摘要:

We report experiments on bilayer light emitting diodes made with organically capped CdSe(CdS) core/shell type semiconductor nanocrystals and an electroluminescent (EL) semiconducting polymer [poly(p-phenylenevinylene) or PPV]. The devices emit from red to green with external quantum efficiencies of up to 0.22&percent; at brightnesses of600 cd/m2and current densities of1 A/cm2.They have operating voltages as low as 4 V and lifetimes under constant current flow of hundreds of hours. Most of these numbers are significant improvements over similar devices made with CdSe nanocrystals. The devices show either nanocrystal-only EL or a combination of nanocrystal and PPV EL, depending on nanocrystal layer thickness. The nanocrystal EL is dependent on nanocrystal size. Some devices show a voltage dependent spectral output. The spectral output is consistent with a field dependent electron range in the nanocrystal layer limited by carrier trapping. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366452

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

We propose a novel AlN/GaN insulated gate heterostructure field effect transistor (FET) with modulation doping. The vertical structure of the FET was AlN(1)/AlGaN(2)/InGaN(3)/AlGaN(4)/AlGaN(5)/GaN(substrate)(6). The typical widths of gate insulator (1) and channel (3) are 4 and 5 nm, respectively. Charge control in the FET was simulated in one dimension by solving Poisson and Schro¨dinger equations self-consistently. The dependence of transconductance(Gm)and the cutoff frequency(fT)on the gate voltage(Vgs)was obtained, then the optimum structure was determined. We found: (i) In the above structure, without the electron supplying layer AlGaN(2) in the gate side, the FET has highGm(max=2.9 S/mm)andfT(max=120 GHz;Lg(gate length)=2.5 &mgr;m) values in the broadVgsregion (about 3 V) inGm−VgsandfT−Vgscharacteristics. (ii) BothGm−VgsandfT−Vgscharacteristics show high values in theVgsregion, which becomes broader as the conduction band discontinuity between the channel (3) and electron supplying layers, (2) and (4), increases. (iii) The optimum channel width(w)is2 nm⩽w⩽10 nmfor the structure with only an electron supplying layer (4). This condition prevents lowering ofGmin the lowVgsregion, and keeps the parasitic resistance between gate and source/drain low. (iv) There is an optimum doping concentration and an optimum width of the electron supplying layer, which depend on the conduction band discontinuity between the channel and the electron supplying layer. (v) Channel doping reduces intrinsicGmandfTin the lowVgsregion inGm−VgsandfT−Vgscharacteristics and does not necessarily increase significantly the equilibrium two-dimensional electron gas concentration. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366453

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

In this communication, we present a study of tip artifacts in atomic force microscope images of nanometer-scale cellular structures created on germanium surfaces by ion bombardment. It is demonstrated that the appearance of a columnar/granular morphology is due to severe image distortion when the tip size is comparable with the mean cell/hole diameter. These tip artifacts can often be deconvoluted by inverting the image and the lateral extension of the cell/hole can be reproduced with reasonable accuracy. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366454

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Thermal and field electron emission from a modified electron microscope W source were measured with an energy-dispersive counting system. Thermal-emission spectra were consistent with random emission of single electrons, while field-emission spectra were consistent with multiple-electron emission in random events. As many as 11 electrons were detected in isolated random field-emission events. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366462

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Amorphous silicon (a-Si) was crystallized by metal-induced crystallization (MIC) using a Ni standard absorption solution. The a-Si films spin-coated with a 5000 ppm Ni solution were crystallized at as low as 500 °C. Needlelike morphology, developed as a result of the migration of NiSi2precipitates, appears in the MIC poly-Si. The growth of the needlelike crystallites proceeds to a direction parallel to⟨111⟩. The a-Si can be fully crystallized at 500 °C for 20 h. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366455

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

Randomly scattered depth profiles of refractive index are experimentally observed on thin silicon dioxide films on silicon substrates by means of conventional ellipsometry and gradually chemical etching. Computer simulations with an abrupt model and random uncertainties in ellipsometric angles &PSgr; and &Dgr; show very similar behavior as experiments, and the distribution of the measured profile in the near interface region is in good agreement with 0.02° standard deviation in &PSgr;. Simulations also indicate that even very small errors in &PSgr;, as small as 0.001°, can result in divergent depth profile of the refractive index in the near interface region. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366404

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

A current annealing procedure is proposed. Heat sinks were positioned along the sample, while annealing with current, inducing tailored temperature profile along its axis.Fe77.5Si7.5B15amorphous wires were current annealed with this technique so that, magnetically soft and hard local regions develop. As a measure of this magnetic composite character, the coercivity profile was verified after annealing. Results are explained in terms of different power losses along the sample. Some possible applications as security labels of the annealed material are discussed. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366456

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

It is pointed out that there is not a certain universal relation for the power outputs of continuous endoreversible and reversible Carnot heat engine cycles operating between the same temperature limits, and the relevant conclusion obtained by Blank and Bhattacharyya in a recent article of this journal is incorrect. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366405

出版商:AIP    

年代:1997

数据来源: AIP

ISSN:0021-8979    

DOI:10.1063/1.366457

出版商:AIP    

年代:1997

数据来源: AIP

摘要:

It has come to our attention that images of static domain patterns in Permalloy using a quadrant-detection scheme were first obtained by Clegg, Heyes, Hill, and Wright in 1991.12Thus, our claim to have been the first group to image static domains using such a method was incorrect. The description of the instrument and its principle of operation remain correct. The quality of the image presented3represents an improvement over previously published results using a similar detection scheme, permitting an unambiguous determination ofNe´elwall polarity within the imaged domain structures. ©1997 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.366406

出版商:AIP    

年代:1997

数据来源: AIP