Se Precursor Research Articles

Structural and optical properties of SbxSey thin films obtained by chemical molecular beam deposition method from Sb and Se precursors

SbxSey thin-films were obtained by chemical-molecular beam deposition (CMBD) on soda-lime glass from Sb and Se precursors. By the precise control of the Sb/Se ratio, Sb2Se3 thin films with stoichiometric composition were successfully obtained. The elemental and phase composition, as well as the crystal structure of SbxSey thin-films, were studied by energy-dispersive X-ray microanalysis, X-ray diffraction, Raman spectroscopy, scanning electron microscopy and atomic force microscopy. The optical bandgap of the films was determined from the absorption spectra acquired by a spectrophotometer. The physical properties of SbxSey thin films with different compositions were investigated.

Impact of synthesis temperature and precursor ratio on the crystal quality of MOCVD WSe2 monolayers

Structural defects in transition metal dichalcogenide (TMDC) monolayers (ML) play a significant role in determining their (opto)electronic properties, triggering numerous efforts to control defect densities during material growth or by post-growth treatments. Various types of TMDC have been successfully deposited by MOCVD (metal-organic chemical vapor deposition), which is a wafer-scale deposition technique with excellent uniformity and controllability. However, so far there are no findings on the extent to which the incorporation of defects can be controlled by growth parameters during MOCVD processes of TMDC. In this work, we investigate the effect of growth temperature and precursor ratio during MOCVD of tungsten diselenide (WSe2) on the growth of ML domains and their impact on the density of defects. The aim is to find parameter windows that enable the deposition of WSe2 ML with high crystal quality, i.e. a low density of defects. Our findings confirm that the growth temperature has a large influence on the crystal quality of TMDC, significantly stronger than found for the W to Se precursor ratio. Raising the growth temperatures in the range of 688 °C to 791 °C leads to an increase of the number of defects, dominating photoluminescence (PL) at low temperatures (5.6 K). In contrast, an increase of the molar precursor ratio (DiPSe/WCO) from 1000 up to 100 000 leads to less defect-related PL at low temperatures.

A reactivity-controlled epitaxial growth strategy for synthesizing large nanocrystals

Large ZnSe nanocrystals are expected to be promising blue-light emitters with an emission peak of 455–475 nm, which is important for the construction of display apparatus. The final size of ZnSe nanocrystals via one-step injection can be varied by the reactivity of the Zn and Se precursors; however, it has a limit of <5 nm. To describe the key factors in determining the final size of ZnSe nanocrystals, we proposed a nuclei number-considered LaMer model based on the Maxwell–Boltzmann distribution of crystal embryos. As a result, a general strategy of reactivity-controlled epitaxial growth was developed to synthesize large ZnSe nanocrystals through sequential injection of high-reactivity and low-reactivity Zn and Se precursors. The resultant ZnSe nanocrystals achieved pure blue emission between 455 and 470 nm. We further fabricated stable, large ZnSe/ZnS core–shell nanocrystals with photoluminescence quantum yields up to approximately 60%. Moreover, the reactivity-controlled epitaxial growth strategy is versatile and could be used to synthesize large ZnSe, CdSe and PbSe nanocrystals with average sizes up to 35 nm, 76 nm and 87 nm, respectively. The control of quantum-confined and classical effects in these large semiconductor nanocrystals will open up new directions for fundamental research and application exploration. Synthesizing Se-based nanocrystals with large diameters remains challenging. Here, a reactivity-controlled epitaxial growth strategy was demonstrated to synthesize nanocrystals of ZnSe, CdSe and PbSe with average diameters of 35 nm, 76 nm and 87 nm, respectively. The large ZnSe nanocrystals emitted pure blue light, which is important for display technology.

Luminescent AgGaSe2/ZnSe nanocrystals: rapid synthesis, color tunability, aqueous phase transfer, and bio-labeling application.

