PbS Films Research Articles

Highly Photosensitive Lead Sulfide Thin Films Grown by H2 S Free MOCVD Using a Single Source Metal-Organic Precursor.

High-quality lead sulfide (PbS)films are deposited on selected substrate chemistries by an H2 S-free metal-organic chemicalvapordeposition (MOCVD) process using a single-source metal-organic complex (Pb(dmampS)2 ). The complex is synthesized via a salt metathesis reaction betweenPbCl2 andlithium1-(dimethylamino)-2-methylpropane-2-thiolate (Li(dmampS))in diethyl ether. Subsequent film deposition is conducted by a simple thermolysis process in the absence of H2 S, yet chemical and structural analysis confirm chemically stoichiometric and homogenous films. Mechanistic studies with electron impact mass spectroscopy (EIMS) and gas chromatography mass spectroscopy (GCMS) suggest the selective cleavage of C-S bonds in the complex as the reason for the facile PbS formation with negligible impurity incorporation. The high crystallinity, low hole concentrations, and charge transport properties comparable and in many cases superior to films produced by atomic layer deposition (ALD) testify to the quality of the films. Lastly, rigid and flexible photodetectors fabricated with the PbS films exhibit considerably high photocurrents, reliable switching characteristics, and high sensitivity over a broad spectral bandwidth, highlighting the potential for realizing practical broadband photodetectors.

Synthesis of nano-sized lead sulfide thin films from Avocado (Glycosmis cochinchinensis) Leaf extracts to empower pollution remediation

The translucent and nano-crystalline PbS films were equipped with the CBD techniques on metal substrates by the temperature of 90 °C through aqueous solutions of Lead Nitrate and Thiourea. The XRD phases verify the crystalline property of synthesized thin films that the shape falls in the cubic structures with favourite orientations. It revealed that the prepared material is cubic crystal oriented as (111), (110), (100) and (101) crystal planes. The crystalline size varied between 0.4 and 0.7 nm. The band gap was assessed using UV–vis captivation spectra and Tau relations. The average energy band gap was found to be 2.43 eV which is greater than bulk materials of PbS; because of quantum confinements of Lead Sulfide Nano Crystalline thin films, and PL also confirms this result. The variation in band gap with Leaf extracts and particle sizes displayed blue shifts characteristic of electrons quantum confinements. SEM micrograph shows extremely uniform and adherent PbS films are found at higher PH values. It was evidently observed that the viscosity of the synthesized thin films reduced from 563 to 111 nm with a rise in pH value. The sample prepared at pH 4 shows good performance, and thin films deposited from Avocado (Glycosmis cochinchinensis) leaf extracts are a promising method to empower pollution remediation and future energy.

Fabrication, microstructure, and nonlinear/linear optical parameters of polymeric‐based poly(vinyl alcohol)/poly(vinyl pyrrolidone) nanocomposites films for optical attenuation applications

AbstractHerein, a novel proposed optical attenuator poly(vinyl alcohol)/poly(vinyl pyrrolidone) (PVA/PVP) doped PbS (NPs) nanoparticles nanocomposites films. The samples are fabricated by casting‐method to analyze the linear optical properties and estimate the nonlinear optical parameters. The crystal and molecular structure of the fabricated nanocomposites thick (PVA/PVP) films of different PbS (NPs) doping ratios were analyzed by XRD technique and FT‐IR, respectively. The semi‐crystalline nature of the fabricated PVA/PVP is influenced through all samples and the crystallinity is increased. The particle size of PbS (NPs) is increased in the doped samples and the strain parameter is increased. The measured transmission of the fabricated PVA/PVP doped PbS (NPs) films are decreased as the doping ratio of PbS (NPs) is increased. The absorption coefficient is incremented and shows large absorption values in the UV regions, may be utilized in UV‐blocking for saving the human skin, dramatically, and a noticed red‐shift in the edge of absorption for all samples as the doping ratio is increased. The most probable transition is indirect, and the evolved values of the energy gaps between HOMO and LUMO levels are decrement from 3.97 to 2.65 eV as doping ratio of PbS (NPs) is increased. Different models are utilized to evaluate the average values of the real refractive index (2.175–2.438). The fabricated PVA/PVP doped PbS (NPs) samples are investigated for normal light and laser attenuations. The mass attenuation coefficient increases, gradually, with increment of PbS (NPs), but the half value layer (HVL) parameter decreases with increasing of the doping ratio. These experimental results confirm the applicability of the fabricated samples to attenuate Red‐632 nm and Green‐532 nm laser radiation. It is possible to utilize PVA/PVP doped PbS (NPs) nanocomposites in different, wide‐scale optical filters.

