Heisenberg exchange coupling (HC) and biquadratic exchange coupling (BQC) are known to occur in magnetic tunnel junctions (MTJ) and nanoscale spintronics structures. MTJ-based molecular spintronics devices (MTJMSD) provide a platform to study these interactions and the correlated magnetic behavior they generate. Molecular spin channels formed along the exposed MTJ edge have been shown to produce strong exchange interactions that include HC and BQC, which can drive perpendicular alignment of spin vectors in adjacent ferromagnetic electrodes. Despite their importance, the competing roles of HC and BQC in MTJMSDs remain unclear. Monte Carlo simulations using a three-dimensional Heisenberg model were performed to systematically vary BQC strength under three conditions: no molecular HC, strong parallel HC, and strong antiparallel HC. The resulting magnetic and physical properties of the MTJMSDs were analyzed. Increasing BQC strength produced minimal changes in overall magnetization when strong HC was present, indicating that HC dominates device magnetization. Temporal evolution studies showed that devices with only BQC failed to reach magnetic stability, while devices with both HC and BQC achieved stable magnetic states due to the stabilizing influence of HC. These results show that BQC plays a secondary role in magnetization dynamics and cannot overcome the stronger stabilizing effect of HC. The presence of BQC offers a plausible explanation for experimentally observed magnetic phase orientations beyond simple parallel and antiparallel states in MTJMSDs.

Understanding the magnetic molecules’ interaction with different combinations of metal electrodes is vital to advancing the molecular spintronics field. This paper describes experimental and theoretical understanding showing how paramagnetic single-molecule magnet (SMM) catalyzes long-range effects on metal electrodes and, in that process, loses its basic magnetic properties. For the first time, our Monte Carlo simulations, verified for consistency with regards to experimental studies, discuss the properties of the whole device and a generic paramagnetic molecule analog (GPMA) connected to the combinations of ferromagnet-ferromagnet, ferromagnet-paramagnet, and ferromagnet-antiferromagnet metal electrodes. We studied the magnetic moment vs. magnetic field of GPMA exchange coupled between two metal electrodes along the exposed side edge of cross junction-shaped magnetic tunnel junction (MTJ). We also studied GPMA-metal electrode interfaces’ magnetic moment vs. magnetic field response. We have also found that the MTJ dimension impacted the molecule response. This study suggests that SMM spin at the MTJ exposed sides offers a unique and high-yield method of connecting molecules to virtually endless magnetic and nonmagnetic electrodes and observing unprecedented phenomena in the molecular spintronics field.

The intra-molecular coupling within multiple units of paramagnetic molecules can produce various effects on molecular spintronics devices (MSD). This paper focuses on double-segmented molecules as the device element to advance understanding of the Impact of internal molecular structure on magnetic tunnel junction-based MSD (MTJMSD). We performed Monte Carlo simulations (MCS) to fill the knowledge gap about the intramolecular coupling role in the magnetic properties of the MTJMSD. This study explored a double-segmented molecule containing two atomic sections, each with a net spin state interacting via Heisenberg exchange coupling within molecules and with ferromagnetic electrodes at different thermal energies, magnetic fields, and coupling strengths. This study also investigated the effect of magnetic field on the double-segmented molecule-based cross-junction-shaped MTJMSD. We also compared the effect of the magnetic field on the mono and double-segmented molecules when connected to two ferromagnetic electrodes. In the strong coupling regime, the intramolecular coupling and molecule coupling with the two ferromagnetic electrodes dominated the MTJMSD response near the molecular junction area. This study provides insight for evaluating the Impact of molecular nanostructure internal connectedness on the integrated MSD.

