Substrate Engineering Research Articles

Ab initio investigation of the interface between [formula omitted] nanoflakes and the [formula omitted] surface: Interplay between interaction energy and morphology

MoS2 nanoflakes have attracted wide attention due to their outstanding catalytic activity induced by their active zigzag edges. Nanoflakes morphologies dictate their electronic properties, and factors such as size, doping, and interaction with a substrate determines their behavior. Herein, we investigate the role of the Au(111) substrate in the morphology of Mo10S24 nanoflakes via first-principles density functional theory calculations combined with the k-means clustering algorithm for structure selection. From our initial calculations for gas-phase nanoflakes, we found that asymmetric morphologies are about 2.7eV lower in energy than the symmetric ones. Thus, we deposited a few nanoflakes on the Au(111) substrate to investigate their effects. Here, we obtain a strong nanoflake/gold interaction ruled by features such as symmetry, roughness, and vertical S–Au stacking. The S–Au interaction is large enough to change the relative energies between the nanoflakes in the gas-phase by more than 2.0eV, which indicates the relevance of substrate engineering for the nanoflake morphology.

Strain-Induced Performance Enhancement of a Monolayer Photodetector via Patterned Substrate Engineering.

Two-dimensional (2D) materials exhibit tremendous potential for applications in next-generation photodetectors. Currently, approaches aiming at enhancing the device's performance are limited, mainly relying on complex hybrid systems such as heterostructures and sensitization. Here, we propose a new strategy by constructing patterned nanostructures compatible with the conventional silicon substrate. Using CVD-grown monolayer MoS2 on the periodical nanocone arrays, we demonstrate a high-performance MoS2 photodetector via manipulating strain distribution engineered by the substrate at the nanoscale. Compared to the pristine MoS2 counterpart, the strained MoS2 photodetector exhibits a much enhanced performance, including a high signal-to-noise ratio over 105 and large responsivity of 3.2 × 104 A W-1. The physical mechanism responsible for the enhancement is discussed by combining Kelvin probe force microscopy with theoretical simulation. The enhanced performances can be attributed to the improved light absorption, the fast separation of photo-excited carriers, and the suppression of dark currents induced by the designed periodical nanocone arrays. This work depicts an alternative method to achieve high-performance optoelectronic devices based on 2D materials integrated with semiconductor circuits.

Substrate-Induced Dissipative and Non-Linear Effects in RF Switches: Probing Ultimate Performance Based on Laser-Machined Membrane Suspension

With the evolution of radio frequency (RF)/microwave technology, there is a demand for circuits that are able to meet highly challenging RF front end specifications. Silicon-on-insulator (SOI) technology is one of the leading platforms for upcoming wireless generation. The degradation of performance due to substrate coupling is a key problem to address for telecommunication circuits, especially for the high throw count switches in RF front ends. In this context, a fast, flexible and local laser ablation technique of the silicon handler allows for the membrane suspension of large millimeter-scale circuits. This approach enables the evaluation of the ultimate performance in the absence of the substrate, i.e., without dissipative losses and substrate-induced non-linear effects, on capacitive comb coupling structures and RF switches. Compared to high-resistivity SOI substrates, the high frequency characterization of RF membrane switches reveals a superior linearity performance with a reduction in second and third harmonics by 17.7 dB and 7.8 dB, respectively. S-parameter analysis also reveals that membrane suspension entails insertion losses that are improved by 0.38 dB and signal reflection lowered by 4 dB due to a reduced off-state capacitance. With reference to a trap-rich substrate, the membrane suspension also achieves an additional 7.8 dB reduction in the second harmonic, indicating that there is still scope for improvement in this figure of merit. The obtained results demonstrate a new way to evaluate optimized circuit performance using post-fabrication substrate engineering.

