Te Precursor Research Articles

General and fast patterning of semiconductor nanocrystals by femtosecond laser direct writing

Semiconductor nanocrystals have shown remarkable performance in the field of displays, solar cells, and photodetectors. But, a rapid method to produce localized stable nanocrystals remains a challenge, impeding the step toward device miniaturization. Here, we present a general and fast approach, femtosecond laser direct writing, for manufacturing these nanocrystals as well as integrating them into substrates in one step. The high peak power of the femtosecond laser induces a nonlinear absorption of the CatX (Cat = Cd or Pb, X = S, Se or Te) precursor at the focal spot. Once the temperature reaches the nucleation temperature, the CatX nanocrystals form immediately. By moving the displacement platform, arbitrary microscale patterns made of nanoscale crystals are obtained, which shows great potential in high-resolution displays and on-chip light sources.

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.

Redox-controlled chalcogen-bonding at tellurium: impact on Lewis acidity and chloride anion transport properties.

Our interests in the chemistry of atypical main group Lewis acids have led us to devise strategies that augment the affinity of chalcogen-bond donors for anionic guests. In this study, we describe the oxidative methylation of diaryltellurides as one such strategy along with its application to the synthesis of [Mes(C6F5)TeMe]+ and [(C6F5)2TeMe]+ starting from Mes(C6F5)Te and (C6F5)2Te, respectively. These new telluronium cations have been evaluated for their ability to complex and transport chloride anions across phospholipid bilayers. These studies show that, when compared to their neutral Te(ii) precursors, these Te(iv) cations display both higher Lewis acidity and transport activity. The positive attributes of these telluronium cations, which originate from a lowering of the tellurium-centered σ* orbitals and a deepening of the associated σ-holes, demonstrate that the redox state of the main group element provides a convenient handle over its chalcogen-bonding properties.

Phosphine-free synthesis of FeTe2 nanoparticles and self-assembly into tree-like nanoarchitectures**Project supported by the National Natural Science Foundation of China (Grant No. 11874027) and the China Postdoctoral Science Foundation (Grant Nos. 2019T120233 and 2017M621198).

Manipulating the self-assembly of transition metal telluride nanocrystals (NCs) creates opportunities for exploring new properties and device applications. Iron ditelluride (FeTe2) has recently emerged as a new class of magnetic semiconductor with three-dimensional (3D) magnetic ordering and narrow band gap structure, yet the self-assembly of FeTe2 NCs has not been achieved. Herein, the tree-like FeTe2 nanoarchitectures with orthorhombic crystal structure have been successfully synthesized by hot-injection solvent thermal approach using phosphine-free Te precursor. The morphology, size, and crystal structure have been investigated using transmission electron microscopy (TEM), high-resolution TEM (HRTEM), and powder x-ray diffraction (XRD). We study the formation process of tree-like FeTe2 NCs according to trace the change of the sample morphology with the reaction time. It was found that the FeTe2 nanoparticles show oriented aggregation and self-assembly behavior with the increase of reaction time, which is attributed to size-dependent magnetism properties of the samples. The magnetic interaction is thought to be the driving force of nanoparticle self-organization.

Cyclic Voltammetry of Ge and Te in Basic Conditions: An Investigation of Surface Coverages.

Cyclic Voltammetry of Ge and Te precursors in basic solution can lead to a better understanding of the surface limited reactions taking place at the substrate-solution interface. GeTe is a phase-change chalcogenide material with excellent stability for the crystalline and amorphous phases. The stoichiometry of the film is very important as the 1:1 compound is shown to have the highest switching rates.1 Controlling the stoichiometry has proven to be difficult using conventional methods, so in this study, deposition conditions for stoichiometric GeTe are sought using Electrochemical Atomic Layer Depostion (E-ALD). EALD is a process developed by this author’s lab which makes use of underpotential deposition (UPD) to put down fractions of a monolayer of the desired material. This process can then be repeated for as many cycles as are needed to grow films of the desired thickness. Before a deposition sequence can be made, the interactions of the individual elements must be investigated, both on the substrate, and on each other. This is achieved through the use of cyclic voltammetry, which measures the current generated as each element is either deposited or stripped from the surface as a function of electrochemical potential. By quantifying the current, the number of deposited or stripped atoms can be calculated, giving an estimate of the surface coverage. Investigations have identified the surface limited and bulk potentials for each element on the substrate as well as their substrate coverage. The next step will be to develop a sequence using these potentials to develop high quality, epitaxial films.

