Keywords : Thin films

Gas Sensing Investigation of Porous Hot-wire Molybdenum Disulphide Thin Films

Giorgos Papadimitropoulos; Angelika Balliou; Dimitris Kouvatsos; Dimitris Davazoglou

Advanced Materials Letters, 2022, Volume 13, Issue 1, Pages 2201-1689
DOI: 10.5185/amlett.2022.011689

The gas sensing properties of porous hot-wire MoS2 (hwMoS2) thin films have been studied. The films were deposited on oxidized silicon substrates by heating a molybdenum filament in a vacuum chamber in H2S environment. The samples remain at room temperature during the deposition and the grown films are amorphous and porous.  Reversible changes of the current values in the hwMoS2 films were observed due to the presence or upon removal of chemical gases such as hydrogen (H2) and carbon monoxide (CO). The sensitivity, was dependent on the concentrations of the gases and the temperature of measurement. The response time was found to be comparable to the recovery time and of the order of a few seconds. It is important to note that the surface of the hwMoS2 films was not activated with any catalyst, which is a common practice in most thin films used for gas sensing, rendering our process simpler and cheaper.

Structural, Optical and Photo Catalytic Properties of CdS Thin Films Synthesized by Green-CBD Method

Vikas Sawant; D.A. Lavate; A.S. Khomane

Advanced Materials Letters, 2021, Volume 12, Issue 11, Pages 1-5
DOI: 10.5185/amlett.2021.111677

Aim of this work is to study the synthesis of CdS thin films by eco-friendly rout and analyze the change in structural and optical properties of material due to use of biomolecules as a stabilizing agent. The CdS thin films were deposited in lemon extract and ammonia solution separately by maintaining the same physical parameters and analyzed for tailoring of structural and optical properties. Green-CBD method minimizes the use of toxic precursors and volatilization of ammonia solution. X-Ray Diffraction study indicates formation of face centered cubic crystalline phase predominantly for CdS thin films materials with change in grain size. SEM analysis revealed the formation of CdS nanospheres in ammonia while CdS nanocubes in lemon extract. The direct allowed band gap energy was observed in the order of 2.45 eV and 2.25 eV which were interesting for optical studies. UV-Vis Absorption spectra and PL spectra of thin films indicates the CdS thin film material has absorption maxima in visible (400-800 nm) region. As synthesized CdS thin films were applied for photodegradation of Rhodamine-B dye solution under sunlight. The CdS thin film material deposited by Green-CBD rout shows high efficiency for degradation of Rhodamine-B solution as compared to films deposited by CBD method.

Effect of Incident Light on Transport Properties of Pulsed Laser Deposited Manganite Thin Films

Pankaj Solanki; Pratik Lakhani; Ashish Ravalia; Bharat Kataria

Advanced Materials Letters, 2020, Volume 11, Issue 4, Pages 1-5
DOI: 10.5185/amlett.2020.041502

In this communication, we report the results of different light illumination on electrical transport properties of La0.67Ca0.33Mn0.9Ga0.1O3 (LCMGO) thin films grown on Si (100) ( n-type phosphorus-doped) wafer using Pulsed Laser Deposition (PLD) System. The variation in deposition time changes the thickness of the films. X-ray Diffraction (XRD) reveals the polycrystalline structure of LCMGO thin films. The cross-sectional SEM were taken to determine the thickness of the films with changing deposition time. Atomic Forced Micrographs (AFM) show that island type grains diffuse into one another to form a more uniform distribution of grains as the thickness of the film increases. The charge transport properties have been studied using the I-V measurement at LCMGO/Si interfaces. I-V measurement shows the backwards-diode like the behaviour of the LCMGO/Si p-n junction. The reverse bias current changes under the influence of different incident light illumination. The built-in electric field is generated at the interface when the film was illuminated with UV light. The tunnelling process for backward diode like p-n junction is explained using a modified Simmons model.

