Atomic Dimensions Research Articles

Física quântica e misticismo no ensino de ciências

A Física Quântica surgiu em 1900 na tentativa de explicar uma série de fenômenos que a Física Clássica não era capaz. Sua consolidação se deu na década de 1920 enquanto área de conhecimento na tentativa de explicar o funcionamento das coisas ao nível das dimensões dos átomos e partículas subatômicas. Com intuito de fazer um contraponto entre os pontos de vista científico e filosófico-religioso, da mecânica, coloca-se em evidência as interpretações de viés acadêmico e espiritual de modo a explicitar aos leigos, através de uma linguagem acessível, os fatos científicos e as versões desses fatos. Como objetivo específico, adotou-se a análise e aplicabilidade da mecânica quântica nos mais diversos contextos ao longo da história, assim como a deturpação das ideias e da utilização dos termos científicos. Percebe-se que com os resultados desta pesquisa que a tentativa de se fazer uma ligação entre a mecânica e a espiritualidade não tem validade científica. Com o estudo das revisões bibliográficas, conclui-se que o conhecimento científico é fundamental para o desenvolvimento do senso crítico, e consequentemente para o crescimento humano em diversos aspectos e perspectivas de conhecer e interpretar o mundo não apenas em seus aspectos físicos, mas também em filosofia, sociologia e demais campos que propõe uma maior reflexão. Através dos conceitos estruturantes desta área, poderemos entender melhor alguns aspectos do que trata a Física Quântica, sendo uma proposta interessante para percebermos evolução histórica dos conceitos e concepções que podem ser encontradas nas mais diversas épocas, desde a antiguidade até os tempos modernos.

Bose-Hubbard physics in synthetic dimensions from interaction Trotterization

Activating transitions between a set of atomic internal states has emerged as an elegant scheme by which lattice models can be designed in ultracold atomic gases. In this approach, the internal states can be viewed as fictitious lattice sites defined along a synthetic dimension, hence offering a powerful method by which the spatial dimensionality of the system can be extended. Inter-particle collisions generically lead to infinite-range interactions along the synthetic dimensions, which a priori precludes the design of Bose-Hubbard-type models featuring on-site interactions. In this article, we solve this obstacle by introducing a protocol that realizes strong and tunable "on-site" interactions along an atomic synthetic dimension. Our scheme is based on pulsing strong intra-spin interactions in a fast and periodic manner, hence realizing the desired "on-site" interactions in a digital (Trotterized) manner. We explore the viability of this protocol by means of numerical calculations, which we perform on various examples that are relevant to ultracold-atom experiments. This general method, which could be applied to various atomic species by means of fast-response protocols based on Fano-Feshbach resonances, opens the route for the exploration of strongly-correlated matter in synthetic dimensions.

Structure-Controlled Perovskite Thin Layer Formation on Au Single-Crystal Substrate via Self-Assembled Monolayer of 4-Aminothiophenol

