Karim Raafat Gadelrab

Massachusetts Institute of Technology | MIT · Department of Materials Science and Engineering

Multifrequency atomic force microscopy (AFM) enhances resolving power, provides extra contrast channels, and is equipped with a formalism to quantify material properties pixel by pixel. On the other hand, multifrequency AFM lacks the ability to extract and examine the profile to validate a given force model while scanning. We propose exploiting dat...

The multifrequency formalism is generalized and exploited to quantify attractive forces, i.e., van der Waals interactions, with small amplitudes or gentle forces in bimodal and trimodal atomic force microscopy (AFM). The multifrequency force spectroscopy formalism with higher modes, including trimodal AFM, can outperform bimodal AFM for material pr...

Quantification of conservative forces in multifrequency atomic force microscopy requires solving the general equations of the theory expressed in terms of the virials of interaction. Power law expressions are commonly utilized when dealing with electrostatic, ferroelectric, magnetic, or long range (van der Waals) forces. Here, we discuss long range...

jats:p>A mesoscale model is proposed to characterize coarsening of platinum-based catalyst particles with the aim of understanding cathode degradation and power loss in proton exchange membrane fuel cells (PEMFC). The microstructure of a cathode catalyst layer is more complex than the ones typically described by Ostwald-ripening models, such as the...

Since the inception of the atomic force microscope (AFM), dynamic methods (dynamic atomic force microscopy) have been very fruitful by establishing methods to quantify dissipative and conservative forces in the nanoscale and by providing a means to apply gentle forces to the samples with high resolution. Here, we discuss developments that cover ove...

The characteristics of a new architecture of bottlebrush copolymers (BBCPs) self-assembly were studied using self-consistent field theory. In this molecule, a series of AB linear diblock side chains were connected at the diblock junction using a C backbone. The control over the linker length and its chemical nature created an additional constraint...

Since the inception of the atomic force microscope AFM, dynamic methods have been very fruitful by establishing methods to quantify dissipative and conservative forces in the nanoscale and by providing a means to apply gentle forces to the samples with high resolution. Here we review developments that cover over a decade of our work on energy dissi...

A robust and transparent silica-like coating that imparts superhydrophobicity to a surface through its hierarchical multilevel self-assembled structure is demonstrated. This approach involves iterative steps of spin-coating, annealing, and etching of polystyrene-block-polydimethylsiloxane block copolymer thin films to form a tailored multilayer nan...

The directed self-assembly (DSA) of block copolymers (BCPs) has shown promise in fabricating customized two-dimensional (2D) geometries at the nano- and meso-scale. Here, we discover spontaneous symmetry breaking and superlattice formation in DSA of BCP. We observe the emergence of low symmetry phases in high symmetry templates for BCPs that would...

Using 4₄ and 3₂434 Archimedean tiling templates that are incompatible with BCP six-fold symmetry created low symmetry patterns with an emergent behavior dependent on pattern size and shape. A variation of DSA is studied using modulated substrates. Layer-by-layer deposition of cylinder forming BCPs was investigated. Self-consistent field theory (SCF...

In this work, ladder-shaped block copolymer structures consisting of parallel bars, bends, and T-junctions are formed inside square confinement. We define binary states by the two degenerate alignment orientations, and study properties of the two-state system. We control the binary states by creating openings around the confinement, changing the co...

Self-consistent field theory (SCFT) and strong segregation theory (SST) are used to explore the parameter space governing the self-assembly of cylinder forming block copolymers (BCPs) on a modulated substrate. The stability of in-plane cylinders aligning parallel or perpendicular to substrate corrugation is investigated for different barrier height...

The self-assembly of block copolymers (BCPs) with novel architectures offers tremendous opportunities in nanoscale patterning and fabrication. Here, the thin film morphology, annealing kinetics, and topographical templating of an unconventional Janus-type "PS-branch-PDMS" bottlebrush copolymer (BBCP) is described. In the Janus-type BBCP, each segme...

