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Atomically smooth hexagonal boron nitride (hBN) flakes have revolutionized two-dimensional (2D) optoelectronics. They provide the key substrate, encapsulant, and gate dielectric for 2D electronics while offering hyperbolic dispersion and quantum emission for photonics. The shape, thickness, and profile of these hBN flakes affect device functionality. However, researchers are restricted to simple, flat flakes, limiting next-generation devices. If arbitrary structures were possible, enhanced control over the flow of photons, electrons, and excitons could be exploited. Here, we demonstrate freeform hBN landscapes by combining thermal scanning-probe lithography and reactive-ion etching to produce previously unattainable flake structures with surprising fidelity. We fabricate photonic microelements (phase plates, grating couplers, and lenses) and show their straightforward integration, constructing a high-quality optical microcavity. We then decrease the length scale to introduce Fourier surfaces for electrons, creating sophisticated Moiré patterns for strain and band-structure engineering. These capabilities generate opportunities for 2D polaritonics, twistronics, quantum materials, and deep-ultraviolet devices. ISSN:1530-6984 ISSN:1530-6992

Rocking Brownian motors achieve directional motion in highly diffusive environments by combining an inherently asymmetric static potential energy landscape and an oscillating “rocking” force [1, 2]. Our nanofluidic imple- mentation [3] features a confining wall with a ratchet-type nano-topography and AC electric fields as driving force. The potential energy landscape is due to electrostatic interactions between the charged particles and wall surfaces in close proximity. Based on this scheme, we have developed a nanoparticle size-separation device [4]. Along the particle transport direction, one of the confining walls features a sawtooth-like topography with a superimposed slope. In turn, we obtain a ratchet-shaped potential with increasing potential energy barrier heights caused by the decreasing nanofluidic gap. A sharp drop in particle current occurs as the potential barriers increase. The drop happens the later, the smaller the particle size. This allows for a sequential separation of the particle suspension into multiple sub-populations. The device was modeled by solving the Fokker-Planck equation. We show that the physics of the separation mechanism is governed by the energy landscape under forward tilt of the ratchet. The separation resolution is thus only dependent on the applied force. Experimentally, we demonstrate the separation of spherical gold particles of nominal 80 and 100 nm diameters with an applied voltage of 3.5 V and a sorting time of 20 s. We achieve a resolution of 2 nm, in accordance with our simulation results.

Thermal silicon probes have demonstrated their potential to investigate the thermal properties of various materials at high resolution. However, a thorough assessment of the achievable resolution is missing. Here, we present a probe-based thermal-imaging technique capable of providing sub-10 nm lateral resolution at a sub-10 ms pixel rate. We demonstrate the resolution by resolving microphase-separated PS-b-PMMA block copolymers that self-assemble in 11 to 19 nm half-period lamellar structures. We resolve an asymmetry in the heat flux signal at submolecular dimensions and assess the ratio of heat flux into both polymers in various geometries. These observations are quantitatively compared with coarse-grained molecular simulations of energy transport that reveal an enhancement of transport along the macromolecular backbone and a Kapitza resistance at the internal interfaces of the self-assembled structure. This comparison discloses a tip-sample contact radius of a ≈ 4 nm and identifies combinations of enhanced intramolecular transport and Kapitza resistance.

We present a nanoparticle size-separation device based on a nanofluidic rocking Brownian motor. It features a ratchet-shaped electrostatic particle potential with increasing barrier heights along the particle transport direction. The sharp drop of the particle current with barrier height is exploited to separate a particle suspension into multiple sub-populations. By solving the Fokker--Planck equation, we show that the physics of the separation mechanism is governed by the energy landscape under forward tilt of the ratchet. For a given device geometry and sorting duration, the applied force is thus the only tunable parameter to increase the separation resolution. For the experimental conditions of 3.5 V applied voltage and 20 s sorting, we predict a separation resolution of $\sim 2$ nm, supported by experimental data for separating spherical gold particles of nominal 80 and 100 nm diameters., 5 pages, 4 figures plus supplemental material

Local bandgap tuning in two-dimensional (2D) materials is of significant importance for electronic and optoelectronic devices but achieving controllable and reproducible strain engineering at the nanoscale remains a challenge. Here, we report on thermomechanical nanoindentation with a scanning probe to create strain nanopatterns in 2D transition metal dichalcogenides and graphene, enabling arbitrary patterns with a modulated bandgap at a spatial resolution down to 20 nm. The 2D material is in contact via van der Waals interactions with a thin polymer layer underneath that deforms due to the heat and indentation force from the heated probe. Specifically, we demonstrate that the local bandgap of molybdenum disulfide (MoS2) is spatially modulated up to 10% and is tunable up to 180 meV in magnitude at a linear rate of about −70 meV per percent of strain. The technique provides a versatile tool for investigating the localized strain engineering of 2D materials with nanometer-scale resolution., Nano Letters, 20 (11), ISSN:1530-6984, ISSN:1530-6992