Oxygen vacancy filament-based resistive switching in Hf0.5Zr0.5O2 thin films for non-volatile memory

Mark Kracklauer; Fabian Ambriz-Vargas; Gitanjali Kolhatkar; Bernhard Huber; Christina Schindler; Andreas Ruediger

Advanced Materials Letters, 2019, Volume 10, Issue 6, Pages 405-409
DOI: 10.5185/amlett.2019.2225

The continued evolution of electronic devices relies on the development of new semiconductor memory technology. Given the high compatibility of the Hf0.5Zr0.5O2 thin films with the CMOS technology, we investigate the charge transport mechanisms that occur in a relative thick Hf0.5Zr0.5O2 thin film (4 to 6 nm-thick) when subjected to electrical stresses. To that end we fabricate Hf0.5Zr0.5O2 heterostructures with a Pt tip as the top electrode and TiN and Pt as bottom electrode by radio-frequency magnetron sputtering. After analyzing the surface morphology of the as-received and as-deposited films by atomic force microscopy, the transfer of the desired chemical stoichiometry from the sputtering target to the substrate surface is studied by Raman spectroscopy. The ferroelectricity of the Hf0.5Zr0.5O2 thin films is confirmed by piezoresponse force microscopy measurements, and a retention of 22 h is obtained, attesting to the non-volatility of the samples. Nano-scale electrical measurements reveal the presence of resistive switching, where the low resistance state (ON state) in both Pt-tip/Hf0.5Zr0.5O2/TiN and Pt-tip/Hf0.5Zr0.5O2/Pt heterostructures can be created by the formation of a conductive filament based on oxygen vacancies.

Study of the properties of La-doped ZnS thin Films synthesized by Sol-gel method

Amel Tounsi; Djahida Talantikite-Touati; Hamid Merzouk; Hadjira Haddad; Roumaïssa Khalfi

Advanced Materials Letters, 2018, Volume 9, Issue 3, Pages 216-219
DOI: 10.5185/amlett.2018.1963

The thin layers of undoped ZnS and ZnS doped La with different concentrations (2, 4, 6, 8 and 10%) were deposited on glass substrates using sol-gel and dip-coating methods. The structural characterization of these samples was carried out by the  X-rays diffraction (XRD), scanning electron microscopy (SEM) and atomic force microscopy (AFM). UV-visible and Fourier Transform Infrared spectroscopy (FTIR) have been used to study the effect of dopant on the optical properties of ZnS doped La thin films. Atomic force microscopy images of the films have revealed homogeneous and granular structure and the SEM micrographies show deposit films with uniform and porous structure. The optical transmission spectra in the UV - visible range have shown that all the doped films present a good optical transmission in the visible domain.

Nanoengineered plasma polymer films for biomedical applications

Krasimir Vasilev; Melanie Ramiasa-MacGregor

Advanced Materials Letters, 2018, Volume 9, Issue 1, Pages 42-52
DOI: 10.5185/amlett.2018.1691

This forward looking concise review describes recent advances in the field of nanoengineered plasma polymer films. These types of coatings are relevant in many fields of application and have gained substantial research and technological interest over the last decade. The review starts with an introduction of plasma polymerization as a technique for preparation for nanometer thin polymer-like coatings. This is followed by the examples of the use of nanoengineered plasma polymer coatings in applications relevant to biomedical devices. Applications in antibacterial coatings and drug delivery vehicles are discussed. Significant section of this paper is dedicated to cell guidance surfaces which have an extensive range of applications ranging from coatings for medical devices to research tools that can help unraveling complex biological questions and vehicles for the growing field of cell therapies. The vision of the authors about the future directions of the field have also been presented, including a section on novel oxazoline based coatings that carry great promise for advances in the biomaterial and biomedical fields.