The unique optoelectronic properties of I-III-VI2 nanocrystals (NCs) have attracted extensive attention. Herein, element Se in oleylamine reduced by alkythiol, which has been demonstrated to generate highly reactive alkylammonium selenide, was selected as the Se precursor by us to successfully synthesize high-quality tetragonal AgGaSe2 NCs via a facile colloidal method in just 2 minutes. Further, the photoluminescence (PL) properties of the as-synthesized AgGaSe2 NCs were systematically optimized through utilizing one Zn precursor to integrate shell coating and anionic/cationic alloying strategies into our reactive system, resulting in not only the obvious improvement of PL intensity but also tunable PL color from blue to red. Furthermore, the ligand exchange approach was adopted for the aqueous phase transfer of the oleophilic AgGaSe2/ZnSe NCs. Our data suggest that either metalated mercaptopropionic acid (Zn-MPA) short- or 11-mercaptoundecanoic acid long-chain ligand exchanged NCs all could maintain the original high crystallinity, present good water solubility, and retain up to nearly 95% and 70% of the initial PL intensity, respectively. Benefiting from the low cytotoxicity, the water-soluble AgGaSe2/ZnSe NCs can be applied as a fluorescent probe in cell imaging and signal labels for the fluoroimmunoassay of prostate-specific antigen, implying their potential in biological application.

Electrocatalytic Applications of 2D Molybdenum Dichalcogenides By Atomic Layer Deposition

2D semiconductor transition metal dichalcogenides have attracted considerable attention due to their layered structure, suitable band gap, electrochemically active unsaturated edges and relatively good stability against photocorrosion. These properties result promising for different applications including, Li-ion batteries, photocatalysis and hydrogen evolution reaction (HER). Apart from the widely studied 2D MoS2, 2D selenide and telluride equivalents, MoSe2 and MoTe2, have recently gained considerable interest due to their higher electrical conductivity, wider inter-layer distance and narrower bandgap as compared to MoS2, high surface area and close to zero Gibbs free energy edges for hydrogen adsorption.Unlike sulfide dichalcogenides, the lack of Se and Te precursors have prevented the synthesis of selenide and telluride dichalcogenides by ALD. In order to surpass such impediment, we present a set of novel in-house synthesized Se and Te compounds, which were successfully combined with commercial Mo precursor to synthesize MoSe2 and MoTe2 by ALD [1-5]. The as-deposited ALD MoSe2 and MoTe2 on substrates of different nature were extensively characterized by different techniques, which confirmed the chemical composition and revealed the growth of 2D flaky nano-crystalline MoSe2 and MoTe2.In parallel, MoSe2 and MoTe2@TiO2 nanotube layers (TNTs) heterostructures were fabricated in a simple and fast fashion to explore and exploit the MoSe2 and MoTe2 photo- and electrocatalytic properties. TNTs act as excellent photoactive supporting material providing a high surface area, unique directionality for charge separation, and highly effective charge collection.The presentation will introduce and describe the synthesis of the 2D Mo dichalcogenides, the corresponding physical and electrochemical characterization and encouraging results obtained in HER [4,5], photocatalysis [4-6] and Li-ion batteries [7].[1] R. Zazpe et al, FlatChem (2020) 21 100166[2] J. Charvot et al, Chempluschem (2020) 85 576[3] J. Charvot et al, RSC Adv. (2021) 11 22140[4] R. Zazpe et al, ACS Appl. Nano Mater. (2021) 3 12 12034[5] R. Zazpe et al, Appl. Mater. Today (2021) 23 101017[6] M. Motola et al, Nanoscale (2019) 11 23126[7] H. Sopha et al FlatChem (2019) 17 100130

Mechanochemical Synthesis of Nickel Mono- and Diselenide: Characterization and Electrical and Optical Properties.

Nickel mono- (NiSe) and diselenide (NiSe2) were produced from stoichiometric mixtures of powdered Ni and Se precursors by the one-step, undemanding mechanochemical reactions. The process was carried out by high-energy milling for 30 and 120 min in a planetary ball mill. The kinetics of the reactions were documented, and the products were studied in terms of their crystal structure, morphology, electrical, and optical properties. X-ray powder diffraction confirmed that NiSe has hexagonal and NiSe2 cubic crystal structure with an average crystallite size of 10.5 nm for NiSe and 13.3 nm for NiSe2. Their physical properties were characterized by the specific surface area measurements and particle size distribution analysis. Transmission electron microscopy showed that the prepared materials contain nanoparticles of irregular shape, which are agglomerated into clusters of about 1–2 μm in diameter. The first original values of electrical conductivity, resistivity, and sheet resistance of nickel selenides synthesized by milling were measured. The obtained bandgap energy values determined using UV–Vis spectroscopy confirmed their potential use in photovoltaics. Photoluminescence spectroscopy revealed weak luminescence activity of the materials. Such synthesis of nickel selenides can easily be carried out on a large scale by milling in an industrial mill, as was verified earlier for copper selenide synthesis.

