Nanoscale science and technology demand novel approaches and new knowledge to further advance. Nanoscale fabrication has been widely employed in both modern science and engineering. Micro/nano lithography is the most common technique to deposit nanostructures. Fundamental research is also being conducted to investigate structural, physical and chemical properties of the nanostructures. This research contributes fundamental understanding in surface science through development of a new methodology. Doing so, experimental approaches combined with energy analysis were carried out. A delicate hardware system was designed and constructed to realize the nanometer scale lithography. We developed a complete process, namely laser-assisted scanning probe alloying nanolithography (LASPAN), to fabricate well-defined nanostructures in gold-silicon (Au-Si) system. As a result, four aspects of nanostructures were made through different experimental trials. A non-equilibrium phase (AuSi3) was discovered, along with a non-equilibrium phase diagram. Energy dissipation and mechanism of nanocrystalization in the process have been extensively discussed. The mechanical energy input and laser radiation induced thermal energy input were estimated. An energy model was derived to represent the whole process of LASPAN.

In recent years, nanowires have become increasingly important due to their unique properties and applications. Thus, processes in the fabrication to nanostructures has come a focal point in research. In this research, a new method to fabricate nanowires has been developed. The new technique is called the Scanning Probe Alloying Nanolithography (SPAN). The SPAN was processed using an Atomic Force Microscope (AFM) in ambient environment. Firstly, an AFM probe was coated with gold (Au), and then slid on a silicon (Si) substrate. The contact-sliding motion generated a nanostructure on the substrate, instead of wear. Subsequently, careful examination was carried out at the scale relevant to an AFM probe, in terms of physical dimension and electrical conductivity. The measured conductivity value of the generated microstructures was found to be between the conductivity values of pure silicon and gold. Simple analysis indicated that the microstructures were formed due to frictional energy dispersed in the interface forming a bond to sustain mechanical wear. This research proves the feasibilities of tip-based nanomanufacturing. The SPAN process was developed to increase efficiency of the technique. This study also explored the possibility of the applications as a biosensor and a flexible device. This dissertation contains nine sections. The first section introduces backgrounds necessary to understand the subject matter. It reviews current status of the nanofabrication technologies. The basic concepts of AFM are also provided. The second section discusses the motivation and goals in detail. The third section covers the new technology, scanning probe alloying nanolithography (SPAN) to fabricate nanostructures. The fourth talks about characterization of nanostructures. Subsequently, the characterized nanostructures and their mechanical, chemical, and electrical properties are discussed in the fifth section. In the sixth section, the new process to form a nanostructure is evaluated and its mechanism is discussed. The seventh section discusses the feasibility of the nanostructures to be used in biosensors and flexible devices. The conclusion of the research is summarized in the seventh section.

The quest for smaller and faster integrated circuits (ICs) continues, but traditional photolithography, the patterning process used to fabricate them, is rapidly approaching its physical limits. Step and Flash Imprint Lithography (S-FIL®) is a low-cost patterning technique which has shown great potential for next generation semiconductor manufacturing. To date, all methods of imprint lithography have utilized a sacrificial resist to produce device features. Our goal has been to develop functional materials such as insulators that can be directly patterned by S-FIL and then remain as a part of the end product. Directly patternable dielectric (DPD) materials must meet multiple mechanical and physical requirements for application in microelectronic devices. In some cases these requirements are conflicting, which leads to material design challenges. Many different materials and curing methods have been evaluated. Thiol-ene based approaches to patterning hyperbranched materials incorporating Polyhedral Oligomeric Silsesquioxanes (POSS) have shown the greatest promise. Thiol-ene polymerization takes place by a free radical mechanism, but it has the advantage over acrylates of not being inhibited by the presence of oxygen. This greatly eases some engineering design challenges for the S-FIL process. A number of thiol-ene formulations have been prepared and their mechanical and electrical properties evaluated. SFIL-R has been introduced as an alternative technology to SFIL. SFIL-R offers improvements to SFIL in several ways, but requires a high silicon content, low viscosity, planarizing material. Photopolymerizable branched siloxanes were synthesized and evaluated to function as a planarizing topcoat for this technology. Both SFIL and SFIL-R require a clean separation of the template from the resist material. Fouling of templates is a major concern in imprint lithography and fluorinated materials are used to treat templates to lower their surface energy for better separation. It has been observed that the template treatment degrades over time and needs to be replaced for further imprinting. A fluorinated silazane was designed to repair the degraded areas. This material was evaluated and functions as designed. / text

