In2Se3 Nanowires Research Articles

Growth of necklace-like In2Se3 nanowires using MoS2 seed layer during PVD method

In the present work, we have fabricated one-dimensional indium selenide (In2Se3) nano wires by physical vapor deposition method. III-VI group compound semiconductor nanostructure having potential applications in optoelectronics field such as mainly solar cells, data storage, photo-detectors. Here, In2Se3 nanowires are grown on MoS2 coated SiO2/Si substrate, wherein thin MoS2 layer has been used as a seed layer. Surface morphology, structure and phase of these nanowires were further characterized using scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and high-resolution transmission electron microscopy (HRTEM), respectively. This work suggests an effective way to form various novel nanostructures, open a new window towards the development in the field of optoelectronic applications.

Controlling Growth High Uniformity Indium Selenide (In2Se3) Nanowires via the Rapid Thermal Annealing Process at Low Temperature

High uniformity Au-catalyzed indium selenide (In2Se3) nanowires are grown with the rapid thermal annealing (RTA) treatment via the vapor-liquid-solid (VLS) mechanism. The diameters of Au-catalyzed In2Se3 nanowires could be controlled with varied thicknesses of Au films, and the uniformity of nanowires is improved via a fast pre-annealing rate, 100 °C/s. Comparing with the slower heating rate, 0.1 °C/s, the average diameters and distributions (standard deviation, SD) of In2Se3 nanowires with and without the RTA process are 97.14 ± 22.95 nm (23.63%) and 119.06 ± 48.75 nm (40.95%), respectively. The in situ annealing TEM is used to study the effect of heating rate on the formation of Au nanoparticles from the as-deposited Au film. The results demonstrate that the average diameters and distributions of Au nanoparticles with and without the RTA process are 19.84 ± 5.96 nm (30.00%) and about 22.06 ± 9.00 nm (40.80%), respectively. It proves that the diameter size, distribution, and uniformity of Au-catalyzed In2Se3 nanowires are reduced and improved via the RTA pre-treated. The systemic study could help to control the size distribution of other nanomaterials through tuning the annealing rate, temperatures of precursor, and growth substrate to control the size distribution of other nanomaterials.Graphical Rapid thermal annealing (RTA) process proved that it can uniform the size distribution of Au nanoparticles, and then it can be used to grow the high uniformity Au-catalyzed In2Se3 nanowires via the vapor-liquid-solid (VLS) mechanism. Comparing with the general growth condition, the heating rate is slow, 0.1 °C/s, and the growth temperature is a relatively high growth temperature, > 650 °C. RTA pre-treated growth substrate can form smaller and uniform Au nanoparticles to react with the In2Se3 vapor and produce the high uniformity In2Se3 nanowires. The in situ annealing TEM is used to realize the effect of heating rate on Au nanoparticle formation from the as-deposited Au film. The byproduct of self-catalyzed In2Se3 nanoplates can be inhibited by lowering the precursors and growth temperatures.

High pressure γ-to-β phase transition in bulk and nanocrystalline In2Se3

ABSTRACTPressure-dependent phase transitions of In2Se3 bulk powders and nanowire samples were studied at room temperature using synchrotron X-ray diffraction and a diamond anvil cell. γ-In2Se3, metastable under ambient conditions, transforms into to the stable high pressure β phase between 2.8 and 3.2 GPa in bulk powder samples and at slightly higher pressures, between 3.2 and 3.7 GPa, in nanowire samples. While the γ phase bulk modulus is similar to that of the β phase, the decrease due to pressure in the unit cell parameter ratio, c/a, is less than half the decrease seen in the β phase. First-principles calculations show that γ-In2Se3 has a higher energy and unit-cell volume than β-In2Se3, consistent with the experimental observations.

Generation and the role of dislocations in single-crystalline phase-change In2Se3 nanowires under electrical pulses

We report the observation of the generation of dislocations in single-crystal phase-change In2Se3 nanowires under electrical pulses and the impact of these dislocations on electrical properties. Particularly, we correlated the atomic-scale structural characteristics with local electrical resistance variations, by performing transmission electron microscopy and scanning Kelvin probe microscopy on the same nanowires. By coupling the experimental results with first-principles density functional theory calculations, we show that the immobile dislocations are generated via vacancy condensations. Importantly, these dislocations lead to several orders of magnitude increase in the electrical resistance, while maintaining the single crystallinity of the lattice. These results significantly advance the fundamental understanding of the structure-property relation in this phase-change material under transient electrical excitations. From a practical perspective, the significant increase in the electrical resistance, driven by the formation of dislocations, can be exploited as a new electronic state in the single-crystalline phase in this phase-change material.

