Martin L. Kaplan

Structural and morphological investigation of the development of electrical conductivity in ion‐irradiated thin films of an organic material

Thin films of 3,4,9,10‐perylenetetracarboxylic dianhydride (PTCDA) develop low electrical resistivity ( 5×1...

Relationship between the conduction‐band discontinuities and band‐gap differences of InGaAsP/InP heterojunctions

We have measured the magnitude of the conduction‐band discontinuities at heterojunctions for several compositions of InGaAsP grown lattice matched on InP. We find that the conduction‐band discontinuity (ΔEc) is related to the difference in band gaps (ΔEg) between the InGaAsP and InP layers via ΔEc =0.39(ΔEg). Thus, 40% of the band‐gap difference lies in the conduction band of this material system. The measurements were made on a series of composition of InGaAsP spanning the alloy range from In0.53Ga0.47As (with energy gap Eg =0.75 eV) to InP (Eg =1.35 eV) using capacitance‐voltage techniques. Depletion deep into the semiconductor layers was facilitated by the formation of organic‐on‐inorganic semiconductor contact barriers on the InGaAsP surface.

Ion‐beam‐induced conductivity in polymer films

Polymer films darken upon irradiation with energetic ion beams. At high doses (1016–1017 cm−2) of 2‐MeV Ar+ ions, the resistivity of these insulating films decreases dramatically to 3.5×10−3 Ω cm. Furthermore, over a wide range of doses (1014–1015 cm−2) these films exhibit a temperature‐dependent resistivity characteristic of carrier transport via hopping between isolated conducting islands. Rutherford backscattering measurements indicate that while a substantial amount of the carbon is retained in the film, other constituent elements are lost. Raman spectra show that the films are highly disordered at large ion doses.

Optical and electrical properties of ion‐beam‐irradiated films of organic molecular solids and polymers

Thin films of several nonpolymeric and polymeric organic compounds become optically dark and electrically conducting on irradiation with energetic particle beams. Using 2‐MeV Ar+ ion beam irradiation, we have generated conducting patterns in otherwise high‐resistivity, organic thin films among which are 3, 4, 9, 10‐perylenetetracarboxylic dianhydride, 1, 4, 5, 8‐napthalenetetracarboxylic dianhydride, and Ni phthalocyanine. The room‐temperature resistivity of the films changes by 14 orders of magnitude from its as‐deposited value of ρ>1010 Ω cm to ρ=5×10−4 Ω cm at ion doses of 1017 cm−2. The temperature (T) dependence of the resistivity follows ρ(T)∝exp(+(T0/T)1/2 ) over a wide range of dose and temperature. The characteristic temperature T0 is found to be a function of dose. The observed behavior of ρ(T) is consistent with charge transport due to hopping between isolated, conducting islands. The dependence on ion energy, ion species, and ion dose rate has been examined. The effectiveness of an ionic speci...

Carbon films with relatively high conductivity

The pyrolysis of organic dianhydrides (e.g., 3,4,9,10‐perylenetetracarboxylic dianhydride) in an evacuated system results in the loss of hydrogen, CO, and CO2 and the deposition of a chemically inert, metallic‐appearing mirrolike film. The films are highly conducting (σRT250 Ω−1 cm−1) and can evidence either metallic or semiconducting behavior, depending on the preparation temperature. Superconducting films are obtained when niobium is used as a dopant. Preparation of films on doped silicon semiconductor chips results in the formation of p‐n junctions. ESR spectra exhibit a moderately strong line at g=2.0025. The resonance intensity remains almost constant to 20 °K, characteristic of a highly delocalized spin system.

Reactivity of C60 in pure oxygen

In pure oxygen at moderate temperatures of 200 °C, an fcc C60 transforms into amorphous carbon‐oxygen compounds and the icosahedral C60 molecular structure is destroyed. The maximum oxygen uptake of pure C60, O/C60, is 12. Isothermal TGA transformation curves are sigmoid‐shaped with the kinetic exponent n∼5/2 which conforms with a two‐dimensional nucleation and growth mode. The heat of formation for the carbon‐oxygen compounds is 90 kcal/mol O, and the formation energy for the reaction: 60C (graphite)→C60 molecule is estimated to be ∼600 kcal/mol.

