P. G. Van Patten

Visible emission from electroluminescent devices using an amorphous AlN:Er3+ thin-film phosphor

Electroluminescence (EL) studies of AlN:Er alternating-current thin-film electroluminescent (ACTFEL) devices were performed at 300 K. Thin films of Er-doped AlN, ∼200 nm thick, were grown on indium–tin–oxide/aluminum–titanium–oxide/glass substrates using rf magnetron sputtering in a nitrogen atmosphere. The turn-on voltage was found to be around 70–80 and 100 V for ACTFEL devices without and with a top insulator layer. Sharp emission lines in the visible region were observed which correspond to known transitions of the Er3+ ion. Temperature-dependent cathodoluminescence studies corroborate the EL results, and show that optimum device performance is attained near 300 K.

Emission properties of an amorphous AlN:Cr3+ thin-film phosphor

Chromium-doped aluminum nitride (AlN:Cr) films were grown on p-doped silicon (111) by rf magnetron sputtering in a nitrogen atmosphere at a pressure of 10−4 Torr. Film thickness was typically 200 nm. After growth, the films were “activated” at ∼1300 K for 30 min in a nitrogen atmosphere. Films activated in this manner exhibit intense cathodoluminescence and photoluminescence emission. Spectral evidence demonstrates conclusively that the luminescent centers are Cr3+ ions.

Placement of conjugated oligomers in an alkanethiol matrix by scanned probe microscope lithography

We report the in situ replacement of conjugated molecules in an insulating matrix by scanned probe microscope lithography. High yield, programmable patterning of a self-assembled monolayer of dodecanethiol was performed by applying voltage pulses from a scanning tunneling microscope. Conjugated oligomers were observed to be subsequently chemisorbed onto the patterned sites.

Visible emission from amorphous AlN thin-film phosphors with Cu, Mn, or Cr

Luminescence studies of amorphous AlN incorporated with pure Cu, Mn, or Cr and codeposited with (Cu, Tb, Mn) were performed at 300 K. Thin films of Cu, Mn, and Cr amorphous AlN, ∼200 nm thick, were grown on p-Si(111) substrates using rf magnetron sputtering in a nitrogen atmosphere. Cathodoluminescence showed that pure Cu incorporated amorphous AlN films have strong emission in the blue (∼420 nm) and Mn and Cr incorporated films luminescence in the red (∼690 nm). Cr3+ emission is likely more intense than Mn4+ because chromium does not suffer from incomplete charge compensation in the III–V semiconductor. Luminescence studies of layered structures where pure Cu incorporated films are grown on top of pure Cr incorporated films reveal emission from both Cr and Cu ions. The migration of Cr ions during the 1000 °C luminescence activation step is confirmed with secondary ion mass spectrometry depth profiling. Co-deposited films of Cu, Tb, and Mn show Cu emission around 530 nm instead of 420 nm due to coactivati...

Thin-film electroluminescent devices grown on plastic substrates using an amorphous AlN:Tb3+ phosphor

An alternating current thin-film electroluminescent device has been constructed on a flexible polymer substrate using an amorphous AlN:Tb3+ film as the phosphor. When the device is operated at 170 Vac and at a frequency of 1 kHz, a stripe of green light can be seen emanating from the 0.6 mm×14 mm active area. The electroluminescence spectrum from the device is very similar to the cathodoluminescence and photoluminescence spectra from the amorphous AlN:Tb3+ phosphor. Luminance for this phosphor on plastic substrates is about 1 cd/m2 under optimal conditions. Time-resolved photoluminescence measurements were used to gain insight into the nature of the Tb3+ excited states. The relatively slow (τ=850 μs), single exponential decay of the excited state suggests that quenching via excited state energy migration to trap sites in the semiconductor is negligible.

Visible Luminescent Activation of Amorphous AlN:Eu Thin-Film Phosphors with Oxygen

We have investigated the effects of oxygen incorporation on cathodoluminescence (CL) and photoluminescence (PL) from sputtered amorphous films of AlN:Eu 3+ . Ordinarily, these materials must be activated at elevated temperatures (~1000K) before appreciable luminescence can be observed. We have shown that oxygen doping is an effective alternative to thermal activation. Studies of CL intensity versus oxygen contamination indicate that luminescence turns on if the oxygen content of the sputtering plasma exceeds a few percent. Significantly, oxygen appears to have a greater impact (>600-fold) on luminescence than does thermal activation (100-fold). The oxygen dependence of PL intensity varies slightly from that of CL intensity. A possible explanation for this observation is proposed. The results suggest that low temperature alternatives to the customary thermal activation process may be available. Such alternatives would eliminate materials constraints and would permit the facile integration of plastic components or substrates with rare-earth-doped III-N luminescent devices.

Flow injection system for the scanning tunneling microscope

A flow injection scanning tunneling microscopy (FISTM) system is described and characterized which permits observation of surface chemical processes. This modification to a standard scanning tunneling microscope consists of a peristaltic pump attached via a manual HPLC‐type flow injector to a constant‐volume sample cell. Images recorded as fluids continuously exchange in the cell are reported. Evidence supports that analytes are transported into the tip region through a stagnant fluid domain by diffusion from the adjacent, circulating bulk solution. Electrochemical measurements of the exposed tip surface area and rates of diffusion of analytes are presented and interpreted. Erosion of contaminants on a gold surface exposed to hydrogen peroxide was observed using FISTM, and these results are presented.

Visible Emission from Thin-Film Phosphors of Amorphous AlN:Cu, Mn, and Cr

Luminescence studies of amorphous AlN doped with Cu, Mn, or Cr were performed at 300 K. Thin films of Cu, Mn, and Cr doped amorphous AlN, ∼200 nm thick, were grown on p-doped silicon (111) substrates using RF magnetron sputtering in a nitrogen atmosphere. Cathodoluminescence (CL) showed that pure Cu doped amorphous AlN has strong emission in the blue (∼420 nm) and Mn and Cr doped films luminesce in the red (∼690 nm). Cr +3 emission is more intense than Mn+4 because chromium does not suffer from incomplete charge compensation in the III-V semiconductor. Luminescence studies of crystalline and amorphous AlN:Mn thin films showed a red shift in the emission peak by almost 100 nm and is believed to be caused by the different crystal field of the amorphous host compared to the crystalline host material. Secondary ion mass spectrometry (SIMS) depth profiling was conducted to confirm the presence of the Cu and Cr in the films and to show the amount of dopant in relation to the Si substrate.

Nanometer-Scale Qualitative Analysis of Surfaces With a Modified Scanning Tunneling Microscope/ Field Emission Source

We have designed and constructed modifications to the scanning tunneling microscope that allow the bias voltage to be used as an excitation source for arc atomic emission spectroscopy. The purpose of this addition to the instrument is to allow unambiguous elemental analysis of species present on the surface. The light emitted from the arc across the tunneling gap is collected by appropriate means (such as optical fibers positioned in close proximity to the tip) and directed into a high resolution spectrometer for spectral analysis by a multichannel detector (such as a charge-coupled device (CCD) or photodiode array). Present progress includes completion of the hardware and software modifications to the instrument, verification of emission and verification that the light is substantively collected into optical fibers using a scheme described in this paper.