Investigation on the Stability of MoS2(1-x)Te2x Fabricated By Tellurization Using Organic Precursor (i-C3H7)2te

Recent work on the research of layered materials has revealed the material’s unique physical properties, its applications in various fields, and fabrication processes to produce high quality samples. We have been focusing on transition metal dichalcogenides (TMD) and its alloys. Fabrication of TMD alloys enables bandgap/band offset tuning which expands the application of TMD materials in various fields to a further extent. Although it has been predicted the fabrication of TMD alloys is difficult since the alloys are expected to be thermodynamically unstable [1,2], we have so far fabricated metal alloy, Mo1-x W x S2 [3], and chalcogen alloy, MoS2(1-x)Te2x [4]. In these studies, we have confirmed the control of composition by adjusting sputtering condition as well as bandgap and band offset shift according to the composition. However, the stability of the material, especially the change of physical properties over certain period of time, has not been discussed in depth despite the fact that such alloy material are thermodynamically unstable, as mentioned above. In addition, although there are numerous results on the fabrication differences, there are not many reports discussing on the stability of the fabricated films for TMDs [5]. In this study, we focused on the stability of the materials and optimization of fabrication condition in order to prevent degradation. MoS2(1-x)Te2x alloys are fabricated by co-sputtering MoS2 and MoTe2 followed by tellurization by inorganic Te precursor, (i-C3H7)2Te, in H2 or N2 ambient. The samples were stored in a vacuum dessicator for a period of time (which we will refer as “storage time”) and then evaluated with X-ray photoelectron spectroscopy (XPS). It was revealed that depending on the carrier gas, or the ambient, during tellurization, the amount by which Mo is oxidized after the storage time is different despite the fact that the samples showed almost identical chemical state right after the tellurization. This may be attributed to the difference in grain size where H2 ambient may have produced films with smaller grain size, i.e. longer or more grain boundaries, resulting in more area to be oxidized compared to N2 ambient. This work was partly supported by JST CREST Number JPMJCR16F4, Japan. This work was also partly supported by JSPS KAKENHI Grant Number 18F22879 and 16J11377. Reference H. P. Komsa, et al., J. Phys. Chem. Lett. 3, 3652 (2012)J. Kang, et al., J. Appl. Phys. 113, 143703 (2013)Y. Hibino, et al., Jpn. J. Appl. Phys. 57, 06HB04 (2018)Y. Hibino, et al., J. Mater. Res. 32, 3021 (2017)R. Samnakay, et al., Appl. Phys. Lett. 106, 023115 (2015) Figure caption: The Mo 3d spectra of MoS2(1-x)Te2x samples fabricated with different gas ambient, obtained by XPS. The bottom spectra show there is no or only subtle oxidation, whereas after the storage time, samples undergo oxidation with sample fabricated in H2 ambient further oxidized than that fabricated in N2 ambient. Figure 1

Formation of colloidal alloy semiconductor CdTeSe magic-size clusters at room temperature

Alloy semiconductor magic-size clusters (MSCs) have received scant attention and little is known about their formation pathway. Here, we report the synthesis of alloy CdTeSe MSC-399 (exhibiting sharp absorption peaking at 399 nm) at room temperature, together with an explanation of its formation pathway. The evolution of MSC-399 at room temperature is detected when two prenucleation-stage samples of binary CdTe and CdSe are mixed, which are transparent in optical absorption. For a reaction consisting of Cd, Te, and Se precursors, no MSC-399 is observed. Synchrotron-based in-situ small angle X-ray scattering (SAXS) suggests that the sizes of the two samples and their mixture are similar. We argue that substitution reactions take place after the two binary samples are mixed, which result in the formation of MSC-399 from its precursor compound (PC-399). The present study provides a room-temperature avenue to engineering alloy MSCs and an in-depth understanding of their probable formation pathway.