Solution processed 2D SnSe nanosheets catalysts: Temperature dependent oxygen reduction reaction performance in alkaline media

• Single phase SnSe synthesis with non-toxic Se precursor, the monetary synthetic route is employed. • The SnSe catalysts 4-electron pathway for oxygen reduction. • The current density and charge transfer number of SnSe-500 catalysts are 4.50 mA/cm 2 and 3.62. One of the most effective synthesis routes is the simple solution process, which is an inexpensive way to make single phase 2-Dimensional (2D) Tin Selenide (SnSe) nanosheets. X-ray diffraction (XRD), X-ray Photoelectron spectroscopy (XPS), and Field Emission Scanning Electron Microscope (FESEM) were used to confirm the structural and topographical investigations. 2D SnSe served for Oxygen Reduction Reaction (ORR) electrochemical performance in KOH solution. Later, 2D SnSe is annealed at 300, 400 and 500 °C later termed as SnSe-300, SnSe-400 and SnSe-500 respectively to investigate the electrochemical behavior of catalyst. As the temperature increases ORR performance improved. For the first time, 2- and 4-electron transfer pathway mechanism of SnSe catalysts is discussed. As enhancement in the performance of as prepared 2D SnSe catalysts ensured with various parameters like current density, electron charge transfer number and half-wave potential. SnSe-500 has a half-wave potential of −0.75 V, which is lower than other catalysts in this case. In addition, a current density of 4.50 mA/cm 2 was recorded, which is superior to other catalysts in this case.

Properties and White Light Photoresponses of CdSe Colloidal Nanoparticles

II–VI nanocrystalline semiconductor materails provide a wide range of applications in electronics, optoelectronics and photonics. The present paper reports the preparation of colloidal Cadmium selenide (CdSe) nanoparticles and study their optical properties. (CdSe) was produced by a chemical route procedure, with the ligand tri sodium citrate (TSC) serving as a complexing agent. Cadmium acetate is used as a Cd source, and sodium selenide is used as a Se precursor. The morphological and optical properties of the produced nanoparticles were determined using a Transmission electron microscopy (TEM) and Ultraviolet – Visible spectroscopy (UV-VIS).Thin films of CdSe capped with are deposited on the glass and aluminum substrates . AL/ CdSe/Ag MSM photodetectors have been fabricated and the electrical properties were measured in dark and light. The output data display that the photo currents of all diodes are increased with light. The fact that the films had dark electrical conductivity and photoconductivity indicates that they were semiconducting materials.

ZnCl2 Mediated Synthesis of InAs Nanocrystals with Aminoarsine.

The most developed approaches for the synthesis of InAs nanocrystals (NCs) rely on pyrophoric, toxic, and not readily available tris-trimethylsilyl (or tris-trimethylgermil) arsine precursors. Less toxic and commercially available chemicals, such as tris(dimethylamino)arsine, have recently emerged as alternative As precursors. Nevertheless, InAs NCs made with such compounds need to be further optimized in terms of size distribution and optical properties in order to meet the standard reached with tris-trimethylsilyl arsine. To this aim, in this work we investigated the role of ZnCl2 used as an additive in the synthesis of InAs NCs with tris(dimethylamino)arsine and alane N,N-dimethylethylamine as the reducing agent. We discovered that ZnCl2 helps not only to improve the size distribution of InAs NCs but also to passivate their surface acting as a Z-type ligand. The presence of ZnCl2 on the surface of the NCs and the excess of Zn precursor used in the synthesis enable the subsequent in situ growth of a ZnSe shell, which is realized by simply adding the Se precursor to the crude reaction mixture. The resulting InAs@ZnSe core@shell NCs exhibit photoluminescence emission at ∼860 nm with a quantum yield as high as 42±4%, which is a record for such heterostructures, given the relatively high mismatch (6%) between InAs and ZnSe. Such bright emission was ascribed to the formation, under our peculiar reaction conditions, of an In–Zn–Se intermediate layer between the core and the shell, as indicated by X-ray photoelectron spectroscopy and elemental analyses, which helps to release the strain between the two materials.

