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In a recent communication (A. Shivhare, B. Dehariya, S. R. Gadre and M. M. Deshmukh, Phys. Chem. Chem. Phys. , 2024, 26 , 21332), we proposed a method for calculating the energy of a hydrogen bond (HB), which is common to two or more cyclic networks of HBs in water (H 2 O) n clusters. For this purpose, the sum of the cooperativity contributions (CCs) of these cyclic structures, estimated using the molecular tailoring approach (MTA)-based method, was added to the energy of this HB in the respective water dimer isolated from the cluster. The HB energies calculated in this fashion ( E SynergeticHB) were in excellent agreement with their actual cluster counterparts ( E clusterHB). In this work, we test the generality of this methodology. For this purpose, we employed clusters of ammonia (NH3)n, hydrogen sulphide (H2S)n, mixed (H2S)m(H2O)n, (NH3)m(H2O)n, methanol-water (CH3OH)m(H2O)n, and hydrogen fluoride-water (HF)m(H2O)n exhibiting HBs of variable strength (1 to 19 kcal mol -1 ). The HB energies in all these molecular clusters calculated using the present method were found to be accurate. The absolute difference between the E SynergeticHB and E clusterHB values in these clusters is found to be less than 0.5 kcal mol -1 . Importantly, the present method not only enables accurate HB energy estimation in molecular clusters, but also offers qualitative guidelines for this purpose. The latter are based on the nature of cyclic cooperativity, exhibiting either full cyclic cooperativity (FCC), partial cyclic cooperativity (PCC) or anti-cooperativity (AC).

We report a direct application of the molecular tailoring approach-based (MTA-based) method to calculate the individual hydrogen bond (HB) energy in molecular crystal. For this purpose, molecular crystals of nitromalonamide (NMA) and salicylic acid (SA) were taken as test cases. Notably, doing a correlated computation using a large molecular crystal structure is difficult. Among 15 density functional theory functionals, the B3LYP provides accurate estimates of HB energies closed to the CCSD(T) ones using the 6-311 + G(d,p) basis set for all atoms. The direct application of the MTA-based method to these crystal structures is although straightforward. For instance, the calculated energy suggests that three intramolecular HBs in NMA crystal are of stronger strength (7.3-17.0 kcal/mol) than the intermolecular ones (2.7-4.0 kcal/mol). On the other hand, intermolecular HB in SA crystal is moderately stronger (9.9 kcal/mol) than intramolecular one (8.1 kcal/mol). However, these energy calculations by the MTA-based method are very expensive. For instance, the time needed to evaluate the energy of all seven HBs in NMA crystal (having molecules within maximum of 15 unit cells) is 122,681 min (~2.7 months). In view of this, we assessed our recently proposed linear-scaling Fragments-in-Fragments (Frags-in-Frags) method for estimating the single-point energies of parent molecular crystal and fragments of the MTA-based method. It has been found that the estimated HB energies by the Frags-in-Frags method are in excellent linear agreement with their MTA-based counterparts (R 2  = 0.9993). Furthermore, root mean square deviation is 0.12 kcal/mol. Mean and maximum absolute errors are 0.10 and 0.5 kcal/mol, respectively, and the standard deviation is 0.14 kcal/mol. Importantly, the Frags-in-Frags method is computationally efficient; it needs only 18,289 min (~12.7 days) for the estimation of energy of all HBs in NMA crystal and 3499 min (~2.4 days) for all HBs in SA crystal., (© 2025 Wiley Periodicals LLC.)

The study investigates the phenomenon of bond stretch isomerism (BSI) in complexes formed between alkali metals (Li, Na, K) and various non-aromatic, aromatic hydrocarbons, as well as heteroaromatic systems. The research employs density functional theory (DFT) calculations to optimize complex geometries and analyze their electronic structures using molecular electrostatic potential (MESP), charge, and spin density analyses. The results reveal that these complexes can exist in two distinct configurations: 'loose' long-bond isomers (lbi) that retain the original hydrocarbon geometry and 'tight' short-bond isomers (sbi) that undergo geometrical distortion upon complexation, with sbi generally being more stable. The interconversion between lbi and sbi occurs through a transition state. The study highlights the crucial role of electron transfer in BSI, with sbi involving valence electron transfer from the metal to the hydrocarbon, leading to zwitterionic radical complexes. In contrast, lbi exhibit a slight electron density transfer from the hydrocarbon to the metal. The presence of low-energy transition states between lbi and sbi suggests a dynamic shuttling mechanism for alkali metals, particularly Li, on hydrocarbon surfaces. The study identifies Li complexes as potential candidates for anode materials in batteries due to their stability and electron transfer properties, offering valuable insights into the design of advanced materials for energy storage applications.

Members of a new class of bifunctional amino quaternary phosphonium salts have been synthesized and utilized as catalysts in aldol condensation reactions, as demonstrated herein. These secondary amines feature a phosphonium ion connected by a carbon chain, enabling the quaternary phosphonium ion to engage in distinct cooperative noncovalent interactions. These interactions work in tandem to stabilize different transition state complexes, exclusively controlling competing amine-catalyzed aldol pathways via the Mannich mechanism. Comprehensive mechanistic investigations were conducted through theoretical calculations. This study uncovers a proximity-driven catalytic mechanism in which the distance between the N and the P + of the bifunctional catalyst emerges as a critical factor determining catalytic efficacy. The method has been demonstrated through its application to the total synthesis of several bioactive natural products.

The present study delves into the question of how the strength of a hydrogen bond (HB) common to two or more cyclic HB networks is influenced by the cooperativity contributions (CCs) of these cycles. We employ the molecular tailoring approach-based method to calculate the cyclic CCs in water clusters, W n ( n = 6-20). The energy of an HB in a W n cluster is estimated by adding the total cyclic CC to its counterpart in the respective dimer. The resulting HB energies closely match their full cluster counterparts, typically within 1.0 kcal mol -1 , with substantial CCs of these cyclic networks.

The noncovalent interactions (NCIs) are omnipresent in chemistry, physics, and biology. The study of such interactions offers insights into various physicochemical phenomena. Some indirect approaches proposed in the literature for exploring the NCIs are briefly reviewed in Section 1 of this Perspective. These include: (i) Shift in the stretching frequency of an X-Y bond involved in X-Y···Z interaction. (ii) Topological analysis of molecular electron density. (iii) Empirical equations derived employing experimental and theoretical quantities. However, a direct method for estimating individual intramolecular/intermolecular interaction energies has been conspicuous by its absence from the literature. We have developed a molecular tailoring approach (MTA)-based method enabling a direct and reliable estimation of the energy of intra- as well as intermolecular interactions. This method offers a direct and reliable estimation of these interactions, in particular of the hydrogen bonds (HB) in molecules/weakly bound clusters along with the respective cooperativity contribution. In Section 2, the basis of our method is discussed, along with some illustrative examples. The application of this method to a variety of molecules and clusters, with a special emphasis on estimating the HB energy along with the energy of other NCIs is presented in Section 3. Section 4 discusses some computational strategies for applying our method to large molecular clusters. The last Section provides a summary and a discussion on future developments.