Electrodeposition of bismuth telluride from a weakly coordinating, non-aqueous solution

We report the electrodeposition of bismuth telluride thin films on to titanium nitride (TiN) electrodes from a weakly coordinating solvent, dichloromethane (CH2Cl2), using the halometallates, [NnBu4][BiCl4] and [NnBu4]2[TeCl6] with 0.1M [NnBu4]Cl as the supporting electrolyte. The elemental composition of the electrodeposited films was found to be independent of the deposition potential between −0.6 and −2.0V vs. Ag/AgCl but to be dependent on ratio of the concentrations of the Bi and Te precursors in the solution, with the amount of bismuth in the films increasing when the concentration of [NnBu4][BiCl4] in solution was increased. All the electrodeposited films were found to be homogenous in composition across the electrode surface and to be reproducible in composition for replicate experiments. As the deposition potential was taken less negative, the morphology of the deposits changed from uniform films to films with a compact micro/nano particle structure as seen by scanning electron microscopy (SEM). Using this system, the electrodeposition of crystalline Bi2Te3 and Bi4Te3 was confirmed by energy dispersive spectroscopy (EDX) and grazing incidence X-ray diffraction.

Tellurium Precursor for Nanocrystal Synthesis: Tris(dimethylamino)phosphine Telluride.

Preparations of CdTe quantum platelets, magic-size (CdTe)13 nanoclusters, and CdTe quantum wires are described using (Me2N)3PTe (with (Me2N)3P) as a Te precursor. The (Me2N)3PTe/(Me2N)3P precursor mixture is shown to be more reactive than mixtures of trialkylphosphine tellurides and the corresponding trialkylphosphines, R3PTe/R3P, which are commonly employed in nanocrystal syntheses. For syntheses conducted in primary amine solvents, (Me2N)3PTe and (Me2N)3P undergo a transamination reaction, affording (Me2N) x(RHN)3- xPTe and (Me2N) x(RHN)3- xP (R = n-octyl or oleyl). The transaminated (Me2N) x(RHN)3- xPTe derivatives are shown to be the likely Te precursors under those conditions. The enhanced reactivities of the tris(amino)phosphine tellurides are ascribed to increased nucleophilicity due to the amino-N lone pairs.

Synthesis of ultra-narrow PbTe nanorods with extremely strong quantum confinement

Monodisperse, high-quality, ultra-narrow PbTe nanorods were synthesized for the first time in a one-pot, hot-injection reaction using trans-2-decenoic acid as the agents for lead precursors and tris(diethylamino)phosphine telluride together with free tris(diethylamino)phosphine as the telluride precursors. High monomer reactivity, rapid nucleation and fast growth rate derived from the new precursors led to the anisotropic growth of PbTe nanocrystals at low reaction temperatures (<150 °C). In addition, the aspect ratio of PbTe nanorods could be largely adjusted from 4 to 15 by tuning the Pb to Te precursor molar ratio and reaction temperatures. Moreover, the synthesized ultra-narrow PbTe nanorods exhibited extremely strong quantum confinement and presented unique optical properties. We revealed that the diameter and length of PbTe nanorods could significantly affect their optical properties, which potentially offer them new opportunities in the application of optoelectronic and thermoelectric devices and make them desired subjects for multiple exciton generation and other fundamental physics studies.

