Structural and optical properties of Mn-doped ZnO nanocrystalline thin films with the different dopant concentrations

The transparent nanocrystalline thin films of undoped zinc oxide and Mn-doped (Zn_1−xMn_xO) have been deposited on glass substrates via the sol–gel technique using zinc acetate dehydrate and manganese chloride as precursor. The as-deposited films with the different manganese compositions in the range of 2.5–20 at% were pre-heated at 100 °C for 1 h and 200 °C for 2 h, respectively, and then crystallized in air at 560 °C for 2 h. The structural properties and morphologies of the undoped and doped ZnO thin films have been investigated. X-ray diffraction (XRD) spectra, scanning electron microscopy (SEM), atomic force microscopy (AFM), and X-ray photoelectron spectroscopy (XPS) were used to examine the morphology and microstructure of the thin films. Optical properties of the thin films were determined by photoluminescence (PL) and UV/Vis spectroscopy. The analyzed results indicates that the obtained films are of good crystal quality and have smooth surfaces, which have a pure hexagonal wurtzite ZnO structure without any Mn related phases. Room temperature photoluminescence is observed for the ZnO and Mn-doped ZnO thin films.     

Comparison of the optical properties of undoped and Ga-doped ZnO thin films deposited using RF magnetron sputtering at room temperature

The optical properties of undoped zinc oxide (ZnO) thin films of various thicknesses were compared with those of Ga-doped (GZO) thin films. Transparent, high-quality undoped ZnO and GZO films were deposited successfully using radio-frequency (RF) sputtering at room temperature. The films were polycrystalline with a hexagonal structure and a strongly preferred orientation along the c-axis. The films had an average optical transmission >85% in the visible part of the electromagnetic spectrum. The undoped ZnO thin films were more transparent than the GZO thin films. In the photoluminescence (PL) spectrum, ZnO film has higher quality than GZO as a result of decrease in the green emission intensity.     

In掺杂ZnO薄膜的制备及其特性研究

采用射频反应溅射技术在硅(100)衬底上制备了未掺杂和掺In的ZnO薄膜。掠角X射线衍射测试表明,实验中制备的掺In样品为ZnO薄膜。用X射线衍射仪、原子力显微镜和荧光分光光度计分别对两样品的结构、表面形貌和光致发光特性进行了表征,分析了In掺杂对ZnO薄膜的结构和发光特性的影响。与未掺杂ZnO薄膜相比,掺In ZnO薄膜具有高度的C轴择优取向,同时样品的晶格失配较小,与标准ZnO粉末样品之间的晶格失配仅为0．16％;掺In ZnO薄膜表面平滑,表面最大不平整度为7nm。在掺In样品的光致发光谱中观察到了波长位于415nm和433nm处强的蓝紫光双峰,对掺In样品的蓝紫双峰的发光机理进行了讨论,并推测出该蓝紫双峰来源于In替位杂质和Zn填隙杂质缺陷。     

Effect of solution concentrations on crystal structure,surface topographies and photoluminescence properties of ZnO thin films

Zinc oxide thin films were deposited on silicon substrates via hydrothermal method. Microstructures, surface topographies and optical properties of ZnO thin films were systematically investigated by X-ray diffraction, atomic force microscopy and fluorescence spectrophotometer. The mean grain size and surface roughness of the thin films decrease first and then increase with increasing the concentration of zinc nitrate hexahydrate. The photoluminescence spectra of ZnO thin films, excited by the 240, 320, 360, 380 and 400 nm excitation wavelength, were investigated in detail. Based on our analysis, it can be noted that mechanisms of the ultraviolet, violet and blue emissions are attributed to the transitions from the localized levels below the conduction band, zinc vacancy, interstitial zinc and extended interstitial zinc levels to the valance band, respectively. Blue–violet emissions of ZnO have great potential in light emitting and biological fluorescence labeling applications.     

Mn doped ZnO nanostructured thin films prepared by ultrasonic spray pyrolysis method

Mn-doped ZnO thin films with different percentage of Mn content (0, 1, 3 and 5 at.%) and substrate temperature of 350 °C, were deposited by a simple ultrasonic spray pyrolysis method under atmospheric pressure. We have studied the structural and optical properties by using X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR) and ultra-violet visible near infrared (UV–Vis-NIR) spectroscopy. The lattice parameters calculated for the Mn-doped ZnO from XRD pattern were found to be slightly larger than those of the undoped ZnO, which indicate substitution of Mn in ZnO lattice. Compared with the Raman spectra for ZnO pure films, the Mn-doping effect on the spectra is revealed by the presence of additional peak around 524 cm⁻¹ due to Mn incorporation. With increasing Mn doping the optical band gap increases indicating the Burstein–Moss effect.     

