Single Atomic Layer Research Articles

An automatic multi-precursor flow-type atomic layer deposition system

Designs for two automated atomic layer deposition (ALD) flow reactors are presented, and their capabilities for coating additively manufactured (AM) metal prints are described. One instrument allows the coating of several AM parts in batches, while the other is useful for single part experiments. To demonstrate reactor capabilities, alumina (Al2O3) was deposited onto AM 316L stainless steel by dosing with water (H2O) vapor and trimethylaluminum (TMA) and purging with nitrogen gas (N2). Both instruments are controlled by custom-programmed LabVIEW software that enables in situ logging of temperature, total pressure, and film thickness using a quartz crystal microbalance. An initial result shows that 150 ALD cycles led to a film thickness of ∼55 nm, which was verified with Rutherford backscattering spectroscopy. This indicates that the reactors were indeed depositing single atomic layers of Al2O3 per ALD cycle, as intended.

Conductive Nanocomposites Based on Graphene and Natural Polymers

This thesis focuses on the development of conductive nanocomposite materials based on graphene and natural polymers such as cellulose and chitosan. Graphene, a single layer of carbon atoms arranged in a honeycomb lattice, exhibits exceptional electrical, mechanical, and thermal properties, making it an attractive filler for polymer composites. However, the challenge lies in effectively dispersing graphene sheets within polymer matrices. The work presented explores new strategies for grafting polysaccharide chains onto oxidized graphite (graphene oxide) to improve its compatibility and dispersion in cellulose and chitosan matrices. The resulting composites were doped with gold or nickel nanoparticles to further enhance their electrical and catalytic properties. Detailed characterization techniques, including spectroscopic and microscopic methods, were employed to analyze the structure, morphology, and properties of the developed nanocomposites. The thesis is organized into three main parts: 1) a literature review on graphene, polysaccharides, and their biocomposites; 2) a description of the experimental materials and methods; and 3) a scientific discussion of the results, presented in the form of three research publications. The findings demonstrate the successful synthesis of conductive nanocomposites with improved compatibility and performance, opening up new avenues for the application of these sustainable and multifunctional materials in areas such as electronics, catalysis, and electromagnetic shielding.

Coexistence of ferroelectricity and antiferroelectricity in 2D van der Waals multiferroic

Multiferroic materials have been intensively pursued to achieve the mutual control of electric and magnetic properties. The breakthrough progress in 2D magnets and ferroelectrics encourages the exploration of low-dimensional multiferroics, which holds the promise of understanding inscrutable magnetoelectric coupling and inventing advanced spintronic devices. However, confirming ferroelectricity with optical techniques is challenging in 2D materials, particularly in conjunction with antiferromagnetic orders in single- and few-layer multiferroics. Here, we report the discovery of 2D vdW multiferroic with out-of-plane ferroelectric polarization in trilayer NiI2 device, as revealed by scanning reflective magnetic circular dichroism microscopy and ferroelectric hysteresis loops. The evolution between ferroelectric and antiferroelectric phases has been unambiguously observed. Moreover, the magnetoelectric interaction is directly probed by magnetic control of the multiferroic domain switching. This work opens up opportunities for exploring multiferroic orders and multiferroic physics at the limit of single or few atomic layers, and for creating advanced magnetoelectronic devices.

Single Layer Control of Nanoscale Metal-Insulator Transition at the LaAlO3/SrTiO3 Interface.

Modern quantum device fabrication often requires precisely adding and removing materials in situ at nanoscales, which is challenging for high-quality correlated oxide devices. In this work, we present a novel nanofabrication method that remotely controls the interfacial metal-insulator transition at the LaAlO3/SrTiO3 interface by selectively removing an LaAlO3 overlayer using a diamond tip. Remarkably, we observe a large force window within which single atomic layer precision of control is achievable. Our results confirm the critical thickness and charge transfer mechanism through a layer-by-layer removal process at the interface. Additionally, high-quality nanodevices, including nanochannels and single electron transistors, are successfully fabricated using this method. This nonvolatile and high-precision nanofabrication method provides a promising oxide platform for quantum engineering by harnessing the rich electron correlations at the nanoscale.

