Fabrication Of Nanoscale Devices Research Articles

Influence of B, Si, Ge, and As impurities on the electronic properties of graphene quantum dot: A density functional theory study

The electronic features of chemically functionalized graphene quantum dots (GQDs) are investigated using density functional theory (DFT). The fabrication of nanoscale devices needs to enhance- the electronic performance of customized GQDs, which is crucial in many applications. GQDs can be used as a model with the molecule C24H12. We investigated the effects of adding metalloid impurities) boron B, silicon Si, germanium Ge, and arsenic As) on the structure and electronic properties of the dots at the B3LYP/6–31 level using the Gaussian 09 program package. The obtained results show efficient adding impurities B, Si, Ge, and As on the structure and electronic properties of GQDs, where it is noted that the energy gap change with -3.085, -12.340, -13.907, and -66.846 %, respectively.These results not only advance our knowledge of the mechanisms behind chemical doping, which may change the electronic features of quantum dots, but they also provide support for the development of nanodevices that have better electronic performance. As observed with As/GQD, it is anticipated that this system, which has the lowest possible chemical hardness values, will function as an effective corrosion inhibitor.

A review of gallium phosphide nanophotonics towards omnipotent nonlinear devices

Abstract Gallium phosphide (GaP) has been increasingly prioritized, fueled by the enormous demands in visible light applications such as biomedical and quantum technologies. GaP has garnered tremendous attention in nanophotonics thanks to its high refractive index, indirect bandgap width of 2.26 eV, lattice perfectly matched with silicon, and omnipotent and competitive nonlinear optical properties. Herein, we review the progress and application of GaP in nanoscale devices over the past two decades. The material properties of bulk GaP are first listed, followed by a summary of the methodologies for fabricating nanoscale devices and related integration techniques. Then, we digest the operational mechanisms across different GaP-based devices on their optical linear responses. Following this, we categorize the GaP nonlinear optical effects into multiple aspects including second-harmonic generation, four-wave mixing, Kerr optical frequency combs, etc. Ultimately, we present a perspective on GaP nanophotonics in the context of coexisting and competing modes of various nonlinear effects. We believe that a comprehensive overview of unique GaP will propel these nanophotonic devices toward a mature state, underpinning foundational understanding and leveraging practical innovations.

High-Throughput, Label-Free Detection of DNA Origami in Single-Cell Suspensions Using origamiFISH-Flow.

Structural DNA nanotechnology enables custom fabrication of nanoscale devices and promises diverse biological applications. However, the effects of design on DNA nanostructure (DN)-cell interactions in vitro and in vivo are not yet well-characterized. origamiFISH is a recently developed technique for imaging DNs in cells and tissues. Compared to the use of fluorescent tags, origamiFISH offers label-free and structure-agnostic detection of DNs with significantly improved sensitivity. Here, the origamiFISH technique is extended to quantify DNs in single-cell suspensions, including in nonadherent cells such as subsets of immune cells, via readout by flow cytometry. This method, referred to as origamiFISH-Flow, is high-throughput (e.g., 10000 cells per second) and compatible with immunostaining for concurrent cell-type and cell-state characterization. It is shown that origamiFISH-Flow provides 20-fold higher signal-to-noise ratio for DN detection compared to dye labeling approaches, leading to the capture of >25-fold more DN+ cells under single-picomolar DN uptake concentrations. Additionally, the use of origamiFISH-Flow is validated to profile the uptake of various DN shapes across multiple cell lines and splenocytes, as well as to quantify in vivo DN accumulation in lymphoid organs. Together, origamiFISH-Flow offers a new tool to interrogate DN interactions with cells and tissues, while providing insights for tailoring their designs in bio-applications.

Observing ferroelastic switching in Hf0.5Zr0.5O2 thin film

Abstract Hafnium zirconium oxides (HZO), which exhibit ferroelectric properties, are promising materials for nanoscale device fabrication due to their high CMOS compatibility. In addition to piezoelectricity, ferroelectricity, and flexoelectricity, this study reports the observation of ferroelasticity using piezoelectric force microscopy (PFM) and scanning transmission electron microscopy (STEM). The dynamics of 90° ferroelastic domains in HZO thin films are investigated under the influence of an electric field. Switching of the retentive domains is observed through repeated wake-up measurements. This study presents a possibility of enhancing polarization in HZO thin films during wake-up processes.

Effects of Inorganic Substitutions and Different Metal Electrode Materials on Electronic Transport Properties of Organic Molecular Devices.