The behavior of nanoparticles under nanofluidic confinement depends strongly on their distance to the confining walls; however, a measurement in which the gap distance is varied is challenging. Here, we present a versatile setup for investigating the behavior of nanoparticles as a function of the gap distance, which is controlled to the nanometer. The setup is designed as an open system that operates with a small amount of dispersion of ≈20 μL, permits the use of coated and patterned samples and allows high-numerical-aperture microscopy access. Using the tool, we measure the vertical position (termed height) and the lateral diffusion of 60 nm, charged, Au nanospheres as a function of confinement between a glass surface and a polymer surface. Interferometric scattering detection provides an effective particle illumination time of less than 30 μs, which results in lateral and vertical position detection accuracy ≈10 nm for diffusing particles. We found the height of the particles to be consistently above that of the gap center, corresponding to a higher charge on the polymer substrate. In terms of diffusion, we found a strong monotonic decay of the diffusion constant with decreasing gap distance. This result cannot be explained by hydrodynamic effects, including the asymmetric vertical position of the particles in the gap. Instead we attribute it to an electroviscous effect. For strong confinement of less than 120 nm gap distance, we detect the onset of subdiffusion, which can be correlated to the motion of the particles along high-gap-distance paths.

Surface assembly is often decomposed into two classes: diffusion and reaction limited processes. The transition between the two cases is complex because the dynamics are so different. In this article, we simulate, explain, and experimentally discuss the evolution of the spatial distribution for surface assemblies with diffusion limited and reaction limited processes. Explicitly, we demonstrate that diffusion limited and reaction limited processes show some temporal differences, but more importantly, we show that the spatial arrangements are different enough to discriminate between the two cases. Using fundamental properties, such as the diffusion constant, we calculate the evolution of the spatial profile and derive from physical, heuristic models the assembly rate for reaction and diffusion limited processes based on the individual particle's interactions with the surface. Finally, we confirm the spatial profile differences between diffusion and reaction limited cases by experimentally measuring the surface assembly between two molecules of similar size, but having different assembly routes. Unique to our description is that we have derived and simulated everything through the particle picture in place of ensemble descriptions such as the diffusion equation, and we show the equivalence between our heuristic formulas and those derived from the diffusion equation.

Diffusion relates the flux of particles to the local gradient of the particle density in a deterministic way. The question arises as to what happens when the particle density is so low that the local gradient becomes an ill-defined concept. The dilemma was resolved early last century by analyzing the average motion of particles subject to random forces whose magnitude is such that the particles are always in thermal equilibrium with their environment. The diffusion dynamics is now described in terms of the probability density of finding a particle at some position and time and the probabilistic flux density, which is proportional to the gradient of the probability density. In a time average sense, the system thus behaves exactly like the ensemble average. Here, we report on an experimental method and test this fundamental equivalence principle in statistical physics. In the experiment, we study the flux distribution of 20 nm radius polystyrene particles impinging on a circular sink of micrometer dimensions. The particle concentration in the water suspension is approximately 1 particle in a volume element of the dimension of the sink. We demonstrate that the measured flux density is exactly described by the solution of the diffusion equation of an infinite system, and the flux statistics obeys a Poissonian distribution as expected for a Markov process governing the random walk of noninteracting particles. We also rigorously show that a finite system behaves like an infinite system for very long times despite the fact that a finite system converges to a zero flux empty state.

High-resolution lithography often involves thin resist layers which pose a challenge for pattern characterization. Direct evidence that the pattern was well-defined and can be used for device fabrication is provided if a successful pattern transfer is demonstrated. In the case of thermal scanning probe lithography (t-SPL), highest resolutions are achieved for shallow patterns. In this work, we study the transfer reliability and the achievable resolution as a function of applied temperature and force. Pattern transfer was reliable if a pattern depth of more than 3 nm was reached and the walls between the patterned lines were slightly elevated. Using this geometry as a benchmark, we studied the formation of 10-20 nm half-pitch dense lines as a function of the applied force and temperature. We found that the best pattern geometry is obtained at a heater temperature of ∼600 °C, which is below or close to the transition from mechanical indentation to thermal evaporation. At this temperature, there still is considerable plastic deformation of the resist, which leads to a reduction of the pattern depth at tight pitch and therefore limits the achievable resolution. By optimizing patterning conditions, we achieved 11 nm half-pitch dense lines in the HM8006 transfer layer and 14 nm half-pitch dense lines and L-lines in silicon. For the 14 nm half-pitch lines in silicon, we measured a line edge roughness of 2.6 nm (3σ) and a feature size of the patterned walls of 7 nm.

Thermal scanning probe lithography (t-SPL) is a direct-write patterning method that creates high-resolution features with a heated scanning probe tip in an organic resist material. It is able to produce dense high-resolution patterns with sub-20 nm half-pitch at ambient conditions which can be transferred into silicon substrates using a hard-mask patterning stack and reactive ion etching (RIE). Feature sizes of transferred lines can be as small as 7 nm. Linear write speeds of up to 20 mm/s can be achieved. Different from e-beam lithography (EBL), in t-SPL proximity effects are absent and substrate damage of sensitive materials caused by high energy electrons is avoided. A direct inspection of the patterned area is provided during the writing process. Overlay patterning without additional alignment marks onto pre-existing structures is another feature of the t-SPL method. Existing device structures can be located precisely under a resist stack with the local probe tip and the additional target structures can then be generated with $\lt 5$ nm-precise overlay alignment. One further strength of tSPL is the capability of producing 3D patterns. The process can be controlled to produce 3D structures with $\approx 1$ nm $(1 \sigma)$ depth accuracy. Examples of unique devices fabricated by tSPL will be discussed.

