Se Precursor Research Articles

Zn(Te1−xSex) quantum dots synthesized through a facile route and their band-edge and surface state driven visible-light emission

Zn(Te1−xSex) quantum dots (QDs) were synthesized by the hot-injection method using zinc acetate as a zinc source. The composition, x, of the Zn(Te1−xSex) QDs was easily controlled in the range from 0 to 0.28 by changing the molar ratio between Te and Se precursors in the reaction solutions. The Zn(Te1−xSex) QDs with x = 0.24 ± 0.04 having various sizes (diameters from 3.8 to 6.0 nm) exhibited size-dependent photoluminescence (PL) emission with a peak wavelength in the visible region from 530 to 579 nm. The PL emission band involved not only the band-edge emission, but also defect-related emission. The defect responsible for the PL emission was attributed to the Te dangling bond on the surface of the QDs. The electronic transition for the surface state PL emission was concluded to be the transition from the 1Se quantum level to the acceptor level arising from the Te dangling bond.

High-performance Li–Se battery: Li2Se cathode as intercalation product of electrochemical in situ reduction of multilayer graphene-embedded 2D-MoSe2

Lithium–selenium (Li–Se) batteries are considered as promising candidates for next-generation battery technologies, as they have high energy density and low cost. A new class of electrochemical intercalation of interlayer MoSe2 to graphene (Gr) Li2Se based cathode materials for room temperature Li–Se batteries is reported. An advanced approach preparing spatially confined Li2Se cathode active materials inside carbon materials to minimize the shuttle effects of Se compounds is confirmed by XRD, XPS, TEM and electrochemical analysis studies. The starting chalcogenide Gr–MoSe2 were synthesized by applying a closed reflux system in diethylene glycol solvent, polypropylviologen as a carbon (C) precursor source, and selenoacetamide were used as Se precursor and followed by calcination under the Ar and N2 atmosphere to form Gr- layers between MoSe2 interlayers. Then, Mo in Gr–MoSe2 nanocomposites are electrochemically reduced (lithiation process) to give multi-layered graphene structures, and selenide compounds, Li2Se is generated inside graphene multi-layers, simultaneously in Li-Se battery. The capacity decay rate of the cell is 0.04% per cycle for 100 cycles, with nearly 100% coulombic efficiency throughout the cycling at current density of 1 Ag−1. Nyquist plots, were reported for electrochemical impedance Gr–MoSe2 as active materials after pretreatment step of 2 cycles (0.01–3 V) at 3 V and 0.01 V vs Li+/Li. Based on the conductivity of Gr–MoSe2 characteristics, reporting here also a new class of cathode of Li2Se, there is no conductive additive of carbon black to the active material.

Electrodeposition of Tin Selenide from Oxalate-Based Aqueous Solution

In this work, we report a study of the electrodeposition of SnSe. Considering the difficulty to stabilize the baths containing Sn(II) and Se(IV) precursors, we investigated the benefits of using sodium oxalate as a complexing agent. Preliminary cyclic voltammetric (CVs) experiments were performed to study the electrochemical behavior of tin and selenium redox systems within this specific electrolyte solution. The study revealed that the oxalate reagent stabilizes the bath chelating Sn(II) and then preventing the precipitation of SnO2. From the CVs, a growth mechanism is proposed and a synthesis potential window is defined, in which the electrodeposition of SnSe films was investigated. Between −0.5 and −0.6 V vs sat. AgCl/Ag, the deposits exhibit typical polycrystalline SnSe needle-like grains. SnSe was shown by Raman spectroscopy and the XRD patterns display an orthorhombic single-phase for this compound. Additional Mössbauer analyses confirm the presence of Sn(II), which is in good agreement with the chemical composition of SnSe films. Moreover, a cross-analysis between the methods shows also the presence of SnSe2 in minor proportion. The depth profile analyses of the samples reveal an in-depth homogeneity as well as the presence of oxygen at the layer surface.