Vapour–liquid–solid growth of one-dimensional In2Se3 nanostructures and their promising field emission behaviour

Single crystalline ultra long In2Se3 nanowires have been grown via thermal evaporation route on Au/Si substrates and explored its field emission investigations at ∼1 × 10−8 mbar.

Thermally phase-transformed In2Se3 nanowires for highly sensitive photodetectors.

The photoresponse characteristics of In2Se3 nanowire photodetectors with the κ-phase and α-phase structures are investigated. The as-grown κ-phase In2Se3 nanowires by the vapor-liquid-solid technique are phase-transformed to the α-phase nanowires by thermal annealing. The photoresponse performances of the κ-phase and α-phase In2Se3 nanowire photodetectors are characterized over a wide range of wavelengths (300-900 nm). The phase of the nanowires is analyzed using a high-resolution transmission microscopy equipped with energy dispersive X-ray spectroscopy and X-ray diffraction. The electrical conductivity and photoresponse characteristics are significantly enhanced in the α-phase due to smaller bandgap structure compared to the κ-phase nanowires. The spectral responsivities of the α-phase devices are 200 times larger than those of the κ-phase devices. The superior performance of the thermally phase-transformed In2Se3 nanowire devices offers an avenue to develop highly sensitive photodetector applications.

Investigation of electromigration in In2Se3 nanowire for phase change memory devices

The decomposition of In2Se3 nanowire phase change memory devices during current-driving operation was investigated. The devices were subjected to thermal/electrical stress with current density and electric field during the reset operation at 0.24–0.38 MA/cm2 and 5.3–6.4 kV/cm, respectively. After multiple operation cycles, a change in morphology and composition of the In2Se3 nanowire was observed and led to the device failure. The transmission electron microscopy and energy dispersive analysis indicate that electromigration causes the catastrophic failure by void formation where In atoms migrate toward the cathode and Se atoms migrate toward the anode depending on their electronegativities.

Thermally efficient and highly scalable In2Se3 nanowire phase change memory

The electrical characteristics of nonvolatile In2Se3 nanowire phase change memory are reported. Size-dependent memory switching behavior was observed in nanowires of varying diameters and the reduction in set/reset threshold voltage was as low as 3.45 V/6.25 V for a 60 nm nanowire, which is promising for highly scalable nanowire memory applications. Also, size-dependent thermal resistance of In2Se3 nanowire memory cells was estimated with values as high as 5.86×1013 and 1.04×106 K/W for a 60 nm nanowire memory cell in amorphous and crystalline phases, respectively. Such high thermal resistances are beneficial for improvement of thermal efficiency and thus reduction in programming power consumption based on Fourier's law. The evaluation of thermal resistance provides an avenue to develop thermally efficient memory cell architecture.

CuInSe2 Nanowires from Facile Chemical Transformation of In2Se3 and Their Integration in Single-Nanowire Devices

Nanowire solar cells are receiving a significant amount of attention for their potential to improve light absorption and charge collection in photovoltaics. Single-nanowire solar cells offer the ability to investigate performance limits for macroscale devices, as well as the opportunity for in-depth structural characterization and property measurement in small working devices. Copper indium selenide (CIS) is a material uniquely suited to these investigations. Not only could nanowire solar cells of CIS perhaps allow efficient macroscale photovoltaics to be fabricated while reducing the amount of CIS required, important for a system with possible resource limitations, but it is also a photovoltaic material for which fundamental understanding has been elusive. We here present a recipe for a scaled up vapor liquid solid based synthesis of CIS nanowires, in-depth material and property correlation of single crystalline CIS nanowires, and the first report of a single CIS nanowire solar cell. The synthesis was accomplished by annealing copper-coated In2Se3 nanowires at a moderate temperature of 350 °C, leading to solid-state reaction forming CIS nanowires. These nanowires are p-type with a resitivity of 6.5 Ωcm. Evidence is observed for a strong diameter dependence on the nanowire transport properties. The single-nanowire solar cells have an open-circuit voltage of 500 mV and a short-circuit current of 2 pA under AM 1.5 illumination.

