Effect of Different Substrate Temperature on Phosphorus-Doped ZnO Thin Films Prepared by PLD on Sapphire Substrates

Phosphorus-doped ZnO （ZnO：P） thin films are deposited on a c-plane sapphire in oxygen at 350℃, 450℃, 550℃ and 650℃, respectively, by pulsed laser deposition （PLD）, then all the ZnO：P samples are annealed at 650℃ in oxygen with a pressure of 1 × 10^5 Pa. X-ray diffraction measurements indicate that the crystalline quality of the ZnO：P thin films is improved with the increasing substrate temperature from 350℃ to 550℃. With a further increase of the deposition temperature, the crystalline quality of the ZnO：P sample is degraded. The measurements of low-temperature photoluminescence spectra demonstrate that the samples deposited at the substrate temperatures of 350℃ and 450℃ show a strong acceptor-bound exciton （A^0X） emission. The electrical properties of ZnO：P films strongly depend on the deposition temperature. The ZnO：P samples deposited at 350℃ and 450℃ exhibit p-type conductivity. The p-type ZnO：P film deposited at 450℃ shows a resistivity of 1.846Ω·cm and a relatively high hole concentration of 5.100 × 10^17 cm^-3 at room temperature.     

Effect of Different Substrate Temperature on Sb-Doped ZnO Thin Films Prepared by Pulsed Laser Deposition on Sapphire Substrates

Sb-doped ZnO thin films are deposited on c-plane sapphire substrates by pulsed laser deposition. Hall results indicate that the conductivity of the Sb-doped ZnO thin films is strongly dependent on the substrate temperature. The sample deposited at the temperature of 550°C exhibits p-type conductivity. It gives a resistivity of 15.25Ω＆#12539;cm, with a Hall mobility of 1.79cm2V-1s-1 and a carrier concentration of 2.290×1017cm-3 at room temperature. The x-ray diffraction indicates that the Sb-doped ZnO thin films deposited in the range of 450-650°C are high c-axis oriented. Low-temperature photoluminescence spectra indicate that the sample deposited at 550°C shows the strong acceptor-bound exciton （A0X） emission.     

Transformation behaviors,structural and magnetic characteristics of Ni-Mn-Ga films on MgO （001）

Ferromagnetic Ni-Mn-Ga films were fabricated by depositing on MgO （001） substrates at temperatures from 673 K to 923 K. Microstructure, crystal structure, martensitic transformation behavior, and magnetic properties of the films were studied. With increasing deposition temperature, the surface morphology of the films transforms from granular to continu- ous. The martensitic transformation temperature is not dependent on deposition temperature; while transformation behavior is affected substantially by deposition temperature. X-ray analysis reveals that the film deposited at 873 K has a 7M marten- site phase, and its magnetization curve provides a typical step-increase, indicating the occurrence of magnetically induced reorientation （MIR）. In situ magnetic domain structure observation on the film deposited at 873 K reflects that the marten- sitic transformation could be divided into two periods： nucleation and growth, in the form of stripe domains. The MIR occurs at the temperature at which martensitic transformation starts, and the switching field increases with the decrease of temperature due to damped thermal activation. The magnetically induced martensitic transformation is related to the difference of magnetization between martensite and austenite. A shift of martensite temperature of dT/dH = 0.43 K/T is observed, consistent with the theoretical value, 0.41 K/T.     

Effects of Substrate Temperature on Helium Content and Microstructure of Nanocrystalline Titanium Films

Helium-charged nanocrystalline titanium films have been deposited by HeAr magnetron co-sputtering. The effects of substrate temperature on the helium content and microstructure of the nanocrystalline titanium films have been studied. The results indicate that helium atoms with a high concentration are evenly incorporated in the deposited titanium films. When the substrate temperature increases from 60℃ to 350℃ while the other deposition＇parameters are fixed, the helium content decreases gradually from 38.6 at.% to 9.2at.%, which proves that nanocrystalline Ti films have a great helium storage capacity. The 20 angle of the Bragg peak of （002） crystal planes of the He-charged Ti film shifts to a lower angle and that of （100） crystal plane is unchanged as compared with that of the pure Ti film, which indicates that the lattice parameter c increases and a keeps at the primitive value. The grain refining and helium damage result in the diffraction peak broadening.     