Synthesis of rock salt Pb1-xSrxTe with unusual stabilized compositions and their electrochemical performance

The cubic crystal structure Pb1-xSrxTe polyhedral microcrystals with unusual stabilized compositions were synthesized using a facile solvothermal approach through balancing chemical reactivity of metal complex precursor and Te precursor. The presence of EDTA plays a crucial role in the formation of pure phase polyhedrons, avoiding the formation of SrCO3 impurity. The various reaction kinetic experimental parameters, including proper metal complex precursors, mixed solvent ratios, the appropriate temperature, and the amount of KOH, were able to control the morphology of Pb0.95Sr0.05Te and achieve much higher level of Sr alloyed into the PbTe matrix (5.2–6.5 mol% SrTe/PbTe), which is beyond its thermodynamic solubility limit of 1 mol% in bulk. Furthermore, these materials were successfully used as the electrodes of lithium ion batteries, possessing better cycling stability and the improved rate capability compared to pristine PbTe. We envision that the established strategy is general and robust, and offers easy access to other ternary PbTe-based alloy materials through careful balancing precursor chemical reactivity.

Effect of capping agent on selectivity and sensitivity of CdTe quantum dots optical sensor for detection of mercury ions

Cadmium telluride (CdTe) quantum dots (QDs) were prepared from an aqueous solution containing CdCl2 and Te precursor in the presence of thioglycolic acid (TGA) or l-cysteine as capping agents. Two optical sensors have been developed for Hg2+ ions with very low concentration in the range of nanomolar (nM) or picomolar (pM) depending on the type of capping agents and based on photoluminescence (PL) quenching of CdTe QDs. It was observed that low concentrations of Hg2+ ions quench the fluorescence spectra of CdTe QDs and TGA capped CdTe QDs exhibited a linear response to Hg2+ ions in the concentration range from 1.25 to 10 nM. Moreover, it was found that l-cysteine capped CdTe QDs optical sensor with a sensitivity of 6 × 109 M−1, exhibited a linear coefficient of 0.99 and showed a detection limit of 2.7 pM in range from 5 to 25 pM of Hg2+ ions was achieved. In contrast to the significant response that was observed for Hg2+, a weak signal response was noted upon the addition of other metal ions indicating an excellent selectivity of CdTe QDs towards Hg2+.

Synthesis of Atomically Thin Transition Metal Ditelluride Films by Rapid Chemical Transformation in Solution Phase

The controlled synthesis of large-area, atomically thin molybdenum and tungsten ditelluride (MoTe2 and WTe2) crystals is crucial for their emerging applications based on the attractive electronic properties. However, the solution phase synthesis of high-quality and large-area MoTe2 or WTe2 ultrathin films have not been achieved yet. In this study, we synthesized for the first time, large-area atomically thin MoTe2 and WTe2 films in solution phase, through rapid crystal formation directly on a conducting substrate. For the synthesis, we developed a new Te precursor. The crystal growth involves an in situ chemical transformation from Te nanoparticles into MoTe2 or WTe2 thin films. The synthesis enables precise control of the number of atomic layers over a large area, from a monolayer to multilayers. Micropatterned MoTe2 thin films are also readily synthesized in situ using the same process. The photodetector made of 3-layer semiconducting MoTe2 thin films exhibits high photoresponsivity (Rλ) over a broad sp...

NiTe2 Nanowire Outperforms Pt/C in High-Rate Hydrogen Evolution at Extreme pH Conditions.

Better hydrogen generation with nonprecious electrocatalysts over Pt is highly anticipated in water splitting. Such an outperforming nonprecious electrocatalyst, nickel telluride (NiTe2), has been fabricated on Ni foam for electrocatalytic hydrogen evolution in extreme pH conditions, viz., 0 and 14. The morphological outcome of the fabricated NiTe2 was directed by the choice of the Te precursor. Nanoflakes (NFs) were obtained when NaHTe was used, and nanowires (NWs) were obtained when Te metal powder with hydrazine hydrate was used. Both NiTe2 NWs and NiTe2 NFs were comparatively screened for hydrogen evolution reaction (HER) in extreme pH conditions, viz., 0 and 14. NiTe2 NWs delivered current densities of 10, 100, and 500 mA cm-2 at the overpotentials of 125 ± 10, 195 ± 4, and 275 ± 7 mV in 0.5 M H2SO4. Similarly, in 1 M KOH, overpotentials of 113 ± 5, 247 ± 5, and 436 ± 8 mV were required for the same current densities, respectively. On the other hand, NiTe2 NFs showed relatively poorer HER activity than NiTe2 NWs, which required overpotentials of 193 ± 7, 289 ± 5, and 494 ± 8 mV in 0.5 M H2SO4 for the current densities of 10 and 100 mA cm-2 and 157 ± 5 and 335 ± 6 mV in 1 M KOH for the current densities of 10 and 100 mA cm-2, respectively. Notably, NiTe2 NWs outperformed the state-of-the-art Pt/C 20 wt % loaded Ni foam electrode of comparable mass loading. The Pt/C 20 wt % loaded Ni foam electrode reached 500 mA cm-2 at 332 ± 5 mV, whereas NiTe2 NWs drove the same current density with 57 mV less. These encouraging findings emphasize that a NiTe2 NW could be an alternative to noble and expensive Pt as a nonprecious and high-performance HER electrode for proton-exchange membrane and alkaline water electrolyzers.