Optical properties of ZnO and ZnO:Ce layers grown by spray pyrolysis

In this paper, zinc oxide (ZnO) and cerium-doped zinc oxide (ZnO:Ce) films were deposited by reactive chemical pulverization spray pyrolysis technique using zinc and cerium chlorides as precursors. The effects of Ce concentration on the structural and optical properties of ZnO thin films were investigated in detail. These films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and photoluminescence (PL) measurements. All deposited ZnO layers at the temperature 450 °C are polycrystalline and indicate highly c-axis oriented structure. The dimension of crystallites depends on incorporation of Ce atoms into the ZnO films. The photoluminescence spectra of the films have been studied as a function of the deposition parameters such as doping concentrations and post grows annealing. Photoluminescence spectra were measured at the temperature range from 13 K to 320 K.     

ZnO：V薄膜后退火处理前后的微结构与发光特性

利用溶胶-凝胶(Sol-gel)法在单晶硅(100)衬底上分别制备了ZnO:V薄膜和纯ZnO薄膜。为进一步研究后退火对ZnO:V薄膜结构和发光性质的影响,在两段式快速退火后又在800℃下进行了后退火处理。X射线衍射的结果表明:后退火处理前,钒(V)的掺入使ZnO结晶质量变差,而800℃退火处理后,从ZnO的衍射峰中可以看出,相对于无V杂样品其结晶质量变好。扫描电子显微镜形貌图中可以看出制备的样品薄膜颗粒大小均匀,薄膜致密度较高。光致发光(PL)谱的研究表明:ZnO:V薄膜在800℃退火处理后,紫外和绿带发光峰均增强,但紫外发光峰增强得更多;与同样条件下制备的纯ZnO薄膜的PL谱比较,发现V掺杂后样品的紫外激子复合发光峰的强度明显增强且峰位发生蓝移,而缺陷引起的绿带发光峰的强度降低。     

Effects of doping concentration on properties of Mn-doped ZnO thin films

This paper reports that the radio frequency magnetron sputtering is used to fabricate ZnO and Mn-doped ZnO thin films on glass substrates at 500~°C. The Mn-doped ZnO thin films present wurtzite structure of ZnO and have a smoother surface, better conductivity but no ferromagnetism. The x-ray photoelectron spectroscopy results show that the binding energy of Mn_2p3 / 2 increases with increasing Mn content slightly, and the state of Mn in the Mn-doped ZnO thin films is divalent. The chemisorbed oxygen in the Mn-doped ZnO thin films increases with increasing Mn doping concentration. The photoluminescence spectra of ZnO and Mn-doped ZnO thin films have a similar ultraviolet emission. The yellow green emissions of 4~wt.% and 10~wt.% Mn-doped thin films are quenched, whereas the yellow green emission occurs because of abundant oxygen vacancies in the Mn-doped ZnO thin films after 20~wt.% Mn doping. Compared with pure ZnO thin film, the bandgap of the Mn-doped ZnO thin films increases with increasing Mn content.     

Effects of oxygen pressures on pulsed laser deposition of ZnO films

Zinc oxide (ZnO) thin films on Si (1 1 1) substrates were deposited by pulsed laser ablation of ZnO target at different oxygen pressures. A pulsed Nd:YAG laser with wavelength of 1064 nm was used as laser source. The deposited thin films have been characterized by X-ray diffraction (XRD), Atomic force microscopy (AFM), and Raman spectroscopy. XRD measurements indicate that the ZnO thin films deposited at the oxygen pressure of 1.3 Pa have the best crystalline quality. AFM results show that the surface roughness of ZnO film increases with the increase of oxygen pressure. The Raman results indicate that oxygen ambient plays an important role in removing defects due to excess zinc.     

Effect of temperature on pulsed laser deposition of ZnO films

ZnO thin films have been deposited on Si(1 1 1) substrates at different substrate temperature by pulsed laser deposition (PLD) of ZnO target in oxygen atmosphere. An Nd:YAG pulsed laser with a wavelength of 1064 nm was used as laser source. The influences of the deposition temperature on the thickness, crystallinity, surface morphology and optical properties of ZnO films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), selected area electron diffraction (SAED), photoluminescence (PL) spectrum and infrared spectrum. The results show that in our experimental conditions, the ZnO thin films deposited at 400 °C have the best surface morphology and crystalline quality. And the PL spectrum with the strongest ultraviolet (UV) peak and blue peak is observed in this condition.     

