共查询到20条相似文献,搜索用时 46 毫秒
1.
M. Jhabvala S. Gunapala D. Reuter K. K. Choi S. Bandara J. Liu A. La S. Banks J. Cho T. Hwang S. Tsay D. Rafol H. Huet N. Chauvet T. Huss 《Infrared Physics & Technology》2003,44(5-6):445-455
In the on-going evolution of GaAs quantum well infrared photodetectors (QWIPs) we have developed a four band, 640 × 512, 23 μm × 23 μm pixel array which we have subsequently integrated with a linear variable etalon (LVE) filter providing over 200 spectral bands across the 4–15.4 μm wavelength region. This effort was a collaboration between NASA’s Goddard Space Flight Center (GSFC), the Jet Propulsion Laboratory (JPL) and the Army Research Laboratory (ARL) sponsored by the Earth Science Technology Office of NASA. The QWIP array was fabricated by graded molecular beam epitaxial (MBE) growth that was specifically tailored to yield four distinct bands (FWHM): Band 1; 4.5–5.7 μm, Band 2; 8.5–10 μm, Band 3; 10–12 μm and Band 4; 13.3–14.8 μm. Each band occupies a swath that comprises 128 × 640 elements. The addition of the LVE (which is placed directly over the array) further divides the four “broad” bands into 209 separate spectral bands ranging in width from 0.02 μm at 5 μm to 0.05 μm at 15 μm. The detector is cooled by a mechanical cryocooler to 46 K. The camera system is a fully reflective, f/4.2, 3-mirror system with a 21° × 25° field of view. The project goals were: (1) develop the 4 band GaAs QWIP array; (2) develop the LVE and; (3) implement a mechanical cryocooler. This paper will describe the efforts and results of this undertaking with emphasis on the overall system characteristics. 相似文献
2.
N. V. Gaponenko A. V. Mudryi O. V. Sergeev M. Stepikhova L. Palmetshofer W. Jantsch J. C. Pivin B. Hamilton A. S. Baran A. I. Rat''ko 《Journal of luminescence》1998,80(1-4):399-403
Sol–gel derived Fe2O3 films containing about 10 wt% of Er2O3 were deposited on porous silicon by dipping or by a spin-on technique followed by thermal processing at 1073 K for 15 min. The samples were characterized by means of PL, SEM and X-ray diffraction analyses. They exhibit strong room-temperature luminescence at 1.5 μm related to erbium in the sol–gel derived host. The luminescence intensity increases by a factor of 1000 when the samples are cooled from 300 to 4.2 K. After complete removal of the erbium-doped film by etching and partial etching the porous silicon, the erbium-related luminescence disappears. Following this, luminescence at 1.5 μm originating from optically active dislocations (“D-lines”) in porous silicon was detected. The influence of the conditions of synthesis on luminescence at 1.5 μm is discussed. 相似文献
3.
Enhanced field emission of electrons from silicon surfaces was obtained by surface microstructuring, by means of electrochemical oxidation in organic solutions containing HF. Morphological characterisations showed the formation of cylindrical rods, randomly distributed with relative spacing of a few microns. They are originated at the top of silicon pyramids and have typical diameter in the 100 nm range. Variable length in the 1–50 μm range was obtained, by adjusting the process parameters. Electron field emission properties were characterised for several samples, prepared in different conditions: the emission threshold was found to be strongly correlated with the overall charge exchanged during electrochemical oxidation. In the most favourable conditions, the threshold field for the emission of an electron current Ith = 10−10 A was 11.1 V/μm. 相似文献
4.
