Atomic layer deposition of cobalt using H\u3csub\u3e2\u3c/sub\u3e-, N\u3csub\u3e2\u3c/sub\u3e-, and NH\u3csub\u3e3\u3c/sub\u3e-based plasmas:on the role of the Co-reactant

\u3cp\u3eThis work investigates the role of the co-reactant for the atomic layer deposition of cobalt (Co) films using cobaltocene (CoCp\u3csub\u3e2\u3c/sub\u3e) as the precursor. Three different processes were compared: an AB process using NH\u3csub\u3e3\u3c/sub\u3e plasma, an AB process using H\u3csub\u3e2\u3c/sub\u3e/N\u3csub\u3e2\u3c/sub\u3e plasma, and an ABC process using subsequent N\u3csub\u3e2\u3c/sub\u3e and H\u3csub\u3e2\u3c/sub\u3e plasmas. A connection was made between the plasma composition and film properties, thereby gaining an understanding of the role of the various plasma species. For NH\u3csub\u3e3\u3c/sub\u3e plasma, H\u3csub\u3e2\u3c/sub\u3e and N\u3csub\u3e2\u3c/sub\u3e were identified as the main species apart from the expected NH\u3csub\u3e3\u3c/sub\u3e, whereas for the H\u3csub\u3e2\u3c/sub\u3e/N\u3csub\u3e2\u3c/sub\u3e plasma, NH\u3csub\u3e3\u3c/sub\u3e was detected. Moreover, HCp was observed as a reaction product in the precursor and co-reactant subcycles. Both AB processes showed self-limiting half-reactions and yielded similar material properties, that is, high purity and low resistivity. For the AB process with H\u3csub\u3e2\u3c/sub\u3e/N\u3csub\u3e2\u3c/sub\u3e, the resistivity and impurity content depended on the H\u3csub\u3e2\u3c/sub\u3e/N\u3csub\u3e2\u3c/sub\u3e mixing ratio, which was linked to the production of NH\u3csub\u3e3\u3c/sub\u3e molecules and related radicals. The ABC process resulted in high-resistivity and low-purity films, attributed to the lack of NH\u3csub\u3ex,x≤3\u3c/sub\u3e species during the co-reactant exposures. The obtained insights are summarized in a reaction scheme where CoCp\u3csub\u3e2\u3c/sub\u3e chemisorbs in the precursor subcycle and NH\u3csub\u3ex\u3c/sub\u3e species eliminate the remaining Cp in the consecutive subcycle.\u3c/p\u3

Atomic layer deposition of aluminum fluoride using Al(CH\u3csub\u3e3\u3c/sub\u3e)\u3csub\u3e3\u3c/sub\u3e and SF\u3csub\u3e6\u3c/sub\u3e plasma

\u3cp\u3eMetal fluorides typically have a low refractive index and a very high transparency and find many applications in optical and optoelectronic devices. Nearly stoichiometric, high-purity AlF\u3csub\u3e3\u3c/sub\u3e films were deposited by atomic layer deposition (ALD) using trimethylaluminum [Al(CH\u3csub\u3e3\u3c/sub\u3e)\u3csub\u3e3\u3c/sub\u3e] and SF\u3csub\u3e6\u3c/sub\u3e plasma. Self-limiting growth was confirmed and the growth per cycle was determined to range from 1.50 Å to 0.55 Å for deposition temperatures between 50 °C and 300 °C. In addition, the film density of ∼2.8 g cm\u3csup\u3e-3\u3c/sup\u3e was found to be relatively close to the bulk value of 3.1 g cm\u3csup\u3e-3\u3c/sup\u3e. Vacuum ultraviolet spectroscopic ellipsometry measurements over the wavelength range of 140-2275 nm showed a refractive index n of 1.35 at 633 nm, and an extinction coefficient k of <10\u3csup\u3e-4\u3c/sup\u3e above 300 nm, for all deposition temperatures. Optical emission spectroscopy during the SF\u3csub\u3e6\u3c/sub\u3e plasma exposure step of the ALD cycle revealed the formation of C\u3csub\u3e2\u3c/sub\u3eH\u3csub\u3e2\u3c/sub\u3e and CF\u3csub\u3e2\u3c/sub\u3e species, resulting from the interaction of the plasma with the surface after Al(CH\u3csub\u3e3\u3c/sub\u3e)\u3csub\u3e3\u3c/sub\u3e exposure. On the basis of these results, a reaction mechanism is proposed in which F radicals from the SF\u3csub\u3e6\u3c/sub\u3e plasma participate in the surface reactions. Overall, this work demonstrates that SF\u3csub\u3e6\u3c/sub\u3e plasma is a promising co-reactant for ALD of metal fluorides, providing an alternative to co-reactants such as metal fluorides, HF, or HF-pyridine.\u3c/p\u3

