Room Temperature Annealing Research Articles

Initial growth of Al 2 O 3 on NiAl(001)

O3 films were prepared by oxygen exposure at room temperature and subsequent annealing. The initial stages of oxidation such as the reconstruction of the clean NiAl(001) surface, oxygen adsorption on the bare surface, and finally the growth of the ordered Al2O3 films on a NiAl(001) have been explained on the basis of scanning tunnelling microscopy (STM) measurements. The main result is the identification of the oxide growth of ordered Al2O3 as a thermally activated, fast, local ordering process of a precovered amorphous oxide phase arising from oxygen stimulated Al segregation after exposure at room temperature. The surface morphology is determined by the density of the disordered Al2O3 nuclei in the amorphous oxide phase which can be controlled by oxygen exposure.

Growth of Al 2O 3 stripes in NiA(001)

Structure and growth mechanism of ultra-thin Al 2O 3 films on NiAl(001) have been investigated with 180°-neutral impact collision ion scattering spectroscopy, high resolution spot profile analysis of low energy electron diffraction, and scanning tunnelling microscopy (STM). Ordered Al 2O 3 films have been prepared by oxygen exposure at room temperature and subsequent annealing at T = 1200 K. The formation of epitaxial oxide films is unaffected by the initial composition or reconstruction of the substrate. The oxidized surface being covered by Al 2O 3 appears to be microscopically rough, reversible stepped with step heights of about 3 Å and consists of a network of elongated equally distributed oxide stripes along 〈100〉 and 〈010〉 directions of the NiAl(001) surface. The lateral anisotropy of the oxide is probably caused by the build up of internal stress in the growth process. After oxygen saturation exposure at room temperature and subsequent annealing, regions with rather regular arranged parallel oxide stripes show up in the STM images (mean width ≈ 27 A ̊ , period ≈ 54 A ̊ ). The corresponding low energy electron diffraction pattern shows the existence of orthogonal (2 × 1) antiphase domains with a (9 × 1) superstructure (period 26.02 Å) close to the mean width of oxide stripes. Next to the oxide stripes, regrowing NiAl terraces and thin layers of amorphous Al 2O 3 have been found.

Long term instabilities in the defect assembly in irradiated high resistivity silicon detectors

Transformation of radiation induced, carbon related defects in high resistivity silicon detectors under multistep irradiation and annealing has been investigated in connection with the problem of reverse annealing of the effective space charge concentration, N/sub eff/, in the space charge region of irradiated detectors. Kinetic behavior of these defects as possible candidates which affect N/sub eff/ has been studied using C-DLTS (capacitance deep level transient spectroscopy) technique after room temperature and elevated temperature annealing. Defect transformation has been identified in the form the decay of radiation induced interstitial carbon, which follows the equation of a first order reaction, and the simultaneous generation of C/sub i/-O/sub i/ and C/sub i/-C/sub s/ complexes. It has been shown that the concentration of the C/sub i/-O/sub i/ complex increased at RT (room temperature, 22/spl deg/C) annealing and obeyed the second order reaction. Successive steps of irradiation and annealing were performed, which stimulated excessive concentration of the C/sub i/-O/sub i/ complex; it also generated additional centers in silicon detectors with increased oxygen content from heat treatment applied in the detector manufacturing. The results imply that the instability in the defect assembly in irradiated silicon can arise from the complexes including impurities of carbon and oxygen.

Room temperature reduction of MERIE-like plasma-induced interface states

The possibility for room temperature annealing of defects in MOS capacitors, induced from a MERIE-like reactor, has been investigated. It is established that, as time proceeds, plasma induced interface states density only decreases (3–5 times), but interface states are not completely annealed. The reduction depends only on the starting post-plasma treatment level of interface states. If the plasma conditions lead to an interface state level of ∼10 12–10 13 cm −2 eV −1, a reduction occurs. The results demonstrate that the effects responsible for room temperature reduction of the plasma defects take place very close to the Si–SiO 2 interface. (The fixed oxide charge is stable and it does not change at all.) The process seems to be controlled by moisture transport to the Si–SiO 2 interface.