1. IntroductionIn order to solve recent energy and environmental problems, construction of a photoelectric conversion device using a perovskite structure has recently attracted much attention because perovskite structure absorbs visible light very much [1]. In this type of photoelectric conversion device, it is necessary to construct on a solid substrate while maintaining the perovskite structure. In order to improve efficiency, moreover, it is important to control the interfacial structure between the solid substrate and the perovskite film by an atomic dimension. In the present study, we tried to construct a perovskite layer on a Au(100) single-crystal substrate while maintaining the perovskite structure completely and control the interfacial structure between the substrate and the perovskite layer by using a self-assembled monolayer (SAM) of 4-aminothiophenol (4-ATP) by an atomic level.2. ExperimentalAu(100) single-crystal as a substrate and 4-ATP having an amino terminal group as a SAM molecule were chosen. After annealed and quenched the Au(100) substrate, it was immersed in the hexane solution containing 1 mM 4-ATP for 3 hours at room temperature (RT). Then, the 4-ATP SAM modified Au(100) substrate was sequentially immersed in each DMF solution containing 1 mM PbBr2 and 1 mM MABr for 24 hours for 3 cycles, followed by heating at 135 °C, and then MAPbBr3 perovskite thin films were constructed on 4-ATP SAM modified Au(100) surface [2]. The structure and composition of 4-ATP SAM modified Au(100) substrate after immersion in each solution were evaluated by X-ray photoelectron spectroscopy (XPS) and the crystal structure of the constructed perovskite thin film was evaluated by surface x-ray diffraction (SXRD) as compared with XRD of the corresponding perovskite crystal.3. Results & Discussion Figure 1 shows the SXRD profile of the perovskite thin film and the XRD profile of the perovskite crystal. In the SXRD profile, only the (0kl) reflections such as (002) and (012) of the perovskite crystal, which was indicated by triangles in Fig. 1(a), and no diffraction peaks of the (hkl) (h is not zero) reflections such as (112) and (122), which was indicated by stars in Fig. 1(b), were observed. Based on these results, it is indicated that the constructed perovskite thin film was grown along the [100] direction, and we can conclude that it is succeeded to construct the structure-controlled perovskite thin film on the Au(100) surface.

(Invited) Spatial ALD Challenges and Opportunities in Advanced Integrated Circuit Manufacturing

Miniaturization in Integrated Circuit fabrication has scaled to atomic dimensions in recent times. With critical device dimensions moving into the range of ~10nm, atomic layer processing control is becoming essential. Atomic Layer Deposition (ALD) uses separated film components at (or near) self-limiting conditions for atomic level uniformity and thickness control. The unique nature of ALD processing has opened the opportunity for a deposition technique that presents deposition components in a spatially separated method compared to sequential component exposure of traditional systems. Spatial ALD has differentiating characteristics that can benefit IC Fabrication at current fabrication dimensions. Historically, deposition systems for IC fabrication use batch furnace or single wafer configurations. The economic benefit of batch furnace processing has been challenged by the enhanced capabilities of single wafer processing as IC scaling emphasized critical film properties and uniformity. ALD processing has rejuvenated batch furnace benefits since separate exposures of deposition components provides excellent uniformity from self-limiting deposition layers, and lower particle defectivity since the components don’t mix. However, the sequential processing of individual components has strained the efficiencies of batch furnace and single wafer ALD processing. Spatial ALD moves substrates (wafers) through each deposition component separately in space, compared to the time sequential processing of batch furnaces and single wafer processing. There are several advantages to Spatial ALD processing, and several unique capabilities that can apply to IC fabrication. By depositing through movement, the deposition components can be maintained through a steady state, which is advantageous for plasma processing and for limiting peripheral equipment film accumulation. By its nature, the deposition rate of Spatial ALD is controlled by the speed of substrates passing through the deposition zones, which can provide unique controls for deposition. Deposition chemistry and process conditions can be designed to take advantage of Spatial ALD properties for unique benefits in IC fabrication. The presentation will explore some fundamental aspects of Spatial ALD processing, the dependency and opportunities of relevant chemistries, and potential applications for the unique capabilities of Spatial ALD, including unsaturated process conditions.

Atomic imprinting in the absence of an intrinsic length scale

Bulk metallic glasses (BMGs) have successfully been used to replicate molds that are structured at the nano- and even atomic scale through thermoplastic forming (TPF), an ability that was speculated to be rooted in the glass’ featureless atomic structure. These previous demonstrations of atomically precise imprinting, however, were performed under conditions where mold atomic feature dimensions coincided with the unit cell size of constituents in the BMG. In order to evaluate if accurate atomic-scale replication is possible in general, i.e., independent of the accidental presence of favorable constituent size/feature size relationships, we have used Pt57.5Cu14.7Ni5.3P22.5 to replicate three different crystalline facets of LaAlO3 single crystals, each exposing distinct atomic step heights. We find that in all cases, the terraced surface termination can be copied with remarkable fidelity, corroborating that BMGs when thermoplastic formed are capable of adapting to any externally imposed confinement with sub-angstrom precision without being limited by factors related to the specifics of their internal structure. This unprecedented capability of quasi-limitless replication fidelity reveals that the deformation mechanism in the supercooled liquid state of BMGs is essentially homogeneous and suggests TPF of BMGs to be a versatile toolbox for atomic and precision nanoscale imprinting.