Size matters: Steric hindrance of precursor molecules controlling the evolution of CdSe magic-size clusters and quantum dots.

Little is known about how to precisely promote the selective production of either colloidal semiconductor metal chalcogenide (ME), magic-size clusters (MSCs), or quantum dots (QDs). Recently, a two-pathway model has been proposed to comprehend their evolution; here, we reveal for the first time that the size of precursors plays a decisive role in the selected evolution pathway of MSCs and QDs. With the reaction of cadmium myristate (Cd(MA)2) and tri-n-octylphosphine selenide (SeTOP) in 1-octadecene (ODE) as a model system, the size of Cd precursors was manipulated by the steric hindrance of carboxylic acid (RCOOH) additive. Without RCOOH, the reaction produced both CdSe MSCs and QDs (from 100 to 240 °C). With RCOOH, the reaction produced MSCs or QDs when R was small (such as CH3−) or large (such as C6H5−), respectively. According to the two-pathway model, the selective evolution is attributed to the promotion and suppression of the self-assembly of Cd and Se precursors, respectively. We propose that the addition of carboxylic acid may occur ligand exchange with Cd(MA)2, causing the different sizes of Cd precursor. The results suggest that the size of Cd precursors regulates the self-assemble behavior of the precursors, which dictates the directed evolution of either MSCs or QDs. The present findings bring insights into the two-pathway model, as the size of M and E precursors determine the evolution pathways of MSCs or QDs, the understanding of which is of great fundamental significance toward mechanism-enabled design and predictive synthesis of functional nanomaterials.Electronic Supplementary MaterialSupplementary material (additional optical absorption spectra, TEM, NMR, FT-IR, and XRD) is available in the online version of this article at 10.1007/s12274-022-4421-4.

Epitaxial Orientation Angle Tuned Disk-on-Rod Nanoheterostructures for Boosting Charge Transfer.

Controlling the compositions of Se(VI) and Te(VI) ions in a 2D disk on 1D structures of Sb(V) chalcogenides, disk-on-rod heterostructures having three different epitaxial angles with different surface facets are reported. Te injection temperature determined the composition, ensuring heterostructure formation with trigonal Sb2SexTe3-x disks on orthorhombic Sb2Se3 rods having orientation angles 180°, 135°, and 90°. The growth kinetics of disks connected at one/two heads of parent rods is manipulated using an Se precursor as a limiting reagent. Theoretical calculations established the energy minimization of different orientations, their possible formation, and suitability in energy transfer applications. Electrochemical measurements were also in agreement with theoretical calculations. Hence, this is a case study of advanced modular synthesis of disk-on-rod nanostructures, leading a step further in nanocrystal engineering for more desirable complex structures and their charge transfer property.

Optical, morphological, electrical properties and white light photoresponse of CdSe nanoparticles

ABSTRACT II–VI nanocrystalline semiconductors offer a wide range of applications in electronics, optoelectronics, and photonics. The study of the morphological, electrical, and optical properties of Cadmium selenide (CdSe) nanoparticles prepared with tri ethanolamine (TEA) as a complex agent is reported in the paper. Cadmium acetate as a Cd source and (Na2SeO3) as a Se precursor. Transmission electron microscope (TEM), field emission scanning electron microscope (FESEM), energy dispersive x-ray (EDX), and ultraviolet-visible spectroscopy (UV-VIS) were used to characterise the synthesised nanoparticles for their optical, compositional, morphological, and electrical properties. The film of CdSe was deposited on the glass substrate. The electrical characterisation of CdSe thin films at various temperatures dark electrical conductivity and photoconductivity reveal that the films were semiconducting in nature, indicating the suitability of these films for photo sensor applications.