Direct current electrical conductivity of a Ge - Au composite thin film near the critical threshold

The Ge - Au polycrystalline film was prepared by room-temperature ageing and thermal annealing with amorphous film. A transmission electron microscopy investigation showed that the Au grains grow from a size of 10 nm in the unannealed sample to a size of 100 nm in the annealed sample. The correlation length was calculated in order to give a description of morphology geometry. The DC electrical resistance was measured over the temperature range of 77 - 300 K. Percolation theory was used to interpret the conductivity dependence on metal content, which can be expressed as , where is about 50.45% and t is about 1.34 for unannealed samples and 1.55 for annealed samples. The similar electrical conductance of the unannealed and annealed samples shows that the electrical conductivity is not sensitive to the growth of Au grains.

Correlation between latent interface trap buildup and 1/f noise in metal–oxide–semiconductor transistors

A long-term delayed increase in the 1/f noise of p-channel metal–oxide–semiconductor (MOS) transistors is observed in devices that show significant latent interface-trap buildup after exposure to ionizing radiation. During positive-bias postirradiation anneal, the noise increases by more than an order of magnitude above the level observed after irradiation. The increase in noise precedes the latent buildup of interface traps by at least 4.5 days during room-temperature annealing, and by ∼1 h during 100 °C annealing. The time and temperature dependencies of the increases in noise and interface trap buildup are consistent with the thermally activated motion of protons into the near-interfacial region of the oxide, followed by increases in border trap and interface trap densities. These results suggest hydrogen-related species can significantly affect the 1/f noise of MOS devices.

Electron Scattering by Mn Impurities in Si Detected by Cyclotron Resonance Measurement

In this paper, we report on investigation of the low-temperature transport properties of silicon doped with transition metals, using the cyclotron resonance technique. For clarification of the states of metal impurities in silicon, secondary ion mass spectroscopy (SIMS), deep level transient spectroscopy (DLTS), and electron spin resonance (ESR), photoluminescence (PL) and Hall measurements were also performed. It was shown that of the various transition metals used, only manganese significantly affects the probability of electron scattering. The inverse relaxation time obtained from the cyclotron resonance linewidth varies with the square root of temperature. This temperature dependence cannot be explained by the typical scattering theories such as neutral shallow impurity scattering and ionized impurity scattering. We used high-resistivity silicon to display the contribution of transition metals effectively. Transition metals were doped by thermal diffusion at 1100°C after being evaporated onto the silicon surface. ESR measurements revealed the existence of interstitial manganese, while Hall measurements revealed a rather high density of Mn clusters. Following room temperature annealing, the intensity of the ESR signal for interstitial manganese rapidly decreased due to clustering, while the density of Mn clusters and the inverse relaxation time did not change significantly. Thus, the electron scattering was mainly caused by manganese clusters efficiently produced in the pure silicon host.

BaLiF 3(Eu 2+): A promising X-ray storage phosphor

The TSL glow of X-irradiated BaLiF 3 crystallite vanished within 15 min of sunlight bleaching or after 2~3 days of room temperature annealing, which indicate that X-irradiation damage is light and can be easily erased. It is also found that BaLiF 3:Eu 2+ is photostimulatable and seems be a promising X-ray storage phosphor for practical utilization.

Photoluminescence of laser ablated silicon

The change in silicon morphology can induce silicon to luminescence in the visible spectrum range. Several examples were reported; porous silicon[1], spark eroded silicon[2], and plasma deposited silicon cluster[3]. In this report we used a Nd-YAG laser to ablate single crystal silicon, and anodically prepared porous silicon. The ablated sites were subjected to photoluminescence measurement. The 325 nm line of HeCd laser was used for excitation, and a photoluminescence spectrum with a peak at about 450 nm was obtained. However, this peak was only observed after the samples were exposed to air for several days. The violet photoluminescence spectrum was considered to be due to room temperature annealing of ablated sites.