Influence of strain/stress on the nonlinear-optical properties of sprayed deposited ZnO:Al thin films

Nanocrystalline ZnO:Al thin films were deposited by reactive chemical pulverization spray pyrolysis technique on heated glass substrates at 450 °C to study their crystalline structure, composition, strain, stress, roughness characteristics and nonlinear optical susceptibility as a function of Al concentration (0, 2, 3, 5 at.%). The films were characterized by X-ray diffractometer (XRD), EDAX 9100 analyser, atomic force microscopy (AFM) and third harmonic generation (THG). The Al (3 at.%) doped ZnO thin films exhibited the lower strain/stress than undoped films. The nonlinear properties of the ZnO:Al thin films have been found to be influenced by the films strain/stress.     

Effect of excimer laser annealing on the properties of ZnO thin film prepared by sol-gel method

Pristine ZnO thin films have been deposited with zinc acetate [Zn(CH₃COO)₂], mono-ethanolamine (stabilizer), and isopropanol solutions by sol-gel method. After deposition, pristine ZnO thin films have been irradiated by excimer laser (λ = 248, KrF) source with energy density of 50 mJ/cm² for 30 sec. The effect of excimer laser annealing on the optical and structural properties of ZnO thin films are investigated by photoluminescence and field emission scanning electron microscope. As-grown ZnO thin films show a huge peak of visible region and a wide full width at half maximum (FWHM) of UV region due to low quality with amorphous ZnO thin films. After KrF excimer laser annealing, ZnO thin films show intense near-band-edge (NBE) emission and weak deep-level emission. The optically improved pristine ZnO thin films have demonstrated that excimer laser annealing is novel treatment process at room temperature.     

Microstructure and electro-optical properties of sol–gel derived Cd-doped ZnO films

The microstructure, and the electrical and optical properties of undoped zinc oxide (ZnO) and cadmium-doped ZnO (CZO) films deposited by a sol–gel method have been investigated. The films have a polycrystalline structure with hexagonal wurtzite ZnO. Scanning electron microscopy (SEM) images indicated that the films have a wrinkle network with uniform size distributions. The elemental analyses of the CZO films were carried out by energy dispersive X-ray analysis. The fundamental absorption edge changed with doping. The optical band gap of the films decreased with Cd dopant. The optical constants of the films such as refractive index, extinction coefficient and dielectric constants changed with Cd dopant. A two-probe method was used to investigate the electrical properties, and the effect of Cd content on the electrical properties was investigated. The electrical conductivity of the films was improved by incorporation of Cd in the ZnO film.     

镉掺杂氧化锌纳米花的制备及其光催化活性

以氯化锌、氯化镉、氢氧化钠为原料,采用水热法合成Cd掺杂纳米花状ZnO光催化剂,并通过该样品对罗丹明B水溶液的降解来研究其光催化活性。利用X射线衍射（XRD）、扫描电子显微镜（SEM）、X射线能量色散谱（EDS）、光致发光谱（PL）及紫外-可见分光光度计（UV-Vis）等测试手段对材料物性进行表征。实验结果表明：当掺杂Cd²⁺时,样品形貌发生变化、粒径减小;掺杂Cd²⁺后的ZnO的吸收边和紫外峰对比于纯ZnO均发生红移,禁带宽度由3.24 eV 减小到3.16 eV。通过光催化实验分析可知,掺杂后纳米ZnO光催化剂对罗丹明B 水溶液的降解率有所提高,光照3 h其降解率高达98%,说明与纯ZnO相比,Cd掺杂ZnO纳米花具有更高的光催化活性。     

Growth and characterization of pulsed laser deposited ZnO thin films

One of the most important and promising materials from metal oxides is ZnO with specific properties for near UV emission and absorption optical devices. The properties of ZnO thin films strongly depend on the deposition method. Among them, pulsed laser deposition (PLD) plays an important role for preparing various kinds of ZnO films, e.g. doped, undoped, monocrystalline, and polycrystalline. Different approaches — ablation of sintered ZnO pellets or pure metallic Zn as target material are described. This contribution is comparing properties of ZnO thin films deposited from pure Zn target in oxygen atmosphere and those deposited from sintered ZnO target. There is a close connection between final thin film properties and PLD conditions. The surface properties of differently grown ZnO thin films are measured by secondary ion mass spectrometry (SIMS), atomic force microscopy (AFM) and scanning electron microscopy (SEM). Furthermore, different approaches — ablation of sintered ZnO pellet or pure metallic Zn as target materials are described. The main results characterize typical properties of ZnO films versus technological parameters are presented. Presented at 5-th International Conference Solid State Surfaces and Interfaces, November 19–24, 2006, Smolenice Castle, Slovakia     