Microstructural and tribological studies of Al2O3/ZrO2 nano multilayer thin films prepared by pulsed laser deposition

Balakrishnan G; Elangovan T; Shin-Sung Yoo; Dae-Eun- Kim; Kuppusami P; Venkatesh Babu R; Sastikumar D; Jung il Song

Advanced Materials Letters, 2017, Volume 8, Issue 4, Pages 410-417
DOI: 10.5185/amlett.2017.6434

Nanostructured single layer aluminium oxide (Al2O3), single layer zirconium oxide (ZrO2) and the (Al2O3/ZrO2) nano multilayer films were deposited on Si (100) substrates at an optimized oxygen pressure of 3×10 -2 mbar at room temperature by pulsed laser deposition. The Al2O3 layer was kept constant at 5 nm, while ZrO2 layer thickness was varied from 5 nm to 20 nm. The X-ray diffraction (XRD) studies of single layer of Al2O3 film indicated the cubic γ-Al2O3, while the single layer of ZrO2 indicated both the monoclinic and tetragonal phases. The Al2O3/ZrO2 multilayer films of 5/5 nm and 5/10 nm indicated the tetragonal phase of ZrO2 with nanocrystalline nature. The FESEM and AFM studies showed the dense and smooth morphology of the films. The pin-on disc revealed that the 5/10 nm multilayer film has low friction coefficient ~ 0.10. The wear rate of multilayers film is half of the wear rate of the single layer films and 5/10 nm multilayer film showed a reduced wear rate when it is compared to other single and multilayers. The Al2O3-ZrO2 ceramics find wide applications in wear and corrosion resistance components, high temperature applications and bio-implant materials.

Titanium dioxide (TiO2) and silver/titanium dioxide (Ag/TiO2) thin films with self-cleaning properties

Ana Flávia R. Silva; Nelcy D. S. Mohallem; Marcelo M. Viana

Advanced Materials Letters, 2017, Volume 8, Issue 4, Pages 444-448
DOI: 10.5185/amlett.2017.7093

In this work, TiO2 and Ag/TiO2 thin films were synthesized on glass by combination of sol-gel method and dip-coating deposition technique. Thermal treatment in temperatures ranging from 100 °C to 500 °C was used to evaluate changes in structure, morphology and texture of these materials. Adherent and microcrack-free films were obtained. The structural and morphological evolution with temperature was studied by X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM). Average particle size and roughness were determined by atomic force microscopy (AFM). The films were tested for wettability by measuring the contact angle between a drop of distilled water and the material surface. Results of hydrophobic/hydrophilic tests using UV-C irradiation showed that the films change their hydrophobic character to hydrophilic reaching even the superhydrophilic character which indicates their potential application as self-cleaning coatings. 

ZnO sol-gel oxide coatings as materials for UV optical filters

Karolina Moszak; Anna Szczurek; Bartosz Babiarczuk; Beata Borak; Justyna Krzak

Advanced Materials Letters, 2017, Volume 8, Issue 4, Pages 542-545
DOI: 10.5185/amlett.2017.7108

Ultraviolet light influences materials structure causing the decomposition and degradation of organic compounds. One of the ideas to reduce the harmful effects of light is to protect materials by sol-gel coatings. ZnO sol-gel thin films on a glass substrate were obtained as optical filters. The filter effect of synthesized coatings stabilized in different temperatures were characterized by UV-Vis transmittance spectroscopy. The morphology and elemental composition of coating surface was determined by SEM and EDX. Scratch resistance and adhesion have been evaluated by scratch test. The coatings present high transparency in the visible region and absorption in the UV region (270-360 nm). The results suggest that the obtained materials have proper parameters for UV optical filters. 

Flexible cefalexin-immobilized graphene oxide film for antibacterial and drug delivery

Xun Xu; Fangwang Ming; Jinqing Hong; Zhoucheng Wang

Advanced Materials Letters, 2017, Volume 8, Issue 3, Pages 309-314
DOI: 10.5185/amlett.2017.7103

The flexible and freestanding graphene oxide (GO) film was fabricated for drug delivery and antibacterial. The film was synthesized by covalently attaching cefalexin onto graphene oxide sheets and then made by filtration of the colloidal suspension. SEM and optical images show that the Cefalexin-grafted graphene oxide (GO-CE) film possesses the unique 2D layer-by-layer structure and it could form channels for drug release when immersed in water. The drug loading and release tests certify that the GO-CE film is a promising drug delivery membrane with high load capacity (0.621 mg mg -1 ) and long-acting release properties (72 h), and can effectively inhibit the growth of E. coli and S. aureus bacteria while showing minimal cytotoxicity for a long time. The cellular culture results of the HeLa Cells indicate that the GO-CE film exhibits excellent biocompatibility. Based on these advantages, the GO-CE film is expected to be used in the environmental and medical applications.