Optoelectronic characterization of ZnS/PS systems

ZnS thin films are deposited on porous silicon （PS） substrates with different porosities by pulsed laser deposition （PLD）. The photoluminescence （PL） spectra of the samples are measured at room temperature. The results show that the PL intensity of PS after deposition of ZnS increases and is associated with a blue shift. With the increase of PS porosity, a green emission at about 550 nm is observed in the PL spectra of ZnS/PS systems, which may be ascribed to the defect-center luminescence of ZnS films. Junction current- voltage （I-V） characteristics were studied. The rectifying behavior of I-V characteristics indicates the formation of ZnS/PS heterojunctions, and the forward current is seen to increase when the PS porosity is increased.     

Effects of Annealing Temperature on Structural and Optical Properties of ZnO Thin Films

The effects of annealing temperature on the structural and optical properties of ZnO films grown on Si （100） substrates by sol-gel spin-coating are investigated. The structural and optical properties are characterized by x-ray diffraction, scanning electron microscopy and photoluminescence spectra. X-ray diffraction analysis shows the crystal quality of ZnO films becomes better after annealing at high temperature. The grain size increases with the temperature increasing. It is found that the tensile stress in the plane of ZnO films first increases and then decreases with the annealing temperature increasing, reaching the maximum value of 1.8 GPa at 700℃. PL spectra of ZnO films annealed at various temperatures consists of a near band edge emission around 380 nm and visible emissions due to the electronic defects, which are related to deep level emissions, such as oxide antisite （OZn）, interstitial oxygen （Oi）, interstitial zinc （Zni） and zinc vacancy （VZn^-）, which are generated during annealing process. The evolution of defects is analyzed by PL spectra based on the energy of the electronic transitions.     

Photoluminescence of ZnO and Mn-Doped ZnO Polycrystalline Films Prepared by Plasma Enhanced Chemical Vapour Deposition

ZnO and Mn-doped ZnO polycrystalline films are prepared by plasma enhanced chemical vapour deposition at low temperature （220℃）, and room-temperature photoluminescence of the films is systematically investigated. Analysis from x-ray diffraction reveals that a11 the prepared films exhibit the wurtzite structure of ZnO, and Mndoping does not induce the second phase in the films. X-ray photoelectron spectroscopy confirms the existence of Mn^2＋ ions in the films rather than metalic Mn or Mn^4＋ ions. The emission efficiency of the ZnO film is found to be dependent strongly on the post-treatment and to degrade with increasing temperature either in air or in nitrogen ambient. However, the enhancement of near band edge （NBE） emission is observed after hydrogenation in ammonia plasma, companied with more defect-related emission. Furthermore, the position of NBE shifts towards to high-energy legion with increasing Mn-doped concentration due to Mn incorporation into ZnO lattice.     

Ahnormal Crystallization of Silicon Thin Films Deposited by ICP-CVD

Silicon thin films are deposited by inductively coupled plasma chemical vapour deposition （ICP-CVD） at a low temperature of 350℃ using a mixture of SiH4 and H2. The structures of the films are characterized by x-ray diffraction and Raman spectra. Under the optimum experimental conditions, we observe that the crystallinity of Si films becomes more excellent and the preferred orientation changes from （111） to （220） with the decreasing dilution of SiH4 in H2. Such an abnormal crystallization is tentatively interpreted in term of the high density, low electron temperature and spatial confinement of the plasma in the process of ICP-CVD.     

Multiferroic ZnO obtained by substituting oxygen with nitrogen

N-doped ZnO films were prepared in nitrogen plasma by pulsed laser deposition.Clear room temperature ferro-magnetism has been observed in the film prepared at a substrate temperature of 500 C.The structural characterizations of X-ray diffraction,Raman,and X-ray photoelectron spectroscopy confirm the substitution of O by N in ZnO,which has been considered to be the origin of the observed ferromagnetism.Furthermore,ferroelectricity has been observed at room temperature by piezoelectric force microscopy,indicating the potential multiferroic applications.     

Photoluminescence and Optically Pumped Ultraviolet Lasing from Nanocrystalline ZnO Thin Films Prepared by Thermal Oxidation of High—Quality ZnS Thin Films

We present a simple and useful method for preparing high-quality nanocrystalline ZnO thin films,i.e.the thermal oxidation of high-quality ZnS films prepared by the low-pressure metal-organic chemical vapour deposition technique.The x-ray diffraction measurements reveal that the nanocrystalline ZnO has a hexagonal wurtzite structure.Raman spectra show that the longitudinal optical phonon with the E1-mode appears at 578 cm^-1.The multiple phonon scattering process is also observed,indicating the formation of a high-quality nanocrystalline ZnO thin film.The photoluminescence spectrum has a single emission peak at 3.264eV from the free-exciton mission,under the condition of low excitation power at room temperature.However,when excitation intensities exceed the threshold of 150kW/cm^2,a new and narrow peak emerges at lower energies,which are attributed to exciton-exciton collisions,and is called the P line.The intensity of this peak increases superlinearly with the pumping power over a threshold value.This supplies strong evidence of stimulated emission.The multiple longitudinal cavity modes observed in the stimulated emission spectrum indicate the successful realization of optically pumped lasing from nanocrystalline ZnO films at room temperature.     