Theoretical Study on the Compounds of Chlorine Fluoride (ClF3, ClOF3) and Superhalogens (BeF2, MgF2): Preferred Structures and Significant Nonlinear Optical Properties

A new class of chlorine fluoride-superhalogen compounds, ClF3(O)–MF2, (M = Be, Mg) are theoretically studied using density functional theory (DFT). The results show that the interaction between ClF3(O) and MF2 is strong and exist in ionic form. Bond energies of these compounds are in the range of 143.23 to 161.40 kcal mol–1 at the level of B3LYP/6-311++G(d, p), which are larger than the traditional ionic bond energy of 130.1 kcal mol–1 for LiF. The energy gaps between the highest occupied and lowest unoccupied molecular orbitals are large thus they are stable at the normal temperature and pressure. Furthermore, because of their delocalized electron character, these species exhibit extraordinarily large first hyperpolarizabilities with α0 ranging from 45.26 to 55.15 a.u. The present investigation provides hints to scientists in extending the research in atomic dimension to direct the interaction between superatoms, and using superatoms as building blocks to synthesize novel meaningful materials with unusual performences such as nonlinear optical materials.

Construction of Structure-Controlled Perovskite Ultra-Thin Layers on Au(100) Single-Crystal Surface via Self-Assembled Monolayer of 4-Aminothiophenol

Abstract In order to control a crystal configuration of MAPbBr3 (MA = CH3NH3+) perovskite ultra-thin layers, the Au(100) single-crystal, the self-assembled monolayer (SAM) of 4-aminothiophenol (4-ATP), and the layer-by-layer alternating immersion were employed as a substrate, a linker between the perovskite thin layer and gold substrate, and a preparation method, respectively. Structure and crystal configuration of the constructed MAPbBr3 perovskite ultra-thin layers on 4-ATP SAM modified Au(100) were investigated by X-ray photoelectron spectroscopy (XPS), scanning tunneling microscopy (STM), and grazing incidence surface X-ray diffraction (GISXRD). As a result, we succeeded to construct the structure-controlled MAPbBr3 perovskite ultra-thin layers on the 4-ATP SAM modified Au(100) surface with an atomic dimension.

Conductance quantization in atomic-sized gold contacts using a low-cost mechanically controllable break junction setup

The mechanically controllable break junction (MCBJ) experimental setup is one of the main techniques employed in the study of electronic transport properties at the atomic and molecular scales. This work presents the construction of an inexpensive and simple but robust setup that shows the emergence of conductance quantization as a macroscopic gold wire is pulled to atomic dimensions. The homemade device is based on the MCBJ principle and allows repeatedly forming and breaking the metallic contact to perform a statistical analysis of the data extracting the most frequent electron transport structure. The histogram built from conductance measurements, at room temperature in air, show that the quality of the MCBJ equipment developed here is comparable to that of more sophisticated devices used in research laboratories. It is able to resolve up to three conductance peaks associated with gold nanowires reported in the literature. Such an experiment is suggested to be implemented as a powerful pedagogical tool in modern undergraduate physics labs.

