Structural characterization of AlGaN/GaN superlattices by x-ray diffraction and Rutherford backscattering

We report on structural characterization of AlGaN/GaN superlattices grown on sapphire. The superlattice formation is evidenced by high-resolution x-ray diffraction and transmission electron microscopy. The high resolution x-ray diffraction spectra exhibit a pattern of satellite peaks. The in-plane lattice constants of the superlattices indicate the coherent growth of the AlGaN layer onto GaN. The average At composition in the superlattices is determined to be 0.08 by Rutherford backscattering spectroscopy. The average parallel and perpendicular elastic strains for the SLs are determined to be (e(parallel to)) = +0.25% and (e(perpendicular to)) = -0.17%. (c) 2006 Elsevier Ltd. All rights reserved.

Depth dependent elastic strain in ZnO epilayer: combined Rutherford backscattering/channeling and X-ray diffraction

A ZnO layer was grown by metalorganic chemical vapor deposition (MOCVD) on a sapphire (0 0 0 1) substrate. The perpendicular and parallel elastic strain of the ZnO epilayer, e(perpendicular to) = 0.19%, e(parallel to) = -0.29%, respectively, were derived by using the combination of Rutherford backscattering (RBS)/channeling and X-ray diffraction (XRD). The ratio vertical bar e(parallel to)/ e(perpendicular to)vertical bar = 1.5 indicates that ZnO layer is much stiffer in the a-axis direction than in the c-axis direction. By using RBS/C, the depth dependent elastic strain was deduced. The strain is higher at the depth close to the interface and decreases towards the surface. The negative tetragonal distortion was explained by considering the lattice mismatch and thermal mismatch in ZnO thin film. (c) 2004 Elsevier B.V. All rights reserved.

Depth distribution of the strain in the GaN layer with low-temperature AlN interlayer on Si(111) substrate studied by Rutherford backscattering/channeling

The depth distribution of the strain-related tetragonal distortion e(T) in the GaN epilayer with low-temperature AlN interlayer (LT-AlN IL) on Si(111) substrate is investigated by Rutherford backscattering and channeling. The samples with the LT-AlN IL of 8 and 16 nm thickness are studied, which are also compared with the sample without the LT-AlN IL. For the sample with 16-nm-thick LT-AlN IL, it is found that there exists a step-down of e(T) of about 0.1% in the strain distribution. Meanwhile, the angular scan around the normal GaN <0001> axis shows a tilt difference about 0.01degrees between the two parts of GaN separated by the LT-AlN IL, which means that these two GaN layers are partially decoupled by the AlN interlayer. However, for the sample with 8-nm-thick LT-AlN IL, neither step-down of e(T) nor the decoupling phenomenon is found. The 0.01degrees decoupled angle in the sample with 16-nm-thick LT-AlN IL confirms the relaxation of the LT-AlN IL. Thus the step-down of e(T) should result from the compressive strain compensation brought by the relaxed AlN interlayer. It is concluded that the strain compensation effect will occur only when the thickness of the LT-AlN IL is beyond a critical thickness. (C) 2004 American Institute of Physics.

Depth dependence of the tetragonal distortion of a GaN layer on Si(111) studied by Rutherford backscattering/channeling

Rutherford backscattering and channeling have been used to characterize the structure of a GaN layer grown on a Si(111) substrate. The results show that a 1.26 mum GaN epitaxial layer with a rather abrupt interface and a good crystalline quality (chi(min)=3.4%) can be grown on a Si(111) substrate. Using the channeling angular scan around an off-normal <1 (2) over bar 13> axis in the {10 (1) over bar0} plane of the GaN layer, the tetragonal distortion e(T), which is caused by the elastic strain in the epilayer, can be determined. Moreover, the depth dependence of the e(T) can be obtained using this technique. A fully relaxed (e(T)=0) GaN layer for a thickness <2.8 mum is expected. (C) 2002 American Institute of Physics.