Plasma-assisted atomic layer deposition of germanium antimony tellurium compounds

Plasma atomic layer deposition of Ge-Sb-Te (GST) thin films using halogen-free precursors is reported. The Sb and Te precursors tris(aziridinyl)antimony (III) (Sb[cyclo-NC2H4]3) and di-n-butylditelluride [Te2(n-C4H9)2] were employed for the first time in the deposition of GST thin films. Conformal filling of trenches has been demonstrated. The film thickness ratio between the top and the wall/bottom of trenches was evaluated: for “wide” (7:1 aspect ratio) trenches—dbottom/dtop ≈ 0.65, and for “narrow” (23:1 aspect ratio) trenches dwall/dtop &amp;gt; 0.63. Due to the use of amino precursors the as-deposited GST films were doped with nitrogen.

Investigation of Novel Te precursor (i-C3H7)2Te for MoTe2 Fabrication

ABSTRACTWe report the investigation on the properties of a novel Te precursor (i-C3H7)2Te and its effectiveness in fabricating MoTe2. The vapor pressure of the precursor was obtained by measuring the pressure as a function of its temperature in a sealed chamber. As a result it showed a high vapor pressure of 552.1 Pa at room temperature. The decomposition of the precursor was also investigated using DFT calculation. It was shown that the most likely reaction during the course of the decomposition of (i-C3H7)2Te is (i-C3H7)2Te → H2Te + 2 C3H7. The effectiveness of the precursor on the fabrication of MoTe2 was also investigated. Sputter-deposited MoO3 was tellurized in a quartz-tube furnace at the temperature up to 440°C. The resulting film showed that the 80% of the original MoO3 was tellurized to form MoTe2. It was also shown that further optimization of tellurization is required in order to prevent formation of metal Mo and elemental Te.

Phosphine-free engineering toward the synthesis of metal telluride nanocrystals: the role of a Te precursor coordinated at room temperature.

A colloidal strategy offers opportunities for the rational design and synthesis of metal telluride nanocrystals (NCs) with the desired crystal structure, uniform geometry, and composition. However, it remains a challenge to use the paradigm to construct metal telluride NCs by a phosphine-free synthesis procedure for promising applications such as luminescence, photovoltaics and thermoelectricity. Here, we developed a new strategy for fabricating metal telluride nanocrystals, e.g. CdTe and PbTe NCs, by using a highly reactive phosphine-free Te precursor. The ability to reduce a TeO2 powder with dodecanethiol (DDT) has been achieved in the presence of oleylamine (OLA) to generate a soluble alkylammonium telluride at room temperature. We provide direct experimental evidence that the OLA-Te complexes were formed in an order of second magnitude kinetic process based on an in situ UV-vis absorption test. In the case of the CdTe NC system, the straightforward measurement of luminescence and the fabrication of LED devices are presented that can semiquantitatively assess the quality of preparation and the reactivity of this air-stable precursor. The proposed strategy highlights several unique features of this solution-based green chemistry that can be useful for synthesizing other metal telluride NCs to develop novel functional materials.