Improved linear and nonlinear optical properties of PbS thin films synthesized by spray pyrolysis technique for optoelectronics: An effect of Gd3+ doping concentrations

In the present article, the pure PbS and different concentrations of Gd doped PbS (Gd:PbS) films were developed using the spray pyrolysis route by growing thin films on the glass substrate. The estimated crystallite sizes were found from 15.5 to 20.8 nm for as-deposited films. The spherical shape morphology of grains was observed by FESEM. The obtained average grain sizes varied from 52.8 to 108.2 nm were obtained from the grain size distributions for 0.0, 0.5, 1.5, and 2.5 wt % Gd: PbS films, respectively. Extinction coefficients of as-deposited films were measured from 0.04 to 0.12 in the range of wavelength 200–2500 nm. Refractive indices of films were obtained from 5.4 to 1.22 in range of 200–2500 nm wavelength. The band gaps of 2.75, 2.64, 2.45, and 3.10 eV for 0.0, 0.5, 1.0 and 2.5 wt % Gd thin films were estimated using Tauc's relation respectively. The values of the dielectric constant, dielectric loss, and optical conductivity were recorded in the range of 1.32–29.6, 0.30–0.61, and 2.34 × 1014–3.08 × 1013 between 200 and 2500 nm wavelengths for as-deposited thin films respectively. The optimum values of linear susceptibility, non-linear susceptibility and refractive index were recorded in the range of 1.23–2.93, 5.21 × 10−10 - 120 × 10−10, 3.54 × 10−9 – 74.2 × 10−9 (esu) between 1.46 and 0.52 eV respectively for as-deposited thin films. The Gd: PbS thin films improve the physical properties and therefore, it becomes suitable candidature for the applications in optoelectronic devices.

Limiting Factors of Detectivity in Near-Infrared Colloidal Quantum Dot Photodetectors.

Lead sulfide colloidal quantum dots (PbS CQDs) have shown great potential in photodetectors owing to their promising optical properties, especially their strong and tunable absorption. However, the limitation of the specific detectivity (D*) in CQD near-infrared (NIR) photodetectors remains unknown due to the ambiguous noise analysis. Therefore, a clear understanding of the noise current is critically demanded. Here, we elucidate that the noise current is the predominant factor limiting D*, and the noise is highly dependent on the trap densities in halide-passivated PbS films and the carriers injected from the Schottky contact (EDT-passivated PbS films/metal). It is found that the thickness of CQDs is proportional to their interface trap density, while it is inversely proportional to their minimal bulk trap density. A balance point can be reached at a certain thickness (136 nm) to minimize the trap density, giving rise to the improvement of D*. Utilizing thicker PbS-EDT films broadens the width of the tunneling barrier and thereby reduces the carrier injection, contributing to a further enhancement of D*. The limiting factors of D* determined in this work not only explain the physical mechanism of the influence on detection sensitivity but also give guidance to the design of high-performance CQD photodetectors.