Deposition of ZnO thin films on (100) γ-LiAlO2 substrate

Optical properties for ZnO thin films grown on (100) γ-LiAlO2 (LAO) substrate by pulsed laser deposition method were investigated. The c-axis oriented ZnO films were grown on (100) γ-LiAlO2 substrates at the substrate temperature of 550 C. The transmittance of the films was over 85%. Peaks attributed to excitons were shown in absorption spectra, which indicated that thin films had high crystallinity. Photoluminescence spectra with the maximum peak at 540 nm were observed at room temperature, which seemed to be ascribed to oxygen vacancy in the ZnO films caused by diffusion of Li from the substrates into the films during the deposition.     

Room-Temperature Ferromagnetic ZnMnO Thin Films Synthesized by Plasma Enhanced Chemical Vapour Deposition Method

Room-temperature ferromagnetic Mn-doped ZnO films are grown on Si （001） substrates by plasma enhanced chemical vapour deposition （PECVD）. X-ray diffraction measurements reveal that the Znl-xMn.O films have the single-phase wurtzite structure. X-ray photoelectron spectroscopy indicates the existence of Mn^2＋ ions in Mndoped ZnO films. Furthermore, the decreasing additional Raman peak with increasing Mn-doping is considered to relate to the substitution of Mn ions for the Zn ions in ZnO lattice. Superconducting quantum interference device （SQUID） measurements demonstrate that Mn-doped ZnO films have ferromagnetic behaviour at room temperature.     

Effect of substrate temperature on the morphological,structural,and optical properties of RF sputtered Ge_(1-x)Sn_x films on Si substrate

In this study, Ge_(1-x)Sn_x alloy films are co-sputtered on Si(100) substrates using RF magnetron sputtering at different substrate temperatures. Scanning electron micrographs, atomic force microscopy(AFM), Raman spectroscopy, and x-ray photoemission spectroscopy(XPS) are conducted to investigate the effect of substrate temperature on the structural and optical properties of grown Ge Sn alloy films. AFM results show that RMS surface roughness of the films increases from 1.02 to 2.30 nm when raising the substrate temperature. This increase could be due to Sn surface segregation that occurs when raising the substrate temperature. Raman spectra exhibits the lowest FWHM value and highest phonon intensity for a film sputtered at 140?C. The spectra show that decreasing the deposition temperature to 140?C improves the crystalline quality of the alloy films and increases nanocrystalline phase formation. The results of Raman spectra and XPS confirm Ge–Sn bond formation. The optoelectronic characteristics of fabricated metal-semiconductor-metal photodetectors on sputtered samples at room temperature(RT) and 140?C are studied in the dark and under illumination. The sample sputtered at 140?C performs better than the RT sputtered sample.     

Effect of Temperature on Structural and Magnetic Properties of Laser Ablated Iron Oxide Deposited on Si（100）

We fabricate Fe3O4 thin films on Si（100） substrates at different temperatures using pulsed laser deposition, and study the effect of annealing and deposition temperature on the structural and magnetic properties of Fe3O4 thin films. Subsequently, the films are characterized by x-ray diffraction （XRD）, scanning electron microscopy （SEM） and vibrating sample magnetometery （VSM）. The XRD results of these films confirm the presence of the Fe3O4 phase and show room-temperature ferromagnetism, as observed with VSM. We demonstrate the optimized deposition and annealing conditions for an enhanced magnetization of 854 emu/cm3 that is very high when compared to the bulk sample.     

Enhanced ferroelectricity and ferromagnetism in Bio.9Bao. 1FeO3/Laz/3Srl/3MnO3 heterostructure grown by pulsed laser deposition

Bi0.9Ba0.lFeO3 （BBFO）/La2/3Srl/3MnO3 （LSMO） heterostructures are fabricated on LaA103 （100） substrates by pulsed laser deposition. Giant remnant polarization value （~ 85 μC/cm2） and large saturated magnetization value （~ 12.4 emu/cm3） for BBFO/LSMO heterostructures are demonstrated at room temperature. Mixed ferroelectric domain structures and low leakage current are observed and in favor of enhanced ferroelectrie properties in the BBFO/LSMO het- erostructures. The magnetic field-dependent magnetization measurements reveal the enhancement in the magnetic moment and improved magnetic hysteresis loop originating from the BBFO/LSMO interface. The heterostructure is proved to be effective in enhancing the ferroelectric and ferromagnetic performances in multiferroic BFO films at room temperature.     