A new class of molecular spintronic devices can be fabricated by chemically bonding magnetic molecular channels to the electrodes of a prefabricated tunnel junction with exposed side edges. Prior experimental studies showed that the cyanide-bridged octametallic molecular cluster, [(pzTp)FeIII(CN)3]4[NiII(L)]4 not sign [O3SCF3]4 [(pzTp) = tetra(pyrazol-1-yl)borate; L = 1-S(acetyl)tris(pyrazolyl)decane] molecule impact depended on the type of metallic electrodes used in the tunnel junction testbed. Experimental magnetization and transport studies showed a dramatic difference in molecule response on tunnel junctions with different combinations of metallic electrodes. Transport via paramagnetic molecular channels on a tunnel junction involving paramagnetic and ferromagnetic metal electrodes was dramatically different than the suppressed current state observed on tunnel junctions involving two ferromagnetic electrodes. We conducted theoretical studies to understand the experimental data and explore a wide range of electrode materials on tunnel junction-based molecular spintronics devices (TJMSD). Here, we report a Monte Carlo simulation study that focuses on understanding the effect of electrodes on the magnetic and physical properties of TJMSD. A 3D Heisenberg model of cross-junction-shaped TJMSD was used for the simulation study. We studied the effects of ferromagnetic, paramagnetic, and antiferromagnetic electrode materials. This study provides insights for designing and understanding futuristic molecular spintronics devices.

Engineering Research Innovation Commercialization (ERIC) seeks to translate products or services from the research laboratory to the marketplace or the end-user for societal benefit. Research indicates that universities have distinctive capabilities that allow them to play an important role in the process of research innovation commercialization. Historically Black Colleges and Universities (HBCUs), though originally established mainly as teaching and blue-collar trade institutions to educate African Americans, have been gradually commercializing several research innovations through patenting. However, this is significantly lower compared to that of their counterparts (specifically, Predominately White Institutions – PWIs). This according to available research is mainly because HBCUs have been traditionally under-served and under-resourced. Currently several programs such as the National Science Foundation (NSF) I-Corps and National Science Foundation Center of Research Excellence in Science and Technology (NSF-CREST) Center for Nanotechnology Research and Education (CNRE)) are being implemented by HBCUs to promote the commercialization of research innovations by training innovators about commercializing innovations. However, little research has been done to assess the level of awareness of engineering undergraduate students at an HBCU about the commercialization of engineering research innovations. This pilot study, therefore, seeks to investigate the level of awareness of engineering undergraduate students at an HBCU about engineering research innovation commercialization. The authors of this study have conducted a similar study that focused only on engineering graduate students in an HBCU. To achieve the purpose of this study, we developed a survey that adopts both binary and ordinal scales of question and administered it to 30 engineering undergraduate students in an ABET-accredited HBCU. After collation and analysis, the results indicate a low level of awareness of engineering research innovation commercialization by engineering undergraduate students at this University. Though at a pilot stage (to be validated by a larger study in different HBCUs), the study recommends that HBCUs initiate new or strengthen ongoing innovation commercialization training programs by including it in undergraduate engineering first-year courses such as “Introduction to Engineering” and related courses to help students become more aware of the opportunities in engineering research innovation commercialization processes.

The hysteresis loop investigations of different size magnetic tunnel junction molecular spintronics devices (MTJMSD) have been done by Monte Carlo simulation (MCS). We employed a continuous MCS algorithm to investigate single-molecule magnet SMM's spin state's impact as a function of molecular exchange coupling strength. The applied magnetic fields were ramped at a variety of ranges of increments, unfolding physics behind the magnetization nature of each MTJMSD. The magnetic moment changes with applied magnetic fields exhibit the characteristics of devices being studied. The MTJMSDs were studied for ferromagnetic and antiferromagnetic exchange couplings. The magnetic moment saturation, retentivity, coercivity, and permeability are studied.

The hydrogen-based economy is gaining momentum with the advent of fuel cell electric cars and other systems. Hence hydrogen production becomes critically important to meet a supply demand in the near future. One of the cheapest hydrogen generation sources can be solar energy and seawater or water in the lakes and rivers. One can utilize solar energy to provide electricity or energy for the photocatalytic process to split water into hydrogen and oxygen. Under electrolysis, electricity is supplied to provide the energy required for water splitting converting hydrogen ions into hydrogen gas from the aqueous medium. There is a strong need to create innovative electrodes for hydrogen generation that are economical in production and highly efficient. To address this issue, we focused on designing electrodes for photocatalytic electrolysis for hydrogen generation. We used 3D printing to produce different electrodes with various surface features to provide optimum surface area and used electroless nickel to coat the surface of the 3D printed metal components. It is noteworthy that nickel is a promising metal to produce hydrogen economically. We used the Taguchi Design of Experiment approach to optimize the nickel coating on the 3D printed metal electrodes. We used cyclic voltammetry to quantify the volume of H-2 produced by the nickel-coated 3D printed electrodes.

