heating.

Asghar W, Ilyas A, Billo JA, Iqbal SM - Nanoscale Res Lett (2011)

Pore fabrication process and EDS analysis of membrane. (a) The schematic showing a cross-section view of the device. It consists of 250 nm thick free-standing SiO2 membrane, in 200 μm thick wafer. The small circle on the top of the membrane depicts a nanopore drilled using FIB. (b) EDS spectrum from SiO2 membrane confirming the presence of only Si and O. TEM micrograph (inset) shows the nanopore in free-standing membrane drilled with FIB.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3211463&req=5

Figure 1: Pore fabrication process and EDS analysis of membrane. (a) The schematic showing a cross-section view of the device. It consists of 250 nm thick free-standing SiO2 membrane, in 200 μm thick wafer. The small circle on the top of the membrane depicts a nanopore drilled using FIB. (b) EDS spectrum from SiO2 membrane confirming the presence of only Si and O. TEM micrograph (inset) shows the nanopore in free-standing membrane drilled with FIB.
Mentions: A boron-doped double-side-polished Si (100) wafer was thermally oxidized to a thickness of 400 nm. Square etch-start windows were opened in the SiO2 using standard photolithography. Free-standing SiO2 membranes (30 × 30 μm2) were achieved using wet tetramethylammonium hydroxide (TMAH) anisotropic etching through the whole wafer thickness. The schematic in Figure 1(a) depicts the membrane formed after anisotropic etching. Bulk membrane composition was determined by energy dispersive X-ray spectroscopy (EDS). The EDS analysis showed that the membranes contained only Si and O, as shown in Figure 1(b). The EDS analysis revealed 31% Si and 69% O. This was in good agreement with the expected stoichiometric film ratio of 33.33% Si and 66.66% O in SiO2. A FIB was then employed to drill nanopores in free-standing SiO2 membranes operated at a 30 kV acceleration voltage [23]. A larger portion of the drilled nanopores were in the diameter range of 100 to 300 nm. The high-resolution transmission electron microscope operating at 300 kV was used to image the nanopores after FIB drilling as shown in the inset of Figure 1(b). The nanopore dyes were kept in heating furnace at specific temperature for pore shrinking. The nitrogen flow rate of 20 sccm was maintained during this process.

Bottom Line: Direct heating results in shrinking of the silicon dioxide nanopores.The inbuilt stress in the oxide film is also reduced due to annealing.The surface composition of the pore walls remains the same during the shrinking process.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Electrical Engineering, University of Texas at Arlington, Arlington, TX 76019, USA. smiqbal@uta.edu.

ABSTRACT
Solid-state nanopores have emerged as useful single-molecule sensors for DNA and proteins. A novel and simple technique for solid-state nanopore fabrication is reported here. The process involves direct thermal heating of 100 to 300 nm nanopores, made by focused ion beam (FIB) milling in free-standing membranes. Direct heating results in shrinking of the silicon dioxide nanopores. The free-standing silicon dioxide membrane is softened and adatoms diffuse to a lower surface free energy. The model predicts the dynamics of the shrinking process as validated by experiments. The method described herein, can process many samples at one time. The inbuilt stress in the oxide film is also reduced due to annealing. The surface composition of the pore walls remains the same during the shrinking process. The linear shrinkage rate gives a reproducible way to control the diameter of a pore with nanometer precision.

No MeSH data available.