The strength of scanning probe lithography (SPL) lies in the operation at ambient conditions, sub-10 nm resolution capabilities, the in situ non-destructive inspection of the fabricated structures, the nanometric accuracy in positioning, the versatility in modifying any kind of materials, and the freedom in the patterning geometries. On the other hand, the tip size and lifetime-related issues hinder the achievable throughput, and a precise niche of application has yet to be determined for its implementation in technological applications. The complementarity of the high-resolution and precise positioning patterning by SPL and the high throughput and low-resolution patterning by other well-established lithographies (optical, electron beam, nanoimprint) can be achieved by the development of mix-and-match lithography strategies.

Graphene and layered materials in general exhibit rich physics and application potential owing to their exceptional electronic properties which arise from the intricate p orbital coupling and the symmetry breaking in twisted bilayer systems1 2 3 4 5 6 7 8 9 10 11 12 13 14. Here we report room temperature experiments to study electrical transport across a bilayer graphene interface with a well defined rotation angle between the layers that is controllable in situ. This twisted interface is artificially created in mesoscopic pillars made of highly oriented pyrolytic graphite by mechanical actuation. The overall measured angular dependence of the conductivity is consistent with a phonon assisted transport mechanism that preserves the electron momentum of conduction electrons passing the interface15. The most intriguing observations are sharp conductivity peaks at interlayer rotation angles of 21.8° and 38.2°. These angles correspond to a commensurate crystalline superstructure leading to a coherent two dimensional (2D) electronic interface state. Such states predicted by theory16 17 form the basis for a new class of 2D weakly coupled bilayer systems with hitherto unexplored properties and applications.

Polyphthalaldehyde is a self-developing resist material for electron beam and thermal scanning probe lithography (t-SPL). Removing the resist in situ (during the lithography process itself) simplifies processing and enables direct pattern inspection, however, at the price of a low etch resistance of the resist. To convert the material into a etch resistant hard mask, we study the selective cyclic infiltration of trimethyl-aluminum (TMA)/water into polyphthalaldehyde. It is found that TMA diffuses homogeneously through the resist, leading to material expansion and formation of aluminum oxide concurrent to the exposure to water and the degradation of the polyphthalaldehyde polymer. The plasma etch resistance of the infiltrated resist is significantly improved, as well as its stability. Using a silicon substrate coated with 13 nm silicon nitride and 7 nm cross-linked polystyrene, high resolution polyphthalaldehyde patterning is performed using t-SPL. After TMA/H2O infiltration, it is demonstrated that patter...

A reversal of the particle current in rocking Brownian motors was predicted more than 20 years ago; however, an experimental verification and a deeper insight into the underlying mechanisms remained elusive. Here, we investigate the high frequency behaviour of a rocking Brownian motor for charged nanoparticles based on electrostatic interactions in a 3D shaped nanofluidic slit and electro-osmotic forcing of the particles. A sub ms temporal and $\approx\,10\,$nm spatial resolution of the 60 nm gold spheres allows us to measure the time-resolved and frequency dependent evolution of the particle probability density in-situ. At 250 Hz the particle current changes sign, in agreement with a theoretical model based on the time-dependent Fokker-Planck equation. From this fit-parameter free description and its excellent agreement with the observed behaviour, we trace the origin of the current reversal to the asymmetric and increasingly static probability density at high frequencies., Comment: 6 pages, 4 figures, SM: 14 pages, 14 figures

Stabilizing and manipulating topological magnetic quasiparticles in thin films is of great interest for potential applications in data storage and information processing. Here, we present a strategy for stabilizing magnetic vortices and Bloch lines with controlled position, vorticity, and chirality in a continuous exchange bias system. By tailoring vectorially the unidirectional anisotropy of the system at the nanoscale, via thermally assisted magnetic scanning probe lithography, we show experimentally and via micromagnetic simulations the non-volatile creation of vortex-antivortex pairs. In addition, we demonstrate the deterministic stabilization of cross and circular Bloch lines within patterned Neel magnetic domain walls. This work enables the implementation of complex functionalities based on the control of tailored topological spin-textures in spintronic and magnonic nanodevices.Stabilizing and manipulating topological magnetic quasiparticles in thin films is of great interest for potential applications in data storage and information processing. Here, we present a strategy for stabilizing magnetic vortices and Bloch lines with controlled position, vorticity, and chirality in a continuous exchange bias system. By tailoring vectorially the unidirectional anisotropy of the system at the nanoscale, via thermally assisted magnetic scanning probe lithography, we show experimentally and via micromagnetic simulations the non-volatile creation of vortex-antivortex pairs. In addition, we demonstrate the deterministic stabilization of cross and circular Bloch lines within patterned Neel magnetic domain walls. This work enables the implementation of complex functionalities based on the control of tailored topological spin-textures in spintronic and magnonic nanodevices.

