Source Boat Research Articles

Mechanism for the separation of organic semiconductors via thermal gradient sublimation

Two common hole transporting materials, N,N′-di(1-naphthyl)-N,N′-diphenyl-(1,1′-biphenyl)-4,4′-diamine (NPD) and tris(4-carbazoyl-9-ylphenyl)amine (TCTA) are separated and purified using thermal gradient sublimation. Their sublimation rates are proportional to the tube diameter squared and inversely proportional to the distance from the source boat to the deposition region. The deposition of these materials exponentially decays with distance down the tube. A theory predicting these results is derived. This theory suggests that diffusion and surface capture are the dominant steps in this purification, not processes in the source boat. It provides a rationale for improving the separation between multiple components and suggests routes for producing larger quantities of these materials.

Solid-State Acquisition of Fingermark Topology using Dense Columnar Thin Films

Various vacuum techniques are employed to develop fingermarks on evidentiary items. In this work, a vacuum was used to deposit columnar thin films (CTFs) on untreated, cyanoacrylate-fumed or dusted fingermarks on a limited selection of nonporous surfaces (microscope glass slides and evidence tape). CTF deposition was not attempted on fingermarks deposited on porous surfaces. The fingermarks were placed in a vacuum chamber with the fingermark side facing an evaporating source boat containing either chalcogenide glass or MgF(2). Thermal evaporation of chalcogenide glass or MgF(2) under a 1 μTorr vacuum for 30 min formed dense CTFs on fingermark ridges, capturing the topographical features. The results show that it is possible to capture fingermark topology using CTFs on selected untreated, vacuumed cyanoacrylate-fumed or black powder-dusted nonporous surfaces. Additionally, the results suggested this might be a mechanism to help elucidate the sequence of deposition.

Production of stable tellurium evaporated targets

Due to the low melting point of tellurium metal, self-supporting Te targets degrade quickly when exposed to particle beams. This situation is greatly improved if the tellurium material is evaporated onto C foil backings. Elastic scattering in target and backing layers broadens the Te peak, making measurements difficult, while too little material reduces the reaction rate. Therefore, it is necessary to optimize the target thickness. Evaporated metallic and oxide Te targets were prepared at Argonne National Laboratory by vacuum deposition from a resistively heated source boat. The stability of the targets was then tested by exposing them to a varying intensity alpha beam with an energy range from 17 to 27 MeV using the FN Tandem Van de Graaff accelerator at the University of Notre Dame. Optimal target thicknesses and beam currents were then obtained for p-process experiments. A description of the apparatus and production method will be presented.

Experimental design for acoustic characterization of a seismic exploration airgun array

The Littoral Acoustic Demonstration Center (LADC) (participating institutions given in author list) is scheduled to perform an experiment in the Gulf of Mexico to characterize the underwater acoustic field of a seismic exploration airgun array. The design is constrained by the array lengths and hydrophone spacings of the ten four‐channel LADC calibrated environmental acoustic recording system (EARS) buoys available for the measurements. Placement of the EARS arrays is determined to achieve best the design goals, given the constraints. The fixed mooring EARS hydrophone depths will vary from 100 to 1171 m, and near‐surface ship‐deployed phones will be used for shallower depths. Straight‐line source boat paths of varying length and spacing have been calculated that redundantly fill all solid angle bins whose size is determined by small uncertainties in the array location and orientation [Robert Laws (2006), private communication]. Shot spacing is also a factor. Care is taken to have nearby shots to the EARS arrays for all bins. All direct paths are calculated including refraction. Data are presented in spherical and planar images to show angular and bin coverages and shot ranges. [Work supported in part by the Joint Industry Project through the International Association of Oil and Gas Producers.]

Improved evaporation geometry for powdered materials

This note reports the design of an improved evaporation geometry for the deposition of thin films of powdered materials. The geometry makes use of the fact that if the powdered material is heated in a chamber covered with two perforated strips with perforations misaligned, the paths for particle ejection are eliminated and reproducible pin-hole free film deposition is observed. The geometry is found to be compatible with other materials which do not react with the source boat construction material.

The measurement of electrical properties of uncontaminated PbTe films prepared by molecular beam deposition

Describes the methods used to prepare uncontaminated PbTe films on mica substrates by molecular beam deposition from a single source boat and the techniques used to make in situ electrical measurements on the films down to 100K. The as-grown carrier concentration was found to be determined by source conditions and controllable n-type carrier concentrations between 1022 and 5*1024 m-3 could be obtained. Measurements on films having the lowest carrier concentration indicated that they contained a low residual doping level (<1021 m-3). Room-temperature Hall mobilities improved as the runs progressed and a maximum value of 0.195 m2 V-1 s-1 was obtained. Films with carrier concentrations greater than 5*1023 m-3 had field effect mobilities of approximately 0.08 m2 V-1 s-1. Exposure of the films to low pressures of oxygen after growth enabled the n-type doping to be reduced to any level down to intrinsic carrier concentrations.