CdS Nanobelts Research Articles

The aggregation of Mn2+, its d-d transition in CdS:Mn(II) nanobelts and bound magnetic polaron formation at room temperature

Tuning the photoluminescence (PL) and magnetic properties of 1D semiconductor nanostructures is extremely important in processing light, improving the speed and storage capacity for optoelectronic and spintronic applications. Here, we have reported the 1D Cd1−xMnxS (x = 0–0.102) nanobelts (NBs) and investigated their optical and magnetic properties. These NBs were synthesized by chemical vapor deposition method. The successful incorporation of Mn ions into an individual CdS NB has been confirmed through several characterization tools: SEM-EDX analysis, significant higher angle and phonon mode shifts were observed in the XRD and Raman spectra. Room-temperature PL showed two emission peaks at the near band edge. The first peak is related to exciton magnetic polaron (EMP) and the second one appeared on the low-energy side of the band edge emission and showed very large red-shift (∼33 nm) compared to EMP, which is attributed to bound magnetic polaron (BMP). BMP emission was detected for the first time in CdS low-dimensional nanostructures. Our study showed that Mn ions tuned CdS emission more than 400 nm (from 512 to 929 nm) covering the whole visible spectral region up to the near infrared region for the first time, and significantly boosted the room-temperature ferromagnetism, which shows promise for optoelectronic and spintronic applications.

In-situ growth of CdS nanobelts by annealing Cd foil at H2S atmosphere

We report here a simple in-situ methodology to grow CdS nanobelts on Cd foil via annealing under H2S/N2 flux. The maximum size of CdS nanobelt reaches 4 μm in width and 200 μm in length. CdS nanobelts crystallize in wurtzite structure, growing along (1 0 1¯ 0) direction. Grain boundaries in Cd foil induce the formation of the mesh pattern structure overwide the surface. And the cluster structure of CdS nanbelts is a result of rapid reaction between H2S and liquid form Cd outpouring through loopholes on the surface.

Killing two birds with one stone: To eliminate the toxicity and enhance the photocatalytic property of CdS nanobelts by assembling ultrafine TiO2 nanowires on them

Although CdS has been proven to be one of the best photocatalysts in visible light region, its photocorrosion characteristics and toxicity prohibit its practical applications in photocatalytic hydrogen generation and photodegradation of organic pollutants in waste water. In addition, the photocatalytic efficiency of single phase CdS nanostructure is still low due to the recombination of photo-induced carriers. In this paper, a facile modification of CdS nanobelts approach is proposed by assembling TiO2 nanowire on the surface of CdS nanobelts to form TiO2 nanowire/CdS nanobelt hybrid nanstructures. This approach can kill two birds with one stone, that is, to eliminate the photocorrosion induced nontoxicity, and enhance photocatalytic properties by inducing UV light active TiO2 nanowires, and enhance the photo-induced carrier separation ability. The cell cyto-compatibility experiments on TiO2 nanowire/CdS nanobelt hybrid photocatalyst proved that the toxicity of CdS nanobelts can be totally eliminated. At the same time, photodegradation performance of for CdS/TiO2 is over 3 times of that for CdS nanobelts and10 times of that for TiO2. This work gives a new insight in the field of photocatalytic water treatment.

Strong modulation of second-harmonic generation with very large contrast in semiconducting CdS via high-field domain

Dynamic control of nonlinear signals is critical for a wide variety of optoelectronic applications, such as signal processing for optical computing. However, controlling nonlinear optical signals with large modulation strengths and near-perfect contrast remains a challenging problem due to intrinsic second-order nonlinear coefficients via bulk or surface contributions. Here, via electrical control, we turn on and tune second-order nonlinear coefficients in semiconducting CdS nanobelts from zero to up to 151 pm V−1, a value higher than other intrinsic nonlinear coefficients in CdS. We also observe ultrahigh ON/OFF ratio of >104 and modulation strengths ~200% V−1 of the nonlinear signal. The unusual nonlinear behavior, including super-quadratic voltage and power dependence, is ascribed to the high-field domain, which can be further controlled by near-infrared optical excitation and electrical gating. The ability to electrically control nonlinear optical signals in nanostructures can enable optoelectronic devices such as optical transistors and modulators for on-chip integrated photonics.