Using friction to guide fabrication Ultralow friction found in certain layered materials such as graphite is important in the construction of nanomechanical devices. Koren et al. combined measurements and modeling to characterize the interaction of sliding graphite planes (see the Perspective by Liechti). This helped them to make small graphite devices that featured rotational pivots and multiple locking positions. Science , this issue p. 679

Thermal scanning probe lithography (t-SPL) has demonstrated unique capabilities for maskless lithography. A heated atomic force microscope tip is used to locally remove a thermally sensitive resist. This process is able to fabricate precise 3D patterns and high resolution structures without the use of charged particles, such as electrons, which have been implicated in substrate damage. Here we outline our work to improve the throughput of t-SPL via integration with a laser writer for the patterning of large features and the development of independently addressable cantilever arrays.

Detection and precise localization of nano-scale structures buried beneath spin coated films are highly valuable additions to nano-fabrication technology. In principle, the topography of the final film contains information about the location of the buried features. However, it is generally believed that the relation is masked by flow effects, which lead to an upstream shift of the dry film's topography and render precise localization impossible. Here we demonstrate, theoretically and experimentally, that the flow-shift paradigm does not apply at the sub-micron scale. Specifically, we show that the resist topography is accurately obtained from a convolution operation with a symmetric Gaussian Kernel whose parameters solely depend on the resist characteristics. We exploit this finding for a 3 nm precise overlay fabrication of metal contacts to an InAs nanowire with a diameter of 27 nm using thermal scanning probe lithography., 23 pages, 5 figures

The thermo-electrical properties of a complex silicon cantilever structure used in thermal scanning probe lithography are modeled based on well established empirical laws for the thermal conductivity in silicon, the electrical conductivity in the degenerate silicon support structure, and a comprehensive physical model of the electrical conductivity in the low-doped heater structure. The model calculations are performed using a set of physically well defined material parameters and finite element methods to solve the coupled thermal and electrical diffusion equations in the cantilever. The material parameters are determined from a non-linear regression fit of the numerical results to corresponding measured data which also includes Raman measurements of the heater temperature. Excellent agreement between predicted and measured data in the absence of air cooling is obtained if a tapered doping profile in the heater is used. The heat loss through the surrounding air is also studied in a parameter free three-dimensional simulation. The simulation reveals that the heater temperature can be accurately predicted from the electrical power supplied to the cantilever via a global scaling of the power in the power-temperature correlation function which can be determined from the vacuum simulation., Comment: 24 pages, 10 figures

Thermal scanning probe lithography combines high-resolution patterning capabilities with the ability to read topography without causing resist exposure. As such, it is an ideal candidate for the implementation of markerless pattern overlay. This approach eliminates errors arising from marker degradation and inconsistencies in the positioning hardware used for reading and writing. Here, we outline our implementation and characterization of a markerless lithography process. We demonstrate theoretically and experimentally that alignment errors below 5 nm are possible for micron-sized features having an amplitude of just 4 nm. Further, we show that following proper calibration, a limiting overlay accuracy of 1.1 nm per axis is achievable.

The use of different phosphazene bases as catalysts has been investigated in the polymerization of ortho-phthalaldehyde (PA) in the presence of an alcohol used as the initiator. Among the catalysts considered (P1-t-Bu, P2-t-Bu and P4-t-Bu) only the less active one (P1-t-Bu) allows a very good control of the PA polymerization in terms of mass parameters (Mn, Mw and molar mass dispersity) and end-group fidelity. To confirm the structure and the mass range of the newly synthesized PPA, mass spectrometry and gel permeation chromatography have been selected as main characterization techniques. By comparison with the state-of-the-art, the kinetics of polymerization has also been significantly improved by reducing the polymerization time from several hours to a few minutes. The judicious choice of catalyst also allowed expanding the macromolecular engineering by preparing in a one-step procedure a defined and controlled polyphthalaldehyde-block-polyethylene oxide amphiphilic diblock copolymer.

The effects of increasing the driving forces for a 1-D assembly of nanoparticles onto a surface are investigated with experimental results and models. Modifications, which take into account not only the particle-particle interactions but also particle-surface interactions, to previously established extended random sequential adsorption simulations are tested and verified. Both data and model are compared against the heterogeneous random sequential adsorption simulations, and finally, a connection between the two models is suggested. The experiments and models show that increasing the particle-surface interaction leads to narrower particle distribution; this narrowing is attributed to the surface interactions compensating against the particle-particle interactions. The long-term advantage of this work is that the assembly of nanoparticles in solution is now understood as controlled not only by particle-particle interactions but also by particle-surface interactions. Both particle-particle and particle-surface interactions can be used to tune how nanoparticles distribute themselves on a surface.

In the presented work solvent-free film preparation from molecular glass resists, the evaluation of the patterning performance using thermal scanning probe lithography (tSPL) and an efficient etch transfer process are demonstrated. As the presented materials have a high tendency to crystallize and thus form crystalline films of bad quality when processed by solution casting, two component mixtures prepared by coevaporation were investigated. Stable amorphous films were obtained by selecting compatible material pairs for the coevaporation. One optimized material pair is based on trissubstituted, twisted resist materials with a distinct difference in molecular design. Here a high resolution tSPL prepared pattern of 18 nm half pitch in a 10 nm thick film is demonstrated. A further optimization is reported for “small” cubic silsequioxane molecules. Again single component films show independent to applied film preparation techniques bad film forming properties due to the high crystallinity of the symmetric cubic silsequioxane molecules. But coevaporation of the phenyl substituted octaphenylsilsequioxane combined with the fully aromatic 2,2',7,7'-tetraphenyl-9,9'-spirobi[fluorene] results in stable amorphous thin films. tSPL investigations demonstrate the patternability by writing high resolution line features of 20 nm half pitch. An important advantage of such a silicon rich resist material is that it can be directly converted to SiO2, yielding to a patterned hardmask of SiO2. This proof of principle is demonstrated and an efficient pattern transfer of 60 nm half pitch line into the underlying HM8006 is reported.