Nucleation and Growth of Copper on Cobalt in Advanced Interconnect Metallization

Copper was implemented as a conductor for advanced back-end-of-line (BEOL) interconnects based on its low electrical resistivity and improved electromigration life relative to the aluminum baseline.1, 2 Over the past two decades, the smallest dimension of Cu interconnects has decreased from about 300 to the range of 10-20 nanometers.3 Until recently, damascene Cu electroplating on PVD Cu seed has been optimized to provide void-free Cu metallization using a process relying on inorganic and organic additives toenable bottom-up growth from the base of vias and trenches.1,2,4 With ever-decreasing feature size, the conventional damascene process is becoming increasingly limited by the inability to deposit a sufficiently continuous Cu seed on a barrier/Co liner stack without resulting in pinch-off of the PVD seed.In this talk we will report on the development of direct Cu plating on Co using a range of deposition processes to illustrate the challenges and possible direction for improvement of the nucleation and subsequent growth of Cu on the Co seed. One challenge is to create a Cu layer without significantly etching the Co in the plating bath. This can be achieved by reducing the electrode potential difference between Cu electrodeposition and Co corrosion using proper additives in the plating bath to increase suppression (Figure 1). Such a large overpotential translates into improved nucleation density, which effectively inhibits the complete dissolution of the ultrathin Co layers. This effect is also illustrated by measuring the galvanic displacement reaction between Cu ions and Co at open circuit potential (OCP). Figure 2 reveals quick deposition of a monolayer equivalent of Cu followed by a slight increase in Cu thickness over time.A second challenge involves generation of dense nucleation which results in a smooth initially plated Cu film. The number of protrusions is reduced noticeably when a potential-controlled entry is replaced by leaving the electrode at OCP for a short time before any current is applied (Figures 3a and 3b). A short OCP time allows Co oxides to first dissolve, thereby making more surface sites available for nucleation. The smoothness can be further enhanced by increasing the acidity of the bath (Figure 3c). Higher acid could have modulated the reactivities of additive(s) to promote lateral growth. Improved nucleation can also be attained through substrate engineering. This is shown in Figure 4(a-c), where the morphology/continuity of the electroless film exhibits a strong dependency on Co thickness. Furthermore, agglomeration caused by diffusion of Cu across the substrate during deposition can have a large effect on the final film morphology. This can be seen in figure 4 (d-f), in which differences in deposition morphology across a range of conditions are captured in a simple lateral diffusion simulation.We will discuss the mechanisms leading to these effects and their impact on the design of systems to produce improved film morphology.References(1) P.C. Andricacos, C. Uzoh, J. O. Dukovic, J. Horkans, H. Deligianni, IBM J. Res. Develop. 42, 567 (1998)(2) J. Reid, Jpn. J. Appl. Phys. 40, 2650 (2001)(3) I. Ciofi, P. J. Roussel, R. Baert, A. Contino, A. Gupta, K. Croes, C. J. Wilson, D. Mocuta, Z. Tokei, IEEE Trans. Electron. Devices, 66, 2339 (2019).(4) T.P. Moffat, D. Wheeler, S. K. Kim, D. Josell, J. Electrochem. Soc. 153, C127, (2006) Figure 1

Engineering the Activity of Old Yellow Enzyme NemR-PS for Efficient Reduction of (E/Z)-Citral to (S)-Citronellol

The cascade catalysis of old yellow enzyme, alcohol dehydrogenase and glucose dehydrogenase has become a promising approach for one pot, two-step reduction of (E/Z)-citral to (S)-citronellol, serving as a chiral alcohol with rose fragrance. During the multi-enzymatic cascade catalysis, old yellow enzyme is responsible for the reduction of the conjugated C=C and the introduction of the chiral center, requiring high activity and (S)-enantioselectiviy. Herein, to improve the activity of the old yellow enzyme from Providencia stuartii (NemR-PS) with strict (S)-enantioselectivity, the semi-rational design on its substrate binding pocket was performed through a combination of homology modeling, molecular docking analysis, alanine scanning and iterative saturation mutagenesis. The NemR-PS variant D275G/F351A with improved activity was obtained and then purified for characterization, obeying the substrate inhibition kinetics. Compared with the wild type, the parameters Ki and Kcat/Km were increased from 39.79 mM and 2.09 s−1mM−1 to 128.50 mM and 5.01 s−1mM−1, respectively. Moreover, the variant D275G/F351A maintained strict (S)-enantioselectivity, avoiding the trade-off effect between activity and enantioselectivity. Either the enzyme NemR-PS or the variant D275G/F351A was co-expressed with alcohol dehydrogenase from Yokenella sp. WZY002 (YsADH) and glucose dehydrogenase from Bacillus megaterium (BmGDHM6). In contrast to the whole-cell biocatalyst co-expressing NemR-PS, that co-expressing the variant D275G/F351A shortened the reaction time from 36 h to 12 h in the reduction of 400 mM (E/Z)-citral. In the manner of substrate constant feeding, the accumulated product concentration reached up to 500 mM and completely eliminate the residual intermediate and by-product, suggesting the effectiveness of protein engineering and substrate engineering to improve catalytic efficiency.