Assembling atomic layers of van der Waals materials (vdW) combines the physics of two materials, offering opportunities for novel functional devices. Realization of this has been possible because of advancements in nanofabrication processes which often involve chemical processing of the materials under study; this can be detrimental to device performance. To address this issue, we have developed a modified micro-manipulator setup for cryogenic exfoliation, pick up, and transfer of vdW materials to assemble heterostructures. We use the glass transition of a polymer PDMS to cleave a flake into two, followed by its pick-up and drop to form pristine twisted junctions. To demonstrate the potential of the technique, we fabricated twisted heterostructure of Bi 2 Sr 2 CaCu 2 O 8+x (BSCCO), a van der Waals high-temperature cuprate superconductor. We also employed this method to re-exfoliate NbSe 2 and make twisted heterostructure. Transport measurements of the fabricated devices indicate the high quality of the artificial twisted interface. In addition, we extend this cryogenic exfoliation method for other vdW materials, offering an effective way of assembling heterostructures and twisted junctions with pristine interfaces., (© 2024. The Author(s).)

Many superconducting systems with broken time-reversal and inversion symmetry show a superconducting diode effect, a non-reciprocal phenomenon analogous to semiconducting p-n-junction diodes. While the superconducting diode effect lays the foundation for realizing ultralow dissipative circuits, Josephson-phenomena-based diode effect (JDE) can enable the realization of protected qubits. The superconducting diode effect and JDE reported thus far are at low temperatures (~4 K), limiting their applications. Here we demonstrate JDE persisting up to 77 K using an artificial Josephson junction of twisted layers of Bi 2 Sr 2 CaCu 2 O 8+δ . JDE manifests as an asymmetry in the magnitude and distributions of switching currents, attaining the maximum at 45° twist. The asymmetry is induced by and tunable with a very small magnetic field applied perpendicular to the junction and arises due to interaction between Josephson and Abrikosov vortices. We report a large asymmetry of 60% at 20 K. Our results provide a path towards realizing superconducting Josephson circuits at liquid-nitrogen temperature., (© 2024. The Author(s), under exclusive licence to Springer Nature Limited.)

The superconducting coplanar waveguide (SCPW) cavity plays an essential role in various areas like superconducting qubits, parametric amplifiers, radiation detectors, and studying magnon-photon and photon-phonon coupling. Despite its wide-ranging applications, the use of SCPW cavities to study various van der Waals 2D materials has been relatively unexplored. The resonant modes of the SCPW cavity exquisitely sense the dielectric environment. In this work, we measure the charge compressibility of bilayer graphene coupled to a half-wavelength SCPW cavity. Our approach provides a means to detect subtle changes in the capacitance of the bilayer graphene heterostructure, which depends on the compressibility of bilayer graphene, manifesting as shifts in the resonant frequency of the cavity. This method holds promise for exploring a wide class of van der Waals 2D materials, including transition metal dichalcogenides (TMDs) and their moiré, where DC transport measurement is challenging.

A procedure, derived from the fragmentation-based molecular tailoring approach (MTA), has been proposed and extensively applied by Deshmukh and Gadre for directly estimating the individual hydrogen bond (HB) energies and cooperativity contributions in molecular clusters. However, the manual fragmentation and high computational cost of correlated quantum chemical methods make the application of this method to large molecular clusters quite formidable. In this article, we report an in-house developed software for automated hydrogen bond energy estimation (H-BEE) in large molecular clusters. This user-friendly software is essentially written in Python and executed on a Linux platform with the Gaussian package at the backend. Two approximations to the MTA-based procedure, viz. the first spherical shell (SS1) and the Fragments-in-Fragments (Frags-in-Frags), enabling cost-effective, automated evaluation of HB energies and cooperativity contributions, are also implemented in this software. The software has been extensively tested on a variety of molecular clusters and is expected to be of immense use, especially in conjunction with correlated methods such as MP2, CCSD(T), and so forth., (© 2023 Wiley Periodicals LLC.)

A green approach for the synthesis of electrophilic alkenes has been developed via Knoevenagel condensation between active methylene compounds and carbonyl compounds using Mg powder under aqueous conditions. In this strategy, Mg(OH) 2 acts as a catalyst, which was generated in situ by the reaction between metallic Mg (20 mol %) and water. Mg was found to be an efficient, nontoxic, and inexpensive metal catalyst system for producing a range of electrophilic alkenes in excellent yields (≤98%). A gram-scale synthesis of electrophilic alkenes has been developed, and Mg metal was recovered and recycled up to three times without an appreciable loss of catalytic activity. A catalytic cycle was proposed, and the reaction mechanism was investigated using density functional theory. The key steps are enolization of ethyl cyanoacetate, C-C bond formation, and then regeneration of the catalyst via metathesis with H 2 O. The overall reaction occurs easily with a maximum Δ G ° ⧧ value of 7.9 kcal/mol for the rate-determining C-C bond formation step. Our protocol has several advantages and can be further extended to one-pot sequential Knoevenagel condensation and Michael addition, and one-pot sequential Knoevenagel condensation and chemoselective reduction can be used for the synthesis of valuable precursors of pharmaceutical products under green and aqueous conditions.

Nitric oxide (NO) and its redox congeners (NO + and NO - ), designated as X, play vital roles in various atmospheric and biological events. Understanding the interaction between X and water is inevitable to explain the different reactions that occur during these events. The present study is a unified attempt to explore the noncovalent interactions in microhydrated networks of X using the MP2/aug-cc-pVTZ//MP2/6-311++G(d,p) level of theory. The interactions between X and water have been probed by the molecular electrostatic potential (MESP) by exploiting the features of the most positive ( V max ) and most negative potential ( V min ) sites. The individual energy and cooperativity contributions of various types of noncovalent interactions present in X(H 2 O) n =1-5 complexes are estimated with the help of a molecular tailoring-based approach (MTA-based). The MTA-based analysis reveals that among various possible interactions in NO(H 2 O) n complexes, the water···water hydrogen bonds (HBs) are the strongest. Neutral NO can form hydrogen and pnicogen bonds (PBs) with water depending on the orientation; however, such HBs and PBs are the weakest. On the other hand, in the NO + (H 2 O) n complexes, the NO + ···water interactions that occur through PBs are the strongest; the next one is the chalcogen bonding (CB), and the water···water HBs are the weakest. In the case of the NO - (H 2 O) n complexes, the HB interactions via both N and O atoms of NO - and water molecules are the strongest ones. The strength of water···water HB interactions is also seen to increase with the increase in the number of water molecules in NO - (H 2 O) n . The present study exemplifies the applicability of MTA-based calculations for quantifying various types of individual noncovalent interactions and their interplay in microhydrated networks of NO and its related ions.