Sputtering by multiply-charged ions, and preferential sputtering of isotopic mixtures

Collector-type experiments have been conducted to investigate two different aspects of sputtering induced by keV ions. The first study looked for possible ejection mechanisms related to the primary charge state of the projectile. Targets of CsI and LiNbO_3 were bombarded with 48 keV Ar^(q+), and a Au target was bombarded with 60 keV Ar^(q+), for q = 4, 8, and 11. The collectors were analyzed using heavy-ion Rutherford backscattering spectroscopy to determine the differential angular sputtering yields; these and the corresponding total yields were examined for variations as a function of projectile charge state. For the Au target, no significant changes were seen, but for the insulating targets slight (~10%) enhancements were observed in the total yields as the projectile charge state was increased from 4+ to 11+.

In the second investigation, artificial ^(92)Mo/^(100)Mo targets were bombarded with 5 and 10 keV beams of Ar^+ and Xe^+ to study the isotopic fractionation of sputtered neutrals as a function of emission angle and projectile fluence. Using secondary ion mass spectroscopy to measure the isotope ratio on the collectors, material ejected into normal directions at low bombarding fluences (~ 10^(15) ions cm^(-2)) was found to be enriched in the light isotope by as much as ~70‰ compared to steady state. Similar results were found for secondary Mo ions sputtered by 14.5 keV O^-. For low-fluence 5 keV Xe^+ bombardment, the light-isotope enrichment at oblique angles was ~20‰ less than the corresponding enrichment in the normal direction. No angular dependence could be resolved for 5 keV Ar^+ projectiles at the lowest fluence. The above fractionation decreased to steady-state values after bombarding fluences of a few times 10^(16) ions cm^(-2) , with the angular dependence becoming more pronounced. The fractionation and total sputtering yield were found to be strongly correlated, indicating that the above effects may have been related to the presence of a modified target surface layer. The observed effects are consistent with other secondary ion measurements and multiple-interaction computer simulations, and are considerably larger than predicted by existing analytic theory.

Structural characterization of mn implanted AlInN

AlInN/GaN thin films were implanted with Mn ions and subsequently annealed isochronically at 750 and 850 degrees C. X-ray diffraction and Rutherford backscattering spectroscopy (RBS) techniques were employed to study the microstructural properties of the implanted/annealed samples. The effect of annealing on implantation-induced strain in thin films has been studied in detail. The strain was found to increase with dose until it reached a saturation value and after that it started decreasing with a further increase in the dose. RBS measurements indicated the atomic diffusion of In, Al, Ga and Mn in implanted samples. The in- and out-diffusion of atoms has been observed after annealing at 750 degrees C and 850 degrees C, respectively. Strong decomposition of the samples took place when annealed at 850 degrees C.

Composition deviation of arrays of FePt nanoparticles starting from poly(styrene)-poly(4-vinylpyridine) micelles

Ordered arrays of FePt nanoparticles were prepared using a diblock polymer micellar method combined with plasma treatment. Rutherford backscattering spectroscopy analyses reveal that the molar ratios of Fe to Pt in metal-salt-loaded micelles deviate from those when metal precursors are added, and that the plasma treatment processes have little influence upon the compositions of the resulting FePt nanoparticles. The results from Fourier transform infrared spectroscopy show that the maximum loadings of FeCl3 and H2PtCl6 inside poly( styrene)-poly(4-vinylpyridine) micelles are different. The composition deviation of FePt nanoparticles is attributed to the fact that one FeCl3 molecule coordinates with a single 4-vinylpyridine (4VP) unit, while two neighboring and uncomplexed 4VP units are required for one H2PtCl6 molecule. Additionally, we demonstrate that the center-to-center distances of the neighboring FePt nanoparticles can also be tuned by varying the drawing velocity.