Incorporating inorganic components into organic molecular devices offers one novel alternative to address challenges existing in the fabrication and integration of nanoscale devices. In this study, using a theoretical method of density functional theory combined with the nonequilibrium Green's function, a series of benzene-based molecules with group III and V substitutions, including borazine molecule and XnB3-nN3H6 (X = Al or Ga, n = 1-3) molecules/clusters, are constructed and investigated. An analysis of electronic structures reveals that the introduction of inorganic components effectively reduces the energy gap between the highest occupied molecular orbital and the lowest unoccupied molecular orbital, albeit at the cost of reduced aromaticity in these molecules/clusters. Simulated electronic transport characteristics demonstrate that XnB3-nN3H6 molecules/clusters coupled between metal electrodes exhibit lower conductance compared to prototypical benzene molecule. Additionally, the choice of metal electrode materials significantly impacts the electronic transport properties, with platinum electrode devices displaying distinct behavior compared to silver, copper, and gold electrode devices. This distinction arises from the amount of transferred charge, which modulates the alignment between molecular orbitals and the Fermi level of the metal electrodes by shifting the molecular orbitals in energy. These findings provide valuable theoretical insights for the future design of molecular devices incorporating inorganic substitutions.

Direct Visualization of Subnanometer Variations in the Excitonic Spectra of 2D/3D Semiconductor/Metal Heterostructures

The integration of metallic contacts with two-dimensional (2D) semiconductors is routinely required for the fabrication of nanoscale devices. However, nanometer-scale variations in the 2D/metal interface can drastically alter the local optoelectronic properties. Here, we map local excitonic changes of the 2D semiconductor MoS2 in contact with Au. We utilize a suspended and epitaxially grown 2D/metal platform that allows correlated electron energy-loss spectroscopy (EELS) and angle resolved photoelectron spectroscopy (nanoARPES) mapping. Spatial localization of MoS2 excitons uncovers an additional EELS peak related to the MoS2/Au interface. NanoARPES measurements indicate that Au-S hybridization decreases substantially with distance from the 2D/metal interface, suggesting that the observed EELS peak arises due to dielectric screening of the excitonic Coulomb interaction. Our results suggest that increasing the van der Waals distance could optimize excitonic spectra of mixed-dimensional 2D/3D interfaces and highlight opportunities for Coulomb engineering of exciton energies by the local dielectric environment or moiré engineering.

Nonparaxial solitons and their interaction dynamics in coupled nonlinear Helmholtz systems

It is well-known that the nonparaxiality plays an important role in the fabrication of nanoscale devices. In this paper, we study the existence of nonparaxial solitons in a dimensionless coupled nonlinear Schrödinger system with cross-phase modulation (XPM), which enables the propagation of ultra-broad nonparaxial pulses in a birefringent optical waveguide. Despite the fact that the system is a nonintegrable one (Tamilselvan et al., 2020), we obtain a bright soliton solution analytically by employing the standard Hirota’s bilinearization method. Subsequently we numerically investigate the scattering dynamics of two and three bright solitary waves using the general solution as the seed one by adopting the split-step Fourier method based on the Feit-Flock algorithm. We explain how the soliton parameters such as separation distance and relative phase influence the interaction between the nonparaxial bright solitons. In particular, we report a bunch of interesting phenomena of soliton interactions, which include oscillating bound solitons when the phase of the two solitary waves are equal and parallel propagation as the phase is changed to out-of phase with a zig-zag pattern. Similarly the in-phase three solitary waves also exhibit a novel interaction which mimics a triple knot structure which has never been observed before in the framework of coupled nonlinear Helmholtz systems. We believe that our results would pave a way for future research generating optical memories based on the nonparaxial solitons.

Controlled optical near-field growth of individual free-standing well-oriented carbon nanotubes, application for scattering SNOM/AFM probes

Abstract Exploiting localized heat-generation density and the resulting enhanced temperature-rise for controlled growth of carbon nanotubes (CNTs) is reported, and its potentials for batch-production of high-quality CNT probes are demonstrated. Optical near field chemical vapor deposition (ONF-CVD) benchtop fabrication schemes are developed for the localized integration of individual well-aligned carbon nanotubes without bending/buckling exactly at desired nanoscale sites. It is demonstrated that generating self-aligned catalyst nanoparticles superimposed on top of silicon nanotips, along with near-field induced absorption confinement, provide the ability to localize the generated heat at the nanotips apexes, and control the CNT growth locations. The nanoscale maskless controllability of the growth site is shown by properly tailoring ONF-CVD conditions to overcome overall heat exposure of the substrate for selective activation of catalyst nanoparticles located at apexes, from those dispersing all over the tips. The calculated local power densities and temperature profiles of the simulated tips, clearly demonstrate the confined heat and optimal gradient of generated temperature rise as the main factors affecting the growth. In addition to determining necessary processing conditions to control the localization and orientation of the growth, parameters affecting the length and diameter of the localized individually grown nanotubes are also presented. Optical near-field-based growth schemes can be extended for localized maskless fabrication of other nanoscale devices, beyond the diffraction limit, using photothermal effects.