Magnetic tunnel junction-based molecular spintronics devices (MTJMSDs) are designed by covalently connecting the paramagnetic molecules across two ferromagnets (FM) electrodes of a magnetic tunnel junction (MTJ). MTJMSD provides opportunities to connect FM electrodes of a vast range of anisotropy properties to a variety of molecules of length scale. Our prior studies showed that the paramagnetic molecules can produce strong antiferromagnetic coupling with FM electrodes. The device properties of MTJMSD depend upon various factors such as anisotropy, spin fluctuation, thermal energy, etc. In this paper, we report a theoretical Monte Carlo Simulation (MCS) study to explain the impact of anisotropy on the MTJMSD equilibrium properties. We studied the energy variation of the MTJMSD system with time as a function of FM electrode anisotropy. Experimentally designed FM electrodes of MTJMSD contain multi-layers of different ferromagnetic materials. These materials possess in-plane and out-of-plane magnetic anisotropy characteristics. To understand the competing effect of in-plane and out-of-plane anisotropy, we have computationally applied anisotropies on the left FM electrode. For the MCS study, the orientation of the device was kept along YZ plane. As a result, the applied anisotropy along the X-direction (A_Lx) and Y-direction (A_Ly) represent out-of-plane and in-plane anisotropy, respectively. We found that increasing anisotropy strength starts exhibiting diverse domain structures within an FM electrode. Increasing the magnitude of anisotropy was found to create stripe-shaped domains with opposite spins. These domains represent the different magnetic phases. However, the application of equal magnitude of in-plane and out-of-plane cancels the strip domain formation and lowers the magnetic moment of overall MTJMSD.

A promising 3D nanoprinting method, used to deposit nanoscale mesh style objects, is prone to non-linear distortions which limits the complexity and variety of deposit geometries. The method, focused electron beam-induced deposition (FEBID), uses a nanoscale electron probe for continuous dissociation of surface adsorbed precursor molecules which drives highly localized deposition. Three dimensional objects are deposited using a 2D digital scanning pattern-the digital beam speed controls deposition into the third, or out-of-plane dimension. Multiple computer-aided design (CAD) programs exist for FEBID mesh object definition but rely on the definition of nodes and interconnecting linear nanowires. Thus, a method is needed to prevent non-linear/bending nanowires for accurate geometric synthesis. An analytical model is derived based on simulation results, calibrated using real experiments, to ensure linear nanowire deposition to compensate for implicit beam heating that takes place during FEBID. The model subsequently compensates and informs the exposure file containing the pixel-by-pixel scanning instructions, ensuring nanowire linearity by appropriately adjusting the patterning beam speeds. The derivation of the model is presented, based on a critical mass balance revealed by simulations and the strategy used to integrate the physics-based analytical model into an existing 3D nanoprinting CAD program is overviewed.

An artifact limiting the reproduction of three-dimensional (3D) designs using nanoprinting has been quantified. Beam-induced heating was determined through complementary experiments, models, and simulations to affect the deposition rate during the 3D nanoprinting of mesh objects using focused electron beam induced deposition (FEBID). The mesh objects are constructed using interconnected nanowires. During nanowire growth, the beam interaction driving deposition also causes local heating. The temperature at the beam impact region progressively rises as thermal resistance increases with nanowire growth. Heat dissipation resembles the classical mode of heat transfer from extended surfaces; heat must flow through the mesh object to reach the substrate sink. Simulations reveal that beam heating causes an increase in the rate of precursor desorption at the BIR, causing a concomitant decrease in the deposition rate, overwhelming an increase in the deposition rate driven by thermally enhanced precursor surface diffusion. Temperature changes as small as 10 K produce noticeable changes in deposit geometry; nanowires appear to deflect and curve toward the substrate because the vertical growth rate decreases. The 3D FEBID naturally ensues from the substrate surface upward, inducing a vertical temperature gradient along the deposit. Simulations, experiments, temperature-controlled studies, and process current monitoring all confirm the cause of nanowire distortion as beam-induced heating while also revealing the rate-determining physics governing the final deposit shape.

