Wendong Song

Annealing and oxidation of silicon oxide films prepared by plasma-enhanced chemical vapor deposition

We have investigated phase separation, silicon nanocrystal (Si NC) formation and optical properties of Si oxide (SiOx, 0<x<2) films by high-vacuum annealing and dry oxidation. The SiOx films were deposited by plasma-enhanced chemical vapor deposition at different nitrous–oxide/silane flow ratios. The physical and optical properties of the SiOx films were studied as a result of high-vacuum annealing and thermal oxidation. X-ray photoelectron spectroscopy (XPS) reveals that the as-deposited films have a random-bonding or continuous-random-network structure with different oxidation states. After annealing at temperatures above 1000u2009°C, the intermediate Si continuum in XPS spectra (referring to the suboxide) split to Si peaks corresponding to SiO2 and elemental Si. This change indicates the phase separation of the SiOx into more stable SiO2 and Si clusters. Raman, high-resolution transmission electron microscopy and optical absorption confirmed the phase separation and the formation of Si NCs in the films. Th...

Annealing of ultrashallow p+/n junction by 248 nm excimer laser and rapid thermal processing with different preamorphization depths

Ultrashallow p+/n junctions formed by B+-ion implantation and annealed by spike rapid thermal annealing (RTA) or laser annealing were studied. The effect of the preamorphizing depth on the redistribution of boron atoms after annealing has also been investigated. Our results show that for ultrashallow junctions formed by ultra-low-energy ion implantation and spike RTA, the depth of the preamorphizing implant has very little impact on the junction depth. By optimizing the laser fluence and preamorphization depth, a highly activated, ultrashallow, and abrupt junction can be obtained using a 248 nm excimer laser. The secondary-ion-mass spectrometry results clearly indicate that a step-like profile with a junction depth of 370 A (for a B+ implant at 1 keV) can be formed with a single-pulse laser irradiation at 0.5 J/cm2.

Properties of BaFe12O19 films prepared by laser deposition with in situ heating and post annealing

BaFe12O19 films on (001) sapphire substrates are prepared by laser deposition with in situ heating and postannealing. The properties of the films are analyzed by x-ray diffractometry, vibrating sample magnetometer, atomic force microscopy, and Raman spectroscopy. The relationship among the coercivity, crystalline orientation, and grain shape and size is discussed. The film with coercivity of 5.1 kOe has been obtained by laser deposition with postannealing. The film with a preferential c-axis orientation normal to the film plane and the grains having good crystallinity with hexagonal symmetry have been obtained by laser deposition with in situ heating.

Optical properties of SiOx nanostructured films by pulsed-laser deposition at different substrate temperatures

Silicon oxide (SiOx) nanostructured films have been formed by pulsed-laser deposition of Si in oxygen at different substrate temperatures, in order to study the structures and optical properties related to quantum confinement effects. After laser ablation, the single-crystal Si(100) target is converted to a polycrystal structure and shows weak photoluminescence (PL). The as-deposited SiOx nanostructured films show large particles (i.e., droplets) on a uniform background film. The droplets with weak PL emission have the same high crystallinity as the Si(100) target. Strong PL is observed from the amorphouslike background films rather than from the crystalline droplets. As substrate temperatures increase from room temperature (23°C)to800°C, the PL band continually redshifts from 1.9to1.6eV and the optical band gap decreases from 2.9to2.1eV due to the increased Si concentration in the films. After high-vacuum annealing at 800°C, both the PL and optical absorption are enhanced. The optical band gap also decre...

Strain Engineering of Octahedral Rotations and Physical Properties of SrRuO3 Films

Strain engineering is an effective way to modify functional properties of thin films. Recently, the importance of octahedral rotations in pervoskite films has been recognized in discovering and designing new functional phases. Octahedral behavior of SrRuO3 film as a popular electrode in heterostructured devices is of particular interest for its probable interfacial coupling of octahedra with the functional overlayers. Here we report the strain engineering of octahedral rotations and physical properties that has been achieved in SrRuO3 films in response to the substrate-induced misfit strains of almost the same amplitude but of opposite signs. It shows that the compressively strained film on NdGaO3 substrate displays a rotation pattern of a tetragonal phase whilst the tensilely strained film on KTaO3 substrate has the rotation pattern of the bulk orthorhombic SrRuO3 phase. In addition, the compressively strained film displays a perpendicular magnetic anisotropy while the tensilely strained film has the magnetic easy axis lying in the film plane. The results show the prospect of strain engineered octahedral architecture in producing desired property and novel functionality in the class of perovskite material.

Effect of oxygen vacancies on the electronic structure and transport properties of SrRuO3 thin films

Epitaxial SrRuO3 films were grown under different oxygen partial pressures inducing different amounts of oxygen vacancies. In spite of microstructural disorders, a considerable improvement in the conductivity was observed at ambient temperature with increasing the oxygen vacancies. The oxygen vacancies are responsible for the conductivity improvement by enhancing the orbital overlap between Ru dz2 and O pz orbitals. The finding indicates that the oxygen vacancy plays an important role in determining the transport properties of perovskite oxides, by modifying their electronic structures.Epitaxial SrRuO3 films were grown under different oxygen partial pressures inducing different amounts of oxygen vacancies. In spite of microstructural disorders, a considerable improvement in the conductivity was observed at ambient temperature with increasing the oxygen vacancies. The oxygen vacancies are responsible for the conductivity improvement by enhancing the orbital overlap between Ru dz2 and O pz orbitals. The finding indicates that the oxygen vacancy plays an important role in determining the transport properties of perovskite oxides, by modifying their electronic structures.