Synthesis of nanostructured TiO2 thin films with highly enhanced photocatalytic activity by atom beam sputtering

Jaspal Singh; Kavita Sahu; Sini Kuriakose; Nishant Tripathi; D. K. Avasthi; Satyabrata Mohapatra

Advanced Materials Letters, 2017, Volume 8, Issue 2, Pages 107-113
DOI: 10.5185/amlett.2017.6432

Nanostructured TiO2 thin films with highly enhanced photocatalytic activity were prepared by atom beam sputtering technique. The effects of thermal annealing on the structural, morphological and photocatalytic properties of TiO2 thin films were investigated using X-ray diffraction, atomic force microscopy, field emission scanning electron microscopy, Raman spectroscopy and UV-visible absorption spectroscopy. X-ray diffraction studies showed that the as-deposited TiO2 thin films made up of anatase TiO2 nanoparticles transformed into anatase/ rutile mixed-phase TiO2 nanoparticles upon annealing. Field emission scanning electron microscopy and atomic force microscopy studies revealed growth of TiO2 nanoparticles from 16 nm to 29 nm upon annealing at 600  o C. The photocatalytic activities of the nanostructured TiO2 thin films were studied by monitoring photocatalytic degradation of methylene blue in water. Our results showed that the as-deposited nanostructured TiO2 thin films exhibited highly enhanced photocatalytic efficiency as compared to the annealed samples. The mechanism underlying the enhanced photocatalytic activity of nanostructured TiO2 thin film is tentatively proposed.

Structure Dependent Room Temperature Ferromagnetism In Co, Nb Co-doped BaTiO3 Thin Films Prepared By RF Sputtering

R. Siddheswaran; Petr Nov

Advanced Materials Letters, 2016, Volume 7, Issue 6, Pages 445-448
DOI: 10.5185/amlett.2016.6183

Thin films of BaTiO3 and Co, Nb co-doped BaTiO3 on glass and Si (100) substrates were deposited by RF sputtering (at 350 ºC), and annealed. The amorphous and crystalline phases were observed for the as-deposited and annealed samples, respectively from the X-ray diffraction (XRD) studies. The magnetic behaviour of the pure and doped BaTiO3 films was studied by vibrating sample magnetometry (VSM). In this study, the ferromagnetic behaviour at room temperature was observed in the Co, Nb co-doped BaTiO3 of both amorphous and crystalline films. The annealed polycrystalline Co, Nb co-doped BaTiO3 films have the larger saturation magnetization and coercivity than the amorphous films. The room temperature ferromagnetic responses were also observed by the Magneto-optical Kerr effect (MOKE) measurements for both as-deposited and annealed samples. 

Ferromagnetism In Sol-gel Derived ZnO: Mn Nanocrystalline Thin Films

M.Tanemura and P. K. Shishodia; M.Tanemura;P. K. Shishodia

Advanced Materials Letters, 2016, Volume 7, Issue 2, Pages 116-122
DOI: 10.5185/amlett.2016.5966

This paper reports the growth of Mn doped ZnO thin films by sol-gel technique with different Mn concentration (0-20 %). Structural and vibrational properties have been measured by X-ray diffraction and Raman spectroscopy. The films exhibit crystalline nature with (002) preferential orientation. The crystallite size and lattice parameters have been estimated as a function of Mn concentration. The Raman spectrum of the ZnO film shows the peaks corresponding to E2 (high) mode at 434 cm -1 assigned to Zn-O bond and A1 (LO) mode at 575 cm -1 . The elemental analysis of the films have been performed using X-ray photoelectron spectroscopy confirms the presence of Zn, O and Mn in doped films. Surface morphology and roughness of the films are observed by atomic force microscopy. The optical bandgap is found to decrease with Mn concentration as estimated by Tauc’s plots. Room temperature ferromagnetism has been obtained in ZnO: Mn thin films by superconducting quantum interference device. 