A study of ageing in an AlCuMgZn foundry alloy

A coupled differential scanning calorimetry (DSC) and transmission electron microscopy (TEM) study of the ageing mechanism at 190 °C after solution treatment, quenching and room temperature annealing was carried out for an Al Cu4.5 Mg0.35 Zn3 foundry alloy of standard 249.0. It was found that three different precipitation sequences are present during the ageing process: ( i ) α sss → GPZ → θ " → θ ' → θ – CuA l 2 ( ii ) α sss → GPBZ → S ' → S – CuMgA l 2 ( iii ) α sss → GPZI → GPZII → η ' − η - MgZ n 2 There are no indications of possible interactions between the different sequences which seem to develop independently. The sequence based on the θ-CuAl 2 phase is clearly accelerated in comparison with AlCuMg alloys having the same Cu:Mg ratio already investigated and reported in literature. In particular GPZ, θ″ and θ′ precipitates are already detected after room temperature annealing, and a number of equilibrium θ-phase particles is present after 15 min ageing at 190 °C, which grow during the annealing. The acceleration of the precipitation kinetics is explained in terms of a decrease in the stacking fault energy induced by the presence of Zn atoms.

Investigations of donor and acceptor removal and long term annealing in silicon with different boron/phosphorus ratios

Studies of radiation damage of silicon detectors have shown that in most elementary particle physics applications, the major problem caused by non-ionizing interactions in silicon will be the change in the concentration of the electrically active impurity states. For many silicon applications in high radiation environments, the increase in the relative acceptor concentration during long term room temperature annealing is the limiting factor. The first step in developing radiation hardened silicon is to identify the defects which are responsible for this effect. In earlier work, we developed a model which describes the experimentally observed fast neutron induced changes in the net electrically active impurity concentration and provides a method to determine the phosphorus and boron concentration of the starting material. Our previous work has been extended with experiments using silicon with different original boron/phosphorus ratios, larger neutron fluences and to long term room temperature annealing. The donor removal rate of phosphorus was measured and the acceptor removal rate of boron evaluated. Extending our model, we propose that slow restoration of the damage induced boron interstitial back to its original substitutional state is responsible for the acceptor increase observed during long term annealing. This model, which involves only the behavior of the known shallow donors and acceptors present in the starting material, fits our data and the data of other experimenters without the need to invoke unidentified deep levels.

Radiation damage of amorphous silicon, thin‐film, field‐effect transistors

The effect of 60Co radiation on the noise and drain-source current characteristics of hydrogenated amorphous silicon (alpha-Si:H) field-effect transistors (FETs) was examined as a function of dose to cumulative doses as high as approximately 2 x 10(4) Gy. Following these measurements, room-temperature and elevated-temperature annealing of induced radiation damage was examined. The FETs examined are representative of those incorporated in alpha-Si:H arrays under development for various x-ray medical imaging applications. No significant effect upon the noise characteristics of the FETs was observed as a result of the radiation. The predominant drain-source current effect with increasing dose was a shift of the transfer characteristic toward negative gate voltage and/or a decrease of the transfer characteristic subthreshold slope. This resulted in large increases in leakage current for gate voltages where the FETs were initially highly nonconducting. This leakage current increase was less pronounced for more negative gate voltages and was further diminished by maintaining the FETs at a more negative gate voltage during the irradiation. Following the radiation measurements, room-temperature annealing resulted in a 10% to 50% reduction in the leakage current in the first day followed by a logarithmic decrease thereafter. Elevated-temperature annealing for 2 h at 200 degrees C restored FET leakage current and threshold voltage properties to their preirradiation values. The irradiation effects are small for cumulative doses less than approximately 100 Gy, which is larger than the clinical lifetime dose for an imaging detector for chest radiography or for fluoroscopy (with infrequent exposure to the direct beam). For significantly higher dose applications such as mammography, fluoroscopy (with frequent direct beam exposure), and radiotherapy imaging, the results suggest that periodic elevated-temperature annealing or operation of the arrays at more negative gate voltages may be necessary.