Automated Instrument for the Deposition of Thin Films Using Successive Ionic Layer Adsorption and Reaction

The development and improvement of thin film deposition techniques is an important research topic to obtain new materials at submicro and nano scale with high homogeneity and thickness control. Here, we designed and built an automated device for the deposition of binary or ternary compound films using Successive Ionic Layer Adsorption and Reaction (SILAR). The instrument is integrated by three different systems. The first system consists of a mobile platform of two degrees of freedom. The second part has an 8-bit microcontroller used to adjust the velocities along the horizontal and vertical axes. The third, the control system, uses a mobile app that can be implemented in smart devices, developed in free code software for programming and monitoring the main deposition parameters of the SILAR device such as the number of cycles, the immersion and emersion velocities, the residence time at each step, and the number of reactors. The performance of our instrument was verified through the deposition of PbS films, varying the number of deposition cycles to study the variations in the film thickness and structure, and assessed by profilometry, Raman spectroscopy, X-ray diffraction and atomic force microscopy. The system demonstrated is useful to obtain crystalline films with controllable thicknesses.

Laser Induced Plasma of PbS Thin Films: Effects of Laser Power on Morphology, Structure, and Optical Properties

AbstractThe structural and optical characteristics of lead sulfide (PbS) nanoparticles from PbS films are investigated in this study. Laser induced plasma of thin samples on glass substrates is performed using an Nd:Yak laser with a wavelength of 1064 nm and a range of laser intensities (160, 200, 260, 300) mJ. The effect of increasing the laser intensity on the structural characteristics of the material is investigated using atomic force microscopy (AFM), X‐ray diffraction (XRD), and scanning electron microscopy (SEM). The XRD data indicate that the membrane produced is polycrystalline in nature, with the (111) and (200) planes being the main phases. Additionally, the (AFM) measurements revealed that the smallest particle size is produced with the lowest laser deposition energy (160 mJ). The results indicated that it is possible to fabricate thin films with medium grain sizes. The impact of altering the laser intensity on the optical characteristics is investigated, and it is discovered that they have direct acceptable transitions in the range (1.65–1.95) electron volts.

Morphology and permeability of bio-based poly(butylene adipate-co-terephthalate) (PBAT), poly(butylene succinate) (PBS) and linear low-density polyethylene (LLDPE) blend films control shelf-life of packaged bread

Poly(butylene adipate-co-terephthalate) (PBAT), poly(butylene succinate) (PBS) and linear low-density polyethylene (LLDPE) were blended to produce bio-based packaging via blown-film extrusion. Blend ratios modified morphology, crystallinity and relaxation temperatures (T α ) of the films. Binary mixtures caused phase separation and non-homogeneous fibrous microstructures of immiscible polymers. Bio-based blend films containing LLDPE (LLDPE/PBAT and LLDPE/PBS) gave less homogeneous structures than PBAT/PBS films. The formation of oriented fibrous networks subsequently controlled mechanical and barrier properties of the blend films. LLDPE blending modified C=O carbonyl groups in PBAT and PBS, forming voids in topographic images indicating incompatibility. PBAT and PBS blends showed good compatibility and adhesion of polymer interface, causing smooth and compact structures with minimal surface roughness. Incorporation of PBAT and PBS sharply reduced crystallinity of LLDPE/PBAT and LLDPE/PBS films. LLDPE/PBAT blends had lower T α than neat PBAT and LLDPE, while T α of PBAT/PBS blends proportionally decreased at increasing PBS which indicated diverse polymer miscibility and molecular mobility. Water vapor permeability (WVP) and oxygen permeability (OP) fitted with polynomial and exponential equations, respectively and depended on blend ratios. Films containing higher PBS had combined higher WVP and lower OP, delaying fungal growth in packaged bread due to dehydration. Ratios of PBAT, PBS and LLDPE blend films clearly affected mold growth and crumb hardness during storage. Regardless of film components, the firmness of bread crumbs increased linearly with package WVP. Conversely, mold growth had insignificant correlation with OP. Moisture loss from bread crumbs due to high WVP showed dominant effects on microbial growth. Blending PBAT and PBS modified the morphology and permeability of bio-based films and increased the shelf-life of packaged bread. • Systematic investigations for packaging properties in bio-based PBAT/PBS/PE blends. • FTIR intensity ratios effectively monitor bonding and morphology modifications. • H 2 O and O 2 permeability in PBAT/PBS/PE blends fitted to cubic and exponential model. • Hardness of packaged bread linearly increased with water vapor permeability. • Water vapor permeability majorly affected mold growth and increasing crumb hardness.