Blue luminescence from Ce-doped ZnO thin films prepared by magnetron sputtering

The photoluminescence properties of undoped and Ce-doped ZnO thin films that were prepared by DC magnetron sputtering were investigated. It was found that the incorporation of Ce could intensively affect the structural, optical, and photoluminescence properties of the ZnO thin films. The undoped ZnO thin films showed a sharp UV luminescence, whereas the Ce-doped ZnO thin films showed a broad blue luminescence. The effects of excitation wavelength and annealing atmosphere on the photoluminescence properties of Ce-doped ZnO thin films were also studied. After post-annealing in air and oxygen atmospheres, the blue emissions of the prepared films were drastically suppressed. Our results indicate that the blue emissions of Ce-doped ZnO thin films are related to zinc interstitials and the intrinsic transition of Ce³⁺ ions.     

A correlation for crystallite size of undoped ZnO thin film with the band gap energy – precursor molarity – substrate temperature

Transparent conducting undoped zinc oxide thin films were deposited on glass substrate by ultrasonic spray and spray pyrolysis techniques. The thin films were deposited at different substrate temperatures ranging between 300 and 450 °C with various precursor molarities. The correlation between the structural and optical properties suggests that the crystallites sizes of the films are predominantly influenced by the band gap energy of the thin films. The data of the correlation is suspected of involving some experimental measurement errors and therefore discarded in the development of the present correlation. The coefficient of correction is equal to 0.01, indicating high quality representation of data based on Eq. (1). The correlation also indicates that the crystallites sizes of the films are predominantly influenced by the band gap energy and the precursor molarity of the thin films. The model proposed of undoped ZnO thin film with substrate temperature was investigated.     

RF溅射钕掺杂ZnO薄膜的结构与发光特性

通过射频磁控溅射技术在Si(111)衬底上制备了未掺杂ZnO薄膜和Nd掺杂ZnO薄膜。应用XRD分析了ZnO:Nd薄膜的晶格结构,通过AFM观察了ZnO:Nd薄膜的表面形貌。结果表明,Nd掺入了ZnO晶格中,由于Nd原子半径大于Zn原子半径,Nd以替位原子的形式存在于ZnO晶格中。ZnO:Nd薄膜为纳米多晶薄膜,表面形貌粗糙。ZnO:Nd薄膜的室温光致发光谱表明,相同条件下制备的未掺杂ZnO薄膜和Nd掺杂ZnO薄膜都出现了395nm的强紫光带和495nm的弱绿光带。我们认为,紫光发射峰窄而锐且强度远大于绿光峰,源于薄膜中激子复合;绿光峰强度较弱,源于薄膜中的氧空位(VO)及氧反位锌缺陷(OZn)。Nd掺杂没有影响ZnO:Nd薄膜的PL谱的发射峰的峰位。由于Nd3 离子电荷数与Zn2 离子电荷数不相等,为了保持ZnO薄膜的电中性,间隙锌(VZn)可以作为Nd替位补偿性的受主杂质而存在,影响ZnO薄膜的激子浓度。同时,Nd掺入使ZnO的晶格畸变缺陷浓度改变增强,因而发射峰的强度随Nd掺杂浓度不同而变化。     

退火对ZnO薄膜的结构和光学性质的影响

采用射频磁控溅射法在Si衬底上制备了高c轴择优取向的ZnO薄膜,研究了退火对ZnO薄膜的晶粒尺度和发光光谱的影响。XRD结果显示退火可以改善ZnO薄膜的结构特性,PL谱结果显示退火对ZnO薄膜的发光强度产生很大影响。     

Photoluminescence, FTIR and X-ray diffraction studies on undoped and Al-doped ZnO thin films grown on polycrystalline α-alumina substrates by ultrasonic spray pyrolysis

Undoped and aluminum-doped zinc oxide (ZnO) thin films have been grown on polycrystalline α-alumina substrates by ultrasonic spray pyrolysis (USP) technique using zinc acetate dihydrate and aluminum chloride hexahydrate (Al source) dissolved in methanol, ethanol and deionized water. A number of techniques, including X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, and photoluminescence (PL) were used to characterize the obtained ZnO thin films. It was seen that the orientation changed with increase in substrate temperature. During the ZnO deposition Zn source reacted with polycrystalline α-Al₂O₃ substrate to form an intermediate ZnAl₂O₄ spinel layer. It has been interestingly found that the intensity of green emission at 2.48 eV remarkably increased when the obtained ZnO:Al films were deposited at 380 °C. The FTIR absorbance intensity of spectroscopic band at 447±6 cm⁻¹ is very sensitive to oxygen sublattice disorder resulting from non-stoichiometry, which is consistent with the result of PL characterization.