Structural, Electrical and Optical Properties Of Molybdenum Doped Zinc Oxide Films Formed By Magnetron Sputtering

R. Subba Reddy; K. Radhamma; A. Sivasankar Reddy; S. Uthanna

Advanced Materials Letters, 2015, Volume 6, Issue 9, Pages 834-839
DOI: 10.5185/amlett.2015.5920

Thin films of molybdenum doped (2.7 at.%) zinc oxide (MZO) were deposited on glass substrates held at room temperature by RF magnetron sputtering of mosaic target of Mo-Zn at different substrate bias voltages. The influence of substrate bias voltage on the structural, electrical and optical properties was investigated. The MZO films deposited on unbiased substrate were of amorphous, while those formed at substrate bias voltage of -40 V and above were of nanocrystalline. The crystallite size of the films improved with the applied bias voltage. At higher substrate bias voltage of -120 V the ion bombardment induced the high defect density in the films hence decrease in the crystallinity. The films formed at substrate bias voltage of -80 V exhibited low electrical resistivity of 1.2x10 -2 Ωcm and optical transmittance of about 79 %. These films showed optical band gap of 3.29 eV and figure of merit of 19 Ω -1 cm -1 .

 Structural, Optical And Electrical Properties Of Cu(InGa)SeTe Device With The Varying Laser Pulses

Abhay Kumar Singh; R. Ganesan; Jong Tae Park

Advanced Materials Letters, 2015, Volume 6, Issue 6, Pages 513-517
DOI: 10.5185/amlett.2015.5774

Next-generation high-performance heterojunction photovoltaic (PV) modules can be fabricated with an appropriate active layer material. Therefore, it is worth to examine physical properties of the recent developed Cu25(In16Ga9)Se40Te10 (CIGST) material for the potential photovoltaic application. This, report demonstrates the structural, optical and electrical properties of the 8000 and 16000 pulses deposited CIGST films on top of the ITO coated soda lime substrate (CIGST/ITO/substrate); whereas, the substrate temperature was 550 0 C. The 16000 pulses deposited thin film surface roughness (45 nm) and thickness (~1.4 μm) are obtained lower and higher than the 8000 pulses thin film. The cross sectional EDS elemental mapping also gives the fewer interlayer inclusions for the 8000 pulses deposited thin film. With the increasing thin films thicknesses a distinguishable UV/Visible peak shift toward the high wavelength side and enhance in optical energy band gap (1.13 and 1.2 eV) are noticed. Device fabricated (CIGST/ITO/substrate) with the 16000 pulses have a sharp current growth upto 2.0 × 10 -2 amp with a lower resistance under the applied voltage range 0-20V. The internal (IQE) and external (EQE) quantum efficiencies charge carriers transport for the fabricated devices are also discussed.

Structural and Optical Properties of Sol-gel Processed ZnCdMgO Nanostructured Films as Transparent Conductor

Praveen Kumar; Amritpal Singh; Dinesh Pathak; Ludek Hromadko; Tomas Wagner

Advanced Materials Letters, 2014, Volume 5, Issue 10, Pages 587-592
DOI: 10.5185/amlett.2014.6586