Hierarchically porous nanoarchitecture constructed by ultrathin CoSe2 embedded Fe-CoO nanosheets as robust electrocatalyst for water oxidation

The sluggish kinetics and high cost of the noble-metal based electrocatalyst for oxygen evolution reaction (OER) still seriously limits the efficiencies of water splitting. Herein, for the first time, we rationally design a porous hierarchical nanoarchitecture, constructed by ultrathin CoSe2 embedded Fe-CoO nanosheets (CoSe2@Fe-CoO), which is synthesized via self-assembly hydrolysis driven in-situ synergetic selenization of Fe/Co/O/Se precursor followed by Ostwald ripening. As an OER catalyst, the porous CoSe2@Fe-CoO hybrid with abundant CoOOH electroactive sites delivers a small Tafel of 56.2 mV/dec with very low onset overpotential of 280 mV@10 mA/cm2 and excellent long-term physicochemical stability till 62 h without obvious decay, which outperforms well-established benchmark electrocatalysts (RuO2). The boosted OER performance of CoSe2@Fe-CoO nanosheets is mainly attributed to its iron-doping effect, porous nanoarchitecture, and multicomponent synergetic/interfacial effect between ultrathin cobalt (II) oxide and conductive cobalt selenide (CoSe2) nanoframework. This work presents a facile construction strategy to find a nonprecious hybrid OER electrocatalyst with excellent performance and long-term stability.

Excess Se-doped MoSe2 and nitrogen-doped reduced graphene oxide composite as electrocatalyst for hydrogen evolution and oxygen reduction reaction

Noble metal catalysts (e.g., Pt, Ru, and Ir) are expensive and scarce and cannot be synthesized at a large scale. The cheap and stable chalcogenides seem to be an attractive alternative and are most likely to replace the precious metal catalysts. However, the poor conductivity, limited number of active sites, and other properties of the chalcogenides limit their applications. In this work, we synthesized defect-rich MoSe2 with nitrogen-doped reduced graphene oxide (MoSe2/NG) in a simple hydrothermal process by introducing excess Se precursor. The catalyst with optimal performance (MoSe2/NG-4) exhibits good bifunctional properties in the oxygen reduction reaction and hydrogen evolution reaction (HER). It exhibits a small overpotential of 120 mV at a current density of 10 mA cm −2 in the HER, with a smaller Tafel slope of 69 mV dec−1, which is much lower than the values of most reported most reported Mo-based catalysts. Besides, it behaves as an effective catalyst in the ORR and adopts a four-electron reaction pathway. This excellent bifunctional catalytic property is mainly due to the rich heterostructure of MoSe2/NG-4 and synergistic effect of nitrogen doping, excellent conductivity of graphene, and the rich active sites. This work provides a new approach for the synthesis and application of chalcogenides and their complexes in the field of catalysis.

Molybdenum Disulfides and Diselenides By Atomic Layer Deposition

The success of graphene opened a door for a new class of chalcogenide materials with unique properties that can be applied in the semiconductor technology [1]. Monolayers of two-dimensional transition metal dichalcogenides (2D TMDCs) possess a direct band gap [2] that is crucial for optoelectronic applications. Additionally, the direct band gap can be easily tuned by either chemical composition or external stimuli. Next to the optoelectronic applications, where a monolayer planar structure is necessary to employ, a layer of standing flakes, which possesses a large surface area, can be used for hydrogen evolution [3] a photodegradation of organic dyes [4] or as electrodes in Li ion batteries [5].In principle, TMDCs can be prepared by various top-down (e.g. exfoliation) and bottom-up techniques, such as chemical vapor deposition (CVD) and atomic layer deposition (ALD) growth techniques [1]. MoS2, a typical representative of TMDCs, has been widely studied for many applications. Recently, the possibility to employ ALD as a technique to grow MoS2 has been reported. In these works (CH3)2S2 [6] or H2S [7, 8] were used as the S precursor and Mo(CO)6 [6], MoCl5 [7] or Mo(thd)3 [8] as the Mo precursors. From the practical point of view, MoSe2 is even more interesting than MoS2 since MoSe2 possesses a higher electrical conductivity than MoS2 [9, 10]. Recently, we have shown that ALD deposition of MoSe2 [11] or Mo-O-Se [12] using ((CH3)3Si)2Se as the Se precursor and the MoCl5 or Mo(CO)6, respectively, as the Mo precursors is feasible.The presentation will focus on the synthesis of MoS2 and MoSe2 by ALD, their characterization and applications in various fields. Experimental details and some recent results for photocatalytic, battery and hydrogen evolution applications will be presented and discussed.