Three-terminal photodetectors based on chemical vapor deposition-grown triangular MoSe2 flakes

Two-dimensional (2D) transition metal dichalcogenides (TMDs) materials play a significant role in the fabrication of nano-scale devices. To construct high-performance devices with rich functions for adaptation to specific applications, a strategy for engineering 2D nanostructures must be developed. In addition, multi-channel devices with superior optoelectronic characteristics have attracted great interest because they can be used in nano-chip systems. Herein, we synthesized high-quality and homogenous MoSe2 flakes with the assistance of sodium hydroxide (NaOH) powder by the chemical vapor deposition (CVD) method. Three-terminal photodetectors were fabricated based on the triangular MoSe2 flakes. A high photoresponse can be achieved from the photodetectors with a photoresponsivity of 1.79 mA·W−1 and a specific detectivity of 13.55 × 109 Jones at a bias voltage of 3 V. The key benefits of this type of multi-terminal photodetectors on regular 2D flakes include their usefulness in detecting high-precision light at different locations on a single-chip device. Therefore, this work provides a facile way to fabricate position detection photodetectors on various 2D materials.

Effect of different pulse modes during Cl2/Ar inductively coupled plasma etching on the characteristics of nanoscale silicon trench formation

The etch characteristics of silicon trenches masked with various SiO2/Si3N4pattern distances were investigated using synchronously and asynchronously pulse modes in addition to the continuous wave (CW) mode for Ar/Cl2inductively coupled plasmas. By using synchronously and asynchronously pulse modes instead of CW mode, the selectivity between Si and the mask layer was increased by 2 and 10 times, respectively. Also,the etch rate differences between wide and narrow pattern distance patterns (aspect ratio dependent etching, ARDE) was decreased from 35% to 21 and to 8%,respectively. The increased etch selectivity andreduction of ARDE for the synchronously pulsed mode were related to the increased conduction of Cl radicals/byproductsthrough the high aspect ratio trench, therefore, increased chemisorption/byproduct removal on the silicon trench surface during the pulse-off period. For the asynchronously pulsed mode, the further improved etch selectivity and reduced ARDE were believed to be related to the time separated etch cycle composed of Cl chemical adsorption on the silicon trench surface and the removal of the chemisorbed species by ion bombardment. It is believed that, the asynchronously pulsed plasma etching method can be applicable to various next generation deep nanoscale device fabrication requiring high etch selectivity and low ARDE.

Si doping-induced phase control, formation of p-type and n-type GaAs nanowires

We realized the control on the crystal structure of GaAs nanowires (NWs) by silicon (Si) doping and V/III ratio. This viewpoint has been clearly evidenced by Raman spectrum combined with high-resolution transmission electron microscopy (HRTEM). Undoped GaAs NWs generally show a mixture of zinc blende (ZB) and wurtzite (WZ) phases; the addition of Si dopant and high V/III ratio are beneficial for the nucleation of ZB structure. Field effect transistor (FET) devices were fabricated to show that Si-doped GaAs NWs exhibit p-type conductivity in the low V/III ratio of 25.8 and n-type conductivity in the high V/III ratio of 51.6. These results provide a clear route for achieving GaAs NWs phase control and different conductivity types, which is an essential step towards the fabrication of nanoscale devices.