Field emission properties and surface structure of nickel containing amorphous carbon 总被引:1,自引:0,他引:1
G. Y. Chen J. S. Chen Z. Sun Y. J. Li S. P. Lau B. K. Tay J. W. Chai 《Applied Surface Science》2001,180(3-4):185-190
Nickel containing amorphous carbon (a-C:Ni) films have been deposited by filtered cathodic vacuum arc (FCVA) technique by introducing pure nickel into the graphite target. The field electron emission property of a-C:Ni was improved when compared to that of pure tetrahedral amorphous carbon (ta-C) by FCVA. The emission threshold field of a-C:Ni film is about 5 V μm−1, whilst the threshold field of the ta-C film is about 13 V μm−1. Raman spectroscopy suggests that the sp2 clusters in the carbon film increase both in size and number when Ni is introduced. However, the emission was found to degrade to threshold fields beyond 20 V μm−1 after the a-C:Ni film was left in ambient for a week. This observation is attributed to surface absorption of oxygen on the a-C:Ni film, as determined by X-ray Photoelectron Spectroscopy. 相似文献
5.
The O3 absorption coefficients for the rotational lines P(12)–P(28) of the 9.4 μm emission band of the CO2 laser are presented. Measurements were made in O3–air dilute mixtures (20–600 ppm) at 25°C and a total pressure of 1013.25 h Pa using a frequency stabilized cw CO2 laser and values have been determined with greater precision than in previously reported studies. 相似文献
6.
Single-walled carbon nanotubes (SWCNTs) have been synthesized in high yield by the dc arc discharge technique under heat-pretreatment of the graphite rod conditions. Before executing arc discharge, the graphite rods containing the catalysts were heat treated at 600, 700, 800 and 900 °C for 1–3 h, respectively. Effects of heat-pretreatment of the graphite rod on the quality of SWCNTs by arc discharge were investigated. The heat-treatment temperature and time were found to be crucial for a high yield of high-purity SWCNTs. Optimum parameter was found to be at the heat-treatment temperature of 800 °C for 2 h. The SWCNTs synthesized under the optimum condition have better field-emission characteristics. The turn-on field needed to produce a current density of 10 μA/cm2 is found to be 1.9 V/μm and the threshold field where current density reaches 10 mA/cm2 is 3.9 V/μm. 相似文献
7.
S.V. Bandara S.D. Gunapala D.Z. Ting J.K. Liu C.J. Hill J.M. Mumolo S. Keo 《Infrared Physics & Technology》2007,50(2-3):211-216
A multi-band focal plane array sensitive in near-infrared (near-IR) and mid-wavelength infrared (MWIR) is been developed by monolithically integrating a near-infrared (1–1.5 μm) p–i–n photodiode with a mid-infrared (3–5 μm) QWIP. This multiband detector involves both intersubband and interband transitions in III–V semiconductor layer structures. Each detector stack absorbs photons within the specified wavelength band, while allowing the transmission of photons in other spectral bands, thus efficiently permitting multiband detection. Monolithically grown material characterization data and individual detector test results ensure the high quality of material suitable for near-infrared/QWIP dual-band focal plane array. 相似文献
8.
A.N. Banerjee C.K. Ghosh S. Das K.K. Chattopadhyay 《Physica B: Condensed Matter》2005,370(1-4):264-276
P-type transparent-conducting CuAlO2+x thin films were deposited on silicon and glass substrates by reactive direct current sputtering of a prefabricated metal powder target having 1:1 atomic ratio of Cu and Al in oxygen-diluted argon atmosphere. XRD spectrum confirmed the proper phase formation of the material. UV-Vis-NIR spectrophotometric measurements showed high transparency of the films in the visible region with direct and indirect band gap values around 3.90 and 1.89 eV, respectively. The room temperature conductivity of the film was of the order of 0.22 S cm−1 and the activation energy was 0.25 eV. Seebeck coefficient at room temperature showed a value of +115 μV/K confirming the p-type nature of the film. Room temperature Hall effect measurement also indicated positive value of Hall coefficient with a carrier concentration 4.4×1017 cm−3. We have also observed the low macroscopic field emission, from the wide band gap p-CuAlO2+x thin film deposited on glass substrate. The emission properties have been studied for different anode-sample spacing. The threshold field was found to be as low as around 0.5–1.1 V/μm. This low threshold is attributed primarily to the internal nanostructure of the thin film, which causes considerable geometrical field enhancement inside the film as well as at the film/vacuum interface. 相似文献
9.