Atomistic structures and phase transition of In2Se3 nanowires studied by DFT calculations and synchrotron radiation X-ray diffraction

In2Se3 has potential application in photovoltaic cell, solid-state batteries, phase change memories, and in the manufacture of detectors of ionizing radiation. Here we study the crystal structures and phase transition of In2Se3 by using DFT calculations. Crystal structures of In2Se3 include layered structures and vacancy-ordered-in-screw-form structures. Combining with SR-XRD techniques, our studies show that thermal annealing will merge the layer structures of In2Se3 and improves conductivity of In2Se3. Our results provide structural information for different phases and phase transition mechanism of In2Se3.

Improved performance of In2Se3 nanowire phase-change memory with SiO2 passivation

The resistive switching and low frequency noise characteristics in In2Se3 nanowire PRAM devices with SiO2 passivation have been studied. The SiO2 passivation of the nanowires was adopted to lessen the thermal energy dissipation to the surroundings and as a result, the set/reset voltages and the corresponding power requirements have been reduced. The measured low frequency noise characteristics exhibit a typical 1/f noise behavior and show the same noise level after the SiO2 passivation.

Electronically Driven Amorphization in Phase-Change In2Se3 Nanowires

We show that the amorphization process in phase-change In2Se3 nanowires grown by chemical vapor deposition can be driven by electronic effects and does not require the conventional thermal melt-quench process. In particular, using transmission electron microscopy, in situ single-nanowire Raman spectroscopy, scanning Kelvin probe microscopy, and finite-element simulations, we demonstrate that the electronic amorphization can be achieved under optical excitations at temperatures far below the thermal melting point. The mechanism of this electronic amorphization is likely related to the presence of atomic bonds with different strengths in the crystalline phase In2Se3 and the weakening of the weaker bonds by nonequilibrium electrons. Our findings suggest that In2Se3 is a promising candidate for phase-change memory applications, with potential advantages including energy-efficient memory switching due to the electronic amorphization process and highly stable data storage as a result of a high melting point compared to Ge/Sb–Te alloys. On a more general level, these results indicate the need to take into account the electronic effects in modeling and understanding the phase transition processes in phase-change memories.

High performance single In2Se3 nanowire photodetector

The single indium selenide (In2Se3) nanowire photodetectors were fabricated, and the performance characteristics of the nanowire devices were systematically investigated. The single In2Se3 nanowire photodetectors show high and stable photoresponse in wide light wavelength (254-800 nm) and temperature range (7-300 K). The spectra response indicates that the absorption coefficient of the In2Se3 nanowires at certain wavelength dominates the performance of the devices. The good linearity of the photocurrents with the incident irradiation over a wide wavelength range has been obtained, demonstrating that the In2Se3 nanowire photodetectors work in a typical light-dependent resistor mode.

Thermal phase transformation of In2Se3 nanowires studied by in situ synchrotron radiation X-ray diffraction

We report the preparation of α- and κ-phase In2Se3 nanowires by thermal evaporation and investigation of their phase transformations in situ by synchrotron radiation X-ray diffraction (XRD) during a thermal annealing process. The κ-phase transformed into the α-phase at 500 °C and eventually transformed to high temperature α-phase with a layered structure of 5 atoms-5 atoms at 700 °C irreversibly. Different atomistic structures of In2Se3 were modeled and optimized by DFT, which correlate well with the XRD results. The In2Se3 nanowires also exhibit a large difference in resistivity before and after annealing.

Fabrication of High-Quality In2Se3 Nanowire Arrays toward High-Performance Visible-Light Photodetectors

The synthesis of high-quality In2Se3 nanowire arrays via thermal evaporation method and the photoconductive characteristics of In2Se3 individual nanowires are first investigated. The electrical characterization of a single In2Se3 nanowire verifies an intrinsic n-type semiconductor behavior. These single-crystalline In2Se3 nanowires are then assembled in visible-light sensors which demonstrate a fast, reversible, and stable response. The high photosensitivity and quick photoresponse are attributed to the superior single-crystal quality and large surface-to-volume ratio resulting in fewer recombination barriers in nanostructures. These excellent performances clearly demonstrate the possibility of using In2Se3 nanowires in next-generation sensors and detectors for commercial, military, and space applications.