An innovative approach to control the Hf/Ti ratio in monolayers grown via atomic partial layer deposition

The Hf/Ti ratio was precisely controlled at monolayer thickness using atomic partial layer deposition (APLD). HfxTi1−xO2 films with varying Hf concentrations were deposited by adjusting the pulse time of Hf precursors within a single atomic layer. Characterization using x-ray reflectivity, x-ray photoelectron spectroscopy, and spectroscopic ellipsometry confirmed the presence of Hf, Ti, and O in the films. Increasing the Hf content caused the binding energies of the O 1s peak to shift to higher values, indicating a chemical environment change from TiO2-like to HfO2-like. A higher Hf content also increased the relative atomic percentages of Hf, Ti, and O, altering the film properties. The mass density and optical properties were notably sensitive to changes in the Hf/Ti ratio at monolayer thickness. The potential of APLD to reduce dimensionality through precise control of both thickness and composition renders it especially appropriate for applications requiring highly specific material properties.

2D Carbonaceous Materials for Molecular Transport and Functional Interfaces: Simulations and Insights.

ConspectusCarbon-based two-dimensional (2D) functional materials exhibit potential across a wide spectrum of applications from chemical separations to catalysis and energy storage and conversion. In this Account, we focus on recent advances in the manipulation of 2D carbonaceous materials and their composites through computational design and simulations to address how the precise control over material structure at the atomic level correlates with enhanced functional properties such as gas permeation, selectivity, membrane transport, and charge storage. We highlight several key concepts in the computational design and tuning of 2D structures, such as controlled stacking, ion gating, interlayer pillaring, and heterostructure charge transfer.The process of creating and adjusting pores within graphene sheets is vital for effective molecular separation. Simulations show the power of controlling the offset distance between layers of porous graphene in precisely regulating the pore size to enhance gas separation and entropic selectivity. This strategy of controlled stacking extends beyond graphene to include covalent organic frameworks (COFs) such as covalent triazine frameworks (CTFs). Experimental assembly of the layers has been achieved through electrostatic interactions, thermal transformation, and control of side chain interactions.Graphene can interface with ionic liquids in various forms to enhance its functionality. A computational proof-of-concept showcases an ion-gating concept in which the interaction of anions with the pores in graphene allows the anions to dynamically gate the pores for selective gas transport. Realization of the concept has been achieved in both porous graphene and carbon molecular sieve membranes. Ionic liquids can also intercalate between graphene layers to form interlayer pillaring structures, opening the slit space. Grand canonical Monte Carlo simulations show that these structures can be used for efficient gas capture and separation. Experiments have demonstrated that the interlayer space can be tuned by the density of the pillars and that, when fully filled with ionic liquids and forming a confined interface structure, the graphene oxide membrane achieves much higher selectivity for gas separations. Moreover, graphene can interface with other 2D materials to form heterostructures where interfacial charge transfers take place and impact the function. Both ion transport and charge storage are influenced by both the local electric field and chemical interactions.Fullerene can be used as a building block and covalently linked together to construct a new type of 2D carbon material beyond a one-atom-thin layer that also has long-range-ordered subnanometer pores. The interstitial sites among fullerenes form funnel-shaped pores of 2.0-3.3 Å depending on the crystalline phase. The quasi-tetragonal phases are shown by molecular dynamics simulations to be efficient for H2 separation. In addition, defects such as fullerene vacancies can be introduced to create larger pores for the separation of organic solvents.In conclusion, the key to imputing functions to 2D carbonaceous materials is to create new interactions and interfaces and to go beyond a single-atom layer. First-principles and molecular simulations can further guide the discovery of new 2D carbonaceous materials and interfaces and provide atomistic insights into their functions.

