HFCVD of diamond at low substrate and low filament temperatures

It has been discovered that the addition of a small amount of oxygen to the CH{sub 4} and H{sub 2} feed gas permits HFCVD of diamond at significantly lower filament and substrate temperatures. The effective O/C ratio here is much lower than that used in most studies of the oxygen effect. Careful control of the O/C and C/H ratios were found to be crucial to success. The effects of substrate and filament temperatures on growth rate and film quality were studied. Optimum conditions were found that gave reasonable growth rates ( {approximately}0.5 {mu}m/h ) with high film quality at filament temperatures below 1750{degrees}C and substrate temperatures below 600C. As a result, low temperature deposition has been realized. Power consumption can be reduced 50%, and the filament lifetime is extended indefinitely

Multi-photon ionisation spectroscopy for rotational state preparation of N+2

In this paper we investigate the 2 + 1′ resonance enhanced multi-photon ionisation (REMPI) of molecular nitrogen via the a1Πg(v = 6) intermediate state and analyse its feasibility to generate molecular nitrogen ions in a well defined ro-vibrational state. This is an important tool for high precision experiments based on trapped molecular ions, and is crucial for studying the time variation of the fundamental constant mp/me using N+2. The transition is not reported in the literature and detailed spectral analysis has been conducted to extract the molecular constants of the intermediate state. By carefully choosing the intermediate ro-vibrational state, the ionisation laser wavelength and controlling the excitation laser pulse energy, unwanted formation of rotationally excited molecular ions can be suppressed and ro-vibrational ground state ions can be generated with high purity

Laser ionization of molecular clusters

Multiphoton ionization coupled with mass spectrometry was used to investigate molecular cluster distributions. Three examples will be discussed in this presentation. First, in studies of neat nitric oxide clusters, (NO){sub m}, an interesting odd-even intensity alternation was observed and will be discussed in terms of electron-pairing considerations. In a separate study, the binary clusters comprising nitric oxide and methane preferentially form a stoichiometric cluster made up of repeating units of (NO){sub 2}CH{sub 4}. These presumably represent a particularly strongly bound {open_quotes}van der Waals{close_quotes} subunit. Finally, in similar studies of neat carbon disulfide clusters, (CS{sub 2}){sub m}, additional photon absorption after the two-photon ionization step stimulates a series of intracluster ion-molecular reactions leading to formation of S{sub m}{sup +} and (CS){sub m}{sup +} polymers, as well as intermediate species such as S{sub m}{sup +} (CS{sub 2}). This molecular cluster analogue of {open_quotes}laser snow{close_quotes} will be described in detail

Fluorometric Measurement and Modeling of Droplet Temperature Changes in an Electrospray Plume

The evolution of droplet temperatures in an electrospray plume was measured via ratiometric fluorescence. Under typical operating conditions, droplet temperatures decrease ∼30 K over the first 5.0 mm along the spray axis, followed by a slight (∼2–3 K) rewarming. Experimental axial profiles (<i>Z</i>-axis) were fit by use of diffusion-controlled and surface-controlled evaporation models. Both models fit the experimental data well for the cooling portion of the spray (Pearson correlation coefficient <i>R</i> ≥ 0.994), but the surface-controlled model required unrealistic droplet radius values to obtain a good fit. In lateral profiles at a given <i>Z</i> near the emitter tip, temperatures are lower (by 3.0–10 K) in the periphery than on the spray axis. This behavior is consistent with the expected enrichment of the spray periphery with smaller droplets. At longer axial distances, lateral profiles were relatively flat. Droplet temperature as a function of axial displacement fell more rapidly at lower liquid flow rates, possibly attributable to changes in droplet size and/or velocity with flow rate