Thesis advisor: Michael J. Naughton / The nanoscale coaxial cable (nanocoax) has demonstrated sub-diffraction-limited optical confinement in the visible and the near infrared, with the theoretical potential for confinement to scales arbitrarily smaller than the free space wavelength. In the first part of this thesis, I define in clear terms what the diffraction limit is. The conventional resolution formulae used by many are generally only valid in the paraxial limit. I performed a parametric numerical study, employing techniques of Fourier optics, to resolve precisely what that limit should be for nonparaxial (i.e. wide angle) focusing of scalar spherical waves. I also present some novel analytical formulae born out of Debye’s approximation which explain the trends found in the numeric study. These new functional forms remain accurate under wide angle focusing and could materially improve the performance, for example, in high intensity focused ultrasound surgery by further concentrating the power distributed within the point spread function to suppress the side lobes. I also comment of some possible connections to the focusing of electromagnetic waves. In the second part of this thesis I report on a novel fabrication process which yields optically addressable, sub-micron scale, and high aspect ratio metal-insulator-metal nanocoaxes made by atomic layer deposition of Pt and Al2O3. I discuss the observation of optical transmission via the fundamental, TEM-like mode by excitation with a radially polarized optical vortex beam. Also, Laguerre-Gauss beams are shown to overlap well with cylindrical waveguide modes in the nanocoax. My experimental results are based on interrogation with a polarimetric imager and a near-field scanning optical microscope. Various optical apparatus I built during my studies are also reviewed. Numerical simulations were used with uniaxial symmetry to explore 3D adiabatic taper geometries much larger than the wavelength. Finally, I draw some conclusions by assessing the optical performance of the fabricated nanocoaxial structures, and by giving some insights into future directions of investigation. / Thesis (PhD) — Boston College, 2019. / Submitted to: Boston College. Graduate School of Arts and Sciences. / Discipline: Physics.

Dip-pen nanolithography (DPN) is a scanning probe microscopy-based nanofabrication method that relies on a fluid-coated atomic force microscope probe for the deposition of material on a substrate with nanometer-scale resolution. The ability to tailor the structure and chemical composition of materials at the nanometer length scale is enabling in elds ranging from medical diagnostics to nano-electronics. While DPN is among the highest resolution additive manufacturing techniques to date, the conguration of ink on the probe and the process of ink transport are poorly understood. Specically, the inking and patterning procedures are susceptible to variations in the ambient environmental conditions and currently not all aspects of the processes are reliably controlled. Thus, a key challenge barring the widespread adoption of DPN beyond a research tool is reproducibility. We hypothesize that closed-loop control over the inking and patterning process could address this irreproducibility, however techniques to monitor the quantity and concentration of ink on the tip of the probe have not been yet developed. Here, we study the mechanics of atomic force microscope (AFM) probes throughout the inking and patterning process to understand if the behavior of the ink can be studied in situ. In particular, we develop an approach for conning ink to the tip of an AFM probe, which is critical for reliable patterning and modeling the mechanics of the probe. Then, we nd that the quantity of ink on an AFM probe can be determined in situ by observing the shift in the natural frequency of the probe. Finally, we show that this method allows for the observation and quantication of the ink deposited on a substrate, in real time. Collectively, these approaches lay the groundwork for a closed-loop implementation of DPN in which the inking and patterning processes are performed with drastically improved reliability. Given that these techniques are easily implemented on any commercial AFM, we expect that they could lead to new applications in the study of nanoscale soft materials. / 2017-11-04T00:00:00Z

This thesis describes methods for constructing nanopatterned surfaces to array DNA. These surfaces enable direct observation of heretofore-unseen single-molecule reactions, eliminating bulk effects and enabling scientists to examine DNA mismatch repair and replication, including the first direct visualization of proteins binding to a target mismatch. This also facilitates directed self-organization of nanoscale features on a patterned substrate using DNA as an assembly tool. To make techniques for single-molecule visualization of biological processes more accessible, we have developed a novel technology called "DNA curtains," in which a combination of fluid lipid bilayers, nanofabricated barriers to lipid diffusion, and hydrodynamic flow can organize lipid-tethered DNA molecules into dened patterns on the surface of a microfluidic sample chamber. Using DNA curtains, aligned DNA molecules can be visualized by total internal reflection fluorescence microscopy, allowing simultaneous observation of hundreds of individual molecules within a field-of-view. Ultimately, this results in a 100X improvement in experimental throughput, and a corresponding increase in statistically signicant amounts of data. We also demonstrate site-specific labeling of DNA using DNA analogues, such as peptide nucleic acid (PNA), locked nucleic acid (LNA), and techniques such as nick-translation. Through PNA invasion, labeled DNA was self-assembled in arrays on surfaces and tagged with gold nanoparticles. In this work, DNA formed a template to self-assemble a nanoparticle in between nanoimprinted AuPd dots. Surface-based self-assembly methods offer potential for DNA employment in bottom-up construction of nanoscale arrays. This offers further proof that DNA can be useful in directed self-assembly of nanoscale architectures.