Nanomechanics has been slow in entering nanotechnology because of extreme conditions resulting from scaling. This is an issue in particular for polymers, although widely used in macroscale applications. Highly repetitive nanoscale deformation cycling in combination with excellent shape retention and thermal stability is demonstrated. While generic principles described are pertinent to a range of applications, this demonstration is made on the example of polymer media in high-density data storage. The information, represented as indents, is written and erased using a heated tip. A high-performance polymer with a flexible aryletherketone backbone is designed with phenylethynyl crosslink chemistry. After optimization ofcrosslink density and topology, unprecedented performance is achieved in all relevant metrics. Demonstrations of endurance and retention are performed at 1 Tb in -2 density, showing 10 8 write cycles using the same tip, 10 3 erase cycles and 3 × 10 5 read cycles of the media, and extrapolated to 10 years of retention at 85 °C.

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.

We report on the swelling behavior and the corresponding morphological behavior of cylinder-forming polystyrene-b-polybutadiene diblock copolymers, which are confined to several layers of structures. The equilibration of thin films has been done under controlled atmosphere of a nonselective solvent. In situ spectroscopic ellipsometry measurements revealed more than 10% increase of the solvent uptake with decreasing film thickness. With scanning force microscopy of the microphase separated patterns in quenched films, the correlation between the degree of the long-range order of cylinder domains and the degree of the macroscopic swelling has been established. In the case of spontaneously formed micrometer-sized topographic features with discreet film thickness (terraces), the increased solvent uptake by thinner films holds true even for isolated terraces on the mesoscale. The observation of nonhomogeneous swelling of the films on the micrometer scale brings novel insights into the properties of confined soft matter, and suggests new approaches toward the fabrication of polymer-based nanostructured responsive materials.

The roughness of spin-cast polymer films arises from thermally activated capillary waves during preparation and typically amounts to about 0.5 nm(rms) measured on a micrometer-sized surface area. Templating from atomically flat mica substrates allows the creation of polymer films with a surface roughness approaching the molecular scale. Three regimes of spatial frequencies are identified in which the roughness is controlled by different physical mechanisms. We find that frozen-in elastic pressure waves ultimately limit the flatness of polymer films.

Ultrahigh storage densities can be achieved by using a thermomechanical scanning-probe-based data-storage approach to write, read back, and erase data in very thin polymer films. High data rates are achieved by parallel operation of large two-dimensional arrays of cantilevers that can be batch fabricated by silicon-surface micromachining techniques. The very high precision required to navigate the storage medium relative to the array of probes is achieved by microelectromechanical system (MEMS)- based x and y actuators. The ultrahigh storage densities offered by probe-storage devices pose a significant challenge in terms of both control design for nanoscale positioning and read-channel design for reliable signal detection. Moreover, the high parallelism necessitates new dataflow architectures to ensure high performance and reliability of the system. In this paper, we present a small-scale prototype system of a storage device that we built based on scanning-probe technology. Experimental results of multiple sectors, recorded using multiple levers at 840 Gb/in2 and read back without errors, demonstrate the functionality of the prototype system. This is the first time a scanning-probe recording technology has reached this level of technical maturity, demonstrating the joint operation of all building blocks of a storage device.

The dynamics of early stage of terrace formation in thin supported films of cylinder forming triblock copolymers was studied both theoretically using self-consistent-field theory (DSCFT) and experimentally by insitu scanning force microscopy (SFM). In experiment, an initially flat film of incommensurable thickness was imaged continuously, and the evolution of a vertical orientation of cylinders into a parallel one as well as the respective development of thickness gradient (terrace formation) was captured in detail. On the grounds of these experimental observations, the parameters of the computational model A3B12A3 were determined to match the structures in experiment. Both systems show excellent agreement in details of structural phase transitions and in the dynamics of the step development, suggesting that the underlying transport mechanisms are governed by diffusion. The early stage of terrace formation is characterized by the development of the step height up to 80 of its equilibrium value and associated reorientation of cylindrical domains. © 2007 American Chemical Society.

Local surface potential measurements on alkoxy-substituted poly (p-phenylene ethynylene), poly (EHO-OPPE), as an electron transport material (ETM) and poly (triphenyl diamine), poly (TPD), as a hole transport material (HTM) and their blends in three different compositions (1 : 3, 1 : 1, 3 : 1) were performed by using scanning Kelvin force microscopy (SKFM). Simultaneously the topography of all surfaces was obtained using atomic force microscopy (AFM). In this paper, we propose a new principle for mapping out the local surface potential distributions of macrophase separated segments in the model polymer blend systems through the combined mode of intermittent contact AFM–SKFM techniques. The energetics and kinetics involved are also discussed in terms of potential distributions in the different phases of surface morphologies in the single-layered pristine as well as single-layered two component polymer blend systems. The experimental results provide considerable insight into the electrical/electronic properties of these ETM and HTM materials and reveal highly qualitative information for the first time to show a direct conformation of apparent work function difference between the ETM rich and HTM rich components. Finally, an attempt has been made to perform the combined approaches of valuable and high resolution complementary techniques such as scanning electron microscopy, absorption and photoluminescence spectra in order to correlate the observed contact potential difference/surface potential difference between the two rich ETM and HTM components obtained from microscopic and macroscopic scans.