A palladium(II)-catalyzed regio- and stereoselective difunctionalization of alkynoic acids has been achieved using sodium sulfinates and isocyanides to synthesize ( E )-β-sulfonylacrylamides. The reaction proceeds via decarboxylative isocyanide addition, followed by sulfonylation. This three-component process works well with aromatic, heteroaromatic, and aliphatic alkynoic acids with good functional group tolerance and excellent regio- and stereoselectivity. DFT calculations were carried out to explain the reaction mechanism and the stereoselective formation of ( E )-β-sulfonylacrylamides.

The knowledge of individual hydrogen bond (HB) strength in molecular clusters is indispensable to get insights into the bulk properties of condensed systems. Recently, we have developed the molecular tailoring approach based (MTA-based) method for the estimation of individual HB energy in molecular clusters. However, the direct use of this MTA-based method to large molecular clusters becomes progressively difficult with the increase in the size of a cluster. To overcome this caveat, herein, we propose the use of linear scaling method (such as the original MTA method) for the estimation of single-point (SP) energies of large-sized parent molecular cluster and their respective fragments. Because the fragments of the MTA-based method, for the estimation of HB energy, are further fragmented, this proposed strategy is called as Fragments-in-Fragments (Frags-in-Frags) method. The SP energies of fragments and parent cluster calculated by the Frags-in-Frags approach were utilized to estimate the individual HB energy. The estimated individual HB energies, in various molecular clusters, by Frags-in-Frags method are found to be in excellent linear agreement with their MTA-based counterparts (R 2  = 0.9975 of 348 data points). The difference being less than 0.5 kcal/mol in most of the cases. Furthermore, RMSD is 0.43 kcal/mol, MAE is 0.33 kcal/mol, and the standard deviation is 0.44 kcal/mol. Importantly, the Frags-in-Frags method not only enables the reliable estimation of HB energy in large molecular clusters but also requires less computational time and can be possible even with off-the-shelf hardware., (© 2023 Wiley Periodicals LLC.)

The variation in the hydrogen bond (HB) strength has considerable consequences on the physicochemical properties of molecular clusters. Such a variation mainly arises due to the cooperative/anti-cooperative networking effect of neighboring molecules connected by HBs. In the present work, we systematically study the effect of neighboring molecules on the strength of an individual HB and the respective cooperativity contribution toward each of them in a variety of molecular clusters. For this purpose, we propose a use of a small model of a large molecular cluster called the spherical shell-1 (SS1) model. This SS1 model is constructed by placingg the spheres of an appropriate radius centered on X and Y atoms of the X-H···Y HB under consideration. The molecules falling within these spheres constitute the SS1 model. Utilizing this SS1 model, the individual HB energies are calculated within the molecular tailoring approach-based framework and the results are compared with their actual counterparts. It is found that the SS1 is a reasonably good model of large molecular clusters, providing 81-99% of the total HB energy estimated using the actual molecular clusters. This in turn suggests that the maximum cooperativity contribution toward a particular HB is due to the fewer number of molecules (in the SS1 model) directly interacting with two molecules involved in its formation. We further demonstrate that the remaining part of the energy or cooperativity (∼1 to 19%) is captured by the molecules falling in the second spherical shell (SS2) centered on the hetero-atom of the molecules in the SS1 model. The effect of increasing size of a cluster on the strength of a particular HB, calculated by the SS1 model, is also investigated. The calculated value of the HB energy remains unchanged with the increase in the size of a cluster, emphasizing the short-ranged nature of the HB cooperativity in neutral molecular clusters.

The study of molecular clusters to understand the properties of condensed systems has been the subject of immense interest. To get insight into these properties, the knowledge of various noncovalent interactions present in these molecular clusters is indispensable. Our recently developed molecular tailoring approach-based (MTA-based) method for the estimation of the individual hydrogen bond (HB) energy in molecular clusters is useful for this purpose. However, the direct application of this MTA-based method becomes progressively difficult with the increase in the size of the cluster. This is because of the difficulty in the evaluation of single-point energy at the correlated level of theory. To overcome this caveat, herein, we propose a two-step method within the our own N-layer integrated molecular orbital molecular mechanics (ONIOM) framework. In this method, the HB energy evaluated by the MTA-based method employing the actual molecular cluster at a low Hartree-Fock (HF) level of theory is added to the difference in the HB energies evaluated by the MTA-based method, employing an appropriate small model system, called the shell-1 model, calculated at high (MP2) and low (HF) levels of theory. The shell-1 model of a large molecular cluster is made up of only a few molecules that are in direct contact (by a single HB) with the two molecules involved in the formation of an HB under consideration. We tested this proposed two-step ONIOM method to estimate the individual HB energies in various molecular clusters, viz., water (W n , n = 10-16, 18 and 20), (H 2 O 2 ) 12 , (H 2 O 3 ) 8 , (NH 3 ) n and strongly interacting (HF) 15 and (HF) m (W) n clusters. Furthermore, these estimated individual HB energies by the ONIOM method are compared with those calculated by the MTA-based method using actual molecular clusters. The estimated individual HB energies by the ONIOM method, in all these clusters, are in excellent linear one-to-one agreement ( R 2 = 0.9996) with those calculated by the MTA-based method using actual molecular clusters. Furthermore, the small values of root-mean-square deviation (0.06), mean absolute error (0.04), |Δ E max | (0.21) and Sε (0.06) suggest that this two-step ONIOM method is a pragmatic approach to provide accurate estimates of individual HB energies in large molecular clusters.

In the current work, a systematic evaluation of the different types of non-covalent interactions (NCIs) in acetaldehyde dimers, including dimers of mono-halo (XCH 2 CHO) 2 , di-halo (X 2 CHCHO) 2 and tri-halo substituted (X 3 CCHO) 2 acetaldehydes via the associated stabilization energy of these dimers has been performed. Furthermore, a topological analysis of the electron density based on the quantum theory of atoms in molecules (QTAIM) and non-covalent interaction reduced density gradient (NCI-RDG) isosurfaces has also been performed to evaluate the nature of these NCIs. The geometrical and electronic characteristics have been evaluated via the presence of different electron-donating groups (EDGs) and electron-withdrawing groups (EWGs) or substituents in dimers of these molecules, namely, XCH(Y)CHO and X 2 C(Y)CHO (wherein X = -F, -Cl, and -Br and Y = -SO 3 H, -CN, -NO 2 , -NH 2 , -CH 3 , -OCH 3 , and -SMe 3 ). The C-H⋯O, C-H⋯X, X⋯X, X⋯O and C⋯O tetrel bonded contacts have been recognized to play an important role in the stabilization of the formed dimers. This study also establishes the fact that the overall stability of the dimeric assemblies is governed by the contributions from the mutual and complex interplay of a variety of interactions in the investigated dimers. Hence considerations based on strong H-bond donor-acceptor characteristics hold relevance for simple systems only, but slight alteration in the electronic environment can affect the overall stabilization energies of the system being investigated and the nature of the interactions that contribute towards the same.