Chemical composition and elastic strain in AlInGaN quaternary films

High-quality AlInGaN quaternary layers were grown on c-Al2O3 using a thick GaN template. A full width at half maximum of 0.075 degrees from AlInGaN(0004) rocking curve and a minimum yield of 5.6% from Rutherford backscattering/channelling spectrometry (RBS) prove the AlInGaN layer of a comparable crystalline quality with GaN layers. The chemical compositions (both of Al and In contents) of AlInGaN layers are directly obtained from RBS and elastic recoil detection analysis. The lattice parameters both in perpendicular and parallel directions are deduced from X-ray diffraction. The AlInGaN layer is found to process a compressive strain in parallel direction and a tensile strain in perpendicular direction. (c) 2006 Elsevier B.V. All rights reserved.

Relaxed GexSi1-x layer formation with reduced dislocation density grown by ultrahigh vacuum chemical vapor deposition

A new alternative method to grow the relaxed Ge0.24Si0.76 layer with a reduced dislocation density by ultrahigh vacuum chemical vapor deposition is reported in this paper. A 1000-Angstrom Ge0.24Si0.76 layer was first grown on a Si(100) substrate. Then a 500-Angstrom Si layer and a subsequent 5000-Angstrom Ge0.24Si0.76 overlayer followed. All these three layers were grown at 600 degrees C. After being removed from the growth system to air, the sample was first annealed at 850 degrees C for 30 min, and then was investigated by cross-sectional transmission electron microscopy and Rutherford backscattering spectroscopy. It is shown that the 5000-Angstrom Ge0.24Si0.76 thick over layer is perfect, and most of the threading dislocations are located in the embedded thin Si layer and the lower 1000-Angstrom Ge0.24Si0.76 layer. The relaxation ratio of the over layer is deduced to be 0.8 from Raman spectroscopy.

INDIUM OHMIC CONTACTS TO N-ZNSE

The reaction between an indium over layer and high purity MBE grown n-ZnSe chlorine doped (2x 10(18) cm-3) epilayers has been investigated using X-ray diffraction, Rutherford backscattering spectroscopy, X-ray photoelectron and Auger electron spectroscopy, and by electrical function tests (I-V and C-V). Good ohmic contacts were formed after annealing at 250 or 300-degrees-C for a few minutes in forming gas. Annealing at lower or higher temperatures resulted in higher resistance or rectifying contacts. The data show that no compounds were formed at the interface; instead In appeared to diffuse into the ZnSe. High surface doping densities appear to allow an ohmic contact, but the electrical data suggest that compensation effects are also very significant in the formation of the contact. These effects must be considered for successful formation of the ohmic contact.

Estudo de defeitos em filmes finos de ZnO depositados por Rf-sputtering

Neste trabalho foram estudados diferentes filmes finos de ZnO depositados por Rf-Sputtering. Filmes finos de ZnO com diferentes propriedades óticas foram obtidos intencionalmente variando os parâmetros de deposição. De modo a correlacionar as propriedades óticas e estruturais com os parâmetros de deposição, foram utilizadas diferentes técnicas de caracterização avançadas, tais como, fotoluminescência, microscopia de força atómica, difração de raios- X e retrodispersão de Rutherford. Este trabalho centra-se na discussão e análise das bandas de emissão vermelha, verde e azul, comumente observadas em amostras de ZnO e cuja natureza tem sido objeto de grande controvérsia na literatura. A utilização de técnicas de caracterização estrutural revelou-se de extrema importância para correlacionar as propriedades físicas de composição e estrutura com os centros óticos observados nos filmes. Nesta base, foram propostos e discutidos diferentes modelos de recombinação ótica associados à qualidade estrutural dos filmes, considerando modelos de camadas que descrevem a heterogeneidade lateral e em profundidade. Desta análise verificou-se a presença de heterogeneidade estrutural e composicional, que aumenta a complexidade na compreensão da correlação dos parâmetros de deposição com as propriedades óticas dos filmes. Foi discutida a limitação e validade de diferentes modelos tendo em conta a presença da heterogeneidade existente nos filmes estudados. Este trabalho contribui assim para uma melhor compreensão da complexidade de interação dos diferentes defeitos e o seu efeito nas propriedades óticas, nomeadamente o papel dos defeitos de interface, na superfície, nas fronteiras de grão e junto ao substrato.

