Dynamics Of Nanomaterials Research Articles

Light-Induced Redox Dynamics in Plasmonic Nanostructures and Photosensitizer Transition Metal Compounds

Solar energy harvesting is a nuanced scientific field that involves precise control across energy, time, and nanometer length scales. The understanding of how to harness sunlight to promote chemical reactions is vital for the advancement of renewable energy applications and a sustainable future. Limited knowledge of the precise chemical mechanisms underlying solar energy harvesting restricts widespread technological use and the development of photovoltaic devices that utilize light-harvesting biodegradable materials. My research focuses on developing a fundamental understanding of visible light-activated excited state chemistry that is of great importance in elucidating the mechanisms, structures, and design features for catalysis. In this talk, we will examine excited-state chemical structure dynamics in nanomaterials that use light-matter interactions to drive interfacial or intramolecular charge transfer. Steady-state and time-resolved optical/X-ray spectroscopy allow for the observation of these dynamics across an expansive timescale—from the seconds timescale of oxygen-evolving reactions to the ultrafast timescales of electronic and vibrational motion. Novel light-matter interactions in plasmonic nanostructures, biomimetic metal oxides, and molecular transition metal complexes will be discussed. The talk will conclude with future opportunities for expanding the scope of nanoscale photocatalysis and for designing enhanced localized control over excited-state chemistry.[1] E. A. Sprague-Klein*, X. He, M. W. Mara, B. J. Reinhart, S. Lee, L. M. Utschig, K. L. Mulfort, L. X. Chen*, D. M. Tiede*. “Photo-Electrochemical Effect in the Water Oxidation Catalyst Cobalt-Phosphate (CoPi),” ACS Energy Letters, 2022, 7, 9, 3129–3138. [2] N. L. Warren, U. Yunusa, A. B. Singhal, E. A. Sprague-Klein*. "Facilitating Excited-State Plasmonics and Photochemical Reaction Dynamics," Chemical Physics Reviews, (Accepted December 2023).[3] U. Yunusa, N. Warren, D. Schauer, P. Srivastava, E. Sprague-Klein*. "Plasmon resonance dynamics and enhancement effects in Tris(bipyridine)ruthenium(II) gold nanosphere oligomers," Nanoscale, (Under Review).

Probing the Boundary between Classical and Quantum Mechanics by Analyzing the Energy Dependence of Single-Electron Scattering Events at the Nanoscale

The relation between the energy-dependent particle and wave descriptions of electron-matter interactions on the nanoscale was analyzed by measuring the delocalization of an evanescent field from energy-filtered amplitude images of sample/vacuum interfaces with a special aberration-corrected electron microscope. The spatial field extension coincided with the energy-dependent self-coherence length of propagating wave packets that obeyed the time-dependent Schrödinger equation, and underwent a Goos-Hänchen shift. The findings support the view that wave packets are created by self-interferences during coherent-inelastic Coulomb interactions with a decoherence phase close to Δφ = 0.5 rad. Due to a strictly reciprocal dependence on energy, the wave packets shrink below atomic dimensions for electron energy losses beyond 1000 eV, and thus appear particle-like. Consequently, our observations inevitably include pulse-like wave propagations that stimulate structural dynamics in nanomaterials at any electron energy loss, which can be exploited to unravel time-dependent structure-function relationships on the nanoscale.

Nutation Excitations in the Gyrotropic Vortex Dynamics in a Circular Magnetic Nanodot.

A significant activity is devoted to the investigation of the ultrafast spin dynamic processes, holding a great potential for science and applications. However, a challenge of the understanding of the mechanisms of underlying spin dynamics in nanomaterials at pico- and femtosecond timescales remains under discussion. In this article, we explore the gyrotropic vortex dynamics in a circular soft magnetic nanodot, highlighting the impacts given by nutations in the high-frequency part of the dot spin excitation spectrum. Using a modified Thiele equation of the vortex core motion with a nutation term, we analyze the dynamic response of the vortex to an oscillating magnetic field applied in the dot plane. It is found that nutations affect the trajectory of the vortex core. Namely, we show that the directions of the vortex core motion in the low-frequency gyrotropic mode and the high-frequency nutation mode are opposite. The resonant frequencies of gyrotropic and nutational vortex core motions reveal themselves on different scales: gigahertz for the gyrotropic motion and terahertz for the nutations. We argue that the nutations induce a dynamic vortex mass, present estimates of the nutational mass, and conduct comparison with the mass appearing due to moving vortex interactions with spin waves and Doering domain wall mass.