A.B. Weerasekara M.B.M. Rinzan S.G. Matsik A.G.U. Perera M. Buchanan H.C. Liu G. von Winckel A. Stintz S. Krishna 《Infrared Physics & Technology》2007,50(2-3):194-198
Terahertz detection capability of an n-type heterojunction interfacial work function internal photoemission (HEIWIP) detector is demonstrated. Threshold frequency, f0, of 3.2 THz (93 μm) was obtained by using n-type GaAs emitter doped to 1 × 1018 cm−3 and Al0.04Ga0.96As single barrier structure. The detector shows a broad spectral response from 30 to 3.2 THz (10–93 μm) with peak responsivity of 6.5 A/W at 7.1 THz under a forward bias field of 0.7 kV/cm at 6 K. The peak quantum efficiency and peak detectivity are 19% and 5.5 × 108 Jones, respectively under a bias field of 0.7 kV/cm at 6 K. In addition, the detector can be operated up to 25 K. 相似文献
10.
Cory J. Hill Jian V. Li Jason M. Mumolo Sarath D. Gunapala 《Infrared Physics & Technology》2007,50(2-3):187-190
We report on the status of GaSb/InAs type-II superlattice diodes grown and fabricated at the Jet Propulsion Laboratory designed for infrared absorption 2–5 μm and 8–12 μm bands. Recent LWIR devices have produced detectivities as high as 8 × 1010 Jones with a differential resistance–area product greater than 6 Ohm cm2 at 80 K with a long wavelength cutoff of approximately 12 μm. The measured internal quantum efficiency of these front-side illuminated devices is close to 30% in the 10–11 μm range. MWIR devices have produced detectivities as high as 8 × 1013 Jones with a differential resistance–area product greater than 3 × 107 Ohm cm2 at 80 K with a long wavelength cutoff of approximately 3.7 μm. The measured internal quantum efficiency of these front-side illuminated MWIR devices is close to 40% in the 2–3 μm range at low temperature and increases to over 60% near room temperature. 相似文献
11.
Heishun Zen Toshiteru Kii Kai Masuda Hideaki Ohgaki Tetsuo Yamazaki 《Infrared Physics & Technology》2008,51(5):382-385
A mid-infrared free electron laser (FEL) has been constructed for energy science in the Institute of Advanced Energy, Kyoto University. The FEL system consists of a compact S-band Linac and an undulator to generate 4–13 μm coherent mid-infrared radiations. The Linac consists of a 4.5 cell rf gun with a thermionic cathode and a 3-m traveling-wave-type accelerator tube fed by 10 MW and 20 MW rf power, respectively. We have succeeded to produce 40 MeV, 40 mA and 3 μs electron beams. Last December, the 9.2 μm spontaneous emission from the undulator generated by 29.5 MeV electron beams was observed for the first time. Further optimization parameters of both the electron beam and the optical cavity are being pursued for an FEL lasing in the near future. 相似文献
12.
O. B. Gusev M. S. Bresler E. I. Terukov K. D. Tsendin I. N. Yassievich 《Journal of luminescence》1998,80(1-4):335-338
We have studied electroluminescence (EL) in the amorphous silicon-based erbium-doped structures under reverse bias in the temperature range 77–300 K. The intensity of electroluminescence at the wavelength of 1.54 μm exhibits a maximum near the room temperature. The excitation of erbium ions occurs by an Auger process which involves the capture of conduction electrons by neutral dangling bonds (D0-centers) located close to erbium ions. The stationary current through the structure is kept by a reverse process of thermally activated tunnel emission of electrons from negatively charged dangling-bond defects (D−-centers) to the conduction band of the amorphous matrix. A theoretical model proposed explains consistently all of our experimental data. 相似文献
13.