A combined experimental and self-consistent field theoretical (SCFT) investigation of the phase behavior of poly(stryrene-b-dimethylsiloxane-b-styrene) (PS-b-PDMS-b-PS or SDS32) thin films during solvent vapor annealing is presented. The morphology of the triblock copolymer is described as a function of the as-cast film thickness and the ratio of t...

Understanding the conditions under which defects appear in self-assembling soft-matter systems is of great importance, for example, in the development of block-copolymer (BCP) nanolithography. Here, we explore the limits of directed self-assembly of BCPs by deliberately adding random imperfections in the template. Our results show that defects emer...

Directed self-assembly of block copolymers (BCPs) provided by shear-stress can produce aligned sub-10 nm structures over large areas for applications in integrated circuits, next-generation data storage, and plasmonic structures. In this work, we present a fast, versatile BCP shear-alignment process based on coefficient of thermal expansion mismatc...

Recent success of inverse design methodologies in the realm of self-assembled materials has allowed us to envision an inverse path of discovery where we go from a desired target function to building blocks. In this review we examine recent advances of such inverse design methods in soft materials containing block copolymers, colloids, or DNA. By co...

Here we present the Mendeleev-Meyer Force Project which aims at tabulating all materials and substances in a fashion similar to the periodic table. The goal is to group and tabulate substances using nanoscale force footprints rather than atomic number or electronic configuration as in the periodic table. The process is divided into: (1) acquiring n...

We report the synthesis of Janus bottlebrush block copolymers by graft-through polymerization of branched diblock macromonomers. Self-assembly of the bottlebrushes was characterized by small-angle X-ray scattering, atomic force microscopy, and scanning electron microscopy. Phase separation and packing models of the bottlebrushes were computed, and...

Continued scaling-down of lithographic-pattern feature sizes has brought templated self-assembly of block copolymers (BCPs) into the forefront of nanofabrication research. Technologies now exist that facilitate significant control over otherwise unorganized assembly of BCP microdomains to form both long-range and locally complex monolayer patterns....

Perpendicular orientation of lamellar microdomains in a high interaction parameter block copolymer was obtained within high aspect ratio gratings functionalized with a preferential sidewall brush. The experiments used polystyrene-block-polydimethylsiloxane BCP with molecular weight 43 kg/mol within trenches made using interference lithography. The...

The photoactive properties of TiO2 are employed to develop surfaces with self-cleaning capabilities. Clearly, the fine-tuning of such surfaces for different applications relies on a holistic understanding of the different aspects that induce the self-cleaning behavior. Among those, the mechanisms responsible for the photoinduced surface alteration...

The monitoring of the deflection of a micro-cantilever, as the end of a sharp probe mounted at its end, i.e. the tip, interacts with a surface, forms the foundation of atomic force microscopy AFM. In a nutshell, developments in the field are driven by the requirement of obtaining ever increasing throughput and sensitivity, and enhancing the versati...

Here, we enhance the capabilities of the atomic force microscope (AFM) to show that force profiles can be reconstructed without restriction by monitoring the wave profile of the cantilever during a single oscillation cycle. Two approaches are provided to reconstruct the force profile in both the steady and transient states in what we call single-cy...

Here, processes through which the energy stored in an atomic force microscope cantilever dissipates in the tip-sample interaction are first decoupled qualitatively. A formalism is then shown to allow quantification of fundamental aspects of nanoscale dissipation such as deformation, viscosity and surface energy hysteresis. Interactions originating...

Multifrequency atomic force microscopy holds promise as a tool for chemical and topological imaging with nanoscale resolution. Here, we solve the equation of motion exactly for the fundamental mode in terms of the cantilever mean deflection, the fundamental frequency of oscillation, and the higher harmonic amplitudes and phases. The fundamental fre...

For monitoring and improving mechanical properties of BEoL (back-end of line) interconnect structures in microprocessor technology, it is crucial to analyze their adhesion and crack propagation properties. In the present investigation, a camera assisted 4-point bending beam technique has been used to obtain fast and reliable adhesion measurements i...