Rationally Controlled Synthesis of CdSexTe1-x Alloy Nanocrystals and Their Application in Efficient Graded Bandgap Solar Cells.

CdSexTe1−x semiconductor nanocrystals (NCs), being rod-shaped/irregular dot-shaped in morphology, have been fabricated via a simple hot-injection method. The NCs composition is well controlled through varying molar ratios of Se to Te precursors. Through changing the composition of the CdSexTe1−x NCs, the spectral absorption of the NC thin film between 570–800 nm is proved to be tunable. It is shown that the bandgap of homogeneously alloyed CdSexTe1−x active thin film is nonlinearly correlated with the different compositions, which is perceived as optical bowing. The solar cell devices based on CdSexTe1−x NCs with the structure of ITO/ZnO/CdSe/CdSexTe1−x/MoOx/Au and the graded bandgap ITO/ZnO/CdSe(w/o)/CdSexTe1−x/CdTe/MoOx/Au are systematically evaluated. It was found that the performance of solar cells degrades almost linearly with the increase of alloy NC film thickness with respect to ITO/ZnO/CdSe/CdSe0.2Te0.8/MoOx/Au. From another perspective, in terms of the graded bandgap structure of ITO/ZnO/CdSe/CdSexTe1−x/CdTe/MoOx/Au, the performance is improved in contrast with its single-junction analogues. The graded bandgap structure is proved to be efficient when absorbing spectrum and the solar cells fabricated under the structure of ITO/ZnO/CdSe0.8Te0.2/CdSe0.2Te0.8/CdTe/MoOx/Au indicate power conversion efficiency (PCE) of 6.37%, a value among the highest for solution-processed inversely-structured CdSexTe1−x NC solar cells. As the NC solar cells are solution-processed under environmental conditions, they are promising for fabricating solar cells at low cost, roll by roll and in large area.

Atomic Layer Deposition of GeTe and Ge–Sb–Te Films Using HGeCl3, Sb(OC2H5)3, and {(CH3)3Si}2Te and Their Reaction Mechanisms

In this paper, a new atomic layer deposition (ALD) process for depositing binary GeTe and ternary Ge–Sb–Te thin films is reported, where HGeCl3 and ((CH3)3Si)2Te were used as Ge and Te precursors, respectively. The precursors reacted together to form the films at a low substrate temperature of 50–100 °C, without involving any additional reactive process gas. HCl elimination from the Ge precursor to form the divalent Ge intermediate, GeCl2, is proposed to explain the formation of 1:1 composition stoichiometric GeTe films. The GeTe films are promising for use in phase change memory applications. Ternary Ge–Sb–Te films were deposited by combining the GeTe ALD process with a previously developed ALD process for Sb2Te3 films, where Sb(OC2H5)3 and ((CH3)3Si)2Te were employed respectively as the Sb and Te precursors. However, the composition of the ternary GeSbTe films deviated slightly from the desired GeTe–Sb2Te3 pseudobinary composition suggesting that a certain unwanted reaction was involved between the prev...

Room Temperature Synthesis of HgTe Quantum Dots in an Aprotic Solvent Realizing High Photoluminescence Quantum Yields in the Infrared

A computer controlled, automated synthesis method has been used to grow HgTe quantum dots (QDs) entirely at room temperature, using an aprotic solvent, dimethyl sulfoxide. The growth is carried out with small iterative additions of the Te precursor, which allows frequent sampling of the products to assess the growth trajectory in terms of the relationship between the QD concentration and QD diameters as the reaction proceeds. As such, this approach is a useful tool to develop a detailed understanding of the growth process and to work toward optimizing the reaction conditions in terms of the quality of the resulting QDs. HgTe QDs with emission spectra ranging up to 3000 nm and with photoluminescence quantum yields of up to 17% at 2070 nm have been produced by this method. Although coupling of the exciton to ligand vibrations is inevitable in this energy range, attention to the growth conditions and QD quality can influence the detailed coupling mechanisms, with fewer carrier traps reducing the extent of po...