J. Krauser

XPS, TEM and NRA investigations of Zn(Se, OH)/Zn(OH)2 films on Cu(In, Ga)(S, Se)2 substrates for highly efficient solar cells

Abstract Structural and compositional properties of Zn(Se,OH)/Zn(OH) 2 buffer layers deposited by chemical bath deposition(CBD) on Cu(In,Ga)(S,Se) 2 (CIGSS) absorbers are investigated. Due to the aqueous nature of the CBD process, oxygen and hydrogen were incorporated into the ‘ZnSe’ buffer layer mainly in the form of Zn(OH) 2 as is shown by X-ray photoelectron spectroscopy and nuclear reaction analysis (NRA) measurements leading to the nomenclature ‘Zn(Se,OH)’. Prior to the deposition of Zn(Se,OH), a zinc treatment of the absorber was performed. During that treatment a layer mainly consisting of Zn(OH) 2 grew to a thickness of several nanometer. The whole buffer layer therefore consists of a Zn(Se,OH)/Zn(OH) 2 structure on CIGSS. Part of the Zn(OH) 2 in both layers (i.e. the Zn(Se,OH) and the Zn(OH) 2 layer) might be converted into ZnO during measurements or storage. Scanning electron microscopy pictures showed that a complete coverage of the absorber with the buffer layer was achieved. Transmission electron microscopy revealed the different regions of the buffer layer: An amorphous area (possibly Zn(OH) 2 ) and a partly nanocrystalline area, where lattice planes of ZnSe could be identified. Solar cell efficiencies of ZnO/Zn(Se,OH)/Zn(OH) 2 /CIGSS devices exceed 14% (total area).

Conductivity of nanometer-sized ion tracks in diamond-like carbon films

Amorphous diamond-like carbon films were irradiated with high-energy heavy ions like 1 GeV uranium or 340 MeV gold. The large energy deposition along the ion track leads to a transformation of the material from insulating diamond-like to conducting graphite-like carbon. The ion tracks form thin straight channels (nanowires) with a diameter of approximately 8 nm and a conductivity of the order of 1–10 S/cm. The conductivity in the tracks is up to eight orders of magnitude larger than in the surrounding material. The surface topography and the conduction properties of these channels were studied with an atomic force microscope.

Hydrogen implantation and diffusion in silicon and silicon dioxide

Depth profiles of hydrogen implanted into crystalline silicon in random direction at different fluences have been measured by the15N technique and by SIMS. Whereas hydrogen implanted at a fluence of 1015 ions/cm2 shows some limited mobility, no such mobility is observed for higher implantation fluences. In these cases, ballistic computer codes describe the depth distributions well, within the ranges of both experimental and theoretical accuracy. Annealing up to 510 K does not change the hydrogen distributions.Furthermore, high-fluence hydrogen implantation into silicon dioxide has been examined. There is some indication for radiation-enhanced diffusion during the implantation process. Upon subsequent thermal annealing, the hydrogen is found to diffuse, probably via a trapping/detrapping mechanism associated with an OH/H2 transformation of the hydrogen bonding.

Ion induced nanoscale surface ripples on ferromagnetic films with correlated magnetic texture

We have investigated the correlation between nanoscale surface ripple patterns and the magnetic texture of polycrystalline iron and nickel thin films. The ripple patterns were created by ion beam sputter erosion of films evaporated on Si substrates with 5 keV Xe ions under grazing incidence and fluences between 1015 and 1017 cm−2. The as-deposited films with an rms roughness of about 1 nm are magnetically isotropic. Sputter erosion reduced the coercive field of the films for all erosion conditions investigated. Sputter erosion at an incidence angle of 80° with respect to the surface normal produces rather smooth films and for ion fluences exceeding 1 × 1016 cm−2 formation of ripples parallel to the ion beam direction with wavelength between 30 and 80 nm is observed. Magneto-optical Kerr effect (MOKE) measurements reveal a pronounced uniaxial magnetic anisotropy of the only 1–2 nm thin irradiated surface region of the films with orientation parallel to the ripple orientation and also parallel to the ion beam direction. Almost complete sputter erosion of Fe films resulted in the formation of Fe nanorods oriented parallel to the ion beam direction with 100% uniaxial magnetic texture.