An efficient dual Pd-catalytic system was developed for one-pot synthesis of 3-sulfenylindoles via C-C, C-N and C-S bond construction directly from unactivated 2-iodo( NH )anilines under mild reaction conditions. Furthermore, 3-selenyl/halo/carbon-functionalized indoles were synthesized in good yields and a short reaction time. The synthetic utility of 3-sulfenylindole was also demonstrated. The key role of solvent in palladium catalysis was unravelled by DFT.

Moiré superlattices engineer band properties and enable observation of fractal energy spectra of Hofstadter butterfly. Recently, correlated-electron physics hosted by flat bands in small-angle moiré systems has been at the foreground. However, the implications of moiré band topology within the single-particle framework are little explored experimentally. An outstanding problem is understanding the effect of band topology on Hofstadter physics, which does not require electron correlations. Our work experimentally studies Chern state switching in the Hofstadter regime using twisted double bilayer graphene (TDBG), which offers electric field tunable topological bands, unlike twisted bilayer graphene. Here we show that the nontrivial topology reflects in the Hofstadter spectra, in particular, by displaying a cascade of Hofstadter gaps that switch their Chern numbers sequentially while varying the perpendicular electric field. Our experiments together with theoretical calculations suggest a crucial role of charge polarization changing concomitantly with topological transitions in this system. Layer polarization is likely to play an important role in the topological states in few-layer twisted systems. Moreover, our work establishes TDBG as a novel Hofstadter platform with nontrivial magnetoelectric coupling., (© 2022. The Author(s).)

In the present work, the energies of various types of individual HBs observed in neutral (NH 3 ) m (H 2 O) n , (m+n=2 to 7) clusters were estimated using the molecular tailoring approach (MTA)-based method. The calculated individual HB energies suggest that the O-H…N HBs are the strongest (1.21 to 12.49 kcal mol -1 ). The next ones are the O-H…O (3.97 to 9.30 kcal mol -1 ) HBs. The strengths of N-H…N (1.09 to 5.29 kcal mol -1 ) and N-H…O (2.85 to 5.56 kcal mol -1 ) HBs are the weakest. The HB energies in dimers also follow this rank ordering. However, the HB energies in dimers are much smaller than those obtained by the MTA-based method due to the loss in cooperativity contribution in the dimers. Thus, the calculated cooperativity contributions, for different types of HBs, fall in the range 0.64 to 5.73 kcal mol -1 . We wish to emphasize based on the energetic rank ordering obtained by the MTA-based method that the O-H of water is a better HB donor than the N-H of ammonia. The reasons for the observed energetic rank ordering are two folds: (i) intrinsically stronger O-H…N HBs than the O-H…O ones as revealed by dimer energies and (ii) the higher cooperativity contribution in the former than the later ones. Indeed, the MTA-based method is useful in providing the missing energetic rank ordering of various type of HBs in neutral (NH 3 ) m (H 2 O) n clusters, in the literature., (© 2022 Wiley-VCH GmbH.)

Josephson junctions (JJs) and their tunable properties, including their nonlinearities, play an important role in superconducting qubits and amplifiers. JJs together with the circuit quantum electrodynamics architecture form many key components of quantum information processing 1 . In quantum circuits, low-noise amplification of feeble microwave signals is essential, and Josephson parametric amplifiers (JPAs) 2 are the widely used devices. The existing JPAs are based on Al-AlO x -Al tunnel junctions realized in a superconducting quantum interference device geometry, where magnetic flux is the knob for tuning the frequency. Recent experimental realizations of two-dimensional (2D) van der Waals JJs 3-5 provide an opportunity to implement various circuit quantum electrodynamics devices 6-8 with the added advantage of tuning the junction properties and the operating point using a gate potential. While other components of a possible 2D van der Waals circuit quantum electrodynamics architecture have been demonstrated, a quantum-noise-limited amplifier, an essential component, has not been realized, to the best of our knowledge. Here we implement a quantum-noise-limited JPA using a graphene JJ, that has a linear resonance gate tunability of 3.5 GHz. We report 24 dB amplification with 10 MHz bandwidth and -130 dBm saturation power, a performance on par with the best single-junction JPAs 2,9 . Importantly, our gate-tunable JPA works in the quantum-limited noise regime, which makes it an attractive option for highly sensitive signal processing. Our work has implications for novel bolometers; the low heat capacity of graphene together with JJ nonlinearity can result in an extremely sensitive microwave bolometer embedded inside a quantum-noise-limited amplifier. In general, this work will open up the exploration of scalable device architectures of 2D van der Waals materials by integrating a sensor with the quantum amplifier., (© 2022. The Author(s), under exclusive licence to Springer Nature Limited.)

Superconducting nanowires are very important due to their applications ranging from quantum technology to astronomy. In this work, we implement a non-invasive process to fabricate nanowires of high- T c superconductor Bi 2 Sr 2 CaCu 2 O 8+ δ . We demonstrate that our nanowires can be used as bolometers in the visible range with very high responsivity of 9.7 × 10 3 V W -1 . Interestingly, in a long (30 μ m) nanowire of 9 nm thickness and 700 nm width, we observe bias current-dependent localized spots of maximum photovoltage. Moreover, the scalability of the bolometer responsivity with the normal state resistance of the nanowire could allow further performance improvement by increasing the nanowire length in a meander geometry. We observe phase slip events in nanowires with small cross-sections (12 nm thick, 300 nm wide, and 3 μ m long) at low temperatures. Our study presents a scalable method for realizing sensitive bolometers working near the liquid-nitrogen temperature., (© 2022 IOP Publishing Ltd.)

Recently, we have developed and tested a method, based on the molecular tailoring approach (MTA-based) to directly estimate the individual hydrogen bond (HB) energies in molecular clusters. Application of this MTA-based method to large molecular clusters is prohibitively difficult due to the evaluation of the energy of large-sized fragments. We propose here a smaller model system called the shell model, to overcome this difficulty. The shell model represents the first hydration shell of water molecules involved in the formation of HB under consideration. Utilizing the shell model as a parent system, fragmentation is carried out, in a fashion similar to the actual MTA-based method, to estimate individual HB energies in large water clusters (W n , n = 10-16, 18 and 20). The estimated individual HB energies in these W n clusters, employing the shell model, fall between 0.2 and 12.5 kcal mol -1 at the MP2/aug-cc-pVTZ level, with no net loss in the cooperativity contribution. We have also applied this shell model-based approach to estimate individual HB energies in the two lowest energy conformers of ammonia octamers (NH 3 ) 8 and mixed hydrogen fluoride-water clusters. The estimated individual HB energies employing the shell model, in all these molecular clusters studied in this work, are in good agreement with their actual MTA-based counterparts. The typical difference is less than 1 kcal mol -1 . Importantly, the shell model has a huge computational time advantage over the actual MTA-based method and it requires only modest hardware.