Ultra‐Thin Metal Oxide Superstructure of Pd(001) as Passivation Interlayer at Organic/Metal Interface

AbstractAt organic molecule/metal interfaces for electronic applications, it is required of the metal surface to be passivated in view of preserving the molecular properties of the ordered organic layer. This can be achieved by screening the metal with a single atomic layer of O, namely, ultra‐thin metal oxide (UTMO) layers. Cobalt tetraphenylporphyrins (CoTPP) on oxygen passivated Fe(001), with 1 ML O coverage, have revealed a molecule/substrate decoupling effect due to the formation of an ultra‐thin Fe oxide layer at the interface. However, the threshold concentration of surface O required to observe the decoupling effect has not been assessed yet. In this work, the possibility of stabilizing different ultra‐thin Pd oxide superstructures, characterized by a different number of O atoms per unit cell, is exploited to investigate the O decoupling effect on CoTPP films. Two Pd oxide superstructures are considered: Pd(001)‐p(2 × 2)O and Pd(001)‐p(√5 × √5)R27°O, with 0.25 and 0.80 ML O coverages, respectively, which are characterized by low‐energy electron diffraction (LEED), X‐ray and ultra‐violet photoelectron spectroscopies (XPS/UPS) and inverse photoemission spectroscopy (IPES). The results suggest a lower limit of 0.80 ML O coverage as a passivation interlayer to obtain an ordered and decoupled CoTPP monolayer on Pd(001).

Growing highly ordered Pt and Mn bimetallic single atomic layers over graphdiyne

Controlling the precise growth of atoms is necessary to achieve manipulation of atomic composition and atomic position, regulation of electronic structure, and an understanding of reactions at the atomic level. Herein, we report a facile method for ordered anchoring of zero-valent platinum and manganese atoms with single-atom thickness on graphdiyne under mild conditions. Due to strong and incomplete charge transfer between graphdiyne and metal atoms, the formation of metal clusters and nanoparticles can be inhibited. The size, composition and structure of the bimetallic nanoplates are precisely controlled by the natural structure-limiting effect of graphdiyne. Experimental characterization clearly demonstrates such a fine control process. Electrochemical measurements show that the active site of platinum-manganese interface on graphdiyne guarantees the high catalytic activity and selectivity (~100%) for alkene-to-diol conversion. This work lays a solid foundation for obtaining high-performance nanomaterials by the atomic engineering of active site.

(Invited) Developing a Graphene Field-Effect Biosensor for Genetic Biomarkers: Simulations Unveil How the Device Sensitivity Is Related to DNA-Graphene Interactions at the Nanoscale

Graphene field-effect transistor biosensors (GFETs) offer a promising platform to detect cancer DNA biomarkers at low concentration [1]. At their core, they have an electronic circuit containing a graphene sheet – a two-dimensional nanomaterial made of a single layer of carbon atoms – whose electronic properties are very sensitive to nearby electric charges. Leveraging that feature, the electrical current generated by a GFET can thus be made very sensitive to the concentration of a specific DNA sequence in a biological sample. To achieve this, the complementary DNA sequence is linked to the graphene to bind specifically the target DNA. In most GFETs, the link is done using 1-pyrenebutanoic acid succinimidyl ester (PBASE) because its pyrene group stacks on the graphene through pi-pi interactions, without disrupting the electronic properties of the graphene. However, recent experiments in the Bouilly group have shown variations in GFET sensitivity depending on the incubation time of graphene with PBASE.Here, we use a computational approach developed in our previous work [2] to investigate at the nanoscale the role of PBASE linker molecules on the sensitivity of the GFET. First, we use molecular dynamics simulations to characterize the conformational ensemble of a 10-nt single-stranded DNA sequence linked to a graphene sheet using PBASE. Second, we estimate the electrical response of the GFET from the electrostatic potential generated by these DNA conformations on the graphene, as determined using electrostatic Poisson-Boltzmann simulations. Our results show that the conformational ensemble of DNA is strongly affected by the presence of other PBASE adsorbed on the graphene, thus changing the electrostatic potential generated on the graphene. The predicted change of the electrostatic potential should impact measurably the detection signal of the GFET.We are now using these simulations to explain the experimental characterizations of a GFET designed to detect a genetic biomarker important in breast cancer profiling. Our simulations have the potential to support the development of GFETs with better sensitivity for DNA detection.[1] Béraud, A., Sauvage, M., Bazán, C. M., Tie, M., Bencherif, A., and Bouilly, D. (2021) Graphene field-effect transistors as bioanalytical sensors: design, operation and performance. Analyst. 146:403-428.[2] Côté, S., Mousseau, N., and Bouilly, D. (2022) The molecular origin of the electrostatic gating of single-molecule field-effect biosensors investigated by molecular dynamics simulations. Phys. Chem. Chem. Phys. 24:4174-4186.