Bias Voltage Controlled Positive Magnetoresistance of Fe0.05-C0.95/Si Heterostructures

Fe-doped amorphous carbon films of about lOOnm in thickness are deposited on n-type silicon substrates by pulsed laser deposition （PLD）, and positive magnetoresistance （MR） is observed for these Fe-doped amorphous carbon/n-Si heterostructures under current-perpendicular-to-plane configuration at forward bias. Two MR peaks are observed in the temperature range 40-120 K and the positive MR varies with applied bias voltage. This bias voltage controlled MR may be related to the maguetic-field-controlled freeze out effect and recombination through the deep trapping states in the Fe-doped carbon films.     

Effect of substrate temperature on microstructure and optical properties of single-phased Ag20 film deposited by using radio-frequency reactive magnetron sputtering method

Using a radio-frequency reactive magnetron sputtering technique, a series of the single-phased Ag20 films are deposited in a mixture of oxygen and argon gas with a flow ratio of 2：3 by changing substrate temperature （Ts）. Effects of the Ts on the microstructure and optical properties of the films are investigated by using X-ray diffractometry, scanning electron microscopy and spectrophotometry. The single-phased Ag20 films deposited at values of Ts below 200℃ are （111） preferentially oriented, which may be due to the smallest free energy of the （111） crystalline face. The film crystallization becomes poor as the value of Ts increases from 100℃ to 225℃. In particular, the Ag20 film deposited at Ts=225℃ loses the （111） preferential orientation. Correspondingly, the film surface morphology obviously evolves from a uniform and compact surface structure to a loose and gullied surface structure. With the increase of Ts value, the transmissivity and the reflectivity of the films in the transparent region are gradually reduced, while the absorptivity gradually increases, which may be attributed to an evolution of the crystalline structure and the surface morphology of the films.     

Zn/O ratio and oxygen chemical state of nanocrystalline ZnO films grown at different temperatures

ZnO nanocrystalline films are prepared on Si substrates at different temperatures by using metal-organic chemical vapour deposition(MOCVD).It is observed that when the growth temperature is low,the stoichiometric ratio between Zn and O atoms has a large deviation from the ideal ratio of 1:1.The ZnO grains in the film have small sizes and are not well crystallized,resulting in a poor photoluminescence(PL) property.When the temperature is increased to an appropriate value,the Zn/O ratio becomes optimized,and most of Zn and O atoms are combined into Zn-O bonds.Then the film has good crystal quality and good PL property.If the temperature is fairly high,the interfacial mutual diffusion of atoms between the substrate and the epitaxial film appears,and the desorption process of the oxygen atoms is enhanced.However,it has no effect on the film property.The film still has the best crystal quality and PL property.     

Characterization of zirconium thin films deposited by pulsed laser deposition

Zirconium(Zr) thin films deposited on Si(100) by pulsed laser deposition(PLD) at different pulse repetition rates are investigated. The deposited Zr films exhibit a polycrystalline structure, and the X-ray diffraction(XRD) patterns of the films show the α Zr phase. Due to the morphology variation of the target and the laser–plasma interaction, the deposition rate significantly decreases from 0.0431 /pulse at 2 Hz to 0.0189 /pulse at 20 Hz. The presence of droplets on the surface of the deposited film, which is one of the main disadvantages of the PLD, is observed at various pulse repetition rates. Statistical results show that the dimension and the density of the droplets increase with an increasing pulse repetition rate. We find that the source of droplets is the liquid layer formed under the target surface. The dense nanoparticles covered on the film surface are observed through atomic force microscopy(AFM). The root mean square(RMS) roughness caused by valleys and islands on the film surface initially increases and then decreases with the increasing pulse repetition rate.The results of our investigation will be useful to optimize the synthesis conditions of the Zr films.     

Piezoresistive Effect of Doped carbon Nanotube／Cellulose Films

The strain-induced resistance changes in iodine-doped and undoped carbon nanotube films were investigated by a three-point bending test. Carbon nanotubes were fabricated by hot filament chemical vapour deposition. The experimental results showed that there has a striking piezoresistive effect in carbon nanotube films. The gauge factor for I-doped and undoped carbon nanotube films under 500 microstrain was about 125 and 65 respectively at room temperature, exceeding that of polycrystalline silicon (30) at 35℃. The origin of the piezoresistivity in the films may be ascribed to a strain-induced change in the band gap for the doped tubes and to the intertube contact resistance for the undoped tubes.