Near-Room-Temperature Soft Plasma Pulsed Deposition of SiCxNy from 1,3,5-tri(isopropyl)cyclotrisilazane

The silicon-nitrogen material system, primarily in the form of silicon nitride (SiNx) and silicon silicon carbo-nitride (SiNxCy) (where 0<x<1.33 and 0<y<1) continues to witness tremendous research and development interest. This interest is driven by its highly desirable combination of physical, mechanical, electrical, and optoelectronic properties, making it one of the most useful materials in integrated circuitry (IC) applications. However, the drive towards more complex and smaller IC and hetero-device structures is significantly challenging established SiNx deposition methodologies. Low thermal exposure during fabrication of the device structures is becoming essential due to the complexity and thermally fragile nature of these structures, where temperature changes can induce undesirable reactions within substructures. Furthermore, with the thickness of films approaching atomic dimensions, thermally-induced migration, in addition to electromigration, can significantly alter film properties and performance. Another consideration is the desire to move towards more flexible substrates, such as plastic or polymer substrates, which typically cannot withstand the same process temperatures as traditional substrates, such as Si or GaN. Given these emerging thermal budget limitations, work by the present investigators has focused on the development and optimization of a remote plasma-activated ALD and/or pulsed CVD process for SiNxCy at exceptionally low temperatures as protective coatings on thermally and chemically fragile substrates such as polymers and plastics. In this presentation, results are presented for low temperature remote plasma-activated pulsed CVD (P-CVD) SiNxCy using 1,3,5-triisopropylcyclotrisilazane (C9H27Si3N3, TICZ) as source precursor. This presentation will provide the following: (i) the process window for deposition of SiNxCy through the P-CVD decomposition of TICZ as a single-source precursor without a co-reactant and using ammonia (NH3) as co-reactant; (ii) the lowest deposition temperature that can be achieved using this process; (iii) the chemical, compositional, morphological, and structural properties of the resulting films as function of processing parameters, with particular emphasis on film composition, density, etch rate, and structure (amorphous versus crystalline); (iv) the effects of the process on thermally and chemically fragile substrates, such as polymers and plastics; and (v) how to deposit good quality SiNxCy while maintaining the structural and chemical integrity of such substrates, including in particular at the film-substrate interface? The instantaneous growth of the SiNxCy film on multiple types of substrates during the remote plasma pulse of the P-CVD process was observed by in-situ, real-time, ellipsometry (an example is provided in Figure 1) and the resulting films were further analyzed by XPS and wet etch rate studies. Figure 1

Challenges facing systematic biology

AbstractSystematic biology is fundamental for providing organized information about the living world. It clarifies what organisms share our planet, and it also reveals the basic short‐term and long‐term processes that have given rise to this diversity. Human society is rapidly modernizing, largely through increased digital communications tied closely to satellite innovations. Communication is now global and instantaneous, allied with an awareness of place made possible by global positioning technology. Despite many positive recent developments, numerous tensions remain that threaten a tranquil world order and negatively impact biodiversity, such as between developed and developing countries, democratic and authoritarian governments, and among religious groups. The increasing human population is also bringing pressures to bear on global biodiversity through activities that result in air and water pollution, topsoil erosion, deforestation, ozone depletion, global warming, and taxic loss. The systematic biology community has been unable to respond effectively to these many new challenges due to fragmentation and lack of cohesion. Systematists have tended to focus more on issues relevant to their own taxonomic groups (e.g., bacteria, ferns, fungi, reptiles, mammals, etc.) and much less on global concerns. Systematists must become better organized to allow the global priority of inventorying the planet to be achieved as soon as practicable. A global organization, an International Federation for Systematic Biology, should be formed to serve as a coordinator to help articulate five‐year and longer plans. Large‐scale funding (billions of dollars) must be sought to allow implementation of shared goals. Projects must be created that more obviously connect in some fashion to major societal problems such as poverty, water resources, food production, and human health. The astronomy and nuclear physics communities provide models of successful planning and implementation, the former on understanding the extreme distant reality of our existence, and the latter on the extremely small atomic dimensions. Systematic biology focuses largely on understanding the middle range of reality that we can see and more easily directly experience. Making the case for understanding at this level should, in principle, be the easiest of all. Fundamental is that projects be simple in concept, visionary in perspective, and offering economic stimulus for participants (i.e., the creation of new jobs).