In this work, we examine the strength of various types of individual hydrogen bond (HB) in mixed methanol-water M n W m , (n+m=2 to 7) clusters, with an aim to understand the relative order of their strength, using our recently proposed molecular tailoring-based approach (MTA). Among all the types of HB, it is observed that the O M -H…O W HBs are the strongest (6.9 to 12.4 kcal mol -1 ). The next ones are O M -H…O M HBs (6.5 to 11.6 kcal mol -1 ). The O W -H…O W (0.2 to 10.9 kcal mol -1 ) and O W -H…O M HBs (0.3 to 10.3 kcal mol -1 ) are the weakest ones. This energetic ordering of HBs is seen to be different from the respective HB energies in the dimer i. e., O M -H…O M (5.0 to 6.0 kcal mol -1 )>O W -H…O M (1.5 to 6.0 kcal mol -1 )>O M -H…O W (3.8 to 5.6 kcal mol -1 )>O W -H…O W (1.2 to 5.0 kcal mol -1 ). The plausible reason for the difference in the HB energy ordering may be attributed to the increase or decrease in HB strengths due to the formation of cooperative or anti-cooperative HB networks. For instance, the cooperativity contribution towards the different types of HB follows: O M -H…O W (2.4 to 8.6 kcal mol -1 )>O M -H…O M (1.3 to 6.3 kcal mol -1 )>O W -H…O W (-1.0 to 6.5 kcal mol -1 )>O W -H…O M (-1.2 to 5.3 kcal mol -1 ). This ordering of cooperativity contribution is similar to the HB energy ordering obtained by the MTA-based method. It is emphasized here that, the interplay between the cooperative and anti-cooperative contributions are indispensable for the correct energetic ordering of these HBs., (© 2022 Wiley-VCH GmbH.)

Two-dimensional van der Waals heterostructures (vdWH) can result in novel functionality that crucially depends on interfacial structure and disorder. Bubbles at the vdWH interface can modify the interfacial structure. We probe the dynamics of a bubble at the interface of a graphene-hBN vdWH by using it as the drumhead of a NEMS device because nanomechanical devices are exquisite sensors. For drums with different interfacial bubbles, we measure the evolution of the resonant frequency and spatial mode shape as a function of electrostatic pulling. We show that the hysteretic detachment of layers of vdWH is triggered by the growth of large bubbles. The bubble growth takes place due to the concentration of stress resembling the initiation of fracture. The small bubbles at the heterostructure interface do not result in delamination as they are smaller than a critical fracture length. We provide insight into frictional dynamics and interfacial fracture of vdWH.

As the magnetic field penetrates the surface of a superconductor, it results in the formation of flux vortices. It has been predicted that the flux vortices will have a charged vortex core and create a dipolelike electric field. Such a charge trapping in vortices is particularly enhanced in high- T c superconductors (HTS). Here, we integrate a mechanical resonator made of a thin flake of HTS Bi 2 Sr 2 CaCu 2 O 8+δ into a microwave circuit to realize a cavity-electromechanical device. Due to the exquisite sensitivity of cavity-based devices to the external forces, we directly detect the charges in the flux vortices by measuring the electromechanical response of the mechanical resonator. Our measurements reveal the strength of surface electric dipole moment due to a single vortex core to be approximately 30 | e | a B , equivalent to a vortex charge per CuO 2 layer of 3.7 × 10 -2 | e |, where a B is the Bohr radius and e is the electronic charge.

In this work, our recently proposed molecular tailoring approach (MTA)-based method is employed for the evaluation of individual hydrogen-bond (HB) energies in linear (L) and cyclic (C) hydrogen fluoride clusters, (HF) n ( n = 3 to 8). The estimated individual HB energies calculated at the MP2(full)/aug-cc-pVTZ level for the L-(HF) n are between 6.2 to 9.5 kcal/mol and those in the C-(HF) n lie between 7.9 to 11.4 kcal/mol. The zero-point energy corrections and basis set superposition corrections are found to be very small (less than 0.6 and 1.2 kcal/mol, respectively). The cooperativity contribution toward individual HBs is seen to fall between 1.0 to 4.8 kcal/mol and 3.2 to 6.9 kcal/mol for linear and cyclic clusters, respectively. Interestingly, the HB energies in dimers, cleaved from these clusters, lie in a narrow range (4.4 to 5.2 kcal/mol) suggesting that the large HB strength in (HF) n clusters is mainly due to the large cooperativity contribution, especially for n ≥ 5 (50 to 62% of the HBs energy). Furthermore, the HB energies in these clusters show a good qualitative correlation with geometrical parameters (H···F distance and F-H···F angles), stretching frequencies of F-H bonds, and electron density values at the (3, -1) bond critical points.

In this work, we propose and test a method, based on the molecular tailoring approach (MTA), for the evaluation of individual hydrogen bond (HB) energies in ammonia (NH 3 ) n clusters. This methodology was tested, in our earlier work, on water clusters. Liquid ammonia being a universal, non-aqueous ionizing solvent, such information of individual HB strength is indispensable in many studies. The estimated HB energies by an MTA-based method, in (NH 3 ) n for n = 3-8, were calculated to be in the range of 0.65 to 5.54 kcal mol -1 with the cooperativity contribution falling between -0.54 and 1.88 kcal mol -1 both calculated at the MP2(full)/aug-cc-pVTZ level of theory. It is seen that the strong HBs in (NH 3 ) n clusters were additionally strengthened by the large contribution of HB cooperativity. The accuracy of these estimated HB energies was validated by approximately estimating the molecular energy of a given cluster by adding the sum of HB energies to the sum of monomer energies. This approximately estimated molecular energy of a given cluster was found to be in excellent agreement with the actual calculated values. The negligibly small difference (less than 5.6 kcal mol -1 ) in these two values suggests that the estimated individual HB energies in ammonia clusters are quite reliable. Furthermore, these estimated HB energies by MTA are in excellent qualitative agreement with the other indirect measures of HB strength, such as HB bond distances and angles, N-H stretching frequency and the electron density values at the (3,-1) bond critical points.