Etching Characteristics of Low-k Dielectric Using C5H2F10 Liquefied Gas Plasma for Mitigating of Global Warming Potential

In this work, we studied the etch characteristics and dielectric constant change of SiOC thin films by plasma etching for the fabrication of nanoscale devices to evaluate the C5H2F10 as alternative etching gas. We performed plasma etching of SiOC films with inductively coupled plasma using the CF4+X+O2 mixed gas, where X = CHF3 and C5H2F10. Plasma diagnosis such as optical emission spectroscopy and double Langmuir probe measurements were carried. We analyzed the chemical compositions of residues on the etched SiOC film surface using X-ray photoelectron spectroscopy. After the process, contact resistance was measured using the transmission line method to analyze the degree of polymer on the surface of the silicon. Ellipsometry were used to evaluate the change in the dielectric constant of the thin film due to plasma exposure. It was confirmed that the etched profile was more vertical than that of the CHF3 gas plasma, and the increase in the dielectric constant of the SiOC thin film by C5H2F10 gas plasma is less than that of CHF3 gas plasma. These results confirmed that C5H2F10 gas was a powerful alternative to CHF3 gas in semiconductor processing for the fabrication of nanoscale devices.

Preparation of Ultrathin Gold Films with Subatomic Surface Roughness.

Nanoscale device fabrication requires control over film growth at the atomic scale. Growth conditions must be tuned in consideration of interface parameters like chemical bonding, surface free energy, and lattice matching. In metals, electronic properties may also be utilized for control of physical parameters. Quantum size effects can induce metals to spontaneously form specific shapes and sizes according to their electronic structure. Unfortunately, such electronic growth is generally known only for a few systems and is typically only stable under cryogenic conditions. In this work, we explore a recently discovered class of electronic growth systems in which metal films are grown upon the relatively inert surfaces of van der Waals crystals. In this class of materials, the electronic growth is highly stable at room temperature and actually requires higher temperature annealing to achieve proper equilibrium. We work with the Au/MoS2 system, which shows excellent stability and can readily form discrete and atomically flat nanostructures. Here, we show how the electronic growth modes facilitate the formation of atomically flat films with nanometer scale thickness. The surface roughness of these films was found to be less than a single atom over several square microns, creating nearly perfect surfaces for studies of self-assembled monolayers or other applications.

Advanced Scanning Probe Nanolithography Using GaN Nanowires.

A fundamental understanding and advancement of nanopatterning and nanometrology are essential in the future development of nanotechnology, atomic scale manipulation, and quantum technology industries. Scanning probe-based patterning/imaging techniques have been attractive for many research groups to conduct their research in nanoscale device fabrication and nanotechnology mainly due to its cost-effective process; however, the current tip materials in these techniques suffer from poor durability, limited resolution, and relatively high fabrication costs. Here, we report on employing GaN nanowires as a robust semiconductor material in scanning probe lithography (SPL) and microscopy (SPM) with a relatively low-cost fabrication process and the capability to provide sub-10 nm lithography and atomic scale (<1 nm) patterning resolution in field-emission scanning probe lithography (FE-SPL) and scanning tunneling microscopy (STM), respectively. We demonstrate that GaN NWs are great candidates for advanced SPL and imaging that can provide atomic resolution imaging and sub-10 nm nanopatterning on different materials in both vacuum and ambient operations.

Formation of Multiple‐Helical Core‐Shell Structure from Polyphenyl and Boron Nitride Nanotube

AbstractIn this manuscript, a multiple‐helical core‐shell structure is studied from polyphenyl and boron nitride nanotube (BNNT) through the molecular dynamics simulation. The results exhibited that polyphenyl is constrained in the inside of BNNT and self‐coiled to a helical configuration. In these systems, both the van der Waals potential well and the π–π stacking interaction between the polyphenyl and BNNT play a key role in the formation of helical nanostructures. The final configuration of composites can be influenced by many factors such as the diameter of BNNT, the chain number of polymer, the length of polymer, and the simulation temperature which are investigated in detail. This theory research about polyphenyl and BNNT may supply more theoretical foundation in chemical functionalization and helical polymer synthesis, which can be helpful for fabricating nanoscale devices.

(Invited) Novel Chemistries for Layer-by-Layer Etching of 2D Semiconductor Coatings and Organic-Inorganic Hybrid Materials