Synthesis and characteristics of p-type CdS nanobelts

We report, for the first time, the synthesis of single crystalline p-type CdS nanobelts using a simple thermal evaporation of mixture of CdS and trace tin (Sn) powder. Single-crystal Sn doped CdS nanobelts are grown along the direction. The Raman spectrum of Sn-doped CdS nanobelts has a ~2 cm−1 red-shift in comparison with that of undoped CdS nanobelts. The neutral-acceptor bound exciton (AOX) and donor–acceptor pair (DAP) emissions in the low temperature photoluminescence spectroscopy of Sn doped CdS nanobelts studies support the p-type conduction in Sn doped CdS. Electrical transport measurements reveal that the tin-doped CdS nanobelts show p-type conductivity. The synthesis of p-type CdS nanobelts is expected to shed light on p-type doping difficulty of II–VI wide semiconductor.

Defect-Mediated CdS Nanobelt Photoluminescence Up-Conversion

Laser cooling in semiconductors has recently been demonstrated in cadmium sulfide nanobelts (NBs) as well as in organic–inorganic lead halide perovskites. Cooling by as much as 40 K has been shown in CdS nanobelts and by as much as 58 K in hybrid perovskite films. This suggests that further progress in semiconductor-based optical refrigeration can ultimately lead to solid state cryocoolers capable of achieving sub 10 K temperatures. In CdS, highly efficient photoluminescence (PL) up-conversion has been attributed to efficient exciton–longitudinal optical (LO) phonon coupling. However, the nature of its efficient anti-Stokes emission has not been established. Consequently, developing a detailed understanding about the mechanism leading to efficient PL up-conversion in CdS NBs is essential to furthering the nascent field of semiconductor laser cooling. In this study, we describe a detailed investigation of anti-Stokes photoluminescence (ASPL) in CdS nanobelts. Temperature- and frequency-dependent band edge ...

Synthesis, optical, structural, and electrical properties of single-crystalline CdS nanobelts

CdS nanobelts (NBs) were synthesized by vapor transport of CdS powders. The growth was carried out without any catalyst on quartz and Si (100) substrates. The synthesized CdS NBs were examined by transmission electron microscopy (TEM), field emission scanning electron microscopy (FE-SEM) and selected area electron diffraction (SAED), high-resolution transmission electron microscopy (HR-TEM), X-ray powder diffraction (XRD), energy dispersion analysis of X-ray (EDAX), spectrophotometer, and photoluminescence spectroscopy. CdS NBs were indexed as hexagonal wurtzite structure. The growth was via vapor–solid growth mechanism and along the [100] direction. The refractive index was evaluated in the transparent region, as suggested by Swanepoel, using the envelope method. The refractive index values and the extinction coefficient were decreased by increasing the wavelength. The calculated optical band gap was 2.50 eV. The photoluminescence (PL) spectrum of the synthesized CdS NBs exhibited a green emission peak at 510 nm and a broad red emission peak at 696 nm. The conductivity measurements were achieved, in the temperature range from 300 to 600 K, using the conventional two-probe technique. Two different slopes with different activation energies of 0.618 and 0.215 eV were obtained. The CdS NBs are likely being novel functional materials. Thus, they can be used in the manufacture of innovative optoelectronic nanodevices.

MWCNT/CdS nanobelt based hybrid structures and their enhanced photoelectrical performance

In this work, we report on single CdS nanobelts (NB), Multi-walled carbon nanotube (MWCNT)/CdS NB and MWCNT:Cu/CdS NB based hybrid devices for photodetector applications. The electrical properties of the MWCNT:Cu/CdS NB devices tends to exhibit excellent photo to dark current ratio and a higher photoresponse of 7.5 times than that of pristine CdS device. The results also suggest MWCNT:Cu/CdS NB for potential application in photodetectors that require high photocurrent to dark current ratio and remarkable stability.

Bosonic Lasing from Collective Exciton Magnetic Polarons in Diluted Magnetic Nanowires and Nanobelts

Exciton magnetic polarons (EMPs) are self-organized magnetic quasiparticles that can be formed by excitons in diluted magnetic semiconductors (DMSs). The optical response of EMPs in DMS microstructures is not yet well understood because it is affected by many competing factors, including spin-dependent exchange interactions, phonon coupling, and collective and nonlinear effects upon the dopant concentration and structural relaxation. Here, we report on lasing from collective EMP states in Co(II)-doped CdS nanowires (NWs) and nanobelts (NBs) that we interpret in terms of bosonic lasing, the spontaneous emission of radiation by a single quantum state macroscopically populated by bosonic quasiparticles. The lasing threshold coincides with the appearance of ferromagnetic domains, indicating an important role of spin ordering in the formation of coherent collective EMPs. These results pave the way to the realization of a new type of bosonic laser, different from exciton-polariton lasers, where formation of the...

