Rapid nucleation and optimal surface-ligand interaction stabilize wurtzite MnSe.

Non-native structures (NNS) differ in discrete translational symmetry from the bulk ground state native structure (NS). To explore the extent of deconvolution of various factors relevant to the stabilization of the wurtzite/NNS of MnSe a heat-up method, we performed experiments using various ligands (oleic acid, oleylamine, octadecylamine, stearic acid, and octadecene), solvents (tetraethylene glycol and octadecene), and precursor salts (manganese chloride and manganese acetate). Experiments suggest that oleic acid in the presence of tetraethylene glycol and oleylamine in the presence of octadecene stabilize wurtzite/NNS.

Design of iso-material heterostructures of TiOvia seed mediated growth and arrested phase transitions.

Stabilization of different morphologies of iso-material native/non-native heterostructures is important for electron-hole separation in the context of photo-electrochemical and opto-electronic devices. In this regard, we explore the stabilities of different morphologies of rutile ("native", ground state phase) and anatase ("non-native" phase) TiO heterostructures through (1) seed-mediated growth and (2) a thermally induced arrested phase transition synthesis protocol. Furthermore, the experimental results are analyzed through a combination of Density Functional Tight Binding (DFTB) and Finite Element Model (FEM) methods.

Should All Electrochemical Energy Materials Be Isomaterially Heterostructured to Optimize Contra and Co-varying Physicochemical Properties?

Sustainable energy and chemical/material transformation constrained by limited greenhouse gas generation impose a grand challenge and posit outstanding opportunities to electrochemical material devices. Dramatic advancements in experimental and computational methodologies have captured detailed insights into the working of these material devices at a molecular scale and have brought to light some fundamental constraints that impose bounds on efficiency. We propose that the coupling of molecular events in the material device gives rise to contra-varying or co-varying properties and efficiency improving partial decoupling of such properties can be achieved via introducing engineered heterogeneities.

Gas-Induced Confinement-Deconfinement Interplay in Organic-Inorganic Hybrid Perovskite Thin Film Results in Systematic Band Modulation.

Gas-induced growth of organic-inorganic hybrid perovskites, especially methylammonium lead iodide (MAPbI), has shown interesting properties and applications in the area of optoelectronics. In this report, we introduce a method of gas-induced band gap engineering of thin films of MAPbI due to systematic dimensional confinement-deconfinement along the crystallographic axis of growing MAPbI. Interestingly, such a restricted growth phenomenon was observed when the hexylammonium lead iodide (two-dimensional hybrid perovskite) film was exposed to methylamine gas instead of the conventional PbI film-methylamine gas precursor pair.

Volatility and Chain Length Interplay of Primary Amines: Mechanistic Investigation on the Stability and Reversibility of Ammonia-Responsive Hybrid Perovskites.

Hybrid organic-inorganic perovskites possess promising signal transduction properties, which can be exploited in a variety of sensing applications. Interestingly, the highly polar nature of these materials, while being a bane in terms of stability, can be a boon for sensitivity when they are exposed to polar gases in a controlled atmosphere. However, signal transduction during sensing induces irreversible changes in the chemical and physical structure, which is one of the major lacuna preventing its utility in commercial applications.

Coupled optical absorption, charge carrier separation, and surface electrochemistry in surface disordered/hydrogenated TiO2 for enhanced PEC water splitting reaction.

The central governing factors that influence the efficiency of photoelectrochemical (PEC) water splitting reaction are photon absorption, effective charge-carrier separation, and surface electrochemistry. Attempts to improve one of the three factors may debilitate other factors and we explore such issues in hydrogenated TiO2, wherein a significant increase in optical absorption has not resulted in a significant increase in PEC performance, which we attribute to the enhanced recombination rate due to the formation of amorphization/disorderness in the bulk during the hydrogenation process. To this end, we report a methodology to increase the charge-carrier separation with enhanced optical absorption of hydrogenated TiO2.

Kinetically stabilized aliovalent europium-doped magnesium oxide as a UV sensitized phosphor.

Doping of size mismatched aliovalent ions is challenging due to the associated elastic and electronic stress making the thermodynamics unfavorable. Despite such features, its utilization may be viable if such systems can be made metastable by suppressing the kinetics of phase segregation. In light of such a possibility, we utilize sol-gel synthesis for preparing a size mismatched trivalent europium doped MgO (Mg(1-x)Eu(x)O:(x/2)V"(Mg)) system, which can be potentially used in optical applications.

Generic process for highly stable metallic nanoparticle-semiconductor heterostructures via click chemistry for electro/photocatalytic applications.

Metallic nanoparticles (MNP) are utilized as electrocatalysts, cocatalysts, and photon absorbers in heterostructures that harvest solar energy. In such systems, the interface formed should be stable over a wide range of pH values and electrolytes. Many current nonthermal processing strategies rely on physical interactions to bind the MNP to the semiconductor.

Hydroxylation induced stabilization of near-surface rocksalt nanostructure on wurtzite ZnO structure.

We present a density functional study of the structural behavior of zinc oxide nanostructures in basic growth condition which consequently leads to the formation of few layers of hydroxylated rocksalt structure over the wurtzite ZnO structure. We demonstrate the greater stability of the few layers of hydroxylated zinc oxide polar surface in rocksalt structure as compared to wurtzite structure. This coerces the near-surface layers of the nanostructure to acquire rocksalt structure giving rise to a trilayer structure consisting of a layer of hydroxyls on ZnO surface, rocksalt near-surface layers, and wurtzite bulk(or wurtzite sub-surface).

Stabilization and growth of non-native nanocrystals at low and atmospheric pressures.

The stabilization and growth of nanocrystals in "non-native" structures is explored via density functional calculations. Non-native and "native" bulk structures differ in their discrete translational symmetry. Computations suggest that the lower surface energy of the non-native structures always facilitates their stabilization in the early stages of crystal growth.

Nature of reactive O2 and slow CO2 evolution kinetics in CO oxidation by TiO2 supported Au cluster.

Recent experiments on CO oxidation reaction using seven-atom Au clusters deposited on TiO2 surface correlate CO2 formation with oxygen associated with Au clusters. We perform first principles calculations using a seven-atom Au cluster supported on a reduced TiO2 surface to explore potential candidates for the form of reactive oxygen. These calculations suggest a thermodynamically favorable path for O2 diffusion along the surface Ti row, resulting in its dissociated state bound to Au cluster and TiO2 surface.

Critical epinucleation on reconstructured surfaces and first-principle calculation of homonucleation on Si(100).

We introduce the concept of "critical epinucleation to distinguish nucleation on surfaces with and without reconstruction. On a reconstructed surface, the critical classical nucleus is stable against dissociation, but may not yet break the underlying surface reconstruction. Consequently, there must exist a "critical epinucleus" that is not only stable but also has established the epiconfiguration by unreconstructing the underlying substrate.

Determining the adsorptive and catalytic properties of strained metal surfaces using adsorption-induced stress.

We demonstrate a model for determining the adsorptive and catalytic properties of strained metal surfaces based on linear elastic theory, using first-principles calculations of CO adsorption on Au and K surfaces and CO dissociation on Ru surface. The model involves a single calculation of the adsorption-induced surface stress on the unstrained metal surface, which determines quantitatively how adsorption energy changes with external strain. The model is generally applicable to both transition- and non-transition-metal surfaces, as well as to different adsorption sites on the same surface.