Here we report two new advances in atomic layer etching (ALEt) that extend our range of capabilities in nanoscale device fabrication. Semiconductor device manufacturing is limited by our ability to precisely deposit and remove thin film layers at the various levels of multistep device fabrication processes. Consequently, innovations in atomic layer deposition (ALD) and etching methods are essential. ALD-based methods have matured significantly and are now used extensively in semiconductor fabs. Recently, there has been an intense focus on developing ALEt methods. In particular, thermal ALEt has been shown to precisely remove ALD inorganic thin films selectively and on complex structures. These capabilities have opened new possibilities for nanoscale device design. Here, we report a new thermal etching process similar to ALEt for removing hybrid inorganic-organic layers that we call molecular layer etching (MLEt). This MLEt process uses vapor phase lithium organic salts in combination with trimethyl aluminum to perform layer-by-layer etching of molecular layer deposition (MLD) coatings.Ultra-thin layers of two dimensional (2D) transition metal dichalcogenide (TMD) semiconductors can exhibit exceptional electrical, optical, magnetic, mechanical and chemical properties. This allows the exploration of internal quantum degrees of freedom of electrons and their potential application in optoelectronic, energy, and sensor devices. Among the various 2D-TMDs, MoS2 has shown exciting material properties and this has stimulated the exploration of a variety thin film synthesis methods such as physical vapor deposition (PVD), chemical vapor deposition (CVD), and solution based methods. In addition, the ALD community is investigating ALD methods for MoS2 growth. Here we report the thermal ALEt of ALD MoS2 thin films. We believe the successful combination of both ALD and ALEt of MoS2 and other TMDs can pave the way to control the synthesis of 2D-TMD layers over large areas. Combining ALD and ALEt will allow MoS2 interface engineering and enable MoS2 integration into the large-scale manufacturing of future complex device structures.

Formation of “hemp flowers” structures from polyphenyl induced by C70

In this manuscript, the structure liking a Chinese food “hemp flowers” is formed through polyphenyl which is induced by C70. The whole formation process is tracked by the molecular dynamics simulation. The results exhibited that C70 induced polyphenyl to form a “hemp flowers” structure experiencing four stages which are transfer, wrap, maintain and twist. Both the van der Waals potential well and the π–π stacking interaction between the polyphenyl and C70 play the major role in the formation of helical nanostructures. The position of C70 makes the configuration different from the “hemp flowers”. Furthermore, the final configuration of polymer is also depended on the number of C70, the length of polymer and the simulation temperature. The new geometrical structures between polyphenyl and C70 may supply more theoretical foundation in chemical functionalization and helical polymer synthesis, which may be helpful insight for fabricating nanoscale devices.

Formation of helical polyphenyl nanostructures on carbon nanotubes

In this manuscript, helical polyphenyl (PP) nanostructures were formed on single-wall carbon nanotubes (SWCNT) through self-assemble process which was investigated by a molecular dynamics simulation. The results displayed that the linear polyphenyl changed into helical structure and finally a core–shell structure was formed. The formation mechanism of whole process was also exhibited. Furthermore, some influence factors such as the initial angle between polyphenyl chain and nanotube axis, the diameter of carbon nanotube were also displayed. Moreover, the interactions between different halogenated benzene polymer and carbon nanotube were also studied. The new geometrical structures between polyphenyl and single-wall carbon nanotubes may attract more attention in chemical functionalization and helical polymer synthesis, which may be helpful for fabricating nanoscale devices.

Formation of multiple helical structures induced by boron nitride nanotubes

• Multiple helical nanostructures are formed which are induced by the boron nitride nanotubes. • The chain number of polyacetylene influences the final configuration of polymer. • Some other influence factors are also displayed. In this manuscript, a molecular dynamics simulation was used to investigate the formation process of multiple helical nanostructures which was induced by the boron nitride nanotubes. The results displayed that three chains of polyacetylene changed to helical nanostructures in the boron nitride nanotube through self-assemble process. The combined action of the van der Waals potential well and the π–π stacking interaction between the polyacetylene and the inner surface of boron nitride nanotubes results in the formation of helical nanostructures. The chain number of polyacetylene influences the final configuration of polymer. Furthermore, some other influence factors such as the diameter of boron nitride nanotube and the length of polymer were also displayed. The new geometrical structures between polyacetylene and boron nitride nanotubes may attract more attention in chemical functionalization and helical polymer synthesis, which may be helpful for fabricating nanoscale devices.

Soft Chemical Mechanical Polishing Pad for Oxide CMP Applications

Chemical mechanical polishing (CMP) is widely accepted as the best planarization technique for fabricating nanoscale devices. A soft CMP pad that can enable higher oxide removal rates (RRs) and good planarity has been proposed for oxide CMP applications. In this study, three pads namely, Pad-1 (hard), Pad-2 (soft), and a commercial pad (hard) were used to polish blanket oxide, and STI patterned wafers. The Pad-2 demonstrated significantly higher RRs and better planarization than the hard pads. Post-polish pad texture analysis on Pad-2 showed a uniform surface asperity distribution. This is due to the novel method of pad manufacturing, which enables precise material placement and consistent pore construction.