While many plasmonic phenomena have been realized by using standard nanoscale synthesis in a single 2-dimensional plane, enhanced functionality should be possible by extending into the third dimension. Several nanoscale synthesis approaches have been explored to achieve 3-dimensional (3d) geometries; however, a robust strategy for synthesizing complex 3d plasmonic architectures is lacking. In this study, we utilize a hybrid of direct-write 3d nanoprinting and thin film deposition to fabricate 3d plasmonic structures. Focused electron beam induced deposition (FEBID) is used to deposit nonplasmonic 3d scaffolds, which are subsequently isolated with a conformal SiO2 layer and coated with a gold layer to create functional 3d plasmonic nanostructures. A variety of rod antennae, split-ring nanoresonators, and ring resonators are synthesized, and low-loss electron energy loss spectroscopy (EELS) is utilized to characterize their full plasmonic spectra with nanoscale resolution. Complementary EELS simulations are performed to interpret the spectra and elucidate the associated electric and magnetic field distributions of the infrared and near optical modes. This work demonstrates the flexibility that FEBID scaffolds offer for the advancement of 3d plasmonic devices and future advanced optical and magnetic metamaterials.

Currently, there are few techniques that allow true 3D-printing on the nanoscale. The most promising candidate to fill this void is focused electron-beam-induced deposition (FEBID), a resist-free, nanofabrication compatible, direct-write method. The basic working principles of a computer-aided design (CAD) program (3BID) enabling 3D-FEBID is presented and simultaneously released for download. The 3BID capability significantly expands the currently limited toolbox for 3D-nanoprinting, providing access to geometries for optoelectronic, plasmonic, and nanomagnetic applications that were previously unattainable due to the lack of a suitable method for synthesis. The CAD approach supplants trial and error toward more precise/accurate FEBID required for real applications/device prototyping.

Understanding spatial and temporal neuronal activities is crucial for finding the cure for brain related ailments and advancement of our knowledge about the brain itself. This paper discusses our recent finding of the patternable rough textured gold microwire for neurochemical sensing. We have successfully fabricated the ∼5 µm wide and ∼ 60 nm thick gold microwires based electrochemical sensor. We produced these microwires along the edge of lithographically patterned nickel thin film. A nickel thin film edge was shadowed by the photoresist overhang during electrochemical growth only to allowgold deposition along the edges. Our electrochemical growth conditions yielded very rough textured sensor. Rough textured biosensors are highly desirable for increasing surface/volume ratio for efficient electrochemical sensing. These rough-textured microwires were transformed into the functional neurochemical sensor to detect dopamine. Our voltammetry and chronoamperometry studies on rough textured microwires based sensor confirmed the successful detection of dopamine.

Focused ion beam interaction profiles and nanomachining mechanisms are very different for membrane and bulk samples. In this work, a detailed empirical study was carried out to understand these differences by observing the progression of helium ion milling in silicon single crystalline membranes and bulk samples using cross-sectional transmission electron microscopy. The components of backward sputter yield and forward sputter yield unique to the membrane samples were observed, analyzed, and contrasted with the bulk sample sputter yield.

Gallium-based liquid metals are of interest for a variety of applications including flexible electronics, soft robotics, and biomedical devices. Still, nano- to microscale device fabrication with these materials is challenging because, despite having surface tension 10 times higher than water, they strongly adhere to a majority of substrates. This unusually high adhesion is attributed to the formation of a thin oxide shell; however, its role in the adhesion process has not yet been established. In this work, we demonstrate that, dependent on dynamics of formation and resulting morphology of the liquid metal-substrate interface, GaInSn adhesion can occur in two modes. The first mode occurs when the oxide shell is not ruptured as it makes contact with the substrate. Because of the nanoscale topology of the oxide surface, this mode results in minimal adhesion between the liquid metal and most solids, regardless of substrate's surface energy or texture. In the second mode, the formation of the GaInSn-substrate interface involves rupturing of the original oxide skin and formation of a composite interface that includes contact between the substrate and pieces of old oxide, bare liquid metal, and new oxide. We demonstrate that in this latter mode GaInSn adhesion is dominated by the intimate contact between new oxide and substrate. We also show that by varying the pinned contact line length using varied degrees of surface texturing, the adhesion of GaInSn in this mode can be either decreased or increased. Lastly, we demonstrate how these two adhesion modes limit microcontact printing of GaInSn patterns but can be exploited to repeatedly print individual sub-200 nm liquid metal drops.

Data associated to this publication. It includes original SEM images, text, excel and Matlab files for experiments and fits.