There is no general method available for the estimation of individual intermolecular interaction energies in weakly bound molecular clusters, and such studies are limited only to the dimer. Recently, we proposed a molecular tailoring approach-based method for the estimation of individual O-H···O hydrogen bond energies in water clusters. In the present work, we extend the applicability of this method for estimating the individual intermolecular interaction energies in benzene clusters, which are expected to be small. The basis set superposition error (BSSE)-corrected individual intermolecular interaction energies in linear (LN) benzene clusters, LN-(Bz) n n = 3-7, were calculated to be in the range from -1.75 to -2.33 kcal/mol with the cooperativity contribution falling between 0.05 and 0.20 kcal/mol, calculated at the MP2.5/aug-cc-pVDZ level of theory. In the case of non-linear (NLN) benzene clusters, NLN-(Bz) n n = 3-5, the BSSE-corrected individual intermolecular interaction energies exhibit a wider range from -1.16 to -2.55 kcal/mol with cooperativity contribution in the range from 0.02 to -0.61 kcal/mol. The accuracy of these estimated values was validated by adding the sum of interaction energies to the sum of monomer energies. These estimated molecular energies of clusters were compared with their actual calculated values. The small difference (<0.3 kcal/mol) in these two values suggests that our estimated individual intermolecular interaction energies in benzene clusters are quite reliable.

Hydrogen bonds (HBs) play a crucial role in many physicochemical and biological processes. Theoretical methods can reliably estimate the intermolecular HB energies. However, the methods for the quantification of intramolecular HB (IHB) energy available in the literature are mostly empirical or indirect and limited only to evaluating the energy of a single HB. During the past decade, the authors have developed a direct procedure for the IHB energy estimation based on the molecular tailoring approach (MTA), a fragmentation method. This MTA-based method can yield a reliable estimate of individual IHB energy in a system containing multiple H-bonds. After explaining and illustrating the methodology of MTA, we present its use for the IHB energy estimation in molecules and clusters. We also discuss the use of this method by other researchers as a standard, state-of-the-art method for estimating IHB energy as well as those of other noncovalent interactions.

Spin waves are studied for data storage, communication, and logic circuits in the field of spintronics based on their potential to substitute electrons. The recent discovery of magnetism in 2D systems such as monolayer CrI 3 and Cr 2 Ge 2 Te 6 has led to a renewed interest in such applications of magnetism in the 2D limit. Here, direct evidence of standing spin waves is presented along with the uniform precessional resonance modes in the van der Waals magnetic material, CrCl 3 . This is the first direct observation of standing spin-wave modes, set up along a thickness of 20 mm, in a van der Waals material. Standing spin waves are detected in the vicinity of both branches, optical and acoustic, of the antiferromagnetic resonance. Magnon-magnon coupling and softening of resonance modes with temperature enable extraction of interlayer exchange field as a function of temperature., (© 2020 Wiley-VCH GmbH.)

2D materials based superlattices have emerged as a promising platform to modulate band structure and its symmetries. In particular, moiré periodicity in twisted graphene systems produces flat Chern bands. The recent observation of anomalous Hall effect (AHE) and orbital magnetism in twisted bilayer graphene has been associated with spontaneous symmetry breaking of such Chern bands. However, the valley Hall state as a precursor of AHE state, when time-reversal symmetry is still protected, has not been observed. Our work probes this precursor state using the valley Hall effect. We show that broken inversion symmetry in twisted double bilayer graphene (TDBG) facilitates the generation of bulk valley current by reporting experimental evidence of nonlocal transport in a nearly flat band system. Despite the spread of Berry curvature hotspots and reduced quasiparticle velocities of the carriers in these flat bands, we observe large nonlocal voltage several micrometers away from the charge current path - this persists when the Fermi energy lies inside a gap with large Berry curvature. The high sensitivity of the nonlocal voltage to gate tunable carrier density and gap modulating perpendicular electric field makes TDBG an attractive platform for valley-twistronics based on flat bands.

High-temperature superconductors (HTSs) are important for potential applications and for understanding the origin of strong correlations. Bi 2 Sr 2 CaCu 2 O 8+δ (BSCCO), a van der Waals material, offers a platform to probe the physics down to a unit-cell. Guiding the flow of electrons by patterning 2DEGS and oxide heterostructures has brought new functionality and access to new science. Similarly, modifying superconductivity in HTS locally, on a small length scale, is of immense interest for superconducting electronics. A route to modify superconductivity locally by depositing metal on the surface is reported here by transport studies on few unit-cell thick BSCCO. Deposition of chromium (Cr) on the surface over a selected area of BSCCO results in insulating behavior of the underlying region. Cr locally depletes oxygen in CuO 2 planes and disrupts the superconductivity in the layers below. This technique of modifying superconductivity is suitable for making sub-micrometer superconducting wires and more complex superconducting devices., (© 2020 Wiley-VCH GmbH.)

No direct method for estimating the individual O-H···O hydrogen bond (H-bond) energies in water clusters (W n ) exists in the literature. In this work, we propose such a direct method based on the molecular tailoring approach, which also enables the estimation of the cooperativity contributions. The calculated H-bond energies at MP2(full)/aug-cc-pVTZ and CCSD(T)/aug-cc-pVDZ levels for W n , n = 3 to 8, agree well with one another and fall between 0.3 and 11.6 kcal mol -1 with the cooperativity contributions in the range of -1.2 and 7.0 kcal mol -1 . For gauging the accuracy of our H-bond energies for a cluster, the H-bond energy sum is added to the sum of monomer energies, and the results are compared with the respective total energy. These two values agree with each other to within 8.3 mH (∼5 kcal mol -1 ), testifying the accuracy of our estimated H-bond energies. Further, these H-bond strengths show a good correlation with the respective O-H stretching frequencies and the molecular electron density values at the (3, -1) O-H···O H-bond critical point.

We present a quick and reliable method to cut 2D materials for creating 2D twisted heterostructures and devices. We demonstrate the effectiveness of using a tapered fibre scalpel for cutting graphene. Electrical transport measurements show evidence of the desired twist between the graphene layers fabricated using our technique. Statistics of the number of successfully twisted stacks made using our method is compared with h-BN assisted tear-and-stack method. Also, our method can be used for twisted stack fabrication of materials that are few nanometers thick. Finally, we demonstrate the versatility of the tapered fibre scalpel for other shaping related applications for sensitive 2D materials.

Quantum oscillations provide a notable visualization of the Fermi surface of metals, including associated geometrical phases such as Berry's phase, that play a central role in topological quantum materials. Here we report the existence of a new quantum oscillation phase shift in a multiband system. In particular, we study the ABA-trilayer graphene, the band structure of which is composed of a weakly gapped linear Dirac band, nested within a quadratic band. We observe that Shubnikov-de Haas (SdH) oscillations of the quadratic band are shifted by a phase that sharply departs from the expected 2π Berry's phase and is inherited from the nontrivial Berry's phase of the linear band. We find this arises due to an unusual filling enforced constraint between the quadratic band and linear band Fermi surfaces. Our work indicates how additional bands can be exploited to tease out the effect of often subtle quantum mechanical geometric phases., (Copyright © 2019 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works. Distributed under a Creative Commons Attribution NonCommercial License 4.0 (CC BY-NC).)