Yolk-like Pt nanoparticles as cathode catalysts for low-Pt-loading proton-exchange membrane fuel cells

Currently, how to reduce the Pt loading in proton-exchange membrane fuel cell (PEMFC) is an urgent task for its practical application. Here, we propose a substrate engineering strategy of Pt catalysts to achieve low-Pt-loading PEMFC application, i.e., using the N-doped porous carbon (NC) with ultrahigh specific surface area (SSA) to trap Pt nanoparticle (NP). The egg-yolk-like Pt NP catalysts (Ptey/NC) have been synthesized successfully by using the strategy. The Ptey/NC not only possesses an ultrahigh SSA of 2271 m2/g and a relatively low-Pt content of 5.48 wt% but also shows better ORR activity and stability in acidic media than commercial 20% Pt/C. Using Ptey/NC as a cathode catalyst, the assembled PEMFC shows a high peak power density. At the ultralow-Ptey/NC loading of 0.03 mgPt/cm2, the Ptey/NC exhibits extremely high mass activity of 1.63 A/mgPt and 1.1 A/mgPt under 250 kPa and 150 kPa back pressure at 0.9 ViR-free in H2/O2 PEMFC, which are mainly attributed to the ultrahigh SSA plus low-Pt-content, rich mesopore structure, fully exposure of Pt (111), and the yolk-like special structure. DFT results further reveal that the interface effect between Pt NPs and NC significantly reduces the adsorption energy of oxygen species and, therefore, boosts its catalytic activity. This work provides a useful solution of using ultrahigh SSA catalyst plus low-Pt content to solve the low-Pt-loading problem, which would speed up the development of low-Pt-loading PEMFCs.

Engineering Fe(II)/α-Ketoglutarate-Dependent Halogenases and Desaturases.

Fe(II)/α-ketoglutarate-dependent dioxygenases (α-KGDs) are widespread enzymes in aerobic biology and serve a remarkable array of biological functions, including roles in collagen biosynthesis, plant and animal development, transcriptional regulation, nucleic acid modification, and secondary metabolite biosynthesis. This functional diversity is reflected in the enzymes' catalytic flexibility as α-KGDs can catalyze an intriguing set of synthetically valuable reactions, such as hydroxylations, halogenations, and desaturations, capturing the interest of scientists across disciplines. Mechanistically, all α-KGDs are understood to follow a similar activation pathway to generate a substrate radical, yet how individual members of the enzyme family direct this key intermediate toward the different reaction outcomes remains elusive, triggering structural, computational, spectroscopic, kinetic, and enzyme engineering studies. In this Perspective, we will highlight how first enzyme and substrate engineering examples suggest that the chemical reaction pathway within α-KGDs can be intentionally tailored using rational design principles. We will delineate the structural and mechanistic investigations of the reprogrammed enzymes and how they begin to inform about the enzymes' structure-function relationships that determine chemoselectivity. Application of this knowledge in future enzyme and substrate engineering campaigns will lead to the development of powerful C-H activation catalysts for chemical synthesis.

Folding and Fracture of Single-Crystal Graphene Grown on a Cu(111) Foil.

A single-crystal graphene film grown on a Cu(111) foil by chemical vapor deposition (CVD) has ribbon-like fold structures. These graphene folds are highly oriented and essentially parallel to each other. Cu surface steps underneath the graphene are along the <110>and <211>directions, leading to the formation of the arrays of folds. The folds in the single-layer graphene (SLG) are not continuous but break up into alternating patterns. A "joint" (an AB-stacked bilayer graphene) region connects two neighboring alternating regions, and the breaks are always along zigzag or armchair directions. Folds formed in bilayer or few-layer graphene are continuous with no breaks. Molecular dynamics simulations show that SLG suffers a significantly higher compressive stress compared to bilayer graphene when both are under the same compression, thus leading to the rupture of SLG in these fold regions. The fracture strength of a CVD-grown single-crystal SLG film is simulated to be about 70GPa. This study greatly deepens the understanding of the mechanics of CVD-grown single-crystal graphene and such folds, and sheds light on the fabrication of various graphene origami/kirigami structures by substrate engineering. Such oriented folds can be used in a variety of further studies.