The lithography process for chip manufacturing has been playing a critical role in keeping Moor's law alive. Even though the wavelength used for the process is bigger than actual device feature size, which makes it difficult to transfer layout patterns from the mask to wafer, lithographers have developed a various technique such as Resolution Enhancement Techniques (RETs), Multi-patterning, and Optical Proximity Correction (OPC) to overcome the sub-wavelength lithography gap. However, as feature size in chip design scales down further to a point where manufacturing constraints must be applied to early design phase before generating physical design layout. Design for Manufacturing (DFM) is not optional anymore these days. In terms of the lithography process, circuit designer should consider making their design as litho-friendly as possible. Lithography hotspot is a place where it is susceptible to have fatal pinching (open circuit) or bridging (short circuit) error due to poor printability of certain patterns in a design layout. To avoid undesirable patterns in layout, it is mandatory to find hotspots in early design stage. One way to find hotspots is to run lithography simulation on a layout. However, lithography simulation is too computationally expensive for full-chip design. Therefore, there have been suggestions such as pattern matching and machine learning (ML) technique for an alternative and practical hotspot detection method. Pattern matching is fast and accurate. Large hotspot pattern library is utilized to find hotspots. Its drawback is that it can not detect hotspots that are unseen before. On contrast, ML is effective to find previously unseen hotspots, but it may produce false positives. This research presents a novel geometric pattern matching methodology using edge driven dissected rectangles and litho award machine learning for hotspot detection. 1. Edge Driven Dissected Rectangles (EDDR) based pattern matching EDDR pattern matching employs member concept inside a pattern bounding box. Unlike the previous pattern matching, the idea proposed in this thesis uses simple Design Rule Check (DRC) operations to create member rectangles for pattern matching. Our approach shows significant speedup against a state-of-art commercial pattern matching tool as well as other methods. Due to its simple DRC edge operation rules, it is flexible for fuzzy pattern match and partial pattern match, which enable us to check previously unseen hotspots as well as the exact pattern match. 2. Litho-aware Machine Learning A new methodology for machine learning (ML)-based hotspot detection harnesses lithography information to build SVM (Support Vector Machine) during its learning process. Unlike the previous research that uses only geometric information or requires a post-OPC (Optical Proximity Correction) mask, our method utilizes detailed optical information but bypasses post-OPC mask by sampling latent image intensity and use those points to train an SVM model. Our lithography-aware machine learning guides learning process using actual lithography information combined with lithography domain knowledge. While the previous works for SVM modeling to identify hotspots have used only geometric related information, which is not directly relevant to the lithographic process, our SVM model was trained with lithographic information which has a direct impact on causing pinching or bridging hotspots. Furthermore, rather than creating a monolithic SVM trying to cover all hotspot patterns, we utilized lithography domain knowledge and separated hotspot types such as HB(Horizontal Bridging), VB (Vertical Bridging), HP(Horizontal Pinching), and VP(Vertical Pinching) for our SVM model. Out results demonstrated high accuracy and low false alarm, and faster runtime compared with methods that require a post-OPC mask. We also showed the importance of lithography domain knowledge to train ML for hotspot detection.

Due to a lack of fundamental knowledge about the role of molecular structures in molecular electronic devices, this research is focused on the development of instruments to understand the relation between device design and the electronic properties of electroactive components. The overall goal is to apply this insight to obtain a more efficient and reliable scheme and greater functional control over each component. This work developed a fabrication method for porphyrinoids on graphene-based field effect transistors (FETs), and a chemical sensing platform under an ambient environment by integrating a tip-enhanced Raman spectroscope (TERS), atomic force microscope (AFM), and electronic testing circuit. The study is divided into three aspects. The first is aimed at demonstrating fabrication processes of nanoscale FETs of graphene and porphyrinoid composites based entirely on scanning probe lithography (SPL). A nanoshaving mechanism was used to define patterns on octadecanethiol self-assembled monolayers on gold film evaporated on graphene flakes, followed by metal wet etching and/or oxygen plasma etching to develop patterns on Au films and graphene, respectively. The integrity and optoelectronic properties were examined to validate the processes. The second area of study focused on the development of the chemical sensing platform, enabling chemical changes to be monitored during charge transports under an ambient environment. The localized Raman enhancement was induced by exciting surface plasmon resonance in nanoscale silver enhancing probes made by thermal silver evaporation on sharp AFM tips. As the system was designed along an off-axis illumination/collection scheme, it was demonstrated that it was capable of observing molecular decomposition on opaque and conductive substrates induced by an electric bias. The third line of work proposed a novel TERS system and a probe preparation method. Silver nanowires mounted on AFM tips were used to locally enhance the Raman scattering. The observed Raman enhancement allows quick chemical analysis from a nanoscale region, and thus enables chemical mapping beyond the diffraction limit. Compared with other TERS geometries, the new optical design not only allows analysis on large or opaque samples, but also simplifies the design of the optical components and the alignment processes of the setup.