A systematic study of an isomorphous series of organic solid state conductors based on tetrathiafulvalene

The solid state physical properties of an isomorphous series of TTF salts (TTF11 (SCN)6, TTF11 (SeCN)6, and TTF7I5) were examined. While there was no noticeable trend in the conductivity (as a function of temperature and anion), the effective Fermi energy (?F) and the magnetic susceptibility transition temperature exhibited a definite trend as a function of anion. There is a correlation between the above properties and subtle variations in solid state structure of each of the above salts.

The preparation, spectral properties, and X-ray structural features of 2,3-naphthalocyanines

Abstract We have prepared a series of 2,3-naphthalocyanine (H2NPc) compounds and examined their spectroscopic properties. All of them can be vacuum sublimed as thin films which absorb strongly in the near infrared and thus make them potentially useful as optical data recording media. In addition, we have measured the electrical resistivities, at room temperature, of several of the compacted 2,3-naphthalocyanines and find them to be semiconductors. Doping with bromine vapor enhances the conductivities only slightly (H2NPc actually becomes more resistive).

Structural and chemical analysis of ion beam produced conductive regions on highly resistive organic films

Thin films of both polymeric and nonpolymeric organic solids turn optically dense and electrically conductive on irradiation with high energy ion beams (e.g., 2 MeV Ar+). The structural and chemical properties of these films were investigated by ultraviolet (UV) visible, infrared (IR), Raman spectroscopic techniques, electron spin resonance (ESR), electron spectroscopy for chemical analysis (ESCA), and Rutherford backscattering (RBS) measurements. Specifically, in the case of 3,4,9,10‐perylenetetracarboxylic dianhydride (PTCDA) and nickel phthalocyanine (NiPc), and UV visible, IR, and Raman spectra show the loss of the initial molecular structure at low irradiation doses (1013–1014 cm−2) followed by the appearance, at high doses, of a spectrum similar to that observed for amorphous carbon. The Raman spectra indicate the absence of any long range graphitic microcrystalline structure and suggest that the films are nearly amorphous at higher doses. The RBS spectra indicate gradual loss of oxygen in PTCDA with increasing irradiation dose. There is negligible oxygen left in the film at high doses and a maximum loss of ∼35% (∼15%) of the carbon atoms in PTCDA (NiPc) is observed. The resistivity of the films decreases with increasing dose, reaching a minimum of ∼5×10−4 Ω cm at a dose of ∼1017 Ar+/cm2. Surprisingly, the resistivity of these films at high doses (∼1017 Ar+/cm2) is considerably lower than that of any amorphous phase of carbon. In the case of NiPc, such a low resistivity is obtained even though 60% of the N and 100% of the Ni originally contained in the films are retained. In situ measurements of the evolution rate of molecular fragments during the bombardment indicate a decrease with dose, suggestive of an irreversible modification of the material with ion bombardment.Thin films of both polymeric and nonpolymeric organic solids turn optically dense and electrically conductive on irradiation with high energy ion beams (e.g., 2 MeV Ar+). The structural and chemical properties of these films were investigated by ultraviolet (UV) visible, infrared (IR), Raman spectroscopic techniques, electron spin resonance (ESR), electron spectroscopy for chemical analysis (ESCA), and Rutherford backscattering (RBS) measurements. Specifically, in the case of 3,4,9,10‐perylenetetracarboxylic dianhydride (PTCDA) and nickel phthalocyanine (NiPc), and UV visible, IR, and Raman spectra show the loss of the initial molecular structure at low irradiation doses (1013–1014 cm−2) followed by the appearance, at high doses, of a spectrum similar to that observed for amorphous carbon. The Raman spectra indicate the absence of any long range graphitic microcrystalline structure and suggest that the films are nearly amorphous at higher doses. The RBS spectra indicate gradual loss of oxygen in PTCDA wit...

A three-chamber diffusion apparatus for the growth of single crystals of organic donor-acceptor salts

Abstract The usefulness of a simple three-chamber apparatus for the growth of organic donor-acceptor salts has been demonstrated. Relatively large, well-formed crystals of one such salt, TTF-TCNQ, have been grown in this manner and exemplify the method.