Substrate and Process Engineering for Biocatalytic Synthesis and Facile Purification of Human Milk Oligosaccharides.

Innovation in process development is essential for applying biocatalysis in industrial and laboratory production of organic compounds, including beneficial carbohydrates such as human milk oligosaccharides (HMOs). HMOs have attracted increasing attention for their potential application as key ingredients in products that can improve human health. To efficiently access HMOs through biocatalysis, a combined substrate and process engineering strategy is developed, namely multistep one-pot multienzyme (MSOPME) design. The strategy allows access to a pure tagged HMO in a single reactor with a single C18-cartridge purification process, despite the length of the target. Its efficiency is demonstrated in the high-yielding (71-91 %) one-pot synthesis of twenty tagged HMOs (83-155 mg), including long-chain oligosaccharides with or without fucosylation or sialylation up to nonaoses from a lactoside without the isolation of the intermediate oligosaccharides. Gram-scale synthesis of an important HMO derivative - tagged lacto-N-fucopentaose-I (LNFP-I) - proceeds in 84 % yield. Tag removal is carried out in high efficiency (94-97 %) without the need for column purification to produce the desired natural HMOs with a free reducing end. The method can be readily adapted for large-scale synthesis and automation to allow quick access to HMOs, other glycans, and glycoconjugates.

Enantioselective Synthesis of α-Trifluoromethyl Amines via Biocatalytic N-H Bond Insertion with Acceptor-Acceptor Carbene Donors.

The biocatalytic toolbox has recently been expanded to include enzyme-catalyzed carbene transfer reactions not occurring in Nature. Herein, we report the development of a biocatalytic strategy for the synthesis of enantioenriched α-trifluoromethyl amines through an asymmetric N–H carbene insertion reaction catalyzed by engineered variants of cytochrome c552 from Hydrogenobacter thermophilus. Using a combination of protein and substrate engineering, this metalloprotein scaffold was redesigned to enable the synthesis of chiral α-trifluoromethyl amino esters with up to >99% yield and 95:5 er using benzyl 2-diazotrifluoropropanoate as the carbene donor. When the diazo reagent was varied, the enantioselectivity of the enzyme could be inverted to produce the opposite enantiomers of these products with up to 99.5:0.5 er. This methodology is applicable to a broad range of aryl amine substrates, and it can be leveraged to obtain chemoenzymatic access to enantioenriched β-trifluoromethyl-β-amino alcohols and halides. Computational analyses provide insights into the interplay of protein- and reagent-mediated control on the enantioselectivity of this reaction. This work introduces the first example of a biocatalytic N–H carbenoid insertion with an acceptor–acceptor carbene donor, and it offers a biocatalytic solution for the enantioselective synthesis of α-trifluoromethylated amines as valuable synthons for medicinal chemistry and the synthesis of bioactive molecules.

Water-assisted controllable growth of atomically thin WTe2 nanoflakes by chemical vapor deposition based on precursor design and substrate engineering strategies

WTe2 nanostructures have intrigued much attention due to their unique properties, such as large non-saturating magnetoresistance, quantum spin Hall effect and topological surface state. However, the controllable growth of large-area atomically thin WTe2 nanostructures remains a significant challenge. In the present work, we demonstrate the controllable synthesis of 1T′ atomically thin WTe2 nanoflakes (NFs) by water-assisted ambient pressure chemical vapor deposition method based on precursor design and substrate engineering strategies. The introduction of water during the growth process can generate a new synthesized route by reacting with WO3 to form intermediate volatile metal oxyhydroxide. Using WO3 foil as the growth precursor can drastically enhance the uniformity of as-prepared large-area 1T′ WTe2 NFs compared to WO3 powders. Moreover, highly oriented WTe2 NFs with distinct orientations can be obtained by using a-plane and c-plane sapphire substrates, respectively. Corresponding precursor design and substrate engineering strategies are expected to be applicable to other low dimensional transition metal dichalcogenides, which are crucial for the design of novel electronic and optoelectronic devices.