Electrical and optoelectrical modification of cadmium sulfide nanobelts by low-energy electron beam irradiation

In this report, we describe a method for modifying electrical and optoelectrical properties of CdS nanobelts using low-energy (lower than 10 keV) e-beam irradiation in a scanning electron microscope. The electrical conductivity of the nanobelts was dramatically improved via the irradiation of e-beams. The modified conductivity of the nanobelts depends on the energy of the e-beam; it exhibits a larger photocurrent and higher external quantum efficiency but slower time-response than that before the modification. A possible mechanism about the modification is the increase of electron accumulation (injected electrons) in the nanobelts due to e-beam irradiation. In addition, the optoelectrical modification could be caused by the trapped electrons in the nanobelts and the decrease of contact resistance between the nanobelts and metal electrodes induced by e-beam irradiation. The results of this work are significant for the in situ study of semiconductor nanostructures in the electron microscope. Besides, the method of electrical and optoelectrical modification presented here has potential application in electronics and optoelectronics.

Synthesis and Photoluminescence of Single-Crystalline Fe(III)-Doped CdS Nanobelts.

In this paper, we report the synthesis and optical properties of Fe(III) doped CdS nanobelts (NBs) via simple Chemical Vapor Deposition (CVD) technique to explore their potential in nano-optics. The energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD) analysis manifested the presence of Fe(III) ions in the NBs subsequently confirmed by the peak shifting to lower phonon energies as recorded by Raman spectra and shorter lifetime in ns. Photoluminescence (PL) spectrum investigations of the single Fe(III)-doped CdS NBs depicted an additional PL peak centered at 573 nm (orange emission) in addition to the bandedge(BE) emission. The redshift and decrease in the BE intensity of the PL peaks, as compared to the bulk CdS, confirmed the quenching of spectra upon Fe doping. The synthesis and orange emission for Fe-doped CdS NBs have been observed for the first time and point out their potential in nanoscale devices.

Strain-induced spatially indirect exciton recombination in zinc-blende/wurtzite CdS heterostructures

Strain engineering provides an effective mean of tuning the fundamental properties of semiconductors for electric and optoelectronic applications. Here we report on how the applied strain changes the emission properties of hetero-structures consisting of different crystalline phases in the same CdS nanobelts. The strained portion was found to produce an additional emission peak on the low-energy side that was blueshifted with increasing strain. Furthermore, the additional emission peak obeyed the Varshni equation with temperature and exhibited the band-filling effect at high excitation power. This new emission peak may be attributed to spatially indirect exciton recombination between different crystalline phases of CdS. First-principles calculations were performed based on the spatially indirect exciton recombination, and the calculated and experimental results agreed with one another. Strain proved to be capable of enhancing the anti-Stokes emission, suggesting that the efficiency of laser cooling may be improved by strain engineering.

Synthesis of Novel Sea-Urchin-Like CdS and Their Optical Properties.

A novel morphology of CdS sea-urchin-like microstructures is synthesized by simple thermal evaporation process. Microstructures with average size of 20-50 μm are composed of single crystalline CdS nanobelts. The structural, compositional, morphological characterization of the product were examined by X-ray diffraction, energy dispersive X-ray spectroscopy, Raman spectroscopy, scanning electron microscope, transmission electron microscopy and selected area electron diffraction while optical properties are investigated by Photoluminescence spectroscopy and time-resolved Photoluminescence measurements. The tentative growth mechanism for the growth of sea-urchin-like CdS is proposed and described briefly. A strong green emission with a maximum around 517 nm was observed from the individual CdS microstructure at room temperature, which was attributed to band-edge emission of CdS. These Novel structures exhibit excellent lasing (stimulated emission) with low threshold (9.07 μJ cm(-2)) at room temperature. We analyze the physical mechanism of stimulated emission. These results are important in the design of green luminescence, low-threshold laser and display devices in the future.

Cooperative Enhancement of Second-Harmonic Generation from a Single CdS Nanobelt-Hybrid Plasmonic Structure

Semiconductor nanostructures (e.g., nanowires and nanobelts) hold great promise as subwavelength coherent light sources, nonlinear optical frequency converters, and all-optical signal processors for optoelectronic applications. However, at such small scales, optical second-harmonic generation (SHG) is generally inefficient. Herein, we report on a straightforward strategy using a thin Au layer to enhance the SHG from a single CdS nanobelt by 3 orders of magnitude. Through detailed experimental and theoretical analysis, we validate that the augmented SHG originates from the mutual intensification of the local fields induced by the plasmonic nanocavity and by the reflections within the CdS Fabry-Pérot resonant cavity in this hybrid semiconductor-metal system. Polarization-dependent SHG measurements can be employed to determine and distinguish the contributions of SH signals from the CdS nanobelt and gold film, respectively. When the thickness of gold film becomes comparable to the skin depth, SHG from the gold film can be clearly observed. Our work demonstrates a facile approach for tuning the nonlinear optical properties of mesoscopic, nanostructured, and layered semiconductor materials.