Study on chemical synthesis of SnSSe nanosheets and nanocrystals

Two kinds of raw material combinations for the hot injection method were investigated for the chemical synthesis of SnSSe nanosheets and nanocrystals, which are low-toxic optoelectronic materials. When SnSe quantum dots were synthesized by mainly using oleic acid as the Se precursor solvent, the quantum dots changed from spherical to cubic as the size increased. The growth condition dependence of the nanocrystal formation process was discussed. When SnSSe nanocrystals were synthesized by mainly using trioctylphosphine as the S Se precursor solvent, it was found that the nanocrystal shape changed from dot to rod or sheet by reducing the proportion of S. The bandgap energy did not simply depend on the composition ratio of S but was affected by the change in the nanocrystal shape depending on the quantum confinement effect.

2D Molybdenum Dichalcogenides by Atomic Layer Deposition

2D semiconductor transition metal dichalcogenides have attracted considerable attention due to their layered structure, suitable band gap, electrochemically active unsaturated edges and relatively good stability against photocorrosion. These properties result promising for different applications including, Li-ion batteries, photocatalysis and hydrogen evolution reaction (HER). Apart from the widely studied 2D MoS2, 2D selenide and telluride equivalents, MoSe2 and MoTe2, have recently gained considerable interest due to their higher electrical conductivity, wider inter-layer distance and narrower bandgap as compared to MoS2, high surface area and close to zero Gibbs free energy edges for hydrogen adsorption. Unlike sulfide dichalcogenides, the lack of Se and Te precursors have prevented the synthesis of selenide and telluride dichalcogenides by ALD. In order to surpass such impediment, we present a set of novel in-house synthesized Se and Te compounds, which were successfully combined with commercial Mo precursor to synthesize MoSe2 and MoTe2 by ALD [1-5]. The as-deposited ALD MoSe2 and MoTe2 on substrates of different nature were extensively characterized by different techniques, which confirmed the chemical composition and revealed the growth of 2D flaky nano-crystalline MoSe2 and MoTe2. In parallel, MoSe2 and MoTe2@TiO2 nanotube layers (TNTs) heterostructures were fabricated in a simple and fast fashion to explore and exploit the MoSe2 and MoTe2 electrocatalytic properties. TNTs act as excellent photoactive supporting material providing a high surface area, unique directionality for charge separation, and highly effective charge collection.The presentation will introduce and describe the synthesis of the 2D Mo dichalcogenide family, the corresponding physical and electrochemical characterization and encouraging results obtained in HER [4,5], photocatalysis [4-6] and Li-ion batteries [7].[1] R. Zazpe et al, FlatChem (2020) 21 100166[2] J. Charvot et al, Chempluschem (2020) 85 576[3] J. Charvot et al, RSC Adv. 2021, revision submitted[4] R. Zazpe et al, ACS Appl. Nano Mater. 2021, 3, 12, 12034[5] R. Zazpe et al, Appl. Mater. Today 2021, in revision[6] M. Motola et al, Nanoscale 11 (2019) 23126[7] H. Sopha et al FlatChem 17 (2019) 100130

Conductivity of SbxSey films grown by CMBD from Sb and Se precursors for use in solar cells

Antimony selenide (Sb2Se3) has been developed as attractive, non-toxic and earth-abundant solar absorber candidate among the thin-film photovoltaic devices. The growth of SbxSey thin films, by atmospheric pressure chemical molecular beam deposition (CMBD) method, from separate Sb and Se precursors has been reported. The conductivity of the films was investigated as a function of the vapor phase mixture of Sb and Se. By the precise control of the Sb/Se ratio we succeeded in obtaining stoichiometric Sb2Se3 films. It is also found out that we can control the conductivity by deliberately introducing the deviation from the stoichiometry. The conductivity was varied in the wide range of 10−5 ÷ 102 (Ohm × cm)−1 and samples had p- and n-type conductivity depending on Sb/Se ratio. The obtained results were explained by the formation of intrinsic point defects.