Deposition of PbS Films by Pyrolysis of Atomized Solutions of Lead Thiourea Complexes

Deposition of PbS Films by Pyrolysis of Atomized Solutions of Lead Thiourea Complexes

Structure, morphology, and local photoelectrical characterization of PbS films grown by SILAR

In this work, the structure, morphology, and local electrical properties of lead sulfide films growth by Successive Ionic Layer Adsorption and Reaction was studied. Films were deposited from 100 to 500 cycles onto glass substrates. Film thickness increase from 100 to 800 nm with the number of deposition cycles. The deposited films are single phase, cubic PbS. Raman spectra present a band at 969 cm−1 arising from surface oxidation during deposition, as well as a band at 138 cm−1 related with the growth mode. Films prepared at 100 cycles have a mixed layer-island growth mode, while the films prepared at 200 and 500 cycles have granular morphologies with voids. The local electrical characterization indicates that films electrical and photo response depend on the film morphology.

Preparation of spin coated PbS thin films using bis-tetrahydroquinolinedithiocarbamatolead(II) complex as a single source precursor

Recently, the incorporation of single-source molecular precursors in synthetic protocols has been identified as an effective and easy route toward tuning the sought-after properties of thin films. In this work, bis-tetrahydroquinolinedithiocarbamato complex of lead(II) has been used as a single-source molecular precursor to deposit PbS thin films at elevated temperatures. The spin coating method was chosen as a deposition technique to afford PbS thin films. The morphology of the obtained films was observed to be influenced by the variation of temperature. Formations of compact thick and agglomerated spherical granules were observed at a lower temperature whereas elevated temperatures afforded the formation of cubic and multipodal shaped structures. From the energy dispersive X-ray spectroscopy (EDS) results, the elemental ratio of the finally formed films agree with the PbS composition. X-ray diffraction studies further revealed the formation of the crystalline cubic phase of PbS films with a calculated crystallite size in the range of 50 − 58 nm.

Structural, morphology and optical properties of PbS (Lead Sulfide) thin film

We report here the synthesis, structural and optical properties of PbS thin film. The growth rate in the chemical path deposition time was optimized during film deposition. The surface of the PbS film is compact and well covered, with a smooth surface and irregularly shaped spherical grain of random sizes. The electrical studies were measure with the Hall effect and Hot probe for the optimized film and the transmittance and band gap of the films were measure by the UV–VIS–NIR Spectrometer in the range of 400–2500 nm. It was observed that the band gap decreases and thickness increased with the increases in deposition time. The room temperature photoluminescence emission spectra of the as grown PbS thin films. Radiation of wavelength 425 nm was used for excitation.

The influence of iodide addition on the composition, morphology, crystal structure, and semiconductor and photoelectric properties of PbS films.