A.G.U. Perera G. Ariyawansa M.B.M. Rinzan M. Stevens M. Alevli N. Dietz S.G. Matsik A. Asghar I.T. Ferguson H. Luo A. Bezinger H.C. Liu 《Infrared Physics & Technology》2007,50(2-3):142-148
Results are reported on dual-band detectors based on a GaN/AlGaN structure operating in both the ultraviolet–midinfrared (UV–MIR) and ultraviolet–farinfrared (UV–FIR) regions. The UV detection is due to an interband process, while the MIR/FIR detection is from free carrier absorption in the emitter/contact followed by internal photoemission over the barrier at the GaN/AlGaN interface. The UV detection, which was observed from 300 K to 4.2 K, has a threshold of 360 nm with a peak responsivity of 0.6 mA/W at 300 K. The detector shows a free carrier IR response in the 3–7 μm range up to 120 K, and an impurity response around 54 μm up to 30 K. A response in the range 7–13 μm, which is tentatively assigned to transitions from C impurities and N vacancies in the barrier region, was also observed. It should also be possible to develop a detector operating in the UV–visible–IR regions by choosing the appropriate material system. A dual-band detector design, which allows not only to measure the two components of the photocurrent generated by UV and IR radiation simultaneously but also to optimize the UV and IR responses independently, is proposed. 相似文献
14.
Ruchirej Yongsunthon Steven K. Lower 《Journal of Electron Spectroscopy and Related Phenomena》2006,150(2-3):228-234
Inter- and intra-molecular forces are the driving forces responsible for the creation of an interface between a microorganism and a naturally occurring mineral or man-made material. We have used atomic force microscopy to directly measure forces between a Staphylococcus aureus bacterium and each of two materials (silica and polystyrene) in an electrolyte solution. Force “spectra” were collected by placing a glass or polystyrene bead (10 μm diameter) in contact with a living cell and then pulling the two surfaces apart. An attractive, adhesion force was observed in approximately 40 and 50% of the measurements for silica and polystyrene, respectively. The strength of the adhesion bond was 38 ± 4 pN (10−12 N) and 52 ± 9 pN for glass and polystyrene, respectively. The origin of the attractive interaction appears to be non-specific (e.g., van der Waals force) although a small number (2–3%) of force spectra contained distinct sawtooth like profiles indicative of a protein bond between S. aureus and glass or polystyrene. 相似文献
15.
Toshiyuki Usagawa Jianguo Wen Tadashi Utagawa Satoshi Koyama Youichi Enomoto 《Physica C: Superconductivity and its Applications》2000,340(4):269-275
We report on I–V characteristics for in situ formed Nb/Au/(1 1 0)YBa2Cu3O7−δ (YBCO) Josephson junction, where the homoepitaxial (1 1 0)YBCO film shows ultra-smooth surface morphology. The field dependence of critical supercurrent Ic shows anisotropic large junction behavior with normal Fraunhofer patterns expected from BCS model of dx2−y2 wave superconductors. This strongly suggests that the Nb/Au/(1 1 0)YBCO junctions cannot be regarded as atomic scaled corner junctions, in contrast with (0 0 1)/(1 1 0)YBCO grain boundary junctions to show “π-junction” with a pronounced dip near zero fields in field modulation of Ic. 相似文献
16.
Junichiro Takeda Masashi Akabori Junichi Motohisa Takashi Fukui 《Applied Surface Science》2002,190(1-4):236-241
A two-dimensional (2D) periodic array having air/semiconductor interfaces can be applied to photonic crystals (PCs), which are expected to control spontaneous emission and optical transports in the next-generation devices. In this paper, we report on the selective area metal-organic vapor phase epitaxial (SA-MOVPE) growth of a AlxGa1−xAs 2D periodic array on a GaAs (1 1 1)B substrate for application to 2DPCs having GaAs/AlGaAs heterostructures. AlxGa1−xAs (x=0, 0.25 and 0.50) growth was carried out on triangular lattice array of hexagonal GaAs openings and hexagonal SiNx masks. A uniform Al0.50Ga0.50As hexagonal pillar array and a GaAs hexagonal air-hole array with a 1 μm-period were successfully obtained. The important growth parameter for uniform 2DPC structure formation by SA-MOVPE was clarified. Furthermore, we describe the successful demonstration of a 400 nm-period pillar array and an air-hole array, which corresponds to the optical communication wavelength λ=1.3–1.55 μm. The results indicate that SA-MOVPE method is very promising for the formation of uniform semiconductor 2DPCs without the occurrence of process-induced damages. 相似文献
17.