Transient bioconvection and activation energy impacts on Casson nanofluid with gyrotactic microorganisms and nonlinear radiation

Novel applications of bioconvection and activation energy in the progress of Casson nanomaterials with gyrotactic microorganisms involve mechanical energy, bioinformatics, biotechnology, engineering, and biosensors captivated the attraction of scientists and investigators. The prime focus of the present communication is to devise new mathematical modeling for unsteady bioconvection flow of chemically reactive Casson nanoliquid with nonlinear radiation and gyrotactic microorganisms for axisymmetric flow case. Furthermore, activation energy and viscous dissipation ramifications are accounted. A revised nanofluid model is deployed to perceive flow dynamics in nanomaterials. Fundamental PDEs of the presumed study are developed with boundary layer conjecture and then reorganized into coupled ODEs by employing appropriate transformation. Numerical solutions of considered appraisal are derived via Fehlberg (RK45) shooting. Numerical simulations of the density number of microorganisms, mass transfer rate, Nusselt number, and surface drag force are executed. For the justification of the presumed investigation, a comparison with the published study is conducted and divulged in a great agreement. It is fascinating that microorganism density number is deprecated for higher approximation of Peclet number and microorganism difference parameter.

The Effect of Mechanical Strain on Lithium Staging in Graphene

AbstractThe development of next‐generation electrodes for metal‐ion batteries requires an understanding of intercalation dynamics in nanomaterials. Herein, it is shown that microscale mechanical strain significantly affects the formation of ordered lithium phases in graphene. In situ Raman spectroscopy of graphene microflakes mechanically constrained at the edge during lithium intercalation reveals a thickness‐dependent increase of up to 1.26 V in the electrochemical potential that induces lithium staging. While the induced mechanical strain energy increases with graphene thickness to the fourth power, its magnitude is small compared to the observed increase in electrochemical energy. It is hypothesized that the mechanical strain energy increases a nucleation barrier for lithium staging, greatly delaying the formation of ordered lithium phases. These results indicate that electrode assembly may critically impact lithium staging dynamics. The present work demonstrates strain engineering in two dimensional (2D) nanomaterials as an effective approach to manipulate phase transitions and chemical reactivity.

Modeling Auger Processes with Nonadiabatic Molecular Dynamics.

Auger-type energy exchange plays key roles in the carrier dynamics in nanomaterials due to strong carrier-carrier interactions. However, theoretical descriptions are limited to perturbative calculations of scattering rates on static structures. We develop an accurate and efficient ab initio technique to model Auger scattering with nonadiabatic molecular dynamics. We incorporate the many-body Coulomb matrix into several surface hopping methods and describe simultaneously charge-charge and charge-phonon scattering in the time-domain and in a nonperturbative, configuration-dependent manner. The approach is illustrated with a CdSe quantum dot. Auger scattering between electrons and holes breaks the phonon bottleneck to electron relaxation. The bottleneck is recovered when electrons and holes are decoupled. The simulations correctly reproduce all experimental processes and time scales, including Auger- and phonon-assisted cooling of hot electrons, intraband carrier relaxation, and carrier recombination. Providing detailed insights into the energy flow, the developed method allows studies of carrier dynamics in nanomaterials with strong carrier-carrier interactions.

Synchrotron Scattering Methods for Nanomaterials and Soft Matter Research.

This article aims to provide an overview of broad range of applications of synchrotron scattering methods in the investigation of nanoscale materials. These scattering techniques allow the elucidation of the structure and dynamics of nanomaterials from sub-nm to micron size scales and down to sub-millisecond time ranges both in bulk and at interfaces. A major advantage of scattering methods is that they provide the ensemble averaged information under in situ and operando conditions. As a result, they are complementary to various imaging techniques which reveal more local information. Scattering methods are particularly suitable for probing buried structures that are difficult to image. Although, many qualitative features can be directly extracted from scattering data, derivation of detailed structural and dynamical information requires quantitative modeling. The fourth-generation synchrotron sources open new possibilities for investigating these complex systems by exploiting the enhanced brightness and coherence properties of X-rays.