The concentration conditions for the deposition of lead sulfide and hydroxide in a citrate-ammonia reaction system by varying the pH value and the concentration of the ammonium iodide dopant are calculated. Kinetic studies of the process of conversion of lead salt into sulfide by varying the concentration of NH4I in solution within the range of 0.0-0.4 M show an inhibitory effect of ammonium iodide, which reduces the constant of the effective rate of the conversion process by almost 20 times. Thin films of lead sulfide with a thickness of 100 to 650 nm are synthesized by chemical bath deposition in the presence of NH4I on sitall and glass substrates. The introduction of NH4I into the reaction mixture decreases the size of crystallites forming the films and increases the fraction of nanoparticles to 17%. The films deposited during 90 min contain 48.5-51.7 at% of lead, 47.4-47.9 at% of sulfur, and up to 3.7 at% of iodine; the content of iodine can reach 17.1 at% in the initial period of deposition (after 20 min of deposition). The calculated fractal dimension of the surface of the iodine-doped PbS(I) films (Dc = 2.04-2.14) corresponds to the process of film formation by the cluster-cluster aggregation mechanism with small sticking probability (reaction-limited cluster aggregation model (RLCA)). According to the X-ray diffraction data, the PbS(I) films have a cubic structure of the NaCl (B1) type; an increase in the concentration of NH4I in the solution results in an increase in the lattice parameter from 0.59315(1) to 0.59442(3) nm, which is probably due to the substitution of sulfur ions for iodine ones. According to optical studies, the introduction of ammonium iodide into the reaction mixture leads to a shift of the absorption edge to the high-energy region and the appearance of an additional (impurity) band. The PbS films deposited in the presence of NH4I do not require additional photosensitization operations and show a relatively high volt-watt sensitivity to IR radiation at anomalously small values of the time constant.

Kimyasal Banyo Biriktirme Yöntemiyle Elde Edilen İğne Deliksiz PbS İnce Filmler

In this study, the (Lead Sulfide) PbS thin films with one, two, and three layers were fabricated by employing the chemical bath deposition method. Layer by layer production of PbS thin films was realized for the first time as seen in the literature review. For investigating the crystal structures, the X-ray diffraction (XRD) analysis was used. The structural analyses indicated that the crystallite size was decreased from about 40 nm to 8-10 nm depending on the number of layers. The surface micrographs of the films were obtained using scanning electron microscopy (SEM). When the PbS film was obtained in one layer, some cracks, pinholes, and voids were observed on the sample surface. However, no cracks, voids, or pinhole formation were found on the film surface when the films were coated in two and three layers.

Biofilm Formation Reduction by Eugenol and Thymol on Biodegradable Food Packaging Material.

Biofilm is a structured community of microorganisms adhering to surfaces of various polymeric materials used in food packaging. Microbes in the biofilm may affect food quality. However, the presence of biofilm can ensure biodegradation of discarded packaging. This work aims to evaluate a biofilm formation on the selected biodegradable polymer films: poly (lactic acid) (PLA), poly (butylene adipate-co-terephthalate) (PBAT), and poly (butylene succinate) (PBS) by selected bacterial strains; collection strains of Escherichia coli, Staphylococcus aureus; and Bacillus pumilus, Bacillus subtilis, Bacillus tequilensis, and Stenotrophomonas maltophilia isolated from dairy products. Three different methods for biofilm evaluation were performed: the Christensen method, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, and fluorescence microscopy. High biofilm formation was confirmed on the control PBS film, whereas low biofilm formation ability was observed on the PLA polymer sample. Furthermore, the films with incorporated antimicrobial compounds (thymol or eugenol) were also prepared. Antimicrobial activity and also reduction in biofilm formation on enriched polymer films were determined. Therefore, they were all proved to be antimicrobial and effective in reducing biofilm formation. These films can be used to prepare novel active food packaging for the dairy industry to prevent biofilm formation and enhance food quality and safety in the future.

Antimicrobial, Antibiofilm, and Antioxidant Activity of Functional Poly(Butylene Succinate) Films Modified with Curcumin and Carvacrol.

The use of food industry waste as bioactive compounds in the modification of biodegradable films as food packaging remains a major challenge. This study describes the preparation and bioactivity characterization of poly(butylene succinate) (PBS)-based films with the addition of the bioactive compounds curcumin (CUR) and carvacrol (CAR). Films based on PBS modified with curcumin and carvacrol at different concentration variations (0%/0.1%/1%) were prepared by solvent casting method. The antioxidant, antimicrobial, and antibiofilm properties were investigated against bacteria (Escherichia coli, Staphylococcus aureus) and fungi (Candida albicans). As a result of the modification, the films exhibited free radicals scavenging (DPPH up to 91.47% and ABTS up to 99.21%), as well as antimicrobial (6 log, 4 log, and 2 log reductions for E. coli, S. aureus, and C. albicans, respectively, for samples modified with 1% CUR and 1% CAR) activity. Moreover, antibiofilm activity of modified materials was observed (8.22–87.91% reduction of biofilm, depending on bioactive compounds concentration). PBS films modified with curcumin and carvacrol with observed bifunctional properties have many potential applications as active packaging.