Substrate Engineering-Tailored Fabrication of Aligned Graphene Nanoribbon Arrays: Implications for Graphene Electronic Devices

Along with carbon nanotubes and other low-dimensional materials, graphene nanoribbons (GNRs) are an active area of research and are candidates for the next generation of semiconductors with unparalleled electrical performance. An effective method was demonstrated to fabricate aligned GNR arrays of various lengths and densities by etching the wrinkle arrays that we created by substrate engineering. The width of the GNR could be 10 nm, and density of the GNR array was highly tailorable with a maximum average of 2.5 ribbons/μm, which could form in any position on the substrate. We tailored the length of the array to be within the 200–800 nm range by adjusting the parameters of the substrate structure. The as-prepared GNRs could be organized in both single and array manners, which shows an on/off ratio of >10 indicated by an open band gap of graphene. This result provides a route to fabricate aligned GNR arrays conveniently, efficiently, and with high controllability and allows for large-scale integration of GNRs into nanoelectronics or optoelectronics.

Phosphorescence Tuning of Fluorine, Oxygen-Codoped Carbon Dots by Substrate Engineering

Phosphorescence Tuning of Fluorine, Oxygen-Codoped Carbon Dots by Substrate Engineering

Surface Engineering of Substrates for Chemical Vapor Deposition Growth of Graphene and Applications in Electronic and Spintronic Devices

Controllable synthesis of large-scale and high-quality graphene film is a basis for development of electronic and spintronic devices. Chemical vapor deposition (CVD) has been considered as a potential method for the industrialized preparation of high-quality graphene. The substrate in CVD is used to support graphene and even help graphene grow. Different substrates may lead to different graphene growth results. Therefore, it is of great importance to select appropriate substrates and growth strategies. In addition, the performance demands of advanced device also urgently require high-quality CVD-derived graphene supports. In this review, we summarize the current advances in surface engineering on substrates for CVD growth of graphene. Surface engineering involves anisotropic disordered, anisotropic ordered, and isotropic homogeneous surfaces of catalytic substrates, and surfaces of insulating substrates. Meanwhile, we describe how to use different surface engineering techniques to control the orientation of graphene domains, grow large-area single-crystal graphene domains, and regulate graphene layers. This information will provide a reference for the effective selection of substrates. Moreover, we review the current progress of graphene in the fields of charge and spin transport, demonstrating that graphene has broad prospects in the next generation of communications and storage. Finally, the opportunities and challenges in the controllable CVD-derived preparation of graphene and its application are discussed.

Plasmonic hotspot engineering of Ag-coated polymer substrates with high reproducibility and photothermal stability

Plasmonic silver nanoparticles (AgNPs) arranged on polyimide (PI) nanopillars (AgNP/PI) were developed as a stable photothermal surface-enhanced Raman spectroscopy (SERS) platform. The AgNP/PI substrates were prepared via maskless plasma etching and metal deposition using an in situ vacuum sputtering system. The AgNP/PI with high periodicity and high areal density led to high sensitivity, with a SERS enhancement factor (EF) of 2.2 × 108, and excellent reproducibility (relative standard deviation of 7.6%), as evaluated using the high-precision Raman mapping technique. To support the high SERS EF and sensitivity, the near-field enhancements of the dense AgNP array were calculated using a finite-difference time domain method. Notably, compared with AgNPs on polyethylene terephthalate (PET) nanopillar substrates, the AgNPs formed on the thermally stable PI nanopillar substrates exhibited excellent photothermal stability under illumination with a high-powered laser. The PI and PET surface changes induced by photoinduced local heating were investigated in terms of the glass-transition temperature, coefficient of thermal expansion, and thermal conductivity. The new plasmonic SERS platform has strong potential for reliable molecular detection in practical sensing applications with high-powered laser illuminations.

Cover Feature: Harnessing P450 Enzyme for Biotechnology and Synthetic Biology (ChemBioChem 3/2022)

P450s have attracted increasing attention in synthetic biology and biotechnology. To leverage their catalytic efficiency, different strategies have been developed including substrate engineering, allosteric effectors, decoy-based small molecules, artificial enzyme cascades, one-pot multienzyme reactions (OPME), and enzyme-materials hybridization. These research efforts also have important implications for the study of other enzymes and many fields of application. More information can be found in the Minireview by L. Zhang and Q. Wang.