Conductivity of ion tracks in diamond-like carbon films

AbstractHigh-energy heavy ions (e.g. 1 GeV uranium ions ) passing through a diamond-like carbon (DLC ) film create conductingtracks along their path. The conductivity of these channels is due to a conversion of diamond sp bonds to graphite sp bonds 32 caused by the large energy deposited along the ion track. The tracks have a diameter of approximately 10 nm and representconducting filaments embedded in the insulating diamond-like matrix. They might be used as electron field emitters in vacuumelectronic devices. 2003 Elsevier Science B.V. All rights reserved. Keywords: Diamond-like carbon, Ion tracks, Field emission, Nanostructures 1. IntroductionFig. 1 shows the concept of a field emission cathodebased on ion tracks in diamond-like carbon films. Theelectron–emitting layer consists of an amorphous dia-mond-like carbon (DLC ) film containing cylindrical iontracks as conductive filaments. These tracks are createdwhen energeticheavy ions pass through the DLC layerw1,2x. The large energy deposition along the ion pathleads to graphitization of the material within a cylindri-cal zone of a few nanometers in diameter. These con-ducting channels facilitate the electron transport fromthe back contact to the surface. Due to their large aspectration, field emission of electrons is expected and hasto be investigated.In this paper, we report the characterization of theseion tracks by means of scanning force microscopy(SFM ). Some preliminary measurements on the fieldemission behavior were performed.2. Experimental detailsThe DLC films were produced by ion deposition onheavily doped Si substrates. Two different methods, the

Magnetic texturing of ferromagnetic thin films by sputtering induced ripple formation

Ripple patterns created by sputter erosion of iron thin films induce a correlated magnetic texture of the surface near region. We investigated the magnetic anisotropy as a function of the residual film thickness and determined the thickness of the magnetically anisotropic layer as well as the magnitude of the magnetic anisotropy using by magneto-optical Kerr effect (MOKE) and Rutherford backscattering spectroscopy measurements. Ripple patterns were created by sputter erosion with 5keV Xe ions under grazing incidence of 80° with respect to the surface normal. For ion fluences of above 1×1016cm−2, the formation of ripples, with wavelengths between 30 and 80nm oriented parallel to the ion beam direction, is observed. MOKE measurements reveal a pronounced uniaxial magnetic anisotropy of the surface region of the films with orientation parallel to the ripple orientation and the ion beam direction. We find a layer thickness of 12±3nm, in accordance with the average grain size. The magnetic anisotropy within thi...

Measurement and analysis of hydrogen depth profiles in MOS-structures by using the 15N nuclear reaction method

Abstract The application of the 1H(15N, αγ)12C nuclear reaction analysis method promises to become the preferred measurement tool for hydrogen depth profiling in solids. A depth resolution of approximately 5 nm in the near surface region and a sensitivity

Study of hydrogen incorporation in MOS-structures after various process steps using nuclear reaction analysis (NRA)

Abstract We present hydrogen depth profiles in thin multilayer films determined by the use of the 1 H( 15 N,αγ) 12 C nuclear reaction analysis method. Samples of aluminum gate MOS capacitors with a different annealing history show significant differences in hydrogen content in the bulk SiO 2 as well as at the interfaces of the MOS system. The measured profiles are brought into correlation with the radiation induced increase of oxide charge density N ot and interface state density N it . Along with this study we describe the use of a computer program to simulate the folding of certain model hydrogen profiles with the excitation function of the NRA method to get the true hydrogen distribution out of the measured gamma ray yield.

Nano-hillock formation in diamond-like carbon induced by swift heavy projectiles in the electronic stopping regime: Experiments and atomistic simulations

The formation of surface hillocks in diamond-like carbon is studied experimentally and by means of large-scale molecular dynamics simulations with 5 × 106 atoms combined with a thermal spike model. The irradiation experiments with swift heavy ions cover a large electronic stopping range between ∼12 and 72 keV/nm. Both experiments and simulations show that beyond a stopping power threshold, the hillock height increases linearly with the electronic stopping, and agree extremely well assuming an efficiency of approximately 20% in the transfer of electronic energy to the lattice. The simulations also show a transition of sp3 to sp2 bonding along the tracks with the hillocks containing almost no sp3 contribution.

Self-aligned nanostructures created by swift heavy ion irradiation

In tetrahedral amorphous carbon (ta-C) swift heavy ions create conducting tracks of about 8 nm in diameter. To apply these nanowires and implement them into nanodevices, they have to be contacted and gated. In the present work, we demonstrate the fabrication of conducting vertical nanostructures in ta-C together with self-aligned gate electrodes. A multilayer assembly is irradiated with GeV heavy ions and subsequently exposed to several selective etching processes. The samples consist of a Si wafer as substrate covered by a thin ta-C layer. On top is deposited a SiNx film for insulation, a Cr layer as electrode, and finally a polycarbonate film as ion track template. Chemical track etching opens nanochannels in the polymer which are self-aligned with the conducting tracks in ta-C because they are produced by the same ions. Through the pores in the polymer template, the Cr and SiNx layers are opened by ion beam sputtering and plasma etching, respectively. The resulting structure consists of nanowires embed...