Thermal scanning probe lithography

Thermal scanning probe lithography (tSPL) is a nanofabrication method for the chemical and physical nanopatterning of a large variety of materials and polymer resists with a lateral resolution of 10 nm and a depth resolution of 1 nm. In this Primer, we describe the working principles of tSPL and highlight the characteristics that make it a powerful tool to locally and directly modify material properties in ambient conditions. We introduce the main features of tSPL, which can pattern surfaces by locally delivering heat using nanosized thermal probes. We define the most critical patterning parameters in tSPL and describe post-patterning analysis of the obtained results. The main sources of reproducibility issues related to the probe and the sample as well as the limitations of the tSPL technique are discussed together with mitigation strategies. The applications of tSPL covered in this Primer include those in biomedicine, nanomagnetism and nanoelectronics; specifically, we cover the fabrication of chemical gradients, tissue-mimetic surfaces, spin wave devices and field-effect transistors based on two-dimensional materials. Finally, we provide an outlook on new strategies that can improve tSPL for future research and the fabrication of next-generation devices

Scanning probe lithography of chemically functionalised surfaces

A facile route to the production of highly uniform, ultra-thin metal oxide films has-been demonstrated using a combination of self-assembly and Langmuir-Blodgett techniques. Initial modification of a Si/SiO(_2) substrate through self-assembly of an octadecylsiloxane monolayer provides a hydrophobic surface suitable for the "tail down" deposition of a Langmuir-Blodgett monolayer of octadecylphosphonic acid, giving. The resulting –PO(_3)H(_2) functionalised film provides a suitable surface for binding of metal ions (e.g. Zr(^4+), Hf(^4+), Mg(^2+)). The tendency of these metal species to form polymeric structures in aqueous solution allows for the assembly of nanometre thick inorganic metal layers upon the –PO(_3)H(_2) surface. Thermal treatment of the Langmuir-Blodgett films was used to decompose the organic film components, whilst simultaneously calcining the inorganic metal layer, resulting in the formation of highly uniform metal oxide films, typically ca. 1.3 - 1.9 nm thick. Nanoscale patterning of the metal-stabilised Langmuir-Blodgett monolayers has also been demonstrated, by using an AFM probe to apply sufficiently high vertical forces upon the Langmuir-Blodgett surface to selectively displace the monolayer film material within spatially defined surface regions. Pattern resolutions dowm to 30 nm were achieved using this AFM "nanodisplacement" lithographic process. Excellent levels of structural retention of the patterns were also observed upon decomposition of the organic film components to generate the final metal oxide. Similarly, nanodisplacement patterning of metal-stabilised Langmuir-Blodgett monolayers deposited upon amino-flinctionalised substrates has been used for the fabrication of amine patterned surfaces. Selective binding of Au nanoparticles within the amine regions was demonstrated, highlighting the potential of such patterned surfaces as chemical templates for directing the assembly and organisation of other material

Patterning graphene nanostripes in substrate-supported functionalized graphene: A promising route to integrated, robust, and superior transistors

It is promising to apply quantum-mechanically confined graphene systems in field-effect transistors. High stability, superior performance, and large-scale integration are the main challenges facing the practical application of graphene transistors. Our understandings of the adatom-graphene interaction combined with recent progress in the nanofabrication technology indicate that very stable and high-quality graphene nanostripes could be integrated in substrate-supported functionalized (hydrogenated or fluorinated) graphene using electron-beam lithography. We also propose that parallelizing a couple of graphene nanostripes in a transistor should be preferred for practical application, which is also very useful for transistors based on graphene nanoribbon.Comment: Frontiers of Physics (2012) to be publishe

Controlling resonant surface modes by arbitrary light induced optical anisotropies

In this work the sensitivity of Bloch Surface Waves to laser-induced anisotropy of azo-polymeric thin layers is expe rimentally shown . The nanoscale reshaping of the films via thermal-Scanning Probe Lithography allows to couple light to circular photonic nanocavities, tailoring on-demand resonant BSW confined within the nanocavity

In-plane gate single-electron transistor in Ga[Al]As fabricated by scanning probe lithography

A single-electron transistor has been realized in a Ga[Al]As heterostructure by oxidizing lines in the GaAs cap layer with an atomic force microscope. The oxide lines define the boundaries of the quantum dot, the in-plane gate electrodes, and the contacts of the dot to source and drain. Both the number of electrons in the dot as well as its coupling to the leads can be tuned with an additional, homogeneous top gate electrode. Pronounced Coulomb blockade oscillations are observed as a function of voltages applied to different gates. We find that, for positive top-gate voltages, the lithographic pattern is transferred with high accuracy to the electron gas. Furthermore, the dot shape does not change significantly when in-plane voltages are tuned.Comment: 4 pages, 3 figure

Thermochemical scanning probe lithography of protein gradients at the nanoscale

Patterning nanoscale protein gradients is crucial for studying a variety of cellular processes in vitro. Despite the recent development in nano-fabrication technology, combining nanometric resolution and fine control of protein concentrations is still an open challenge. Here, we demonstrate the use of thermochemical scanning probe lithography (tc-SPL) for defining micro- and nano-sized patterns with precisely controlled protein concentration. First, tc-SPL is performed by scanning a heatable atomic force microscopy tip on a polymeric substrate, for locally exposing reactive amino groups on the surface, then the substrate is functionalized with streptavidin and laminin proteins. We show, by fluorescence microscopy on the patterned gradients, that it is possible to precisely tune the concentration of the immobilized proteins by varying the patterning parameters during tc-SPL. This paves the way to the use of tc-SPL for defining protein gradients at the nanoscale, to be used as chemical cues e.g. for studying and regulating cellular processes in vitro