Free-standing PbSe nanocrystals, including quantum wires, multipods, quantum rods, quantum dots, and cubes, were produced in a colloidal solution in the presence of alkyl-diamine solvent at 10−117 °C. The morphology of the nanocrystals was governed by a solvent coordinating molecular template mechanism, which was further adjusted by the temperature and duration of the reaction. Crystalline wires with diameters of approximately 20 nm and lengths of 1−5 μm were formed at the lowest temperatures, while quantum rods (with an aspect ratio of ∼5) and cubes (with 100−500 nm edge) were formed at elevated temperatures.

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A convenient piezoelectric driven Kelvin probe for the measurement of work function changes is described. The probe has a simple construction, is small, bakeable, and can be mounted on any 35-mm-i.d. UHV flange. As the piezoelectric device is inside the vacuum chamber, only one electrical feedthrough is needed for operating the probe. The distance between reference electrode and sample can be varied within ±0.5 mm simply by applying a dc voltage to the piezoelectric device in addition to the ac oscillator-driving voltage, not requiring any mechanical driving and feedthrough provisions. The probe was tested studying the adsorption of O2 on Pt(111). The sensitivity for contact potential measurements is better than 0.1 mV at a response time of 10 sec.

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Articles you may be interested inUltrathin zirconium silicate gate dielectrics with compositional gradation formed by self-organized reactions Appl. Phys. Lett. 81, 4221 (2002); 10.1063/1.1525392 Ultrathin nitrided-nanolaminate ( Al 2 O 3 / ZrO 2 / Al 2 O 3 ) for metal-oxide-semiconductor gate dielectric applications J.ZrO 2 films were deposited on Si͑100͒ wafers by the rapid thermal chemical vapor deposition process using a zirconium ͑IV͒ t-butoxide Zr͑OC 4 H 9 ͒ 4 precursor and oxygen. Interfacial zirconium silicate formation was observed by high resolution transmission electron microscopy and medium energy ion scattering. The intermixing of the interface can be suppressed by forming a thin silicon nitride layer on the silicon substrate prior to ZrO 2 deposition. The dielectric constant of ZrO 2 achieved in this work is 15-18 with very small capacitance-voltage hysteresis, ideal for metal-oxidesemiconductor field effect transistor ͑MOSFET͒ application. The NMOSFET device has good turn-on characteristics, however, the transconductance is lower than expected due to the incomplete removal of zirconium silicate at the source and drain contacts and poses integration challenges to use ZrO 2 as the gate dielectric material.

Thin BaTiO 3 ͑BTO͒ layers were deposited by magnetron sputtering on a Si substrate between two thin LaNiO 3 ͑LNO͒ electrodes ͑LNO/BTO/LNO/Si structure͒. The thickness of the BTO layer was varied between 35 nm and 1 m. The stress, dielectric permittivity, and ferroelectric hysteresis loop were measured after deposition and during heating. It was found that the BTO layers are under tensile stress at the Curie temperature. The tensile stress increases with decreasing layer thickness leading to a shift of the Curie point to a lower temperature, a decrease of remanent polarization, and an increase of the coercive field. The effect of tensile stress on the Curie temperature is dominant within a restricted range of stresses between 300 and 450 mega Pascals ͑MPa͒, where the Curie temperature decreases linearly by about 0.16°C/MPa. A good correlation was found between stress and dielectric measurements with respect to the temperature of the Curie point. The ferroelectric hysteresis loops showed that the ferroelectric-paraelectric phase transition starts at the Curie temperature of the BTO layer and continues within a range of temperatures until about the Curie temperature of the bulk BTO material. The ferroelectric behavior indicates dominance of domains within the interior part of the BTO layer and minor contribution of surface domains. The results are compared with a theoretical approach of size-driven phase transition in stress-induced ferroelectric thin films.

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