Catalytic synthesis of dihydropyridine by transition-metal complex is one of the important research targets, recently. Density functional theory calculations here demonstrate that nickel(I) hydride complex (bpy)Ni I H (bpy = 2,2'-bipyridine) 1 is a good catalyst for hydrosilylation of both quinoline and pyridine. Two pathways are possible; in path 1, substrate reacts with 1 to form stable intermediate Int1. After that, N 3 ─C 1 bond of substrate inserts into Ni─H bond of 1 via TS1 to afford N-coordinated 1,2-dihydroquinoline Int2 with the Gibbs activation energy (ΔG° ‡ ) of 21.8 kcal mol -1 . Then, Int2 reacts with hydrosilane to form hydrosilane σ-complex Int3; this is named path 1A. In the other route (path 1B), Int1 reacts with phenylsilane in a concerted manner via hydride-shuttle transition state TS2 to afford Int3. In TS2, Si atom takes hypervalent trigonal bipyramidal structure. Formation of hypervalent structure is crucial for stabilization of TS2 (ΔG° ‡ = 17.3 kcal mol -1 ). The final step of path 1 is metathesis between Ni─N 3 bond of Int3 and Si─H bond of PhSiH 3 to afford N-silylated 1,2-dihydroproduct and regenerate 1 (ΔG° ‡ = 4.5 kcal mol -1 ). In path 2, 1 reacts with hydrosilane to form Int5, which then forms adduct Int6 with substrate through Si-N interaction between substrate and PhSiH 3 . Then, N-silylated 1,2-dihydroproduct is produced via hydride-shuttle transition state TS5 (ΔG° ‡ = 18.8 kcal mol -1 ). The absence of N-coordination of substrate to Ni I in TS5 is the reason why path 2 is less favorable than path 1B. Quinoline hydrosilylation occurs more easily than pyridine because quinoline has the lowest unoccupied molecular orbital at lower energy than that of pyridine. © 2019 Wiley Periodicals, Inc., (© 2019 Wiley Periodicals, Inc.)

The sequence of the zeroth Landau levels (LLs) between filling factors ν=-6 to 6 in ABA-stacked trilayer graphene (TLG) is unknown because it depends sensitively on the nonuniform charge distribution on the three layers of ABA-stacked TLG. Using the sensitivity of quantum Hall data on the electric field and magnetic field, in an ultraclean ABA-stacked TLG sample, we quantitatively estimate the nonuniformity of the electric field and determine the sequence of the zeroth LLs. We also observe anticrossings between some LLs differing by 3 in LL index, which result from the breaking of the continuous rotational to C&#95;{3} symmetry by the trigonal warping.

Graphene is a promising candidate for optoelectronic applications. In this report, a double gated bilayer graphene FET has been made using a combination of electrostatic and electrolytic gating in order to form an abrupt p-n junction. The presence of two Dirac peaks in the gating curve of the fabricated device confirms the formation of a p-n junction. At low temperatures, when the electrolyte is frozen intentionally, the photovoltage exhibits a six-fold pattern indicative of the hot electron induced photothermoelectric effect that has also been seen in graphene p-n junctions made using metallic gates. We have observed that the photovoltage increases with decreasing temperature indicating a dominant role of supercollision scattering. Our technique can also be extended to other 2D materials and to finer features that will lead to p-n junctions which span a large area, like a superlattice, that can generate a larger photoresponse. Our work creating abrupt p-n junctions is distinct from previous works that use a source-drain bias voltage with a single ionic gate creating a spatially graded p-n junction.

In this work, we demonstrate a simple technique to grow high-quality whiskers of Bi 2 Sr 2 CaCu 2 O 8+δ - a high T c superconductor. Structural analysis shows the single-crystalline nature of the grown whiskers. To probe electrical properties, we exfoliate these whiskers into thin flakes (~50 nm thick) using the scotch-tape technique and develop a process to realize good electrical contacts. We observe a superconducting critical temperature, T c , of 86 K. We map the evolution of the critical current as a function of temperature. With 2-D materials emerging as an exciting platform to study low-dimensional physics, our work paves the way for future studies on two-dimensional high-T c superconductivity.

Quantum Hall effect provides a simple way to study the competition between single particle physics and electronic interaction. However, electronic interaction becomes important only in very clean graphene samples and so far the trilayer graphene experiments are understood within non-interacting electron picture. Here, we report evidence of strong electronic interactions and quantum Hall ferromagnetism seen in Bernal-stacked trilayer graphene. Due to high mobility ∼500,000 cm 2  V -1  s -1 in our device compared to previous studies, we find all symmetry broken states and that Landau-level gaps are enhanced by interactions; an aspect explained by our self-consistent Hartree-Fock calculations. Moreover, we observe hysteresis as a function of filling factor and spikes in the longitudinal resistance which, together, signal the formation of quantum Hall ferromagnetic states at low magnetic field.

Selective alkenylation of pyridine is challenging in synthetic organic chemistry due to the poor reactivity and regioselectivity of the aromatic ring. We theoretically investigated Ni-catalyzed selective alkenylation of pyridine with DFT. The first step is coordination of the pyridine-AlMe 3 adduct with the active species Ni (0) (NHC)(C 2 H 2 ) 1 in an η 2 -fashion to form an intermediate Int1. After the isomerization of Int1, the oxidative addition of the C-H bond of pyridine across the nickel-acetylene moiety occurs via a transition state TS2 to form a Ni (II) (NHC) pyridyl vinyl intermediate Int3. This oxidative addition is rate-determining. The next step is C-C bond formation between pyridyl and vinyl groups leading to the formation of vinyl-pyridine (P1). One of the points at issue in this type of functionalization is how to control the regioselectivity. With the use of Ni(NHC)/AlMe 3 catalyst, the C 4 - and C 3 -alkenylated products (ΔG° ⧧ = 17.4 and 21.5 kcal mol -1 , respectively) are formed preferably to the C 2 one (ΔG° ⧧ = 22.0 kcal mol -1 ). The higher selectivity of the C 4 -alkenylation over the C 3 and the C 2 ones is attributed to the small steric repulsion between NHC and AlMe 3 in the C 4 -alkenylation. Interestingly, with Ni(P(i-Pr) 3 )/AlMe 3 catalyst, the C 2 -alkenylation occurs more easily than the C 3 and C 4 ones. This regioselectivity arises from the smaller steric repulsion induced by P(i-Pr) 3 than by bulky NHC. It is notable that AlMe 3 accelerates the alkenylation by inducing the strong CT from Ni to pyridine-AlMe 3 . In the absence of AlMe 3 , pyridine strongly coordinates with the Ni atom through the N atom, which increases Gibbs activation energy (ΔG° ⧧ = ∼27 kcal mol -1 ) of the C-H bond activation. In other words, AlMe 3 plays two important roles, acceleration of the reaction and enhancement of the regioselectivity for the C 4 -alkenylation.

