Wet chemical etching mechanism of silicon

We review what can be said on wet chemical etching of single crystals from the viewpoint of the science of crystal growth. Starting point is that there are smooth and rough crystal surfaces. The kinetics of smooth faces is controlled by a nucleation barrier that is absent on rough faces. The latter therefore etch faster by orders of magnitude. The analysis of the diamond crystal structure reveals that the {111} face is the only smooth face in this lattice-other faces might be smooth only because of surface reconstruction. In this way we explain the minimum of the etch rate in KOH:H2O in the <001> direction. Two critical predictions concerning the shape of the minimum of the etch rate close to <001> and the transition from isotropic to anisotropic etching in HF:HNO3 based solutions are tested experimentally. The results are in-agreement with the theor

Chemiluminescent measurement of atmospheric acid

The design and construction of a gas phase acid sensitive analyzer are reported. These studies showed that the chemical system was a practical analytical method. A complete instrument was developed and prepared for field testing. A Titan 3-C rocket was scheduled for launching on February 11, 1974. Through preparations made by NASA Langley the instrument was set up to monitor the acid concentration in the rocket exhaust. Due to adverse wind conditions no acid was detected. This entire trip is described in detail

Preparing multi-partite entanglement of photons and matter qubits

We show how to make event-ready multi-partite entanglement between qubits which may be encoded on photons or matter systems. Entangled states of matter systems, which can also act as single photon sources, can be generated using the entangling operation presented in quant-ph/0408040. We show how to entangle such sources with photon qubits, which may be encoded in the dual rail, polarization or time-bin degrees of freedom. We subsequently demonstrate how projective measurements of the matter qubits can be used to create entangled states of the photons alone. The state of the matter qubits is inherited by the generated photons. Since the entangling operation can be used to generate cluster states of matter qubits for quantum computing, our procedure enables us to create any (entangled) photonic quantum state that can be written as the outcome of a quantum computer.Comment: 10 pages, 4 figures; to appear in Journal of Optics

Triangle Diagram with Off-Shell Coulomb T-Matrix for (In-)Elastic Atomic and Nuclear Three-Body Processes

The driving terms in three-body theories of elastic and inelastic scattering of a charged particle off a bound state of two other charged particles contain the fully off-shell two-body Coulomb T-matrix describing the intermediate-state Coulomb scattering of the projectile with each of the charged target particles. Up to now the latter is usually replaced by the Coulomb potential, either when using the multiple-scattering approach or when solving three-body integral equations. General properties of the exact and the approximate on-shell driving terms are discussed, and the accuracy of this approximation is investigated numerically, both for atomic and nuclear processes including bound-state excitation, for energies below and above the corresponding three-body dissociation threshold, over the whole range of scattering angles.Comment: 22 pages, 11 figures, figures can be obtained upon request from the Authors, revte

Locoregional hyperthermia of deep-seated tumours applied with capacitive and radiative systems. A simulation study

Background: Locoregional hyperthermia is applied to deep-seated tumours in the pelvic region. Two very different heating techniques are often applied: capacitive and radiative heating. In this paper, numerical simulations are applied to compare the performance of both techniques in heating of deep-seated tumours. Methods: Phantom simulations were performed for small (30 × 20 × 50 cm 3 ) and large (45 × 30 × 50 cm 3 ), homogeneous fatless and inhomogeneous fat-muscle, tissue-equivalent phantoms with a central or eccentric target region. Radiative heating was simulated with the 70 MHz AMC-4 system and capacitive heating was simulated at 13.56 MHz. Simulations were performed for small fatless, small (i.e. fat layer typically 3 cm) patients with cervix, prostate, bladder and rectum cancer. Temperature distributions were simulated using constant hyperthermic-level perfusion values with tissue constraints of 44 °C and compared for both heating techniques. Results: For the small homogeneous phantom, similar target heating was predicted with radiative and capacitive heating. For the large homogeneous phantom, most effective target heating was predicted with capacitive heating. For inhomogeneous phantoms, hot spots in the fat layer limit adequate capacitive heating, and simulated target temperatures with radiative heating were 2–4 °C higher. Patient simulations predicted therapeutic target temperatures with capacitive heating for fatless patients, but radiative heating was more robust for all tumour sites and patient sizes, yielding target temperatures 1–3 °C higher than those predicted for capacitive heating. Conclusion: Generally, radiative locoregional heating yields more favourable simulated temperature distributions for deep-seated pelvic tumours, compared with capacitive heating. Therapeutic temperatures are predicted for capacitive heating in patients with (almost) no fat