Robust structural superlubricity under gigapascal pressures

Structural superlubricity (SSL) is a state of contact with no wear and ultralow friction. SSL has been characterized at contact with van der Waals (vdW) layered materials, while its stability under extreme loading conditions has not been assessed. By designing both self-mated and non-self-mated vdW contacts with materials chosen for their high strengths, we report outstanding robustness of SSL under very high pressures in experiments. The incommensurate self-mated vdW contact between graphite interfaces can maintain the state of SSL under a pressure no lower than 9.45 GPa, and the non-self-mated vdW contact between a tungsten tip and graphite substrate remains stable up to 3.74 GPa. Beyond this critical pressure, wear is activated, signaling the breakdown of vdW contacts and SSL. This unexpectedly strong pressure-resistance and wear-free feature of SSL breaks down the picture of progressive wear. Atomistic simulations show that lattice destruction at the vdW contact by pressure-assisted bonding triggers wear through shear-induced tearing of the single-atomic layers. The correlation between the breakdown pressure and material properties shows that the bulk modulus and the first ionization energy are the most relevant factors, indicating the combined structural and electronic effects. Impressively, the breakdown pressures defined by the SSL interface could even exceed the strength of materials in contact, demonstrating the robustness of SSL. These findings offer a fundamental understanding of wear at the vdW contacts and guide the design of SSL-enabled applications.

A Narrative Review on the Promising Potential of Graphene in Vaccine Design: Evaluating the Benefits and Drawbacks of Carbon Nanoplates in Nanovaccine Production.

Graphene, a two-dimensional material consisting of a single layer of carbon atoms arranged in a honeycomb lattice, has shown great potential in various fields, including biomedicine. When it comes to vaccine development, graphene can offer several advantages due to its unique properties. Potential applications of graphene in vaccine development include improved vaccine delivery, adjuvant properties, improved vaccine stability, improved immune response, and biosensing capabilities. Although graphene offers many potential benefits in vaccine development, there are also some drawbacks and challenges associated with its use. Although graphene shows promising potential for vaccine development, overcoming the challenges and limitations associated with its use is critical to realizing its full potential in the field of immunization. Further research and development efforts are needed to overcome these drawbacks and take advantage of graphene for improved vaccine formulations. In this review, we focus on the advantages and disadvantages of graphene for vaccine development.

Synthesis of goldene comprising single-atom layer gold

The synthesis of monolayer gold has so far been limited to free-standing several-atoms-thick layers, or monolayers confined on or inside templates. Here we report the exfoliation of single-atom-thick gold achieved through wet-chemically etching away Ti3C2 from nanolaminated Ti3AuC2, initially formed by substituting Si in Ti3SiC2 with Au. Ti3SiC2 is a renown MAX phase, where M is a transition metal, A is a group A element, and X is C or N. Our developed synthetic route is by a facile, scalable and hydrofluoric acid-free method. The two-dimensional layers are termed goldene. Goldene layers with roughly 9% lattice contraction compared to bulk gold are observed by electron microscopy. While ab initio molecular dynamics simulations show that two-dimensional goldene is inherently stable, experiments show some curling and agglomeration, which can be mitigated by surfactants. X-ray photoelectron spectroscopy reveals an Au 4f binding energy increase of 0.88 eV. Prospects for preparing goldene from other non-van der Waals Au-intercalated phases, including developing etching schemes, are presented.

Enhancing Heat Exchangers with Graphene as Al2O3 Nanofluid Coatings

A well-designed heat exchanger improves the effectiveness of the heat exchanger. A hairpin heat exchanger resembles a hairpin when a shell-and-tube heat exchanger with a single-pass unit is folded in half, which can be used where space is a constraint. Design, CFD analysis and evaluation of various parameters of hairpin heat exchanger with graphene layer and its comparison with hairpin heat exchanger without graphene layer is the main aim of this paper. The heat exchanger is modified with the addition of a graphene layer on both the side (inner and outer side) of the tube of the heat exchanger. Graphene is an allotropic form of carbon having a single layer of atoms distributed in a 2-D honeycomb lattice. The coefficient of thermal conductivity of graphene is very high as compared to other materials. In addition to it, nanofluid Al2O3 is introduced as cold fluid. Nanofluids are colloidal suspensions made of nanoparticles in some base fluid. ANSYS FLUENT 2020 has been used to model the geometry and to perform numerical simulation. Turbulent flow conditions were used to analyse the heat exchanger. CFD analysis has been done on hairpin heat exchangers using graphene layer. The results indicate that the high thermal conductivity of graphene increases rate of heat transfer, and the numerical value of convective heat transfer coefficient is also high.