Mechanical resonators are ubiquitous in modern information technology. With the possibility of coupling them to electromagnetic and plasmonic modes, they hold promise as the key building blocks in future quantum information technology. Graphene-based resonators are of interest for technological applications due to their high resonant frequencies, multiple mechanical modes and low mass. The tension-mediated nonlinear coupling between various modes of the resonator can be excited in a controllable manner. Here we engineer a graphene resonator with large frequency tunability at low temperatures, resulting in a large intermodal coupling strength. We observe the emergence of new eigenmodes and amplification of the coupled modes using red and blue parametric excitation, respectively. We demonstrate that the dynamical intermodal coupling is tunable. A cooperativity of 60 between two resonant modes of ∼100 MHz is achieved in the strong coupling regime. The ability to dynamically control the coupling between the high-frequency eigenmodes of a mechanical system opens up the possibility of quantum mechanical experiments at low temperatures.

We study the effect of localized Joule heating on the mechanical properties of doubly clamped nanowires under tensile stress. Local heating results in systematic variation of the resonant frequency; these frequency changes result from thermal stresses that depend on temperature dependent thermal conductivity and expansion coefficient. The change in sign of the linear expansion coefficient of InAs is reflected in the resonant response of the system near a bath temperature of 20 K. Using finite element simulations to model the experimentally observed frequency shifts, we show that the thermal conductivity of a nanowire can be approximated in the 10-60 K temperature range by the empirical form κ = bT W/mK, where the value of b for a nanowire was found to be b = 0.035 W/mK(2), significantly lower than bulk values. Also, local heating allows us to independently vary the temperature of the nanowire relative to the clamping points pinned to the bath temperature. We suggest a loss mechanism (dissipation ~10(-4)-10(-5)) originating from the interfacial clamping losses between the metal and the semiconductor nanostructure.

Various ab initio calculations using the density-functional (DFT), the second order Möller-Plesset perturbation (MP2) and self-consistent reaction field (SCRF) theories were performed on thirteen theoretically possible inositol stereoisomers. Gas phase calculations reveal that the myo- and neo-isomers of inositol (bearing one and two axial hydroxyl groups, respectively) are marginally more stable (by 0.5 kcal mol(-1)) than the all equatorially substituted scyllo-inositol. The calculations when done in different polar solvents show that the scyllo-inositol becomes the most stable inositol isomer, a fact attributed to weaker intramolecular hydrogen bonds. The individual hydrogen bond energy in all the isomers of inositol was also estimated using the molecular tailoring approach (MTA). The calculated hydrogen bond energies in these isomers are in excellent agreement with reported O-H···O hydrogen bond distances and ν(O-H) stretching frequencies. The estimated H-bond energy values suggest that the order of the intramolecular hydrogen bond strength follows: axial-axial > equatorial-axial > axial-equatorial > equatorial-equatorial hydrogen bonds. The intramolecular hydrogen bonds in the scyllo isomer are much weaker than those in other conformers, thus making this isomer more stable in polar solvents.

The ability to understand and model the performance limits of nanowire transistors is the key to the design of next generation devices. Here, we report studies on high-mobility junctionless gate-all-around nanowire field effect transistor with carrier mobility reaching 2000 cm(2)/V·s at room temperature. Temperature-dependent transport measurements reveal activated transport at low temperatures due to surface donors, while at room temperature the transport shows a diffusive behavior. From the conductivity data, the extracted value of sound velocity in InAs nanowires is found to be an order less than the bulk. This low sound velocity is attributed to the extended crystal defects that ubiquitously appear in these nanowires. Analyzing the temperature-dependent mobility data, we identify the key scattering mechanisms limiting the carrier transport in these nanowires. Finally, using these scattering models, we perform drift-diffusion based transport simulations of a nanowire field-effect transistor and compare the device performances with experimental measurements. Our device modeling provides insight into performance limits of InAs nanowire transistors and can be used as a predictive methodology for nanowire-based integrated circuits.

The influence of multiple substituents (F, CH3, NO2, CN, Cl, OH and NH2) on the C-H···π interaction in benzene-ethylene complex was investigated using the estimated CCSD(T) method and complete basis set limit. The results were compared with our earlier reported complexes of benzene-acetylene and benzene-methane, thus completing the sp, sp(2) and sp(3) series of C-H donors. The stabilization energy values for multiple fluoro-substituted benzene-ethylene complexes are found to be very close to those of the multiple fluoro-substituted benzene-methane complexes. Expectedly, the stabilization energies for the multiple methyl-substituted benzene-ethylene complexes lie between those of the multiple methyl-substituted benzene-methane and benzene-acetylene complexes. Energy decomposition analysis using the DFT-SAPT method predicts the dispersion energy to be dominant, similar to the benzene-methane complexes. For the symmetrically disubstituted complexes (-OH, -Cl, -NH2, -CN and -NO2), additional C-H···X interaction was observed, possibly due to the angular orientation of the ethylene molecule. Multidimensional correlation analysis between the electrostatic, dispersion and exchange-repulsion with the C-H···π interaction distance (r), Hammett constant (σ) and the molar refractivity (MR) revealed strong correlation between dispersion energy and the C-H···π interaction distance (r) as well as molar refractivity (MR).

Generation of H2 from methanol/water and hydrosilylation of CO2 catalyzed by [tris(2-pyridylthio)methyl]zinc hydride [κ(3)-Tptm]ZnH 1 were investigated with DFT and MP2 methods. The hydrosilylation of CO2 occurs via the CO2 insertion into the Zn-H bond of 1 followed by the metathesis of a Zn-(η(1)-OCOH) bond with hydrosilane to yield silyl formate and regenerate 1. The CO2 insertion easily occurs, but the metathesis is difficult because of the formation of a very stable Zn-(η(2)-O2CH) species before the metathesis. The ΔG°(‡) value of the metathesis with triethoxysilane is much smaller than that with phenylsilane because electronegative methoxy groups stabilize the transition state bearing hypervalent Si center, which is consistent with the experimental result that triethoxysilane is used in the hydrosilylation of CO2. It is theoretically predicted here that hydrosilane with two electronegative OEt groups or one to three F groups can be applied to this reaction. In the generation of H2 from methanol/water by 1, the first step is the metathesis of 1 with the O-H bond of methanol/water to produce [κ(3)-Tptm]Zn(OMe)/[k(3)-Tptm]Zn(OH) and dihydrogen molecule. The next step is the metathesis of the Zn-OMe/Zn-OH bond with hydrosilane to yield silyl ether and regenerate 1. The first metathesis is rate-determining but the second one occurs with very small activation energy, indicating that various hydrosilanes can be applied to this reaction.

We demonstrate a simple technique to transfer chemical vapour deposited (CVD) graphene from copper and platinum substrates using a soak-and-peel delamination technique utilizing only hot deionized water. The lack of chemical etchants results in cleaner CVD graphene films minimizing unintentional doping, as confirmed by Raman and electrical measurements. The process allows the reuse of substrates and hence can enable the use of oriented substrates for growth of higher quality graphene, and is an inherently inexpensive and scalable process for large-area production.