Origin of anomalously high exchange field in antiferromagnetically coupled magnetic structures: Spin reorientation versus interface anisotropy

Magnetization reorientation from in-plane to perpendicular direction, observed in Co thin film coupled antiferromagnetically to high perpendicular magnetic anisotropy (Co/Pd) multilayers, is studied systematically for Co thickness ranging from 0 to 2.4u2009nm. The sample with 0.75u2009nm thick Co showed an exchange coupling field (Hex) exceeding 15 kOe at room temperature and 17.2 kOe at 5u2009K. With an increase of Co thickness, Hex decreased as expected and beyond certain thickness, magnetization reorientation was not observed. Indeed, three regions were observed in the thickness dependence of magnetization of the thin layer; one in which the thin layer (in the thickness range up to 0.8u2009nm) had a perpendicular magnetic anisotropy due to interface effects and antiferromagnetic coupling, another in which the thin layer (0.9–1.2u2009nm) magnetization had no interface or crystallographic anisotropy but was reoriented in the perpendicular direction due to antiferromagnetic coupling, and the third (above 1.2u2009nm) in which the...

Ultra-low magnetic damping of perovskite La0.7Sr0.3MnO3 thin films

The perovskite La0.7Sr0.3MnO3 (LSMO) films grown on different substrates were investigated by an angle resolved broadband ferromagnetic resonance technique. All films exhibited a four-fold magnetocrystalline anisotropy, which is in accord with the crystal structure. Moreover, a perpendicular uniaxial anisotropy changed from the (001)pc easy plane to the [001]pc easy direction when the strain of LSMO films varies from tensile to compressive. The ultra-low magnetic damping constant of 5.2u2009×u200910−4 was obtained for a 44.6u2009nm LSMO film on an NdGaO3 (110) substrate. The breathing Fermi surface model in which the damping constant is proportional to the density of states at Fermi energy is the dominant mechanism for the intrinsic magnetic relaxation.

Barium ferrite films prepared by pulsed laser deposition with a varying substrate temperature

Barium femte is one of the candidates for high-density magnetic recording. So far, bilrium femte films have been prepared by sputtering and laser deposition [I-51. These thin films have been obtained by either applying in-situ substrate heating during film growth or through a postannealing process. For in-situ heating, substrates are heated up to a certllin temperature before deposition starting, then substrate temperature is kept constant during film growth. After that, films are cooled down to room temperature. In contrast, for post annealing, films are grown at room temperature or a low temperature. The films are then processed with a post annealing. Both methods have been widely used in spultering and laser deposition. For these two methods, the substrate temperature is always constant during film growth. Since substrate temperature is one of the key parameters to the film quality, it is of interest to investigate the influence of a varying substrate temperature on film properties. In this paper, we report an approach to fabricate barium ferrite films by laser deposition with a varying substrate temperature during film growth. The experimental setup was described in a previous paper 141. During film growth. substrate temperature varied linearly at a rate of 50 Chin and reached 800 C in about 15 minutes. Films were grown for 15 minutes at a laser fluence of about 3 Jlcmand a repetition rate of 5 Hz. After laser deposition, films were cooled down to room temperature in an oxygen atmosphere. The profile of substrate temperature with time during film growth and after deposition is shown in Fig. I. The magnetization hysteresis loops of the barium ferrite film deposited with a varying substrate temperature are shown in Fig. 2. It is found that the magnetization hysteresis loops are similar for both magnetic fields applicd parallel and perpendicular to the substrate surface, indicating that the film exhibits almost isotropic propeaies. The perpendicular and in-plane coercivities are 4149 and 4291 Oe, respectively. Comparison of the magnetization hysteresis loops of the film with those films deposited with a post annealing suggests the similar magnetic properties such as isotropic properties and high coercivity 151. While the films deposited with insitu beating has large magnetic anirusotropy and lower coervicity [SI. Atomic force microscopy (AFM) profile of the barium ferrite film deposited with a varying substrate temperature is shown in Fig. 3. It was observed that the grains in the film show both circular and elongated shapes, which are similar to those in the film deposited with a post annealing. Since the c-axis is normal to the long axis of the grain for barium femte smcture, the c-axis is in the plane for that elongated shape grain. Therefore, a significant amount of crystals with in-plane c-axis orientation exist in the film except those with c-axis orientation normal tu the film plane. While the grains in the film deposited with in-situ heating have good crystallinity with hexagonal symmetry, indicating that the film is grown with c-axis normal to the film plane. In summary, laser dcposition of barium ferrite films with a varying substrate temperature has becn studied for the first time. The film exhibits both c-axis orientation normal to the film plane and in-plane c-axis orientation and the grains in the film show both circular and elongated shapes. The perpendicular and in-plane coercivities are 4149 and 4291 Oe and the film has almost isotropic properties. The magnetic properties, grain shape and crystalline orientation of the film with a varying substrate temperature during film growth are close to those of the film deposited with a post annealing and different to those of the film deposited with in-situ heating.