Ballistic Electron Emission Microscopy (BEEM) and Spectroscopy of Buried Semiconductor Heterostructures and Quantum Dots(STM-BEEM interfaces)

BEEM is a powerful, new low energy electron microscopy for imaging and spectroscopy of buried quantum objects and nondestructive local characterization of buried semiconductor heterostructures. We will present several applications : 1) Imaging and spectroscopy of 300Å InAs islands confined by GaAs potential barriers 2) Local conduction band offsets of GaSb self assembled quantum dots in GaAs 3) Spatial probing of the order-disorder transition in GaInP/GaAs heterostructures 4) Imaging of misfit dislocations at the InGaAs/GaAs interface buried 600Å below the surface 5) Conduction band structure of Ga

Monte Carlo calculations for metal-semiconductor hot-electron injection via tunnel-junction emission

We present a detailed description of a scheme to calculate the injection current for metal-semiconductor systems using tunnel-junction electron emission. We employ a Monte Carlo framework for integrating over initial free-electron states in a metallic emitter and use interfacial scattering at the metal-semiconductor interface as an independent parameter. These results have implications for modeling metal-base transistors and ballistic electron emission microscopy and spectroscopy

BEEM imaging and spectroscopy of buried structures in semiconductors

Ballistic Electron Emission Microscopy (BEEM) has been shown to be a powerful tool for nanometer-scale characterization of the spatial and electronic properties of semiconductor structures. In this article, we will discuss general aspects of BEEM experiment and theory in true ballistic and quasi-ballistic hot carrier transport. We will review the current state and recent progress in the use of the BEEM imaging and spectroscopy to study metal-semiconductor and metal-insulator-semiconductor interfaces, buried semiconductor heterojunctions and novel quantum objects. Various theoretical BEEM models are discussed, and their ability to describe BEEM experiments is examined. Special attention is drawn to the role of the electron scattering in the metal base layer, at the metal-semiconductor interface and in the semiconductor heterostructure on BEEM spectra

Vegetable proteins. I. The proteins of Dolichos lab lab.

The field bean (Dolichos lab lab; Tamil name, Mochai; Kanarese, Avarai) is a legume which is widely cultivated in South India often as a mixed crop with cereals. The kernel of the seed enters into the diet of many South Indian households, and in the Mysore State the seeds are used as a delicacy when they are green for over four months in the year. The haulm, husk and pods are commonly used as fodder. As the kernel, which is widely used as an article of food and considered to be very nutritious, contains about 24 % of protein hitherto uninvestigated and as the quality of protein plays an important role in nutrition, the present work was undertaken

The nature of tyrosinase

The view that tyrosinase is a mixture of a number of components has been held by several investigators. Haehn [1920] reported that potato tyrosinase lost its activity on dialysis or ultrafiltration, but regained it on addition of the ultrafiltrate or boiled juice. He concluded that the activator was inorganic in nature. Raper and Wormall [1923], while partially confirming Haehn's finding, noticed that the boiled juice of new but not of old potatoes had an accelerating effect. They also adduced evidence to show that the activator in potato juice is organic in nature. In an earlier paper [Narayanamurti and Ramaswami, 1929] it was shown that on ultrafiltration of Dolichos tyrosinase the residual liquid on the ultrafilter was active and that the addition of the ultrafiltrates to the residual liquid did not cause any acceleration. The following additional results have so far been obtained

A two-colour heterojunction unipolar nanowire light-emitting diode by tunnel injection

We present a systematic study of the current-voltage characteristics and electroluminescence of gallium nitride (GaN) nanowire on silicon (Si) substrate heterostructures where both semiconductors are n-type. A novel feature of this device is that by reversing the polarity of the applied voltage the luminescence can be selectively obtained from either the nanowire or the substrate. For one polarity of the applied voltage, ultraviolet (and visible) light is generated in the GaN nanowire, while for the opposite polarity infrared light is emitted from the Si substrate. We propose a model, which explains the key features of the data, based on electron tunnelling from the valence band of one semiconductor into the conduction band of the other semiconductor. For example, for one polarity of the applied voltage, given a sufficient potential energy difference between the two semiconductors, electrons can tunnel from the valence band of GaN into the Si conduction band. This process results in the creation of holes in GaN, which can recombine with conduction band electrons generating GaN band-to-band luminescence. A similar process applies under the opposite polarity for Si light emission. This device structure affords an additional experimental handle to the study of electroluminescence in single nanowires and, furthermore, could be used as a novel approach to two-colour light-emitting devices.Comment: 9 pages, 11 figure

Radiation induced zero-resistance states in GaAs/AlGaAs heterostructures: Voltage-current characteristics and intensity dependence at the resistance minima

High mobility two-dimensional electron systems exhibit vanishing resistance over broad magnetic field intervals upon excitation with microwaves, with a characteristic reduction of the resistance with increasing radiation intensity at the resistance minima. Here, we report experimental results examining the voltage - current characteristics, and the resistance at the minima vs. the microwave power. The findings indicate that a non-linear V-I curve in the absence of microwave excitation becomes linearized under irradiation, unlike expectations, and they suggest a similarity between the roles of the radiation intensity and the inverse temperature.Comment: 3 color figures; publishe

Size-dependent surface luminescence in ZnO nanowires

Nanometer sized whiskers (nanowires) offer a vehicle for the study of size-dependent phenomena. While quantum-size effects are commonly expected and easily predicted, size reduction also causes more atoms to be closer to the surface. Here we show that intensity relations of below-band-gap and band-edge luminescence in ZnO nanowires depend on the wire radius. Assuming a surface layer wherein the surface-recombination probability is 1 (surface-recombination approximation), we explain this size effect in terms of bulk-related to surface-related material-volume ratio that varies almost linearly with the radius. This relation supports a surface-recombination origin for the deep-level luminescence we observe. The weight of this surface-luminescence increases as the wire radius decreases at the expense of the band-edge emission. Using this model, we obtain a radius of 30 nm, below which in our wires surface-recombination prevails. More generally, our results suggest that in quantum-size nanowires, surface-recombination may entirely quench band-to-band recombination, presenting an efficient sink for charge carriers that unless deactivated may be detrimental for electronic devices