Modeling of an efficient airblast atomizer for liquid jet into a supersonic crossflow

The liquid jet from an airblast atomizer into supersonic air crossflow with a Mach number of 1.94 was investigated numerically. The detached eddy simulation was used as the turbulence model to compromise the merits of both large eddy simulation and k−ε models. The Kelvin-Helmholtz and Rayleigh-Taylor (KHRT) model was used to simulate the droplet breakup process. The location and velocity of the child droplets are tracked efficiently by the automated tracking scheme. The model was validated using previous experimental data and a good agreement was obtained. In the present study, the airblast atomizer, which allows core and annular air flows with the injected liquid, is utilized instead of the ordinary orifice nozzle to improve the breakup process and the droplet distribution. The airblast atomizer dimensions were represented as factors of the ordinary orifice nozzle and the air mass flow rates through the atomizer were adjusted as ratios from the liquid mass flow rate. The effects of these parameters on the spray structure characteristics were presented. Then, a new proposed design for the airblast atomizer was suggested based on the improvements in spray characteristics dimensions and sauter mean diameter distribution. The core and annular air flows significantly enhanced the spray characteristic dimensions and spray breakup compared with the ordinary orifice nozzle.

Magneto-luminescent zinc/iron oxide core-shell nanoparticles with tunable magnetic properties

Abstract Core-shell nanospheres with tailorable magnetic properties and strong luminescence promise versatile and efficient biomedical and electronic applications. We report a low-cost sonochemical synthesis of ZnO/iron oxide core-shell nanostructures with tunable magnetic properties. The high-resolution transmission electron microscopy (HRTEM) illustrates the distinguished dispersity of the oxide nanoparticles, whereas elemental profiling using line scan data confirm the formation of the distinguished core and shell phases. Annealing in N2–H2 and Ar–H2 ambient alters the magnetic properties such as coercive field, saturation magnetization, and remnant magnetization within the inverse spinel iron oxide with space group Fd3m. Subtle structural changes between maghemite (γ-Fe2O3) and its reduced form, magnetite (Fe3O4), have been identified in the thin (0.5–3 nm) shell region of atomic dimensions. Structural composition including phase transitions and defect states are investigated using XRD, XPS, and Raman measurements. Coexistence of ferromagnetism (from the shell and characterized by magnetic measurements) and strong luminescence (from ZnO core and obtained from photoluminescence spectroscopy) at room temperature indicates exotic magneto-optical coupling, which is supported by the blue-shifted luminescence spectra. Our approach combining nanotechnology and solid-state chemistry opens a new frontier to the building of innovative nanomaterials for integration, especially multifunctional core-shell oxide nanomaterials.

Advantages and Disadvantages of Chemical Methods in the Elaboration of Nanomaterials

Reducing the size of macroscopic systems to nanometers can be achieved by top down synthesis by different chemical or physical methods. The bottom-up approach is a method in which the components of the atomic or molecular dimensions are assembled together to form nanoparticles. The bottom-up method is used for the elaboration of nanoparticles, because it allows the control of their size. This article presents a review of the advantages and disadvantages of chemical methods for the development of nanomaterials.

Room-Temperature Measurement of Electrostatically Coupled, Dopant-Atom Double Quantum Dots in Point-Contact Transistors

Single-atom transistors hold great promise for reducing semiconductor devices to their ultimate scale, approaching atomic dimensions. Typically these transistors use dopant atoms embedded in a semiconductor to form quantum-dot switches; unfortunately, in this approach shallow potential wells restrict device operation to cryogenic temperatures. This work extends the operation of single-atom transistors to $r\phantom{\rule{0}{0ex}}o\phantom{\rule{0}{0ex}}o\phantom{\rule{0}{0ex}}m$ $t\phantom{\rule{0}{0ex}}e\phantom{\rule{0}{0ex}}m\phantom{\rule{0}{0ex}}p\phantom{\rule{0}{0ex}}e\phantom{\rule{0}{0ex}}r\phantom{\rule{0}{0ex}}a\phantom{\rule{0}{0ex}}t\phantom{\rule{0}{0ex}}u\phantom{\rule{0}{0ex}}r\phantom{\rule{0}{0ex}}e$, by embedding dopant atoms in SiO${}_{2}$ tunnel barriers to form deep quantum wells. Nearby dopant atoms can communicate electrostatically, forming double quantum dots, opening a route toward practical, room-temperature atomic-scale quantum electronics.