We study the behavior of charged spherical Au nanoparticles in a nanofluidic slit as a function of the separation of the symmetrically charged confining surfaces. A dedicated setup called the nano-fluidic confinement apparatus (NCA) allows us to parallelize the two confining surfaces and to continuously approach them down to direct contact. Interferometric scattering (iSCAT) detection is used to measure the particle contrast with 2 ms temporal resolution. We obtain the confinement gap distance from the interference signal of the glass and the oxide-covered silicon wafer surface with nanometer accuracy. We present a three parameter model that describes the optical signal of the particles as a function of particle height and gap distance. The model is verified using nanoparticles immobilized at the glass and the substrate surface. For freely diffusing particles, the envelope of the particle signal as a function of gap distance and the known particle height at tight confinement is used to calibrate the particle signal in-situ and obtain all free model parameters. Due to the periodic contrast variation for large gap distances we obtain a set of possible particle heights for a given contrast value. For a range of small gap distances this assignment is unique and the particle height can be measured directly with high accuracy. The high temporal resolution allows us to measure the height occupation probability which provides a direct link to the free energy landscape the particles are probing via the Boltzmann distribution. Accordingly by fitting the results to a physical model based on the linear superposition approximation (LSA), the physical parameters governing the particle-glass interaction are quantified., 28 pages, 6 Figures

In the presented work solvent-free film preparation from tailored molecular glass resists, their thermal analysis, the characterization of etch resistance for plasma etching transfer processes, and the evaluation of the patterning performance using scanning probe lithography (SPL) tools, in particular electric field and thermal based SPL, are demonstrated. Therefore a series of fully aromatic spiro-based and tris-substituted twisted resist materials were systematically investigated. The materials feature very high glass transition temperatures of up to 173 °C, which allows solvent-free thin film preparation by physical vapor deposition (PVD) due to their high thermal stability. The PVD prepared films offer distinct advantages compared to spin coated films such as no pinholes, defects, or residual solvent domains, which can locally affect the film properties. In addition, PVD prepared films do not need a post apply bake (PAB) and can be precisely prepared in the nanometer range layer thickness. An observed sufficient plasma etching resistance is promising for an efficient pattern transfer even by utilizing only 10 nm thin resist films. Their lithographic resolution potential is demonstrated by a positive and a negative tone patterning using electric field, current controlled scanning probe lithography (EF-CC-SPL) at the Technical University of Ilmenau or thermal scanning probe lithography (tSPL) investigations at the IBM Research - Zurich. High resolution tSPL prepared patterns of 11 nm half pitch and at 4 nm patterning depth are demonstrated.

A novel alternative to E-beam lithography, in particular for plasmonic and nanophotonic devices, is presented. Patterning resolution and speed are similar; however, the novel technique enables direct 3D lithography and markerless overlay with sub-5 nm accuracy.

The thermomechanical scanning-probe-based data storage concept, internally known as the ''millipede'' project, combines ultrahigh density, small form factor, and high data rates. Ultrahigh storage densities of more than 1 Tb/in^2 can be achieved by using local-probe techniques to write, read back, and erase data in very thin polymer films. In this paper special focus is given to the crucial role of the polymer storage medium in thermomechanical probe storage systems. High data rates are achieved by parallel operation of large 2D arrays with thousands micro/nanomechanical cantilevers/tips that can be batch-fabricated by silicon surface-micromachining techniques. The very high precision required to navigate the probe tips over the storage medium is achieved by MEMS-based x/y actuators that position the large arrays of probe tips for parallel write/read/erase operations. The inherent parallelism, the ultrahigh areal densities and the small form factor may open up new perspectives and opportunities for application in areas beyond those envisaged today.

The goal of this project is to explore the possibilities of fabricating mechanical logic devices. A macroscopic model shows the idea and the feasibility of this concept. Two-photon polymerization is chosen to fabricate the required complex three-dimensional devices on a length scale of less than 100@mm. The writing process is characterized by evaluating test structures written by single laser lines. Complex MEMS resonators were fabricated and electrodes for actuation and sensing implemented. A first concept and fabrication of a MEMS mechanical mixer are shown.

Terrace formation and morphological behavior in thin films of polystyrene-block-polybutadiene block copolymer have been studied on two chemically different substrates by means of scanning force microscopy. Cylinders parallel to the film plane (C∥) are found on weakly interacting substrates in up to five-layer-thick films. A bottom layer of half cylinders is stabilized at the substrate. On strongly interacting substrates, the development of the C∥ microdomains and nonbulk perforated lamella (PL) and lamella (L) phases depends on the local film thickness. The sequence of structures at transition thickness (in between the steps) suggests a few percent increase of the characteristic microdomain spacing in the order C∥−PL−L. Comparison of the interlayer distances on the two types of substrates points to lamella-like structures in bulk of the films on strongly interacting surfaces.