Evidence for the interaction between room-temperature annealing after quenching and persistent photoconductivity in oxygen-deficient Y 1Ba 2Cu 3O x thin films

Room-temperature annealing effects in oxygen-deficient YBaCuO thin films and persistent photoconductivity are correlated phenomena. A photoresponse was induced by laser illumination ( t = 60 s, λ = 670 nm) at various stages during the long-term relaxation of the resistivity after quenching to room temperature. The magnitude of the photoresponse generated during each illumination event follows the progress of the annealing process in time.

Layered Structures HTSC/Ferroelectric, Prepared by Sputtering

We have investigated some formation features of thin film structures PZT/YBCO and YBCO/BSTO. PZT films have been synthesized by reactive ion beam sputtering of a multi-elemental metal target at room temperature and ex-situ annealing at 700-750°C. BSTO and YBCO films have been deposited in-situ by magnetron sputtering of stoichiometric ceramic targets in an Ar + 50% O 2 gas mixture (pure oxygen for BSTO) at temperature of 700°C. Si (100) buffered with TiN to prevent the diffusion in YBCO has been used as a substrate in the case PZT / YBCO. The layers YBCO / BSTO have been deposited on MgO (100). The substrates have been chosen according to prospective applications of PZT / YBCO as non-volatile memory cells integrated with existing CMOS transistor circuitry, and of YBCO/BSTO as voltage-tunable microwave devices Films with composition Pb(Zr 0.44 Ti 0.56 )O 3 have been obtained by sputtering of a target with a ratio of 13:36:51 for Pb, Sr and Ti, respectively. The measured dielectric constant at 1 MHz in the structures Au / PZT / YBCO / TiN / Si has been 540 and the -emnant polarization and coercive field values have been 5.4 μC/cm 2 and 25 kV/cm, respectively. Planar capacitors with a dielectric of BSTO thin film and YBCO electrodes have been produced and investigated as voltage-controlled devices at 1 MHz. A controllability of e(0V) /e(50V) = 1.6 has been demonstrated at 77 K. The dielectric hysteresis has been compared in capacitors with YBCO electrodes and with metal ones. It has been shown that the boundary phenomena at the interface of the epitaxially grown layers differ from that in the ferroelectric / metal structures and the hysteresis effect diminishes significantly,

Photoconductive analysis of defect density of hydrogenated amorphous silicon during room-temperature plasma posthydrogenation, light soaking, and thermal annealing.

The photoconductivity (${\ensuremath{\sigma}}_{\mathrm{ph}}$) of thin (\ensuremath{\le}1000 \AA{}) hydrogenated amorphous silicon films ($a$-Si:H) was measured as a function of time to monitor the defect density during remote inductively coupled plasma (ICP) posthydrogenation at room temperature, light soaking (performed both before and after posthydrogenation), and isothermal annealing (performed after posthydrogenation and light soaking), and fitted to a stretched exponential curve. A decrease of ${\ensuremath{\sigma}}_{\mathrm{ph}}(t)$ during posthydrogenation at room temperature was observed and related to the breaking of Si-Si weak bonds by individual hydrogen atoms. Upon thermal annealing, the initial equilibrium defect density was recovered. The stretched exponential parameters $\ensuremath{\beta}$ and $\ensuremath{\tau}$ of ${\ensuremath{\sigma}}_{\mathrm{ph}}(t)$ were the same for the isothermal anneals performed after light soaking and after plasma posthydrogenation, indicating that the defects introduced in both cases were of similar nature. The stretched exponential parameters $\ensuremath{\beta}$ and $\ensuremath{\tau}$ of ${\ensuremath{\sigma}}_{\mathrm{ph}}(t)$ were also the same for the light soaking before and after plasma posthydrogenation, suggesting that posthydrogenation did not alter the susceptibility of the material to light-induced degradation. $a$-Si:H samples deposited by remote ICP, hot-wire, and rf glow discharge were studied. The increase of hydrogen concentration in the samples during posthydrogenation was measured by infrared spectroscopy.

Large-shift Raman scattering features in superconducting YBa2Cu3O6+x.