Atomic layer deposition of molybdenum oxide from (NtBu)2(NMe2)2Mo and O2 plasma

Molybdenum oxide (MoO x ) films have been deposited by atomic layer deposition using bis(tert-butylimido)-bis(dimethylamido)molybdenum and oxygen plasma, within a temperature range of 50–350¿°C. Amorphous film growth was observed between 50 and 200¿°C at a growth per cycle (GPC) around 0.80¿Å. For deposition temperatures of 250¿°C and higher, a transition to polycrystalline growth was observed, accompanied by an increase in GPC up to 1.88¿Å. For all deposition temperatures the O/Mo ratio was found to be just below three, indicating the films were slightly substoichiometric with respect to MoO3 and contained oxygen vacancies. The high purity of the films was demonstrated in the absence of detectable C and N contamination in Rutherford backscattering measurements, and a H content varying between 3 and 11 at. % measured with elastic recoil detection. In addition to the chemical composition, the optical properties are reported as well

Influence of magnetic configuration on edge turbulence and transport in the H-1 Heliac

\u3cp\u3eThe role of the rotational transform (ι) profile on fluctuations and transport is investigated in the H-1 Heliac by means of dynamic (i.e. changing during a shot) and static (fixed during a shot) scans of rotational transform through a range of values where the electron density drops markedly and which correspond to having the point of ℓ located near r/a = 0.75 in a region of magnetic well (such that the surface averaged magnetic field strength increases with radius). The gap is near the ℓ = 4/3 resonance, but as the resonance is not in the plasma for more than half the gap it is not clear that this is relevant. Although this drop is clearly driven by the variation of helical current, under particular circumstances, similar density changes occur spontaneously. Plasma currents are measured throughout the scan and are found to slightly affect the rotational transform profile, and reverse about the configuration of minimum confinement, while induced currents through a toroidal loop voltage in the dynamical scans are not found to be significant. The confinement and fluctuation properties are studied by means of 2D movable Langmuir probes. Large near edge-localised dithering quasi-coherent fluctuations at ∼ 6 kHz develop in a strong density gradient region with low magnetic shear as ι is scanned up to a point where the density collapses in the outer region. This dithering corresponds to an m = 3 mode comprising of standing and propagating components. The net and fluctuation-induced transport components are measured near the plasma edge in a similar discharge, and it is found that fluctuation-induced transport driven by these low frequency coherent modes dominates the particle balance during the low density phase but is only a small component of the net flux when the density is higher.\u3c/p\u3

Concepts and prospects of passivating contacts for crystalline silicon solar cells

\u3cp\u3eTo further increase the conversion efficiency of crystalline silicon solar cells it is vital to reduce the recombination losses between the photoactive part of the solar cell and the metal contacts. This is ideally achieved by fabricating contacts which passivate defects at the silicon surface while being simultaneously selective for only a single type of charge carrier, i.e. either electrons or holes. Despite the extensive research effort aimed at realizing such contacts, no clear overview of the fundamental physics of passivating contacts has appeared yet. Therefore, we present such an overview, introduce a clear classification of passivating contacts, and discuss their design guidelines and future prospects\u3c/p\u3