Electronic and vibrational signatures of ruthenium vacancies in Sr2RuO4 thin films

The synthesis of stoichiometric ${\mathrm{Sr}}_{2}{\mathrm{RuO}}_{4}$ thin films has been a challenge because of the high volatility of ruthenium oxide precursors, which gives rise to ruthenium vacancies in the films. Ru vacancies greatly affect the transport properties and electronic phase behavior of ${\mathrm{Sr}}_{2}{\mathrm{RuO}}_{4}$, but their direct detection is difficult due to their atomic dimensions and low concentration. We applied polarized x-ray absorption spectroscopy at the oxygen $K$ edge and confocal Raman spectroscopy to ${\mathrm{Sr}}_{2}{\mathrm{RuO}}_{4}$ thin films synthesized under different conditions. The results show that these methods can serve as sensitive probes of the electronic and vibrational properties of Ru vacancies, respectively. The intensities of the vacancy-related spectroscopic features extracted from these measurements are well correlated with the transport properties of the films. The methodology introduced here can thus help one to understand and control the stoichiometry and transport properties in films of ${\mathrm{Sr}}_{2}{\mathrm{RuO}}_{4}$ and other ruthenates.

Non-exponential decay of a giant artificial atom

In quantum optics, light-matter interaction has conventionally been studied using small atoms interacting with electromagnetic fields with wavelength several orders of magnitude larger than the atomic dimensions. In contrast, here we experimentally demonstrate the vastly different giant atom regime, where an artificial atom interacts with acoustic fields with wavelength several orders of magnitude smaller than the atomic dimensions. This is achieved by coupling a superconducting qubit to surface acoustic waves at two points with separation on the order of 100 wavelengths. This approach is comparable to controlling the radiation of an atom by attaching it to an antenna. The slow velocity of sound leads to a significant internal time-delay for the field to propagate across the giant atom, giving rise to non-Markovian dynamics. We demonstrate the non-Markovian character of the giant atom in the frequency spectrum as well as nonexponential relaxation in the time domain.

Preface

This year the Risø International Symposium on Materials Science is celebrating its 40th year jubilee. During this 40-year period, significant progress has taken place and new discoveries and understanding in the field of material science and engineering have materialized in advanced metals and alloys with wide applications in society. In parallel, there has been an unprecedented development of 2D, 3D and 4D characterization techniques operating on multiple length scales down to the atomic dimension. The development has led to revision and foundation of fundamental principles and models for example in the areas of deformation, recovery and recrystallization of metals and alloys. This in-turn has led to new and demanding challenges that are addressed in the Proceedings. The challenges include:• Transitional stages in the evolution of deformation microstructure and strengthening mechanisms.• Effects of local microstructural variations on the evolution of microstructures during annealing• 2D, 3D and 4D characterization techniques based on for example x-rays and electron microscope techniques in the laboratory and at international facilities.• Microstructural variations at different length scales which is of critical importance for the properties and performance of metals and alloys for engineering applications.• Advanced and new processing techniques of bulk materials and by application of powder metallurgy in additive manufacturing and spark plasma sintering processes.• Experimental findings in 3D and 4D used as input to as well as validation of analytical and numerical models.The metals and alloys investigated are of fcc, bcc and hcp structure, in bulk form or present as gradients or multilayer structures.The Proceedings contain 15 keynote, 11 invited and 34 contributed presentations covering the above-mentioned key themes. It is our hope that Proceedings can inspire the future development of this field.