In the present work, we report the structural and optical properties of sol-gel synthesized Zn0.9(Cd1-xMgx)0.1O (0 ≤ x ≤ 1.0) nanostructured films investigated by using the X-ray diffraction, scanning electron microscopy, atomic force microscopy, electrical resistivity, optical absorption and photoluminescence spectroscopic techniques. The X-ray diffraction study has revealed the hexagonal wurtzite crystal structure having favorable c-axis orientation for the increase in Mg concentration. The stress-strain calculation reveals the compressive stresses in Cd rich films whereas Mg rich films experience the tensile stress. Reduction of grain size and surface roughness has been observed with the increase in Mg concentration with more spherical grains. The AFM and SEM micrographs reveal the smooth surface morphology of the synthesized films. The magnesium rich films show high transmission in the visible and NIR region but show decrease in it with the increase in Cd concentration. The band gap increases from 3.19 to 3.40 eV with increase in Mg content. The photoluminescence measurement reveals the decrease in the defects and increase in band gap with the increase in Mg content in the films. The electrical resistivity has been found to be increased from 0.3×10 2 to 169.4×10 2 Ω-cm with increase in Mg concentration. The present study reports that the compositions x=0.4 and x=0.6 have the optimized combination of optical transmittance and better electrical resistivity values in this system for their possible applications as transparent conductors. The present results provide important data for TCOs processing with an optimized content of metal dopants for better transparency and conductivity.

Electrical And Microstructural Properties Of (Cu, Al, In)-doped SnO2 Films Deposited By Spray Pyrolysis

Sibel Gurakar; Tulay Serin; Necmi Serin

Advanced Materials Letters, 2014, Volume 5, Issue 6, Pages 309-314
DOI: 10.5185/amlett.2014.amwc.1016

The effect of Cu, Al and In doping on the microstructural and the electrical properties of the SnO2 films were studied. The undoped, Cu, Al and In (2 at. %) doped SnO2 films were deposited on the glass substrate by spray pyrolysis from 0.8 M SnCl2–ethanol solution at substrate temperature 400 °C. The microstructural properties of films were investigated by X-ray diffraction (XRD) method. It was determined that the films formed at polycrystalline structure in tetragonal phase and structure was not changed by dopant species. The lattice parameters (a), (c) and crystallite size (D) were determined and obtained in the range of 4.90-4.92 Å, 3.26-3.31 Å and 34-167 Å, respectively. The optical transmittance of thin films was measured and the optical band gap Eg values of the films were obtained in the range of 3.96-4.00 eV, using the Tauc relation. The electrical transport properties of undoped, Cu, Al and In-doped SnO2 films were investigated by means of conductivity measurements in a temperature range of 120-400 K. The electrical transport mechanism of the undoped, Cu, Al and In-doped SnO2 films was determined by means of the tunneling model through the back-to-back Schottky barrier and the thermionic field emission model in the temperature range of 120-300 K and 300-400 K, respectively.

Growth Of Tin Catalyzed Silicon Nanowires By Electron Beam Evaporation

R. Rakesh Kumar; K. Narasimha Rao; K. Rajanna; A. R. Phani

Advanced Materials Letters, 2013, Volume 4, Issue 11, Pages 836-840
DOI: 10.5185/amlett.2013.3449

Silicon nanowires were grown on tin (Sn) coated Si substrates using electron beam evaporation technique at a growth temperature of 350°C. The as grown Si nanowires were characterized by Field Emission Scanning Electron Microscope (FESEM), Transmission Electron Microscopy attached with Energy Dispersive X-Ray Analyser (TEM-EDX) for their morphological, structural, and compositional properties, respectively. The grown Si nanowires were randomly oriented on the substrate with a length of ~ 500 nm for a deposition time of 15 min. Silicon nanowires have shown tin nanoparticle (capped) on top of it confirming the Vapor-Liquid-Solid (VLS) growth mechanism responsible for Si nanowires growth. The nanowire growth rate was measured to be ~30 nm/min. Transmission Electron Microscope (TEM) measurements have revealed single crystalline nature of Si nanowires. The obtained results have indicated good progress towards finding alternative catalyst to gold for the synthesis of Si nanowires.