S. D. Gunapala S. V. Bandara J. K. Liu S. B. Rafol J. M. Mumolo C. A. Shott R. Jones J. Woolaway II J. M. Fastenau A. K. Liu M. Jhabvala K. K. Choi 《Infrared Physics & Technology》2003,44(5-6):411-425
A 9 μm cutoff 640 × 512 pixel hand-held quantum well infrared photodetector (QWIP) camera has been demonstrated with excellent imagery. A noise equivalent differential temperature (NEDT) of 10.6 mK is expected at a 65 K operating temperature with f/2 optics at a 300 K background. This focal plane array has shown background limited performance at a 72 K operating temperature with the same optics and background conditions. In this paper, we discuss the development of this very sensitive long-wavelength infrared camera based on a GaAs/AlGaAs QWIP focal plane array and its performance in quantum efficiency, NEDT, uniformity, and operability. In the second section of this paper, we discuss the first demonstration of a monolithic spatially separated four-band 640 × 512 pixel QWIP focal plane array and its performance. The four spectral bands cover 4–5.5, 8.5–10, 10–12, and 13.5–15 μm spectral regions with 640 × 128 pixels in each band. In the last section, we discuss the array performance of a 640 × 512 pixel broad-band (10–16 μm full-width at half-maximum) QWIP focal plane. 相似文献
18.
Fabio Durante P. Alves G. Karunasiri N. Hanson M. Byloos H.C. Liu A. Bezinger M. Buchanan 《Infrared Physics & Technology》2007,50(2-3):182-186
This paper presents the design, fabrication and characterization of a QWIP photodetector capable of detecting simultaneously infrared radiation within near infrared (NIR), mid wavelength infrared (MWIR) and long wavelength infrared (LWIR). The NIR detection was achieved using interband transition while MWIR and LWIR were based on intersubband transition in the conduction band. The quantum well structure was designed using a computational tool developed to solve self-consistently the Schrödinger–Poisson equation with the help of the shooting method. Intersubband absorption in the sample was measured for the MWIR and LWIR using Fourier transform spectroscopy (FTIR) and the measured peak positions were found at 5.3 μm and 8.7 μm which agree well with the theoretical values obtained 5.0 μm and 9.0 μm for the two infrared bands which indicates the accuracy of the self-consistent model. The photodetectors were fabricated using a standard photolithography process with exposed middle contacts to allow separate bias and readout of signals from the three wavelength bands. The measured photoresponse gave three peaks at 0.84 μm, 5.0 μm and 8.5 μm wavelengths with approximately 0.5 A/W, 0.03 A/W and 0.13 A/W peak responsivities for NIR, MWIR and LWIR bands, respectively. This work demonstrates the possibility of detection of widely separated wavelength bands using interband and intersubband transitions in quantum wells. 相似文献
19.
20.
ε-caprolactam (CL) polymerization to polyamide-6 (Nylon 6) was studied at different contents of water in CL (0.01–2 wt%), with or without ε-amino-caproic acid (ACA) as an activator, applying to the mixture an initial treatment of Ultrasound (US) (17.5–20 kHz) at low temperatures (70–110 °C) and for short times (max 10 min). It was verified that polymerization at 260 °C produces a polymer having a much higher molecular weight (MW) when US is applied with respect to silent (SIL) conditions i.e. without the use of ultrasound. This constitutes a “pre-sonication effect”. The ratio (MW)US/(MW)SIL is inversely proportional to the initial content of water in CL. The action of US converts CL at very low temperatures (70–110 °C) and water content, in comparison with silent conditions where CL was unconverted.
Optimized conditions are studied with respect to nature and pressure of gas inside the reactor, temperature, time and frequency of US irradiation, energy consumption and nature of activator. 相似文献