Advanced design of cathodes and interlayers for high‐performance lithium‐selenium batteries

AbstractLithium‐selenium (Li‐Se) batteries have attracted ever‐increasing attention owing to high volumetric capacity comparable to lithium‐sulfur batteries and excellent electronic conductivity of Se. However, unsatisfactory energy density and cycling life of Li‐Se batteries mainly caused by low utilization of Se and shuttle effect of polyselenides (PSes) seriously prevent their commercial applications. Herein, this work systematically reviews the recent advances of the state‐of‐the‐art cathodes and interlayers in high‐performance Li‐Se batteries. First, the fundamental chemistries of Li‐Se batteries are introduced in terms of various Se precursors and electrochemical behaviors. Second, the main strategies in cathodes and interlayers for addressing poor conductivity of Se and shuttle effects of PSes are summarized as three‐dimensional conductive skeletons for Se, physical confinement of Se, chemisorption and catalytic conversion of PSes, and free‐standing interlayers and interlayers on separators. Further, the synthesis strategies and enhanced electrochemical performance are specially exemplified to highlight the possible enlightenments for constructing advanced cathodes and interlayers. Finally, the future challenges and perspectives of advanced cathodes and interlayers in high‐performance Li‐Se batteries are briefly discussed.

Organoselenium Precursors for Atomic Layer Deposition.

Organoselenium compounds with perspective application as Se precursors for atomic layer deposition have been reviewed. The originally limited portfolio of available Se precursors such as H2Se and diethyl(di)selenide has recently been extended by bis(trialkylsilyl)selenides, bis(trialkylstannyl)selenides, cyclic selenides, and tetrakis(N,N-dimethyldithiocarbamate)selenium. Their structural aspects, property tuning, fundamental properties, and preparations are discussed. It turned out that symmetric four- and six-membered cyclic silyl selenides possess well-balanced reactivity/stability, facile and cost-effective synthesis starting from inexpensive and readily available chlorosilanes, improved resistance toward air and moisture, easy handling, sufficient volatility, thermal resistance, and complete gas-to-solid phase exchange reaction with MoCl5, affording MoSe2 nanostructures. These properties make them the most promising Se precursor developed for atomic layer deposition so far.

α-Cu2Se thermoelectric thin films prepared by copper sputtering into selenium precursor layers

Copper selenide (Cu2Se) is a promising thermoelectric material and α-phase Cu2Se provides relatively safe thermoelectric modules for thin film thermoelectric device in contrast to some toxic materials currently on the market. In this work, nanocrystalline Cu2Se thin film with uniform element distribution was fabricated at room temperature through an effective combination reaction method by implanting sputtered Cu+ ions into Se precursor. Then, self-assembled growth of Cu2Se thin films with desired α-phase and well crystallinity was successfully achieved with optimization of annealing temperature. Interestingly, the growth orientation has obviously affected by the annealing temperature, which significantly affects the thermoelectric properties. Consequently, the Seebeck coefficients increase with the increase in the orientation factor of the (0l0) preferred orientation, which enhances power factor. The high maximum power factor of 9.23 μWcm−1K−2 is achieved for α-Cu2Se thin film with (0l0) preferred orientation, demonstrating that the method used in this work has great potential in developing low-cost and high-performance thermoelectric thin films from relatively earth-abundant elements.

Synthesis of ZnSe Nanocrystals for Solid-state Lighting Applications

We report the large-scale synthesis of highly luminescent ZnSe nanocrystals (NCs) by a simple and low-cost hydrothermal method. XRD (X-ray Diffraction) and HR-TEM (High Resolution Transmission Microscopy) characterization studies confirmed the formation of as-synthesized ZnSe NCs in cubic structure. The optical property of ZnSe NCs were tunable via controlling the Zn:Se molar precursor ratio (0.5:1–1.5:1), reaction temperature (150–200 0C), and reaction time (5–30 h). The resulting ZnSe NCs with the Zn:Se precursor ratio of 1:1, hydrothermally treated at 190 0C for 20 h exhibited the highest photoluminescence quantum yield obtained by PL spectra with the 355 nm excitation. The current–voltage (I–V) characteristics of the ZnSe NCs show its promising application in the solid-state lighting.

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.