Broad spectral response photodetector based on individual tin-doped CdS nanowire

High purity and tin-doped 1D CdS micro/nano-structures were synthesized by a convenient thermal evaporation method. SEM, EDS, XRD and TEM were used to examine the morphology, composition, phase structure and crystallinity of as-prepared samples. Raman spectrum was used to confirm tin doped into CdS effectively. The effect of impurity on the photoresponse properties of photodetectors made from these as-prepared pure and tin-doped CdS micro/nano-structures under excitation of light with different wavelength was investigated. Various photoconductive parameters such as responsivity, external quantum efficiency, response time and stability were analyzed to evaluate the advantage of doped nanowires and the feasibility for photodetector application. Comparison with pure CdS nanobelt, the tin-doped CdS nanowires response to broader spectral range while keep the excellect photoconductive parameters. Both trapped state induced by tin impurity and optical whispering gallery mode microcavity effect in the doped CdS nanowires contribute to the broader spectral response. The micro-photoluminescence was used to confirm the whispering gallery mode effect and deep trapped state in the doped CdS nanowires.

Solid-state semiconductor optical cryocooler based on CdS nanobelts.

We demonstrate the laser cooling of silicon-on-insulator (SOI) substrate using CdS nanobelts. The local temperature change of the SOI substrate exactly beneath the CdS nanobelts is deduced from the ratio of the Stokes and anti-Stokes Raman intensities from the Si layer on the top of the SOI substrate. We have achieved a 30 and 20 K net cooling starting from 290 K under a 3.8 mW 514 nm and a 4.4 mW 532 nm pumping, respectively. In contrast, a laser heating effect has been observed pumped by 502 and 488 nm lasers. Theoretical analysis based on the general static heat conduction module in the Ansys program package is conducted, which agrees well with the experimental results. Our investigations demonstrate the laser cooling capability of an external thermal load, suggesting the applications of II-VI semiconductors in all-solid-state optical cryocoolers.

Plasma enhanced Mn incorporation in CdS nanostructures

Single crystalline CdS nanowires and nanobelts with Mn incorporation were obtained by thermal and plasma enhanced chemical vapor deposition (CVD). The XRD patterns confirmed the incorporation of Mn into CdS lattice in all products. The introduction of plasma significantly increased the Mn concentration in the CdS nanostructure and resulted in a morphology evolution from nanowires to nanobelts, which could be attributed to the activated species in gas phase produced by plasma. The d-d (4T1 to 6A1) emission of Mn2+ was found to be significantly enhanced in the plasma prepared samples, which was mainly due to the plasma enhancement. The results demonstrated plasma as an effective approach to control the incorporating concentration and morphology for nanostructures grown from the vapor phase.

Self-catalytic growth of CdS nanobelt and its Fabry–Perot lasing action

CdS nanobelts were fabricated by a vapor transport method in the absence of a catalyst. The scanning electron microscopy and transmission electron microscopy demonstrated that the CdS nanobelts had regular morphology, smooth surface and single-crystalline structure. Under the excitation of 325nm line of a femtosecond pulsed laser, the amplified spontaneous emission with the typical band narrowing process was observed. The Fabry–Perot mode lasing action in a single CdS nanobelt was observed by the confocal micro-photoluminescence technique. The result indicated that the CdS nanobelt can be used as ideal microlaser material in the future optoelectronic devices.

Photosensing performance of branched CdS/ZnO heterostructures as revealed by in situ TEM and photodetector tests.

CdS/ZnO branched heterostructures have been successfully synthesized by combining thermal vapour deposition and a hydrothermal method. Drastic optoelectronic performance enhancement of such heterostructures was revealed, compared to plain CdS nanobelts, as documented by comparative in situ optoelectronic studies on corresponding individual nanostructures using an originally designed laser-compatible transmission electron microscopy (TEM) technique. Furthermore, flexible thin-film based photodetectors based on standard CdS nanobelts and newly prepared CdS/ZnO heterostructures were fabricated on PET substrates, and comparative photocurrent and photo-responsivity measurements thoroughly verified the in situ TEM results. The CdS/ZnO branched heterostructures were found to have better performance than standard CdS nanobelts for optoelectronic applications with respect to the photocurrent to dark current ratio and responsivity.

Visual monitoring of laser power and spot profile in micron region by a single chip of Zn-doped CdS nanobelts

On the basis of pumping-power-dependent emission property, Zn-doped CdS nanobelts are developed to monitor injected laser power and detect the profile of laser focal spots visually in the micron region through color changes.