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

The Scanning Probe Microscope

Scanning probe microscopy bas evolved into a powerful tool since its inception in 1982. The scanning probe microscope bas found applications in metrology, spectroscopy, and lithography. We will review the background of the technology, discuss the different types of scanning probe microscopes including the scanning tunneling microscope and the scanning force microscope, and present many of the applications for the instrument

Scanning Probe Investigations of Multidentate Thiol and Spatially Confined Porphyrin Nanoassemblies using Nanoscale Lithography

Approaches to prepare spatially selective surfaces were developed in this dissertation for constructing nanopatterns of organic thin film materials. Nanoscale surface patterns were prepared using immersion particle lithography and scanning probe lithography combined with organothiol chemistry. Organic thin films and nanomaterials can be patterned with tunable periodicities and designed shapes by selecting the diameter of mesospheres used as surface masks or scanning probe lithography, respectively. The surface platforms of well-defined nanopatterns are ideal for high resolution investigations using scanning probe microscopy (SPM). Local measurements of surface properties and conductive properties combined with nanolithography were accomplished at the molecular level. Sample characterizations were accomplished with selected modes of SPM. Scanning probe studies can be used to probe the morphological and physical properties of samples, when spatially confined nanomaterials are prepared. Atomic force microscopy (AFM) can be used to analyze many types of samples in ambient and liquid environments. Arrays of nanostructures formed with newly designed molecules and porphyrins were fabricated using the spatial selectivity of chemical patterns prepared with nanolithography. The designed nanopatterns were evaluated for morphological details and physical properties. A newly designed bidentate organosulfur compound, i.e. 16-[3,5-bis(mercaptomethyl)phenoxy] hexadecanoic acid (BMPHA), was selected for study. The solution phase self-assembly onto Au(111) was investigated with scanning probe-based nanolithography and particle lithography. The two thiol groups of BMPHA were specially designed as surface linkers for improved stability. The orientation of BMPHA on Au(111) was investigated by referencing the heights of n-alkanethiols as an in situ molecular ruler. Protocols for patterning porphyrin nanostructures i.e. nanodots and nanorods on Au(111) were developed based on protocols with immersion particle lithography. Porphyrins with and without a central metal ion, 5,10,15,20-tetraphenyl-21H,23H-porphine (TPP) and 5,10,15,20-tetraphenyl-21H,23H-porphine cobalt(II) (TPC) were patterned using immersion particle lithography. Individual nanorods and nanodots of porphyrins were spatially isolated into well-defined, nanoscale arrangements directed by a template film of a nanopatterned thiol monolayer. The conductivity of the nanostructures of the porphyrins was evaluated using conductive probe-atomic force microscopy (CP-AFM). The studies evaluate the applicability of nanolithography for preparing surface platforms for the measurements of morphological and physical properties at the nanoscale

Nanoscale lithography mediated by surface self-assembly of 16-[3,5-bis(mercaptomethyl)phenoxy]hexadecanoic acid on Au(111) investigated by scanning probe microscopy

The solution-phase self-assembly of bidentate 16-[3,5-bis(mercaptomethyl) phenoxy]hexadecanoic acid (BMPHA) on Au(111) was studied using nano-fabrication protocols with scanning probe nanolithography and immersion particle lithography. Molecularly thin films of BMPHA prepared by surface self-assembly have potential application as spatially selective layers in sensor designs. Either monolayer or bilayer films of BMPHA can be formed under ambient conditions, depending on the parameters of concentration and immersion intervals. Experiments with scanning probe-based lithography (nanoshaving and nanografting) were applied to measure the thickness of BMPHA films. The thickness of a monolayer and bilayer film of BMPHA on Au(111) were measured in situ with atomic force microscopy using n-octadecanethiol as an internal reference. Scanning probe-based nanofabrication provides a way to insert nanopatterns of a reference molecule of known dimensions within a matrix film of unknown thickness to enable a direct comparison of heights and surface morphology. Immersion particle lithography was used to prepare a periodic arrangement of nanoholes within films of BMPHA. The nanoholes could be backfilled by immersion in a SAM solution to produce nanodots of n-octadecanethiol surrounded by a film of BMPHA. Test platforms prepared by immersion particle lithography enables control of the dimensions of surface sites to construct supramolecular assemblies

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

Multifunctional Tool for Expanding AFM-Based Applications

A multifunctional tool which expands the application field of atomic force microscope-based surface modification is presented. The AFM-probe can be used for surface modification and in-situ characterization at the same time, due to a special configuration with two cantilevers. Various applications from different fields are presented, which were carried out with one and the same tool: in-situ characterization of wear generated with and without local lubrication (tribology), fountain-pen lithography in which material is deposited or removed (physical chemistry), and electrochemical metal deposition (electrochemistry)