Morphology-tunable In2Se3 nanostructures with enhanced electrical and photoelectrical performances via sulfur doping

Highly ordered In2Se3 nanostructures with different morphologies were first fabricated via a simple and efficient thermal evaporation process. Through manipulating the growth driving force, the morphology of the In2Se3 nanostructures was varied from nanowire arrays, via nanotree arrays to nanowire bundles. Furthermore, the nanostructures were on-demand doped with sulfur by co-evaporating the dopant In2S3 precursor and In2Se3 powder during the growth. Electrical and photoelectrical studies based on individual undoped and doped In2Se3 nanowires revealed that sulfur doping leads to significant improvements in the transport and photoelectronic performances, such as enhancing the conductivity and improving the sensitivity to visible light. These excellent performances demonstrate that S-doped In2Se3 nanowires should offer great potential for next-generation device applications.

Vacancy ordering and lithium insertion in III2VI3 nanowires

Superlattice structures resulting from vacancy ordering have been observed in many materials. Here we report vacancy ordering behavior in III2VI3 nanowires. The formation of layer-like structural vacancies has been achieved during the synthesis of In2Se3 nanowires through a vapor-transport route. Doping In2Se3 nanowires with small amounts of Ga during synthesis can completely change the structural vacancy ordering from a layer-like to a screw-like pattern for (In x Ga1−x )2Se3 nanowires. Lithium atoms can fill in the layer-like structural vacancies of In2Se3 nanowires and generate new types of vacancy and lithium atom ordering superlattices. The screw-patterned vacancies of (In x Ga1−x )2Se3 nanowires show reversible lithium insertion. Our results contribute to the understanding of structure property correlations of III2VI3 materials used in lithium ion storage, photovoltaics, and phase change memory.

Large Anisotropy of Electrical Properties in Layer-Structured In2Se3 Nanowires

Layer-structured indium selenide (In 2Se 3) nanowires (NWs) have large anisotropy in both shape and bonding. In 2Se 3 NWs show two types of growth directions: [11-20] along the layers and [0001] perpendicular to the layers. We have developed a powerful technique combining high-resolution transmission electron microscopy (HRTEM) investigation with single NW electrical transport measurement, which allows us to correlate directly the electrical properties and structure of the same individual NWs. The NW devices were made directly on a 50 nm thick SiN x membrane TEM window for electrical measurements and HRTEM study. NWs with the [11-20] growth direction exhibit metallic behavior while the NWs grown along the [0001] direction show n-type semiconductive behavior. Excitingly, the conductivity anisotropy reaches 10 (3)-10 (6) at room temperature, which is 1-3 orders magnitude higher than the bulk ratio.

Synthesis and Phase Transformation of In2Se3 and CuInSe2 Nanowires

III−VI and I−III−VI semiconductors with anomalous grain boundaries have been actively studied for high efficiency photovoltaic applications. Nanowire morphology can provide a well-defined nanodomain for studying grain boundary and p−n junction physics for improving solar cell efficiency. We report the synthesis of In2Se3 and CuInSe2 single crystalline nanowires via a Au-catalyzed vapor−liquid−solid growth. Superlattice forms in In2Se3 nanowires at room temperature and a reversible superlattice transformation takes place at 200 °C. Cu concentration in CuInSe2 nanowires can be controlled, and nanowires show a dependence of crystal structure on Cu concentration.

III-VI compound semiconductor indium selenide (In2Se3) nanowires: Synthesis and characterization

The authors report the synthesis of one-dimensional indium selenide nanowire, a III-VI group compound semiconductor nanostructure with potential applications in data storage, solar cells, and optoelectronics. Nanoscale gold particles were used as catalysts and growth was also demonstrated using indium as self-catalyst. The growth mechanism is confirmed to be vapor-liquid-solid process by in situ heating experiments in which In and Se were found to diffuse back into the gold catalyst bead forming a Au–In–Se alloy that was molten at elevated temperatures. The morphology, composition, and crystal structure of the In2Se3 nanowires (NWs) were analyzed by scanning electron microscopy, energy dispersive x-ray spectroscopy, and high-resolution transmission electron microscopy.