Annealing temperature dependence of magnetic properties in FeCo ordered alloy thin films fabricated using the nitrogen surfactant effect

L10-FeCo has attracted attention as a new, rare-metal-free magnetic material due to its large uniaxial magnetic anisotropy. However, the low stability of the L10 phase hampers its practical application. We here intend to prepare FeCo alloy thin films by utilizing the nitrogen surfactant effect. The enhancement of the out-of-plane magnetization of this thin film was observed by stacking cobalt single atomic layer on bilayer iron nitride and subsequent annealing at 470 K. This study provides an insight into the relationship between structural changes and magnetic properties of the FeCo interface on the atomic scale, and paves the way for the development of rare metal-free magnetic materials.

In situ differential atomic force microscopy (AFM) measurement for ultra-thin Thiol SAM patterns by area-selective deposition technique

Developing novel characterization methods is crucial to enhancing the accuracy and precision of measurements in semiconductor ultrathin films. By combining "bottom-up" and "top-down" patterning techniques, we successfully fabricated five uniform alkyl thiol-derived self-assembled monolayer (SAM) patterns. Employing the innovative in situ differential Atomic Force Microscopy (AFM) Measurement, we analyzed the thickness, morphology, and mechanical properties of the thiol films. This method greatly reduced errors caused by uneven substrates, resulting in more precise measurements compared to large-area measurements. It is shown that as the thiol chain length increased, the variation in SAM film thickness aligned consistently with the thickness of a single Atomic Layer Deposition (ALD) cycle, and the surface roughness of the SAM surface mirrored that of ALD. Consequently, the experiment affirms the effectiveness of the SAM film in simulating ALD, providing validation for the precision and feasibility of the in situ differential results. Furthermore, adhesion measurement results revealed a diminishing passivation effect of SAM as the chain length increased. This suggests that an appropriate SAM could be selected as a passivation material through real-time monitoring of the mechanical properties of the mask surface during the Area-Selective Deposition (ASD) process.

Optimizing Atomic Layer Deposition Processes with Nanowire‐Assisted TEM Analysis

AbstractAtomic layer deposition (ALD) is one of the premier methods to synthesize ultra‐thin materials on complex surfaces. The technique allows for precise control of the thickness down to single atomic layers, while at the same time providing uniform coverage even for structures with extreme aspect ratios such as deep trenches or wires. While many materials can be readily deposited using ALD there is still a lot of research going on to make other materials more accessible. When establishing a new process or adapting an existing process to a new reactor, precise optimization of the deposition parameters is necessary. However, characterizing the parameters of deposition rate, uniformity, composition, and structure is a challenging and time‐consuming task. Here a method is presented to optimize these process parameters during ALD deposition using high‐aspect ratio nanowires and transmission electron microscopy (TEM). Nanowire samples are prepared directly on TEM grids that are put into the ALD reactor during deposition. Within min of the process the coated nanowires can be analyzed by TEM to obtain the thickness of the layers, chemical composition, crystallinity, and conformality of the coating. This allows for a high testing throughput and subsequently a rapid optimization of deposition parameters.

The quest for harnessing nuclear effects in graphene-based devices

The recent successes of superconducting qubits and the demonstration of quantum supremacy over classical bits herald a new era for information processing. Yet, the field is still in its infancy and there exist viable alternative candidates that can also store quantum information. In this review, we will highlight ideas, attempts, and the experimental progress to address nuclear spins in graphene, a readily available Dirac semimetal that consists of a single layer of carbon atoms. Carbon isotopes with a nuclear spin are rare in natural graphene. However, it is possible to enrich the spin-bearing 13C isotopes to produce large-scale graphene sheets, which constitute the testbed to store, transport, and retrieve spin information, or to engineer nanostructures. Here, the hyperfine interaction between the electron spins and the nuclear spins serves as an experimental control knob and mediator to address nuclear polarization and nuclear spin coherence times through electrical measurements. The exploitation of nuclear spins in graphene is thus an alluring perspective. We will discuss methods to synthesize 13C graphene and show experimental approaches and challenges to exploit the relatively weak hyperfine interaction in two-dimensional 13C graphene devices. The ultimate purpose, i.e., the exploitation of nuclear spins in graphene for information processing, is not within reach, but its potential for future applications merits a revisit of the current state-of-the-art.

