This paper gives an overview of the most commonly used techniques for nanostructuring and nanochannel fabrication employed in nanofluidics. They are divided into two large categories: top-down and bottom-up methods. Top-down methods are based on patterning on large scale while reducing the lateral dimensions to the nanoscale. Bottom-up methods arrange atoms and molecules in nanostructures. Here, we review the advantages and disadvantages of those methods and give some future perspectives. It is concluded that technology in the region of 1–10 nm is lacking and potentially can be covered by using the pulsed-laser deposition method as a controlled way for thin film deposition (thickness of a few nanometers) and further structuring by the top-down method.

Technologies for nanofluidic systems: top-down vs. bottom-up - a review

Cell-material interactions constitute a key fundamental topic in biomaterials study. Various cell cues and matrix cues as well as soluble factors regulate cell behaviors on materials. These factors are coupled with each other as usual, and thus it is very difficult to unambiguously elucidate the role of each regulator. The recently developed material techniques of surface patterning afford unique ways to reveal the underlying science. This paper reviews the pertinent material techniques to fabricate patterns of microscale and nanoscale resolutions, and corresponding cell studies. Some issues are emphasized, such as cell localization on patterned surfaces of chemical contrast, and effects of cell shape, cell size, cell-cell contact, and seeding density on differentiation of stem cells. Material cues to regulate cell adhesion, cell differentiation and other cell events are further summed up. Effects of some physical properties, such as surface topography and matrix stiffness, on cell behaviors are also discussed; nanoscaled features of substrate surfaces to regulate cell fate are summarized as well. The pertinent work sheds new insight into the cell-material interactions, and is stimulating for biomaterial design in regenerative medicine, tissue engineering, and high-throughput detection, diagnosis, and drug screening.

Cell–Material Interactions Revealed Via Material Techniques of Surface Patterning

Reduction of the bit size in conventional magnetic recording media is becoming increasingly difficult due to the superparamagnetic limit. Bit patterned media (BPM) has been proposed as a replacement technology as it will enable hard disk areal densities to increase past 1 Tb in−2. Block copolymer directed self-assembly (BCP DSA) is the leading candidate for forming BPM due to its ability to create uniform patterns over macroscopic areas. Here we review the latest research into two different BCP DSA techniques: graphoepitaxy and chemoepitaxy (or chemical prepatterning). In addition to assessing their potential for forming high density bit patterns, we also review current approaches using these techniques for forming servo patterns, which are required for hard disk drive (HDD) operation. Finally, we review the current state of UV nanoimprint lithography, which is the favoured technique for enabling mass production of BPM HDDs.

https://iopscience.iop.org/article/10.1088/0022-3727/46/50/503001/pdf

Directed self-assembly of block copolymers for use in bit patterned media fabrication

For patterning organic resists, optical and electron beam lithography are the most established methods; however, at resolutions below 30 nanometers, inherent problems result from unwanted exposure of the resist in nearby areas. We present a scanning probe lithography method based on the local desorption of a glassy organic resist by a heatable probe. We demonstrate patterning at a half pitch down to 15 nanometers without proximity corrections and with throughputs approaching those of Gaussian electron beam lithography at similar resolution. These patterns can be transferred to other substrates, and material can be removed in successive steps in order to fabricate complex three-dimensional structures.

https://science.sciencemag.org/content/sci/328/5979/732.full.pdf

Nanoscale Three-Dimensional Patterning of Molecular Resists by Scanning Probes

Metal structures 100 A high with sharply defined linewidths of 80 A have been produced using an electron‐beam fabrication process. A contamination resist pattern is written with a 5‐A 45‐keV scanning electron beam in a 100‐A‐thick Au‐Pd film supported by a 100‐A carbon foil. The unprotected Au‐Pd is removed by dc ion etching with 1‐keV Ar ions. Unlike most electron‐beam microfabrication processes, the resolution of the resulting structure is not limited by electron scattering, but by the grain size of the metal films. These structures should have direct application in a large number of device fabrication problems in electron and x‐ray beam technology and they should provide masks for other microfabrication processes such as x‐ray lithography.

Electron‐beam fabrication of 80‐Å metal structures

A simple technique for the computation of the proximity effect in electron‐beam lithography is presented. The calculations give results of the exposure intensity received at any given point in a pattern area using a reciprocity principle. Good agreement between the computed results and experimental data was achieved.

T. H. P. Chang

Papers

Proximity effect in electron-beam lithography