An electrochemical thermal transistor

The ability to actively regulate heat flow at the nanoscale could be a game changer for applications in thermal management and energy harvesting. Such a breakthrough could also enable the control of heat flow using thermal circuits, in a manner analogous to electronic circuits. Here we demonstrate switchable thermal transistors with an order of magnitude thermal on/off ratio, based on reversible electrochemical lithium intercalation in MoS2 thin films. We use spatially-resolved time-domain thermoreflectance to map the lithium ion distribution during device operation, and atomic force microscopy to show that the lithiated state correlates with increased thickness and surface roughness. First principles calculations reveal that the thermal conductance modulation is due to phonon scattering by lithium rattler modes, c-axis strain, and stacking disorder. This study lays the foundation for electrochemically-driven nanoscale thermal regulators, and establishes thermal metrology as a useful probe of spatio-temporal intercalant dynamics in nanomaterials.

Introduction on Carbon Nanotubes (CNT) and Its Applications in Electronic Circuits

Carbon Nanotubes (CNT) in nanotechnology field are legendary for its strength and chemical inertness. Technically, we can alter carbon nanotubes based on our necessities and requirements such as single layered nanotube, double layered nanotube, multi layered nanotube etc. In this paper usage of carbon nanotubes in semiconductor devices such as nanomaterials, molecular dynamics of nanomaterials, heterojunctions using carbon nanotubes, diodes and Graphene Field Effect Transistor (GFET), its characteristics and data analysis are discussed. The major application of carbon nanotubes in electronic circuits is not limiting to improves the electrical and thermal conductivity due to its high stretchability feature and they also have a long life span and better durability over traditional electronic circuit’s materials.

Picoliter Drop-On-Demand Dispensing for Multiplex Liquid Cell Transmission Electron Microscopy.

Liquid cell transmission electron microscopy (LCTEM) provides a unique insight into the dynamics of nanomaterials in solution. Controlling the addition of multiple solutions to the liquid cell remains a key hurdle in our ability to increase throughput and to study processes dependent on solution mixing including chemical reactions. Here, we report that a piezo dispensing technique allows for mixing of multiple solutions directly within the viewing area. This technique permits deposition of 50 pL droplets of various aqueous solutions onto the liquid cell window, before assembly of the cell in a fully controlled manner. This proof-of-concept study highlights the great potential of picoliter dispensing in combination with LCTEM for observing nanoparticle mixing in the solution phase and the creation of chemical gradients.

Revealing giant internal magnetic fields due to spin fluctuations in magnetically doped colloidal nanocrystals.

Strong quantum confinement in semiconductors can compress the wavefunctions of band electrons and holes to nanometre-scale volumes, significantly enhancing interactions between themselves and individual dopants. In magnetically doped semiconductors, where paramagnetic dopants (such as Mn(2+), Co(2+) and so on) couple to band carriers via strong sp-d spin exchange, giant magneto-optical effects can therefore be realized in confined geometries using few or even single impurity spins. Importantly, however, thermodynamic spin fluctuations become increasingly relevant in this few-spin limit. In nanoscale volumes, the statistical fluctuations of N spins are expected to generate giant effective magnetic fields Beff, which should dramatically impact carrier spin dynamics, even in the absence of any applied field. Here we directly and unambiguously reveal the large Beff that exist in Mn(2+)-doped CdSe colloidal nanocrystals using ultrafast optical spectroscopy. At zero applied magnetic field, extremely rapid (300-600 GHz) spin precession of photoinjected electrons is observed, indicating Beff ∼ 15 -30 T for electrons. Precession frequencies exceed 2 THz in applied magnetic fields. These signals arise from electron precession about the random fields due to statistically incomplete cancellation of the embedded Mn(2+) moments, thereby revealing the initial coherent dynamics of magnetic polaron formation, and highlighting the importance of magnetization fluctuations on carrier spin dynamics in nanomaterials.

Flow Control and Thermal System Design for Wet Cell in the Scanning Electron Microscope

This paper describes a novel device, a wet cell, used for observation in the wet environment inside the scanning electron microscope (SEM). A Wet cell is composed of three counterparts, which are flow control system, thermal system and Wet cell body. The flow system provides continuous buffer liquid to wet cell and maintains cells living at the vacuum environment. It can control different flowrates and switch to different fluidics. Additionally, the thermal system can control the temperature inside the wet cell and maintain at 37 °C. It also offers preheating thermal module to lower the fluctuated of wet cell inside temperature. The wet cell body contains a silicon nitride film based observation window and provides a wet environment for observation between vacuum and anti-vacuum status. In this paper, we introduce the structure and experimental data of flow control and thermal system in Wet cell to let SEM easily provide lots of live imaging information such as dynamics of nano-materials and biological samples in the liquid state.