Effect Of Annealing Temperature On Structural Properties Of nanocrystalline Tl3(PW12O40) Thin Films

S.R. Mane; P.S. Patil;P. N. Bhosale; R. M. Mane

Advanced Materials Letters, 2013, Volume 4, Issue 1, Pages 94-98
DOI: 10.5185/amlett.2013.icnano.117

Thallium (I) doped tungsten heteropolyoxometalate (HPOM) combinatorial thin films have been deposited on glass substrate using simple chemical bath deposition technique. The deposited films were annealed at 100 o C, 150 o C, 200 o C and 250 o C. These annealed thin films were characterized by using SEM, EDAX, AFM, FT-IR, XRD and TGA-DTA techniques for their structural properties. SEM and EDAX results shows that, tungsten HPOM material is polycrystalline in nature and Tl (I) is intercalated in phosphotungustate anion. AFM studies on the films annealed at different temperatures reveal that the surface roughness increases with the increase in annealing temperature, suggesting an increase of crystallization with temperature. FT-IR study confirms the well formation of heteropolyoxometalate material under investigation. Various structural parameters such as lattice constants, crystallite size and grain size have been calculated and they are found temperature dependent. The lattice constant, crystallite size and grain size of tungsten HPOM material increases with increase in temperature. XRD pattern of annealed thin films shows better crystanality of tungsten HPOM material having simple cubic spinel structure. The TGA-DTA study revealed that, Tl3 (PW12 O40) material is thermally stable up to 265.12 o C.

Effect Of Film Thickness On The Structural Morphological And Optical Properties Of Nanocrystalline ZnO Films Formed By RF Magnetron Sputtering

R. Subba Reddy; A. Sreedhar; A. Sivasankar Reddy; S. Uthanna

Advanced Materials Letters, 2012, Volume 3, Issue 3, Pages 239-245
DOI: 10.5185/amlett.2012.3329

Zinc oxide (ZnO) thin films were formed by RF reactive magnetron sputtering onto p-type silicon and glass substrates held at room temperature. The thickness of the films deposited was in the range 160 – 398 nm. The thickness dependence structural, morphological and optical properties of ZnO films were systematically investigated. The maximum crystallite size of 21 nm observed at films thickness of 231 nm by X- ray diffraction. Scanning electron microscopic analysis revealed that the growth of nanowires in all the films. The root mean square roughness of the films increased from 7.3 to 53 nm in the thickness range of investigation. Fourier transform infrared analysis confirmed the Zn-O bonding located at wavenumber of 413 cm -1 . The average optical transmittance of the films was about 89 % in the visible region. The optical band gap of the ZnO films decreased from 3.14 to 3.02 eV with increase of film thickness from 160 to 398 nm respectively.

Solid State Thermochromic Materials

Pragna Kiria; Geoff Hyett; Russell Binions

Advanced Materials Letters, 2010, Volume 1, Issue 2, Pages 86-105
DOI: 10.5185/amlett.2010.8147

Solid-state thermochromic materials undergo semiconductor to metal transitions at a ‘critical temperature’, Tc. This review begins by describing the phenomenon of thermochromism, whereby the optical properties of a material change reversibly as a result of a change in temperature. The various different types of thermochromism will be introduced with a focus on the thermochromism exhibited by solid-state materials. The fundamental chemical principles that describe the electronic structure and properties of solids, and the chronological developments in the theory behind the thermochromic transitions (such as, the effects of electron-electron interactions and structural phase changes due to lattice distortions) that led to the discovery of the semiconductor-to-metal transition, are presented. An extensive discussion of vanadium and titanium oxides is presented with a particular focus on vanadium (IV) oxide since its transition temperature is closest to room temperature. Observations and current understanding of the nature of the semiconductor-to-metal transition exhibited by these materials is detailed. The possibility of fine-tuning the transition temperature by introducing various dopants into the vanadium (IV) oxide lattice is examined and the effects of dopant charge and size is examined. Solid-state thermochromic materials may be exploited in areas such as microelectronics, data storage, or intelligent architectural glazing, thus are required to be synthesised as thin films for use in such applications. The numerous synthetic techniques (PVD, sol-gel method, PLD, CVD, APCVD and AACVD), for making metal oxide thermochromic thin films are described in reference to the production of vanadium (IV) oxide and compared. Finally rare earth nickelates exhibiting thermochromism are described.