The Microelectronics industry has continuously pushed the limit of critical dimensions to sub-20 nm. One of the challenges is pattern collapse, caused by unbalanced capillary forces during the final rinse and drying process. The use of surfactants offers a convenient method to reduce capillary forces but causes another deformation issue. This thesis work focuses on alternative approaches that are compatible with lithographic processes to mitigate pattern collapse. First, an e-beam lithography pattern with a series of varying line and space widths has been specifically designed in order to quantitatively study pattern collapse behavior. This pattern generates increasing stress in the pairs of resist lines as one moves across the pattern array and eventually a sufficiently small space value (critical space, S1c) is reached in each array such that the stress applied to the resist exceeds the critical stress (σc) required for pattern bending and subsequently feature deformation and collapse occurrs. The patterns we designed allow us to qualitatively and quantitatively study pattern collapse and obtain consistent, reproducible results. In the first part of the thesis work, a quick surface crosslink (called a reactive rinse) that involves the strengthening of the resist using crosslinking via carbodiimide chemistry while the resist structures are still in their wet state, has been developed and demonstrated. This technique provides efficient and significant improvement on the pattern collapse issue. In the second part of the thesis work, a triethoxysilane compound, vinyl ether silane (VE), has been successfully synthesized. It can be used to modify the silicon or silicon nitride substrates and form a covalent bond with the resist film instead of manipulating the surface energies using common HMDS. Compared to traditional Hexamethyldisilazane (HMDS) vapor primed surfaces, the implementation of the VE adhesion promoter resulted in a significant improvement in the adhesion and resistance to adhesion based pattern collapse failure in small sub-60 nm resist features. In the third part of the thesis work, the effect of drying rates and drying methods has been systematically studied. SEM analysis and critical stress results showed that fast drying appear to reduce the resist collapse. The line pair orientations in each pattern array with respect to the wafer radius reveal an apparent effect of fluid flow and centrifugal forces on collapse. Finally, a comprehensive pattern collapse model that incorporates adhesion based pattern failure and elastoplastic deformation-based failure, and dimensionally dependent resist modulus properties has been developed. This model provides such an excellent prediction of the experimental data and supports the idea that this level of combined adhesion-failure and elastoplastic-failure based pattern collapse modeling, where one explicitly considers the dimensionally dependent mechanical properties of the resist can be quantitatively predictive and useful for understanding the pattern collapse behavior of polymeric nanostructures.

A method offering precise control over the synthesis conditions to obtain carbon nanotube (CNT) samples of a single chirality (metallic or semi-conducting) is presented. Using this nanolithographic method of catalyst deposition, the location of CNT growth is also precisely defined. This technique obviates three significant hurdles that are preventing the exploitation of CNT in micro- and nano-devices. Microelectronic applications (e.g., interconnects, CNT gates, etc.) require precisely defined locations and spatial density, as well as precisely defined chirality for the synthesized CNT. Conventional CVD synthesis techniques typically yield a mixture of CNT (semi-conducting and metallic types) that grow at random locations on a substrate in high number density, which leads to extreme difficulty in application integration. Dip Pen Nanolithography (DPN) techniques were used to deposit the catalysts at precisely defined locations on a substrate and to precisely control the catalyst composition as well as the size of the patterned catalyst. After deposition of catalysts, a low temperature Chemical Vapor Deposition (CVD) process at atmospheric pressure was used to synthesize CNT. Various types of catalysts (Ni, Co, Fe, Pd, Pt, and Rh) were deposited in the form of metal salt solutions or nano-particle solutions. Various characterization studies before and after CVD synthesis of CNT at the location of the deposited catalysts showed that the CNT were of a single chirality (metallic or semiconducting) as well as a single diameter (with a very narrow range of variability). Additionally, X-ray photoelectron spectroscopy (XPS) was used to characterize the deposited samples before and after the CVD, as was lateral force microscopy (LFM) for determination of the successful deposition of the catalyst material immediately after DPN as well as following the CVD synthesis of the samples. The diameter of the CNT determines the chirality. The diameter of the CNT measured by TEM was found to be consistent with the chirality measurements obtained from Raman Spectroscopy for the different samples. Hence, the results showed that CNT samples of a single chirality can be obtained by this technique. The results show that the chirality of the synthesized CNT can be controlled by changing the synthesis conditions (e.g., size of the catalyst patterns, composition of the catalysts, temperature of CVD, gas flow rates, etc.).