We investigate the influence of incompatibility and dielectric contrast on the reorientation kinetics of concentrated solutions of lamellar block copolymers in the presence of an external DC electric field. We study solutions of AC diblock copolymer and ABC triblock terpolymers. The inclusion of a short, polar middle block B is used to tailor both the degree of incompatibility and the dielectric contrast between the two majority phases. In situ synchrotron radiation small-angle X-ray scattering is used to monitor the reorientation process. For the AC diblock copolymer sample only weak electric field induced reorientation could be achieved, following a very slow kinetics, whereas for the ABC triblock terpolymer, reorientation is observed above a threshold value of 0.3 kV/mm. The orientation kinetics is well described by a single exponential with characteristic time constants varying between a few seconds and several minutes depending on the polymer concentration and the electric field strength. We identify a narrow concentration window, in which the interplay between chain mobility and gain in free energy in the electric field allows the preparation of highly anisotropic bulk polymer samples by exposure to an electric field. The results are compared to free energy calculations revealing a distinct difference in the driving force for reorientation as a consequence of an increase in dielectric contrast and chain mobility upon introduction of the B middle block.

The kinetics of phase transitions is essential for understanding pattern formation in structured fluids1,2. These fluids play a key role in the morphogenesis of biological cells1,3,4,5, and they are very common in pharmaceutical products and plastic materials2. Until now, it has not been possible to follow phase transitions in structured fluids experimentally in real time and with high spatial resolution. Previous work1,2 has relied on static images and indirect experimental evidence from spatially averaging scattering experiments. Simulating the processes with computer models is a further challenge because of the multiple time and length scales involved6,7,8,9,10,11,12,13,14. Our movies based on in situ scanning force microscopy show the time sequence of the elementary steps of a phase transition in a fluid film of block copolymer from the cylinder to the perforated lamella phase. The movies validate a versatile simulation model that gives physical insight into the nature of the process. Our approach provides a means of improving the study and understanding of pattern formation processes in nanostructured fluids. We expect a significant impact on nanotechnology where block copolymers serve as self-organized templates for the synthesis of inorganic nanostructured materials15,16,17,18,19,20,21,22,23,24.

We experimentally establish a phase diagram of thin films of concentrated solutions of a cylinder forming polystyrene-block-polybutadiene-block-polystyrene triblock copolymer in chloroform. During annealing the film forms islands and holes with energetically favored values of film thickness. The thin film structure depends on the local thickness of the film and the polymer concentration. Typically, at a thickness close to a favored film thickness parallel orientation of cylinders is observed, while perpendicular orientation is formed at an intermediate film thickness. At high polymer concentration the cylindrical microdomains reconstruct to a perforated lamella structure. Deviations from the bulk structure, such as the perforated lamella and a wetting layer are stabilized in films thinner than approximately 1.5 domain spacings.

We investigate the microdomain orientation kinetics of concentrated block copolymer solutions exposed to a dc electric field by time-resolved synchrotron small-angle X-ray scattering. As a model system, we use a lamellar polystyrene-b-polyisoprene block copolymer dissolved in toluene. Our results indicate two different microscopic mechanisms, i.e., nucleation and growth of domains and grain rotation. The former dominates close to the order−disorder transition, while the latter prevails under more strongly segregated conditions. This conclusion is corroborated by computer simulations based on dynamic density functional theory. The orientation kinetics follows a single-exponential behavior with characteristic time constants varying from a few seconds to some minutes depending on polymer concentration, temperature, and electric field strength. From the experimental results we deduce optimum conditions for the preparation of highly anisotropic bulk polymer samples via solvent casting in the presence of an ele...

We show that the near surface structure of lamellar ABC triblock copolymer mesostructures can deviate considerably from the “ideal” surface anticipated from the bulk structure of the material. Varying the molecular architecture and the surface energy difference between the respective blocks, we show that such surface reconstructions are caused by a complex balance of enthalpic and entropic contributions to the free energy of the system. The results are compared to the well-known surface behavior of classical crystals and experimental conditions for what may be called “block copolymer surface science” are discussed.

The preparation of polyethylene-block-poly(ethylene-alt-propylene)-block-poly(ethylene oxide) (PE-b-PEP-b-PEO) triblock copolymers by homogeneous catalytic hydrogenation of the precursor poly(1,4-butadiene)-block-poly(1,4-isoprene)-block-poly(ethylene oxide) (PB-b-PI-b-PEO) triblock copolymers, which were synthesized by sequential anionic polymerization, is described. Thermal analysis using differential scanning calorimetry (DSC) reveals differences in the crystallization behavior of the PEO and PE blocks arising from different morphological confinements active during crystallization. If the PEO block is confined into isolated spherical or cylindrical microdomains, crystallization can only be induced by high supercoolings resulting from the vast number of microdomains (spheres or cylinders) compared to the number of available heterogeneities. In contrast, crystallization of PE proceeds via heterogeneous nucleation regardless of the composition, which can be attributed to the miscibility of PEP and PE segm...