We apply the large-shift Raman-scattering technique to explore the metal-insulator transition in ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{6+\mathit{x}}$. In a doping-dependence study for x\ensuremath{\sim}0 to 1, we find that the previously observed ${\mathit{A}}_{2\mathit{g}}$ scattering features near 1.5 eV split in energy as doping is increased and have increasingly mixed ${\mathit{A}}_{1\mathit{g}}$+${\mathit{A}}_{2\mathit{g}}$ symmetry. At the same time, the overall ${\mathit{A}}_{2\mathit{g}}$ Raman intensity decreases. We use an annealing/quenching technique on a x\ensuremath{\sim}0.4 sample to explore the transition region further, and find that the Raman intensity increases just after quenching but the peaks do not shift in energy. Room-temperature annealing of the quenched sample shows an initial drop in ${\mathit{A}}_{2\mathit{g}}$ peak intensity over 100 min, a plateau level from 100 to 500 min, and a final slow drop to the original intensity level from 500 to 1100 min. We see the suppressions of ${\mathit{A}}_{2\mathit{g}}$ Raman intensity from doping and annealing as resulting from increases in the carrier concentration. Peak splitting and mixed-symmetry effects seem to be more closely related to variations in the lattice parameters, probably as a result of changes to the in-plane copper d orbitals. \textcopyright{} 1996 The American Physical Society.

Role of Short-Range Order in Martensitic Transformation

Ohba, Otsuka and Sasaki [1] have established that the rubber-like behavior in the martensitic phase of Au-47.5at%Cd alloys cannot be caused by the change in the long-range order during the room temperature annealing. The rubber-like behavior should be understood in terms of the mechanical relaxation associated with the change in the orientation of the local short range order. It is proposed that, while the short-range order plays a prominent role in the rubber-like behavior in the martensite, it should play a comparably important role also in the austenite.

Sensitivity and fading of pMOS dosimeters with thick gate oxide

Abstract The sensitivity to irradiation and stability with annealing time after irradiation ('fading') of radiation-sensitive pMOS transistors with various gate-oxide thicknesses have been investigated. The obtained results show an improvement of the characteristics of the pMOS dosimeter with an increase of both the oxide thickness and gate bias, which means that the sensitivity increases while the fading decreases. The threshold-voltage shifts, during gamma irradiation as well as during room-temperature annealing, are analyzed in terms of the behavior of the positive gate-oxide charge density and interface trap density.

In-situ EPR study of room-temperature evolution of YBa 2Cu 3O 6+ x ceramics

Cu 2+ EPR has been used to study the process of room-temperature annealing in powdered YBa 2Cu 3O 6+ x (0 ≤ x ≤ 1) samples. The annealing and the consequent changes in the oxygen coordination of the Cu atoms in the basal plane do not affect the EPR signal. The results suggest that for both oxygen-deficient and oxygen-rich samples, the Cu 2+ EPR signal can arise only from defects unrelated to chain ordering. Samples exposed to ambient atmosphere exhibit growth of the EPR signal with time. The nature of this signal is discussed.

Study of the long term stability of the effective concentration of ionized space charges (N/sub eff/) of neutron irradiated silicon detectors fabricated by various thermal oxidation processes

Experimental study of the reverse annealing of the effective concentration of ionized space charges (N/sub eff/, also called effective doping or impurity concentration) of neutron irradiated high resistivity silicon detectors fabricated on wafers with various thermal oxides has been conducted at room temperature (RT) and elevated temperature (ET). Various thermal oxidations with temperatures ranging from 975/spl deg/C to 1200/spl deg/C with and without trichlorethane (TCA), which result in different concentrations of oxygen and carbon impurities, have been used. It has been found that, the RT annealing of the N/sub eff/ is hindered initially (t<42 days after irradiation) for detectors made on the oxides with high carbon concentrations, and there was no carbon effect on the long term (t>42 days after irradiation) N/sub eff/ reverse annealing. No apparent effect of oxygen on the stability of N/sub eff/ has been observed at RT. At elevated temperature (80/spl deg/C), no significant difference in annealing behavior has been found for detectors fabricated on silicon wafers with various thermal oxides. It is apparent that for the initial stages (first and/or second) of N/sub eff/ reverse annealing, there may be no dependence on the oxygen and carbon concentrations in the ranges studied.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>