Caracterização de Fe granular em matriz de Al/sub 2/O/sub 3/

Neste trabalho é apresentada a caracterização de amostras de filmes finos granulares de Fe- Al2O3, obtidas por evaporação em ultra alto vácuo. Duas amostras com composições diferentes foram obtidas. A espectroscopia de Espalhamento de Rutherford (Rutherford Backscattering Spectroscopy - RBS) foi utilizada para determinar a fração volumétrica de metal e a espessura das amostras, cujos valores obtidos foram 43% e 34% respectivamente. A morfologia das amostras foi investigada por difração de raios-x a qual mostrou a existência de grãos de ferro com 30Å de diâmetro e orientação cristalina preferencial (110) embebidos em uma matriz amorfa de Al2O3. As medidas de magnetização também mostraram que as duas amostras apresentavam uma distribuição de tamanhos de grão de ferro com valor médio de 24Å, estando de acordo com os resultados obtidos por difração de raios-x. A magneto-resistência observada em temperatura ambiente pode ser explicada pelo tunelamento dependente de spin dos elétrons de condução entre os grãos de ferro. Os resultados das medidas de RxT e IxV mostraram que o principal mecanismo de transporte foi o tunelamento termicamente ativado, o que está de acordo com a teoria apresentada por Abeles.

Helium ion irradiation of polymer films deposited from TMS-Ar plasmas

Polymer films synthesized from plasmas of a tetramethylsilane - Ar mixture were modified by irradiation with 170 keV He ions at fluences ranging from 1 x 10(14) to 1 x 10(16) cm(-2). As revealed by infrared spectroscopy, the ion beam produced intense bond rearrangements, such as the depletion of bonding groups (C-H and Si-H), and induced the formation of new ones, such as O-H and Si-O. From the nanoindentation measurements, a remarkable increase in the surface hardness of the films was observed as the ion fluence was increased. The increases in hardness were accompanied by an increase in the film compaction as shown by using a combination of RBS and film thickness measurements. From both hardness and infrared measurements A was concluded that, under the He ion bombardment, the polymer structure is transformed into a silicon oxycarbide network.

The effect of N+ ion energy on the properties of ion bombarded plasma polymer films

This work describes the influence of the ion bombardment on the electrical, optical and mechanical properties of polymer films deposited from radio-frequency plasmas of benzene. Irradiations were conducted using N+ at 5 x 10(19) ions/m(2), varying the ion energy, E-0, from 0 to 150 keV. Film elemental composition was determined by Rutherford backscattering spectroscopy. Electrical resistivity and hardness were obtained by the two-point probe and nanoindentation technique, respectively. Ultraviolet-visible spectroscopy was employed to investigate the optical constants of the samples. Etching rate was determined by exposure of the films to reactive oxygen plasmas. Ion bombardment induced gradual loss of H and increase in C and O concentrations with Eo. As a consequence the electrical, optical and mechanical properties were drastically affected. Interpretation of these results is proposed in terms of chain cross-linking and unsaturation. (C) 2001 Elsevier B.V. B.V. All rights reserved.

Fabrication and characterization of GeO2-PbO optical waveguides

This work presents studies of GeO2-PbO thin films deposited by RF Sputtering for fabrication of rib-waveguide. GeO2-PbO vitreous targets were prepared melting the reagents in alumina crucible. Thin films were deposited at room temperature using pure Ar plasma, at 5 mTorr pressure and RF power of 40 W on substrates of (100) silicon wafers. Rutherford Backscattering Spectroscopy (RBS) analyses were employed for the determination of the chemical elements present in the GeO2-PbO film. Geometry and sidewall of the waveguides were investigated by Scanning Electron Microscopy (SEM). The mode propagation in the waveguide structure of GeO2-PbO thin films was analyzed using an integrated optic simulation software to obtain a monomode propagation. © The Electrochemical Society.