In situ doping effect in monolayer MoS2 via laser irradiation

Abstract Two-dimensional (2D) semiconducting materials with a single atomic layer display exceptional structural symmetry and band structures, making them the most promising candidates for investigating the spin-valley coupling effect and fabricating novel optoelectronic devices. Their atomic thinness also makes it easy to adjust their excitonic optical response through plasma treatment or thermal annealing. In this study, we present a simple technique for modifying the optical properties of monolayer MoS2 by briefly exposing it to laser irradiation in ambient conditions. Initially, this exposure resulted in a nearly twofold increase in photoluminescence (PL) intensity, with the neutral exciton intensity increasing while the trion exciton intensity decreased. We propose that oxygen-related functional groups, such as O2 and H2O from the surrounding air, adsorb onto MoS2 and extract extra electrons, which enhances exciton emission while reducing trion emission. In a subsequent stage, both exciton intensities decreased as all extra electrons were depleted. Additionally, any structural distortions or potential damage were found to decrease the PL intensity, and these changes were linked to alterations in the Raman spectra.

Unveiling the contemporary progress of graphene-based nanomaterials with a particular focus on the removal of contaminants from water: a comprehensive review.

Water scarcity and pollution pose significant challenges to global environmental sustainability and public health. As these concerns intensify, the quest for innovative and efficient water treatment technologies becomes paramount. In recent years, graphene-based nanomaterials have emerged as frontrunners in this pursuit, showcasing exceptional properties that hold immense promise for addressing water contamination issues. Graphene, a single layer of carbon atoms arranged in a hexagonal lattice, exhibits extraordinary mechanical, electrical, and chemical properties. These inherent characteristics have led to a surge of interest in leveraging graphene derivatives, such as graphene oxide (GO), reduced graphene oxide and functionalized graphene, for water treatment applications. The ability of graphene-based nanomaterials to adsorb, catalyze, and photocatalyze contaminants makes them highly versatile in addressing diverse pollutants present in water sources. This review will delve into the synthesis methods employed for graphene-based nanomaterials and explore the structural modifications and functionalization strategies implemented to increase their pollutant removal performance in water treatment. By offering a critical analysis of existing literature and highlighting recent innovations, it will guide future research toward the rational design and optimization of graphene-based nanomaterials for water decontamination. The exploration of interdisciplinary approaches and cutting-edge technologies underscores the evolving landscape of graphene-based water treatment, fostering a path toward sustainable and scalable solutions. Overall, the authors believe that this review will serve as a valuable resource for researchers, engineers, and policymakers working toward sustainable and effective solutions for water purification.

Graphene's Potential in Electronic Devices: Characteristics, Applications, Challenges, And Solutions

This comprehensive overview explores the multifaceted world of graphene, a two-dimensional crystal structure composed of a single layer of carbon atoms, and its applications in electronic devices. The discussion begins with an introduction highlighting the remarkable potential of graphene in the field of electronics. Section 2 delves into the basic characteristics of graphene, including its atomic structure, excellent electronic properties, optical and thermal attributes, high conductivity, and mobility, as well as its mechanical strength and flexibility. It also briefly outlines the fundamental methods of graphene preparation. Section 3 delves into the application of graphene in electronic devices, covering topics such as graphene's role in Field Effect Transistors (FETs), including carrier control characteristics and the basic principles of FETs. Additionally, it explores the prospects of graphene in FET technology, its application in flexible electronic devices, and its integration into optoelectronic devices. Section 4 addresses the dilemmas and solutions faced by graphene electronic devices, such as issues related to the preparation process and stability, the impact of defects and impurities, and current solutions to overcome these challenges. Finally, the conclusion underscores the immense potential of graphene in revolutionizing electronic devices while recognizing the ongoing efforts for future innovations in this field.