Plasmonics in Atomically Thin Crystalline Silver Films

Light-matter interaction at the atomic scale rules fundamental phenomena such as photoemission and lasing while enabling basic everyday technologies, including photovoltaics and optical communications. In this context, plasmons, the collective electron oscillations in conducting materials, are important because they allow the manipulation of optical fields at the nanoscale. The advent of graphene and other two-dimensional crystals has pushed plasmons down to genuinely atomic dimensions, displaying appealing properties such as a large electrical tunability. However, plasmons in these materials are either too broad or lying at low frequencies, well below the technologically relevant near-infrared regime. Here, we demonstrate sharp near-infrared plasmons in lithographically patterned wafer-scale atomically thin silver crystalline films. Our measured optical spectra reveal narrow plasmons (quality factor of ∼4), further supported by a low sheet resistance comparable to bulk metal in few-atomic-layer silver films down to seven Ag(111) monolayers. Good crystal quality and plasmon narrowness are obtained despite the addition of a thin passivating dielectric, which renders our samples resilient to ambient conditions. The observation of spectrally sharp and strongly confined plasmons in atomically thin silver holds great potential for electro-optical modulation and optical sensing applications.

Tunable terahertz structure based on graphene hyperbolic metamaterials

Photoexcited graphene can behave as the gain medium aiming to come up with the coherent radiation at low THz spectral region. However, its response is very weak because of its atomic dimensions. Herein, a different design aiming to obtain effective tunable THz amplifiers, having small dimensions and lasers with broadband operation based on active THz hyperbolic metamaterials (HMM) is demonstrated. HMMs are considered by employing multiple stacked photoexcited graphene sheets divided by dielectric spacers. Herein, we study and characterize the hyperbolic THz regime of the studied atomic active HMM. A broadband slow-wave propagation regime takes place if the graphene-based HMM system is periodically patterned. This occurs due to the hyperbolic dispersion. Doing so, reconfigurable amplification of THz waves in a broad-spectrum region is attained. This might be engineered by tuning the quasi-Fermi level of graphene. Moreover, the mechanisms leading to the increase of the frequency region of bound surface wave have been proposed in the frame of the current study.

(Invited) 2D Materials for Nanoelectronics: Prospects and Materials Integration Challenges

The size reduction and economics of integrated circuits, captured since the 1960’s in the form of Moore’s Law, is under serious challenge. Current industry roadmaps reveal that physical limitations include reaching aspects associated with truly atomic dimensions, and the cost of manufacturing is increasing such that only 2 or 3 companies can afford leading edge capabilities. To address some of the “conventions;” material’s physical limitations, “2D materials” such as graphene, phosphorene, h-BN, and transition metal dichalcogenides have captured the imagination of the research community for advanced applications in nanoelectronics, optoelectronics, and other applications. [1,2] Among 2D materials “beyond graphene,” some exhibit semiconducting behavior, such as transition-metal dichalcogenides (TMDs), and present useful bandgap properties for applications even at the single atomic layer level. Examples include “MX2”, where M = Mo, W, Sn, Hf, Zr and X = S, Se and Te. In addition to the potentially useful bandgaps at the monolayer thickness scale, the atomically thin layers should enable thorough electric field penetration through the channel, thus enabling superior electrostatic control. Further, with such thin layers, the integration with suitable gate dielectrics can result in a mobility enhancement. Applications “beyond CMOS” are also under exploration. From an interface perspective, the ideal TMD material may ne expected to have a dearth of dangling bonds on the surface/interface, resulting in low interface state densities which are essential for efficient carrier transport. The ideal TMD materials have much appeal, but the reality of significant densities of defects and impurities will surely compromise the intrinsic performance of such device technologies. This presentation will examine the state-of-the-art of these materials in view of our research on semiconductor device applications, and the challenges and opportunities they present for electronic and optoelectronic applications. [3,4] This research was supported in part by the Semiconductor Research Corporation (SRC) NEWLIMITS Center and NIST through award number 70NANB17H041 and the Erik Jonsson Distinguished Chair at the University of Texas at Dallas.