The optical properties of PbS and PbS/Ag thin films

The chemical bath deposition approach was used to arrange PbS and PbS coated with Ag thin layer thin films. PbS film was deposited at room temperature using thiourea and lead chloride as precursors. After the PbS film had been deposited, it was immersed in Ag precursors for 60 minutes at 50 C to coat its surface. In this study, we looked at absorbance in the 400-1000 nm range. The direct and indirect bandgaps were estimated using the Tauc method and yielded values between 1.3 and 1.45 eV. It resulted in increasing in bandgaps after coating with of Ag layer.

Suppressing the Dark Current in Quantum Dot Infrared Photodetectors by Controlling Carrier Statistics

AbstractLead sulfide colloidal quantum dot photodiodes (PbS QDPDs) exhibit a high energy conversion efficiency for infrared detection. Despite the high photoinduced current, the performance of PbS QDPDs is limited by the high dark current which is rarely investigated. Understanding the dark current in PbS QDPDs is critical to improving the detectivity of PbS QDPDs. Herein, it is demonstrated that minority carriers of I‐passivated PbS films and trap sites of EDT‐passivated PbS films are related to the dark current of PbS QDPD. Utilizing annealing and low‐temperature ligand exchange processes, the dark current density can be decreased almost tenfold by suppressing the minority carrier diffusion in the PN junction and trap‐assisted charge injection from the electrode. PN junction simulation, space charge limited current measurements, as well as structural, optical, and chemical characterizations are conducted to elucidate the origins of the dark current suppression. The authors achieve the lowest dark current density of 2.9 × 10−5 mA cm−2 at −1 V among PbS‐based QDPDs and a high detectivity of 6.7 × 1012 Jones at 980 nm. It is believed that this work provides fundamental understanding of carrier statistics in nanomaterials and device performance as well as a technological basis for realizing low‐cost high‐performance optoelectronic devices.

Low-order optical nonlinearities of PbS quantum dot liquids and films

We demonstrate the variations of the nonlinear optical parameters in the suspensions and thin films containing PbS quantum dots of different sizes (9 and 2.5 nm). We show that these colloidal quantum dots possess the thermal-lens induced negative nonlinear refraction and reverse saturable absorption in the case of the 532-nm, 10-ns probe pulses. The larger nonlinear absorption coefficients of 9-nm quantum dots compared with 2.5-nm species (1 × 10−7 and 8 × 10−9 cm W−1, respectively) in the case of 1064 nm, 10 ns probe pulses were determined. Similar relations between the nonlinear optical parameters of 9- and 2.5-nm species were maintained in the case of twice shorter wavelength (532 nm) of the probe pulses. The almost ten-fold growth of the nonlinear optical parameters in the visible range compared with the near infrared region was attributed to the stronger influence of the excitonic states on the propagation effects in the former case. We show that the thin films containing these quantum dots demonstrate saturable absorption, while the suspensions show mostly the reverse saturable absorption at 532 nm. A significant enhancement of the nonlinear refractive index of films compared with suspensions (−2 × 10−8 cm2 W−1 and -1 × 10−11 cm2 W−1), as well as a large negative nonlinear absorption coefficient (−3.2 × 10−5 cm W−1) in the former case are demonstrated. We discuss the signs of nonlinear refraction and nonlinear absorption of the quantum dots, as well as the role of the sizes of these species in variations of the nonlinear parameters.

Structural and Electrical Properties of PbS Films Doped with Cr3+ Ions during Chemical Deposition

Structural and Electrical Properties of PbS Films Doped with Cr3+ Ions during Chemical Deposition