Atomic Layer Deposition of MoSe2 Using New Selenium Precursors

Among the emerging 2D materials, transition metal chalcogenides are particularly encouraging as alternative semiconducting graphene-like nanomaterial. Recently, 2D MoSe2 has been gaining interest due to its intriguing properties, in many ways exceeding those of the extensively studied MoS2. The deposition of 2D nanomaterials in a conformal and uniform fashion on complex-shaped nanostructures is highly appealing but only achievable by atomic layer deposition (ALD). Unfortunately, the synthesis of MoSe2 by ALD is hindered by a current substantial lack of feasible Se precursors. In this work, we synthesized a set of alkysilyl (R3Si)2Se and alkylstannyl (R3Sn)2Se compounds and studied their suitability as Se ALD precursors. Thus, ALD processes carried out using MoCl5 as Mo precursor counterpart were followed by an extensive characterization of the as deposited material. The corresponding results revealed successful deposition of MoSe2 nanostructures on substrates of different nature with dominant out-of-plane orientation. Eventually, the growth evolution of the MoSe2 during the very early ALD stage was studied and described, displaying concomitant in-plane and out-of-plane MoSe2 growth. All in all, a set of suitable Se precursors presented herein paves the way for the deposition of 2D MoSe2 with all the own ALD benefits and allow the further study of its promising properties in a wide number of applications.

Developing highly crystalline, single-phase and copper-poor Cu2ZnSnSe4 nanoparticles for solar cell application

In this study, we report the synthesis of Cu(Zn,Sn)Se2 (CZTSe) nanoparticles by hot-injection method for application to the absorber layer in solar cells. The composition of elements in the CZTSe nanoparticles depends mainly on the injection speed of the Se precursor. By controlling the injection speed, we obtained complete single-phase CZTSe nanoparticles with high crystallinity and copper-poor composition. The nanoparticle diameter mainly ranged from ~ 7 nm to 18 nm. The obtained CZTSe nanoparticles were used to fabricate a light absorber layer in the CZTSe solar cells. The cell exhibited performance, with short-circuit current density of ~ 30.8 mA/cm2, open-circuit voltage of 0.39 V, fill factor of 0.47 and conversion efficiency of 5.8%.

Morphological and Electrical Properties of Capped CdSe Nanoparticles

In this study, cadmium selenide (CdSe) were synthesized by a chemical route process using complex agent ( tri sodium citrate ) as a ligand. cadmium acetate as a Cd source and Na2SeO3 as a Se precursor. The synthesized nanoparticles were characterized for their compositional, morphological and electrical properties using FESEM, EDAX and I-V characterization.

Cyclic Silylselenides: Convenient Selenium Precursors for Atomic Layer Deposition.

Three cyclic silylselenides were prepared in a straightforward manner. Property tuning has been achieved by varying the ring size and the number of embedded selenium atoms. All silylselenides possess improved resistance towards moisture and oxidation as well as high thermal robustness and sufficient volatility with almost zero residues. The six-membered diselenide proved to be particularly superior Se precursors for atomic layer deposition and allowed facile preparation of MoSe2 layers. Their structure and composition have been investigated by Raman and X-ray photoelectron spectroscopy as well as scanning electron microscopy revealing vertically aligned flaky shaped nanosheets.

Effects of ligand and chemical affinity of S and Se precursors on the shape, structure and optical properties of ternary CdS1−xSex alloy nanocrystals

Colloidal ternary CdS1−xSex (0 ≤ x ≤ 1) alloy semiconductor nanocrystals (NCs) with spherical and tetrapodal shapes were synthesized successfully by wet chemical method using cadmium oxide (CdO), selenium (Se), and sulfur (S) as precursors and oleic acid (OA), tri-n-octylphosphine (TOP) as ligands in 1-octadecene (ODE) solvent. For the first time, by using TOP and changing Se content, the shape of ternary CdS1−xSex alloy NCs could be tuned from spheres to tetrapods and the crystal structure could be transformed from zincblende (ZB) to wurtzite (WZ). The photoluminescence (PL) spectra of CdS1−xSex alloy NCs synthesized with and without TOP were also completely different, corresponding to one and two excitonic emission peaks. The causes of these interesting results have been discussed.

A Directed Route to Colloidal Nanoparticle Synthesis of the Copper Selenophosphate Cu3 PSe4.

The first colloidal nanoparticle synthesis of the copper selenophosphate Cu3 PSe4 , a promising new material for photovoltaics, is reported. Because the formation of binary copper selenide impurities seemed to form more readily, two approaches were developed to install phosphorus bonds directly: 1) the synthesis of molecular P4 Se3 and subsequent reaction with a copper precursor, (P-Se)+Cu, and 2) the synthesis of copper phosphide, Cu3 P, nanoparticles and subsequent reaction with a selenium precursor, (Cu-P)+Se. The isolation and purification of Cu3 P nanoparticles and subsequent selenization yielded phase-pure Cu3 PSe4 . Solvent effects and Se precursor reactivities were elucidated and were key to understanding the final reaction conditions.