Amplitude modulation atomic force microscopy allows quantifying energy dissipation in the nanoscale with great accuracy with the use of analytical expressions that account for the fundamental frequency and higher harmonics. Here, we focus on the effects of sub-harmonic excitation on energy dissipation and its quantification. While there might be se...

Recent advances in atomic force microscopy (AFM) are used here to determine, decouple and quantify the dissipative processes involved in the interaction between a silicon tip and a carbon nanotube (CNT). The energy dissipated per atom due to hysteretic contact processes on the CNT remains constant with increasing cantilever stored energy. The energ...

Multifrequency atomic force microscopy holds promise as a method to provide qualitative and quantitative information about samples with high spatial resolution. Here, we provide experimental evidence of the excitation of subharmonics in ambient conditions in the regions where capillary interactions are predicted to be the mechanism of excitation. W...

A formalism to extract and quantify unknown quantities such as sample deformation, the viscosity of the sample and surface energy hysteresis in amplitude modulation atomic force microscopy is presented. Recovering the unknowns only requires the cantilever to be accurately calibrated and the dissipative processes occurring during sample deformation...

The local mechanical properties of ferritic and austenitic domains in a duplex stainless steel are locally studied by nanoindentation. The elastic and plastic properties of the two phases are determined. Without any specific surface treatment (chemical or electrochemical), the austenitic and ferritic domains present in the duplex stainless steel ar...

We provide a method to characterize the tip radius of an atomic force microscopy in situ by monitoring the dynamics of the cantilever in ambient conditions. The key concept is that the value of free amplitude for which transitions from the attractive to repulsive force regimes are observed, strongly depends on the curvature of the tip. In practice,...

Instantaneous and average energy dissipation distributions in the nanoscale due to short and long range interactions are described. We employ both a purely continuous and a semi-discrete approach to analyze the consequences of this distribution in terms of rate of heat generation, thermal flux, adhesion hysteresis, viscoelasticity and atomic dissip...

Research on thermoelectric (TE) materials has been focused on their transport properties in order to maximize their overall performance. Mechanical properties, which are crucial for system reliability, are often overlooked. The recent development of a new class of high-performance, low-dimension thermoelectric materials calls for a better understan...

The analysis of nanoindentation force data are based on Sneddon’s solution for a linear elastic half space with a rigid axisymmetric indenter. Berkovich indenters commonly used in indentation experiments are normally modeled as cones. The idea of effective tip shape was presented to better explain the behavior of the unloading curve and pressure di...

The mechanisms through which energy is dissipated in nanoscale dynamic interactions might involve tens or hundreds of atoms and might be diverse. Here, a method is presented that provides the means to disentangle, with the use of common experimental parameters, short and long range viscosity and hysteretic dissipative components. While the approach...

Nanoindenter's tip shape plays a significant role in accurately extracting the mechanical properties of materials from nanoindentation measurements. Since tip imperfections may govern results validity, especially at shallow depth, a new framework for estimating the Young's modulus of materials is presented. Real tip geometry obtained from atomic fo...

Imaging with nanoscale resolution has become routine practice with the use of scanning probe techniques. Nevertheless, quantification of material properties and processes has been hampered by the complexity of the tip-surface interaction and the dependency of the dynamics on operational parameters. Here, we propose a framework for the quantificatio...

Nanoindentation results are very sensitive to tip rounding and neglecting the value of the tip radius produces erroneous estimation of the material elastic properties. In this study we investigate the effect of tip radius on the estimation of the Elastic modulus by means of finite element analysis of Berkovich and conical tips with different tip ra...

Fused silica is the reference material used for estimating the area function of nanoindenter tips. Despite being a fundamental step in nanoindentation, little has been done to study its deformation. Under a complex state of stress during indentation, fused silica densifies pointing out that the hydrostatic stress contributes to its yielding. A line...

The analysis of nanoindentation force data are based on Sneddon's solution for a linear elastic half space with a rigid axisymmetric indenter. Berkovich indenters commonly used in indentation experiments are normally modeled as cones. The idea of effective tip shape was presented to better explain the behavior of the unloading curve and pressure di...