"A Study in Yellow": Investigations in the Stereoselectivity of Ene-Reductases.

Ene‐reductases from the Old Yellow Enzyme (OYE) superfamily are a well‐known and efficient biocatalytic alternative for the asymmetric reduction of C=C bonds. Considering the broad variety of substituents that can be tolerated, and the excellent stereoselectivities achieved, it is apparent why these enzymes are so appealing for preparative and industrial applications. Different classes of C=C bonds activated by at least one electron‐withdrawing group have been shown to be accepted by these versatile biocatalysts in the last decades, affording a vast range of chiral intermediates employed in the synthesis of pharmaceuticals, agrochemicals, flavours, fragrances and fine chemicals. In order to access both enantiomers of reduced products, stereodivergent pairs of OYEs are desirable, but their natural occurrence is limited. The detailed knowledge of the stereochemical course of the reaction can uncover alternative strategies to orient the selectivity via mutagenesis, evolution, and substrate engineering. An overview of the ongoing studies on OYE‐mediated bioreductions will be provided, with particular focus on stereochemical investigations by deuterium labelling.

Harnessing P450 Enzyme for Biotechnology and Synthetic Biology.

Cytochrome P450 enzymes (P450s, CYPs) catalyze the oxidative transformation of a wide range of organic substrates. Their functions are crucial to xenobiotic metabolism and steroid transformation in humans and other organisms. The enzymes are promising for synthetic biology applications but limited by several drawbacks including low turnover rates, poor stability, the dependance of expensive cofactors and redox partners, and the narrow substrate scope. To conquer these obstacles, emerging strategies including substrate engineering, usage of decoy and decoy-based small molecules auxiliaries, designing of artificial enzyme cascades and the incorporation of materials have been explored based on the unique properties of P450s. These strategies can be applied to a wide range of P450s and can be combined with protein engineering to improve the enzymatic activities. This minireview will focus on some recent developments of these strategies which have been used to leverage P450 catalysis. Remaining challenges and future opportunities will also be discussed.

Modulation of trion and exciton formation in monolayer WS2 by dielectric and substrate engineering

Photoluminescence (PL) of transition metal dichalcogenide (TMD) monolayers is strongly influenced by the dielectric environment. The defect states present in the substrate induces uncontrollable doping in the TMD monolayer and thereby modifies the PL spectra. There have been enormous efforts to tune and overcome the effect of inevitable substrate defects in PL spectra, but a proper understanding and a convenient way are still lacking. Here, we systematically studied the effect of surface defects by gradually increasing the separation between WS2 monolayer and substrate. Hence, we could precisely modulate the exciton and trion contribution in the PL spectra of WS2. The excitation power dependant measurements on dielectric engineered and patterned substrates helped us to shed light on the mechanism of PL modulation in monolayer WS2. We have also studied the influence of the nature of the charge carried by substrate defects on the PL spectra. These results open a new pathway to modulate and obtain the desired PL spectra of TMDs by engineering the substrates. Our findings will be useful for fabricating excitonic interconnects, valleytronic, and single-photon devices.

Nγ -Hydroxyasparagine: A Multifunctional Unnatural Amino Acid That is a Good P1 Substrate of Asparaginyl Peptide Ligases.

Peptidyl asparaginyl ligases (PALs) are powerful tools for peptide macrocyclization. Herein, we report that a derivative of Asn, namely Nγ -hydroxyasparagine or Asn(OH), is an unnatural P1 substrate of PALs. By Asn(OH)-mediated cyclization, we prepared cyclic peptides as new matrix metalloproteinase 2 (MMP2) inhibitors displaying the hydroxamic acid moiety of Asn(OH) as the key pharmacophore. The most potent cyclic peptide (Ki =2.8±0.5 nM) was built on the hyperstable tetracyclic scaffold of rhesus theta defensin-1. The Asn(OH) residue in the cyclized peptides can also be readily oxidized to Asp. By this approach, we synthesized several bioactive Asp-containing cyclic peptides (MCoTI-II, kB2, SFTI, and integrin-targeting RGD peptides) that are otherwise difficult targets for PAL-catalyzed cyclization owing to unfavorable kinetics of the P1-Asp substrates. This study demonstrates that substrate engineering is a useful strategy to expand the application of PAL ligation in the synthesis of therapeutic cyclic peptides.