A Directed Route to Colloidal Nanoparticle Synthesis of the Copper Selenophosphate Cu3PSe4

AbstractThe first colloidal nanoparticle synthesis of the copper selenophosphate Cu3PSe4, a promising new material for photovoltaics, is reported. Because the formation of binary copper selenide impurities seemed to form more readily, two approaches were developed to install phosphorus bonds directly: 1) the synthesis of molecular P4Se3 and subsequent reaction with a copper precursor, (P‐Se)+Cu, and 2) the synthesis of copper phosphide, Cu3P, nanoparticles and subsequent reaction with a selenium precursor, (Cu‐P)+Se. The isolation and purification of Cu3P nanoparticles and subsequent selenization yielded phase‐pure Cu3PSe4. Solvent effects and Se precursor reactivities were elucidated and were key to understanding the final reaction conditions.

Effects of chemical affinity and injection speed of Se and Te precursors on the development kinetic and optical properties of ternary alloyed CdTe1−xSex nanocrystals

The fabrication of ternary alloyed CdTe1−xSex nanocrystals (NCs) is strongly influenced by the chemical affinities of Se2− and Te2− ions, which are very different from each other. Based on the synthesis procedure, we discovered two possible structures of the alloyed CdTe1−xSex NCs: homogeneous alloyed and gradient alloyed. It was clear that the formation of two different alloyed NC types caused the different results of the emission spectra of ternary alloyed CdTe1−xSex NCs in previous studies. Careful photoluminescence and Raman scattering studies revealed that the formation of the homogeneous alloyed structure or gradient alloyed structure of CdTe1−xSex NCs depended on the injecting method the Se2− and Te2− ions. By slowly injecting the Se2− and Te2− ions into the solution containing Cd2+ ions at 290 °C and annealing the solution for a given period, homogeneous ternary alloyed CdTe1−xSex NCs were fabricated.

Synthesis of CdS/CdSe Core/Shell Heterostructures Using Ultrasonic Assisted Sol–Gel Method

Inverted type CdS/CdSe core/shell heterostructures were synthesized using ultrasonic assisted low cost and environmentally friendly sol–gel route. Cadmium chloride, thiourea and selenium dioxide were used as Cd, S and Se precursors, respectively. The core/shell heterostructures were analyzed by various techniques like X-ray diffraction, high resolution transmission electron microscope (HRTEM), photoluminescence and optical studies. X-ray diffractograms exhibit the cubic phase structure with its peaks shifting towards the lower angle due to compressive strain. Moire fringes are observed in HRTEM images of CdS/CdSe core/shell heterostructure due to lattice mismatch between CdS and CdSe. The interplanar spacing of moire fringes is found to be around 2.38 nm. Photoluminescence studies show the peak shifts towards the higher wavelength due to lattice mismatch between CdS and CdSe. Shift in absorption peak towards the higher wavelength makes them suitable for dye synthesized solar cells.

Facet-Dependent On-Surface Reactions in the Growth of CdSe Nanoplatelets.

Facet-dependent on-surface reactions are systematically studied on zinc-blende CdSe nanoplatelets with atomically-flat {001} basal facets and small yet non-polar side facets. The on-surface half-reactions between the surface Se sites and Cd carboxylates in the solution are qualitatively equivalent to those on the spheroidal counterparts. Conversely, the on-surface half-reactions between the surface Cd sites and the activated Se precursors in solution show a strong facet-dependence, which includes three distinguishable stages. In the first stage, the Se precursors adsorb onto the small and non-polar side facets of the nanoplatelets. The second stage is initiated by the adsorbed Se precursors at the side-basal plane edges and proceeds from the edges to the center of the basal planes in quasi-zeroth-order kinetics. In the third stage, the nanoplatelets are dismantled, which includes the creation of a hole in the middle and a build-up of thick edges.

Facet‐Dependent On‐Surface Reactions in the Growth of CdSe Nanoplatelets

AbstractFacet‐dependent on‐surface reactions are systematically studied on zinc‐blende CdSe nanoplatelets with atomically‐flat {001} basal facets and small yet non‐polar side facets. The on‐surface half‐reactions between the surface Se sites and Cd carboxylates in the solution are qualitatively equivalent to those on the spheroidal counterparts. Conversely, the on‐surface half‐reactions between the surface Cd sites and the activated Se precursors in solution show a strong facet‐dependence, which includes three distinguishable stages. In the first stage, the Se precursors adsorb onto the small and non‐polar side facets of the nanoplatelets. The second stage is initiated by the adsorbed Se precursors at the side‐basal plane edges and proceeds from the edges to the center of the basal planes in quasi‐zeroth‐order kinetics. In the third stage, the nanoplatelets are dismantled, which includes the creation of a hole in the middle and a build‐up of thick edges.