Stacking fault defects are thought to be the root cause for many of the anomalous transport phenomena seen in high-quality graphite samples. In stark contrast to their importance, direct observation of stacking faults by diffractive techniques has remained elusive due to fundamental experimental difficulties. Here we show that the stacking fault density and resistance can be measured by analyzing the non-Gaussian scatter observed in the c-axis resistivity of mesoscopic graphite structures. We also show that the deviation from Ohmic conduction seen at high electrical field strength can be fit to a thermally activated transport model, which accurately reproduces the stacking fault density inferred from the statistical analysis. From our measurements, we conclude that the c-axis resistivity is entirely determined by the stacking fault resistance, which is orders of magnitude larger than the inter-layer resistance expected from a Drude model.

The nanoscale control afforded by scanning probe microscopes has prompted the development of a wide variety of scanning probe-based patterning methods. Some of these methods have demonstrated a high degree of robustness and patterning capabilities that are unmatched by other lithographic techniques. However, the limited throughput of scanning probe lithography has prevented their exploitation in technological applications. Here, we review the fundamentals of scanning probe lithography and its use in materials science and nanotechnology. We focus on the methods and processes that offer genuinely lithography capabilities such as those based on thermal effects, chemical reactions and voltage-induced processes., 27 pages, 5 figures. http://www.nature.com/nnano/journal/v9/n8/full/nnano.2014.157.html

Thermal Scanning Probe Lithography [1] (tSPL) utilises a heated AFM tip to locally evaporate a polymer layer. Using tSPL nanometer precise 3D profiles can be formed in this polymer layer [2]. tSPL offers a resolution and linear scan speed that is competitive [3] with the current state of the art maskless technique, Gaussian electron beam lithography. A recently developed pattern transfer technique allows for the subsequent transfer of these patterns into the substrate [4]. Pattern alignment or overlay is a key challenge both in device fabrication and the investigation of novel nanostructures. tSPL has a pair of unique capabilities for meeting this challenge. Firstly it can read topography with sub-nanometer sensitivity and secondly reading the surface does not lead to resist exposure. This removes the need for dedicated alignment marks which in turn removes difficulties associated with marker degradation and inconsistencies in the positioning hardware used for read and write. Here we describe our efforts to implement and assess a markerless overlay process. In particular we investigate the two sources of error in the overlay process. The first are errors arising in the determination of the position of the existing pattern. We demonstrate theoretically that for our tSPL patterning stack the detection error may be some 200 times smaller than the 1μm feature size present in patterns produced using optical lithography. The second source of error is in the writing of the overlay pattern. We outline the practical steps including feed forward scanner control, on-the-fly drift correction and 3D patterning required to achieve nanometer accuracy in the pattern placement.

We studied solvent-driven ordering dynamics of block copolymer films supported by a densely cross-linked polymer network designed as organic hard mask (HM) for lithographic fabrications. The ordering of microphase separated domains at low degrees of swelling corresponding to intermediate/strong segregation regimes was found to proceed significantly faster in films on a HM layer as compared to similar block copolymer films on silicon wafers. The ten-fold enhancement of the chain mobility was evident in the dynamics of morphological phase transitions and of related process of terrace-formation on a macroscale, as well as in the degree of long-range lateral order of nanostructures. The effect is independent of the chemical structure and on the volume composition (cylinder-/ lamella-forming) of the block copolymers. In-situ ellipsometric measurements of the swelling behavior revealed a cumulative increase in 1-3 vol. % in solvent up-take by HM-block copolymer bilayer films, so that we suggest other than dilution effect reasons for the observed significant enhancement of the chain mobility in concentrated block copolymer solutions. Another beneficial effect of the HM-support is the suppression of the film dewetting which holds true even for low molecular weight homopolymer polystyrene films at high degrees of swelling. Apart from immediate technological impact in block copolymer-assisted nanolithography, our findings convey novel insight into effects of molecular architecture on polymer-solvent interactions., This document is the unedited Author's version of a Submitted Work that was subsequently accepted for publication in Macromolecules, copyright \c{opyright} American Chemical Society after peer review. To access the final edited and published work see http://pubs.acs.org/doi/abs/10.1021/ma500561q

The presented work deals with molecular glass resist materials based on (i) calix[4]resorcinarene resist systems, (ii) twisted fully aromatic biscarbazole-biphenyl materials, and (iii) fully aromatic spiro resist materials as new promising materials for Scanning Probe Lithography (SPL). Because of the non-chemically amplified resist nature and the absence of corresponding material diffusion, the novel SPL resists have the potential to increase the patterning resolution capabilities at a simultaneous reduction of the edge roughness (LER). In addition, these low molecular weight molecular glasses offer the advantage of solvent-free film preparation by physical vapor deposition (PVD). The PVD prepared films offer a number of advantages compared to spin coated ones such as no more pinholes, defects, or residual solvent domains, which can locally affect the film properties. These high-quality PVD films are ideal candidates for the direct patterning by SPL tools. Presented highlights are the thermal scanning probe lithography (tSPL) investigations at IBM Research - Zurich and the patterning by using electric field, current controlled scanning probe lithography (EF-CC-SPL) at the Technical University of Ilmenau. Further investigations on film forming behavior, etch resistance, and etch transfer are presented. Owing to the high-resolution probe based patterning capability in combination with their improved etch selectivity compared to reference polymeric resists the presented molecular glass resists are highly promising candidates for lithography at the single nanometer digit level.