Quantum Trajectory-Electronic Structure Approach for Exploring Nuclear Effects in the Dynamics of Nanomaterials.

A massively parallel, direct quantum molecular dynamics method is described. The method combines a quantum trajectory (QT) representation of the nuclear wave function discretized into an ensemble of trajectories with an electronic structure (ES) description of electrons, namely using the density functional tight binding (DFTB) theory. Quantum nuclear effects are included into the dynamics of the nuclei via quantum corrections to the classical forces. To reduce computational cost and increase numerical accuracy, the quantum corrections to dynamics resulting from localization of the nuclear wave function are computed approximately and included into selected degrees of freedom representing light particles where the quantum effects are expected to be the most pronounced. A massively parallel implementation, based on the message passing interface allows for efficient simulations of ensembles of thousands of trajectories at once. The QTES-DFTB dynamics approach is employed to study the role of quantum nuclear effects on the interaction of hydrogen with a model graphene sheet, revealing that neglect of nuclear effects can lead to an overestimation of adsorption.

Probing Spatially Dependent Photoinduced Charge Transfer Dynamics to TiO2 Nanoparticles Using Single Quantum Dot Modified Atomic Force Microscopy Tips

Using single CdSe/CdS quantum dot (QD) functionalized atomic force microscopy (AFM) tips, we demonstrate that the spatial dependence of photoinduced electron transfer dynamics from the single QD to TiO2 nanoparticles can be controlled and probed with high spatial (subdiffraction-limited) and temporal (limited by fluorescence microscopy) resolutions. This finding suggests the feasibility of using electron donor or acceptor modified AFM tips for simultaneous high resolution imaging of morphology and photoinduced charge transfer dynamics in nanomaterials.

Exciton Dynamics in Semiconductor Nanocrystals

This review article provides an overview of recent advances in the study and understanding of dynamics of excitons in semiconductor nanocrystals (NCs) or quantum dots (QDs). Emphasis is placed on the relationship between exciton dynamics and optical properties, both linear and nonlinear. We also focus on the unique aspects of exciton dynamics in semiconductor NCs as compared to those in bulk crystals. Various experimental techniques for probing exciton dynamics, particularly time-resolved laser methods, are reviewed. Relevant models and computational studies are also briefly presented. By comparing different materials systems, a unifying picture is proposed to account for the major dynamic features of excitons in semiconductor QDs. While the specific dynamic processes involved are material-dependent, key processes can be identified for all the materials that include electronic dephasing, intraband relaxation, trapping, and interband recombination of free and trapped charge carriers (electron and hole). Exciton dynamics play a critical role in the fundamental properties and functionalities of nanomaterials of interest for a variety of applications including optical detectors, solar energy conversion, lasers, and sensors. A better understanding of exciton dynamics in nanomaterials is thus important both fundamentally and technologically.

Local mechanical spectroscopy with nanometer-scale lateral resolution

A new technique has been developed to probe the viscoelastic and anelastic properties of submicron phases of inhomogeneous materials. The measurement gives information related to the internal friction and to the variations of the dynamic modulus of nanometer-sized volumes. It is then the nanoscale equivalent to mechanical spectroscopy, a well-known macroscopic technique for materials studies, also sometimes called dynamic mechanical (thermal) analysis. The technique is based on a scanning force microscope, using the principle of scanning local-acceleration microscopy (SLAM), and allows the sample temperature to be changed. It is called variable-temperature SLAM, abbreviated T-SLAM. According to a recent proposition to systematize names of scanning probe microscope based methods, this technique should be included in the family of “mechanothermal analysis with scanning microscopy.” It is suited for studying defect dynamics in nanomaterials and composites by locating the dissipative mechanisms in submicron phases. The primary and secondary relaxations, as well as the viscoplasticity, were observed in bulk PVC. The wide range of phenomena demonstrate the versatility of the technique. A still unexplained increase of the stiffness with increasing temperature was observed just below the glass transition. All of these observations, although their interpretation in terms of physical events is still tentative, are in agreement with global studies. This technique also permits one to image the variations of the local elasticity or of the local damping at a fixed temperature. This enables the study of, for instance, the homogeneity of phase transitions in multiphased materials, or of the interface morphologies and properties. As an illustration, the homogeneity of the glass transition temperature of PVC in a 50/50 wt % PVC/PB polymer blend has been demonstrated. Due to the small size of the probed volume, T-SLAM gives information on the mechanical properties of the near-surface, which may differ from bulk properties.