Role of surface modification on selenium nanoparticles: Enumerating the optical, thermal and structural properties

The well dispersed and homogenous particles of selenium with nanosized dimension (Se-Nps) in aqueous media were prepared in the current study. Three surfactant with variable nature i.e. cationic (CTAB), anionic (SDS) and non-ionic (Brij-58) were employed to fabricate Se-Nps with high optical and chemical stability. The corresponding effect of variations in the concentration of employed surfactant and Se precursor were investigated on the optical properties, homogeneity rate, polydispersity index (PDI) and hydrodynamic radii of Se-Nps. The thermal changes and nature of nanoparticles as a function of different concentration were investigated out by using differential scanning calorimetric (DSC) analysis. The nature of the utilized surfactants over the surface of the nanoparticles has produced significant effect on the agglomeration number of Se-Nps. The microstructural transformations such as changes in crystalline size, lattice strain were calculated as a function of concentration of employed surfactant and Se precursor. The variations in the deformation stress, strain and energy density for Se-Nps were estimated from X-ray diffraction line broadening methods. The modulation and interacting ability of surfactants with Se was evaluated using Fourier transform infrared (FTIR) spectroscopy. The current studies provide the detailed apprehension into the applications of surfactants to fabricate Se-Nps. The work enumerates that by varying the concentration of surfactant and Se precursor, it is feasible for the tuning of optical, structural and thermal properties of Se-Nps.

Electrochemical Atomic Layer Deposition of CuInSe2 on Au Surface

CuInSe2 (CIS) thin film growth on Au/glass slide surface was investigated by electrochemical atomic layer deposition (E‐ALD) in superlattice sequence in ambient laboratory conditions without any heat treatment processes involved. The electrochemical behavior of Cu, In, and Se on the Au surface was surveyed, the underpotential deposition phenomena of In was demonstrated for the first time and a various set of potentials for the three elements were considered to fabricate thin CIS films by specific superlattice sequencing. The crystal structure, elemental composition, topography, and photoelectrochemical behavior of each film produced were evaluated with the aim of finding a new set of conditions for producing stoichiometric CIS films. A good stoichiometric film of Cu0.99In0.98Se2.00 was successfully prepared by applying 50 periods of the superlattice sequence of 3(In aSe b) + 1(Cu cSe d) with the new deposition potentials of 0.08, −0.55, and −0.05 V for Cu, In, and Se precursor solutions, respectively. The resulting E‐ALD film was found to exhibit a p‐type semiconductivity.

Molybdenum Disulfides and Diselenides By Atomic Layer Deposition

The success of graphene opened a door for a new class of chalcogenide materials with unique properties that can be applied in the semiconductor technology [1]. Monolayers of two-dimensional transition metal dichalcogenides (2D TMDCs) possess a direct band gap [2] that is crucial for optoelectronic applications. Additionally, the direct band gap can be easily tuned by either chemical composition or external stimuli. Next to the optoelectronic applications, where a monolayer planar structure is necessary to employ, a layer of standing flakes, which possesses a large surface area, can be used for hydrogen evolution [3] a photodegradation of organic dyes [4] or as electrodes in Li ion batteries [5]. In principle, TMDCs can be prepared by various top-down (e.g. exfoliation) and bottom-up techniques, such as chemical vapor deposition (CVD) and atomic layer deposition (ALD) growth techniques [1]. MoS2, a typical representative of TMDCs, has been widely studied for many applications. Recently, the possibility to employ ALD as a technique to grow MoS2 has been reported. In these works (CH3)2S2 [6] or H2S [7, 8] were used as the S precursor and Mo(CO)6 [6], MoCl5 [7] or Mo(thd)3 [8] as the Mo precursors. From the practical point of view, MoSe2 is even more interesting than MoS2 since MoSe2 possesses a higher electrical conductivity than MoS2 [9, 10]. Recently, we have shown that ALD deposition of MoSe2 [11] or Mo-O-Se [12] using ((CH3)3Si)2Se as the Se precursor and the MoCl5 or Mo(CO)6, respectively, as the Mo precursors is feasible. The presentation will focus on the synthesis of MoS2 and MoSe2 by ALD, their characterization and applications in various fields. Experimental details and some recent photocatalytic and hydrogen evolution results will be presented and discussed.